Is analysing the nitrogen use at the plant canopy level a matter of choosing the right optimization criterion?

Abstract

Optimization theory in combination with canopy modeling is potentially a powerful tool for evaluating the adaptive significance of photosynthesis-related plant traits. Yet its successful application has been hampered by a lack of agreement on the appropriate optimization criterion. Here we review how models based on different types of optimization criteria have been used to analyze traits—particularly N reallocation and leaf area indices—that determine photosynthetic nitrogen-use efficiency at the canopy level. By far the most commonly used approach is static-plant simple optimization (SSO). Static-plant simple optimization makes two assumptions: (1) plant traits are considered to be optimal when they maximize whole-stand daily photosynthesis, ignoring competitive interactions between individuals; (2) it assumes static plants, ignoring canopy dynamics (production and loss of leaves, and the reallocation and uptake of nitrogen) and the respiration of nonphotosynthetic tissue. Recent studies have addressed either the former problem through the application of evolutionary game theory (EGT) or the latter by applying dynamic-plant simple optimization (DSO), and have made considerable progress in our understanding of plant photosynthetic traits. However, we argue that future model studies should focus on combining these two approaches. We also point out that field observations can fit predictions from two models based on very different optimization criteria. In order to enhance our understanding of the adaptive significance of photosynthesis-related plant traits, there is thus an urgent need for experiments that test underlying optimization criteria and competing hypotheses about underlying mechanisms of optimization.

An evolutionary game theoretical model shows the limitations of the additive partitioning method for interpreting biodiversity experiments

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Interspecific vs intraspecific patterns in leaf nitrogen of forest trees across nitrogen availability gradients

“…There is a vast literature concerning the coordination of leaf N as a function of self‐shading and total crown N (see reviews in Kull, ; Hirose, ; Anten & During, ). A simple theme that emerges from this research is that, because selection acts at the level of the individual plant, not the leaf, plants operating within constraints of plasticity (Kull, ) should optimize whole‐crown C gain, not leaf‐level C gain.…”

Crown depth as a result of evolutionary games: decreasing solar angle should lead to shallower, not deeper crowns

“…Recently, exciting examples of game‐theoretical models that explicitly include the added dimension of competition between individuals, and the effects changing resources have on those interactions, have emerged (Kohyama & Takada, ; Dybzinski et al ., ; Westoby et al ., ; Farrior et al ., ), demonstrating the potential of such models in producing new theory in more complex conditions than the conceptual model presented in this paper. To date, one of the arguments to use game theory has been that, even though other models may produce similar results, game theory better reflects the fact that canopies are the result of competing individuals (Anten & During, ; McNickle & Dybzinski, ). More forcefully, the results presented in this paper suggest that including these competitive interactions may lead to different predictions about the direction of change from current models that implicitly ignore them.…”