Fungal complexity and stability across afforestation areas in changing desert environments

The great achievements in combating desertification are attributed to large-scale afforestation, yet we lack verification of how the stability of the fungal community changes in afforestation areas in desert environments. Here, we present the fungal network structure from different niches (root and bulk soil) of plantations of Mongolian pine, a crucial species for afforestation introduced widely in desertification regions. We assessed changes in community complexity and stability of root-associated fungi (RAF) and soil fungi (SF) among different introduction sites: the Hulunbuir Desert (HB), the Horqin Desert (HQ) and the Mu Us Desert (MU). To illuminate the complexity and stability of the fungal network, the differences in topological properties, fungal function, and vegetation and environmental factors between introduction sites were fully considered. We showed that (1) the SF networks had more nodes and edges than the RAF networks. There was a lower ratio of negative:positive cohesion of RAF networks in HB and MU. For SF but not for RAF, across the three introduction sites, a higher modularity and ratio of negative:positive cohesion indicated higher stability. (2) Ectomycorrhizal (EcM) fungi were the dominant functional group in the RAF network (especially in HQ), and were only significantly correlated with vegetation factor. There was a higher relative abundance and number of OTUs of saprophytic fungi in the SF network and they showed positive correlations with soil nutrients. (3) RAF and SF network complexity and stability showed different responses to environmental and vegetation variables. The key determinant of the complexity and stability of the SF networks in Mongolian pine plantations was soil nutrients, followed by climate conditions. The composition and structure of the RAF community was closely related to host plants. Therefore, clarifying the complexity and stability of fungal communities in afforestation areas in changing desert environments is helpful for understanding the interactions between the environment, plants and fungi.

TMT-Based Proteomic Analysis Reveals the Molecular Mechanisms of Sodium Pheophorbide A against Black Spot Needle Blight Caused by Pestalotiopsis neglecta in Pinus sylvestris var. mongolica

Black spot needle blight is a minor disease in Mongolian Scots pine (Pinus sylvestris var. mongolica) caused by Pestalotiopsis neglecta, but it can cause economic losses in severe cases. Sodium pheophorbide a (SPA), an intermediate product of the chlorophyll metabolism pathway, is a compound with photoactivated antifungal activity, which has been previously shown to inhibit the growth of P. neglecta. In this study, SPA significantly reduced the incidence and disease index and enhanced the chlorophyll content and antioxidant enzyme activities of P. sylvestris var. mongolica. To further study the molecular mechanism of the inhibition, we conducted a comparative proteomic analysis of P. neglecta mycelia with and without SPA treatment. The cellular proteins were obtained from P. neglecta mycelial samples and subjected to a tandem mass tag (TMT)-labelling LC-MS/MS analysis. Based on the results of de novo transcriptome assembly, 613 differentially expressed proteins (DEPs) (p < 0.05) were identified, of which 360 were upregulated and 253 downregulated. The 527 annotated DEPs were classified into 50 functional groups according to Gene Ontology and linked to 256 different pathways using the Kyoto Encyclopedia of Genes and Genomes database as a reference. A joint analysis of the transcriptome and proteomics results showed that the top three pathways were Amino acid metabolism, Carbohydrate metabolism, and Lipid metabolism. These results provide new viewpoints into the molecular mechanism of the inhibition of P. neglecta by SPA at the protein level and a theoretical basis for evaluating SPA as an antifungal agent to protect forests.

Effect of Climate and Competition on Radial Growth of Pinus sylvestris var. mongolica Forest in Hulunbuir Sandy Land of Inner Mongolia, China

(1) Background: The forest of Pinus sylvestris var. mongolica is an important semi-arid ecosystem in Hulunbuir sandy land that plays a key role in the carbon cycle and wind erosion control. It is crucial to explore the main factors affecting the radial growth of trees of P. sylvestris var. mongolica. (2) Methods: The study established the tree-ring chronology of P. sylvestris var. mongolica and analyzed the relationships among the radial growth, competition index, and climate variables using correlation analysis and a linear mixed effect model to explore the influence of competition and climate on radial growth of P. sylvestris var. mongolica. (3) Results: The results indicated that tree growth is mainly affected by the maximum average temperature (T_max) and precipitation in June and July of the current year and that tree growth significantly decreased with increasing competition pressure. Analysis of the linear mixed effect model showed that tree age, competition intensity, self-calibrating Palmer drought severity index (scPDSI) from May to July, and vapor pressure deficit (VPD) have a significant impact on radial growth. (4) Conclusions: The competition plays a dominant role in radial growth of P. sylvestris var. mongolica compared to climate factors. This study helps to understand the growth mechanism of P. sylvestris var. mongolica forests under climate change and provides a scientific basis for effective management of semi-arid forests.

