The combined effects of low light and low water on seedling growth vary in their severity based upon tree species and seedling traits

Environmental stresses rarely occur in isolation; in fact, plants often combat multiple stresses at once. Moreover, while most studies examining the combined effect of different factors have focused on greenhouse experiments, comparing experimental results with field studies is necessary to validate results. Here, we examine the effect of low water and light on the growth of Acer rubrum, Acer saccharum, and Quercus rubra in a greenhouse and the field. We tested whether the combined effects were additive, synergistic, or antagonistic and studied whether these responses were mediated by functional traits. In the greenhouse we found an additive effect of the two stresses across species; however, individual species responded differently with A. rubrum showing additive and A. saccharum and Q. rubra showing antagonistic effects. Species were unique in their trait responses, but species with antagonistic effects tended towards more acquisitive strategies belowground. Our field results partially matched our greenhouse findings, with water and light stress resulting in additive effects in all species except for A. saccharum. Our results suggest that A. saccharum and Q. rubra may be better equipped to cope with low light and water, and that studies should be careful to extrapolate from greenhouse studies on multiple stress response alone.