Genome-Wide Characterization and Functional Validation of the ACS Gene Family in the Chestnut Reveals Its Regulatory Role in Ovule Development

Ovule abortion significantly contributes to a reduction in chestnut yield. Therefore, an examination of the mechanisms underlying ovule abortion is crucial for increasing chestnut yield. In our previous study, we conducted a comprehensive multiomic analysis of fertile and abortive ovules and found that ACS genes in chestnuts (CmACS) play a crucial role in ovule development. Therefore, to further study the function of ACS genes, a total of seven CmACS members were identified, their gene structures, conserved structural domains, evolutionary trees, chromosomal localization, and promoter cis-acting elements were analyzed, and their subcellular localization was predicted and verified. The spatiotemporal specificity of the expression of the seven CmACS genes was confirmed via qRT-PCR analysis. Notably, CmACS7 was exclusively expressed in the floral organs, and its expression peaked during fertilization and decreased after fertilization. The ACC levels remained consistently greater in fertile ovules than in abortive ovules. The ACSase activity of CmACS7 was identified using the genetic transformation of chestnut healing tissue. Micro Solanum lycopersicum plants overexpressing CmACS7 had a significantly greater rate of seed failure than did wild-type plants. Our results suggest that ovule fertilization activates CmACS7 and increases ACC levels, whereas an overexpression of CmACS7 leads to an increase in ACC content in the ovule prior to fertilization, which can lead to abortion. In conclusion, the present study demonstrated that chestnut ovule abortion is caused by poor fertilization and not by nutritional competition. Optimization of the pollination and fertilization of female flowers is essential for increasing chestnut yield and reducing ovule abortion.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including β-1,4-glucosidase, β-D-cellobiosidase, β-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Auxin and CmAP1 regulate the reproductive development of axillary buds in Chinese chestnut (Castanea mollissima)

Auxin accumulation upregulates the expression of APETALA1 (CmAP1) and subsequently activates inflorescence primordium development in axillary buds of chestnut. The architecture of fruiting branches is a key determinant of chestnut yield. Normally, axillary buds at the top of mother fruiting branches develop into flowering shoots and bear fruits, and the lower axillary buds develop into vegetative shoots. Decapitation of the upper axillary buds induces the lower buds to develop into flowering shoots. How decapitation modulates the tradeoff between vegetative and reproductive development is unclear. We detected inflorescence primordia within both upper and lower axillary buds on mother fruiting branches. The level of the phytohormones 3-indoleacetic acid (IAA) and trans-zeatin (tZ) increased in the lower axillary buds in response to decapitation. Exogenous application of the synthetic analogues 1-naphthylacetic acid (NAA) or 6-benzyladenine (6-BA) blocked or promoted, respectively, the development of the inflorescence primordia in axillary buds. The transcript levels of the floral identity gene CmAP1 increased in axillary buds following decapitation. An auxin response element TGA-box is present in the CmAP1 promoter and influenced the CmAP1 promoter-driven expression of β-glucuronidase (GUS) in floral organs in Arabidopsis, suggesting that CmAP1 is induced by auxin. We propose that decapitation releases axillary bud outgrowth from inhibition caused by apical dominance. During this process, decapitation-induced accumulation of auxin induces CmAP1 expression, subsequently promoting the reproductive development of axillary buds.

Impact of 'brown rot' caused by Gnomoniopsis castanea on chestnut fruits during the post-harvest process: critical phases and proposed solutions

BACKGROUND

The brown rot fungus, Gnomoniopsis castanea, is the main organism responsible for the outbreak of chestnut postharvest decay that is threatening the sustainability of the chestnut market in Europe. Currently, no specific strategy is available to mitigate the impact and remediate the high losses of fruits in postharvest storage. In the present study, the different phases of chestnut handling in a standard facility plant were analyzed by evaluating the amount of fruit rot and infection by G. castanea at each phase.

RESULTS

The warm bath (48 °C) was identified as the critical phase, requiring strict parametrization to effectively inactivate G. castanea in fruits. Laboratory tests indicated that maintaining fruits at 50 °C for a maximum of 45 min provided optimal conditions to completely inactivate G. castanea inoculum during postharvest handling. However, the warm bath at 50 °C and over was not effective in inactivating the complex of fungal taxa responsible for contamination and development of molds. Higher temperatures and extended treatment times caused significant losses in fruit quality, as indicated by taste panel evaluation. Upscaling of postharvest facilities is discussed and critically evaluated.

CONCLUSION

The warm bath (50 °C for 45 min) is effective in completely inactivating G. castanea in fruits but did not reduce the impacts of the complex of molds responsible for external contamination and mycotoxin production. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Friendly neighbours: Hydraulic redistribution accounts for one quarter of water used by neighbouring drought stressed tree saplings

Hydraulic redistribution (HR) can buffer drought events of tree individuals, however, its relevance for neighbouring trees remains unclear. Here, we quantified HR to neighbouring trees in single- and mixed-species combinations. We hypothesized that uptake of HR water positively correlates with root length, number of root tips and root xylem hydraulic conductivity and that neighbours in single-species combinations receive more HR water than in phylogenetic distant mixed-species combinations. In a split-root experiment, a sapling with its roots split between two pots redistributed deuterium labelled water from a moist to a dry pot with an additional tree each. We quantified HR water received by the sapling in the dry pot for six temperate tree species. After 7 days, one quarter of the water in roots (2.1 ± 0.4 ml), stems (0.8 ± 0.2 ml) and transpiration (1.0 ± 0.3 ml) of the drought stressed sapling originated from HR. The amount of HR water transpired by the receiving plant stayed constant throughout the experiment. While the uptake of HR water increased with root length, species identity did not affect HR as saplings of Picea abies ((L.) Karst) and Fagus sylvatica (L.) in single- and mixed-species combinations received the same amount of HR water.

Inter- and intra-tree variability of carbon and oxygen stable isotope ratios of modern pollen from nine European tree species

Stable carbon and oxygen isotope ratios of raw pollen sampled from nine abundant tree species growing in natural habitats of central and northern Europe were investigated to understand the intra- and inter-specific variability of pollen-isotope values. All species yielded specific δ13Cpollen and δ18Opollen values and patterns, which can be ascribed to their physiology and habitat preferences. Broad-leaved trees flowering early in the year before leaf proliferation (Alnus glutinosa and Corylus avellana) exhibited on average 2.6‰ lower δ13Cpollen and 3.1‰ lower δ18Opollen values than broad-leaved and coniferous trees flowering during mid and late spring (Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus robur). Mean species-specific δ13Cpollen values did not change markedly over time, whereas δ18Opollen values of two consecutive years were often statistically distinct. An intra-annual analysis of B. pendula and P. sylvestris pollen revealed increasing δ18Opollen values during the final weeks of pollen development. However, the δ13Cpollen values remained consistent throughout the pollen-maturation process. Detailed intra-individual analysis yielded circumferential and height-dependent variations within carbon and oxygen pollen-isotopes and the sampling position on a tree accounted for differences of up to 3.5‰ for δ13Cpollen and 2.1‰ for δ18Opollen. A comparison of isotope ranges from different geographic settings revealed gradients between maritime and continental as well as between high and low altitudinal study sites. The results of stepwise regression analysis demonstrated, that carbon and oxygen pollen-isotopes also reflect local non-climate environmental conditions. A detailed understanding of isotope patterns and ranges in modern pollen is necessary to enhance the accuracy of palaeoclimate investigations on δ13C and δ18O of fossil pollen. Furthermore, pollen-isotope values are species-specific and the analysis of species growing during different phenophases may be valuable for palaeoweather reconstructions of different seasons.

Fruit development of Lithocarpus (Fagaceae) and the role of heterochrony in their evolution

Stone oaks, or Lithocarpus species of Fagaceae are ecologically important canopy trees in the tropical and subtropical forests over East Asia, and the fruits of which are important food sources for insects and vertebrates there. The great fruit morphological variation of this genus represents two fruit types, acorn and enclosed receptacle fruit types. However, the evolutionary mechanisms of differentiation into these two fruit types with contrasting morphology remain a puzzle. To reveal the morphogenetic properties of two fruit types, we observed tissue differentiation and development among 20 Lithocarpus species from fruit set to maturity. Unlike in fruits of Quercus, the endocarp differentiation in Lithocarpus fruits occurred later than exocarp and mesocarp. Cupules provided further protection of developing seeds, particularly of acorn-type fruits. Fruits of Lithocarpus and Quercus acorns share similar insect predators. At fruit set, both acorn and enclosed receptacle types were largely identical, with similar tissue morphology and the sequence of differentiation. The distinct difference between two fruit types at maturity came from varied rates and degrees of development between the pericarp and receptacle tissues. We found that heterochrony between two tissues could create substantially divergent ecological strategies for protection and dispersal of their seeds, which is essential for the evolution of two fruit types.

