The impacts of warming on leaf carbon balance of young woody plants: implications to forest regeneration—a systematic review and meta-analysis

Abstract Tree seedlings play a key role in the conservation and regeneration of local diversity, are essential for the functioning of forest ecosystems and are more susceptible to environmental changes than adult trees due to their lower metabolic reserve and photosynthetic production capacity. To investigate the responses of young plants (seedlings, saplings, juveniles, and young) of different geographical origin to temperature increases, we conducted a systematic review and meta-analysis of experiments published until the last decade of temperature on young woody plants. We investigated the effects of rising temperatures on several leaf traits related to carbon balance, such as stomatal conductance, quantum efficiency of photosystem II, leaf mass per area, and others, in 62 species across 39 papers. Few studies have investigated internal and atmospheric carbon ratio , electron transport rate and maximum Rubisco carboxylation rate indicating a significant knowledge gap that necessitates additional data collection. There was a consistent pattern of acclimation in photosynthetic rate response to warming and an increase in dark respiration and photorespiration, disrupting the carbon balance and potentially affecting the growth and survival of young trees. Our results suggest that young plants exposed to warming may increase in photorespiration, as indicated by the rapid increase in the internal and atmospheric carbon ratio and the decline in maximum Rubisco carboxylation rate with increasing temperature. This evidence suggests that the increase in temperature could affect young plant growth and pose a challenge to forest regeneration in a warming world.