Abstract
The
N fertilizer addition induced higher N2O emission in
various soils including the lawn soil, however, a key gap in knowledge
lies in identifying the ecological consequences of the
N2O emission and potentially associated microbial
mechanisms. This study evaluated the effect of N fertilizer on
N2O emissions and associated microbial mechanism in lawn
soil through incubated experiment under different N application rates.
In addition, the contribution of different microbial communities to
N2O emissions was quantified by combining biological
inhibitors with high-throughput sequencing. The results indicated that N
fertilizer addition induced higher N2O emissions in lawn
soil and the contribution of fungi to N2O emissions was
significantly higher than that of bacteria. We found a positive
correlation between N2O emission and Ascomycota through
RDA analysis. The growth trend of Ascomycota during the four nitrogen
fertilizer treatments was consistent with the N2O
emission trend in lawn soil. The relative abundance ofPyrenochaetopsis , Myrothecium , and Humicola was
positively correlated with N2O emission. Thus,Pyrenochaetopsis , Myrothecium , and Humicola were
found to be the main functional microorganisms leading to
N2O production in lawn soil. Our findings can deepen the
understanding on N2O emission and associated microbial
mechanism in lawn soil with N fertilization.
Keywords: lawn soil, N fertilizer, N2O
emission, biological inhibitors,
fungi
1. Introduction
Lawn, including urban green space, parks, athletic fields, roadsides and
home lawns, is one of the most popular landscapes worldwide and provides
numerous ecological, environmental and economic benefits[1]. However, the rapid increase of lawn area has
raised concerns about turfgrass breeding, resistance of lawn, and
pollution associated with fertilizers and pesticides, which are used for
lawn establishment and maintenance. Still, the N2O
emission from urban lawn soil has received less attention. It is unclear
how the N2O emission from lawn soil change along lawn
management.
Nitrous oxide (N2O) is one of the three major greenhouse
gases [2]. N2O can generate 300
times stronger effect on global warming than carbon dioxide in the
troposphere and is a stable greenhouse gas. It has the capacity to
reacts with ozone and became the dominant substance in ozone depletion[3]. N2O is also an important part
of the nitrogen cycle in terrestrial ecosystems. Not always are high. It
depends on the ecosystem and management practice. The impact of those
practices (tillage, fertilization, irrigation) is studied aiming to
reduce their contribution to N2O emissions. More
attention that the addition of exogenous nitrogen, such as atmospheric
nitrogen deposition and fertilization, alters the pathway of
N2O production [4–6]. Meanwhile,
previous studies have shown that the addition of a nitrogen fertilizer
could increase N2O emissions[7-10] For instance, compared with unfertilized
lawn soil, nitrogen fertilization significantly increased
N2O emission in Baltimore, USA[11]. Further, a fertilization addition experiment
in lawn in Phoenix, Arizona, USA also reported urbanization increased
N2O emissions compared to native landscapes, primarily
due to large amount of nitrogen fertilizer applied to lawn[12]. However, other studies found that the
addition of nitrogen fertilizer did not increase N2O
emission, for instance, studies on sandy loam and grasslands in the UK
found that the addition of nitrogen fertilizer did not increase
N2O emissions [13]. Similar
results were also found in a farmland soil study in Shandong Province,
China [14]. These results indicate that the effect
of exogenous nitrogen addition on N2O emission has not
been elucidated yet, and emissions could be either inhibited or
promoted, which likely was related to uncertain factors such as nitrogen
fertilizer form, vegetation type, soil properties, and microbial action.
Thus, it is important to understand the effect of fertilization on soil
N2O emission when formulating the scientific rational
for nitrogen regulation.
N2O is generally produced in soils through
microbiological nitrification and denitrification in soils. Therefore,
Microorganisms play a key role in soil nitrogen transformation. Previous
studies suggested that N2O emission in soil was caused
by bacterial nitrification and denitrification, because the conventional
nitrogen transformation is thought to be dominated primarily by bacteria[15]. However, recent studies have shown that
fungi are the main players in N2O emission. In the arid
grassland of the southwestern United States, N2O was
mainly produced by the nitrification and denitrification processes of
fungi, not bacterial ammonia oxidation [16].
N2O in the Qinghai-Tibet Plateau within China was also
found to be largely produced by fungi [17]. These
studies debunked the conventional idea that soil N2O was
produced primarily by bacteria. With the mature application of 15N
labelling technology, the contribution of heterotrophic nitrification to
N2O emissions has attracted increasing attention, and
fungi are considered the largest functional microorganisms[18,19]. Some studies also suggested that fungi
played an even greater role in N2O emission. In the
temperate grassland, fungi contributed to 86-89% of the
N2O emissions [20]. Fungi
contributed to 54% of N2O emissions during the
nitrification process and 63% in the denitrification process in an
alpine grassland [17]. Moreover, some studies have
showed that bacteria are the main contributors to N2O
emissions. For instance, bacterial denitrification was dominant in
farmland soils in northern China (winter wheat and summer maize rotation
farmland) [21]. Therefore, the microbiological
mechanism involved in N2O emission from different
vegetation types and ecological regions varies considerably. Clarifying
the microbial mechanism of N2O emission is a
prerequisite o for managing N2O emissions.
Lawn, which has the characteristics of high coverage, more roots, and
more fertilization, is the main vegetation of sports fields and urban
park green spaces and is quite different from natural grassland and
farmland soil. In 2001, China’s urban lawn area was 0.94 million ha,
while in 2010, it grew to 2.13 million ha, an increase of 1.3 times[22]. With the policy about greenbelt issued, lawn
area will continue to increase in China. Therefore, proper management of
this ground cover is important for improving urban environmental quality
and formulating more accurate emission reduction measures. In a previous
study, we found that fertilization promoted N2O emission
of lawn soil, and heterotrophic nitrification contributed to
N2O emission by 63% [23]. Yet, we
still know very little on the associated microbial mechanism of
N2O emission from lawn soils. In this study, we
investigated N2O emission from lawn soil and the
associated microbial mechanism under three fertilization gradients
(N300, N255, and N150). Our study provides insights into the impacts of
N fertilizer addition on N2O emission in lawn soil and
the improvement of fertilizer utilize strategy. We hypothesized that
N2O emission increased with the increase of nitrogen
application, and fungi contributed more to N2O emissions
than bacteria in lawn soil.