Fertilization Effects on Water Use of 8-year-old Loblolly Pine (Pinus taeda L.) Vary with Throughfall Treatment

Abstract

Loblolly pine (Pinus taeda L.) plantations in the southern U.S. generate more timber than any other country in the world and therefore reductions in net primary productivity associated with climate variability may have significant economic impacts. As part of PINEMAP (www.pinemap.org), the objective of this research was to determine whether tree and stand-level water use are influenced by the main and interactive effects of reduced water availability from throughfall reduction and fertilization. We hypothesized that greater leaf area and related soil water depletion in response to fertilization would increase the impact of precipitation reduction on canopy level processes. Sap flow measurements were initiated in January 2013. An interactive effect of fertilization and throughfall treatments on monthly transpiration on a ground area (EG) and leaf area (EL) basis and canopy stomatal conductance (GS) was observed during 2013. Over the one year study period, which was a wetter than normal year, fertilization increased average monthly EG in the ambient throughfall treatment from January through July, but fertilization had no effect on EG in the throughfall reduction treatment, because of a decrease in EL and GS in response to fertilization combined with throughfall reduction. These results indicate a more conservative water use strategy, such that greater leaf area associated with fertilization results in a greater sensitivity of canopy-level processes to water availability.