Differences in water use efficiency between dry and rainy seasons and their controlling factors in Eucalyptus plantation in Leizhou Peninsula

doi:10.17521/cjpe.2024.0277

Abstract

Abstract:

Aims Examining how water use efficiency (WUE) in plantations responds to environmental factors is crucial for understanding vegetation’s water strategies and assessing ecosystems’ carbon and water recycling capacity.

Methods In the present study, we leveraged eddy covariance flux data alongside concurrent meteorological data from the Positioning Observation and Research Station of Eucalyptus Plantation Ecosystem, spanning the years 2018 to 2022, to analyze the temporal variations and seasonal differences in WUE within the Eucalyptus plantation ecosystem. The analytical methods employed included stepwise regression analysis, path analysis, and redundancy analysis. We analytically examined the relationship between WUE and various environmental factors, with a particular focus on the distinctions between drought and rainy seasons, as well as the primary factors influencing these variations.

Important findings (1) Throughout the study period, the mean WUE of the Eucalyptus plantation ecosystem was recorded at 3.85 g C·kg^-1H₂O during the dry season (November to April) and 2.61 g C·kg^-1H₂O during the rainy season (May to October). The annual mean WUE was determined to be 3.22 g C·kg^-1H₂O. (2) WUE exhibited distinct diurnal variation patterns, with similar trends observed during both the dry and rainy seasons. A extremely significant negative correlation was identified between diurnal WUE and variables such as vapor pressure deficit (VPD), air temperature (T_air), soil temperature (T_soil), photosynthetically active radiation (PAR), and soil moisture (SM). Furthermore, stepwise regression analysis indicated that VPD serves as the primary environmental factor influencing the diurnal variation of WUE. (3) The temporal variation of daily-scale WUE exhibited an inverse relationship with gross primary productivity (GPP) and evapotranspiration (ET). Path analysis indicated that WUE is predominantly influenced by direct negative impacts from VPD and T_soil, in addition to indirect negative influences from PAR. The responses of WUE to VPD and T_soil demonstrated significant discrepancies between dry and rainy seasons, while the seasonal responses to PAR were found to be consistent. (4) On a monthly basis, WUE was predominantly influenced by temperature and VPD during the dry season, while PAR played a significant role in the rainy season. The variations in WUE across different seasons were primarily influenced by alterations in ET, which were governed by temperature, VPD, and PAR. The WUE of the Eucalyptus plantation ecosystem exhibited marked variations between the drought and rainy seasons, and the diurnal changes were mainly affected by VPD. In addition to being affected by VPD, the daily and monthly changes are also affected by light and temperature.

Key words: Eucalyptus plantation, eddy covariance, water use efficiency, biological environmental factor

ZHU Wan-Kuan, XU Yu-Xing, HUANG Run-Xia, DU A-Peng, WANG Zhi-Chao. Differences in water use efficiency between dry and rainy seasons and their controlling factors in Eucalyptus plantation in Leizhou Peninsula[J]. Chin J Plant Ecol, 2025, 49(12): 2015-2029.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0277

https://www.plant-ecology.com/EN/Y2025/V49/I12/2015

Figures/Tables 13

Fig. 1 Variations in environmental factors during the observation period in the study area in the Eucalyptus plantation of Leizhou Peninsula. Air temperature, soil temperature, vapour pressure deficit, and soil moisture are daily means. Precipitation and photosynthetically active radiation are cumulative values. Normalized difference vegetation index is the monthly maximum. The shade represents the rainy season.

Table 1 Differences of environmental factors between dry and rainy seasons in Eucalyptus plantation in Leizhou Peninsula (mean ± SE)

季节 Season	环境因子 Environmental factor
季节 Season	T_air (°C)	VPD (hPa)	T_soil (°C)	SM (m³·m^-3)	PAR (mol·m^-2·d^-1)	NDVI	P (mm)
旱季 Dry season (2018-2019)	21.20 ± 0.31^c	2.99 ± 0.14^g	21.54 ± 0.18^c	0.16 ± 0.03^e	23.02 ± 0.72^d	0.84 ± 0.01^d	228.95^c
雨季 Rainy season (2019)	27.73 ± 0.16^ab	5.22 ± 0.18^bc	26.76 ± 0.08^a	0.20 ± 0.03^b	34.92 ± 0.91^b	0.88 ± 0.02^ab	1 246.63^a
旱季 Dry season (2019-2020)	20.64 ± 0.22^cd	4.61 ± 0.17^de	20.95 ± 0.12^d	0.14 ± 0.02^g	24.69 ± 0.72^d	0.86 ± 0.01^c	307.34^bc
雨季 Rainy season (2020)	28.25 ± 0.16^a	5.63 ± 0.20^b	26.63 ± 0.11^a	0.19 ± 0.04^c	36.31 ± 0.82^ab	0.89 ± 0.02^a	1 306.32^a
旱季 Dry season (2020-2021)	20.32 ± 0.33^d	3.84 ± 0.16^f	20.38 ± 0.20^e	0.15 ± 0.03^f	27.22 ± 0.75^c	0.87 ± 0.01^bc	232.84^c
雨季 Rainy season (2021)	28.27 ± 0.17^a	4.88 ± 0.16^cd	26.81 ± 0.09^a	0.17 ± 0.04^d	37.49 ± 0.90^a	0.90 ± 0.01^a	988.20^ab
旱季 Dry season (2021-2022)	19.34 ± 0.31^e	4.20 ± 0.19^ef	19.99 ± 0.16^f	0.15 ± 0.03^f	27.35 ± 0.98^c	0.87 ± 0.01^c	364.20^bc
雨季 Rainy season (2022)	27.28 ± 0.19^b	7.41 ± 0.28^a	26.00 ± 0.11^b	0.21 ± 0.03^a	38.48 ± 1.04^a	0.89 ± 0.02^a	1 585.70^a

