Responses of absolute and specific enzyme activity to consecutive application of composted sewage sludge in a Fluventic Ustochrept.

Xiao Liu,Zhengyu Ji,Kangli Guo,Jianfeng Zhang,Huimin Jiang,Hu Li,Lin Huang,Jorge Paz-Ferreiro

doi:10.1371/journal.pone.0177796

Xiao Liu, Zhengyu Ji + Show 6 more

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https://doi.org/10.1371/journal.pone.0177796

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Abstract

Composted sewage sludge (CS) is considered a rich source of soil nutrients and significantly affects the physical, chemical, and biological characteristics of soil, but its effect on specific enzyme activity in soil is disregarded. The present experiment examined the absolute and specific enzyme activity of the enzymes involved in carbon, nitrogen, and phosphorus cycles, the diversity of soil microbial functions, and soil community composition in a Fluventic Ustochrept under a maize—wheat rotation system in North China during 2012–2015. Application of CS led to increase in MBC and in its ratio to both total organic carbon (TOC) and microbial biomass nitrogen (MBN). Absolute enzyme activity, except that of phosphatase, increased in CS-treated soils, whereas specific activity of all the enzymes declined, especially at the highest dose of CS (45 t ha−1). The diversity of soil microbial community also increased in CS-treated soils, whereas its functional diversity declined at higher doses of CS owing to the lowered specific enzyme activity. These changes indicate that CS application induced the domination of microorganisms that are not metabolically active and those that use resources more efficiently, namely fungi. Redundancy analysis showed that fundamental alterations in soil enzyme activity depend on soil pH. Soil specific enzyme activity is affected more than absolute enzyme activity by changes in soil properties, especially soil microbial activity and composition of soil microflora (as judged by the following ratios: MBC/TOC, MBC/MBN, and TOC/LOC, that is labile organic carbon) through the Pearson Correlation Coefficient. Specific enzyme activity is thus a more accurate parameter than absolute enzyme activity for monitoring the effect of adding CS on the activities and structure of soil microbial community.

Highlights

Sewage sludge is widely regarded as a useful soil amendment for improving the biological and physicochemical properties of soil—especially sandy soils—by providing nutrients and organic material [1,2]
The amended soil showed higher levels of total organic carbon (TOC), total nitrogen (TN), available P, and NO3−, and the increase was more marked at higher doses of composted sewage sludge (CS), whereas NH4+ increased significantly only in CS2 and CS3
Soil microbial functional diversity decreased as the dose of CS increased, which resulted from the decrease in specific enzyme activity

Summary

Introduction

Sewage sludge is widely regarded as a useful soil amendment for improving the biological and physicochemical properties of soil—especially sandy soils—by providing nutrients and organic material [1,2] Such use of sewage sludge improves soil quality and offers a way to dispose of sewage sludge—a potential environmental pollutant—in large quantities [3]. One of the properties most sensitive to these changes in the forms of carbon in soil is the activity of enzymes involved in the cycling and availability of nutrients, degradation and synthesis of soil organic matter, and biodegradation of toxic organic pollutants. This sensitivity makes soil enzyme activity a good indicator of soil quality [8]. Not all soil enzymes are affected the same way, which is why the sensitivity of different soil enzymes to CS needs to be examined further [16]

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