Mahmud, K. | Search bioRxiv

bioRxiv2025

Attributing the temperature response of tree seedling growth to underlying mechanisms

Studies of plant responses to temperature often focus on rates photosynthesis and respiration. However, within-plant utilisation and allocation of carbon are also strongly affected. It is unclear how much each of these processes contribute to determining the overall temperature response of growth. We applied a data assimilation framework to a glasshouse experiment with detailed physiological and growth measurements to investigate the relative contribution of different physiological processes to the overall temperature response of tree seedling growth. We found that both short-term effects of temperature and acclimatory responses of photosynthesis and respiration had a significant impact on the temperature response of growth. However, the effect of temperature on biomass allocation patterns to different tissues, non-structural carbohydrate utilisation and C losses to other unmeasured losses were also substantial in determining the temperature response of growth, particularly at sub-optimal temperatures. Our work demonstrates that the growth response to warming cannot be predicted using only the direct effect of temperature on photosynthesis and respiration and emphasizes the importance of temperature acclimation of photosynthesis, respiration and other C balance processes. Our results provide new guidance for process-based models to correctly describe the temperature effects on tree growth.

plant biology↗

bioRxiv2019

The fate of carbon in a mature forest under carbon dioxide enrichment

Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1,2,3,4,5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. While evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3,4,5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7,8,9,10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving an open question about the fate of additional carbon fixed under eCO24, 5, 7,8,9,10,11. Here, using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responds to four years of eCO2 exposure. We show that, although the eCO2 treatment of ambient +150 ppm (+38%) induced a 12% (+247 gCm-2yr-1) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone contributing [~]50% of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on CO2 fertilization as a driver of increased carbon sinks in standing forests and afforestation projects.

ecology↗