mongolica caused by Fusarium oxysporum

Phytic acid (PA) is a new substitutable plant-derived antifungal agent; however, few reports have been published regarding its antifungal effects on pathogenic fungi. The present study explored the in vitro antifungal activity of PA against four phytopathogenic fungi and found that PA was the most effective at inhibiting the growth of Fusarium oxysporum. This study aimed to investigate the in vivo and in vitro antifungal activities of PA against the seedling blight of Pinus sylvestris var. mongolica caused by F. oxysporum and to determine its possible mechanism of action. The results showed that PA inhibited spore germination and mycelial growth of F. oxysporum in a concentration-dependent manner and exhibited strong inhibition when its concentration exceeded 1000 mg/L. It mainly destroyed the integrity of the cell membrane, increasing its cell membrane permeability, causing the cell contents to spill out, and impairing fungal growth. In addition, the leakage of intercellular electrolytes and soluble proteins indicated that PA used at its EC₂₀ and EC₅₀ increased the membrane permeability of F. oxysporum. The increase in malondialdehyde and hydrogen peroxide content confirmed that PA treatment at its EC₂₀ and EC₅₀ damaged the cell membrane of the pathogen. Scanning electron microscopy revealed that PA affected the morphology of mycelia, causing them to shrivel, distort, and break. Furthermore, PA significantly reduced the activities of the antioxidant-related enzymes superoxide dismutase and catalase, as well as that of the pathogenicity-related enzymes polygalacturonase, pectin lyase, and endoglucanase (EG) in F. oxysporum (P < 0.05). In particular, EG enzyme activity was maximally inhibited in F. oxysporum treated with PA at its EC₅₀. Moreover, PA significantly inhibited the incidence of disease, and growth indices in Pinus sylvestris var. mongolica seedling blight was determined. In summary, PA has a substantial inhibitory effect on F. oxysporum. Therefore, PA could serve as a new substitutable plant-derived antifungal agent for the seedling blight of P. sylvestris var. mongolica caused by F. oxysporum.

[Temporal and Spatial Variations in Root-associated Fungi Associated with Pinus sylvestris var. mongolica in the Semi-arid and Dry Sub-humid Desertified Regions of Northern China]

To illuminate the ecological functions of root-associated fungi (RAF) and their interactions with host plants, we revealed the root-associated fungal diversity and community compositions of Pinus sylvestris var. mongolica involving natural forests and plantations (half-mature, nearly mature, and mature forests) in the Hulunbuir Desert, Horqin Desert, and Mu Us Desert and investigated the environmental driving factors (climatic condition and soil property). The results indicated that: 1 the diversity of RAF in the natural forests was significantly lower than that in plantations (P<0.05), and the values were highest in the Mu Us Desert. There was a distinct geographical distribution in the RAF community, but the influence of stand age was not significant (P>0.05). 2 The relative abundance of ectomycorrhizal fungi (50.49%) in natural forests was higher than that in plantations, such as Acephala, Mycena, and Suillus. The indicator genera were diverse involving the natural forests (Acephala) and plantations in the Hulunbuir Desert (Sarcodon), Horqin Desert (Russula and Calostoma), and Mu Us Desert (Geopora, Mallocybe, and Tomentella). 3 The indicator genera were mainly affected by available nitrogen content, available phosphorus content, and stand age, and few indicator genera were related to soil water content, pH, and total nitrogen content. A total of 43.25% of the variation in the RAF community was accounted for by both geographic location and environmental factors. Overall, geographic location and environmental factors shaped the spatial variation in the RAF structure and function of P. sylvestris natural forests and plantations in the semi-arid and dry sub-humid desertified regions; there were no significant temporal variations in RAF across stand ages, but the nonuniformity in fungal distribution with stand ageing cannot be ignored. The large population of symbiotic fungi in natural forests was conducive to the healthy growth of hosts; the ratio of symbiotic, saprophytic, and pathotrophic fungi varied in different plantations, and the increase in the proportion of saprophytic and pathotrophic fungi may have negative effects on the growth and health of plantations. This improved information will provide a theoretical basis for the management of P. sylvestris plantations.

