Abstract
While mid-rotation fertilization increases productivity in many southern pine forests, it remains unclear what impact such management may have on stand water use. We examined the impact of nutrient and water availability on stem volume, leaf area, transpiration per unit ground area (E
C) and canopy conductance per unit leaf area (G
S) of a pine plantation during its 8th and 9th growing seasons. Treatments consisted of a factorial combination of throughfall reduction (30% reduction in throughfall versus ambient)and fertilization (a complete suite of essential nutrients) beginning in April 2012. Overall, our results indicate that despite unusually high rainfall in the study period and a lack of leaf area index (LAI) response, both E
C and G
S decreased in response to fertilization and throughfall reduction. Fertilization increased stem volume increment 21% in 2013. Treatment differences were greatest in the growing season of 2013, when E
C was on average 19%, 13% and 29% lower in the throughfall reduction (D), fertilization (F) and combined treatment (FD) than the control (C), respectively. The responses of G
S to volumetric soil water content (VWC) indicate that lower E
C in F was associated with a decrease relative to C in G
S at high VWC. Decreases of G
S in D relative to C were associated with lower VWC, but little change in the response of G
S to VWC. Decreases observed in FD resulted from a combination of these two factors. The pattern of G
S responses in the different treatments suggests that structural or physiological changes underlie this fertilization response, possibly in fine root area or hydraulic conductivity. In the short term, this led to large increases in the water use efficiency of stem production, which could suggest greater resiliency to minor water stress. However, impacts on long-term sensitivity to drought remain a concern, as the E
C reduction triggered by the fertilization treatment was of comparable magnitude to the 30% throughfall exclusion treatment and the greatest reductions were found in the combined treatment.
Keywords
Fertilization,
Drought,
Gas exchange,
Loblolly pine,
Sap flux,
Transpiration
Citation
Ward, Eric J.; Domec, Jean-Christophe; Laviner, Marshall A.; Fox, Thomas R.; Sun, Ge; McNulty, Steve; King, John; Noormets, Asko. 2015. Fertilization intensifies drought stress: water use and stomatal conductance of Pinus taeda in a midrotation fertilization and throughfall reduction experiment. Forest Ecology and Management. 11 p. 10.1016/j.foreco.2015.04.009
