The effects of wet deposition chemistry on reproductive processes in two pine species: Apparent pollination effectiveness in relation to species pollen sensitivity

A field investigation was carried out to compare the effects of simulated wet deposition of varying chemistry on reproduction in clones of an eastern white pine (Pinus strobus L.) and those of a red pine (Pinus resinosa Ait.). The simulants had a pH of 2.6, 3.6, 4.6, and 5.6 and contained additional concentrations of Pb or Cu (0, 0.05 or 0.01 mg 1^?1, respectively). They were applied to the receptive conelets after controlled pollination. Simulated wet deposition significantly affected (P < 0.05) seed set per bract. However, the trends were in different directions for the two species. Acidity increased apparent pollination effectiveness in red pine but was inhibitory in white pine. This difference apparent in response was also related to the pH sensitivity of the pollen in the two species. Previous experiments have shown that red pine pollen has a substantially lower pH threshold for germination inhibition than white pine. The effects of Cu and Pb were generally not significant; however, they did appear antagonistic to the effect of pH. The direct effects of wet deposition and its chemistry on pollination effectiveness has implications in terms of fertility selection, gametic selection, and the possible manipulation of the pollination mechanism in pines.