Abstract
Fertilization is a common, cost-effective method to increase productivity of managed forests in the southeastern United States; however, little is known about how fertilization will affect the processes that drive total soil CO2 efflux (F S) and ultimately net ecosystem productivity (NEP). The objective of this research was to intensively monitor the response of F S, and its respiratory components during the first year after N and P fertilization in Pinus taeda clones. We monitored F S, heterotrophic respiration (R H), and specific root respiration (R R) and found that F S in fertilized plots differed significantly (P < 0.0001) from that in unfertilized plots, but the direction of this effect was dependent on date. Additionally, R H was consistently lower (P = 0.0001) in fertilized plots relative to control plots, but the magnitude was dependent on the sampling date, and R R significantly (P = 0.04) increased in fertilized plots (+20%) when averaged over the study. Increased R R and decreased R H were probably offsetting each other, resulting in no overall difference in F S 1 year after fertilization. If these short-term trends persisted over the rotation of the stand, increased gross primary productivity accompanied by no change or even a decrease in soil C evolution could result in increased NEP.