FOLIAR ABSORPTION OF DEW INFLUENCES SHOOT WATER POTENTIAL AND ROOT-GROWTH IN PINUS-STROBUS SEEDLINGS

We investigated the effects of foliar absorption of dew by eastern white pine (Pinus strobus L.) seedlings on midday shoot water potential, as well as on other water relations variables and growth. Two-year-old container-grown eastern white pine seedlings were subjected to contrasting watering regimes (normal and deficient) and three frequencies of artificial dew (none, once and three times per week) for 10 weeks in a greenhouse. Midday shoot water potential was measured on four occasions during the study. Other water relations variables (relative water content, stomatal conductance, pressure-volume curves) and growth (hypocotyl diameter, aboveground dry mass, root dry mass) were also measured. Artificial dew significantly increased shoot water potential, stomatal conductance and seedling root growth, with greater responses observed for seedlings subjected to a deficient watering regime than for well-watered seedlings. Because dew can be a frequent microclimatic event in some areas, this finding has practical implications for field studies of water relations of eastern white pine and possibly of other coniferous species.