Plant functional groups mediate drought resistance and recovery in a multisite grassland experiment

Abstract

Climate change predictions suggest that summer droughts will become more intense and recurrent in Europe. While drought‐induced reductions in grassland primary productivity are well documented, the drivers behind drought resistance (the capacity to withstand change) and recovery (the capacity for recovery of function) of above‐ and below‐ground biomass remain poorly understood. Across eight grasslands differing in plant community productivity (CP), we investigated the effects of summer drought on plant and soil microbial variables, plant nutrient content, and soil nitrogen (N) availability. We examined the linkages between CP, soil N, drought responses of plant and microbial communities, and relative drought responses of plant and microbial biomass. Plant and microbial variables were recorded at the end of a 3‐month rainfall exclusion period. Plant variables were also assessed during a 10‐month drought recovery period. Experimental drought decreased plant biomass and increased plant C:N ratios, but had no effect on total microbial biomass across sites. Instead, drought caused shifts in plant and microbial community structures as well as an increase in arbuscular mycorrhiza fungi biomass. Overall, plant biomass drought resistance was unrelated to CP or microbial community structure but was positively related to drought resistance of forbs. In the month after rewetting, soil N availability increased in droughted plots across sites. Two months post‐rewetting, droughted plots had higher plant N concentration, but lower plant N use efficiency. The short‐term drought recovery of plant biomass was unrelated to CP or soil N availability, but positively related to the response of grass biomass, reflecting incomplete recovery at high CP. Ten months after rewetting, drought effects on plant biomass and plant N content were no longer apparent. Synthesis. Our results suggest that drought resistance and recovery are more sensitive to plant community composition than to community productivity. Short‐term recovery of plant biomass may also benefit from increased soil N availability after drought and from a high abundance of soil fungi in low productivity sites. Our findings underline the importance of plant functional groups for the stability of permanent grasslands in a changing climate with more frequent drought.

Using proxies of microbial community‐weighted means traits to explain the cascading effect of management intensity, soil and plant traits on ecosystem resilience in mountain grasslands

“…Ecosystems dominated by exploitative plant species produce more biomass of greater nutritional quality (Gardarin et al, ; Lavorel et al, ), with faster litter decomposition (Fortunel et al, ; Quested, Eriksson, Fortunel, & Garnier, ) and faster mineralization and nitrification (Grigulis et al, ; Orwin et al, ), as compared with ecosystems dominated by conservative plants. Exploitative plant species are also less resistant to drought, but with faster recovery (Karlowsky et al, ; Mackie, Zeiter, Bloor, & Stampfli, ). This continuum from slow to fast nutrient cycling along the plant economics spectrum has also been related to concomitant changes in soil microbial community composition and resilience: bacteria dominate at the exploitative end of the continuum and fungi at the conservative one, with respectively greater resilience and stronger resistance to drought (Cole et al, ; De Vries, Liiri, et al, ; De Vries, Manning, et al, ; De Vries & Shade, ; Grigulis et al, ; Legay et al, ).…”

Timing of drought in the growing season and strong legacy effects determine the annual productivity of temperate grasses in a changing climate

“…Bloor and Bardgett (2012) and also Denton et al (2017) found that drought events promote soil fertility and nutrient retention following drought release. Likewise, Gordon et al (2008) found an increase in microbial activity after a rewetting event, possibly leading to a rapid and sudden influx of plant available nitrogen in the soil (Mackie et al, 2018;Schimel and Bennett, 2004). Hofer et al (2017a) also attributed growth increases relative to control plots in post-drought periods to nitrogen availability in the soil and Karlowsky et al (2018) found evidence that interactions between plants and microbes increase plant nitrogen uptake in grasslands after rewetting events.…”

“…Effects of drought on annual aboveground NPP of grasslands have been shown to vary, depending on the severity of the experienced drought (Vicca et al, 2012;Wilcox et al, 2017), ecosystem type (Byrne et al, 2013;Gherardi and Sala, 2019;Sala et al, 2015;Wilcox et al, 2017), the intensity of land use (Vogel et al, 2012;Walter et al, 2012), the plant functional composition (Gherardi and Sala, 2015;Hofer et al, 2016Hofer et al, , 2017aMackie et al, 2018), or the biodiversity of an ecosystem (Isbell et al, 2015;Kahmen et al, 2005;Wagg et al, 2017). In accordance with work in C4 grasslands, our study shows that the timing of a drought event in the growing season is crucial for the immediate effects of a drought https://doi.org/10.5194/bg-2020-100 Preprint.…”

“…Importantly, however, these studies have also shown that the response of ecosystems to experimental drought can vary quite dramatically (Gherardi and Sala, 2019;Gilgen and Buchmann, 2009;Grant et al, 2014;Hoover et al, 2014;Wilcox et al, 2017). Among others, the drought response of grasslands has been shown to depend on the severity of the experienced drought (Vicca et al, 2012;Wilcox et al, 2017), and important secondary factors such as the type of grassland affected (Byrne et al, 2013;Gherardi and Sala, 2019;Sala et al, 2015;Wilcox et al, 2017), the intensity of land use (Vogel et al, 2012;Walter et al, 2012), the plant functional composition (Gherardi and Sala, 2015;Hofer et al, 2016Hofer et al, , 2017aMackie et al, 2018), or the biodiversity of an ecosystem (Isbell et al, 2015;Kahmen et al, 2005;Wagg et al, 2017). These secondary factors that affect the responses of terrestrial ecosystems to drought are just beginning to be understood (Reichstein et al, 2013;Wu et al, 2011).…”

“…Previously it was believed that the drought history (e.g. previous year annual precipitation deficit) of an ecosystem is crucial for the annual NPP and that the magnitude of the drought history negatively influences current NPP (Mackie et al, 2018;Reichmann et al, 2013;Sala et al, 2012;Yahdjian and Sala, 2006). In contrast, there is now increasing evidence that drought stressed plants or ecosystems can respond to drought release also with an overcompensation of their physiological activity or growth (Griffin-Nolan et al, 2018;Hofer et al, 2017a;Shen et al, 2016).…”