Introduction
Understanding the mechanisms that stabilize ecosystem functions when faced with a changing environment has been a key issue in ecology (Tilman & Downing 1994; Tilman et al. 2006; Isbell et al.2009; Hector et al. 2010; de Mazancourt et al. 2013; Loreau & de Mazancourt 2013; Hautier et al. 2014; Cravenet al. 2018; Wang et al. 2019b). Greater biodiversity, especially plant diversity, usually increases the temporal stability of biomass production, although negative and neutral effects have been occasionally observed (Tilman et al. 2006; Hector et al. 2010; Hautieret al. 2014; Pennekamp et al. 2018; Craven et al.2018; Wang et al. 2019b). However, the vast majority of existing studies focused on the biodiversity of a single trophic group (Tilmanet al. 2006; Isbell et al. 2009; Hector et al.2010; Hautier et al. 2014; Hautier et al. 2015; Maet al. 2017; Wang et al. 2019b), neglecting biodiversity across trophic levels, even though multitrophic biodiversity has been shown to drive multiple ecosystem functions (Soliveres et al.2016; Schuldt et al. 2018; Geisen et al. 2019; Domeignoz-Horta et al. 2020).
Soil biota, comprising an enormous number of consumers and decomposers, represent one of the largest reservoirs of biodiversity on Earth (Orgiazzi et al.2016; Geisen et al. 2019; Thakur et al.2020). A growing number of studies suggest that soil biodiversity has an essential impact on plant diversity, community composition, biomass production, plant-plant interactions and plant tolerance to stress factors, as well as nutrient cycling (Wagg et al. 2014; Bardgett & van der Putten 2014; Delgado-Baquerizo et al. 2016; Wagg et al. 2019; Lianget al. 2019; Domeignoz-Horta et al. 2020; Guerra et al. 2020). Recent work has provided a conceptual framework showing that plant and soil biodiversity can jointly influence the stability of biomass production via regulating these plant attributes (Yang et al. 2018). However, there is increasing concern that soil and plant biodiversity is threatened by anthropogenic environmental change (Tsiafouli et al. 2015; Gossner et al. 2016; Banerjeeet al. 2019; Geisen et al. 2019; Zhou et al. 2020). Hence, it is important to understand how biodiversity loss in both soil and plant communities affects the stability of biomass production will provide a broader perspective.
Here we conducted a fully factorial experiment manipulating plant diversity and soil biodiversity using model grassland microcosms (Fig. 1). We used a dilution-to-extinction approach (Yan et al. 2015; Hol et al. 2015; Roger et al. 2016) to create a gradient of soil biodiversity, and then established grassland microcosms of different plant species richness at each point along the soil biodiversity gradient under greenhouse conditions. We focused on the temporal stability of biomass production, defined as the ratio of the temporal mean to the standard deviation of plant community biomass (Tilmanet al. 2006). Because the constant environment in the greenhouse does not capture natural variability, environmental variation in precipitation was simulated by inducing three wet-dry cycles in all microcosms to investigate the effects of the biodiversity treatments on the temporal stability of biomass production.
Considering the significance of soil biodiversity on plant attributes (Yang et al. 2018), we predicted that soil biodiversity loss will reduce the temporal stability of biomass production. Specifically, we tested whether and how soil biodiversity interacts with plant diversity in terms of species richness and functional diversity to influence temporal stability. Furthermore, we investigated how multitrophic biodiversity, accounting for plant and soil biodiversity, affects temporal stability. We find that both greater plant and soil biodiversity had positive effects on the temporal stability of community biomass production, but plant and soil biodiversity independently affected temporal stability. Multitrophic biodiversity is positively associated with temporal stability.