Genome-wide identification of the Pinus tabuliformis CONSTANS-like gene family and their potential roles in reproductive cone development

The CONSTANS-like (COL) genes, as a core transcription factor in the photoperiod regulation pathway, play a key role in plant reproduction development. However, their molecular characterization has rarely been studied in Pinus tabuliformis. Here, 10 PtCOL genes were identified in the P. tabuliformis genome and multiple sequence alignments have indicated that the PtCOL proteins contained highly conserved B-BOX1 and CCT domains. Sequence similarity analysis showed that PtCOL1 and PtCOL3 had the higher similarity with Norway spruce COLs (PaCOL2 and PaCOL1) and Arabidopsis COLs (AtCOL3, 4 and 5), respectively. Phylogeny and gene structure analyses revealed that PtCOLs were divided into three subgroups, each with identical or similar distributions of exons, introns, and motifs. Moreover, 10 PtCOLs were distributed on 6 chromosomes and PtCOL9 has syntenic gene pairs in both Ginkgo biloba and Sequoiadendron giganteum. Interestingly, in transcriptome profiles, most PtCOLs exhibited a diurnal oscillation pattern under both long (LD) and short (SD) day conditions. Additionally, PtCOLs were highly expressed in needles and female cones, and showed different spatial expression patterns. Among the ten PtCOLs, PtCOL1/3 heterologous overexpression Arabidopsis displayed a delayed-flowering phenotype under SD, indicating that they are likely to play a crucial role in the reproductive development. Additionally, PtCOL1 and PtCOL3 were not only capable of interacting with each other, but they were each capable of interacting with themselves. Furthermore, PtCOL1 and PtCOL3 were also involved in the MADS-box protein-protein interaction (PPI) network in P. tabuliformis cone development. Direct interactions of PtDAL11 with PtCOL1/3 impeded PtCOL1/3 translocation into the nucleus. In summary, this study provided comprehensive understanding for the functions of the PtCOL gene family and revealed their biological roles in the photoperiod-dependent P. tabuliformis cone development.

Elevational changes in soil properties shaping fungal community assemblages in terrestrial forest

Environmental variables shifted by climate change act as driving factors in determining plant-associated microbial communities in terrestrial ecosystems. However, how elevation-induced changes in soil properties shape the microbial community in forest ecosystems remains less understood. Thus, the Pinus tabuliformis forests at elevations of 1500 m, 1900 m, and 2300 m above sea level were investigated to explore the effect of environmental factors on microbial assemblage. Significant changes in the soil physicochemical properties were found across the investigated elevations, such as soil moisture, temperature, pH, nitrogen (N), and phosphorus (P). Soil enzymatic activities, including soil sucrase, phosphatase, and dehydrogenase, were significantly affected by elevation, and sucrase showed a linear correlation with soil organic matter. Furthermore, the richness of fungal communities in the rhizosphere was decreased as elevation increased, while a humpback pattern was found for roots. Certain core microbiota members, such as Agaricomycetes, Leotiomycetes, and Pezizomycetes, were crucial in maintaining a stable ecological niche in both the root and rhizosphere. We also found that shifting of fungal communities in the rhizosphere were more related to physical properties (e.g., pH, soil moisture, and soil temperature), while changes in root fungal communities along elevation gradient were related mostly to soil nutrients (e.g., soil N and P). Overall, this study demonstrates that the assemblage of the root and rhizosphere fungal communities in P. tabuliformis forest primarily depends on elevation-induced changes in environmental variables and highlights the importance of predicting fungal responses to future climate change.

Response of Chinese pine regeneration density to forest gap and slope aspect in northern China: A meta-analysis

Chinese pine is a Chinese endemic species with important ecological functions. Forest gaps and slope aspect are important factors in the regeneration of Chinese pine by influencing light and moisture, but what these effects are is still up for debate. Meanwhile, the effects of forest gaps and slope aspect are poorly studied in response to different forest types and ages, as well as temperature and precipitation. We established literature selection criteria that finally identified 101 and 69 pairs of study cases on forest gaps and slope aspect, respectively. The overall effect values were obtained by meta-analysis and found that gap and shady slope habitats had significant positive effects on the regeneration density of Chinese pine (P < 0.05). The gap most enhanced the regeneration density in a plantation setting (P < 0.05). In pure stands of Chinese pine, shady slopes can significantly increase regeneration density (P < 0.05). Forest gaps and shady slopes contributed most to Chinese pine regeneration density in mature stands compared to near mature stands, and over mature stands (P < 0.05). There was no significant effect of stand gap size on regeneration density (P > 0.05). In particular, the edges of the gap appeared to be well-suited for regeneration (P < 0.05). In our study area, mean annual precipitation resulted in a significant increase in the effects of the gap and shady slope as precipitation declined (P < 0.05). This meta-analysis helps elucidate the effects of forest gap (position or area) and slope aspect on Chinese pine regeneration. With global climate change, Chinese pine regeneration may prefer the edge of forest gaps and shady slopes.

