Abstract
Abstract. Process-based models (PBMs) of vegetation function can be used to interpret and integrate experimental results. Water limitation to plant carbon uptake is a highly uncertain process in the context of environmental change, and many experiments have been carried out that study drought limitations to vegetation function at spatial scales from seedlings to entire canopies. What is lacking in the synthesis of these experiments is a quantitative tool incorporating a detailed mechanistic representation of the water balance that can be used to integrate and analyse experimental results at scales of both the whole-plant and the forest canopy. To fill this gap, we developed an individual tree-based model (MAESPA), largely based on combining the well-known MAESTRA and SPA ecosystem models. The model includes a hydraulically-based model of stomatal conductance, root water uptake routines, drainage, infiltration, runoff and canopy interception, as well as detailed radiation interception and leaf physiology routines from the MAESTRA model. The model can be applied both to single plants of arbitrary size and shape, as well as stands of trees. The utility of this model is demonstrated by studying the interaction between elevated [CO2] (eCa) and drought. Based on theory, this interaction is generally expected to be positive, so that plants growing in eCa should be less susceptible to drought. Experimental results, however, are varied. We apply the model to a previously published experiment on droughted cherry, and show that changes in plant parameters due to long-term growth at eCa (acclimation) may strongly affect the outcome of Ca × drought experiments. We discuss potential applications of MAESPA and some of the key uncertainties in process representation.
Highlights
The response of plant carbon uptake and water use to environmental change is complex because there are many interactions and feedbacks that modify the response to single environmental drivers
Because Process-based models (PBMs) summarize the state-of-art theory of plant functioning in a coherent quantitative framework, they provide a way forward for testing our understanding of how plants respond to environmental change
Under elevated Ca (eCa), EL is initially lower (Fig. 4a), which leads to less negative L (Fig. 4f), and a higher soil water content (Fig. 4e)
Summary
The response of plant carbon uptake and water use to environmental change is complex because there are many interactions and feedbacks that modify the response to single environmental drivers. Process-based models (PBMs) can be used as a research tool to clarify interactions among environmental drivers, plant and canopy structure, leaf physiology and soil water availability and their combined effects on water use and carbon uptake (Luo et al, 2008; Norby and Luo, 2004; Williams et al, 2001b). Because PBMs summarize the state-of-art theory of plant functioning in a coherent quantitative framework, they provide a way forward for testing our understanding of how plants respond to environmental change. In this way, they might be used to improve on empirical metaanalyses of experiments. These meta-analyses have been crucial in determining overall responses of vegetation to manipulation of the environment, but the variability among
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