不同生态系统水分利用效率指标在黄土高原半干旱草地应用的适宜性评价

doi:10.17521/cjpe.2016.0378

摘要/Abstract

摘要：

对近些年提出的两种生态系统水分利用效率指标——内在水分利用效率(IWUE)和固有水分利用效率(uWUE)与经典的水分利用效率(WUE)指标在黄土高原典型半干旱草地生态系统的应用情况进行了比较, 主要分析了不同指标在小时、日和年尺度上的一致性和稳定性, 并提出优化水分利用效率(oWUE)指标, 比较了不同定义的水分利用效率指标在模拟总初级生产力(GPP)逐日动态过程上的表现。结果显示: IWUE和uWUE适合在日和小时尺度分析植被的碳水耦合特征, WUE适合分析年尺度的碳水耦合特征; oWUE指标在描述碳水耦合特征方面与uWUE相比并没有本质性改善, 但在用于模拟GPP动态过程时模拟效果改善明显; 采用oWUE和uWUE指标能改善植被生长盛期的GPP动态过程模拟, 但在生长季早期和晚期的模拟效果比WUE差。IWUE指标不适合模拟GPP动态过程。

关键词: 水分利用效率, 内在水分利用效率, 固有水分利用效率, 优化水分利用效率, 总初级生产力模拟

Abstract:

Aims We evaluated the applicability of different measures of water use efficiency through analyzing the coupled dynamics of GPP and evapotranspiration in the semi-arid steppe in the Loess Plateau of China. Our objective is to explore the applicability of two quantitative measures of ecosystem water use efficiency—inherent water use efficiency (IWUE) and underlying water use efficiency (uWUE) —for the semi-arid steppe and to endeavor necessary modifications.Methods The consistency and stability of three indices of water use efficiency formulations (i.e. WUE, IWUE, uWUE) were calculated and compared at hourly, daily and annual time scales before proposing an optimal water use efficiency (oWUE). These indices were additionally used to quantify their importances in modeling the diel change of gross primary production (GPP). The yielded-accuracy of the prediction was used for justifying their uses.Important findings IWUE and uWUE appeared suitable for examining the coupled water-carbon characteristics of vegetation at hourly and daily scales, whereas WUE was more plausible on the annual and interannual scales. The optimized water use efficiency index did not improve the prediction of the coupled water-carbon characteristics as compared with uWUE, but it improved the prediction of GPP and its dynamics. oWUE and uWUE improved the predictions of GPP in the peak growing period, while WUE predicted the GPP better at the early and late growing season. Interestingly, we found that IWUE was not suitable for predicting GPP and its dynamics. The results will be of great importance in modeling the effects of climate change on the carbon assimilation and water cycle for the future.

Key words: water use efficiency, inherent water use efficiency, underlying water use efficiency, optimal water use efficiency, predicted gross primary production

刘晓, 戚超, 闫艺兰, 袁国富. 不同生态系统水分利用效率指标在黄土高原半干旱草地应用的适宜性评价. 植物生态学报, 2017, 41(5): 497-505. DOI: 10.17521/cjpe.2016.0378

Xiao LIU, Chao QI, Yi-Lan YAN, Guo-Fu YUAN. Revised algorithm of ecosystem water use efficiency for semi-arid steppe in the Loess Plateau of China. Chinese Journal of Plant Ecology, 2017, 41(5): 497-505. DOI: 10.17521/cjpe.2016.0378

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2016.0378

https://www.plant-ecology.com/CN/Y2017/V41/I5/497

图/表 7

表1 不同生态系统水分利用效率指标的定义与单位

Table 1 Basic information for various algorithms of calculating water use efficiency at ecosystem level

类型 Type	符号 Symbol	代号 Code	表达式 Formulation	单位 Unit
水分利用效率 Water use efficiency	WUE	WUE₀	GPP/ET	g ·kg^-1
内在水分利用效率 Inherent water use efficiency	IWUE	WUE_1.0	GPP × VPD /ET	g hPa·kg^-1
固有水分利用效率 Underlying water use efficiency	uWUE	WUE_0.5	GPP × VPD^0.5/ET	g hPa^0.5·kg^-1
优化水分利用效率 Optimal water use efficiency	oWUE	WUE_k*	GPP × VPD^k^*/ET	g hPa^k^*·kg^-1

