Impact of drought on carbon and water fluxes and their coupling in a Quercus variabilis plantation

doi:10.17521/cjpe.2023.0354

Abstract

Abstract:

Aims Water use efficiency (WUE) is an important indicator for understanding the carbon and water cycles and coupling mechanisms in terrestrial ecosystems. Inherent water use efficiency (IWUE) is a more suitable indicator than WUE for analyzing the carbon-water coupling mechanism of ecosystems on a daily scale. Here, we aimed to investigate the mechanism of water and carbon fluxes and their responses to drought in a planted forest ecosystem.

Methods We carried out an in-situobservation on the water and carbon fluxes and environmental factors in a Quercus variabilisplantation using eddy covariance techniques and the micrometeorological observation system. The effects of biophysical factors on the gross primary productivity (GPP), evapotranspiration (ET), and IWUE during 2021-2022 were analyzed.

Important findings GPP, ET, and IWUE showed obvious seasonal variations. GPP and ET in the wet year were 7.9% and 21.0% higher than those in the normal year, respectively, whereas IWUE in the wet year was 21.4% lower than that in the normal year. Vapor pressure deficit (VPD) was the main factor affecting GPP in the normal year, and net radiation (R_n) was the primarily factor limiting GPP in the wet year. ET was mainly determined by R_n in both normal and wet years. Relative extractable soil water (REW) was the main factor regulating IWUE in the normal year, whereas leaf area index (LAI) was the main factor controlling IWUE in the wet year. Environmental factors regulated carbon and water fluxes by affecting canopy conductance, and consequently impacting IWUE. The occurrence of soil drought significantly increased IWUE. The response of GPP and ET to REW showed a time lag of 1 month, while the response of IWUE to REW had no lag.

Key words: water use efficiency, drought, carbon-water coupling, gross primary production, evapotranspiration

WANG Yin, TONG Xiao-Juan, ZHANG Jin-Song, LI Jun, MENG Ping, LIU Pei-Rong, ZHANG Jing-Ru. Impact of drought on carbon and water fluxes and their coupling in a Quercus variabilis plantation[J]. Chin J Plant Ecol, 2024, 48(9): 1157-1171.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2023.0354

https://www.plant-ecology.com/EN/Y2024/V48/I9/1157

Figures/Tables 8

Fig. 1 Seasonal dynamics of biophysical factors in the Quercus variabilis plantation. ET0, potential evapotranspiration; gc, canopy conductance; LAI, leaf area index; P, precipitation; REW, relative extractable soil water; Rn, net radiation; Ta, air temperature; VPD, vapor pressure deficit. ET0, gc, LAI, REW, Rn, Ta and VPD are daily averages. P is the daily sum, and Pcum is the cumulative amount. The shaded area indicates the growing season. The subgraph on the upper left corner of F (precipitation) is the normalized value of precipitation from 2006 to 2022, and the red line represents one standard deviation.

Fig. 2 Seasonal dynamics of gross primary production (GPP), evapotranspiration (ET), and inherent water use efficiency (IWUE) in the Quercus variabilis plantation. The shaded area represents the growing season.

Fig. 3 Relationships between gross primary production (GPP) and biophysical factors under different relative extractable soil water (REW) in the growing season of Quercus variabilis plantation. gc, canopy conductance; LAI, leaf area index; REW, relative extractable soil water; Rn, net radiation; Ta, air temperature; VPD, vapor pressure deficit.

Fig. 4 Relationships between evapotranspiration (ET) and biophysical factors under different relative extractable soil water (REW) in the growing season of Quercus variabilis plantation. LAI, leaf area index; REW, relative extractable soil water; Rn, net radiation; VPD, vapor pressure deficit.

Fig. 5 Relationships between inherent water use efficiency (IWUE) and biophysical factors under different relative extractable soil water (REW) in the growing season of Quercus variabilis plantation. gc, canopy conductance; LAI, leaf area index; REW, relative extractable soil water; Rn, net radiation; Ta, air temperature.

Fig. 6 Pathways of the effects of biophysical factors on gross primary production (GPP), evapotranspiration (ET), and inherent water use efficiency (IWUE) in the growing season of Quercus variabilis plantation in the wet year (2021) and the normal year (2022). Green and red colors denote positive and negative correlations, respectively, with numbers along the pathways representing standardized path coefficients (-1 ≤ ρ ≤ 1). Arrows indicate the direction of causality, and their thicknesses are proportionate to the path coefficients. gc, canopy conductance; LAI, leaf area index; REW, relative extractable soil water; Rn, net radiation; Ta, air temperature; VPD, vapor pressure deficit. CFI, comparative fit index; RMSEA, standardized rooted mean square error of approximation.

Fig. 7 Correlation coefficients of gross primary production (GPP), evapotranspiration (ET) and inherent water use efficiency (IWUE) with air temperature (Ta), precipitation (P) and relative extractable soil water (REW) under different time lags in the Quercus variabilis plantation.

Fig. 8 Differences in gross primary production (GPP), evapotranspiration (ET), potential evapotranspiration (ET0) and inherent water use efficiency (IWUE) between different relative extractable soil water (REW) during the growing season of Quercus variabilis plantation. Error bars represent standard deviation. Percentages and asterisks (*) above or below bars represent mathematical and statistical differences (*, ** and *** represent p < 0.05, p < 0.01 and p < 0.001). Percentages within bars represent coefficients of variation.

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