Seasonal and interannual variation in water vapor and energy exchange over a typical steppe in Inner Mongolia, China

Hao, Yanbin; Wang, Yanfen; Huang, Xiang‐Zhong; Cui, Xiaoyong; Zhou, Xiaoqi; Wang, Shiping; Niu, Haishan; Jiang, Gaoxi

doi:10.1016/j.agrformet.2007.05.005

Cited by 89 publications

(71 citation statements)

References 32 publications

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“…This was different with the results observed in the semiarid steppe, where the vapor pressure deficit influenced the diurnal processes of ET significantly (Hao et al, 2007).…”

Section: Diurnal Processcontrasting

confidence: 55%

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Yuan

Luo

Shao

et al. 2015

Sci. China Earth Sci.

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Evapotranspiration (ET) and its controlling mechanism over the desert riparian forests in arid regions are the important scientific basis for the water resources managements of the lower reaches of the inland rivers of China. Nearly three years of continuous measurements of surface ET, soil water content at different depths and groundwater table over a typical Tamarix spp. stand and a typical Populus euphratica stand were conducted in the lower reach of the Tarim River. The ET seasonal trends in the growing season were controlled by plant phenology, and ET in non-growing season was weak. The diurnal variations of ET resulting from the comprehensive effects of all atmospheric factors were significantly related with reference ET. The spatial pattern of ET was determined by vegetation LAI, more vegetation coverage, more ET amount. Groundwater is the water source of surface ET, and the soil water in shallow layers hardly took part in the water exchange in the groundwatersoil-plant-air system. The temporal processes of ET over the Tamarix stand and the Populus stand were similar, but the water consumption of the well-grown Populus euphratica was higher than that of the well-grown Tamarix spp. Further analysis indicates that plant transpiration accounts for most of the surface ET, with soil evaporation weak and negligible; groundwater table is a crucial factor influencing ET over the desert riparian forests, groundwater influences the processes and amounts of ET by controlling the growth and spatial distribution of desert riparian forests; quantifying the water stress of desert riparian forests using groundwater table is more appropriate, rather than soil water content. Based on the understanding of ET and water movements in the groundwater-soil-plant-air system, a generalized framework expressing the water cycling and its key controlling mechanism in the lower reaches of the inland rivers of China is described, and a simple model to estimate water requirements of the desert riparian forests is presented. lower reaches of the Tarim River, water cycling, evapotranspiration, desert riparian forests, Tamarix spp., Populus euphratica Citation:Yuan G F, Luo Y, Shao M A, et al. 2015. Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River

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“…This was different with the results observed in the semiarid steppe, where the vapor pressure deficit influenced the diurnal processes of ET significantly (Hao et al, 2007).…”

Section: Diurnal Processcontrasting

confidence: 55%

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Yuan

Luo

Shao

et al. 2015

Sci. China Earth Sci.

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“…with an annual β of 2.0), and H exceeded λE during most of the year. Similar β values have been reported for other arid and semiarid ecosystems where low PPT, dry soils and a sparse canopy constrain λE Hao et al 2007;Aires et al 2008b). Daily λE dominated H during the mid-summer of 2012 when rainfall was frequent and LAI was high.…”

Section: Temporal Dynamics Of Carbon Water and Energy Exchange And Tsupporting

confidence: 67%

Dynamics and biophysical controls of carbon, water and energy exchange over a semiarid shrubland in northern China

Jia¹

2017

Diss. For.

