Reductions in net photosynthesis and stomatal conductance vary with time since leaf detachment in three deciduous angiosperms

Abstract

Compared to in situ measurements, net photosynthesis and stomatal conductance were reduced 3–6 min after leaf detachment in Quercus rubra and Quercus alba, and 9 min after leaf detachment in Juglans nigra. Collecting in situ gas-exchange measurements in canopies of mature trees is challenging, because the crown can be several meters above ground. Thus, we investigated the effect of detaching the leaf from the branch and time since detachment for three deciduous angiosperm species: black walnut (Juglans nigra), northern red oak (Quercus nigra), and white oak (Quercus alba). Results showed that net photosynthesis (A) was significantly reduced 3 min after leaf detachment in Quercus rubra, 6 min after leaf detachment in Q. alba, and 9 min after leaf detachment in J. nigra. Compared to the in situ measurement, a 72 ± 13% reduction (mean ± SE) in A occurred after 3 min in Q. rubra, a 74 ± 27% reduction in A occurred after 6 min in Q. alba, while a 41 ± 14% reduction in A occurred after 9 min in J. nigra. Furthermore, once the significant reduction in A occurred, it was maintained over the remaining time period for each species. Responses for stomatal conductance were similar to those of A. Results highlight the importance of measuring gas exchange in situ whenever possible. Otherwise, these results provide threshold time periods to carry out instantaneous gas-exchange measurements in the field for select hardwood species in which the canopy is difficult to access.