Growth Features of Castanea sativa Mill. in Forest Stands Infected by Cryphoneciria parasitica (Murrill) М. Е. Barr. in Abkhazia

Currently, the forest plantations of Castanea sativa Mill. are largely damaged by phytopathogenic organisms, of which Cryphoneciria parasitica (Murrill) М. Е. Barr. has the most negative impact. The spread of this type of disease reduces the vital state and significantly reduces the life expectancy of C. sativa trees. For the first time, using dendrochronological analysis, the specificity of distribution and degree of phytopathogenic damage to C. sativa trunk tissues were assessed. It was revealed that in its lower part the dieback of the peripheral layers of wood occurs fairly evenly with a total degradation of cellular structures in the amount of 18-20%. In the middle segments of the trunk this figure increases almost twice. And the greatest degree of wood dieback is observed in the upper part of damaged trees. It was found that climatic changes of the last decades determine the strengthening of destructive processes in the woodland of C. sativa of the Caucasus.

Distance-dependent seed‒seedling transition in the tree Castanopsis sclerophylla is altered by fragment size

Negative distance-dependence of conspecific seedling mortality (NDisDM) is a crucial stabilizing force that regulates plant diversity, but it remains unclear whether and how fragment size shifts the strength of NDisDM. Here, we surveyed the seed‒seedling transition process for a total of 25,500 seeds of a local dominant tree species on islands of various sizes in a reservoir and on the nearby mainland. We found significant NDisDM on the mainland and large and medium islands, with significantly stronger NDisDM on medium islands. However, positive distance-dependent mortality was detected on small islands. Changes in distance-dependence were critically driven by both rodent attack and pathogen infestation, which were significantly affected by fragment size. Our results emphasize the necessity of incorporating the effects of fragment size on distance-dependent regeneration of dominant plant species into the existing frameworks for better predicting the consequences of habitat fragmentation.

Roles of the GA-mediated SPL Gene Family and miR156 in the Floral Development of Chinese Chestnut (Castanea mollissima)

Chestnut (Castanea mollissima) is a deciduous tree species with major economic and ecological value that is widely used in the study of floral development in woody plants due its monoecious and out-of-proportion characteristics. Squamosa promoter-binding protein-like (SPL) is a plant-specific transcription factor that plays an important role in floral development. In this study, a total of 18 SPL genes were identified in the chestnut genome, of which 10 SPL genes have complementary regions of CmmiR156. An analysis of the phylogenetic tree of the squamosa promoter-binding protein (SBP) domains of the SPL genes of Arabidopsis thaliana, Populus trichocarpa, and C. mollissima divided these SPL genes into eight groups. The evolutionary relationship between poplar and chestnut in the same group was similar. A structural analysis of the protein-coding regions (CDSs) showed that the domains have the main function of SBP domains and that other domains also play an important role in determining gene function. The expression patterns of CmmiR156 and CmSPLs in different floral organs of chestnut were analyzed by real-time quantitative PCR. Some CmSPLs with similar structural patterns showed similar expression patterns, indicating that the gene structures determine the synergy of the gene functions. The application of gibberellin (GA) and its inhibitor (Paclobutrazol, PP₃₃₃) to chestnut trees revealed that these exert a significant effect on the number and length of the male and female chestnut flowers. GA treatment significantly increased CmmiR156 expression and thus significantly decreased the expression of its target gene, CmSPL6/CmSPL9/CmSPL16, during floral bud development. This finding indicates that GA might indirectly affect the expression of some of the SPL target genes through miR156. In addition, RNA ligase-mediated rapid amplification of the 5' cDNA ends (RLM-RACE) experiments revealed that CmmiR156 cleaves CmSPL9 and CmSPL16 at the 10th and 12th bases of the complementary region. These results laid an important foundation for further study of the biological function of CmSPLs in the floral development of C. mollissima.

Mediterranean and Northern Iberian gene pools of wild Castanea sativa Mill. are two differentiated ecotypes originated under natural divergent selection

Nine wild Iberian provenances of Castanea sativa Mill. grouped in two gene pools, North Iberian Peninsula and Mediterranean, were evaluated for several adaptive traits in two provenance-progeny trials with the aim of evaluating the role of natural selection in shaping adaptive variation and increasing our understanding of the genetic structure of this species, as well as reporting complete information on the genetic variation among and within the studied populations. An annual growth rhythm experiment was evaluated during the first 3 years after establishment for phenology, growth, stem form and survival, and a periodic drought-stress experiment was evaluated for dry weight, growth, survival and other related drought traits in both well-watered and drought-stress treatments. The high genetic variability reported in both trials is largely due to the genetic variation among populations. The significant differences reported between quantitative genetic and neutral marker differentiation indicated the local adaptation of these populations through directional selection, mainly for phenology, growth and biomass allocation. A clinal variation among populations was determined through correlations of phenology with latitude and xerothermic index of the provenances, showing that central and southern Mediterranean populations had earlier phenology than northern populations and that drought played a relevant role in this differentiation. The significant correlation between phenological traits and the ancestry values in the Mediterranean gene pool supported the different pattern of behavior between both gene pools and also indicated the existence of two ecotypes: xeric and mesophytic ecotypes, corresponding to Mediterranean and North Iberian gene pools, respectively. The results obtained in the drought-stress experiment confirmed that, in general terms, xeric populations showed a greater adaptability to drought, with more developed root systems and higher survival than northern populations. Moreover, the genetic variability observed within populations indicated the potential response capacity of Iberian C. sativa populations to undergo fast adaptive evolution.

Forecasting effects of tree species reintroduction strategies on carbon stocks in a future without historical analog

American chestnut (Castanea dentata) was once an important component forests in the central Appalachians (USA), but it was functionally extirpated nearly a century ago. Attempts are underway to reintroduce blight-resistant chestnut to its former range, but it is uncertain how current forest composition, climate, and atmospheric changes and disturbance regimes will interact to determine future forest dynamics and ecosystem services. The combination of novel environmental conditions (e.g. climate change), a reintroduced tree species and new disturbance regimes (e.g. exotic insect pests, fire suppression) have no analog in the past that can be used to parameterize phenomenological models. We therefore used a mechanistic approach within the LANDIS-II forest landscape model that relies on physiological first principles to project forest dynamics as the outcome of competition of tree cohorts for light and water as a function of temperature, precipitation, CO₂ concentration, and life history traits. We conducted a factorial landscape simulation experiment to evaluate specific hypotheses about future forest dynamics in two study sites in the center of the former range of chestnut. Our results supported the hypotheses that climate change would favor chestnut because of its optimal temperature range and relative drought resistance, and that chestnut would be less competitive in the more mesic Appalachian Plateau province because competitors will be less stressed. The hypothesis that chestnut will increase carbon stocks was supported, although the increase was modest. Our results confirm that aggressive restoration is needed regardless of climate and soils, and that increased aggressiveness of chestnut restoration increased biomass accumulation. The hypothesis that chestnut restoration will increase both compositional and structural richness was not supported because chestnut displaced some species and age cohorts. Although chestnut restoration did not markedly enhance carbon stocks, our findings provide hope that this formerly important species can be successfully reintroduced and associated ecosystem services recovered.

Functional lifespans of xylem vessels: Development, hydraulic function, and post-function of vessels in several species of woody plants

PREMISE OF THE STUDY

Xylem vessels transition through different stages during their functional lifespan, including expansion and development of vessel elements, transition to vessel hydraulic functionality, and eventual transition to post-functionality. We used information on vessel development and function to develop a model of vessel lifespan for woody plants.

METHODS

We examined vessel functional lifespan using repeated anatomical sampling throughout the growing season, combined with active-xylem staining to evaluate vessel hydraulic transport functionality. These data were combined with a literature review. The transitions between vessel functional lifespans for several species are illustrated, including grapevine (Vitis vinifera L., Vitaceae), English oak (Quercus robur L., Fagaceae), American chestnut [Castanea dentata (Marshall) Borkh.; Fagaceae], and several arid and semi-arid shrub species.

