Effects of nitrogen fertilization and bioenergy crop species on central tendency and spatial heterogeneity of soil glycosidase activities

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

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Enzymes produced by soil microorganisms play a critical role in decomposing plant litter and making nutrients available for plants to use in growth and crop production. The amount of enzymes in soil can depend on the crop species and in the amount of fertilizer applied. A team of university and ARS scientists conducted a study comparing to biomass feedstock species, switchgrass and Eastern gamagrass for soil enzyme production under unfertilized and fertilized conditions. Using spatial analysis, the team shows in this paper that the enzyme beta-xylosidase was increased by fertilization in switchgrass and several other soil enzymes were present in greater amounts in gamagrass than in switchgrass. Also, enzyme amounts varied more spatially in switchgrass compared to gamagrass. Thse findings point to differences in the ways plant roots and soils interact to affect the biochemical processes controlling litter decomposition that require further study in order to optimize nutrient management in these bioenergy crops.

Technical Abstract: Extracellular hydrolases, produced by microorganisms in soil, acted as major agents for decomposing labile soil organic carbon (e.g., cellulose). Soil extracellular hydrolases were significantly affected by nitrogen (N) fertilization but fertilization effects on spatial distributions of soil hydrolases have not been well addressed. Whether the effects of N fertilization vary with bioenergy crop species also remains unknown. In this study, top mineral soil samples (0~15 cm) were taken using a spatially explicit design from two 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 in Middle Tennessee, USA. Four hydrolases, a-glucosidase (AG), ß-glucosidase (BG), ß-xylosidase (BX), cellobiohydrolase (CBH), and their sum associated with C acquisition (e.g. Cacq) were quantified. The three fertilization treatments were no N 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). The descriptive and geostatistical approaches were used to evaluate their central tendency and spatial heterogeneity. Results showed significant interactive effects of N fertilization and crop type on BX such that both LN and HN significantly enhanced BX by 14~44% in SG. The significant effect of crop type revealed higher hydrolase activities by 15~39% in GG than SG except AG. Within-plot variances of hydrolases appeared higher in SG than GG but little differed with N fertilization due to large plot-plot variation. More spatial patterns were generally evident in LN or HN than NN for BG in SG and CBH in GG. This study suggested that N fertilization elevated central tendency and spatial heterogeneity of hydrolase activity and these effects however varied with crop and enzyme types. Future studies need to focus on specific enzyme in certain bioenergy cropland soil when N fertilization effect is evaluated.