Effects of thinning intensity on the understory water-holding capacity of Pinus sylvestris var. mongolica plantation in the Bashang area of north China

The complex terrain and poor climatic conditions in Bashang area of Hebei Province result in water and soil loss and geological disasters, which pose a serious threat to ecological safety in North China. In order to improve local environmental quality, barren-resistant and fast-growing tree species such as Pinus sylvestris var. mongolica and Larix gmelinii are planted with large areas. However, unreasonable plantation density will lead to inefficient utilization of rainfall and intensify the conflict between forest and water. In this study, we analyzed the effects of five thinning intensities (0, 20%, 40%, 60%, 80%) of P. sylvestris var. mongolica plantation on herbs, litter, soil and overall water-holding capacity, with the aim to provide scientific basis for management of P. sylvestris var. mongolica. The results showed that water-holding rate of herb varied from 47.7% to 90.7%, and that the water-holding capacity of herb decreased with increasing thinning intensity. When the thinning intensity was less than 40%, water-holding capacity decreased slowly, and then decreased rapidly. With the increase of thinning intensity, natural water-holding rate and maximum water-holding rate of undecomposed layer and semi-decomposed layer decreased gradually, with the effective water-holding rate being 60%>40%>20%>80%>0, and the water-holding capacity of semi-decomposed layer being better than that of undecomposed layer. The water-holding capacity of soil decreased gradually with the increases of thinning intensity. Thinning intensity less than 40% promoted water holding capacity. Under different thinning intensities, the total water-holding rate of understory was 8.3%-14.3%, with an order of 20%>0>40%>60%>80%. In view of understory all layers and overall changes, the thinning intensity at 20% in the study area could effectively improve the understory water-holding capacity and achieve better ecological benefits.

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.

Effects of Dark Septate Endophytes Strain A024 on Damping-off Biocontrol, Plant Growth and the Rhizosphere Soil Enviroment of Pinus sylvestris var. mongolica Annual Seedlings

Dark septate endophytes (DSEs) exert a vital role in promoting plant growth, improving mineral absorption, biological disease control, and enhancing plant stress resistance. The effects of dark septate endophyte strain, Phialocephala bamuru A024 on damping-off biocontrol, plant development, nutrients within the rhizosphere soil, as well as bacterial communities in the annual seedlings of P. sylvestris var. Mongolica were studied. According to our findings, following P. bamuru A024 inoculation, the damping-off disease morbidity decreased significantly compared with control, some physiological indices such as β-1,3-glucanase, chitinase enzyme activity as well as a soluble protein and proline content in P. sylvestris var. mongolica were elevated under R. solani stress. After inoculation with P. bamuru A024, the biomass in seedlings, nutrients in soil, root structure index, together with activities of soil enzymes were remarkably up-regulated relative to control (p < 0.05). As suggested by the results of high-throughput sequencing, the microbial structure in the rhizosphere soil of the P. sylvestris var. mongolica showed significant differences (p < 0.05) after P. bamuru A024 inoculation compared to control treatment and the rhizosphere soil bacterial community structure after DSE A024 inoculation was positively correlated to the main soil nutrition indices.

Temperature signal recorded in δ2H and δ13C values of wood lignin methoxyl groups from a permafrost forest in northeastern China

Stable isotopes in wood lignin methoxyl groups (δ²H_LM and δ¹³C_LM values) have been suggested as valuable complementary paleoclimate proxies. In permafrost forests, tree growth is influenced by multiple factors, however temperature appears to have the strongest impact on tree growth and, therefore, on carbon cycling. To test whether δ²H_LM and δ¹³C_LM values of trees from permafrost regions might record climate parameters, two dominant tree species (Larix gmelinii, larch, and Pinus sylvestris var. mongolica, pine) collected from a permafrost forest in China's Greater Hinggan Mountains, were investigated. The two tree species larch and pine covered time spans of 1940 to 2013 and 1870 to 2013, respectively. Results showed significant correlations of pine and larch δ²H_LM values and larch δ¹³C_LM values with temperatures and in particular with the mean temperature of the growing season from April to August. However, only weak correlations of δ²H_LM and δ¹³C_LM values with moisture conditions, such as precipitation amount and relative humidity were observed. In addition, species specificity in the climate response was most obvious for δ¹³C_LM values. Compared to a temperature reconstruction based on tree ring width, pine δ²H_LM-based reconstruction showed strongest spatial correlations with regional temperature. Therefore, δ²H_LM values might be a promising proxy to reconstruct growing-season temperatures in permafrost regions.

Effects of afforestation with Pinus sylvestris var. mongolica plantations combined with enclosure management on soil microbial community