KEY RESULTS

In intact woody plants, development and maturation of vessel elements may be gradual. Once hydraulically functional, vessel elements connect to form a vessel network that is responsible for bulk hydraulic flow through the xylem. Vessels become nonfunctional due to the formation of gas emboli. In some species and under some conditions, vessel functionality of embolized conduits may be restored through refilling. Blockages, such as tyloses, gels, or gums, indicate permanent losses in hydraulic functional capacity; however, there may be some interesting exceptions to permanent loss of functionality for gel-based blockages.

CONCLUSIONS

The gradual development and maturation of vessel elements in woody plants, variation in the onset of functionality between different populations of vessels throughout the growing season, and differences in the timing of vessel transitions to post-functionality are important aspects of plant hydraulic function.

Multi-cropping edible truffles and sweet chestnuts: production of high-quality Castanea sativa seedlings inoculated with Tuber aestivum, its ecotype T. uncinatum, T. brumale, and T. macrosporum

The plantation and management of sweet chestnut (Castanea sativa Mill.) orchards is a common and traditional land use system in many areas of Europe that offers the advantage of simultaneous production of nuts and timber. During the last decades, sweet chestnut has declined dramatically in many regions because of the profound social changes in rural areas coupled with pathogen attacks. Truffles, the hypogeous ascocarps of the ectomycorrhizal genus Tuber, are currently cultivated using host trees inoculated with these fungi for improving production in truffle orchards. The production of good forestry quality chestnut seedlings inoculated with European truffles in nurseries is essential for multi-cropping plantation establishment, but so far, it has not been implemented in agroforestry practices. Moreover, it is necessary to assess the physiological condition of the seedlings due to the high calcium amendment needed for the growth of Tuber spp. mycelium that can become toxic for the host plants. In this study, seedlings of C. sativa were inoculated with Tuber aestivum and its ecotypes T. uncinatum, T. brumale, and T. macrosporum and were grown in a greenhouse using culture conditions favorable for the production of high-quality plants for forestry purposes. At the end of the assay, levels of root colonization and morphological and physiological parameters of the seedlings were measured. The colonization of C. sativa with T. aestivum, its ecotype T. uncinatum, and T. brumale was successful, and the seedlings showed normal growth. Inoculation protocols with T. macrosporum need to be improved. Tuber species formed well-developed ectomycorrhizae on C. sativa in nursery conditions.

Comprehensive Transcriptome Analysis of Phytohormone Biosynthesis and Signaling Genes in the Flowers of Chinese Chinquapin (Castanea henryi)

Chinese chinquapin (Castanea henryi) nut provides a rich source of starch and nutrients as food and feed, but its yield is restricted by a low ratio of female to male flowers. Little is known about the developmental programs underlying sex differentiation of the flowers. To investigate the involvement of phytohormones during sex differentiation, we described the morphology of male and female floral organs and the cytology of flower sex differentiation, analyzed endogenous levels of indole-3-acetic acid (IAA), gibberellins (GAs), cytokinins (CKs), and abscisic acid (ABA) in the flowers, investigated the effects of exogenous hormones on flower development, and evaluated the expression profiles of genes related to biosyntheses and signaling pathways of these four hormones using RNA-Seq combined with qPCR. Morphological results showed that the flowers consisted of unisexual and bisexual catkins, and could be divided into four developmental stages. HPLC results showed that CK accumulated much more in the female flowers than that in the male flowers, GA and ABA showed the opposite results, while IAA did not show a tendency. The effects of exogenous hormones on sex differentiation were consistent with those of endogenous hormones. RNA-Seq combined with qPCR analyses suggest that several genes may play key roles in hormone biosynthesis and sex differentiation. This study presents the first comprehensive report of phytohormone biosynthesis and signaling during sex differentiation of C. henryi, which should provide a foundation for further mechanistic studies of sex differentiation in Castanea Miller species and other nonmodel plants.

Identification and expression analysis of starch branching enzymes involved in starch synthesis during the development of chestnut (Castanea mollissima Blume) cotyledons

Chinese chestnut (Castanea mollissima Blume) is native to China and distributes widely in arid and semi-arid mountain area with barren soil. As a perennial crop, chestnut is an alternative food source and acts as an important commercial nut tree in China. Starch is the major metabolite in nuts, accounting for 46 ~ 64% of the chestnut dry weight. The accumulation of total starch and amylopectin showed a similar increasing trend during the development of nut. Amylopectin contributed up to 76% of the total starch content at 80 days after pollination (DAP). The increase of total starch mainly results from amylopectin synthesis. Among genes associated with starch biosynthesis, CmSBEs (starch branching enzyme) showed significant increase during nut development. Two starch branching enzyme isoforms, CmSBE I and CmSBE II, were identified from chestnut cotyledon using zymogram analysis. CmSBE I and CmSBE II showed similar patterns of expression during nut development. The accumulations of CmSBE transcripts and proteins in developing cotyledons were characterized. The expressions of two CmSBE genes increased from 64 DAP and reached the highest levels at 77 DAP, and SBE activity reached its peak at 74 DAP. These results suggested that the CmSBE enzymes mainly contributed to amylopectin synthesis and influenced the amylopectin content in the developing cotyledon, which would be beneficial to chestnut germplasm selection and breeding.

Evaluation of forest structure, biomass and carbon sequestration in subtropical pristine forests of SW China

Very old natural forests comprising the species of Fagaceae (Lithocarpus xylocarpus, Castanopsis wattii, Lithocarpus hancei) have been prevailing since years in the Ailaoshan Mountain Nature Reserve (AMNR) SW China. Within these forest trees, density is quite variable. We studied the forest structure, stand dynamics and carbon density at two different sites to know the main factors which drives carbon sequestration process in old forests by considering the following questions: How much is the carbon density in these forest trees of different DBH (diameter at breast height)? How much carbon potential possessed by dominant species of these forests? How vegetation carbon is distributed in these forests? Which species shows high carbon sequestration? What are the physiochemical properties of soil in these forests? Five-year (2005-2010) tree growth data from permanently established plots in the AMNR was analysed for species composition, density, stem diameter (DBH), height and carbon (C) density both in aboveground and belowground vegetation biomass. Our study indicated that among two comparative sites, overall 54 species of 16 different families were present. The stem density, height, C density and soil properties varied significantly with time among the sites showing uneven distribution across the forests. Among the dominant species, L. xylocarpus represents 30% of the total carbon on site 1 while C. wattii represents 50% of the total carbon on site 2. The average C density ranged from 176.35 to 243.97 t C ha^-1. The study emphasized that there is generous degree to expand the carbon stocking in this AMNR through scientific management gearing towards conservation of old trees and planting of potentially high carbon sequestering species on good site quality areas.

Quantification and identification of microorganisms found on shell and kernel of fresh edible chestnuts in Michigan

BACKGROUND

Chestnut is a relatively new cultivated crop for Michigan, and postharvest loss due to decay has been problematic as production has increased each year. In 2007, more than 25% of chestnuts were lost to postharvest decay, equivalent to approximately 5300 kg of fresh product. To determine the organisms responsible for decay, a microbiological survey was performed in 2006 and 2007 to identify microorganisms involved in postharvest shell (external surface) mold and internal kernel (edible portion) decay of chestnuts.

RESULTS

Filamentous fungi including Penicillium expansum, Penicillium griseofulvum, Penicillium chrysogenum, Coniophora puteana, Acrospeira mirabilis, Botryosphaeria ribis, Sclerotinia sclerotiorum, Botryotinia fuckeliana (anamorph Botrytis cinerea) and Gibberella sp. (anamorph Fusarium sp.) were the predominant microorganisms that negatively impacted fresh chestnuts. Populations of microorganisms varied between farms, harvesting methods and chestnut parts.

CONCLUSION

Chestnuts harvested from the orchard floor were significantly (P < 0.05) more contaminated than chestnuts harvested directly from the tree, by more than 2 log colony-forming units (CFU) g(-1) . In addition, a significant difference (P < 0.05) in the microbial population was seen between chestnuts submitted by different growers, with average count ranges of fungi, mesophilic aerobic bacteria (MAB) and yeasts equal to 4.75, 4.59 and 4.75 log CFU g(-1) respectively. © 2016 Society of Chemical Industry.

