Energy flux and evapotranspiration of two typical plantations in semi-arid area of western Liaoning, China

doi:10.17521/cjpe.2022.0099

Abstract

Abstract:

Aims Under the background of climate warming, the contradiction between forest and water in semi-arid areas is becoming increasingly prominent. Understanding the changes in energy flux and evapotranspiration (ET) of the plantation ecosystems in this area can provide a reference for future selection of afforestation tree species.

Methods In this paper, the water and heat fluxes of Pinus tabuliformis and Pinus sylvestris var. mongolica plantations in semi-arid area of western Liaoning were observed continuously for one year (October 2019 to October 2020) using the eddy covariance method. The length of growing season (April 11 to October 10) was determined using the critical temperature combined with the variation characteristics of normalized differential vegetation index (NDVI). The seasonal dynamics of latent heat flux (LE), sensible heat flux (H), net radiation (R_n), soil heat flux (G) and ET were analyzed. The effects of air temperature (T_a), R_n, vapor pressure deficit (VPD), soil water content (SWC), and NDVI on ET were discussed by applying regression analysis and path analysis.

Important findings The R_n, G and H of P. tabuliformis and P. sylvestrisvar. mongolica plantations showed single-peak seasonal variation trends, and the seasonal dynamics of LE fluctuated more sharply. During the whole year, energy consumption was dominated by H, followed by LE, and G consumed less energy. The average values of Bowen ratio during the growing season were 1.82 and 2.23, respectively, smaller than annual average values (3.43 and 4.44). The ET during the growing season was 302.79 and 247.54 mm, accounting for 82.89% and 84.20% of the annual ET, respectively. The annual ET was 365.29 and 293.99 mm accounting for 87.81% and 72.23% of precipitation in the same period. Priestley-Taylor coefficient (α) and decoupling factor (Ω) were used to analyze the effects of SWC and canopy conductance (g_c) on ET. The annual mean values of α was 0.30 and 0.24, respectively, and the Ω values was 0.12 and 0.07, respectively. During the whole year, SWC was the dominant factor affecting the ET of two plantations, followed by R_n. Under non-water-stressed conditions, R_n had a greater impact on ET.The combined effects of T_a and VPD on ET were small, which were mostly indirect effects. NDVI and g_c were important biological factors affecting the ET of the two plantations, especially during the growing season. This study shows that P. tabuliformis and P. sylvestrisvar. mongolica plantations in the semi-arid area of western Liaoning Province adopt a conservative water consumption strategy to maintain water balance of the ecosystem, and these species are suitable afforestation tree species in this area.

Key words: semi-arid region, plantation, energy flux, evapotranspiration, bioenvironmental factor

WANG Li-Shuang, TONG Xiao-Juan, MENG Ping, ZHANG Jin-Song, LIU Pei-Rong, LI Jun, ZHANG Jing-Ru, ZHOU Yu. Energy flux and evapotranspiration of two typical plantations in semi-arid area of western Liaoning, China[J]. Chin J Plant Ecol, 2022, 46(12): 1508-1522.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0099

https://www.plant-ecology.com/EN/Y2022/V46/I12/1508

Figures/Tables 14

Table 1 Information of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning

树种 Tree species	林龄 Stand age (a)	树高 Tree height (m)	胸径 Diameters at breast height (cm)	林分密度 Stand density (plant·hm^-2)	土壤类型 Soil type
油松 P. tabuliformis	44	8	13.4	1 150	褐土 Brown soil
樟子松 P. sylvestris var. mongolica	36	10	15.9	1?044	褐土 Brown soil

Table 2 Basic information of micrometeorological observation system for Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning

观测要素 Observation element	仪器 Instrument	型号 Product type	生产商 Manufacturer	距地面高度 Height
净辐射 Net radiation	净辐射表 Net radiometer	CNR-1	Kipp & Zonen, Delft, Netherlands	19 m
土壤热通量 Soil heat flux	热通量板 Soil heat flux plate	HFT-3	Campbell Scientific, Logan, USA	-5 cm
空气温湿度 Air temperature and moisture	空气温/湿度传感器 Air temperature/moisture sensor	HMP45C	Vaisala, Helsinki, Finland	19 m
降水量 Precipitation	雨量筒 Rain gauge	TE525MM	Texas Electronics, Dallas, USA	18 m
土壤含水量 Soil moisture content	土壤水分传感器 Soil moisture sensor	CS650	Campbell Scientific, Logan, USA	-10, -20, -30 cm

Fig. 1 Dynamics of environmental and biological factors in Pinus tabuliformis (A-C) and P. sylvestris var. mongolica (D-F) plantations in semi-arid area of western Liaoning. gc, canopy conductance; NDVI, normalized differential vegetation index; P, precipitation; SWC, soil water content; SWC10, SWC20 and SWC30 represent soil water content of 10, 20 and 30 cm, respectively; Ta, air temperature; VPD, vapor pressure deficit. gc, NDVI, SWC, Ta, VPD are daily averages, P is the daily total value. The shaded part is the growing season.

Fig. 2 Energy closure of Pinus tabulaeformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning from October 2019 to October 2020. LE + H, turbulent heat fluxes; Rn - G - S, available energy.

Fig. 3 Seasonal variation of energy fluxes of Pinus tabulaeformis (A-C) and P. sylvestris var. mongolica plantations (D-F) in semi-arid area of western Liaoning. G, soil heat flux; H, sensible heat flux; LE, latent heat flux; Rn, net radiation. The shaded part is the growing season.

