Greening of the earth does not compensate for rising soil heterotrophic respiration under climate change

• Published in: Global change biology Vol. 27; no. 10; pp. 2029 - 2038
• Main Authors: Naidu, Dilip G. T., Bagchi, Sumanta
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2021
• Subjects: Atmospheric models; Carbon; Carbon Cycle; carbon sequestration; Climate Change; Ecosystem; Efflux; Environmental impact; Field tests; Fluxes; Greening; Hydrologic data; Learning algorithms; Long-term changes; Machine learning; microbial decomposition; Net Primary Productivity; Precipitation; Primary production; Respiration; Soil; Soil conditions; soil organic matter; Soil stability; Soil temperature; Soils; Stewardship; Temperature; Tropical environments; Vulnerability; machine-learning; primary production; soil organic matter; carbon sequestration; microbial decomposition
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15531

Stability of the soil carbon (C) pool under decadal scale variability in temperature and precipitation is an important source of uncertainty in our understanding of land–atmosphere climate feedbacks. This depends on how two opposing C‐fluxes—influx from net primary production (NPP) and efflux from heterotrophic soil respiration (Rh)—respond to covariation in temperature and precipitation. There is scant evidence to judge whether field experiments which manipulate both temperature and precipitation align with Earth System Models, or not. As a result, even though the world is generally greening, whether the resultant gains in NPP can offset climate change impacts on Rh, where, and by how much, remains uncertain. Here, we use decadal‐scale global time‐series datasets on NPP, Rh, temperature, and precipitation to estimate the two opposing C‐fluxes and address whether one can outpace the other. We implement machine‐learning tools on recent (2001–2019) and near‐future climate scenarios (2020–2040) to assess the response of both C‐fluxes to temperature and precipitation variation. We find that changes in C‐influx may not compensate for C‐efflux, particularly in wetter and warmer conditions. Soil‐C loss can occur in both tropics and at high latitudes since C‐influx from NPP can fall behind C‐efflux from Rh. Precipitation emerges as the key determinant of soil‐C vulnerability in a warmer world, implying that hotspots for soil‐C loss/gain can shift rapidly and highlighting that soil‐C is vulnerable to climate change despite widespread greening of the world. The direction of covariation between change in temperature and precipitation, rather than their magnitude, can help conceptualize highly variable patterns in C‐fluxes to guide soil‐C stewardship. We investigate how decadal trends in temperature and precipitation translate into responses in two opposing C‐fluxes: primary production and heterotrophic soil respiration. And, how any imbalance between these fluxes can lead to soil‐C vulnerability across the globe. We find evidence for soil‐C loss across both tropics and high latitudes over the past two decades, with precipitation playing a key role under warmer conditions. Near‐future scenarios suggest shifts in hotspots of gain/loss in soil‐C, highlighting that soil‐C is vulnerable to climate change despite widespread greening of the world.