Effects of Soil Nutrients on Plant Nutrient Traits in Natural Pinus tabuliformis Forests

In light of global warming, the interaction between plant nutrient traits and soil nutrients is still unclear. Plant nutrient traits (e.g., N and P) and their stoichiometric relationships (N/P ratio) are essential for plant growth and reproduction. However, the specific role of soil nutrients in driving variation in plant nutrient traits remains poorly understood. Fifty natural Pinus tabuliformis forests were used as the research object to clarify the interaction between plant nutrient traits and soil nutrients. We show that: (1) The N_mass, P_mass and N/P ratios of leaves were significantly higher than those of roots. The N/P ratio of both leaves and roots was less than 14. (2) Leaf nutrient traits showed diverse relationship patterns with root nutrient traits throughout the growing period. Significant changes were found in root nutrient PC2 (the second principal component of root nutrient traits) and leaf nutrient PC1 (the first principal component of leaf traits), and non-significant changes were found in other relationships between leaf and root traits (p > 0.05). Root nutrient traits explained 36.4% of the variance in leaf nutrient traits. (3) With the increase in soil nutrient PC2 (related to N), leaf PC2 (related to N) showed a significant trend of first decreasing and then increasing (p < 0.05). Only the soil N_mass was significantly correlated with the leaf N_mass (p < 0.05), which demonstrated that the growth and survival of Pinus tabuliformis forests were mainly affected by N-limitation.

Ultrasound promotes germination of aging Pinus tabuliformis seeds is associated with altered lipid metabolism

Seed germination is an essential biological process for establishing new organisms of higher plants, it is especially significant for those aged seeds stored in gene banks for years. In this study, we investigated ultrasound treatment induced germination for aged Pinus tabuliformis seeds, which has been used in large scale aircraft sowing based afforestation in North China over 30 years' ago without knowing possible mechanisms. We showed certain strength of ultrasound could increase the germination rate of aged seeds for about 3 times compare with control. Interestingly, although our transcriptome and lipidome analysis showed the differences between control and ultrasound treatments can be observed 1 day after germination by partial least squares discriminant analysis (PLSDA) analysis, majority (75 % or 69 %) of the significantly altered genes or lipids were commonly shared between them. Further analysis for the commonly altered lipids between both treatments showed ultrasound provoked the variations of lipids during germination process. Our investigation also revealed large amount of ultrasound-related genes and lipids that might be involved in germination promotion process. We hypothesis ultrasound provokes seed lipidome which further increases seed germination of Pinus tabuliformis. Our study provides new insides into the role of ultrasound induced lipidome change in seed germination. Moreover, we provide a new method to improve germination of aged seeds which might benefit preservation of seeds in gene banks.

[Responses of radial growth of Pinus tabuliformis to climate change at the northern slopes of Qinling Mountains, China]

A standard chronology (STD) was established with Pinus tabuliformis samples collected from Nanwutai at the northern slopes of the Qinling Mountains. The correlations between radial growth of P. tabuliformis and climatic factors were explored. The results showed that radial growth was positively correlated with moisture factors in previous September and current May. The radial growth was positively correlated with temperature factors in pre-vious November and negatively with that in previous October and current May. There was significant lag effect of climatic factors on the radial growth. The radial growth of P. tabuliformis was well correlated with the PDSI drought severity index, with positive correlations being identified from September to December of the previous year and in May of the current year. The regression model was able to simulate the relationship between STD and PDSI. The formations of extremely wide and narrow tree-ring were mainly a result of drought condition. Combined with climatic factors, PDSI could better reflect the radial growth characteristics of P. tabuliformis.

Genome-wide TCP transcription factors analysis provides insight into their new functions in seasonal and diurnal growth rhythm in Pinus tabuliformis

BACKGROUND

Pinus tabuliformis adapts to cold climate with dry winter in northern China, serving as important commercial tree species. The TEOSINTE BRANCHED 1, CYCLOIDEA, and PROLIFERATING CELL FACTOR family(TCP)transcription factors were found to play a role in the circadian clock system in Arabidopsis. However, the role of TCP transcription factors in P. tabuliformis remains little understood.

RESULTS

In the present study, 43 TCP genes were identified from P. tabuliformis genome database. Based on the phylogeny tree and sequence similarity, the 43 TCP genes were classified into four groups. The motif results showed that different subfamilies indeed contained different motifs. Clade II genes contain motif 1, clade I genes contain motif 1, 8, 10 and clade III and IV contain more motifs, which is consistent with our grouping results. The structural analysis of PtTCP genes showed that most PtTCPs lacked introns. The distribution of clade I and clade II on the chromosome is relatively scattered, while clade III and clade IV is relatively concentrated. Co-expression network indicated that PtTCP2, PtTCP12, PtTCP36, PtTCP37, PtTCP38, PtTCP41 and PtTCP43 were co-expressed with clock genes in annual cycle and their annual cycle expression profiles both showed obvious seasonal oscillations. PtTCP2, PtTCP12, PtTCP37, PtTCP38, PtTCP40, PtTCP41, PtTCP42 and PtTCP43 were co-expressed with clock genes in diurnal cycle. Only the expression of PtTCP42 showed diurnal oscillation.

CONCLUSIONS

The TCP gene family, especially clade II, may play an important role in the regulation of the season and circadian rhythm of P. tabuliformis. In addition, the low temperature in winter may affect the diurnal oscillations.