[Effects of conversion of evergreen broad-leaved forest to Chinese chestnut plantation on soil organic carbon pools.]

Converting natural forests to plantations significantly affects the characteristics of soil organic carbon (C) pools, due to the changes of vegetation cover and management practices. In this paper, to investigate the effects of conversion from evergreen broad-leaved forest (EBF) to Chinese chestnut plantation (CP) on soil organic C pool, the soils from surface (0-20 cm) and subsurface (20-40 cm) layers were sampled from the above two forests (the CP was converted from the EBF and had been intensively managed for 10 years) in Lin'an City, Zhejiang Province. The soil orga-nic C storage, labile organic C pools, and other basic soil properties were determined. The chemical composition of soil organic C was determined by nuclear magnetic resonance (NMR) technique. Results showed that the soil organic C storage, water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC) and readily oxidizable C (ROC) concentrations in the surface layer decreased by 19.7%, 34.4%, 25.8%, 30.4% and 25.2%, respectively, after the conversion from EBF to CP. Such values for the subsurface layers decreased by 13.5%, 38.4%, 19.8%, 34.1% and 22.2%, respectively. The O-alkyl C content, aromatic C content and aromaticity of soil organic C in the surface layer decreased signi-ficantly by the land-use conversion, while alkyl C content, carbonyl C content and alkyl C to O-alkyl C (A/O-A) ratio increased signi-ficantly. The O-alkyl C content of soil organic C in the subsurface layer decreased significantly by the land-use conversion, alkyl C content and A/O-A ratio increased significantly, and aromatic C content, carbonyl C content and aromaticity of soil organic C were not changed. In conclusion, conve-rting EBF to CP and subsequent intensive management significantly decreased the soil organic C sto-rage and labile C pool contents and altered the chemical composition of soil organic C.

[Effects of forest regeneration patterns on the quantity and chemical structure of soil solution dissolved organic matter in a subtropical forest.]

Using the negative pressure sampling method, the concentrations and spectral characte-ristics of dissolved organic matter (DOM) of soil solution were studied at 0-15, 15-30, 30-60 cm layers in Castanopsis carlesii forest (BF), human-assisted naturally regenerated C. carlesii forest (RF), C. carlesii plantation (CP) in evergreen broad-leaved forests in Sanming City, Fujian Pro-vince. The results showed that the overall trend of dissolved organic carbon (DOC) concentrations in soil solution was RF>CP>BF, and the concentration of dissolved organic nitrogen (DON) was highest in C. carlesii plantation. The concentrations of DOC and DON in surface soil (0-15 cm) were all significantly higher than in the subsurface (30-60 cm). The aromatic index (AI) was in the order of RF>CP>BF, and as a whole, the highest AI was observed in the surface soil. Higher fluorescence intensity and a short wave absorption peak (320 nm) were observed in C. carlesii plantation, suggesting the surface soil of C. carlesii plantation was rich in decomposed substance content, while the degree of humification was lower. A medium wave absorption peak (380 nm) was observed in human-assisted naturally regenerated C. carlesii forest, indicating the degree of humification was higher which would contribute to the storage of soil fertility. In addition, DOM characte-ristics in 30-60 cm soil solution were almost unaffected by forest regeneration patterns.

[Fine root production in initial stage of Castanopsis carlesii under different regeneration modes in Sanming, Fujian Province, China]

Fine root biomass and production in initial stage of three different regeneration approaches, i.e., natural regeneration with anthropogenic promotion (AR) , the Castanopsis carlesii plantation ( CC) and the Cunninghamia lanceolata plantation ( CL) on the clear-cutting sites of the secondary forest of C. carlesii (CK), in Sanming, Fujian Province, were investigated by using both minrhizotrons and the soil coring methods. The results of a year observation showed that the average fine root biomass was 422.5, 253.1, 197.2 and 162.8 g · m(-2), and the fine root production was 284.0, 182.6, 136.7 and 15.4 g · m(-2) · a(-1) for AR, CC, CL and CK, respectively. The maximum value of production was found in spring for AR and CC, in autumn for CL, and in winter for CK. Fine root production of other plants was higher than that of target tree species in CC, and vice verse in CL. There was a significant positive correlation between monthly fine root production and monthly precipitation in AR and CC. Significant positive correlation was found between monthly fine root production of other plants and monthly temperature in CL. The fine root under annual production and annual average biomass of these three young forests mainly distributed in the soil layer of 20- 40 cm, and mainly in the diameter class of 0-1 mm. The study demonstrated that the biomass and production of fine root under anthropogenic promotion were greater than that of the plantation, and the method of anthropogenic promotion were more conducive to increase the returning of organic matter, improve soil fertility, and maintain a high productivity in initial stage of forest regeneration.

Experimental evidence for an intraspecific Janzen-Connell effect mediated by soil biota

The negative effect of soil pathogens on seedling survival varies considerably among conspecific individuals, but the underlying mechanisms are largely unknown. For variation between heterospecifics, a common explanation is the Janzen-Connell effect: negative density dependence in survival due to specialized pathogens aggregating on common hosts. We test whether an intraspecific Janzen-Connell effect exists, i.e., whether the survival chances of one population's seedlings surrounded by a different conspecific population increase with genetic difference, spatial distance, and trait dissimilarity between them. In a shade-house experiment, we grew seedlings of five populations of each of two subtropical tree species (Castanopsis fissa and Canarium album) for which we measured genetic distance using intersimple sequence repeat (ISSR) analysis and eight common traits/characters, and we treated them with soil material or soil biota filtrate collected from different populations. We found that the relative survival rate increased with increasing dissimilarity measured by spatial distance, genetic distance, and trait differences between the seedling and the population around which the soil was collected. This effect disappeared after soil sterilization. Our results provide evidence that genetic variation, trait similarity, and spatial distance can explain intraspecific variation in plant-soil biotic interactions and suggest that limiting similarity also occurs at the intraspecific level.

Oviposition preference and offspring performance of Mechoris ursulus (Coleoptera: Attelabidae) in Cyclobalanopsis glaucoides (Fagales: Fagaceae) and Quercus franchetii (Fagales: Fagaceae) in Central Yunnan, China

Mechoris ursulus (Roelofs) (Coleoptera: Attelabidae) is a pest weevil of Fagaceae oak trees in eastern Asia. The female has a distinct branch-cutting behavior in conjunction with oviposition in the acorns of its host plant. This study analyzed the factors influencing oviposition preference by carrying out continuous field surveys over the course of 2009-2010 and through laboratory rearing. The field survey showed that for both of the hosts, Cyclobalanopsis glaucoides Schottky (Fagales: Fagaceae) and Quercus franchetii Skan, M. ursulus preferred branches with fewer acorns and larger acorns on the same branch for oviposition. Laboratory rearing experiments showed offspring performance (i.e., survival rate and fresh weight of larvae) was significantly and positively correlated with acorn size. Preference for larger acorns could maximize the fitness of offspring by providing sufficient food source and space.

Chestnut, European (Castanea sativa)

Development of a system for direct transfer of antifungal candidate genes into European chestnut (Castanea sativa) would provide an alternative approach to conventional breeding for production of chestnut trees that are tolerant to ink disease caused by Phytophthora spp. Overexpression of genes encoding PR proteins (such as thaumatin-like proteins), which display antifungal activity, may represent an important advance in control of the disease. We have used a chestnut thaumatin-like protein gene (CsTL1) isolated from European chestnut cotyledons and have achieved overexpression of the gene in chestnut somatic embryogenic lines used as target material. We have also acclimatized the transgenic plants and grown them on in the greenhouse. Here, we describe the various steps of the process, from the induction of somatic embryogenesis to the production of transgenic plants.

Chestnut, American (Castanea dentata (Marsh.) Borkh.)

