Initial stomatal conductance increases photosynthetic induction of trees leaves more from sunlit than from shaded environments: A meta-analysis.

It has long been held that tree species/leaves from shaded environments show faster rate of photosynthetic induction than species/leaves from sunlit environments. But the evidence so far is conflicting and the underlying mechanisms are still under debate. To address the debate, we compiled a dataset for 87 tree species and compared the initial increasing slope during the first 2-minute induction (SA) and stomatal and biochemical characteristics between sun and shade species from the same study, and those between sun and shade leaves within the same species. In 77% of between-species comparisons, the species with high steady-state photosynthetic rate in the high light (Af) exhibited a larger SA than the species with low Af. In 67% within-species comparisons, the sun leaves exhibited a larger SA than the shade leaves. However, in only a few instances did the sun species/leaves more rapidly achieve 50% of full induction, with an even smaller SA, than the shade species/leaves. At both the species and leaf level, SA increased with increasing initial stomatal conductance before induction (gsi). Despite exhibiting reduced intrinsic water use efficiency in low light, a large SA proportionally enhances photosynthetic carbon gain during the first 2-minute induction in the sun species and leaves. Thus, in terms of the increase in absolute rate of photosynthesis, tree species/leaves from sunlit environments display faster photosynthetic induction responses than those from shaded environments. Our results call for re-consideration of contrasting photosynthetic strategies in photosynthetic adaption/acclimation to dynamic light environments across species.