Phytohormone profiles and related gene expressions after endodormancy release in developing Pinus tabuliformis male strobili

Development after endo-dormancy release ensures perennial plants, such as forest trees, proper response to environmental changes and enhances their adaptability. In northern hemisphere, megasporophore and microsporophore of conifers undergo dormancy to complete their development. Here combined with transcriptome data, we used high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (ESI-HPLC-MS/MS) to quantitatively analyse the various hormones (Abscisic Acid (ABA), 3-Indoleacetic acid (IAA), Gibberellins (GAs), Cytokinin (CTK), Jasmonic acid (JA) and Salicylic acid (SA)) of Chinese pine (Pinus tabuliformis Carr.) male strobili after endo-dormancy release. More specifically, we analysed endogenous hormones and their related-genes and verified the important role of ABA in plants growth and development. We observed rapid decrease in ABA content after dormancy release, resulting in reducing the inhibitory effect on male strobili growth. Similarly, rapid drop in ABA/GA ratio was observed and was associated with the start of male strobili growth and development. Combined with transcriptome data, we found that HAB2-SnRK2.10 played a central role in the ABA pathway in the entire network of hormones regulating male strobili development. Due to external environment warming, the differentially expressed HAB2-SnRK gene led to ABA content rapid decline, thus initiating male strobili growth. We constructed a network of hormone-regulated development to understand the interactions between hormones after male strobili dormancy release of male strobili. This study provided essential foundations for studying megasporophore and microsporophore growth mechanism after endo-dormancy and offered new ideas for flower development in gymnosperms and angiosperms.

[Effects of organic matter addition on the stoichiometric homeostasis of soil microbes in Pinus tabuliformis forest in Taiyue Mountain, China]

In Taiyue Mountain of Shanxi Province, five types of organic matter, i.e., biochar, maize straw, leaves of Quercus mongolica and Pinus tabuliformis, and sawdust of wood stem, were separately added to the soils of a P. tabuliformis forest. Nutrient content, enzyme activity, and microbial biomass were analyzed to elucidate the characteristics of soil ecoenzymatic stoichiometry and the element homeostasis of soil microorganisms. The results showed that the addition of woody sawdust significantly increased soil nitrogen and phosphorus content by 17.1% and 37.6%, and enhanced carbon, nitrogen, and phosphorus contents of soil microbial biomass by 118.0%, 41.0%, and 176.6%, respectively. The activities of carbon-, nitrogen- and phosphorus-targeting enzymes (i.e., β-1, 4-glucosaminosidase, β-1,4-N-acetylglucosaminosidase, leucine aminopeptidase and acid phosphatase) generally increased with the C:N of the added organic matter (biochar<Q. mongolica leaf< P. tabuliformis leaf < maize straw < woody sawdust). This indicated that ecoenzymatic stoichiometry was controlled by soil nutrient content and micro-bial biomass. The limitation of soil microbial growth by phosphorus was not alleviated after the addition of different organic matters, as indicated by the results of enzymatic ratio and its vector value. Soil microbial biomass carbon and nitrogen contents and their stoichiometry (C:N, C:P, N:P) were homeostatic, whereas the microbial biomass phosphorus content fluctuated slightly. The stabilities of microbial element contents and their proportion were mainly ascribed to the allocation of extracellular enzyme production. The susceptibility of soil microbial biomass phosphorus to the addition of organic matter indicated phosphorus limitation of microbial growth.

Screening of Differentially Expressed Genes and Localization Analysis of Female Gametophyte at the Free Nuclear Mitosis Stage in Pinus tabuliformis Carr

Female sterility is a common phenomenon in the plant world, and systematic research has not been carried out in gymnosperms. In this study, the ovules of No. 28 sterile line and No. 15 fertile line Pinus tabuliformis were used as materials, and a total of 18 cDNA libraries were sequenced by the HiSeqTM 4000 platform to analyze the differentially expressed genes (DEGs) and simple sequence repeats (SSRs) between the two lines. In addition, this study further analyzed the DEGs involved in the signal transduction of plant hormones, revealing that the signal pathways related to auxin, cytokinin, and gibberellin were blocked in the sterile ovule. Additionally, real-time fluorescent quantitative PCR verified that the expression trend of DEGs related to plant hormones was consistent with the results of high-throughput sequencing. Frozen sections and fluorescence in situ hybridization (FISH) were used to study the temporal and spatial expression patterns of PtRab in the ovules of P. tabuliformis. It was found that PtRab was significantly expressed in female gametophytes and rarely expressed in the surrounding diploid tissues. This study further explained the molecular regulation mechanism of female sterility in P. tabuliformis, preliminarily mining the key factors of ovule abortion in gymnosperms at the transcriptional level.

Response of Pinus tabuliformis saplings to continuous autumn fertilization treatments in the mountains of Eastern Liaoning Province, China

Autumn fertilization is an important cultivation and management measure used to provide nutrients at the hardening stage during the end of the growing season-bolstering nutrient reserves and promoting additional growth in the following spring. Previous studies mainly focused on short-term or one-time fertilization treatment of container seedlings, and few studies have observed the effects of autumn fertilization of large-area forests over multiple continuous years. The growth dynamics and nutrient changes during autumn in 324 Pinus tabuliformis saplings in the temperate zone of China (in the eastern Liaoning mountains) were studied under field conditions with different fertilizer treatments for three consecutive years. The second year of autumn fertilization promoted the growth of tree height and annual leaf length more significantly than that in the first year, the change in diameter at breast height (DBH) was significant. Tree height (TH) in spring increased at a faster rate than in autumn, while DBH stably increased throughout the year. The increase in TH, DBH, and annual leaf length (ALL) under all fertilization treatments was higher than that of the control group, and the decrease in annual branch length (ABL) was higher than that of the control group. High N significantly increased the concentration of new coniferous N (NLN), soil total N (STN), and soil alkali-hydrolyzable N (SAHN) in P. tabuliformis saplings. High P significantly increased the concentration of P in annual needles and soil total P (STP), and decreased the concentration of N in new needles. In addition, there is a certain correlation between the N and P concentration in the needles and soil, representing the competition and interactions between plant nutrient demand and soil nutrient supply. The most favorable fertilizer treatment consisted of high N and low P (urea 204 g, calcium superphosphate 104 g), which provide support for the formulation of a reasonable fertilization technology for P. tabuliformis in the mountains of Eastern Liaoning Province, China.

