Soil extracellular oxidases mediated nitrogen fertilization effects on soil organic carbon sequestration in bioenergy croplands

Authors: DUAN, JIANJUN - Tennessee State University; YUAN, MIN - Sichuan Academy Of Agricultural Science; JIAN, SIYANG - University Of Oklahoma; GAMAGE, LAHIRU - Tennessee State University; PARAJULI, MADHAV - Tennessee State University; DZANTOR, KUDJO - Tennessee State University; HUI, DAFENG - Tennessee State University; Fay, Philip; LI, JIANWEI - Tennessee State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2021
Publication Date: 5/16/2021
Citation: Duan, J., Yuan, M., Jian, S., Gamage, L., Parajuli, M., Dzantor, K.E., Hui, D., Fay, P.A., Li, J. 2021. Soil extracellular oxidases mediated nitrogen fertilization effects on soil organic carbon sequestration in bioenergy croplands. Global Change Biology Bioenergy. 13(8):1303-1318. https://doi.org/10.1111/gcbb.12860.
DOI: https://doi.org/10.1111/gcbb.12860

Interpretive Summary: This paper examines the effects of nitrogen fertilization on soil enzyme activities in switchgrass and eastern gamagrass, two biomass feedstock crops. Switchgrass and eastern gamagrass were grown in a replicated experiment with unfertilized controls and a low (84 kg per hectare) and high (168 kg per hectare) fertilization applied for three years. Soils were extensively sampled to characterize the overall response to treatments and spatial variability in two soil enzymes, polyphenolic oxidase and peroxidase, which play important roles in breakdown of slow-decomposing soil organic matter, an important contributor to soil carbon sequestration. The study revealed that in switchgrass, total enzyme activities was lower in the low fertilization treatment, while in gamagrass enzyme activities varied less between fertilizer treatments. Fertilization treatments tended to reduce spatial variation in soil enzyme activities compared to unfertilized. Together these results suggest that low fertilization rates reduce activities of enzymes involved in breakdown of slower decomposing soil organic carbon but also reduce spatial variation, which may low losses of carbon from switchgrass cropping systems, and to a lesser extent also from gamagrass systems.

Technical Abstract: Extracellular oxidases in soil are responsible for decomposition of slow turnover and recalcitrant soil organic carbon (e.g., lignin). Nitrogen (N) fertilization significantly affected soil extracellular oxidases but the spatial distribution of soil oxidases under N fertilization were rarely explored. In addition, these effects may co-vary with plant species (e.g., bioenergy crop). Using a spatially explicit design and collecting 288 soil samples in topsoil (0~15 cm) from twelve 15 m2 plots under three fertilization treatments in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) in a three-year long fertilization experiment located in Middle Tennessee, USA, we quantified the activities of two oxidases, polyphenolic oxidase (PHO), peroxidase (PER), and their sum associated with recalcitrant C acquisition (OX). The fertilization treatments included no N fertilizer input (NN), low N input (LN: 84 kg N ha-1 yr-1 in urea) and high N input (HN: 168 kg N ha-1 yr-1 in urea). Besides the statistical analysis of the effects of N fertilization and crop type, the spatial distributions of soil oxidases were evaluated by trend-surface analysis, correlograms, and interpolation map. Results showed that LN significantly depressed PER and OX by 13-19% than NN and HN in SG. Across all fertilization treatments, SG showed significantly higher PER and OX activities by 5-8% than GG. Despite less responses of PHO to fertilization or crop type, within-plot variances of PHO appeared higher than PER and OX. Relative to NN, LN tended to reduce spatial heterogeneity of soil oxidases in SG but HN tended to restructure them in GG. Substantial plot to plot variations were also observed for all enzymes in two croplands. Overall, the three-year long N fertilization generally depressed oxidase activities and their spatial heterogeneity particularly with low fertilization rate in switchgrass. The opposing N fertilization effects on spatial distribution of soil oxidases in two croplands were partly attributed to the less structurally complex SG root materials than GG. Furthermore, the differential responses of PHO and PER were most likely associated with their respective enzyme structure and complexity of reactions they catalyzed. This highlighted the importance of accounting for N fertilization intensity for studying spatiotemporal pattern of specific soil oxidase in bioenergy croplands.