Warming and elevated CO₂ intensify drought and recovery responses of grassland carbon allocation to soil respiration

Abstract

Photosynthesis and soil respiration represent the two largest fluxes of CO2 in terrestrial ecosystems and are tightly linked through belowground carbon (C) allocation. Drought has been suggested to impact the allocation of recently assimilated C to soil respiration; however, it is largely unknown how drought effects are altered by a future warmer climate under elevated atmospheric CO2 (eT_eCO2). In a multifactor experiment on managed C3 grassland, we studied the individual and interactive effects of drought and eT_eCO2 (drought, eT_eCO2, drought × eT_eCO2) on ecosystem C dynamics. We performed two in situ 13CO2 pulse‐labeling campaigns to trace the fate of recent C during peak drought and recovery. eT_eCO2 increased soil respiration and the fraction of recently assimilated C in soil respiration. During drought, plant C uptake was reduced by c. 50% in both ambient and eT_eCO2 conditions. Soil respiration and the amount and proportion of 13C respired from soil were reduced (by 32%, 70% and 30%, respectively), the effect being more pronounced under eT_eCO2 (50%, 84%, 70%). Under drought, the diel coupling of photosynthesis and SR persisted only in the eT_eCO2 scenario, likely caused by dynamic shifts in the use of freshly assimilated C between storage and respiration. Drought did not affect the fraction of recent C remaining in plant biomass under ambient and eT_eCO2, but reduced the small fraction remaining in soil under eT_eCO2. After rewetting, C uptake and the proportion of recent C in soil respiration recovered more rapidly under eT_eCO2 compared to ambient conditions. Overall, our findings suggest that in a warmer climate under elevated CO2 drought effects on the fate of recent C will be amplified and the coupling of photosynthesis and soil respiration will be sustained. To predict the future dynamics of terrestrial C cycling, such interactive effects of multiple global change factors should be considered.

The effect of increased temperature and CO2 air enrichment on the nutritive value of orchard grass (Dactylis glomerata) in permanent grassland

“…There were no alterations of precipitation considered in this study, and all plots were exposed equally to the naturally occurring precipitation. However, further studies in the ClimGrass-project also dealt with the effects of simulated drought on growth (Küsters et al ., 2021), as well as on soil chemical and soil ecological processes (Seneca et al ., 2020; Meeran et al ., 2021).…”

Contrasting drivers of belowground nitrogen cycling in a montane grassland exposed to a multifactorial global change experiment with elevated CO2, warming, and drought

“…The positive correlation between protein depolymerization and ANPP from the “eT eCO 2 ” dataset was lost and the positive relationship with belowground biomass and root turnover time became markedly weaker (Figure 4 ). During drought conditions, gross primary production and plant biomass is reduced along with C input to soil (Meeran et al, 2021 ). Instead, many relationships with microbial‐related parameters became more significant.…”

Low precipitation due to climate change consistently reduces multifunctionality of urban grasslands in mesocosms

“…Moreover, we considered cover and height as structural components of vegetation that, besides productivity [41], relate to above-ground space filling, habitat offer, and soil protection [26,41]. We also measured soil respiration as it correlates to C exchange and represents the largest component of ecosystem respiration [42]. Finally, water retention and water loss through evapotranspiration (ET) were measured using a watering and weighing protocol adopted from studies on green roofs [43,44], and used as a proxy for rainwater regulation functions of urban grasslands in shallow road verges.…”

“…indicates an increased metabolism in the soil accelerating C turnover driven by increased plant photosynthesis, and a higher release of recently allocated C via respiration [42,55], especially under non-water limiting conditions.…”