The key to successful transformation of American chestnut is having the correct combination of explant tissue, selectable markers, a very robust DNA delivery system, and a reliable regeneration system. The most important components of this transformation protocol for American chestnut are the following: starting out with rapidly dividing somatic embryos, treating the embryos gently throughout the Agrobacterium inoculation and cocultivation steps, doing the cocultivation step in desiccation plates, and finally transferring the embryos into temporary-immersion bioreactors for selection. None of these departures from standard Agrobacterium transformation protocols is sufficient by itself to achieve transgenic American chestnut, but each component makes a difference, resulting in a highly robust protocol. The average transformation efficiency that can be expected using the described protocol is approximately 170 stable embryogenic transformation events per gram of somatic embryo tissue, a considerable improvement over the 20 transformation events per gram we reported in 2006 (Maynard et al. American chestnut (Castanea dentata (Marsh.) Borkh.) Agrobacterium protocols, 2nd ed., 2006). We have regenerated nearly 100 of these events, containing 23 different gene constructs, into whole plants. As of the fall of 2013, we had a total of 1,275 transgenic chestnut trees planted at eight locations in New York State and one in Virginia. Based on a combination of field-trial inoculations, greenhouse small-stem inoculations, and detached-leaf assays, we have identified three transgenes that produce stronger resistance to chestnut blight than non-transgenic American chestnut. Depending on the transgene and the event, this resistance can be either intermediate between American chestnut and Chinese chestnut, approximately equal to or even higher than the resistance naturally found in Chinese chestnut.

Leaf physiology and biomass allocation of backcross hybrid American chestnut (Castanea dentata) seedlings in response to light and water availability

Partial canopy cover promotes regeneration of many temperate forest trees, but the consequences of shading on seedling drought resistance are unclear. Reintroduction of blight-resistant American chestnut (Castanea dentata (Marsh.) Borkh.) into eastern North American forests will often occur on water-limited sites and under partial canopy cover. We measured leaf pre-dawn water potential (Ψpd), leaf gas exchange, and growth and biomass allocation of backcross hybrid American chestnut seedlings from three orchard sources grown under different light intensities (76, 26 and 8% full photosynthetically active radiation (PAR)) and subjected to well-watered or mid-season water-stressed conditions. Seedlings in the water-stress treatment were returned to well-watered conditions after wilting to examine recovery. Seedlings growing under medium- and high-light conditions wilted at lower leaf Ψpd than low-light seedlings. Recovery of net photosynthesis (Anet) and stomatal conductance (gs) was greater in low and medium light than in high light. Seed source did not affect the response to water stress or light level in most cases. Between 26 and 8% full PAR, light became limiting to the extent that the effects of water stress had no impact on some growth and morphological traits. We conclude that positive and negative aspects of shading on seedling drought tolerance and recovery are not mutually exclusive. Partial shade may help American chestnut tolerate drought during early establishment through effects on physiological conditioning.

Potential fecundity of a highly invasive gall maker, Dryocosmus kuriphilus (Hymenoptera: Cynipidae)

Fecundity is a key factor in modulating population growth rate, and is of particular significance when considering the invasiveness of introduced species. In insects, fecundity is affected by body size, age, and nutrition. We investigated the potential fecundity of the invasive Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), an introduced parthenogenetic gall former of Asian origin and a global pest of chestnut (Castanea spp.), to better understand its invasiveness. We compared ovarian, egg, and body metrics of adult wasps of different age. We evaluated insect weight, body length, mesosomal and metasomal lengths and widths, hind femur length, number of eggs, and size of eggs in wasps from four age cohorts. Adult weight and metasomal width were positively correlated with number of eggs. Egg load decreased with wasp age, and egg size initially increased before decreasing. Our findings suggest that adult D. kuriphilus, previously reported as proovigenic, may be resorping eggs in the absence of suitable hosts, and reallocating nutritive resources for body maintenance and egg quality to increase fitness, implicating a plasticity in its reproductive strategy. D. kuriphilus may be able to vary its potential fecundity in response to nutrition and host availability, thus increasing its invasiveness.

Effects of roads on Castanopsis carlesii seedlings and their leaf herbivory in a subtropical forest in China

The effects of a forest road on Castanopsis carlesii (Hemsley) Hayata (Fagales: Fagaceae) seedlings and their leaf herbivory were investigated in a subtropical forest at Jiulianshan National Nature Reserve, Jiangxi, China. A total of 1124 seedlings, 33949 leaves, 468 leaf mines, and 205 leaf galls were found. Generally, individual numbers, tree heights, and leaf numbers of C. carlesii seedlings became lower with increasing distances from the road. These results might indicate that old seedlings were fewer and survival rate of seedlings was lower in forest interiors. Leaf miners preferred the seedlings close to the forest road, while leaf gallers preferred the seedlings about 2 m from the road. Species diversity of leaf miners was higher in the forest interior area, while species diversity of leaf gallers was higher near the road. However, both leaf miners and leaf gallers decreased in general from the road to the interior forest. There were interspecific differences in the effects of roads on leaf miner species and leaf galler species. The effects of the road on seedlings and insects could be explained by varying microhabitat conditions and different ecological strategies.

[Effects of tree species diversity on fine-root biomass and morphological characteristics in subtropical Castanopsis carlesii forests]

Fine roots in the Castanopsis carlesii plantation forest (MZ), the secondary forest of C. carlesii through natural regeneration with anthropogenic promotion (AR), and the secondary forest of C. carlesii through natural regeneration (NR) in Sanming City, Fujian Province, were estimated by soil core method to determine the influence of tree species diversity on biomass, vertical distribution and morphological characteristics of fine roots. The results showed that fine root biomass for the 0-80 cm soil layer in the MZ, AR and NR were (182.46 +/- 10.81), (242.73 +/- 17.85) and (353.11 +/- 16.46) g x m(-2), respectively, showing an increased tendency with increasing tree species diversity. In the three forests, fine root biomass was significantly influenced by soil depth, and fine roots at the 0-10 cm soil layer accounted for more than 35% of the total fine root biomass. However, the interaction of stand type and soil depth on fine-root distribution was not significant, indicating no influence of tree species diversity on spatial niche segregation in fine roots. Root surface area density and root length density were the highest in NR and lowest in the MZ. Specific root length was in the order of AR > MZ > NR, while specific root surface area was in the order of NR > MZ > AR. There was no significant interaction of stand type and soil depth on specific root length and specific root surface area. Fine root morphological plasticity at the stand level had no significant response to tree species diversity.

Ectomycorrhizal inoculum potential of northeastern US forest soils for American chestnut restoration: results from field and laboratory bioassays

American chestnut (Castanea dentata) was once a dominant overstory tree in eastern USA but was decimated by chestnut blight (Cryphonectria parasitica). Blight-resistant chestnut is being developed as part of a concerted restoration effort to bring this heritage tree back. Here, we evaluate the potential of field soils in the northern portion of the chestnut's former range to provide ectomycorrhizal (EM) fungus inoculum for American chestnut. In our first study, chestnut seedlings were grown in a growth chamber using soil collected from three sites dominated by red oak (Quercus rubra) as inoculum and harvested after 5 months. Of the 14 EM fungi recovered on these seedlings, four species dominated in soils from all three sites: Laccaria laccata, a Tuber sp., Cenococcum geophilum, and a thelephoroid type. Seedlings grown in the nonsterilized soils were smaller than those growing in sterilized soils. In the second study, chestnut seedlings were grown from seed planted directly into soils at the same three sites. Seedlings with intermingling roots of established trees of various species were harvested after 5 months. Seventy-one EM fungi were found on the root tips of the hosts, with 38 occurring on chestnut seedlings. Multiple versus single host EM fungi were significantly more abundant and frequently encountered. The fungi observed dominating on seedlings in the laboratory bioassay were not frequently encountered in the field bioassay, suggesting that they may not have been active in mycelial networks in the field setting but were in the soils as resistant propagules that became active in the bioassay. These results show that soil from red oak stands can be used to inoculate American chestnut with locally adapted ectomycorrhizal fungi prior to outplanting, a relatively cost effective approach for restoration efforts.

[Allelopathic potential of Phyllostachys edulis on two dominant tree species of evergreen broad-leaved forest in its invasive process]

In order to explore the influence of Phyllostachys edulis invasion on the surrounding forest environment,the effects of aqueous extracts from P. edulis on two dominant species (Castanopsis sclerophylla and Cyclobalanopsis glaunca)in southern China were assessed by germination bioassays. The results showed that seed germination effects depended on the concentration of aqueous extracts and the extract sources. The highest extract concentration showed significant inhibitory effects on seed germination percentage, which was 82. 3% -102. 2% of control for C. sclerophylla and 80% -90. 9% of control for C. glauca, while in the treatment with lowest extract concentration the values were 101.7% - 107.6% of control for C. sclerophylla and 94.9% - 109. 1% of control for C. glauca, respectively. The extracts had inhibitory effects on the germination speed of both species (P < 0.05) , except that no effects on C. sclerophylla were observed in the low concentration treatment. Extracts at the highest concentration reduced the root activity of C. sclerophylla by 41. 1% -62. 4% (P <0.05). There were obvious different effects among the treatments with different extract sources. Seed germination percentage was the lowest in root extract treatments. There was no obvious difference for shoot height of C. sclerophylla in different treatments(P >0.05) , while there was significant difference for C. glauca, its shoot height was higher in the leaf, root, and litter extracts treatments than in the soil extracts treatments. P. edulis possesses allelopathic potential that could possibly facilitate its invasion and monoculture formation, and does harm to the surrounding forest environment.

