General destabilizing effects of eutrophication on grassland productivity at multiple spatial scales

Abstract

Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.

Species asynchrony stabilises productivity under extreme drought across Northern China grasslands

“…Consistent with theoretical predictions (Wang & Loreau, 2014, 2016) and experimental findings (Hautier et al., 2020; Zhang, Feng, et al., 2019), our SEM results further revealed that species stability promoted stability of ANPP under drought, though independent of species richness. More importantly, SEM revealed that drought neither directly nor indirectly reduced stability of ANPP through species stability, rather it reduced stability of ANPP by diminishing the contribution of species richness to asynchrony.…”

“…Instead, SEM analysis revealed species richness contributions to stability of ANPP were indirect through species asynchrony under drought. This SEM finding thus confirms the existing theoretical (Loreau & de Mazancourt, 2013; Wang & Loreau, 2014, 2016) and empirical (Hautier et al., 2014, 2020; Hector et al., 2010; Wilcox et al., 2017) studies that linked the stabilising role of species richness to asynchrony in response to environmental variability.…”

“…Nevertheless, our consistent finding of positive impact of species asynchrony on stability of ANPP under ambient and drought conditions indicates that extreme drought did not erode asynchrony–stability relationships across or within the six natural grasslands. This finding is similar to how asynchrony positively drives ANPP stability under other global changes, like warming or eutrophication (Hautier et al., 2014, 2020; Ma et al., 2017). Despite that the SEM analysis showed that extreme drought indirectly reduced species asynchrony by reducing species richness, species asynchrony was nearly fourfold more important to stability of ANPP than species stability.…”

“…Contrary to our expectations, we found no significant relationship between temporal stability of ANPP and species richness across and within the six natural semi‐arid and arid grasslands under ambient conditions in Northern China. This finding contradicts most previous reports from single‐site manipulative experiments (Isbell et al., 2009; Proulx et al., 2010; Tilman et al., 2006), meta‐analyses (Craven et al., 2018; Isbell et al., 2015), globally distributed natural grasslands studies (Hautier et al., 2014, 2020), as well as a 33‐year study in Inner Mongolia, China (Zhang et al., 2018). Thus, species richness might not have a direct mechanistic effect on ANPP stability in these grasslands because richness and stability could respond differently to environmental fluctuations (Ma et al., 2010).…”

“…Second, species asynchrony—dissimilar responses among species to environmental variability—can increase temporal ecosystem stability through shifts in relative abundances of species with different ecological niches (Hector et al., 2010; Loreau & de Mazancourt, 2013; Wilcox et al., 2017; Xu et al., 2015) such that an increase in the abundance of some species compensates for decline in others as a result of environmental changes (Hautier et al., 2014). Third, theoretical and empirical studies also suggest that high species stability (stability of individual species averaged across all species in a community) results in high temporal ecosystem stability (Hautier et al., 2020; Wang & Loreau, 2014, 2016; Yang et al., 2012; Zhang, Feng, et al., 2019). However, the relative contribution of species richness, species asynchrony and species stability to temporal ecosystem stability remains unclear.…”