Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe

Authors: HONG, XIAO - China Agricultural University; HELONG, YANG - China Agricultural University; MENGLI, ZHAO - Inner Mongolian Agriculture University; Monaco, Thomas; YUPING, RONG - China Agricultural University; DING, HUANG - China Agricultural University; QIAN, SONG - China Agricultural University; KUN, ZHAO - China Agricultural University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2020
Publication Date: 11/6/2020
Citation: Hong, X., Helong, Y., Mengli, Z., Monaco, T.A., Yuping, R., Ding, H., Qian, S., Kun, Z. 2020. Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe. Science of the Total Environment. 741. Article 143541. https://doi.org/10.1016/j.scitotenv.2020.143541.
DOI: https://doi.org/10.1016/j.scitotenv.2020.143541

Interpretive Summary: Atmospheric nitrogen (N) deposition can directly influence ecosystem-level processes, including how soil microbes control nutrient cycling. Consequently, changes in soil nitrogen due to anthropogenic inputs directly impact global change and plant community dynamics. Meadow steppe ecosystems around the globe are influenced by dry nitrogen deposition, but there is not a clear mechanistic understanding of levels of depostion influence microbial abundance and functioning. Moreover, microbial reactions to nitrogen deposition may depend on phosphorus status. In this study, six fertilization levels were applied to a meadow steppe ecosystem in Inner Mongolia for two years to decipher how enzyme activity and gene abundance of microbial groups respond during two growth periods. Results revealed that denitrification processes and gaseous-N loss were increased in the most productive period of the year. Furthermore, results showed that N addition prompted these drastic changes in the N cycle via stimulating extracelular enzyme activity of ammonia oxidizing bacteria, which in turn also led to nitrate leaching. These changes have important ecological consequences that are discussed.

Technical Abstract: Soil availability of nitrogen (N) and phosphorus (P) commonly limit belowground biological processes in terrestrial ecosystems. Soil extracellular enzyme activities (EEAs) and microbial functional groups play critical roles in soil biological processes and nutrient cycling, yet their responses to nutrient addition are poorly understood. Six fertilization treatments composed of combinations of N (0, 1.55, 13.95 g N m-2 yr-1) and P (0, 5.24 P m-2 yr-1) were applied for two years in a meadow steppe of Inner Mongolia. Soils were collected from each plot in July and August and analyzed for gene abundances of N- cycling microbial groups and EEAs, and their relationships with treatments. N addition significantly increased C- acquisition enzyme activity and enzyme C:N and C:P ratio. C- and N-acquisition enzyme activities were positively correlated with NH4+–N concentration. The abundance of amoA significantly increased with N addition and was positively related to mineral N concentration. The abundance of denitrifiers (narG, nirK, nirS and nosZ) and gaseous-N loss were accelerated by N addition in July, while a neutral effect was observed in August. Nitrate leaching was significantly increased by N addition, yet it declined with P addition in July. P addition also suppressed amoA abundance of ammonia oxidizing bacteria. Our results showed that N addition facilitated soil EEAs, ammonia oxidation, and nitrate leaching, which were mainly linked to soil N availability. Denitrification and gaseous-N loss increased in the short term after N addition. P addition decreased nitrate leaching by suppressing ammonia oxidation.