DOI: 10.5061/dryad.5hqbzkh4z
title: Asymmetric responses of resource use efficiency to previous-year precipitation in a semi-arid grassland

description: 1. Intensified inter-annual fluctuations in precipitation could profoundly
 impact terrestrial ecosystems. However, how changes previous-year
 precipitation influence current ecosystem functioning (e.g., resource use
 efficiency) in semi-arid regions remains unclear. 2. In this study, water
 use efficiency (WUE) and light use efficiency (LUE) were investigated in a
 multi-year precipitation gradient experiment with seven treatment levels:
 20%, 40% and 60% decreases and 20%, 40% and 60% increases in the amount of
 natural rainfall plus ambient precipitation. Plots receiving 60% less
 precipitation were representative of extreme dry years whereas the other
 treatment levels fell within the normal year-to-year range in
 precipitation change. Measurements made in both the post-treatment period
 (2013-2015) and the treatment period (2010-2012) provided an opportunity
 to quantify the legacy effects of precipitation on resource use efficiency
 (RUE). 3. Sensitivities of LUE to previous-year precipitation were not
 changed among treatments in 2013. However, asymmetric responses of RUEs
 (i.e., WUE and LUE) to previous-year precipitation were found in
 2014-2015. WUE2014, WUE2015, LUE2014, and LUE2015 responded more strongly
 to previous normal decreased than increased precipitation. Importantly,
 they were more sensitive to previous extreme dry year (represented by 60%
 precipitation reduction) than normal wet year (represented by 60%
 precipitation increment). Aboveground net primary productivity (ANPP)
 rather than resource absorption (Ruptake) drove these asymmetric responses
 of RUE, and biomass of grasses further explained the asymmetric responses
 of ANPP. 4. This study reveals the non-linear responses of RUE to
 previous-year precipitation and highlighted that the legacy effects of
 precipitation on RUE can be ascribed to the changes in vegetation
 composition. Our findings can facilitate the prediction of the legacy
 effects of precipitation variation on grassland ecosystem functions in the
 future.
description: We
 harvested the aboveground biomass by species in August from 2013-2015 by
 two 0.15 m<sup>2</sup> quadrats per plot. This total
 aboveground biomass was then categorized into two functional groups:
 grasses and forbs. ANPP was taken as the total aboveground biomass in
 August. Community cover was measured in August concurrent with biomass
 sampling. We calculated the community
 transpiration using the difference between community evapotranspiration
 and evaporation. Community evapotranspiration was measured using a
 Li-6400XT Portable Photosynthesis System (Li-Cor Inc., Lincoln, NE, USA)
 attached to a static transparent chamber (0.5×0.5×0.5
 m<sup>3</sup>) three times a month. Ecosystem evaporation was
 measured using a Li-8100 Portable Photosynthesis System (Li-Cor Inc.,
 Lincoln, NE, USA). Three months before the measurements, we cleared up the
 aboveground biomass and inserted a PVC circle (50 cm in depths) to cut off
 the ambient roots into the circle , in order to get undamaged soil
 environment without vegetation in PVC circles. We also measured the
 volumetric soil moisture content (VWC, 0–50 cm) using a portable SWC
 device (Diviner 2000, Sentek Pty Ltd, Balmain, Australia) six to ten times
 a month from 2013–2015. In resource use efficiency (RUE)
 models, absorbed resources (R<sub>uptake</sub>) are those
 water and light resources consumed during the growing season. The
 accumulated vegetation transpiration (Tr) refers to the community-level
 water consumption. Tr was calculated as the product of observed community
 transpiration and the time between two sampling dates during the growing
 season. The accumulated absorbed photosynthetically active radiation
 (aPAR) refers to the community-level light absorption. Here, the
 photosynthetically active radiation (PAR) was recorded in real-time by an
 Li-190SB quantum sensor (LI-Cor Inc., Lincoln, NE, USA) in an eddy
 covariance system located near the precipitation experiment. We calculated
 the aPAR by the product of community cover and the remainders of one minus
 reflectance and transmittance (Han et al. 2016). WUE and LUE
 were calculated as the ratios of ecosystem production to
 R<sub>uptake</sub> (Binkley et al., 2004). Here, ANPP was used
 for ecosystem production, and the specific equations for WUE and LUE
 calculations were as following: WUE =
 <i>ANPP</i><i>Tr</i>  (1)     LUE = <i>ANPP</i><i>aPAR</i>  (2)    where Tr and aPAR were the absorbed resources in the WUE and LUE models, respectively. To obtain unit-less versions of WUE and LUE, all measurements were converted into the same unit (g m<sup>-2</sup> year<sup>-1</sup>). The sensitivity of variables (Y) to previous-year precipitation (P-PPT) was calculated as the derivative of response function as follows: Y = a×(P-PPT)<sup>b</sup>  (3) Sensitivity of Y to P-PPT = a×b×(P-PPT)<sup>(b-1)</sup>  (4) where the sensitivity of Y to P-PPT are the derivative of response function in equation (3). “a” and “b” are constant in equation (3). These sensitivities range from -1 to +1, their magnitudes represent the strength of sensitivity of Y to P-PPT. Their directions (positive/negative) represent the changes in Y are identical/opposite to the changes in previous-year precipitation amount. Legacy effect on RUE was calculated as the differences between the observed RUE and the expected RUE (Reichmann, Sala & Peters 2013), the equations were as following: Legacy<sub>RUE</sub> = RUE<sub>observed</sub> - RUE<sub>expected </sub>  (5) Where RUE<sub>observed</sub> refers to RUE values in each plots of altered precipitation in 2013-2015, RUE<sub>expected</sub> refers to the averaged RUE values in control plots in 2013-2015. Legacy<sub>RUE</sub> refers to the values of legacy effects on RUE.