Abstract
In recent years, the increased intensity and duration of droughts have dramatically altered the structure and function of grassland ecosystems, which have been forced to adapt to this change in climate. Combinations of global change drivers such as elevated atmospheric CO2 concentration, warming, nitrogen (N) deposition, grazing, and land-use change have influenced the impact that droughts have on grassland C cycling. This influence, to some extent, can modify the relationship between droughts and grassland carbon (C) cycling in the multi-factor world. Unfortunately, prior reviews have been primarily anecdotal from the 1930s to the 2010s. We investigated the current state of the study on the interactive impacts of multiple factors under drought scenarios in grassland C cycling and provided scientific advice for dealing with droughts and managing grassland C cycling in a multi-factor world. Currently, adequate information is not available on the interaction between droughts and global change drivers, which would advance our understanding of grassland C cycling responses. It was determined that future experiments and models should specifically test how droughts regulate grassland C cycling under global changes. Previous multi-factor experiments of current and future global change conditions have studied various drought scenarios poorly, including changes in precipitation frequency and amplitude, timing, and interactions with other global change drivers. Multi-factor experiments have contributed to quantifying these potential changes and have provided important information on how water affects ecosystem processes under global change. There is an urgent need to establish a systematic framework that can assess ecosystem dynamic responses to droughts under current and future global change and human activity, with a focus on the combined effects of droughts, global change drivers, and the corresponding hierarchical responses of an ecosystem.
Highlights
Grasslands cover around 40% of the global land surface and a large fraction of their biomass is below ground [1]
Long-term declines in grassland productivity had been driven by increased dryness over four decades; to some extent, the water use efficiency that increased through CO2 enrichment in grasslands may have slightly moderated the decline in production of native C3 grasslands, while variations in N had no effects [13]
We found that the relation between drought-derived water stresses imposed on grassland plants is affected by multiple factors and, changes grassland C cycling [17,18]
Summary
Grasslands cover around 40% of the global land surface and a large fraction of their biomass is below ground [1]. While global change drivers such as elevated atmospheric CO2 concentration, warming, N deposition, grazing, and other land-use changes are outside of the grassland ecosystems, they impose chronic, cumulative, and moderate stresses Extreme events such as droughts, often lead to periodic, pulsing, and severe alterations [12]. Long-term declines in grassland productivity had been driven by increased dryness over four decades; to some extent, the water use efficiency that increased through CO2 enrichment in grasslands may have slightly moderated the decline in production of native C3 grasslands, while variations in N had no effects [13] It seems that extreme droughts may change the structure, composition, and functionality of terrestrial ecosystems, thereby influencing C cycling and its feedback to the climate system [14,15,16]. We found that the relation between drought-derived water stresses imposed on grassland plants is affected by multiple factors and, changes grassland C cycling [17,18]
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