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

Abstract

SummaryThe 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.Our results demonstrated that the biomasses or abundances of most components of the two below‐ground communities (microbes and nematodes) were negatively affected byPFGloss and were positively related to above‐ground plant biomass. The removal of dominantPFGs (perennial bunchgrasses and perennial rhizomatous grasses) reduced the biomass or abundance of below‐ground community components while removal of less dominantPFGs (perennial forbs and annuals/biennials) did not change or increased the biomass or abundance of below‐ground community components.The biomass‐based ratio of fungal to bacterial microbes and the number‐based ratio of fungal‐feeding to bacterial‐feeding nematodes decreased with increasingPFGlosses. Variation partitioning analyses showed that the identity ofPFGs together with above‐ground plant biomass explained most of the total variation in soil microbes and that the identity ofPFGs and above‐ground plant biomass together with nematode food resources explained most of the total variation in soil nematodes. The increase inNEEwithPFGloss was mainly explained by decreases in above‐ground plant biomass and the ratio of fungi to bacteria.Synthesis. The shift of below‐ground communities from a fungal‐based to a bacterial‐based energy channel asPFGrichness 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 onNEEindicate thatPFGloss 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 ofCO2fluxes in terrestrial ecosystems.