Grazing and litter removal can alter understory structure and composition after afforestation, posing a serious threat to sustainable forest development. Enclosure is considered to be an effective measure to restore degraded forest restoration. However, little is known about the dynamics of soil nutrients and microbial communities during the forest restoration process. In the present study, the effects of Arachis hypogaea (AH), Pinus sylvestris var. mongolica (PSM) and Pinus sylvestris var. mongolica with enclosure (PSME) on soil chemical properties and soil microbial communities were studied in Zhanggutai, Liaoning Province, China. The results showed that PSME could remarkably contribute to improve soil total C, total N and total P compared to PSM and AH. Additionally, PSM could clearly increase the soil bacterial community diversity and fungal Chao1 index and ACE index. Additionally, PSME could further increase soil Chao1 index and ACE index of soil bacteria. Soil total C, total N and available N were the main factors related to soil microbial diversity. Actinobacteria and Ascomycota were the predominant bacterial and fungal phyla, respectively. Specifically, PSME could increase the relative abundances of Actinobacteria, Gemmatimonadetes, Ascomycota and Mortierellomycota and decreased the relative abundances of Acidobacteria, Chloroflexi and Basidiomycota than PSM. PSM and PSME could clearly change soil microbial communities compared with AH and PSME could remarkably shift soil fungal communities than PSM. What's more, the soil microbial community structure were affected by multiple edaphic chemical parameters. It can be seen that afforestation combined with enclosed management potentially regulate microbial properties through shifting the soil properties. This study can provide new ideas for further understanding the impact of enclosure on PSM and provide theoretical support for the management of PSM.

Community structure and functional group of root-associated Fungi of Pinus sylvestris var. mongolica across stand ages in the Mu Us Desert

Root-associated fungi (RAF) are an important factor affecting the host's growth, and their contribution to Pinus sylvestris var. mongolica plantation decline is substantial. Therefore, we selected three age groups of P. sylvestris plantations (26, 33, and 43 years), in the Mu Us Desert, to characterize the community structure and functional groups of RAF, identified by Illumina high-throughput sequencing and FUNGuild platform, respectively. The effects of soil properties and enzyme activities on fungal diversity and functional groups were also examined. The results indicated that (a) 805 operational taxonomic units of RAF associated with P. sylvestris belonged to six phyla and 163 genera. Diversity and richness were not significantly different in the three age groups, but community composition showed significant differences. Ascomycota and Basidiomycota dominated the fungal community, while Rhizopogon dominated in each plot. (b) The proportion of pathotrophs decreased with increasing age, while that of symbiotrophs increased sharply, which were mainly represented by ectomycorrhizal fungi. (c) Stand age and soil enzyme activity had a greater influence on fungal community composition than did soil properties, whereas environmental variables were not significantly correlated with fungal diversity and richness. Dynamics of fungal community composition and functional groups with the aging plantations reflected the growth state of P. sylvestris and were related to plantation degradation.

mongolica plantations

To reveal the allocation pattern and stoichiometric characteristics of N and P in Pinus sylvestris var. mongolica plantation, we selected three P. sylvestris plantation with different stand ages (middle-aged, near-mature, mature) in the Hulunbuir, Horqin, and Mu Us sandy land as objects, and analyzed the contents of nitrogen, phosphorus and the N:P stoichiometry ratios in the leaf, litter, and soil. The results showed that the contents of N, P and N/P ratios in leaf, litter and soil varied in the range of 0.17-49.02, 0.11-3.01 g·kg^-1 and 0.51-19.74, respectively, with the order of leaf>litter>soil. The content of N and N:P ratio were significantly different between leaf, litter and soil; the P content in leaf was significantly higher than that in litter and soil. The different areas and stand ages affected N, P content and N/P stoichiometry ratio, but the interaction of area and stand age had no significant effect on N/P stoichiometry ratio. The N, P contents in leaf, litter and soil increased with stand age, and were highest in the mature forest. The contents of N, P and N/P ratios were significantly positively correlated among the leaf, litter and soil. In the Hulunbuir and Horqin sandy land, the N/P ratros of leaf were between 14.53 to 15.57, which indicated that the P. sylvestris var. mongolica plantations was restricted by both N and P availability. In Mu Us sand land, the N:P ratios of leaf were between 18.56 to 19.71, which indicated P limitation. The stand age had no significant influence on soil N and P limitation. To improve the productivity of P. sylvestris var. mongolica plantations, we could appropriately add N or P fertilization in the plantation tending management based on local conditions. Our findings could contribute to a further understanding of the mechanism of interactions and constraints between N and P in the leaf-litter-soil system of P. sylvestris var. mongolica plantations, and provide a scientific guidance for the management.

mongolica (Pinaceae)

PREMISE OF THE STUDY

A set of novel expressed sequence tag (EST) microsatellite markers was developed in Pinus sylvestris var. mongolica to promote further genetic studies in this species. •

METHODS AND RESULTS

One hundred seventy-five EST-simple sequence repeat (SSR) primers were designed and synthesized for 31,653 isotigs based on P. tabuliformis EST sequences. The primer pairs were used to identify 25 polymorphic loci in 48 individuals. The number of alleles ranged from two to eight with observed and expected heterozygosity values of 0.0435 to 0.8125 and 0.0430 to 0.7820, respectively. •

CONCLUSIONS

These new polymorphic EST-SSR markers will be useful for assessing genetic diversity, molecular breeding and genetic improvement, and conservation of P. sylvestris var. mongolica.