Data from: Effects of plant functional group loss on soil biota and net ecosystem exchange: a plant removal experiment in the Mongolian grassland

1. The rapid loss of global biodiversity can greatly affect the functioning of above-ground components of ecosystems. However, how such biodiversity losses affect below-ground communities and linkages to soil carbon (C) sequestration is unclear. Here we describe how losses in plant functional groups (PFGs) affect soil microbial and nematode communities and net ecosystem exchange (NEE) in a 4-year removal experiment conducted on the Mongolian plateau, the world's largest remaining natural grassland. 2. Our results demonstrated that the biomasses or abundances of most components of the two below-ground communities (microbes and nematodes) were negatively affected by PFG loss and were positively related to above-ground plant biomass. The removal of dominant PFGs (perennial bunchgrasses and perennial rhizomatous grasses) reduced the biomass or abundance of below-ground community components while removal of less dominant PFGs (perennial forbs and annuals/biennials) did not change or increased the biomass or abundance of below-ground community components. 3. The biomass-based ratio of fungal to bacterial microbes and the number-based ratio of fungal-feeding to bacterial-feeding nematodes decreased with increasing PFG losses. Variation partitioning analyses showed that the identity of PFGs together with above-ground plant biomass explained most of the total variation in soil microbes and that the identity of PFGs and above-ground plant biomass together with nematode food resources explained most of the total variation in soil nematodes. The increase in NEE with PFG loss was mainly explained by decreases in above-ground plant biomass and the ratio of fungi to bacteria. 4. Synthesis. The shift of below-ground communities from a fungal-based to a bacterial-based energy channel as PFG richness decreases indicates that less diverse grassland ecosystems will have lower nutrient retention and hence be more sensitive to land use or climate change. The dominant effects of above-ground plant biomass and below-ground communities on NEE indicate that PFG loss resulting from land use or climate change has the potential to reduce C sequestration in semi-arid grassland soils. These findings suggest that predictive models may need to consider the composition of above-ground and below-ground communities in order to accurately simulate the dynamics of CO2 fluxes in terrestrial ecosystems.

1. 全球生物多样性的快速丧失可显著影响生态系统地上组分的功能运转，但此类生物多样性丧失如何作用于地下群落，以及其与土壤碳（Carbon, C）固存的关联机制仍未明确。本研究依托全球现存规模最大的天然草原——蒙古高原开展的为期4年的植物功能群移除实验，阐明了植物功能群（plant functional groups, PFGs）丧失对土壤微生物、线虫群落以及生态系统净交换（net ecosystem exchange, NEE）的影响。
2. 研究结果表明：两类地下群落（微生物与线虫）的多数组分的生物量或丰度均会因植物功能群丧失而受到负面影响，且与地上植物生物量呈显著正相关关系。移除优势植物功能群（多年生丛生禾草与多年生根茎禾草）会降低地下群落组分的生物量或丰度；而移除非优势植物功能群（多年生杂类草与一年生/二年生植物）则不会改变甚至会提升地下群落组分的生物量或丰度。
3. 基于生物量的真菌与细菌微生物比值，以及基于个体数量的食真菌线虫与食细菌线虫比值均随植物功能群丧失程度的加剧而下降。变异分割分析显示，植物功能群的身份特征与地上植物生物量共同解释了土壤微生物总变异的绝大部分；而植物功能群身份、地上植物生物量与线虫食物资源三者共同解释了土壤线虫总变异的绝大部分。生态系统净交换随植物功能群丧失而升高的现象，主要可由地上植物生物量的下降以及真菌与细菌的比值降低来解释。
4. 综合分析表明：随着植物功能群丰富度降低，地下群落的能量通道会从以真菌为主导转向以细菌为主导，这意味着生物多样性更低的草原生态系统养分保留能力更弱，因此对土地利用或气候变化更为敏感。地上植物生物量与地下群落对生态系统净交换的主导效应提示，由土地利用或气候变化引发的植物功能群丧失，有可能降低半干旱草原土壤的碳固存能力。本研究结果表明，若要精准模拟陆地生态系统的CO₂通量动态，预测模型或许需要纳入地上与地下群落的组成信息。