[Aboveground biomass of natural Castanopsis carlesii-Schima superba community in Xiaokeng of Nanling Mountains, South China]

By the method of clear cutting, a measurement was made on the aboveground biomass (AGB) of 24-year old natural Castanopsis carlesii-Schima superba community in an 800 m2 plot in Xiaokeng of Nanling Mountains, South China. The distribution patterns of the total AGB in different forest layers, tree species, and tree layer organs were investigated, and the AGB regression models were constructed. The results showed that when constructing the AGB regression models, more than 12 samples would be feasible. Based on the measured AGB of 265 felled trees, the AGB models of mixed broadleaved species were AGB = 0. 128D(2.372) and AGB = 242.331(D2H)(0.947). The single tree's AGB model of C. carlesii, S. superba, and Cunninghamia lanceolata was also established. The total AGB of the forest community was 115.20 t x hm(-2), of which, the AGB of tree layer, understory layer, liana, and litter layer was 111.25, 1.01, 0.36, and 2.58 t x hm(-2), respectively. The AGB of C. carlesii and S. superba took up 39.1% and 28.7% of the tree layer AGB, respectively. The AGB of tree stem and branch-leaf occupied 81.0% and 19.0% of the tree layer AGB, respectively.

[Effects of fertilization on soil CO2 flux in Castanea mollissima stand]

In June 2011-June 2012, a fertilization experiment was conducted in a typical Castanea mollissima stand in Lin' an of Zhejiang Province, East China to study the effects of inorganic and organic fertilization on the soil CO2 flux and the relationships between the soil CO2 flux and environmental factors. Four treatments were installed, i. e., no fertilization (CK), inorganic fertilization (IF), organic fertilization (OF), half organic plus half inorganic fertilization (OIF). The soil CO2 emission rate was determined by the method of static closed chamber/GC technique, and the soil temperature, soil moisture content, and soil water-soluble organic carbon (WSOC) concentration were determined by routine methods. The soil CO2 emission exhibited a strong seasonal pattern, with the highest rate in July or August and the lowest rate in February. The annual accumulative soil CO2 emission in CK was 27.7 t CO2 x hm(-2) x a(-1), and that in treatments IF, OF, and OIF was 29.5%, 47.0%, and 50.7% higher than the CK, respectively. The soil WSOC concentration in treatment IF (105.1 mg kg(-1)) was significantly higher than that in CK (76.6 mg x kg(-1)), but was obviously lower than that in treatments OF (133.0 mg x kg(-1)) and OIF (121.2 mg x kg(-1)). The temperature sensitivity of respiration (Q10) in treatments CK, IF, OF, and OIF was 1.47, 1.75, 1.49, and 1.57, respectively. The soil CO2 emission rate had significant positive correlations with the soil temperature at the depth of 5 cm and the soil WSOC concentration, but no significant correlation with soil moisture content. The increase of the soil WSOC concentration caused by fertilization was probably one of the reasons for the increase of soil CO2 emission from the C. mollissima stand.

Disparity in elevational shifts of European trees in response to recent climate warming

Predicting climate-driven changes in plant distribution is crucial for biodiversity conservation and management under recent climate change. Climate warming is expected to induce movement of species upslope and towards higher latitudes. However, the mechanisms and physiological processes behind the altitudinal and latitudinal distribution range of a tree species are complex and depend on each tree species features and vary over ontogenetic stages. We investigated the altitudinal distribution differences between juvenile and adult individuals of seven major European tree species along elevational transects covering a wide latitudinal range from southern Spain (37°N) to northern Sweden (67°N). By comparing juvenile and adult distributions (shifts on the optimum position and the range limits) we assessed the response of species to present climate conditions in relation to previous conditions that prevailed when adults were established. Mean temperature increased by 0.86 °C on average at our sites during the last decade compared with previous 30-year period. Only one of the species studied, Abies alba, matched the expected predictions under the observed warming, with a maximum abundance of juveniles at higher altitudes than adults. Three species, Fagus sylvatica, Picea abies and Pinus sylvestris, showed an opposite pattern while for other three species, such as Quercus ilex, Acer pseudoplatanus and Q. petraea, we were no able to detect changes in distribution. These findings are in contrast with theoretical predictions and show that tree responses to climate change are complex and are obscured not only by other environmental factors but also by internal processes related to ontogeny and demography.

[Effects of biological organic fertilizer on microbial community's metabolic activity in a soil planted with chestnut (Castanea mollissima)]

A field experiment was conducted in Zhashui County of Shaanxi Province, Northwest China in 2011 to study the effects of biological organic fertilizer on the microbial community's metabolic activity in a soil planted with chestnut (Castanea mollissima). Three treatments were installed, i. e., control, compound fertilizer, and biological organic fertilizer. Soil samples were collected at harvest, and the metabolic activity was tested by Biolog method. In the treatment of biological organic fertilizer, the average well color development, Shannon evenness, richness, and McIntosh indices of microbial community were all significantly higher than the other two treatments. As compared with the control, applying biological organic fertilizer improved the ability of soil microbes in utilizing the carbon sources of carbohydrates and polymers, while applying compound fertilizer was in opposite. The principal component analysis demonstrated that there was an obvious difference in the soil microbial community among different treatments, mainly depending on the species of carbohydrates and amino acids.

Light energy management in micropropagated plants of Castanea sativa, effects of photoinhibition

The limited development of photoprotective mechanisms, specifically heat dissipation capacity, found in micropropagated plants may be the result of low xanthophyll cycle pigment content and reduced de-epoxidation capacity making them highly susceptible to photodamage. The effects of gradual or sudden increase of light on Castanea sativa in vitro cultured and during their ex vitro transference was evaluated. The results were compared with those determined in nursery-grown plants. In vitro plants responded poorly to gradual increase in irradiance, exhibiting a low electron transport rate (ETR) agreeing with low non-photochemical quenching (NPQ) and a limited de-epoxidation capacity, not synthesizing detectable amounts of zeaxanthin (Z). Regarding a sudden increase in light (photoinhibition treatment, PhT); post-PhT as in vitro as well nursery plants showed a significant decrease in their maximal efficiency of PSII (F(v)/F(m)), but in vitro the decrease was very drastic (around 0.2) different from that observed in nursery (around 0.69). In vitro, NPQ was mainly determined by the slow relaxing component, NPQ(s) (80.8%), concomitant with a pronounced decrease of D1 protein post-PhT, and a lack of de-epoxidation capacity. During ex vitro transfer, PhT lead to death of some plants, specifically during root induction. The photoprotective mechanisms were activated over time in ex vitro conditions, indicating that micropropagated Castanea sativa display a potential for light acclimation, adjusting their photosynthetic apparatus to the ambient growth irradiance. Understanding the mechanisms that micropropagated plants deployed and how they face high light intensity events, will allow us to search for strategies to improve performance to possible light fluctuations that normally occur in ex vitro conditions during plant acclimation.

