Wheat straw-derived biochar amendment stimulated N
2
O emissions
from rice paddy soils by regulating the amoA genes of
ammonia-oxidizing bacteria
Yongxin Lin
a, b
, Weixin Ding
a, *
, Deyan Liu
a
, Tiehu He
a, b
, Gayoung Yoo
c
, Junji Yuan
a
,
Zengming Chen
a, b
, Jianling Fan
a
a
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
b
University of the Chinese Academy of Sciences, Beijing 10049, China
c
College of Engineering, Kyung Hee University, Yongin 446e701, South Korea
article info
Article history:
Received 29 June 2016
Received in revised form
15 April 2017
Accepted 1 June 2017
Keywords:
Nitrous oxide
amoA genes
Rice paddy soil
Biochar
Soil pH
abstract
Biochar amendment of upland soil has been generally accepted to mitigate nitrous oxide (N
2
O) emis-
sions. However, this is not always the case in rice paddy soil, and the underlying mechanisms are not well
understood. To evaluate how biochar amendment affects N
2
O production and emissions in paddy soil, an
incubation experiment was designed including six treatments: wheat straw-derived biochar (slow py-
rolyzed at 400
C) amendment at rates of 0% (Control), 1% and 4% soil mass (w/w), inorganic nitrogen (N)
fertilizer amendment (with urea), and N fertilizer plus 1% biochar and 4% biochar. The application of 4%
biochar significantly increased N
2
O emissions from N-unfertilized and fertilized soils during the 45-day
incubation, by 291% and 256%, respectively, while 1% biochar amendment significantly increased soil N
2
O
emissions when accompanied by N fertilizer addition. On day 14, when the N
2
O emission peaks occurred,
N
2
O flux was significantly correlated with soil pH in all treatments. Biochar addition also enhanced the
abundance of ammonia-oxidizing bacteria (AOB) amoA genes, which was significantly related to soil pH.
Among all detected N
2
O-forming and reducing microbial genes, the abundance of AOB amoA genes was
most closely related to N
2
O flux. On biochar addition, the AOB community structure shifted from
Nitrosospira-dominated toward Nitrosomonas, and the diversity of AOB was significantly increased.
Compared with the control, biochar amendment decreased, albeit not significantly, the abundance of the
nitrous oxide reductase encoding gene nosZ, but did not alter the abundance of nitrite reductase
encoding genes nirK and nirS. Our study suggests that wheat straw-derived biochar amendment of paddy
soils increased soil pH, which in turn increased the abundance and diversity of AOB and N
2
O emissions.
© 2017 Elsevier Ltd. All rights reserved.
1. Introduction
Increasing demand for nitrogen (N) fertilizer in agriculture im-
pacts global biogeochemical N-cycling and causes many environ-
mental problems, such as increased N
2
O emissions (Duce et al.,
2008; Galloway et al., 2008). Agricultural ecosystems are widely
accepted to be an important source of N
2
O and annual direct and
indirect N
2
O emissions from fertilizer N applied in arable soils
equaled 4 Tg N globally (Bouwman et al., 2010). Rice paddy soil is
regarded as an important source of atmospheric N
2
O, although its
N
2
O emission intensity is not as high as that in upland soils (Yu and
Patrick, 2004; Akiyama et al., 2005). Establishing effective agri-
cultural management practices for mitigation of greenhouse gas
(GHG) emissions is urgent.
Biochar amendment of agricultural soils has been proposed as a
potential way to reduce GHG emissions (Case et al., 2012), enhance
soil carbon sequestration (Lehmann and Joseph, 2012), improve soil
fertility (Novak et al., 2009; Van Zwieten et al., 2010) and increase
crop productivity (Jefferyet al., 2011; Huang et al., 2013; Liu et al.,
2013). Meta-analysis of data reported previously showed that bio-
char amendment generally reduced N
2
O emissions from upland
soils (Cayuela et al., 2014). However, there is conflicting evidence in
the literature about the effect of biochar on N
2
O emissions from
paddy soils. Liu et al. (2012) found that biochar amendment of three
* Corresponding author.
E-mail address: wxding@issas.ac.cn (W. Ding).
Contents lists available at ScienceDirect
Soil Biology & Biochemistry
journal homepage: www.elsevier.com/locate/soilbio
http://dx.doi.org/10.1016/j.soilbio.2017.06.001
0038-0717/© 2017 Elsevier Ltd. All rights reserved.
Soil Biology & Biochemistry 113 (2017) 89e98