Evolutionarily Stable Strategy Carbon Allocation to Foliage, Wood, and Fine Roots in Trees Competing for Light and Nitrogen: An Analytically Tractable, Individual-Based Model and Quantitative Comparisons to Data

Abstract

We present a model that scales from the physiological and structural traits of individual trees competing for light and nitrogen across a gradient of soil nitrogen to their community-level consequences. The model predicts the most competitive (i.e., the evolutionarily stable strategy [ESS]) allocations to foliage, wood, and fine roots for canopy and understory stages of trees growing in old-growth forests. The ESS allocations, revealed as analytical functions of commonly measured physiological parameters, depend not on simple root-shoot relations but rather on diminishing returns of carbon investment that ensure any alternate strategy will underperform an ESS in monoculture because of the competitive environment that the ESS creates. As such, ESS allocations do not maximize nitrogen-limited growth rates in monoculture, highlighting the underappreciated idea that the most competitive strategy is not necessarily the "best," but rather that which creates conditions in which all others are "worse." Data from 152 stands support the model's surprising prediction that the dominant structural trade-off is between fine roots and wood, not foliage, suggesting the "root-shoot" trade-off is more precisely a "root-stem" trade-off for long-lived trees. Assuming other resources are abundant, the model predicts that forests are limited by both nitrogen and light, or nearly so.

Decreased water limitation under elevated CO 2 amplifies potential for forest carbon sinks

“…This pattern is a signature of competitive overinvestment: investment that maximizes a strategy's competitive ability but that decreases its own growth rate when that strategy is in monoculture (22) (SI Appendix 4). Such competitive overinvestment is a common feature of game theoretic models of belowground competition by plants (19,20,22,(32)(33)(34)(35), and evidence of overinvestment has been found in experiments (19,24,36). …”

Patterns of biomass allocation between foliage and woody structure: the effects of tree size and specific functional traits

“…Similarly, in nutrient-limited soils, more biomass would be allocated to roots to increase use of water and nutrient resources (Deng et al 2006. Therefore, biomass allocation among plant organs is driven by above and belowground environmental conditions (Müller et al 2000, Freschet et al 2015, but plant size (Pino et al 2002), ontogenic trends , Xie et al 2012, species competitive abilities (Ninkovic 2003, Dybzinski et al 2011, species identity and functional traits can also act as potential covariates to define the investment in support tissues.…”

Evaluating the effect of alternative carbon allocation schemes in a land surface model (CLM4.5) on carbon fluxes, pools, and turnover in temperate forests

“…Here, we implemented an allocation scheme (D-Litton) that included two dynamic allometric parameters (a 2 and a 3 ) based on Litton et al (2007), assuming that the ratio between allocation to leaf and fine root (a 1 ) is constant. However, some studies suggest that this trade-off includes fine roots Malhi et al, 2011;Chen et al, 2013), probably due to the colimitation of productivity by resources captured aboveground (e.g., light) and belowground (e.g., nutrients and water; Dybzinski et al, 2011;Weng et al, 2016). These growth drivers also vary with time and across spatial ecological gradients (Guillemot et al, 2015).…”