Tracing historical changes, degradation, and original sources of airborne polycyclic aromatic hydrocarbons (PAHs) in Jilin Province, China, by Abies holophylla and Pinus tabuliformis needle leaves

Due to their wide distribution and availability, plant leaves can be considered interesting candidates as biomonitoring substrates for the evaluation of atmospheric pollution. In addition, some species can also retain historical information, for example, related to environmental pollution, due to their leaf class age. In this study, the content of polycyclic aromatic hydrocarbons (PAHs) in Abies holophylla and Pinus tabuliformis needle samples in the function of their class age has been investigated to obtain information regarding the degradation constant for each PAH under investigation (α values ranging from 0.173 to 1.870) and to evaluate the possibility to correlate the presence of PAHs in needles with some important pollution environmental factors. Considering air pollutant variables registered in Jilin Province, interesting correlations (at 95% confidence level) have been found between coal consumption per year and anthracene contents in needles, while fluorene, phenanthrene, and anthracene results correlated with coal consumption. Furthermore, it has been demonstrated that the total PAH concentration in needles, for both species, increased with their age (from 804 to 3604 ng g^-1 dry weight), showing a general tendency to accumulate these substances through years. PAH degradation rates increased instead with molecular complexity. This study could be considered a first trial to obtain historical environmental information by pine needles biomonitoring.

Near-natural transformation of Pinus tabuliformis better improve soil nutrients and soil microbial community

Pinus tabulaeformis plantations have been established around northern China to restore degraded land and provide timber or fuelwood. In recent years, widely distributed monoculture P. tabulaeformis forests have been transformed into mixed forests due to various ecological problems. However, the current research on the influence of near-natural transformation of P. tabulaeformis on soil microbial diversity and community composition remains limited. Therefore, we examined the effect of forest conversion from monoculture Pinus tabuliformis (PT) to P. tabuliformis-Armeniaca vulgaris (PTAU), P. tabuliformis - Robinia pseudoacacia (PTRP), P. tabuliformis - Vitex negundo L. var. heterophylla (PTVN) forests on soil microbial community diversity and composition. The results indicated that compared to PT, PTAU, PTVN, and PTRP could enhance the soil pH, TC, TN, AN, and AK in different degrees, the most obvious in PTAU. Near-natural transformation of P. tabuliformis could improve soil bacterial Pielou_e index, and Simpson index, as well as soil fungal Chao1 index. Proteobacteria and Ascomycota were the dominant soil microbial community at the phylum level. What’s more, both soil bacterial and fungal community among PT, PTAU, PTRP and PTVN showed clear different, and PTAU obviously altered the soil microbial community structure. Proteobacteria was the predominant group in PT, while, Gemmatimonadetes enriched in PTVN. Ascomycota was the predominant group in PTAU, while, Basidiomycota was the predominant group in PTRP. Near-natural transformation of P. tabuliformis could change soil microbial community via altering soil characteristics. In brief, our research results revealed the influence of tree composition and soil nutrient availability on soil microbial diversity and composition, and provided management guidance for introduction soil microbial community in forest protection and management.

The Transcriptional Landscape and Hub Genes Associated with Physiological Responses to Drought Stress in Pinus tabuliformis

Drought stress has an extensive impact on regulating various physiological, metabolic, and molecular responses. In the present study, the Pinus tabuliformis transcriptome was studied to evaluate the drought-responsive genes using RNA- Sequencing approache. The results depicted that photosynthetic rate and H₂O conductance started to decline under drought but recovered 24 h after re-watering; however, the intercellular CO₂ concentration (Ci) increased with the onset of drought. We identified 84 drought-responsive transcription factors, 62 protein kinases, 17 transcriptional regulators, and 10 network hub genes. Additionally, we observed the expression patterns of several important gene families, including 2192 genes positively expressed in all 48 samples, and 40 genes were commonly co-expressed in all drought and recovery stages compared with the control samples. The drought-responsive transcriptome was conserved mainly between P. tabuliformis and A. thaliana, as 70% (6163) genes had a homologous in arabidopsis, out of which 52% homologous (3178 genes corresponding to 2086 genes in Arabidopsis) were also drought response genes in arabidopsis. The collaborative network exhibited 10 core hub genes integrating with ABA-dependent and independent pathways closely conserved with the ABA signaling pathway in the transcription factors module. PtNCED3 from the ABA family genes had shown significantly different expression patterns under control, mild, prolonged drought, and recovery stages. We found the expression pattern was considerably increased with the prolonged drought condition. PtNCED3 highly expressed in all drought-tested samples; more interestingly, expression pattern was higher under mild and prolonged drought. PtNCED3 is reported as one of the important regulating enzymes in ABA synthesis. The continuous accumulation of ABA in leaves increased resistance against drought was due to accumulation of PtNCED3 under drought stress in the pine needles.

