中国北方干旱半干旱区草原生态系统能量平衡闭合的季节和年际变异

doi:10.17521/cjpe.2021.0428

摘要/Abstract

摘要：

能量平衡闭合状况是评估通量观测数据质量的重要参考指标, 为客观评价中国北方干旱半干旱涡度观测数据的质量, 确定数据分析方法和改进策略, 加深对能量闭合度与环境因子之间关系的理解, 该研究基于内蒙古3种不同草原类型(荒漠草原、典型草原和草甸草原) 6个涡度相关通量观测站点(四子王旗站、锡林浩特割草站、锡林浩特围封站、西乌珠穆沁旗站、多伦站和额尔古纳站)的56个站年的能量通量和气象因子测定数据集, 利用能量平衡比率(EBR)和最小二乘法线性回归(OLS)这两种常用的方法, 分析了北方干旱半干旱区不同站点和草原类型能量闭合的状况、季节和年际变异及主要影响因素。主要结果表明: 1) 6个站点多年EBR均值为0.89 ± 0.11, OLS斜率均值为0.96 ± 0.04, 能量闭合程度明显高于国际通量网和中国通量网站点的能量闭合状况。2)不同站点和草原类型间EBR存在明显差异, 表现为荒漠草原(1.01 ± 0.09)和典型草原(0.90 ± 0.11)都高于草甸草原(0.83 ± 0.05), 各站点EBR均存在明显的季节变异, 生长季基本都在1附近并且相对稳定, 非生长季低于1并且变化较大, 主要受气温(T_a)、饱和水汽压差(VPD)、土壤含水量(SWC)和反照率(Albedo)的影响, 其中较低的T_a和较高的Albedo是导致非生长季EBR较低的主要原因。3)不同站点和草原类型EBR存在显著年际变异, 主要受潜热分配(潜热通量/净辐射比值, LE/R_n)、年平均气温(MAT)和生长季Albedo显著影响, 其中LE/R_n的年际波动对EBR年际变异起主要的调控作用, 可解释EBR年际变异的44%。此外, 各站点EBR均表现出随年份逐渐降低的趋势, 植被盖度显著增大后引起Albedo降低可能是造成EBR下降的主要原因。综上所述, 为更加全面地评估能量闭合状况, EBR和OLS斜率两种方法建议结合起来使用。

关键词: 能量平衡闭合, 涡度相关, 季节变异, 年际变异, 草原

Abstract:

Aims Eddy covariance (EC) systems are widely used for measuring the fluxes of carbon, water, and energy, as well as meteorological factors. As one important reference of independently evaluating scalar flux by EC technique, energy balance closure is widely used for evaluating data quality of carbon, water, and energy fluxes.

Methods Using the data of energy fluxes and meteorological variables retrieved from 56 site-year, the energy balance closure of six sites across three ecosystems (i.e. desert steppe, typical steppe, and meadow steppe) was analyzed by two widely used methods: linear regression from the ordinary least squares (OLS) and the energy balance ratio (EBR). The overall evaluation of energy balance closure, the seasonal and interannual variations and the related influencing factors were investigated.

Important findings The results show that: 1) the multiple-year EBR and OLS slope over the six sites had a mean value of 0.89 ± 0.11 and 0.96 ± 0.04, respectively, which are better than the results of the FLUXNET and ChinaFLUX. 2) There were significant differences over different sites and grassland types, with EBR of desert steppe (1.01 ± 0.09) and typical steppe (0.90 ± 0.11) both higher than meadow steppe (0.83 ± 0.05). There were seasonal variations of EBR over the six studied sites, and with better and stable results in growing season than non-growing season. The air temperature (T_a), vapor pressure deficit (VPD), soil moisture (SWC), and Albedo regulated the seasonal variation of EBR, with the low T_a and high Albedo remarkably reducing EBR during the non-growing season. 3) There were significant interannual variations of EBR across different sites and grassland types. The latent heat fraction (the ratio of latent heat flux to net radiation, LE/R_n), mean annual air temperature (MAT) and growing season Albedo significantly influenced interannual variation of EBR. The LE/R_n showed the strongest impact and explained 44% of the interannual variation of EBR. The significantly increasing in leaf area index (LAI) strongly regulated the upward of the available energy (net radiation minus ground heat flux, R_n- G₀), which contributes to the significant downward of EBR during observed years. It should be noted that EBR and OLS slope should be combined to better evaluate the energy balance closure. In conclusion, this study help improve our understanding of the potential linkage between energy balance closure and environmental factors, evaluate the quality of scalar flux estimates from EC technique, as well as improve the data processing protocol of flux data in the semi-arid and arid grassland region.

