Relationships among growth, delta C-13, foliar nitrogen concentration, foliar nitrogen content and intercepted radiation at different cultural intensities, planting densities and site indices reveal the importance of water use efficiency in mid-rotation loblolly pine stands

摘要

Carbon isotope composition (delta C-13), intercepted photosynthetically active radiation (IPAR), foliar nitrogen (N) content and foliar N concentration are all factors related to stand growth and productivity. The relationships between these attributes and growth were studied in 15 and 16-year-old loblolly pine (Pinus teada L.) stands at planting densities ranging from 1483 to 4448 tree ha(-1) grown under two silvicultural management intensities, both having different fertilization inputs. Measurements were conducted on six sites in the lower and upper coastal plains of Florida, Georgia and Alabama at site indices (SI) (base age 25 years) ranging from 18.6 to 29.6 m. The effects of planting density, cultural intensity and SI on the aforementioned attributes were studied. Correlations between delta C-13, foliar N concentration, foliar N content, IPAR and current annual increment (CAI) of stem volume, stem wood biomass, branch biomass, foliage biomass and total above-ground biomass were also studied. We hypothesized that foliar N would be a better predictor of growth than either delta C-13 or IPAR, and that IPAR would be the same across planting densities due to canopy closure.