PS 43-163 - Radial growth responses to heat stress and drought in male and female Acer negundo

Abstract: Dioecious plants tend to display sexual segregation due to the fact that female plants have higher reproduction costs, causing them to typically be located in high moisture, nutrient rich habitats. Females may be maladapted to environments with limited available resources, or those that are diminishing due to climate change, which would lead to reduced fitness and stress survival compared to their male counterparts, furthering skewed sex ratios and sexual segregation of dioecious species. The goal of this study was to evaluate how climate warming potentially leads to enhanced sexual segregation in productivity in one of the most widely distributed dioecious tree species in North America, Acer negundo. We hypothesize that 1) Male Acer negundo trees would display greater mean annual, and inter-annual radial growth than their female counterparts, and that 2) differences in radial growth would be enhanced during conditions of limited soil water availability. We studied 22-year-old A. negundo trees transplanted to a location in Salt Lake City, UT that was 6.5°C warmer than their original source location and were provided constant irrigation for their first 10 years. Afterwards, irrigation was ceased and the trees relied on soil water recharge from natural precipitation only. Nine male and nine female trees were cored using a 12 mm diameter tree borer and ring widths were measured digitally.

Over the 9 years in which we analyzed ring widths (2006-2014), mean annual radial growth was 7.47 mm / year (SE = 1.11) in males compared to 4.72 mm / year (SE = 0.86) in females (T = 4.61, P = 0.0017). Differences across all years were a function of males having a 64% higher annual growth rate than females while irrigated: 12.03 mm (SE = 1.96) and 7.33 mm / year (SE = 1.46), in males and females, respectively (T = 4.24, P = 0.0028). Once irrigation had ceased, mean annual growth dropped to 3.63 mm / year, or 30% of growth when irrigated in males, and to 2.68 mm / year, or 37% of growth when irrigated in females. No differences were detected between sexes after irrigation was ceased (T = 1.80, P = 0.11). Results, indicate that females were likely to become more maladapted to climate warming than males, supporting earlier ecophysiology studies on Acer negundo. However, a combination of drought and heat stress will likely have significant deleterious impacts on both males and females of Acer negundo.