Water Use by Chinese Pine Is Less Conservative but More Closely Regulated Than in Mongolian Scots Pine in a Plantation Forest, on Sandy Soil, in a Semi-Arid Climate

The diversity of plant water use patterns among species and ecosystems is a matter of widespread debate. In this study, Chinese pine (Pinus tabuliformis, CP) and Mongolian Scots pine (Pinus sylvestris var. mongolica, MP), which is co-exist in the shelterbelt plantations in the Horqin Sandyland in northern China, were chosen for comparison of water use traits by monitoring xylem sap flow alongside recordings of the associated environmental factors over four growing seasons. Continuous sap flux density measurements were converted into crown projected area transpiration intensity (T_r) and canopy stomatal conductance (G_s). The results indicated that MP showed a higher canopy transpiration intensity than in CP, with T_r daily means (±standard deviation) of 0.84 ± 0.36 and 0.79 ± 0.43 mm⋅d^-1, respectively (p = 0.07). However, the inter-annual variability of daily T_r in MP was not significant, varying only approximately a 1.1-fold (p = 0.29), while inter-annual variation was significant for CP, with 1.24-fold variation (p < 0.01). In particular, the daily mean T_r value for CP was approximately 1.7-times higher than that of MP under favorable soil moisture conditions, with values for relative extractable soil water within the 0-1.0 m soil layer (REW) being above 0.4. However, as the soil dried out, the value of T_r for CP decreased more sharply, falling to only approximately 0.5-times the value for MP when REW fell to < 0.2. The stronger sensitivity of T_r and/or G_s to REW, together with the more sensitive response of G_s to VPD in CP, confirms that CP exhibits less conservation of soil water utilization but features a stronger ability to regulate water use. Compared with MP, CP can better adapt to the dry conditions associated with climate change.

Comparative transcriptome analysis of the newly discovered insect vector of the pine wood nematode in China, revealing putative genes related to host plant adaptation

BACKGROUND

In many insect species, the larvae/nymphs are unable to disperse far from the oviposition site selected by adults. The Sakhalin pine sawyer Monochamus saltuarius (Gebler) is the newly discovered insect vector of the pine wood nematode (Bursaphelenchus xylophilus) in China. Adult M. saltuarius prefers to oviposit on the host plant Pinus koraiensis, rather than P. tabuliformis. However, the genetic basis of adaptation of the larvae of M. saltuarius with weaken dispersal ability to host environments selected by the adult is not well understood.

RESULTS

In this study, the free amino and fatty acid composition and content of the host plants of M. saltuarius larvae, i.e., P. koraiensis and P. tabuliformis were investigated. Compared with P. koraiensis, P. tabuliformis had a substantially higher content of various free amino acids, while the opposite trend was detected for fatty acid content. The transcriptional profiles of larval populations feeding on P. koraiensis and P. tabuliformis were compared using PacBio Sequel II sequencing combined with Illumina sequencing. The results showed that genes relating to digestion, fatty acid synthesis, detoxification, oxidation-reduction, and stress response, as well as nutrients and energy sensing ability, were differentially expressed, possibly reflecting adaptive changes of M. saltuarius in response to different host diets. Additionally, genes coding for cuticle structure were differentially expressed, indicating that cuticle may be a potential target for plant defense. Differential regulation of genes related to the antibacterial and immune response were also observed, suggesting that larvae of M. saltuarius may have evolved adaptations to cope with bacterial challenges in their host environments.

CONCLUSIONS

The present study provides comprehensive transcriptome resource of M. saltuarius relating to host plant adaptation. Results from this study help to illustrate the fundamental relationship between transcriptional plasticity and adaptation mechanisms of insect herbivores to host plants.

Seasonal Changes in Pinus tabuliformis Root-Associated Fungal Microbiota Drive N and P Cycling in Terrestrial Ecosystem

In terrestrial ecosystems, mycorrhizal roots play a key role in the cycling of soil carbon (C) and other nutrients. The impact of environmental factors on the mycorrhizal fungal community has been well studied; however, the seasonal variations in the root-associated fungal microbiota affected by environmental changes are less clear. To improve the understanding of how environmental factors shape the fungal microbiota in mycorrhizal roots, seasonal changes in Pinus tabuliformis root-associated fungi were investigated. In the present study, the seasonal dynamics of edaphic properties, soil enzymatic activities, root fungal colonization rates, and root-associated fungal microbiota in P. tabuliformis forests were studied across four seasons during a whole year to reveal their correlations with environmental changes. The results indicate that the soil functions, such as the enzymatic activities related to nitrogen (N) and phosphorus (P) degradation, were varied with the seasonal changes in microclimate factors, resulting in a significant fluctuation of edaphic properties. In addition, the ectomycorrhizal fungal colonization rate in the host pine tree roots increased during warm seasons (summer and autumn), while the fungal colonization rate of dark septate endophyte was declined. Moreover, the present study indicates that the fungal biomass increased in both the pine roots and rhizospheric soils during warm seasons, while the fungal species richness and diversity decreased. While the Basidiomycota and Ascomycota were the two dominant phyla in both root and soil fungal communities, the higher relative abundance of Basidiomycota taxa presented in warm seasons. In addition, the fungal microbial network complexity declined under the higher temperature and humidity conditions. The present study illustrates that the varieties in connectivity between the microbial networks and in functional taxa of root-associated fungal microbiota significantly influence the soil ecosystem functions, especially the N and P cycling.

