Drought intensity alters productivity, carbon allocation and plant nitrogen uptake in fast versus slow grassland communities

Abstract

Grasslands face more frequent and extreme droughts; yet, their responses to increasing drought intensity are poorly understood. Increasing drought intensity likely triggers abrupt shifts (thresholds) in grassland ecosystem functioning which can implicate recovery trajectories. Here, we determined how drought intensity affects plant productivity, and plant–soil carbon (C) and nitrogen (N) cycling. We exposed model grassland plant communities with contrasting resource acquisition strategies (a fast‐ vs a slow‐strategy plant community), to a gradient of drought intensity. The drought gradient ranged from well‐watered to severely water‐limited conditions. We identified thresholds of plant community productivity (above‐ground biomass) at peak drought and 2 months after re‐wetting, and measured net ecosystem exchange and ecosystem respiration of C throughout the drought and recovery phases. At peak drought and 1 week after re‐wetting, we traced recently acquired C from plants to the soil and into microbial biomass and fatty acids using 13C pulse labelling, and measured plant and soil N. At peak drought, slow‐strategy plant communities were more drought resistant than fast‐strategy communities, as the threshold in plant productivity occurred at a higher drought intensity for the slow‐ than the fast‐strategy community. Shortly after re‐wetting, microbial uptake of recent plant‐assimilated C increased with increasing past drought intensity, coinciding with an increase in soil N availability and leaf N. Threshold responses to drought intensity at peak drought translated into non‐linear recovery responses, with greater compensatory growth in the fast‐strategy community. At peak drought, increasing drought intensity reduced C uptake and increased relative C partitioning to leaves and microbial biomass. Upon re‐wetting, plant community strategy mediated drought intensity effects on plant and soil C and N dynamics and plant recovery trajectories. The fast‐strategy community recovered quickly, with higher leaf N than the slow community, while the slow community increased C allocation to microbial biomass. Synthesis. Our findings highlight that C and N dynamics in the plant–soil system display non‐linear responses to increasing drought intensity both during and after drought, which has implications for plant community recovery trajectories.

Responses of non‐native and native plant species to fluctuations of water availability in a greenhouse experiment

“…These different responses of non‐native and native plants may be attributed to their different drought tolerance as well as their ability to recover following rewetting events. Previous studies have shown that non‐native plants are less tolerant to drought than native plants (Liu et al., 2017; Oram et al., 2023; Valliere et al., 2019). In contrast, non‐native plants can take more advantages of rewetting events to recover than native plants (Zhang et al., 2022), whereas some native plants cannot recover or even experience waterlogging stress caused by rewetting events (Blom & Voesenek, 1996; Reyer et al., 2013).…”

Field experiments have enhanced our understanding of drought impacts on terrestrial ecosystems—But where do we go from here?

“…Schweiger et al., 2023), designed to explicitly test mechanisms often only inferred from past drought studies (e.g. Oram et al., 2023, see Gilbert & Medina, 2016 for a similar call for crop species). For example, soil fertility and nitrogen availability have been identified as potential mediators of ecosystem sensitivity to drought (Bharath et al., 2020; Cusack et al., 2023; Luo et al., 2021; Ma et al., 2023).…”

Recurrent drought increases grassland community seasonal synchrony

“…Drought events alter grassland nutrient cycling, disrupt interactions between species, result in species extinction, and therewith cause severe disruptions in ecosystem structure and function (Smith et al . 2024; Oram et al . 2023; Bardgett & Caruso 2020; Ingrisch et al .…”