Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems

Martín F Garbulsky,Dario Papale,Iolanda Filella,Michael L Goulden,Jonas Ardö,Josep Peñuelas,Eyal Rotenberg,Gerard Kiely,Andrew D Richardson,Elmar M Veenendaal

doi:10.1111/j.1466-8238.2009.00504.x

Abstract

ABSTRACTAim The controls of gross radiation use efficiency (RUE), the ratio between gross primary productivity (GPP) and the radiation intercepted by terrestrial vegetation, and its spatial and temporal variation are not yet fully understood. Our objectives were to analyse and synthesize the spatial variability of GPP and the spatial and temporal variability of RUE and its climatic controls for a wide range of vegetation types.Location A global range of sites from tundra to rain forest.Methods We analysed a global dataset on photosynthetic uptake and climatic variables from 35 eddy covariance (EC) flux sites spanning between 100 and 2200 mm mean annual rainfall and between −13 and 26°C mean annual temperature. RUE was calculated from the data provided by EC flux sites and remote sensing (MODIS).Results Rainfall and actual evapotranspiration (AET) positively influenced the spatial variation of annual GPP, whereas temperature only influenced the GPP of forests. Annual and maximum RUE were also positively controlled primarily by annual rainfall. The main control parameters of the growth season variation of gross RUE varied for each ecosystem type. Overall, the ratio between actual and potential evapotranspiration and a surrogate for the energy balance explained a greater proportion of the seasonal variation of RUE than the vapour pressure deficit (VPD), AET and precipitation. Temperature was important for determining the intra‐annual variability of the RUE at the coldest energy‐limited sites.Main conclusions Our analysis supports the idea that the annual functioning of vegetation that is adapted to its local environment is more constrained by water availability than by temperature. The spatial variability of annual and maximum RUE can be largely explained by annual precipitation, more than by vegetation type. The intra‐annual variation of RUE was mainly linked to the energy balance and water availability along the climatic gradient. Furthermore, we showed that intra‐annual variation of gross RUE is only weakly influenced by VPD and temperature, contrary to what is frequently assumed. Our results provide a better understanding of the spatial and temporal controls of the RUE and thus could lead to a better estimation of ecosystem carbon fixation and better modelling.

Highlights

At present one of the most important endeavours of ecosystem ecologists is to estimate the photosynthetic carbon uptake by vegetation, its spatial and temporal variability and to understand what controls this variability (Schulze, 2006)
In accordance with global patterns in Above-ground net primary productivity (ANPP) (Huxman et al, 2004) and net primary productivity (NPP, Garbulsky & Paruelo, 2004) gross primary productivity (GPP) is influenced at a global scale by mean annual precipitation (MAP)
Long-term average climatic conditions, represented by MAP, and not the actual rainfall for the analysed period (< 6 years), showed better correlation with GPP. This result is probably evidence for the low capacity of each vegetation type to increase or decrease GPP with changes in water availability at the annual scale, because of the limitations imposed by the structure of the vegetation

Summary

Introduction

At present one of the most important endeavours of ecosystem ecologists is to estimate the photosynthetic carbon uptake by vegetation, its spatial and temporal variability and to understand what controls this variability (Schulze, 2006). Estimates of carbon uptake by terrestrial vegetation at different spatial and temporal scales are often based on the radiation use efficiency (RUE) model (Monteith, 1972). This model proposed that photosynthetic uptake of the vegetation depends on the amount of radiation absorbed by the vegetation and on the efficiency with which the vegetation transforms the absorbed radiation into plant biomass, namely the RUE) (Ruimy et al, 1994): GPP = PAR × FPAR × RUE (1). Where GPP is the gross primary productivity, PAR is the incident photosynthetically active radiation (400–700 nm), FPAR is the fraction of PAR absorbed by the vegetation, and RUE is the gross radiation use efficiency. Remote sensing techniques to estimate the photosynthetic uptake of terrestrial vegetation are commonly based on this model because it is possible to estimate FPAR from remotely sensed data (Tucker & Sellers, 1986)

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