Influence of enhanced ultraviolet-B radiation during rice plant growth on rice straw decomposition with nitrogen deposition

Guixiang Zhou,Xiaomin Guo,Jiabao Zhang,Xiuwen Qiu,Xiaofeng Xu,Feng Wei

doi:10.1038/s41598-018-32863-8

Abstract

Although straw decomposition is important for ecosystem fertility and carbon balance, influence of ultraviolet-B (UV-B) radiation and nitrogen (N) deposition on this process is unclear. In this study, UV-B-exposed rice straw was decomposed under different N addition treatments for 15 months to investigate the indirect effects of UV-B radiation on straw chemistry and direct effects of N deposition on decomposition. UV-B exposure during rice plant growth changed the rice straw chemical composition, increasing the concentrations of acid-insoluble fraction (AIF), acid-soluble fraction, and UV-B-absorbing compounds. High N content had a negative effect on decomposition of rice straw exposed to enhanced and ambient UV-B radiation. Both AIF concentration and FTIR peak intensities indicated that lignin in rice straw was selectively preserved following N addition and UV-B radiation, reducing straw decomposition rate, which corresponded to lower activities of lignin-degrading enzymes in the later stage of decomposition. Thus, enhanced UV-B radiation during rice plant growth produced more recalcitrant substrates (lignin) and N reacted with lignin to produce more resistant compounds, further decreasing straw decomposition rate. UV-B radiation during plant growth and N deposition inhibit litter decomposition in agroecosystem, and their effects should be considered when establishing biogeochemical models in response to global changes.

Highlights

Litter decomposition is an important ecosystem process that affects carbon (C) and nutrients recycling
The acid-insoluble fraction (AIF), acid-soluble fraction (ASF), C/N ratio, AIF/N ratio, and absorbing compounds (AU) of rice straw exposed to enhanced UV-B treatment (UVB) were 19%, 9%, 20%, 51%, and 44% higher than those of rice straw exposed to ambient UV-B treatment (Ambient), respectively
UV-B exposure during rice plant growth changed the initial rice straw chemistry, increasing the concentrations of AIF, ASF, C/N, lignin/N, and AU, which may limit the activities of microbial decomposers, indirectly resulting in a decrease in the straw decomposition rate

Summary

Introduction

Litter decomposition is an important ecosystem process that affects carbon (C) and nutrients recycling. Despite several studies on litter decomposition[1], there are still certain uncertainties on how this essential process is affected by global change drivers such as ultraviolet-B (UV-B) radiation and nitrogen (N) deposition. Some reports did not find any evidence of the influence of supplemental UV-B exposure during plant growth on litter chemistry and decomposition[5]. As a key global change driver, N deposition plays a vital role in litter decomposition process by altering the organic matter composition and enzymes activities of microbial decomposers[8,9,10]; it is still unclear whether this is a broad effect or a chemical-fractions-specific effect on straw. The microbial responses to N addition are clear, there is still a lack of evidence for lower decomposition of specific chemical fractions in decomposing litter following N deposition

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