White pine, Japanese larch, and bear oak respond differently to partial defoliation

Seedlings (2-0 bare root) of Japanese larch (Larix leptolepis), white pine (Finns strobus), and bear oak (Quercus ilicifolia) were partially defoliated by clipping half of each leaf per plant. Control plants were not clipped. Photosynthesis, water potential, leaf nitrogen concentration, leaf mass, and total mass were measured one week and nine weeks after treatment. Compensatory responses varied by species and timing. Defoliated Japanese larch had increased photosynthesis rates and foliar nitrogen concentration relative to control plants one week after treatment. Total biomass was also increased relative to controls by the end of the experiment. Defoliated pine seedlings had increased leaf mass and total biomass relative to controls by the end of the experiment. Defoliated oak seedlings showed no compensatory responses. Leaf lifespan did not appear to be a determinant of response amount or type. Instead, we suggest that degree of allocation of resources to aboveground growth, as indicated by root-to-shoot ratio, may be related to degree of compensation to partial defoliation.