Key words: energy balance closure, eddy covariance, seasonal variation, interannual variation, grassland

王彦兵, 游翠海, 谭星儒, 陈波宇, 许梦真, 陈世苹. 中国北方干旱半干旱区草原生态系统能量平衡闭合的季节和年际变异. 植物生态学报, 2022, 46(12): 1448-1460. DOI: 10.17521/cjpe.2021.0428

WANG Yan-Bing, YOU Cui-Hai, TAN Xing-Ru, CHEN Bo-Yu, XU Meng-Zhen, CHEN Shi-Ping. Seasonal and interannual variations in energy balance closure over arid and semi-arid grasslands in northern China. Chinese Journal of Plant Ecology, 2022, 46(12): 1448-1460. DOI: 10.17521/cjpe.2021.0428

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2021.0428

https://www.plant-ecology.com/CN/Y2022/V46/I12/1448

图/表 9

表1 内蒙古草原生态系统不同站点基本信息概况

Table 1 Site information of different sites in Nei Mongol grasslands

站点 Site	地理位置 Geo-location	海拔 Altitude (m)	年平均气温 Mean annual air temperature (°C)	年降水量 Mean annual precipitation (mm)	土壤类型 Soil type	草地类型 Grassland type	优势种 Dominant species	数据时段 Data period
四子王旗站 Siziwangqi station (SZ)	111.90° E 41.78° N	1 438	3.4	310	栗钙土 Kastanozem	荒漠草原 Desert steppe	短花针茅 Stipa breviflora 冷蒿 Artemisia frigida	2011-2018
锡林浩特割草站 Xilinhot grazed station (XL1)	116.67° E 43.56° N	1 250	2.0	350	栗钙土 Kastanozem	典型草原 Typical steppe	大针茅 Stipa grandis 羊草 Leymus chinensis 冷蒿 Artemisia frigida	2006-2018
锡林浩特围封站 Xilinhot fenced station (XL2)	116.67° E 43.55° N	1 250	2.0	350	栗钙土 Kastanozem	典型草原 Typical steppe	大针茅 Stipa grandis 羊草 Leymus chinensis 羽茅 Achnatherum sibiricum	2006-2018
西乌珠穆沁旗站 Xi Ujimqin Qi station (XW)	117.58° E 44.36° N	1 148	1.5	330	栗钙土 Kastanozem	典型草原 Typical steppe	大针茅 Stipa grandis 羊草 Leymus chinensis	2012-2018
多伦站 Duolun station (DL)	116.28° E 42.05° N	1 350	1.6	385	栗钙土 Kastanozem	典型草原 Typical steppe	西北针茅 Stipa sareptana var. krylovii 冷蒿 Artemisia frigida	2005-2018
额尔古纳站 Ergun station (EG)	119.39 °E 50.19° N	521	-2.5	355	黑钙土 Chernozem	草甸草原 Meadow steppe	狼针草 Stipa baicalensis 寸草 Carex duriuscula	2012-2018

表2 内蒙古草原生态系统不同站点能量平衡闭合状况(平均值±标准差)

Table 2 Energy balance closure of the different sites in Nei Mongol grasslands (mean ± SD)