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To be presented, with the permission of the Faculty of Science and Forestry of the University of Eastern Finland, for public examination in auditorium BOR 100 in borealis building on Joensuu campus of the University of Eastern Finland, Yliopistokatu 7, Joensuu on 23 May 2017 at 12 o' clock noon. ABSTRACTThe main aim of this study was to investigate the dynamics and biophysical controls of carbon, water and energy exchange over a semiarid shrub ecosystem in the Mu Us desert, northern China, using continuous eddy-covariance (EC) measurements. Specific objectives were as follows: (1) To examine intra-annual variations in net ecosystem CO 2 exchange (NEE) and its biophysical controls (Paper I); (2) To quantify the diurnal and seasonal variations in surface energy-balance components, and to examine the partitioning of net radiation (R n ) among different energy components at diurnal and seasonal timescales (Paper II); and (3) To examine how ecosystem production and water use efficiency (WUE) vary inter-annually with contrasting precipitation (PPT) and soil moisture patterns (Paper III).The results showed that, soil water content (i.e. at 30 cm depth, SWC_30), or water deficit, imposed a major control on the seasonal dynamics of carbon assimilation and energy partitioning. Water deficit (i.e. SWC_30 < 0.10 m 3 m -3 ) was a major constraint over daytime NEE, and also interacted with other stresses, e.g. heat stress and photoinhibition (Paper I). Low soil moisture reduced the temperature sensitivity (Q 10 ) of total ecosystem respiration (TER). Rain events triggered immediate pulses of carbon release from the ecosystem, followed by peaks of CO 2 uptake 1-2 days later. Leaf area index (LAI) accounted for 45 and 65% of the seasonal variation in NEE and gross ecosystem production (GEP), respectively. On the other hand, sensible heat flux (H) exceeded latent heat flux (λE) during most time of the year (Paper II). The evaporative fraction (EF, i.e. λE/R n ), Priestley-Taylor coefficient (α), surface conductance (g s ) and decoupling coefficient (Ω) all correlated positively with SWC_30 and LAI. The direct enhancement of λE by high vapor pressure deficit (VPD) was buffered by a concurrent suppression of g s , which controlled EF and α by mediating the effects of LAI, SWC_30 and VPD.At the annual scale, net ecosystem production (NEP, here defined as −NEE) indicated a rapid shift from an annual sink of carbon in 2012 (NEP = 77 ± 10 g C m -2 yr -1 ) to a source of carbon in 2014 (NEP = -22 ± 5 g C m -2 yr -1 ), with the year 2013 being close to carbon neutral (NEP = -4 ± 10 g C m -2 yr -1 ) (Paper III). GEP, TER and evapotranspiration (ET) also declined over the three years. Suppressed annual carbon and water fluxes were observed in years with low spring soil moisture. GEP declined more than TER and ET, leading to reduced carbon sequestration and WUE (i.e. GEP/ET). Neither annual nor growing-season PPT amount could explain the year-to-year variation in carbon fluxes. ET was a better proxy for water available to ecosystem carbon...

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“…Table 1 provides extensive descriptions of the three sites. For further details about the study sites, refer to our previous papers (Fu et al, 2006b;Hao et al, 2007;Shi et al, 2006).…”

Section: Site Descriptionmentioning

confidence: 99%

“…Kato et al, 2004;Zhao et al, 2005;Shi et al, 2006;Hao et al, 2007;Wang et al, 2008), but none synthetically studied the CO 2 exchange and its relationship with environmental factors across different grassland types or biomes. In this study we presented measurements of CO 2 flux over three grassland ecosystems in China in 2004 and 2005.…”

Section: Introductionmentioning

confidence: 99%

Environmental influences on carbon dioxide fluxes over three grassland ecosystems in China

Zheng

et al. 2009

Biogeosciences

125

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Abstract. This study compared carbon dioxide (CO 2 ) fluxes over three grassland ecosystems in China, including a temperate semiarid steppe in Inner Mongolia (NMG), an alpine shrub-meadow in Qinghai (HB), and an alpine meadowsteppe in Tibet (DX). Measurements were made in 2004 and 2005 using the eddy covariance technique. Objectives were to document the seasonality of the net ecosystem exchange of CO 2 (NEE) and its components, gross ecosystem photosynthesis (GEP), and ecosystem respiration (R eco ), and to examine how environmental factors affect the CO 2 exchange in these grassland ecosystems. The 2005 growing season (from May to September) was warmer than that of 2004 across the three sites, and precipitation in 2005 was less than that in 2004 at NMG and DX. The magnitude of CO 2 fluxes (daily and annual sums) was largest at HB, which also showed the highest temperature sensitivity of R eco among the three sites. A stepwise multiple regression analysis showed that the seasonal variation of GEP, R eco , and NEE of the alpine shrubmeadow was mainly controlled by air temperature, whereas leaf area index can likely explain the seasonal variation in GEP, R eco , and NEE of the temperate steppe. The CO 2 fluxes of the alpine meadow-steppe were jointly affected by soil moisture and air temperature. The alpine shrub-meadow acted as a net carbon sink over the two study years, whereas the temperate steppe and alpine meadow-steppe acted as net carbon sources. Both GEP and R eco were reduced by the summer and spring drought in 2005 at NMG and DX, respectively. The accumulated leaf area index during the growCorrespondence to: G. Yu (yugr@igsnrr.ac.cn) ing season (LAI sum ) played a key role in the interannual and intersite variation of annual GEP and R eco across the study sites and years, whereas soil moisture contributed most significantly to the variation in annual NEE. Because LAI sum was significantly correlated with soil moisture at a depth of 20 cm, we concluded that the available soil moisture other than annual precipitation was the most important factor controlling the variation in the CO 2 budgets of different grassland ecosystems in China.

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Seasonal and interannual variation in water vapor and energy exchange over a typical steppe in Inner Mongolia, China

Cited by 89 publications

References 32 publications

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Dynamics and biophysical controls of carbon, water and energy exchange over a semiarid shrubland in northern China

Environmental influences on carbon dioxide fluxes over three grassland ecosystems in China

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