Effects of nitrogen fertilization and bioenergy crop type on spatial distributions of extracellular hydrolases associated with nitrogen and phosphorus acquisition

Extracellular hydrolases associated with nitrogen (N) and phosphorus (P) acquisition are important for soil nutrient cycling. The spatiotemporal patterns of N- and P-hydrolases were rarely studied under N fertilization. It is also unclear whether the N fertilization effects likely vary among different crop species. This study employed a spatially explicit design and clustered soil sampling strategy (288 samples at 0-15 cm) in a fertilization experiment with zero, low and high N input (NN, LN and HN: 0, 84, and 168 kg N ha^{- 1} yr^{- 1} urea, respectively) in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) croplands in Middle Tennessee. N-acquisition hydrolases such as leucine aminopeptidase (LAP), β-N-acetylglucosaminidase (NAG), their sum (N_acq), urease (UREA), and P-acquisition hydrolase acid phosphatase (AP) were quantified. Geostatistical analyses were applied to explore the effects of fertilization and plant type on spatiotemporal variations of N- and P-hydrolases. Results showed large plot-to-plot spatial variation and generally increased variation in soil hydrolyses with N fertilization in both croplands. NAG and N_acq were significantly higher by 15-32% in GG than in SG soils. Relative to NN, HN significantly increased LAP by 54% in SG soils. LAP appeared to be highly responsive to N fertilization. Overall, this study suggested greater sensitivity and responsiveness of spatiotemporal dynamics to N fertilization in SG cropland. Future studies will examine whether a specific peptidase (i.e., LAP) may facilitate soil C and N sequestration under intensive fertilization in switchgrass soil.