Genetic transformation of European chestnut somatic embryos with a native thaumatin-like protein (CsTL1) gene isolated from Castanea sativa seeds

The availability of a system for direct transfer of antifungal candidate genes into European chestnut (Castanea sativa Mill.) would offer an alternative approach to conventional breeding for production of chestnut trees tolerant to ink disease caused by Phytophthora spp. For the first time, a chestnut thaumatin-like protein gene (CsTL1), isolated from chestnut cotyledons, has been overexpressed in three chestnut somatic embryogenic lines. Transformation experiments have been performed using an Agrobacterium tumefaciens Smith and Townsend vector harboring the neomycin phosphotransferase (NPTII) selectable and the green fluorescent protein (EGFP) reporter genes. The transformation efficiency, determined on the basis of the fluorescence of surviving explants, was clearly genotype dependent and ranged from 32.5% in the CI-9 line to 7.1% in the CI-3 line. A total of 126 independent transformed lines were obtained. The presence and integration of chestnut CsTL1 in genomic DNA was confirmed by polymerase chain reaction (PCR) and Southern blot analyses. Quantitative real-time PCR revealed that CsTL1 expression was up to 13.5-fold higher in a transgenic line compared with its corresponding untransformed line. In only one of the 11 transformed lines tested, expression of the CsTL1 was lower than the control. The remaining 115 transformed lines were successfully subjected to cryopreservation. Embryo proliferation was achieved in all of the transgenic lines regenerated and the transformed lines showed a higher mean number of cotyledonary stage embryos and total number of embryos per embryo clump than their corresponding untransformed lines. Transgenic plants were regenerated after maturation and germination of transformed somatic embryos. Furthermore, due to the low plantlet conversion achieved, axillary shoot proliferation cultures were established from partially germinated embryos (only shoot development), which were multiplied and rooted according to procedures already established. Transgenic plants were acclimatized and grown in a greenhouse. No phenotypic differences were found with control plants, suggesting no potential cytotoxic effects of the green fluorescent protein. The results reported in the present work could be considered as a first step toward the production of fungal-disease tolerant cisgenic chestnut plants.

Programmed cell death is responsible for replaceable bud senescence in chestnut (Castanea mollissima BL.)

In the chestnut "replaceable bud" cultivar 'Tima zhenzhu', the auxiliary bud formed on the fruiting branch dies after fruiting, giving rise to a morphology more suitable than the wild type's for intensive cultivation and heightened production. Here, we show that many of the hallmarks of programmed cell death (PCD) occur during the senescence of the replaceable bud, including DNA degradation, a high ratio of PCD cells and the breakdown of cell ultrastructure. The time course of the senescence was followed by sampling the developing bud from 20 to 40 days after flowering. In cv. 'Tima zhenzhu', DNA degradation was detectable prior to any visible sign of bud senescence, while it did not occur in the wild type (cv. 'Dabanhong'). The ratio of PCD cells (as determined by flow cytometry) rose over the sampling period and was consistently higher in cv. 'Tima zhenzhu' than in cv. 'Dabanhong'. After staining the bud cell nuclei with propidium iodide, it was clear that both their chromatin content and overall size fell over the sampling period in cv. 'Tima zhenzhu' while in cv. 'Dabanhong', no such decrease occurred. Other characteristics of PCD were noted in cv. 'Tima zhenzhu''s bud cells, including chromatin condensation, tonoplast invagination and DNA cleavage. We conclude that the replaceable bud senescence phenomenon is driven by PCD. The manipulation of this trait may have potential for remodeling the pattern of development of the fruit-bearing branches of chestnut.

KEY MESSAGE

This paper first reported the occurrence of programmed cell death during the senescence of vegetative buds in a woody species, and the results extend the range of knowledge of PCD.

[Dynamic changes of soil respiration in Citrus reticulata and Castanea henryi orchards in Wanmulin Nature Reserve, Fujian Province of East China]

From January 2009 to December 2009, the soil respiration in the Citrus reticulata and Castanea henryi orchards in Wanmulin Nature Reserve was measured with Li-8100, aimed to characterize the dynamic changes of the soil respiration and its relationships with soil temperature and moisture in the two orchards. The monthly variation of the soil respiration in the orchards was single-peaked, with the peak appeared in July (3.76 micromol x m(-2) x s(-1)) ) and August (2.69 micromol x m(-2) x s(-1)). Soil temperature was the main factor affecting the soil respiration, and explained 73%-86% of the monthly variation of soil respiration. The average annual soil respiration rate was significantly higher in Citrus reticulata orchard than in Castanea henryi orchard, with the mean value being 2.68 and 1.55 micromol x m(-2) x s(-1), respectively. There was a significant positive correlation between the soil respiration rate and soil moisture content in Castanea henryi orchard, but less correlation in Citrus reticulata orchard. The Q10 value of the soil respiration in Citrus reticulata and Castanea henryi orchards was 1.58 and 1.75, and the annual CO2 flux was 10.01 and 5.77 t C x hm(-2) x a(-1), respectively.

[Effects of the conversion from native shrub forest to Chinese chestnut plantation on soil carbon and nitrogen pools]

To investigate the effects of the conversion from native shrub forest (NF) to Chinese chestnut plantation (CP) on the soil carbon (C) and nitrogen (N) pools, soil samples were collected from the adjacent NF and CP in Anji County of Zhejiang Province, with their water-soluble organic C (WSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water-soluble organic N (WSON), and microbial biomass N (MBN) determined. The spectral characteristics of soil organic C were also determined by using nuclear magnetic resonance (NMR) technique. After the conversion from NF to CP, the soil alkalyzable N, available phosphorus, and available potassium contents increased significantly, while the soil WSOC, MBC, ROC, WSON, and MBN were in adverse. The soil organic C in both NF and CP was dominated by alkyl C and O-alkyl C, but the proportions of O-alkyl C and carbonyl C in soil organic C decreased while the proportions of alkyl C and aromatic C as well as the alkyl C/O-alkyl C ratio and the aromaticity of soil organic C all increased significantly after the conversion from NF to CP, indicating that this conversion increased the stability of soil organic C pool significantly. In conclusion, the conversion from NF to CP and the intensive management of CP decreased the contents of soil labile C and soil N but increased the stability of soil C pool significantly.

[Effects of different water-saving irrigation modes on chestnut growth and fruiting in drought hilly land]

Taking the chestnut trees in a semi-arid and semi-humid hilly orchard of Tai' an, Shandong Province of East China as test objects, a field experiment was conducted to study the effects of different water-saving irrigation modes (pottery jar storing water, small hole storing water, and border irrigation with covering) on the soil moisture characteristics and the growth, fruiting, and development of chestnut roots. Comparing with the control (border irrigation), all the three water-saving irrigation modes could prolong the period of soil keeping moist, and the best effect came from pottery, jar treatment, with the soil keeping moist for 32 days, 13 days longer than the control. Under water-saving irrigations, the bearing branches length and number, leaf area and mass, and shoot mixed buds all increased obviously. Both pottery jar storing water and small hole storing water could irrigate deeper roots and induce root growth in deeper soil layers, and thus, relieve the drought stress on superficial roots. The three water-saving irrigation modes could increase chestnut yield markedly, with an increment of 18.8%, 16.5%, and 14.2%, respectively, as compared with the control.

Effect of competitive interactions between ectomycorrhizal and saprotrophic fungi on Castanea sativa performance

In Northeast of Portugal, the macrofungal community associated to chestnut tree (Castanea sativa Mill.) is rich and diversified. Among fungal species, the ectomycorrhizal Pisolithus tinctorius and the saprotroph Hypholoma fasciculare are common in this habitat. The aim of the present work was to assess the effect of the interaction between both fungi on growth, nutritional status, and physiology of C. sativa seedlings. In pot experiments, C. sativa seedlings were inoculated with P. tinctorius and H. fasciculare individually or in combination. Inoculation with P. tinctorius stimulated the plant growth and resulted in increased foliar-N, foliar-P, and photosynthetic pigment contents. These effects were suppressed when H. fasciculare was simultaneously applied with P. tinctorius. This result could be related to the inhibition of ectomycorrhizal fungus root colonization as a result of antagonism or to the competition for nutrient sources. If chestnut seedlings have been previously inoculated with P. tinctorius, the subsequent inoculation of H. fasciculare 30 days later did not affect root colonization, and mycorrhization benefits were observed. This work confirms an antagonistic interaction between ectomycorrhizal and saprotrophic fungi with consequences on the ectomycorrhizal host physiology. Although P. tinctorius is effective in promoting growth of host trees by establishing mycorrhizae, in the presence of other fungi, it may not always be able to interact with host roots due to an inability to compete with certain fungi.

