A synthesis of ecosystem aboveground productivity and its process variables under simulated drought stress

Abstract

1. Projected increases in drought duration and intensity under climate change considerably affect aboveground productivity (ANPP) and associated process variables (photosynthesis rates (P n ), stomatal conductance (g s ), soil respiration (Rs) and soil water content (SWC)).2. Although ANPP has been extensively studied across the ecosystems, there is a little consensus on how the spatiotemporal patterns of ANPP will be altered with increasing drought stress. Here, we present a global meta-analysis of ANPP and the four variables (610 observations from 78 studies) for drought duration, intensity and their combination.3. Forest-ANPP had stronger negative responses to long-term drought (34.44%; ≥4 years) than short-term drought (10.78%; ≤1 year) and decreased more in Mediterranean forests than in tropical forests. Decreases in P n and g s were strongest under long-term moderate drought. In the short term, Rs increased by 5.66% under light drought, but decreased by 14.12% and 28.43% under moderate and severe droughts. Grass-ANPP showed a nonlinear decrease with extended duration and the rate slowed. Within light to severe intensities, ANPP decreased linearly, but became stable under extreme condition. In the short term, ANPP reduced more seriously with increasing drought intensity (12.01%-30.34%). With aggravation of drought stress, the reductions in Rs and SWC increased. There was significant heterogeneity in grassland responses to drought stress. The greatest decreases in ANPP, P n and g s were observed in North America, and the reductions in Rs and SWC were greater in Western Europe. Shrub-ANPP showed stronger negative responses to long-term moderate drought (12.59%). P n and g s declined significantly with increasing drought intensity. Variations in Rs to drought duration, intensity and their combination were more complex, either showing positive or negative responses (dominated). 4.Synthesis. Forest-ANPP shows high sensitivity to long-term moderate drought, whereas grass-ANPP is more responsive to short-term drought. Compared to forests and grasslands, shrub-ANPP exhibits less sensitivity to droughts. Different responses of ecosystems were predominantly driven by physiological mechanisms or species differences in turnover time, community architecture and drought K E Y W O R D Saboveground net primary productivity, drought stress, meta-analysis, photosynthesis rates, soil respiration, soil water content, stomatal conductance | 2521Journal of Ecology GAO et Al.

Contrasting drought impacts on the start of phenological growing season in Northern China during 1982–2015

“…Thus, the drought definition is different from region to region. This drought definition could reflect the fact that the water‐deficit stress tolerance of ecosystem has spatial differentiations (Wu et al ., ; Craine et al ., ; Gao et al ., ). Results shown that the spatial distribution of the drought frequency (Figure ) was similar to that of SPEI‐1 drought frequency (Figure ), and has also reflected those detected by the SPEI in other studies (Xu et al ., ; Zhang et al ., ; Um et al ., ).…”

Deciphering the stability of grassland productivity in response to rainfall manipulation experiments

“…Contrasting results have also been reported for the effect of drought characteristics. When drought intensity was measured as %PPT, a significant and negative relationship was found, with grassland resistance decreasing as drought intensity increased ( n = 65; Gao, Zhang, Tang, & Wu, ). However, no effect was observed when drought intensity was measured as SPEI ( n = 43; Stuart‐Haëntjens et al, ).…”

Critical transitions in rainfall manipulation experiments on grasslands

“…Those linear and nonlinear models of ANPP versus MAP have been useful to predict and optimize biomass production over short periods and under near‐normal conditions (Knapp et al, ). However, they may not capture grassland responses to extreme drier conditions (Gao, Zhang, Tang, & Wu, ). Extreme droughts (see Glossary in Table ) may push the system across critical thresholds of productivity (ANPP crit1 ), triggering discontinuous transition from a high‐productivity state to an alternative low‐productivity state (Figure e).…”

“…However, they may not capture grassland responses to extreme drier conditions (Gao, Zhang, Tang, & Wu, 2019). Extreme droughts (see Glossary in Table 1) may push the system across critical thresholds of productivity (ANPP crit1 ), triggering discontinuous transition from a high-productivity state to an alternative low-productivity state (Figure 1e).…”

“…Actually, most of them have failed to subject grasslands to extreme drought treatments and to monitor biomass production after drought cessation (Estiarte et al, 2016;Gao et al, 2019;Matos et al, 2019). Additionally, most studies have assessed resilience using metrics (Ingrisch & Bahn, 2018) that disregard the possibility that alternative stable states may exist in the system (Kéfi et al, 2019;van Nes et al, 2016).…”