[Reconstruction of the March-April average maximum air temperature over 165 years based on Pinus tabuliformis tree-rings of Zhen'an County, Shaanxi Province, China]

We used tree rings of Pinus tabuliformis sampled in the Muwang National Forest Park to establish a standardized chronology (STD) and calculated the correlation coefficients between the standardized chronology and climatic factors of Zhen'an meteorological station. With linear regression analysis, we reconstructed the March-April mean maximum temperature of Zhen'an over 165 years from 1853 to 2017. The highest correlation coefficient was observed between the standardized chronology and the March-April mean maximum temperature (r=0.596, n=60, P＜0.01). The variance interpretation of the March-April mean maximum temperature reconstruction function was 33.2%, and the reconstruction function and results were credible and reliable. Warm years occurred 25 times and cold years occurred 29 times in the reconstruction sequence. The warm years were more accompanied by flood events, while the cold years were accompanied by more drought events. Temperature fluctuated obviously in the reconstruction sequence, with two cold periods (1902-1917 and 1953-2000) and four warm periods (1868-1892, 1917-1937, 1941-1953 and 2001-2012). The obvious periodic variations of 2-7, 8-15, 18-28, 75-96, and 100-125 years were found in the reconstruction sequence, in which the quasi-113, 88 and 22 years were the first, second and third main periods, respectively. These variations might potentially be the fingerprints of some climate change forces such as solar activity, monsoon and EI Niño-Southern Oscillation (ENSO) activity.

Influence of physiological and environmental factors on the diurnal variation in emissions of biogenic volatile compounds from Pinus tabuliformis

Biological volatile organic compounds (BVOCs) have a large influence on atmospheric environmental quality, climate change and the carbon cycle. This study assesses the composition and diurnal variation in emission rates of BVOCs from Pinus tabuliformis, using an enclosure technique. Environmental parameters (temperature and light intensity) and physiological parameters (net photosynthetic rate, P_n; stomatal conductance, g_s; intercellular CO₂ concentration, C_i; and transpiration rate, T_r) that may affect emission behavior were continuously monitored. The 10 most abundant compound groups emitted by P. tabuliformis were classified by gas chromatography-mass spectrometry. The dominant monoterpenoid compounds emitted were α-pinene, β-myrcene, α-farnesene and limonene. The diurnal emission rate of BVOCs changed with temperature and light intensity, with dynamic analysis of BVOCs emissions revealing that their emission rates were more affected by temperature than light. The variation in monoterpene emission rates was consistent with estimates of P_n, g_s and T_r. Basal emission rates (at 30 °C,) of the main BVOCs ranged from 0.006 to 0.273 μg  ^-1/(hr g), while the basal ER standardization coefficients ranged from 0.049 to 0.144 °C^-1. Overall, these results provide a detailed reference for the effective selection and configuration of tree species to effectively prevent and control atmospheric pollution.

Effects of thinning intensity on understory vegetation and soil microbial communities of a mature Chinese pine plantation in the Loess Plateau

Thinning can effectively improve forest production and maintain ecological stability. However, the changes in soil microbial community compositions after thinning are still not well understood. In this study, we investigated the changes in the soil microbial community of mature Chinese pine (Pinus tabuliformis) plantations in the Loess Plateau after 11years of four different thinning intensity treatments. Furthermore, the responses of the soil microbial community to changes in understory plants and soil properties were analyzed. The ratios of wood removal investigated were 0 (CK), 15% (LIT), 30% (MIT) and 45% (HIT). Compared with the CK, thinning significantly increased the Shannon index, species richness, coverage and biomass of the understory plants, and these values were highest for the HIT. The soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO₃^--N) and available phosphorus (AP) concentrations increased with increasing thinning intensity. Thinning intensity did not significantly affect soil microbial community diversity indices. With respect to the dominant bacterial groups, the relative abundance of Proteobacteria was much higher in the HIT, while that of Acidobacteria was much higher in the LIT and CK. For the dominant fungal groups, the relative abundance of Basidiomycota was lowest in the HIT, while that of Ascomycota was highest in the same treatment. Redundancy analysis (RDA) showed that SOC, TN, and AP significantly correlated with soil bacterial communities and that SOC, TN, TP, AP and NO₃^--N significantly correlated with soil fungal communities. The understory vegetation influenced soil fungal communities rather than soil bacterial communities. These findings suggest that the aboveground vegetation diversity and soil nutrients were improved with the increased thinning intensity after 11years. The copiotrophic groups (e.g. Proteobacteria) and oligotrophic groups (e.g. Acidobacteria) differed significantly among the four thinning treatments, indicating a dependence of the soil microbial community composition on soil nutrients.

