Richness, community structure and spatial autocorrelation of soil fungi along a sharp aridity gradient in monodominant pine forests

Understanding how aridity shapes fungal communities is essential for predicting ecosystem responses to climate change. Monodominant forests of Aleppo pine (Pinus halepensis) occurring along a steep precipitation gradient, offer the opportunity to test the effect of aridity on distance decay patterns of soil fungi, without the confounding effects of vegetation. We conducted nested soil sampling in four Mediterranean, two semi-arid and three arid forests along an aridity gradient (250-800 mm annual precipitation) and examined the distance decay patterns of saprotrophic (SAP) and ectomycorrhizal (ECM) fungi at different spatial scales. ITS2 soil metabarcoding revealed that both fungal richness and diversity increased with precipitation. Fungal communities showed significant spatial autocorrelation at multiple scales, with stronger distance decay patterns in Mediterranean than arid forests. ECM and SAP communities in arid sites were largely subsets of the Mediterranean climate communities. Stochastic assembly processes dominated under mesic conditions, while deterministic processes prevailed in arid regions, particularly for ECM fungi. Our results demonstrate that aridity can reduce fungal richness and stochasticity, and that climate can structure fungal communities independently of vegetation. This study highlights the need to consider scale-dependent ecological processes and emphasizes the role of climate, beyond vegetation, in shaping fungal community assembly in forest soils.

明晰干旱如何塑造真菌群落，对于预测生态系统对气候变化的响应至关重要。沿陡峭降水梯度分布的阿勒颇松（Pinus halepensis）单优林，为我们在排除植被混杂效应的前提下，探究干旱对土壤真菌距离衰减模式的影响提供了理想契机。本研究沿干旱梯度（年降水量250~800 mm）在4片地中海森林、2片半干旱森林与3片干旱森林中开展嵌套式土壤采样，并解析了腐生真菌（saprotrophic, SAP）与外生菌根真菌（ectomycorrhizal, ECM）在不同空间尺度下的距离衰减模式。通过ITS2区土壤宏条形码测序分析，我们发现真菌丰富度与多样性均随降水量升高而增加。真菌群落在多个空间尺度上均表现出显著的空间自相关性，且地中海森林中的真菌距离衰减强度显著高于干旱森林。干旱样地中的ECM与SAP真菌群落，在很大程度上属于地中海气候区真菌群落的子集。中生环境下真菌群落组装以随机过程为主导，而干旱区域则以确定性过程为主，这一现象在外生菌根真菌中尤为明显。本研究结果表明，干旱会降低真菌丰富度与群落组装的随机性，且气候能够独立于植被，对真菌群落结构起到塑造作用。本研究强调了考量尺度依赖型生态过程的必要性，并指出在森林土壤真菌群落组装过程中，气候的作用独立于植被，不容忽视。