Leaf area controls on energy partitioning of a temperate mountain grassland

Hammerle, Albin; Haslwanter, Alois; Tappeiner, Ulrike; Cernusca, Alexander; Wohlfahrt, Georg

doi:10.5194/bg-5-421-2008

Cited by 85 publications

(87 citation statements)

References 66 publications

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“…Canopy structure and LAI regulate energy partitioning via their impacts on surface albedo, roughness and stand transpiration Hammerle et al 2008). Consistent with previous studies in semiarid steppes and grasslands (e.g.…”

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

confidence: 77%

“…For example, in mesic forests and grasslands, shoot growth strongly controls energy partitioning via its impact on eco-physiological processes (e.g. transpiration), surface albedo and roughness (Hammerle et al 2008). In boreal coniferous forests, low radiation and temperature are key factors limiting the energy dissipated as λE (Launiainen 2010).…”

Section: Biophysical Controls On Carbon Water and Energy Exchangementioning

confidence: 99%

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

confidence: 77%

Section: Biophysical Controls On Carbon Water and Energy Exchangementioning

confidence: 99%

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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“…We noted a lower efficiency in the annual radiation budget of alpine meadow compared with the lowland grasslands, which can receive even higher incident radiation [73,74]. The lower efficiency observed on this plateau is attributed to the much higher net longwave radiation compared with lowland grasslands or the global surface [75].…”

Section: The Effect Of Vegetation Characteristics On Etmentioning

confidence: 83%

Spatial-Temporal Patterns and Controls of Evapotranspiration across the Tibetan Plateau (2000–2012)

Zhang

Sun

Xiong

2017

Advances in Meteorology

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Evapotranspiration (ET) is a key factor to further our understanding of climate change processes, especially on the Tibetan Plateau, which is sensitive to global change. Herein, the spatial patterns of ET are examined, and the effects of environmental factors on ET at different scales are explored from the years 2000 to 2012. The results indicated that a steady trend in ET was detected over the past decade. Meanwhile, the spatial distribution shows an increase of ET from the northwest to the southeast, and the rate of change in ET is lower in the middle part of the Tibetan Plateau. Besides, the positive effect of radiation on ET existed mainly in the southwest. Based on the environment gradient transects, the ET had positive correlations with temperature ( > 0.85, < 0.0001), precipitation (R > 0.89, p < 0.0001), and NDVI (R > 0.75, p < 0.0001), but a negative correlation between ET and radiation (R = 0.76, p < 0.0001) was observed. We also found that the relationships between environmental factors and ET differed in the different grassland ecosystems, which indicated that vegetation type is one factor that can affect ET. Generally, the results indicate that ET can serve as a valuable ecological indicator.

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“…Li et al (2006) also investigated the partitioning of surface energy in the grazing lands of Mongolia, and concluded that the energy partitioning was also controlled by vegetation dynamics and soil moisture availability, although soil heat flux is reportedly higher than latent heat flux in most instances. In a temperate mountain grassland in Austria, Hammerle et al (2008) found that the energy partitioning in this climatic region was dominated by latent heat flux, followed by sensible heat flux and lastly soil heat flux.…”

Section: Influence Of Weather Conditions and Seasonalitymentioning

confidence: 97%

Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

Majozi

Mannaerts

Ramoelo

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. Flux towers provide essential terrestrial climate, water, and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based Earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches.In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was also investigated, as well as how it is affected by atmospheric vapour pressure deficit (VPD), and net radiation.After filtering years with low-quality data (2004)(2005)(2006)(2007)(2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed the wet season with 1.17 and spring (1.02) being closest to unity, with the dry season (0.70) having the highest imbalance. Nocturnal surface energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity.The energy partition analysis showed that sensible heat flux is the dominant portion of net radiation, especially between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is correlated with a decrease in LE and increase in H during the wet season, and an increase in both fluxes during the dry season.

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Leaf area controls on energy partitioning of a temperate mountain grassland

Cited by 85 publications

References 66 publications

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

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

Spatial-Temporal Patterns and Controls of Evapotranspiration across the Tibetan Plateau (2000–2012)

Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

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