Fig. 2 Dynamic in water use efficiency (WUE) on a half-hourly basis within the Eucalyptus plantation ecosystem in the Leizhou Peninsula (mean ± SE).

Fig. 3 Temporal dynamics of gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) in Eucalyptus plantation ecosystem. The shade represents the rainy season.

Table 2 Differences of gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) between dry and rainy seasons in Eucalyptus plantation in Leizhou Peninsula (mean ± SE)

季节 Season	GPP (g C·m^-2·d^-1)	ET (mm·d^-1)	WUE (g C·kg^-1 H₂O)
旱季 Dry season (2018-2019)	6.18 ± 0.15^c	2.02 ± 0.08^e	3.66 ± 0.15^b
雨季 Rainy season (2019)	9.29 ± 0.22^a	4.82 ± 0.13^a	2.07 ± 0.06^d
旱季 Dry season (2019-2020)	6.02 ± 0.13^c	2.02 ± 0.07^e	3.66 ± 0.15^b
雨季 Rainy season (2020)	9.16 ± 0.20^a	4.27 ± 0.10^b	2.21 ± 0.04^d
旱季 Dry season (2020-2021)	7.23 ± 0.17^b	2.10 ± 0.06^e	3.82 ± 0.12^b
雨季 Rainy season (2021)	9.42 ± 0.16^a	3.23 ± 0.07^c	3.02 ± 0.05^c
旱季 Dry season (2021-2022)	7.41 ± 0.17^b	1.93 ± 0.06^e	4.28 ± 0.13^a
雨季 Rainy season (2022)	8.90 ± 0.20^a	2.98 ± 0.07^d	3.14 ± 0.08^c

Table 3 Pearson correlation coefficient between water use efficiency (WUE) of Eucalyptus plantation ecosystem and environmental factors

环境因子 Environment factor	WUE
环境因子 Environment factor	日间半小时尺度 Daytime half-hour scale	日尺度 Day scale	月尺度 Month scale
T_air	-0.31^***	-0.40^***	-0.69^***
T_soil	-0.25^***	-0.45^***	-0.73^***
SM	-0.13^***	-0.26^***	-0.40^**
PAR	-0.14^***	-0.39^***	-0.59^***
VPD	-0.28^***	-0.49^***	-0.62^***
NDVI	-	-	-0.41^**
P	-	-	-0.47^***

Table 4 Stepwise regression model parameters of diurnal variation of water use efficiency (WUE) and environmental factors

自变量 Independent variable	旱季 Dry season					雨季 Rainy season
自变量 Independent variable	非标准化系数 Non-standardized coefficient	标准化系数 Standardized coefficient	p	R²	F	非标准化系数 Non-standardized coefficient	标准化系数 Standardized coefficient	p	R²	F
常数 Constant	6.46	-	0.47	0.98	630.54	-4.94	-	<0.001	0.92	197.83
饱和水汽压差 Vapor pressure deficit	-0.32	-0.99	<0.001	0.98	630.54	-0.18	-0.96	<0.001	0.92	197.83

Fig. 4 Regression analysis between water use efficiency (WUE) and vapor pressure deficit (VPD) in Eucalyptus plantation ecosystem.

Fig. 5 Path analysis of water use efficiency (WUE) and environmental factors. PAR, photosynthetically active radiation; SM, soil moisture; Tair, air temperature; Tsoil, soil temperature; VPD, vapor pressure deficit. The arrows in the figure represent positive (solid) and negative (dashed) paths, and the width of the arrows is proportional to the strength of the relationship. All pathways in the figure are statistically significant (p < 0.01). The number in the arrow represents the standardized path coefficient. The total effect of standardization is the sum of direct and indirect effects.

Fig. 6 Relationship between water use efficiency and daily mean value of environmental factors (mean ± SE). PAR, photosynthetically active radiation; Tsoil, soil temperature; VPD, vapor pressure deficit.

Fig. 7 Redundancy analysis between environmental factors and water use efficiency (WUE). ET, evapotranspiration; GPP, gross primary productivity; NDVI, normalized difference vegetation index; P, precipitation; PAR, photosynthetically active radiation; SM, soil moisture; Tair, air temperature; Tsoil, soil temperature; VPD, vapor pressure deficit.

Fig. 8 Correlations between environmental factors and water use efficiency (WUE). ET, evapotranspiration; GPP, gross primary productivity; NDVI, normalized difference vegetation index; P, precipitation; PAR, photosynthetically active radiation; SM, soil moisture; Tair, air temperature; Tsoil, soil temperature; VPD, vapor pressure deficit. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Table 5 Comparison of water use efficiency (WUE) of different types of forest ecosystems

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