Effects of soil water on fungal community composition along elevational gradients on the northern slope of the Central Kunlun Mountains

Abstract

Soil fungi are essential to ecosystem processes, yet their elevational distribution patterns and the ecological mechanisms shaping their communities remain poorly understood and actively debated, particularly in arid regions. Here, we investigated the diversity patterns and underlying mechanisms shaping soil fungal communities along an elevational gradient (1,707-3,548 m) on the northern slope of the Central Kunlun Mountains in northwest China. Results indicated that the dominant phyla identified across the seven elevational gradients were Basidiomycota and Ascomycota, displaying a unimodal pattern and a U-shaped pattern in relative abundance, respectively. Soil saprotroph and nectar/tap saprotroph were the dominant functional groups (>1.0%). Along the elevational gradients, soil fungal α-diversity demonstrated a generally decreasing trend, whereas β-diversity showed a contrasting increasing trend. Among the environmental variables, altitude and climate (mean annual precipitation, MAP; mean annual temperature, MAT) were the strongest predictors for α-diversity. Partial least squares path modeling (PLSPM) analysis revealed that soil water content (Wat) was the most influential factor driving fungal α-diversity, while vegetation coverage (Veg) emerged as the primary determinant of soil fungal community composition. The influence of Wat on fungal α-diversity shifted from indirect to direct as elevation increased, transitioning from lower elevations (≤2,448 m) to higher elevations (≥2,746 m). Similarly, the impact of Veg on soil fungal community composition exhibited a comparable pattern. The null model analysis revealed that homogeneous selection and dispersal limitation dominated the soil fungal community assembly at elevations lower than 2,448 m and higher than 2,746 m, respectively. Variations in ecological processes may be linked to changes in key environmental factors that influence soil fungal communities in an elevation-dependent manner. These findings can enhance our ability to predict soil fungal diversity patterns and their responses to climate change in the ecosystems of the northern slope of the Central Kunlun Mountain.

Keywords: Central Kunlun Mountains; driving factors; ecological processes; elevational gradients; soil ecosystem.

Figure 1

Composition of soil fungal community at the class level and fungal functional guilds along the elevational gradients on the northern slope of the Central Kunlun Mountains. (A) Relative abundances of the dominant fungal classes in the soil fungi community; (B) different biomarkers among the different altitudes based on linear discriminant analysis (LDA); (C) the relative abundances of the fungal functional guilds in the soil samples collected from the different elevations.

Figure 2

Diversity changes of fungal community along the elevational gradients and their relationships with the environmental factors. (A) Differences of Shannon–Weaver indexes; (B) effects of the environmental factors on the composition of soil fungal community based on dbRDA analysis. Alt, altitude; AP, available phosphorus; C_N, the ratio of total organic carbon to total nitrogen; EC, electrical conductivity; MAP, mean annual precipitation; MAT, mean annual temperature; Sal, total water-soluble salt; TN, total nitrogen; TOC, total organic carbon; Veg, vegetation coverage; Wat, water content.

Figure 3

Spearman's correlation analysis of the relatedness between the environmental variables and the diversity, and phylogenetic diversity of soil fungal community. Alt, altitude; AP, available phosphorus; C_N, the ratio of total organic carbon to total nitrogen; EC, electrical conductivity; MAP, mean annual precipitation; MAT, mean annual temperature; Sal, total water-soluble salt; TN, total nitrogen; TOC, total organic carbon; Veg, vegetation coverage; Wat, water content. Significance level, *P < 0.05, **P < 0.01, ***P < 0.001, ns, not significant.

Figure 4

Partial least squares path models (PLSPMs) for the Shannon–Weaver index (A–C) and community composition (D–F). (A, D) Lower elevations (1,707, 1,960, and 2,448 m); (B, E) higher elevations (2,746, 2,905, 3,248, and 3,548 m); (C, F), the whole transect. The models were constructed at the conditions of the removal of some variables, which showed higher collinearities than 0.8 (Spearman's ρ² > 0.8) calculated with the function varclus in the Hmisc package. The variables “Soil.o” include vary on the lower, higher, or whole transect. For the whole transect, “Soil.o” includes total nitrogen, TN; NH4⁺-N, ammonium nitrogen; NO3⁻-N, nitrate nitrogen; Sal, total water-soluble salt; AP, available phosphorus; Veg, vegetation coverage; Wat, water content. Shan, Shannon–Weaver index; Beta, the first two axes of PCoA. GOF: goodness of fit. Loading values of environmental for the modules in partial least squares path modeling (PLSPMs) are available in Supplementary Table S5. Significance level, *P < 0.05, **P < 0.01, ***P < 0.001, ns, not significant.

Figure 5

Profiles of phylogenetic diversities and the ecological processes of soil fungal community along the elevational gradients. (A) Differences of the values of ses.MNTD; (B) difference of the values of βNTI; (C) effects of ecological processes on the soil fungal community construction.