Gross primary production variability associated with meteorology, physiology, leaf area, and water supply in contrasting woodland and grassland semiarid riparian ecosystems

Abstract

[1] Understanding ecosystem-atmosphere carbon exchanges in dryland environments has been more challenging than in mesic environments, likely due to more pronounced nonlinear responses of ecosystem processes to environmental variation. To better understand diurnal to interannual variation in gross primary productivity (GPP) variability, we coupled continuous eddy-covariance derived whole ecosystem gas exchange measurements with an ecophysiologic model based on fundamental principles of diffusion, mass balance, reaction kinetics, and biochemical regulation of photosynthesis. We evaluated the coupled data-model system to describe and understand the dynamics of 3 years of growing season GPP from a riparian grassland and woodland in southern Arizona. The data-model fusion procedure skillfully reproduced the majority of daily variation GPP throughout three growing seasons. While meteorology was similar between sites, the woodland site had consistently higher GPP rates and lower variability at daily and interannual timescales relative to the grassland site. We examined the causes of this variation using a new state factor model analysis that partitioned GPP variation into four factors: meteorology, physiology, leaf area, and water supply. The largest proportion of GPP variation was associated with physiological differences. The woodland showed a greater sensitivity than the grassland to water supply, while the grassland showed a greater sensitivity to leaf area. These differences are consistent with hypotheses of woody species using resistance mechanisms, stomatal regulation, and grassland species using resilience mechanisms, leaf area regulation, in avoiding water stress and have implications for future GPP sensitivity to climate variability following wood-grass transitions.Citation: Jenerette, G. D., R. L. Scott, G. A. Barron-Gafford, and T. E. Huxman (2009), Gross primary production variability associated with meteorology, physiology, leaf area, and water supply in contrasting woodland and grassland semiarid riparian ecosystems,

Remote sensing of annual terrestrial gross primary productivity from MODIS: an assessment using the FLUXNET La Thuile data set

“…In GRA, correlations between anomalies in mean EVI (and NDVI) and anomalies in GPP suggest that interannual variability in GPP in grasslands is tightly coupled to leaf area and supports the hypothesis that grasslands use LAI regulation to avoid moisture stress (Jenerette et al, 2009). Our results suggest that mean EVI and NDVI successfully capture the effect of moisture variability on GPP at GRA and SSMF sites, including moderate drought conditions when GPP can actually increase because of increases in LAI (Nagy et al, 2007;Mirzaei et al, 2008;Aires et al, 2008).…”

Organization of complexity in water limited ecohydrology

“…The degree of each is dependent on self-organizational processes and is in response to specific environmental variability (Carpenter et al, 2001). Often, there is a trade-off associated with the use of either strategy (Orwin et al, 2006;Jenerette et al, 2009). Often, there is a trade-off associated with the use of either strategy (Orwin et al, 2006;Jenerette et al, 2009).…”

“…Models that emphasize the coupling between environmental and system variability will allow better descriptions of system functioning in response to the environment. Recently, theory and data for coupling detailed physiological models with whole-ecosystem measurements at half-hourly scales have shown great success (Desai et al, 2007;Jenerette et al, 2009;Medvigy et al, 2009). Jointly applying these and other statistical approaches to mechanistic models that resolve fine scale temporal resolution would facilitate linking systems theory with new high-resolution data sets (Ruddell and Kumar, 2009).…”

Response of CO2 fluxes and productivity to water availability in two contrasting ecosystems in northern Benin (West Africa)

“…Therefore, the main differences in the patterns of the CO 2 assimilation during the dry seasons between our two sites could be better explained by the differences between the vegetation types (species, green biomass amounts, canopy structures) as observed in Africa (Williams and Albertson 2005). Jenerette et al (2009) found over 3 years at San Pedro River in Southern Arizona, USA that the GPP values were consistently higher and less variable for the woodland than for grassland with some distinct rates and variability during the growing seasons. During the year, while the absolute ER/GPP ratio was relatively constant (71-80 %) for the forest, it was highly variable (69-157 %) for the savannah (Fig.…”