Humectants as Post-plant Soil Amendments: Effects on Growth and Physiological Activity of Drought-stressed, Container-grown Tree Seedlings

Abstract

One-year-old seedlings of red maple (Acer rubrum L.) and yellow poplar (Liriodendron tulipifera L.) were treated with Hydretain ES™(HydES) or EcoSential™(EcoS) applied as a soil drench. A progressive drought cycle was imposed after treatment, and as each seedling wilted, the leaves and roots were harvested. Foliar growth was unaffected by HydES or EcoS, but root growth (roots < 1 mm diameter) was significantly less for seedlings grown in the humectant-treated media. These data, along with measurements of substrate moisture content taken during a similar dry down period, suggest that drought-induced fine root growth in humectant-treated media was slower because there was less need for these roots to extend and proliferate in search of additional soil moisture supplies. In studies conducted the following year, HydES or EcoS were applied as a soil drench to one-year-old seedlings of red maple and river birch (Betula nigra L.) prior to withholding irrigation. In these studies, measurements of chlorophyll fluorescence, leaf gas exchange, and xylem water potential indicate that physiological activity was greater for drought-stressed seedlings grown in HydES-treated media compared to similar seedlings grown in EcoS-treated media, a condition attributed to lower levels of plant-water stress (higher xylem water potentials) in the HydES-treated seedlings.