表2 不同水分利用效率指标在小时、日和年尺度的计算方法

Table 2 Algorithms for calculating water use efficiency (WUE) at hourly, daily and yearly time scale

时间尺度 Time scales	水分利用效率 WUE	内在水分利用效率 IWUE	固有水分利用效率 uWUE
小时尺度 Hourly time scales
日尺度 Daily time scales
年尺度 Yearly time scales

图1 2014-2016年生长季0.5 h尺度GPP (A, D, G)、GPP × VPD (B, E, H)、GPP × VPD0.5 (C, F, I)与ET之间的关系。ET, 蒸散量; GPP, 总初级生产力; VPD, 饱和水汽压差。Slope, 斜率。

Fig. 1 Relationship between GPP (A, D, G), GPP × VPD (B, E, H), GPP × VPD0.5 (C, F, I) and ET at hourly scale during the growing season of 2014-2016. ET, evapotranspiration; GPP, gross primary productivity; VPD, vapor pressure deficit.

图2 2014-2016年生长季日尺度GPP (A, D, G)、GPP × VPD (B, E, H)、GPP × VPD0.5 (C, F, I)与ET之间的关系。ET, 蒸散量; GPP, 总初级生产力; VPD, 饱和水汽压差。Slope, 斜率。

Fig. 2 Relationship between GPP (A, D, G), GPP × VPD (B, E, H), GPP × VPD0.5 (C, F, I) and ET at daily scale during the growing season of 2014-2016. ET, evapotranspiration; GPP, gross primary productivity; VPD, vapor pressure deficit.

表3 2014-2016年日和年尺度水分利用效率(WUE)、内在水分利用效率(IWUE)和固有水分利用效率(uWUE)变化比较

Table 3 Comparisons of the daily and yearly values of water use efficiency (WUE), inherent water use efficiency (IWUE), and underlying water use efficiency (uWUE) in 2014-2016

年份 Year	水分利用效率 WUE				内在水分利用效率 IWUE				固有水分利用效率 uWUE
年份 Year	相关系数 r	变异系数 Cv	日平均值 Mean daily value	年值 Yearly value	相关系数 r	变异系数 Cv	日平均值 Mean daily value	年值 Yearly value	相关系数 r	变异系数 Cv	日平均值 Mean daily value	年值 Yearly value
2014	0.70	0.40	1.655 5	1.523 5	0.81	0.54	20.534 4	23.639 5	0.83	0.38	5.563 9	5.829 7
2015	0.55	0.33	1.134 4	1.075 7	0.81	0.42	16.993 5	18.173 0	0.83	0.30	4.274 9	4.327 4
2016	0.38	0.41	1.177 5	1.097 0	0.77	0.63	8.763 6	10.264 1	0.84	0.38	2.943 6	3.137 0

表4 2014-2016年小时与日尺度优化水分利用效率(oWUE)的k*值及与固有水分利用效率(uWUE)的相关系数(r)比较

Table 4 k* values of optimal water use efficiency (oWUE) and its correlation coefficient (r) with oWUE and underlying water use efficiency (uWUE) at the hourly and daily scales during 2014-2016

年份 Year	k^值 k^ value		r (k = k*)		r (k = 0.5)
年份 Year	小时尺度 Hourly	日尺度 Daily	小时尺度 Hourly	日尺度 Daily	小时尺度 Hourly	日尺度 Daily
2014	0.42	0.40	0.76	0.85	0.75	0.83
2015	0.36	0.40	0.75	0.84	0.74	0.83
2016	0.38	0.37	0.82	0.85	0.80	0.84

图3 2015年日尺度总初级生产力(GPP)实测值与模拟值的比较及其NSE值(A和E为水分利用效率, B和F为内在水分利用效率, C和G为固有水分利用效率, D和H为优化水分利用效率)。NSE, 纳什效率系数。

Fig. 3 Comparisons between observed and predicted daily gross primary production (GPP) in 2015: A and E with water use efficiency, B and F with inherent water use efficiency, C and G with underlying water use efficiency, and D and H with optimal water use efficiency. NSE, Nash-Sutcliffe efficiency coefficient.

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