[Characteristics and affecting factors of sap flow density of Pinus tabuliformis and Hippophae rhamnoides in growing season in the hilly region of the Loess Plateau, China]

The dynamic changes of sap flow density (J_s) of Pinus tabuliformis and Hippophae rhamnoides in plantations from July to September in 2015 was monitored through thermal dissipation probe in the hilly region of the Loess Plateau. In addition, plant physiological characteristics were analyzed to determine the water use types of these two species. The results indicated that the daily changes of J_s of P. tabuliformis and H. rhamnoides showed a single peak during both pre- and post-precipitation. The J_s of P. tabuliformis in growing season (12.62 mL·m^-2·s^-1) was significantly higher than that of H. rhamnoides (2.60 mL·m^-2·s^-1). The J_s of these two species were significantly positively correlated with photosynthetic active radiation, vapor pressure deficit, soil volume-tric water content (SWC). The J_s of these two species were mainly influenced by meteorological factors during pre- and post-precipitation in both August and September. The contribution of SWC to J_s of H. rhamnoides increased by 4.2% after precipitation in September, but the contribution of SWC to J_s of P. tabuliformis decreased by 0.3% after precipitation in both August and September, respectively. Meanwhile, P. tabuliformis showed significantly higher water potential in midday leaf, but lower coefficient of variation (7.3%) than H. rhamnoides with the coefficient of variation of 11.7%. However, H. rhamnoides exhibited higher leaf stomatal conductance. Thus, P. tabuliformis and H. rhamnoides could be considered as isohydry and anisohydry species, respectively.

[Interspecific association and functional group classification of the dominant populations in shrub layer in secondary forest of Pinus tabuliformis in Qinling Mountain, China.]

We analyzed the interspecific association among 20 dominant populations in shrub layer in secondary natural forest of Pinus tabuliformis in Qinling Mountain, China, with X²-test, the association coefficients and the percentage of common occurrence. The results showed that the species pairs with significant positive associations accounted for only 7.4% of the total 190 species pairs. The species pairs such as Lespedeza bicolor and Elaeagnus pungens, Toxicodendron vernicifluum and Pinus tabuliformis, Euonymus alatus and Cerasus tomentosa had extremely significant positive correlations, whereas most of the species pairs showed weak interspecific association. The ratio of positive and negative correlations was less than 1. The results suggested that the interspecific association was relatively weak. Species were with certain independence among dominant populations. Community structure was at an unstable mid-stage with dynamic succession. According to the interspecific association and cluster analysis, combined with biological and ecological characters, the 20 dominant populations in shrub layer were classified into four functional groups. The ecological requirement and resource use pattern of species within the same functional groups were similar, exhibiting a close connection between the shrub species. The connection between different functional groups was relatively loose.

[Growth characteristics of different tree species in shelterbelts in the depression area of Hebei Province, China.]

This research investigated shelterbelt structure indices using the standard sampling method, to study the dynamic changes of different tree species including Ulmus pumila, Populus simonii and Pinus tabuliformis in the depression area in Xiaobazi Township of Fengning County, Hebei Province, China. The results showed that the average age of U. pumila, P. simonii and P. tabuliformis pure forests was 10 years in this area. The average DBH and tree height of P. simonii pure forest were 2.3 times and 3.8 times as those of U. pumila pure forest, as well as, 2.3 times and 3.0 times as those of P. tabuliformis pure forest, respectively. The average DBH, tree height, LAI and height of first live branch of P. simonii pure forest were significantly larger than those of U. pumila pure forest and P. tabuliformis pure forest. Compared with P. simonii mixed forest, the stand density of P. simonii pure forest was 10.8% higher, average DBH of pure forest was 5.2% lower, and average tree height was 11.3% lower. Compared with U. pumila mixed forest, the stand density of U. pumila pure forest was 6.6% higher, average DBH and tree height of pure forest were 7.8% and 14.2% lower. Compared with P. tabuliformis mixed forest, the stand density of P. tabuliformis pure forest was 4.9% larger, but average DBH and tree height were 29.3% and 31.8% lower, respectively. The average DBH, tree height of different forest types showed significant negative correlation with the stand density. Average LAI showed significant positive correlation with density and height of first live branch, and significant negative correlation with the DBH, tree height. There was a significant positive relationship between the average height of first live branch and stand density. The increments of DBH and tree height of coniferous and broad-leaved mixed forest were significantly higher than those of coniferous pure forest. The comprehensive growth potential of the shelterbelts tended to increase, and the lateral growth potential on the whole exhibited a declining trend.

[Dynamic change of Pinus tabuliformis forest productivity and its response to future climate change in Shaanxi Province, China.]

This study analyzed the dynamics of net primary productivity (NPP) of Pinus tabuliformis forest under future climate scenarios in Shaanxi Province during 2015-2100, using a dynamic vegetation model (LPJ-GUESS). The results showed that in the 2015-2100 period, annual mean temperature of this region would significantly increase by 0.12, 0.23 and 0.54 ℃·10 a^-1 under RCP_2.6, RCP_4.5 and RCP_8.5 scenarios, respectively, while the annual precipitation would have no significant change under climate scenarios except RCP_4.5, under which it would significantly increase by 14.36 mm·10 a^-1. Compared with the NPP of P. tabuliformis forest in the historical period (1961-1990), it would increase by 1.6%-29.6% in the future period, and the enhancement could reach 45.4% at the end of this century (2071-2100) under RCP_8.5 scenario. The NPP under the RCP_8.5 scenario was the highest, followed by the RCP_4.5 and RCP_2.6 scenarios. During 2015-2100, the NPP in the northern Shaanxi region would significantly decrease with the rate of 41.00 and 21.00 g C·m^-2·10 a^-1 under the RCP_2.6 and RCP_4.5 scenarios, respectively, implying that this area has the potentiality to be carbon source.

