Increased interannual precipitation variability enhances the carbon sink in a semiarid grassland

1. The amplifying interannual precipitation variability has been observed
globally and is projected to intensify under climate change scenarios.
However, its impacts on terrestrial vegetation and carbon (C) sink have
not been well investigated. 2. As part of a field manipulative experiment
with three precipitation variabilities (20%, 40%, and 60%) in a semiarid
grassland, this study was conducted to examine the responses of ecosystem
C cycling to increased precipitation variability. 3. Across the 3
experimental years from 2010 to 2012, amplified precipitation variability
enhances gross primary productivity (GPP) and ecosystem respiration (ER)
as both GPP and ER were more sensitive to above- than below-average
precipitation. In addition, the larger responses of GPP than ER to
precipitation variability resulted in an enhancement of net ecosystem
productivity (NEP), and the magnitudes of NEP increased with the
increasing precipitation variability. More species with higher sensitivity
to increased precipitation under wet condition and the insensitive
response of root growth to decreased precipitation could largely be
responsible for the above observations, which suggest that the semiarid
grassland was more sensitive to wet treatment yet strongly resistant to
drought. 4. Our results provide empirical evidence that intensified
precipitation variability could stimulate grassland C sink. The findings
revealed in this study could facilitate the mechanistic understanding and
imply the potential positive feedback of climate variability-terrestrial C
sink.