Nutrient identity modifies the destabilising effects of eutrophication in grasslands

Abstract

Nutrient enrichment can simultaneously increase and destabilise plant biomass production, with co‐limitation by multiple nutrients potentially intensifying these effects. Here, we test how factorial additions of nitrogen (N), phosphorus (P) and potassium with essential nutrients (K+) affect the stability (mean/standard deviation) of aboveground biomass in 34 grasslands over 7 years. Destabilisation with fertilisation was prevalent but was driven by single nutrients, not synergistic nutrient interactions. On average, N‐based treatments increased mean biomass production by 21–51% but increased its standard deviation by 40–68% and so consistently reduced stability. Adding P increased interannual variability and reduced stability without altering mean biomass, while K+ had no general effects. Declines in stability were largest in the most nutrient‐limited grasslands, or where nutrients reduced species richness or intensified species synchrony. We show that nutrients can differentially impact the stability of biomass production, with N and P in particular disproportionately increasing its interannual variability.

Impacts of nutrient addition on soil carbon and nitrogen stoichiometry and stability in globally-distributed grasslands

“…Addition of NPK +µ reduced the relative distribution of C and N in MAOM versus POM (fMAOM-C and -N) as compared to the control and P, respectively. These findings align with previous NutNet work that suggests grassland biomass production is co-limited by N, P, and K, as adding these together increases aboveground plant growth (Fay et al 2015;Carroll et al 2021), as we also found in our sites (Supplementary Fig. 3).…”

Multiple global changes drive grassland productivity and stability: A meta‐analysis

“…Plant communities on infertile soils often exhibit resource‐conservative functional traits, which may limit their responses to climate change (Fernandez‐Going et al, 2012). Conversely, they may also be more vulnerable to climate variation once nutrient limitations are relieved under eutrophication (Carroll et al, 2022). At present, the response of the stability of plant communities to various global changes along a soil fertility gradient and the underlying mechanisms remain unelucidated.…”

“…climate, soil properties, treatment intensity and duration) affect the responses of grassland stability? To address these questions, we test three interrelated hypotheses: (1) nutrient addition would decrease the temporal stability of grasslands by lessening nutrient limitations (Bai et al, 2010; Carroll et al, 2022); (2) both plant species richness (Hautier et al, 2015) and dominant plant functional group (Mackie et al, 2019; Shi et al, 2016) would play an important role in regulating stability responses to global changes and (3) community stability would be less affected by global changes in grasslands with lower soil fertility (Fernandez‐Going et al, 2012), higher climate variability (Ciemer et al, 2019), with low intensity treatments and with treatments that occurred only over short durations.…”

Change in functional trait diversity mediates the effects of nutrient addition on grassland stability

“…4). Consistent with previous analyses, we found that nutrient addition may decrease invariability through decreasing species richness (Hautier et al ., 2015; Carroll et al ., 2021), but this indirect negative effect, together with the negative effects through resilience were offset by the positive effects through resistance. Combined, nutrient addition did not impact invariability.…”

“…In grasslands, nutrient addition has been shown to decrease resistance in aboveground primary productivity during dry climate extremes as well as temporal invariability, while its effects on resilience after dry climate extremes are mixed (Tilman & Downing, 1994; Xu et al ., 2014; Hautier et al ., 2015; Bharath et al ., 2020; Meng et al ., 2021; Van Sundert et al ., 2021; Carroll et al ., 2021). However, to date, few empirical studies have investigated the impact of nutrient addition on resistance during and resilience after wet climate extremes, which are becoming increasingly frequent just as dry climate extremes globally (IPCC, 2019).…”