A transcriptomics investigation into pine reproductive organ development

The development of reproductive structures in gymnosperms is still poorly studied because of a lack of genomic information and useful genetic tools. The hermaphroditic reproductive structure derived from unisexual gymnosperms is an even less studied aspect of seed plant evolution. To extend our understanding of the molecular mechanism of hermaphroditism and the determination of sexual identity of conifer reproductive structures in general, unisexual and bisexual cones from Pinus tabuliformis were profiled for gene expression using 60K microarrays. Expression patterns of genes during progression of sexual cone development were analysed using RNA-seq. The results showed that, overall, the transcriptomes of male structures in bisexual cones were more similar to those of female cones. However, the expression of several MADS-box genes in the bisexual cones was similar to that of male cones at the more juvenile developmental stage, while despite these expression shifts, male structures of bisexual cones and normal male cones were histologically indistinguishable and cone development was continuous. This study represents a starting point for in-depth analysis of the molecular regulation of cone development and also the origin of hermaphroditism in pine.

The complete chloroplast genome of the southern Chinese pine Pinus tabuliformis (Pinales: Pinaceae)

The complete nucleotide sequence of Pinus tabuliformis chloroplast genome (cpDNA) was carried out using Illumina Hiseq 2500. The genome is 119 646 bp in length, and the overall base composition of H-strand is 30.6% for A, 19.3% for C, 19.2% for G and 30.9% for T. There are 116 genes in the cpDNA, including 74 protein-coding genes, four ribosomal RNA genes (four rRNA species), and 36 transfer RNA genes (20 tRNA species). Phylogenetic analyses of P. tabuliformis and other 12 species belonging to Pinales were carried out using MEGA 6.0 with Neighbor-Joining methods. The sequences of P. tabuliformis were clustered in subfamily Pinaceae.

Differential drought tolerance in tree populations from contrasting elevations

To predict the ecological consequences of climate change for a widely distributed tree species, it is essential to develop a deep understanding of the ecophysiological responses of populations from contrasting climates to varied soil water availabilities. In the present study, we focused on Pinus tabuliformis, one of the most economically and ecologically important tree species in China. In a greenhouse experiment, we exposed trees from high-elevation (HP) and low-elevation (LP) populations to low (80 % of field capacity, FC), mild (60 % FC), moderate (40 % FC) and severe (20 % FC) water stresses. Leaf gas exchange, biomass production and allocation, as well as water-use efficiency, were measured during the experiment. Increasing soil water stress clearly decreased the relative growth rate (RGR), total dry mass (TDM), light-saturated photosynthetic rate (Asat), stomatal conductance (gs), total water use (TWU) and whole-plant water-use efficiency (WUEWP). In contrast, intrinsic water-use efficiency (WUEi) and carbon isotope composition (δ(13)C) both increased significantly with increasing soil water stress for both populations. Only in the LP did the root/shoot ratio (R/S ratio) significantly increase when the water stress increased. A strong positive correlation between Asat and gs coupled with a reduced intercellular CO2 concentration (Ci) probably suggested that stomatal limitations were the main cause of the decreased Asat. However, all the measured variables from the HP were affected less by drought compared with those of the LP, and most aspects of the HP were canalized against drought stress, which was reflected by the relatively higher RGR, TDM and WUEWP. Overall, the results suggest that the two populations responded differentially to drought stress with the HP showing higher drought tolerance than the LP, which was reflected by its faster seedling growth rate and more efficient water use under drought conditions.

Needle morphological evidence of the homoploid hybrid origin of Pinus densata based on analysis of artificial hybrids and the putative parents, Pinus tabuliformis and Pinus yunnanensis

Genetic analyses indicate that Pinus densata is a natural homoploid hybrid originating from Pinus tabuliformis and Pinus yunnanensis. Needle morphological and anatomical features show relative species stability and can be used to identify coniferous species. Comparative analyses of these needle characteristics and phenotypic differences between the artificial hybrids, P. densata, and parental species can be used to determine the genetic and phenotypic evolutionary consequences of natural hybridization. Twelve artificial hybrid families, the two parental species, and P. densata were seeded in a high-altitude habitat in Linzhi, Tibet. The needles of artificial hybrids and the three pine species were collected, and 24 needle morphological and anatomical traits were analyzed. Based on these results, variations in 10 needle traits among artificial hybrid families and 22 traits among species and artificial hybrids were predicted and found to be under moderate genetic control. Nineteen needle traits in artificial hybrids were similar to those in P. densata and between the two parental species, P. tabuliformis and P. yunnanensis. The ratio of plants with three needle clusters in artificial hybrids was 22.92%, which was very similar to P. densata. The eight needle traits (needle length, the mean number of stomata in sections 2 mm in length of the convex and flat sides of the needle, mean stomatal density, mesophyll/vascular bundle area ratio, mesophyll/resin canal area ratio, mesophyll/(resin canals and vascular bundles) area ratio, vascular bundle/resin canal area ratio) relative to physiological adaptability were similar to the artificial hybrids and P. densata. The similar needle features between the artificial hybrids and P. densata could be used to verify the homoploid hybrid origin of P. densata and helps to better understand of the hybridization roles in adaptation and speciation in plants.