Impacts of droughts and extreme-temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones

Abstract

Abstract. Extreme climatic events, such as droughts and heat stress, induce anomalies in ecosystem–atmosphere CO2 fluxes, such as gross primary production (GPP) and ecosystem respiration (Reco), and, hence, can change the net ecosystem carbon balance. However, despite our increasing understanding of the underlying mechanisms, the magnitudes of the impacts of different types of extremes on GPP and Reco within and between ecosystems remain poorly predicted. Here we aim to identify the major factors controlling the amplitude of extreme-event impacts on GPP, Reco, and the resulting net ecosystem production (NEP). We focus on the impacts of heat and drought and their combination. We identified hydrometeorological extreme events in consistently downscaled water availability and temperature measurements over a 30-year time period. We then used FLUXNET eddy covariance flux measurements to estimate the CO2 flux anomalies during these extreme events across dominant vegetation types and climate zones. Overall, our results indicate that short-term heat extremes increased respiration more strongly than they downregulated GPP, resulting in a moderate reduction in the ecosystem's carbon sink potential. In the absence of heat stress, droughts tended to have smaller and similarly dampening effects on both GPP and Reco and, hence, often resulted in neutral NEP responses. The combination of drought and heat typically led to a strong decrease in GPP, whereas heat and drought impacts on respiration partially offset each other. Taken together, compound heat and drought events led to the strongest C sink reduction compared to any single-factor extreme. A key insight of this paper, however, is that duration matters most: for heat stress during droughts, the magnitude of impacts systematically increased with duration, whereas under heat stress without drought, the response of Reco over time turned from an initial increase to a downregulation after about 2 weeks. This confirms earlier theories that not only the magnitude but also the duration of an extreme event determines its impact. Our study corroborates the results of several local site-level case studies but as a novelty generalizes these findings on the global scale. Specifically, we find that the different response functions of the two antipodal land–atmosphere fluxes GPP and Reco can also result in increasing NEP during certain extreme conditions. Apparently counterintuitive findings of this kind bear great potential for scrutinizing the mechanisms implemented in state-of-the-art terrestrial biosphere models and provide a benchmark for future model development and testing.

Seasonal variability of forest sensitivity to heat and drought stresses: A synthesis based on carbon fluxes from North American forest ecosystems

“…In our study, 14 (out of 21) ENF sites experienced significant GEP decline with increasing temperature for more than 10 days during summer. Since the study conducted by von Buttlar et al () did not consider the timing of the heat waves, it is very likely that the negative heat impact in summer was offset by the positive impact in spring, resulting in a neutral response of GEP to heat stress in ENF over the yearly basis.…”

Seasonal differences in relationships between changes in spring phenology and dynamics of carbon cycle in grasslands

“…, Buttlar et al. ). Since GEP exhibited weaker correlations with the changes of environmental variables compared with ER (Magnus et al.…”

“…Richardson et al (2009) reported that there was no significant relationship between the changes of S/S (date of ecosystem transition from CO 2 source to sink) and the dynamics of spring or annual ER in forests. At the ecosystem level, although GEP has been shown to be positively correlated with ER (Ma et al 2016), GEP and ER responded differently to the changes of temperature and soil moisture (Anderson-Teixeira et al 2015, Buttlar et al 2018. Since GEP exhibited weaker correlations with the changes of environmental variables compared with ER (Magnus et al 2010), the dynamics of ER may be mainly influenced by the environmental variables, and hence, the influences of the changes in spring phenology on ER may be concealed.…”

Drought Occurring With Hot Extremes: Changes Under Future Climate Change on Loess Plateau, China

“…Extreme climate events, such as drought and hot extremes, have been occurring on a wide range of time scales and in many parts of the world in relation to climate change (Bates et al, ; Mishra & Singh, ; von Buttlar et al, ). Heat waves cause water loss, lower the yield of agricultural products, increase energy consumption, and adversely affect human health in a variety of direct, indirect, immediate, and delayed ways (Mazdiyasni & Aghakouchak, ; U.S. Department of Energy, ; Zaitchik et al, ).…”

“…Heat waves cause water loss, lower the yield of agricultural products, increase energy consumption, and adversely affect human health in a variety of direct, indirect, immediate, and delayed ways (Mazdiyasni & Aghakouchak, ; U.S. Department of Energy, ; Zaitchik et al, ). Drought, characterized by less than normal precipitation over a period of months to years (Zhang & Zhou, ), has devastating impacts on the ecological environment and social‐economic sectors, including the urban water supply, modern industries, and also the agricultural production (Food and Agricultural Organisation of United nations (FAO), ; Heim, ; von Buttlar et al, ; World Bank, ). Drought is one of the most expensive natural disasters and causes annual losses estimated at $6–8 billion in the United States (Keyantash & Dracup, ).…”