Identifying differences in carbohydrate dynamics of seedlings and mature trees to improve carbon allocation in models for trees and forests

Carbohydrates play a central role in plant functioning because they are building blocks and energy carriers for plant metabolic processes. Because plants are sessile organisms and cannot escape stressful environments they acclimate to unfavourable conditions by strategically allocating carbohydrate resources to overcome stress and promote survival, and build reserves for later use when demand is greater than supply from photosynthesis, like after defoliation. A mechanistic understanding of how plants and, in particular, long-lived organisms like trees allocate and remobilize stored carbohydrates is still very poor. Without such an understanding, however, integration of carbon dynamics from trees to ecosystems and to the globe becomes highly uncertain, especially under ongoing climate change. Studies of carbohydrate dynamics in trees are often carried out on tree seedlings due to logistical and technical constraints and criticism has been raised whether results can be extrapolated to mature trees. Here we combine a literature review with a critical evaluation of using seedling studies on carbohydrate dynamics to infer mature tree responses that can subsequently be integrated at ecosystem level and beyond. Despite obvious differences between seedlings and mature trees with respect to carbohydrate dynamics, we propose that a combination of approaches, including seedling studies in controlled environments, measurements on mature trees in the field and ecosystem flux measurements, may provide sound estimates of carbohydrate dynamics at larger scales. We show how sensitive predictions of vegetation responses to disturbance are to changes in available reserves and argue that the implementation of more realistic representations of storage dynamics will likely improve simulations of vegetation responses to environmental stress.