时间 Time	站点 Station	最小二乘法线性回归 Linear regression from the ordinary least squares			能量平衡比率 Energy balance ratio
时间 Time	站点 Station	斜率 Slope	截距 Intercept	决定系数 R²	能量平衡比率 Energy balance ratio
全年 (1-12月) Whole year (January-December)	SZ	0.97 ± 0.13	0.30 ± 0.41	0.90 ± 0.03	1.01 ± 0.07
	XL1	0.94 ± 0.10	-0.05 ± 0.44	0.88 ± 0.02	0.92 ± 0.09
	XL2	1.01 ± 0.07	-1.15 ± 0.72	0.89 ± 0.04	0.86 ± 0.07
	XW	0.96 ± 0.05	-1.08 ± 0.13	0.94 ± 0.01	0.78 ± 0.06
	DL	1.00 ± 0.07	0.09 ± 0.25	0.94 ± 0.02	1.02 ± 0.07
	EG	0.88 ± 0.04	-0.69 ± 0.52	0.91 ± 0.04	0.74 ± 0.04
	平均值 Average	0.96 ± 0.04	-0.43 ± 0.57	0.91 ± 0.02	0.89 ± 0.11
非生长季 (10-次年3月) Non-growing season (October-March of next year)	SZ	0.88 ± 0.21	0.42 ± 0.64	0.78 ± 0.08	1.01 ± 0.13
	XL1	0.82 ± 0.14	-0.02 ± 0.48	0.76 ± 0.10	0.80 ± 0.17
	XL2	0.90 ± 0.12	-0.98 ± 0.78	0.77 ± 0.10	0.68 ± 0.15
	XW	0.95 ± 0.09	-1.10 ± 0.12	0.87 ± 0.04	0.58 ± 0.09
	DL	0.98 ± 0.06	0.17 ± 0.24	0.91 ± 0.02	1.04 ± 0.10
	EG	0.52 ± 0.21	-0.69 ± 0.38	0.43 ± 0.22	0.35 ± 0.17
	平均值 Average	0.84 ± 0.15	-0.37 ± 0.58	0.75 ± 0.15	0.74 ± 0.24
生长季 (4-9月) Growing season (April-September)	SZ	0.94 ± 0.12	0.61 ± 1.11	0.76 ± 0.13	1.01 ± 0.09
	XL1	0.86 ± 0.08	0.92 ± 0.52	0.71 ± 0.07	0.96 ± 0.09
	XL2	0.96 ± 0.07	-0.13 ± 0.50	0.87 ± 0.06	0.95 ± 0.06
	XW	0.94 ± 0.06	-0.79 ± 0.24	0.89 ± 0.05	0.86 ± 0.06
	DL	1.04 ± 0.08	-0.26 ± 0.23	0.85 ± 0.03	1.01 ± 0.07
	EG	0.81 ± 0.05	0.13 ± 0.66	0.79 ± 0.12	0.83 ± 0.05
	平均值 Average	0.93 ± 0.07	0.08 ± 0.56	0.81 ± 0.06	0.94 ± 0.07

图1 内蒙古不同草原类型观测站点能量平衡闭合状况的比较。不同大、小写字母分别表示不同草原类型和不同站点间差异显著(p < 0.05); ns, p > 0.05。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。

Fig. 1 Energy balance closure across different grassland types and sites in Nei Mongol based on energy balance ratio (EBR)(A) and ordinary least squares (OLS) slope (B) method. Different uppercase and lowercase letters indicate significant differences among different grassland types and sites, respectively (p < 0.05); ns, p > 0.05. DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xilinhot fenced site and Xi Ujimqin Qi site, respectively.

图2 内蒙古草原不同站点最小二乘法线性回归斜率与摩擦风速(u*)之间的关系。A, 白天。B, 夜间。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。***, p < 0.001。

Fig. 2 Relationships between ordinary least squares (OLS) slope and friction velocity (u*) across different sites in Nei Mongol grasslands. A, Daytime. B, Nighttime. DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xilinhot fenced site and Xi Ujimqin Qi site, respectively. ***, p < 0.001.

图3 内蒙古草原各站点能量闭合平衡比率(EBR)(A)、月平均气温(Ta)(B)、饱和水汽压差(VPD)(C)、土壤含水量(SWC)(D)和反照率(Albedo)(E)季节动态。图中浅绿色阴影表示生长季(4-9月)。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。

Fig. 3 Seasonal variations in energy balance ratio (EBR)(A), mean month air temperature (Ta)(B), vapor press deficit (VPD)(C), soil water content (SWC)(D) at 0-10 cm soil depth and Albedo (E) across different sites in Nei Mongol grasslands. The shallow green shaded area in the graph represents the growing season period (April to September). DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xiwuqi fenced site and Xi Ujimqin Qi site, respectively.