CsSCL1 is differentially regulated upon maturation in chestnut microshoots and is specifically expressed in rooting-competent cells

The Castanea sativa SCL1 gene (CsSCL1) has previously been shown to be induced by auxin during adventitious root (AR) formation in rooting-competent microshoots. However, its expression has not previously been analyzed in rooting-incompetent shoots. This study focuses on the regulation of CsSCL1 during maturation and the role of the gene in the formation of AR. The expression of CsSCL1 in rooting-incompetent microshoots and other tissues was investigated by quantitative reverse transcriptase--polymerase chain reaction. The analysis was complemented by in situ hybridization of the basal segments of rooting-competent and --incompetent microshoots during AR induction, as well as in AR and lateral roots. It was found that CsSCL1 is upregulated by auxin in a cell-type- and phase-dependent manner during the induction of AR. In root-forming shoots, CsSCL1 mRNA was specifically located in the cambial zone and derivative cells, which are rooting-competent cells, whereas in rooting-incompetent shoots the hybridization signal was more diffuse and evenly distributed through the phloem and parenchyma. CsSCL1 expression was also detected in lateral roots and axillary buds. The different CsSCL1 expression patterns in rooting-competent and -incompetent microshoots, together with the specific location of transcripts in cell types involved in root meristem initiation and in the root primordia of AR and lateral roots, indicate an important role for the gene in determining whether certain cells will enter the root differentiation pathway and its involvement in meristem maintenance.

Descriptive sensory analysis and free sugar contents of chestnut cultivars grown in North America

BACKGROUND

Various chestnut (Castanea) species and cultivars are currently produced and marketed in North America including Peach, Qing, AU-Homestead, Eaton, Marrone di Castel del Rio, and Colossal. In spite of their availability in the marketplace, similarities in sensory characteristics of chestnuts, as well as their unique attributes, have not been explored. Therefore, the objectives of this study were to evaluate texture and flavor attributes of commonly grown chestnut cultivars using descriptive sensory analysis and to quantify their free sugar content by gas-liquid chromatography.

RESULTS

Twenty-three sensory terms were used for descriptive analysis of roasted chestnuts. All but two attributes (raw impression and fermented) were common to all chestnut cultivars. Peelability, initial firmness, dissolvability, and mustard, sweet, and sour flavors varied among cultivars. Sucrose, the predominant free sugar in chestnuts, was greatest in Colossal chestnuts from California, while those of Peach had the lowest content. Glucose, fructose and maltose were also present in chestnuts.

CONCLUSION

This study demonstrated that cultivars of various chestnut species share several common sensory attributes, but differ in intensity ratings of six descriptors. Of these attributes, sweetness has been associated with consumer acceptance and can be promoted in the marketplace.

[Dynamics of soil arthropod community structure and its responses to forest fragmentation during the decomposition of Castanopsis eyrei leaf litter]

Five evergreen broad-leaved forests (one continuous forest and four fragmented forests) in the mountain areas in the juncture of Zhejiang, Fujian, and Jiangxi Provinces, East China were selected as test objects to study the dynamics of soil arthropod community structure and its responses to forest fragmentation during the decomposition of dominant tree species Castanopsis eyrei leaf litter. A total of 899 soil arthropods were collected, belonging to 9 classes and 25 orders. Lepidoptera was the dominant taxon, accounting for 10% of the individual, while Hymenoptera, Collembola, Diptera, Prostigmata, and Geophilomorpha were the common taxa. The decomposition rate of C. eyrei leaf litter was the highest in August and lower in April-June and December, which was in accordance with the seasonal dynamics of the taxa number and individual number of soil arthropods. Meanwhile, the taxa number, individual number, and species diversity of soil arthropods differed between continuous forest and fragmented forests, suggesting that both area effect and edge effect affected the dynamics of soil arthropod community structure during the decomposition of C. eyrei leaf litter.

Establishment of the evergreen broad-leaved tree species Castanopsis cuspidata in an abandoned secondary forest in western Japan

Recently, populations of Castanopsis cuspidata have often expanded into secondary forests in western Japan. To determine the establishment processes of this species, we analyzed its spatial distribution in a secondary forest dominated by Quercus variabilis and Quercus serrata that is located adjacent to a stand dominated by C. cuspidata. Saplings, defined as >or=30 cm stem length (SL) and <5 cm diameter at breast height (DBH), were abundant and their size distribution was inversely J-shaped, indicating continuous recruitment. Although seedlings (SL < 30 cm) and small saplings (30 <or= SL < 50 cm) of C. cuspidata were aggregated near flowering trees of this species, some were found >or=40 m from the nearest adults, suggesting that there is animal-aided dispersal of acorns. The distribution of larger-sized individuals (>or=100 cm SL) of C. cuspidata was unrelated to distance from the nearest flowering C. cuspidata or dominant Quercus species (>or=5 cm DBH), but was associated with dead Pinus densiflora trees, which were abundant at the site. Thus, the establishment of C. cuspidata in this forest is controlled mainly by two factors, viz. patterns of acorn dispersal by animals, and forest disturbance regime (i.e., deaths of pine trees).

[Root decomposition characteristics of Castanopsis carlesii stand in Wanmulin Natural Reserve of Fujian Province]

By using litter-bag method, the root decomposition characteristics of Castanopsis carlesii stand in Jian'ou Wanmulin Natural Reserve of Fujian Province were studied over two years. Three classes of roots, i.e., 0-1 mm, 1-2 mm, and 2-4 mm in diameter, were tested. During the 2-year period of decomposition, all classes roots showed a bi-phase pattern, being decomposed faster in prophase and slower in anaphase. The leaching loss of extractable substances in roots made root decomposition faster in prophase, while the increase of the acid-insoluble substances concentration in roots restrained the decomposition in anaphase. In the first year, the decomposition rate of all classes roots was controlled by the initial concentrations of their extractive substances and N; while in the second year, the decomposition rate was controlled by the initial C/N and the initial concentrations of acid-insoluble substances, N and P of the roots. During decomposition, all classes roots showed an increasing N concentration and a decreasing P concentration, and the N showed an enrichment-release pattern, while the P showed a direct release pattern.

[Effects of litter coverage and watering frequency on seed germination and seedling survival of Castanopsis fissa]

Castanopsis fissa is an important pioneer species commonly used in the restoration of degraded subtropical grassland in southern China. The study on the effects of litter coverage and watering frequency on the seed germination and seedling survival of C. fissa showed that the effects of litter coverage depended on soil moisture condition. When the watering frequency was 1 time per day, litter covering could restrain seed germination and increase seedling mortality; while watering 2 or 3 times per day, the covering would ameliorate soil moisture condition, and benefit seed germination and seedling establishment. The biomass of C. fissa seedlings was enhanced significantly by litter covering. It was suggested that keeping a litter layer on soil surface could benefit the seed germination and seedling survival of C. fissa to restore subtropical shrub land.

Involvement of reactive oxygen species during early stages of ectomycorrhiza establishment between Castanea sativa and Pisolithus tinctorius

Evidence for the participation of reactive oxygen species (ROS) and antioxidant systems in ectomycorrhizal (ECM) establishment is lacking. In this paper, we evaluated ROS production and the activities of superoxide dismutase (SOD) and catalase (CAT) during the early contact of the ECM fungus Pisolithus tinctorius with the roots of Castanea sativa (chestnut tree). Roots were placed in contact with P. tinctorius mycelia, and ROS production was evaluated by determining the levels of H(2)O(2) and O(2) (.-) during the early stages of fungal contact. Three peaks of H(2)O(2) production were detected, the first two coinciding with O(2) (.-) bursts. The first H(2)O(2) production peak coincided with an increase in SOD activity, whereas CAT activity seemed to be implicated in H(2)O(2) scavenging. P. tinctorius growth was evaluated in the presence of P. tinctorius-elicited C. sativa crude extracts prepared during the early stages of fungal contact. Differential hyphal growth that matched the H(2)O(2) production profile with a delay was detected. The result suggests that during the early stages of ECM establishment, H(2)O(2) results from an inhibition of ROS-scavenging enzymes and plays a role in signalling during symbiotic establishment.

[Age structure and growth characteristic of Castanopsis fargesii population]

In this paper, the age structure and growth characteristics of Castanopsis fargesii population in a shade-tolerant broadleaved evergreen forest were studied, aimed to understand more about the regeneration patterns and dynamics of this population. The results showed that the age structure of C. fargesii population was of sporadic type, with two death peaks of a 30-year gap. This population had a good plasticity in growth to light condition. Because there were no significant differences in light condition under the canopy in vertical, the saplings came into their first suppression period when they were 5-8 years old, with a height growth rate less than 0. 1 m x a(-1) lasting for 10 years. The beginning time of the first growth suppression period was by the end of the first death peak of the population, and the ending time of the first growth suppression period was at the beginning of the second death peak of the population, demonstrating that growth characteristic was the key factor affecting the age structure of C. fargesii.