Measured and modelled leaf and stand‐scale productivity across a soil moisture gradient and a severe drought

• Published in: Plant, cell and environment Vol. 36; no. 2; pp. 467 - 483
• Main Authors: WRIGHT, J. K., WILLIAMS, M., STARR, G., MCGEE, J., MITCHELL, R. J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.02.2013; Blackwell; Wiley Subscription Services, Inc
• Subjects: Biological and medical sciences; Canopies; Carbon Dioxide - metabolism; Circadian Rhythm - radiation effects; Climate models; Climatic variability; Drought; Droughts; Ecosystem; eddy‐covariance; Environmental control; Forests; Fundamental and applied biological sciences. Psychology; Georgia; GPP; Growing season; Humidity; leaf area index; Light; Models, Biological; Nitrogen; Nitrogen - metabolism; photosynthesis; Photosynthesis - physiology; Photosynthesis - radiation effects; Pinus - physiology; Pinus - radiation effects; Pinus palustris; Plant Leaves - physiology; Plant Leaves - radiation effects; Plant Stomata - physiology; Primary production; Rain; Reproducibility of Results; Sandy soils; Soil; Soil - chemistry; Soil moisture; Soil moisture availability; Soil texture; SPA model; Temperature; Time Factors; Topography; Trees; Water - physiology; Productivity; Gradient; Soil moisture; GPP; Plant ecology; Plant leaf; Modeling; Eddy covariance method; eddy-covariance; Photosynthesis; Drought; Leaf area index; SPA model
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2012.02590.x

ABSTRACT Environmental controls on carbon dynamics operate at a range of interacting scales from the leaf to landscape. The key questions of this study addressed the influence of water and nitrogen (N) availability on Pinus palustris (Mill.) physiology and primary productivity across leaf and canopy scales, linking the soil‐plant‐atmosphere (SPA) model to leaf and stand‐scale flux and leaf trait/canopy data. We present previously unreported ecophysiological parameters (e.g. Vcmax and Jmax) for P. palustris and the first modelled estimates of its annual gross primary productivity (GPP) across xeric and mesic sites and under extreme drought. Annual mesic site P. palustris GPP was ∼23% greater than at the xeric site. However, at the leaf level, xeric trees had higher net photosynthetic rates, and water and light use efficiency. At the canopy scale, GPP was limited by light interception (canopy level), but co‐limited by nitrogen and water at the leaf level. Contrary to expectations, the impacts of an intense growing season drought were greater at the mesic site. Modelling indicated a 10% greater decrease in mesic GPP compared with the xeric site. Xeric P. palustris trees exhibited drought‐tolerant behaviour that contrasted with mesic trees' drought‐avoidance behaviour. Our research addresses the effect of climate variability on longleaf pine forest processes. We show that the effects are complex because responses occur at a range of scales, from leaf to stand, and are modulated by soil conditions. In a combined measurement and modelling study, we quantified the effects of soil texture on leaf and stand production, and showed that stands with lower soil moisture availability (i.e. sandier soils) were more resistant to drought stress than more productive stands on wetter soils.