Influence of Intensive Culture on Leaf Net Photosynthesis and Growth of Sweetgum and Loblolly Pine Seedlings

Abstract

Abstract The influence of (1) complete weed control only, (2) weed control and irrigation, (3) weed control and irrigation with a fertilizer solution (fertigation), and (4) weed control and fertigation plus pest suppression (pine only) on midday light-saturated leaf net photosynthesis (Pn) of sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.) was examined monthly, two growing seasons after plantation establishment. Irrigation but not fertigation increased Pn on all dates and more than doubled height and diameter of sweetgum after the first growing season. Greater Pn in sweetgum in response to irrigation was, in part, a result of reductions in stomatal limitation to Pn and decreased stomatal sensitivity to vapor pressure deficit. In loblolly pine, Pn was increased only by irrigation and only on one date during the first growing season. No effect of treatment on Pn of either species was observed for the second season. After two growing seasons, an eight-fold increase in aboveground biomass and six-fold increase in leaf area were observed in sweetgum in response to fertigation relative to the control treatment. Fertigation plus pest control treatment eliminated tip moth damage to shoots of loblolly pine during the first growing season and resulted in a doubling of total biomass and tripling of leaf area. Maximum biomass accumulation in sweetgum and loblolly pine after two seasons of intensive culture was mainly a function of leaf area rather than Pn For. Sci. 44(2):308-316.