Table 3 Monthly mean (April to October), mean value of growing season and annual daily mean of energy partitioning (LE/Rn, H/Rn, G/Rn) and Bowen ratio (β) of Pinus tabulaeformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning

林分 Forest stand	变量 Variable	生长季 Growing season								年平均值 Mean annual value
林分 Forest stand	变量 Variable	4月 April	5月 May	6月 June	7月 July	8月 August	9月 September	10月 October	平均值 Mean value	年平均值 Mean annual value
油松人工林 P. tabuliformis plantation	LE/R_n	0.10	0.18	0.30	0.43	0.47	0.61	0.45	0.37	0.28
	H/R_n	0.57	0.63	0.53	0.45	0.42	0.27	0.47	0.47	0.67
	G/R_n	0.05	0.07	0.06	0.05	0.03	-0.05	-0.03	0.03	-0.05
	β	5.51	3.61	1.77	1.03	0.85	0.44	1.03	1.82	3.43
樟子松人工林 P. sylvestris var. mongolica plantation	LE/R_n	0.18	0.15	0.35	0.20	0.32	0.47	0.49	0.30	0.22
	H/R_n	0.51	0.61	0.47	0.60	0.45	0.35	0.43	0.49	0.57
	G/R_n	0.06	0.09	0.05	0.06	0.03	-0.04	-0.05	0.04	-0.05
	β	2.79	4.43	1.40	3.07	1.60	0.76	0.95	2.23	4.44

Fig. 4 Seasonal variation of evapotranspiration (ET) of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning. The shaded part is the growing season.

Fig. 5 Seasonal patterns of annual cumulative evapotranspiration (ETcum), precipitation (Pcum) and the difference between ETcum and Pcum of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning.

Fig. 6 Relationship between evapotranspiration (ET) and environmental factors of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning (mean ± SD). Rn, net radiation; SWC, soil water content; Ta, air temperature; VPD, vapor pressure deficit.

Fig. 7 Relationship between evapotranspiration (ET) and normalized differential vegetation index (NDVI) of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning (mean ± SD).

Fig. 8 Seasonal variations of the Priestley-Taylor coefficient (α)(A, C) and the decoupling factor (Ω)(B, D) of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning.

Fig. 9 Relationship between the daily average Priestley-Taylor coefficient (α) and canopy conductance (gc) of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning.

Table 4 Path analysis between evapotranspiration and bioenvironmental factors of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning

林分 Stand	时期 Period	因子 Factor	相关系数 Correlation coefficient	直接通径系数 Direct path coefficient	间接通径系数 Indirect path coefficient
林分 Stand	时期 Period	因子 Factor	相关系数 Correlation coefficient	直接通径系数 Direct path coefficient	总和 Total	T_a	R_n	VPD	SWC	NDVI
油松人工林 P. tabuliformis plantation	生长季 Growing season	T_a	0.40^**	-0.04	0.44		0.19	-0.11	0.03	0.33
		R_n	0.25^**	0.41	-0.16	-0.02		-0.12	-0.13	0.11
		VPD	-0.05	-0.19	0.14	-0.02	0.28		-0.16	0.04
		SWC	0.64^**	0.57	0.07	0.00	-0.10	0.06		0.11
		NDVI	0.64^**	0.43	0.21	-0.03	0.11	-0.02	0.15
	非生长季 Non-growing season	T_a	0.71^**	0.15	0.56		0.11	0.04	0.41	0.00
		R_n	0.49^**	0.24	0.25	0.07		0.02	0.16	0.00
		VPD	0.66^**	0.05	0.61	0.13	0.11		0.36	0.00
		SWC	0.75^**	0.52	0.23	0.12	0.07	0.03		0.01
		NDVI	0.55^**	0.01	0.54	0.09	0.03	0.02	0.40
樟子松人工林 P. sylvestris var. mongolica plantation	生长季 Growing season	T_a	0.17^*	-0.08	0.25		0.15	0.03	-0.08	0.15
		R_n	0.18^**	0.34	-0.16	-0.04		0.04	-0.16	0.00
		VPD	0.02	0.05	-0.03	-0.05	0.22		-0.17	-0.03
		SWC	0.52^**	0.50	0.02	0.01	-0.11	-0.02		0.14
		NDVI	0.50^**	0.34	0.16	-0.04	0.00	-0.01	0.21
	非生长季 Non-growing season	T_a	0.65^**	0.28	0.37		0.12	0.05	0.16	0.04
		R_n	0.60^**	0.37	0.23	0.09		0.02	0.10	0.02
		VPD	0.65^**	0.06	0.59	0.23	0.16		0.16	0.04
		SWC	0.68^**	0.22	0.46	0.20	0.16	0.04		0.06
		NDVI	0.47^**	0.09	0.38	0.13	0.07	0.03	0.15

Table 5 Correlation analysis between canopy conductance and environmental factors of Pinus tabuliformis and P. sylvestris var. mongolica plantations in semi-arid area of western Liaoning under different conditions

	油松人工林 P. tabuliformis plantation			樟子松人工林 P. sylvestris var. mongolica plantation
	T_a	VPD	SWC	T_a	VPD	SWC
T_a ≤ 20 ℃	0.49^**	-0.22^**	0.81^**	0.53^**	0.19^**	0.74^**
T_a > 20 ℃	-0.54^**	-0.81^**	0.73^**	-0.57^**	-0.62^**	0.74^**
VPD ≤ 1.8 kPa	0.28^**	-0.14^**	0.62^**	0.45^**	0.11^*	0.74^**
VPD > 1.8 kPa	0.14	-0.17	0.76^**	-0.20	0.06	0.73^**

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