Patterns and environmental drivers of C, N, and P stoichiometry in the leaf-litter-soil system associated with Mongolian pine forests.

Ecological stoichiometry is an important approach to understand plant nutrient cycling and balance in the forest ecosystem. However, understanding of stoichiometric patterns through the leaf-litter-soil system of Mongolian pine among different stand origins is still scarce. Therefore, to reveal the variations in Mongolian pine carbon (C), nitrogen (N), and phosphorus (P) stoichiometry and stoichiometric homeostasis among different stand origins, we measured C, N, and P concentrations of leaves, litter, and soil, and analyzed the nutrient resorption efficiencies of leaves in differently aged plantations and natural forests from semi-arid and dry sub-humid regions. The results showed that (1) the stand origin had a significant effect on the C-N-P stoichiometry, and also significantly affected leaf N and P reabsorption efficiencies. Leaf N/P ratios indicated that Mongolian pine was co-limited by N and P in the NF, HB and HQ, and was mainly limited by P in MU. (2) With increasing stand age, C concentrations in the leaf-litter-soil system initially increased and then decreased, the N and P concentrations and reabsorption efficiencies in the leaf-litter-soil system were gradually increased. Overall, stand age had a significant effect on N concentrations, C/N and C/P ratios in the leaf-litter-soil system. (3) The C and N elements between the leaf-litter-soil system had a strong coupling relationship, and the P element between litter-soil had a strong coupling relationship. In addition, plantations exhibited greater N/P homeostasis than natural forests, and N/P exhibited greater homeostasis than N and P alone, which may be a nutrient utilization strategy for forests to alleviate N or P limitation. (4) Environmental factors have a significant influence on C-N-P stoichiometry in the leaf-litter-soil system, the most important soil properties and meteorological factors being soil water content and precipitation, respectively. These results will be essential to provide guidance for plantation restoration and management in desert regions.

[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.