[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.

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.

Stoichiometric characteristics of nitrogen and phosphorus in leaf-litter-soil system of Pinus sylvestris var. 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.