Photosynthetic capacity in middle‐aged larch and spruce acclimates independently to experimental warming and elevated CO<sub>2</sub>
Mirindi Eric Dusenge, J. M. Warren, Peter B. Reich, Eric J. Ward, Bridget Murphy, Artur Stefański, Raimundo Bermúdez, Marisol Cruz, David McLennan, A. W. King, Rebecca Montgomery, Paul J. Hanson, Danielle A. Way
Abstract
Abstract Photosynthetic acclimation to both warming and elevated CO 2 of boreal trees remains a key uncertainty in modelling the response of photosynthesis to future climates. We investigated the impact of increased growth temperature and elevated CO 2 on photosynthetic capacity ( V cmax and J max ) in mature trees of two North American boreal conifers, tamarack and black spruce. We show that V cmax and J max at a standard temperature of 25°C did not change with warming, while V cmax and J max at their thermal optima ( T opt ) and growth temperature ( T g ) increased. Moreover, V cmax and J max at either 25°C, T opt or T g decreased with elevated CO 2 . The J max / V cmax ratio decreased with warming when assessed at both T opt and T g but did not significantly vary at 25°C. The J max / V cmax increased with elevated CO 2 at either reference temperature. We found no significant interaction between warming and elevated CO 2 on all traits. If this lack of interaction between warming and elevated CO 2 on the V cmax , J max and J max / V cmax ratio is a general trend, it would have significant implications for improving photosynthesis representation in vegetation models. However, future research is required to investigate the widespread nature of this response in a larger number of species and biomes.