Exogenous Nitrogen Addition Reduced the Temperature Sensitivity of Microbial Respiration without Altering the Microbial Community Composition.

Hui Wei,Jiaen Zhang,Xiaomei Chen,Jinhong He,Weijun Shen

doi:10.3389/fmicb.2017.02382

Abstract

Atmospheric nitrogen (N) deposition is changing in both load quantity and chemical composition. The load effects have been studied extensively, whereas the composition effects remain poorly understood. We conducted a microcosm experiment to study how N chemistry affected the soil microbial community composition characterized by phospholipid fatty acids (PLFAs) and activity indicated by microbial CO2 release. Surface and subsurface soils collected from an old-growth subtropical forest were supplemented with three N-containing materials (ammonium, nitrate, and urea) at the current regional deposition load (50 kg ha-1 yr-1) and incubated at three temperatures (10, 20, and 30°C) to detect the interactive effects of N deposition and temperature. The results showed that the additions of N, regardless of form, did not alter the microbial PLFAs at any of the three temperatures. However, the addition of urea significantly stimulated soil CO2 release in the early incubation stage. Compared with the control, N addition consistently reduced the temperature dependency of microbial respiration, implying that N deposition could potentially weaken the positive feedback of the warming-stimulated soil CO2 release to the atmosphere. The consistent N effects for the surface and subsurface soils suggest that the effects of N on soil microbial communities may be independent of soil chemical contents and stoichiometry.

Highlights

Atmospheric nitrogen (N) deposition has been recognized as an important aspect of global changes for decades, with various ecological and economic consequences observed around the world (Galloway et al, 2008; BassiriRad, 2015)
We found that only urea addition increased soil CO2 release in the early stage at 10 and 20◦C, while ammonium and nitrate additions did not significantly affect soil CO2 emissions in the type of N-rich soils (Figure 1 and Supplementary Figures S1, S2)
The significant increase in soil CO2 emissions by urea addition could be derived from the CO2 released via hydrolysis of the added urea in the early stage, as urea is an organic material that can be rapidly hydrolyzed after it is applied to soils

Summary

Introduction

Atmospheric nitrogen (N) deposition has been recognized as an important aspect of global changes for decades, with various ecological and economic consequences observed around the world (Galloway et al, 2008; BassiriRad, 2015). N deposits are composed of oxidized/reduced and organic/inorganic N-containing materials and could change a series of ecosystem functions and processes, e.g., acidifying soils (Bobbink et al, 2010; Lu et al, 2015), reducing biodiversity. Changes in the chemical compositions of N deposits have been recorded in many places (Rogora et al, 2006; Liu et al, 2013; Hunova et al, 2017) possibly resulting from a combination of many factors, such as economic development policies, motor vehicles, the measures of reducing anthropogenic N emissions and the availability of reliable and cost-effective technologies (Erisman et al, 2001; Liu et al, 2013). Whether change in the composition of N deposits result in diverse ecological consequences remains poorly understood

Methods

Results

Conclusion