PARENT SESSION
Oral Session # 4: Forest Ecology I: Diversity, Suppression, and Release.
Presiding: B Schamp
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.

The effect of resource availability on canopy dynamics and biomass accumulation in fertigated hardwood stands.

Allen, Christopher^*,1, Will, Rodney¹, Coyle, David², Coleman, Mark², ¹ Warnell School of Forest Resources, Athens, GA, USA² USDA Forest Service, New Ellenton, SC, USA

ABSTRACT- To determine how resource availability affects canopy dynamics, leaf-level physiological parameters, and biomass accumulation, we measured the impacts of water and nutrient additions on intercepted photosynthetically active radiation (IPAR), leaf gas exchange parameters, foliar nitrogen concentration, specific leaf area, and xylem water potential () during the 2001 growing season. Four genotypes (Liquidambar styraciflua, Platanus occidentalis, and two Populus deltoides clones with differing drought tolerances) planted in the spring of 2000 received a factorial combination of irrigation and fertilization. The four treatments were: control (0.5 cm water wk^-1), irrigation only (3.0 cm water wk^-1), fertilization only (0.5 cm water wk^-1, 120 kg N ha^-1 yr^-1), and irrigation with fertilization (3.0 cm water wk^-1, 120 kg N ha^-1 yr^-1). Beginning in March 2001, IPAR measurements for each genotype were made every 6 weeks during the growing season. Leaf gas exchange, foliar nitrogen concentration, specific leaf area, and were measured 4 times during the growing season on L. styraciflua and P. occidentalis. The addition of water and nutrients increased biomass accumulation for all species. When between-block variability was removed, IPAR was well correlated with biomass accumulation for all genotypes (r² range from 0.54 to 0.99). While there was no impact of treatment on photosynthetic capacity (A_max), irrigation significantly increased stomatal conductance (g_s) (p = 0.001; p = 0.009) and leaf internal CO₂ concentration (C_i) (p = 0.003; p = 0.02) for L. styraciflua and P. occidentalis, respectively. Foliar nitrogen concentration was not affected by treatment and was a poor predictor of biomass accumulation. There were no treatment effects for either specific leaf area or . These results indicate that IPAR may play a large role in the accumulation of biomass under a broad range of resource availabilities.

Key words: intercepted photosynthetically active radiation (IPAR), gas exchange, fertigation, short rotation woody crops