图4 内蒙古草原不同站点能量闭合平衡比率(EBR)季节变化与气温(Ta)(A)、饱和水汽压差(VPD)(B)、土壤含水量(SWC)(C)和反射率(Albedo)(D)的季节变化之间的关系。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。图中每一个数据点是该站点研究期内所有年份的月平均值。彩色线为每个站点的回归拟合结果, 黑色加粗线是所有站点混合效应模型拟合结果。实线代表相关关系显著(p < 0.05), 虚线代表相关关系不显著(p > 0.05)。ns, p > 0.1; **, p < 0.01; ***, p < 0.001。

Fig. 4 Relationships among seasonal variations of energy balance ratio (EBR) with air temperature (Ta)(A), vapor pressure deficit (VPD)(B), soil water content (SWC)(C), and Albedo (D) across different sites in Nei Mongol grasslands. DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xilinhot fenced site and Xi Ujimqin Qi site, respectively. Each point represents the monthly mean value during observation multiple years in each site. The color lines represent the linear or nonlinear regression model results of each site, the thick black line represents the nonlinear mixed-effects model results for all sites when the site was considered as a random factor. The solid line represents significant relation (p < 0.05) and the dash line represents insignificant relation (p > 0.05). ns, p > 0.1; **, p < 0.01; ***, p < 0.001.

图5 内蒙古草原不同站点能量平衡比率(EBR)(A)、湍流能量(LE + H)(B)、可利用能量(Rn - G0)(C)和反照率(Albedo)(D)的年际变异。黑线是所有站点线性回归拟合结果。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。Slope, 斜率。

Fig. 5 Interannual variations in energy balance ratio (EBR)(A), turbulent energy fluxes (LE + H)(B) available energy fluxes (Rn - G0)(C) and Albedo (D) across different sites in Nei Mongol grasslands. The black lines represent the linear regression model results for all sites. DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xilinhot fenced site and Xi Ujimqin Qi site, respectively.

图6 内蒙古草原不同站点年平均气温(MAT)(A)、潜热分配(LE/Rn)(B)和生长季反照率(Albedo)(C)与能量闭合平衡比率(EBR)年际变异之间的关系。DL、EG、SZ、XL1、XL2和XW分别代表多伦站、额尔古纳站、四子王旗站、锡林浩特割草站、锡林浩特围封站和西乌珠穆沁旗站。彩色线为每个站点的线性回归拟合结果, 黑色加粗线是所有站点混合线型模型拟合结果。实线代表相关关系显著(p < 0.05), 虚线代表相关关系不显著(p > 0.05)。ns, p > 0.1; #, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001。

Fig. 6 Relationships among interannual variations of energy balance ration (EBR) with mean annual temperature (MAT)(A), latent heat fraction (LE/Rn)(B) and growing season Albedo (C) across different sites in Nei Mongol grasslands. DL, EG, SZ, XL1, XL2 and XW represent Duolun site, Ergun site, Siziwangqi site, Xilinhot mowed site, Xilinhot fenced site and Xi Ujimqin Qi site, respectively. The color lines represent the linear regression model results of each site, the thick black line represents the nonlinear mixed-effects model results for all sites when the site was considered as a random factor. The solid line represents significant relation (p < 0.05) and the dash line represents insignificant relation (p > 0.05). ns, p > 0.1; #, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001.

图7 内蒙古草原环境因子对能量闭合平衡比率(EBR)季节(A)和年际变异(B)解释度的重要性排序。#, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001。Albedo、MAT、LE、Rn、SWC、Ta、VPD分别表示生长季反照率、年平均气温、潜热通量、净辐射、土壤含水量、月平均气温和饱和水汽压差。

Fig. 7 Relative importance of individual environmental variable in explaining seasonal (A) and interannual (B) variations of energy balance ratio (EBR) in Nei Mongol grasslands. #, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001. Albedo, MAT, LE, Rn, SWC, Ta, VPD represent growing season albedo, mean annual temperature, latent heat flux, net radiation, soil water content, mean monthly air temperature and vapor pressure deficit.

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