Characteristics of water and carbon fluxes during growing season in three typical arid ecosystems in central Asia

doi:10.3724/SP.J.1258.2014.00075

Abstract

Abstract:

Aims The arid region in central Asia, in the hinterland of Eurasia, is characterized by low precipitation and extremely fragile ecological environment. Study of energy and matter exchange between atmosphere and the land surface is essential to understanding the balance of water resources and ecosystem functioning in arid region. The objective of this study was to investigate the characteristics of water and carbon fluxes and responses to environmental factors in a typical ecosystem of central Asia.
Methods Eddy covariance measurements were made at three sites representing desert and grassland ecosystems in the central Asia. We analyzed the responses of evaporation and gross primary productivity to selective environmental factors using the enveloped curve fitting method, which determines the response of a dependent variable to a given independent factor while fixing other factors at their best values.
Important findings During growing season from April to October, the diurnal variations of energy, water vapor, net ecosystem CO₂ exchange and gross primary productivity showed patterns of “single peak curve” at the three sites; whereas ecosystem respiration in the desert ecosystem kept relatively stable. The ratio of latent heat flux to net solar radiation in the grassland ecosystem (76.3%) was greater than in the desert ecosystem (32.7%). The grassland ecosystem occurred as a strong carbon sink, whilst the desert ecosystem showed weak carbon fixation. Evapotranspiration and gross primary productivity in the two types of ecosystems were susceptible to changes in precipitation, net solar radiation or photosynthetically active radiation, vapor pressure deficit and air temperature.

Key words: central areas of Asia, CO₂ flux, eddy covariance, energy flux, vapor flux

WANG Yu-Hui, JING Chang-Qing, BAI Jie, LI Long-Hui, CHEN Xi, LUO Ge-Ping. Characteristics of water and carbon fluxes during growing season in three typical arid ecosystems in central Asia[J]. Chin J Plant Ecol, 2014, 38(8): 795-808.

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Figures/Tables 10

Fig. 1 Energy balance closure at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China). The slope of the solid line (fitted line) represents energy closure ratio, and the dash line is the 1:1 reference. G, soil heat flux; R2, coefficient of determination; RMSE, root mean square error; Rnet, net radiation flux; Qle, latent heat flux; Qh, sensible heat flux.

Fig. 2 The diurnal variations of energy fluxes at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China) (mean ± SD). G, soil heat flux; Rnet, net radiation flux; Qle, latent heat flux; Qh, sensible heat flux. Positive values indicate the ecosystem absorbs energy from the atmosphere; negative values indicate ecosystem releases energy to the atmosphere. The solid line represents average values of energy fluxes during observational periods, the shading illustrates the standard deviations, and the dash line is the zero reference line. The data period used is May to August 2012 for KZ-Ara, May to September 2012 for KZ-Bal, and April to October 2009 for CN-Fuk.

Fig. 3 The diurnal variations of water fluxes (ET) at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China) (mean ± SD). The solid line represents average values, the shading illustrates the standard deviations, and the dash line is the zero reference. The data period used is May to August 2012 for KZ-Ara, May to September 2012 for KZ-Bal, and April to October 2009 for CN-Fuk.

Fig. 4 Seasonal variations of water fluxes (ET) and precipitation at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China). The line represents ET and bars indicate precipitations. The data period used is May to August 2012 for KZ-Ara, May to September 2012 for KZ-Bal, and April to October 2009 for CN-Fuk.

Fig. 5 Responses of half hourly water flux (ET) to net radiation flux (Rnet) (A, D, G), vapor pressure deficit (VPD) (B, E, H) and air temperature (C, F, I) at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China). Dash line indicates the 95% confidence boundary.

Table 1 Estimated values of the fitted model parameters in Fig. 5 in responses of ET (evaporation) to net solar radiation (Rnet), vapor pressure deficit (VPD) and air temperature at KZ-Ara (site located in Aral Lake, Kazakhstan), KZ-Bal (site located in Balkhash Lake, Kazakhstan) and CN-Fuk (Fukang Desert Ecosystem Observation and Experiment Station, Chinese Academy of Sciences in Xinjiang, China)

站点 Site	ET对R_net的响应 Response of ET to R_net		ET对VPD的响应 Response of ET to VPD				ET对气温的响应 Response of ET to air temperature
站点 Site	ET_max	b	ET_max	k₁	k₂	k₃	ET_max	k₁	k₂	k₃
KZ-Ara	0.27	98.58	0.22	0.06	0.02	0.43	0.22	59.98	17 531.00	35.76
KZ-Bal	1.19	500.64	0.70	-1.27	-23.66	3.37	0.74	0.13	15.24	37.48
CN-Fuk	0.61	371.36	0.37	91 000.00	615 000.00	2.75	0.35	-12 481.00	-1 971 624.00	29.34

Fig. 6 Diurnal variations of gross primary productivity (GPP), ecosystem respiration (Res) and net ecosystem CO2 exchange (NEE) at KZ-Ara (site located in Aral Lake, Kazakhstan) and KZ-Bal (site located in Balkhash Lake, Kazakhstan) during growing season. The positive NEE indicates ecosystem releases CO2 into the atmosphere, while negative NEE indicates ecosystem absorbs CO2 from the atmosphere. The solid line represents average values of CO2 flux during observational periods, the shading illustrates the standard deviations, and the dash line is the zero reference. The data period used is May to August 2012 for KZ-Ara and May to September 2012 for KZ-Bal.

Fig. 7 Seasonal variations of gross primary productivity (GPP), ecosystem respiration (Res), net ecosystem CO2 exchange (NEE), and precipitation at KZ-Ara (site located in Aral Lake, Kazakhstan) and KZ-Bal (site located in Balkhash Lake, Kazakhstan) during growing season. Black bars represent precipitation and the dash line is the zero reference. The data period used is May to August 2012 for KZ-Ara and May to September 2012 for KZ-Bal.

Fig. 8 Responses of half hourly gross primary productivity (GPP) to photosynthetically active radiation (PAR) (A, D), vapor pressure deficit (VPD) (B, E) and air temperature (C, F) at KZ-Ara (site located in Aral Lake, Kazakhstan) and KZ-Bal (site located in Balkhash Lake, Kazakhstan). Dash line indicates the 95% confidence boundary.

Table 2 Estimated values of the fitted model parameters in Fig. 8 in responses of gross primary productivity (GPP) to photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and air temperature at KZ-Ara (site located in Aral Lake, Kazakhstan) and KZ-Bal (site located in Balkhash Lake, Kazakhstan)

站点 Site	GPP对PAR的响应 Response of GPP to PAR		GPP对VPD的响应 Response of GPP to VPD				GPP对气温的响应 Response of GPP to air temperature
站点 Site	GPP_max	b	GPP_max	k₁	k₂	k₃	GPP_max	k₁	k₂	k₃
KZ-Ara	10.29	359.42	7.86	0.08	0.32	1.06	7.72	0.32	62.94	33.04
KZ-Bal	36.24	464.86	29.12	0.06	0.94	4.65	29.58	8 685.86	2 291 884.00	35.37

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