Agriculture, Ecosystems and Environment 308 (2021) 107268
0167-8809/© 2020 Elsevier B.V. All rights reserved.
Elucidating relationship between nitrous oxide emission and functional soil
microbes from tropical lowland rice soil exposed to elevated CO
2
: A path
modelling approach
Anjani Kumar, Soumya Ranjan Padhy, Rasmita Rani Das, Mohammad Shahid,
Pradeep Kumar Dash, Ansuman Senapati, P. Panneerselvam, Upendra Kumar,
Dibyendu Chatterjee, Totan Adak, Rahul Tripathi, P.K. Nayak, A.K. Nayak *
ICAR-National Rice Research Institute, Cuttack, Odisha, India
A R T I C L E INFO
Keywords:
Elevated CO
2
Nitrous oxide emission
Nitrogen mineralization
Water defcit stress
Path analysis
Principal component analysis
ABSTRACT
Understanding the effect of elevated atmospheric CO
2
on nitrous oxide (N
2
O) emission and plant-microbe in-
teractions in rice soils is of great signifcance for predicting the long-term response of rice ecosystems to elevated
CO
2
concentration. Elevated atmospheric CO
2
concentration has the potential to augment rice production and
alter the soil nitrogen (N) dynamics. Because N
2
O emission is controlled by microbial activity, we reasoned that
changes in soil N dynamics and activity of soil microbes may affect N
2
O fux from rice soil. In order to examine
the infuence of elevated CO
2
, different N doses and varying moisture regimes on N
2
O emission from rice soil, we
designed a feld experiment with 3 CO
2
levels [C
1
= ambient CO
2
(400 ± 10 μmol mol
1
), C
2
= elevated CO
2
(550 ± 20 μmol mol
1
), C
3
= elevated CO
2
(700 ± 20 μmol mol
1
)], 3 N doses [No = No nitrogen, N
1
= 100 kg
ha
1
, N
2
= 150 kg ha
1
] and 2 moisture regimes (M
1
= well watered, M
2
= water defcit stress upto 60 kPa). In
this study, path analyses using partial least square path modelling (PLS-PM) approach was used to distinguish the
direct and indirect factors infuencing N
2
O emission under ambient and elevated CO
2
conditions. Signifcant
increase was found for labile N fractions such as microbial biomass-N (32 %; p ≤ 0.03) whereas signifcant
decrease was found for NH
4
+
-N (40 %; p ≤ 0.0005) and NO
3
–N (32 %; p ≤ 0.001) concentration under elevated
over ambient CO
2
. Rhizospheric denitrifer population was increased (39 %; p ≤ 0.001) whereas, nitrifer
population decreased (41 %; p ≤ 0.001) under elevated as compared to ambient CO
2
. Exposure of elevated CO
2
decreased (20 %; p ≤ 0.001) N mineralization whereas it increased N
2
O emission (43 %; p ≤ 0.001). Elevated
CO
2
level increased activities of β- glucosidase, urease and fuorescein diacetate showing signifcant effects on
soil N dynamics. Path modelling (PLS-PM) approach indicated a direct effect of nitrifers and denitrifers pop-
ulation on N
2
O emission and the effect was more pronounced under elevated CO
2
as compared to ambient CO
2
levels. The developed predictive models for N
2
O emission clarifes that the effect of varying CO
2
levels is more
pronounced at rice vegetative stage than reproductive stage.
1. Introduction
Due to extensive anthropogenic activities present atmospheric con-
centration of CO
2
has surpassed 400 μmol mol
1,
which is predicted to
go beyond 550 μmol mol
1
by 2050; and 700 μmol mol
1
by 2100
(IPCC, 2013; Kumar et al., 2019). This anticipated increase in CO
2
concentration of atmosphere is expected to enhance the mean global air
temperature by 1.4–5.8
◦
C (Houghton et al., 2001) which is likely to
change precipitation balance and may lead to frequent occurrence of
abiotic stresses like food and drought (Bates et al., 2008; Ray et al.,
2020). The anticipated drought under the elevated atmospheric CO
2
conditions may alter the water requirement of rice crop considerably
(Kumar et al., 2017a, b). Nevertheless, rice being a C
3
plant, have an
opportunity for increasing yield under elevated CO
2
due to increased
canopy photosynthesis (Baker and Allen, 2005). The higher rate of
photosynthesis under elevated CO
2,
increases the partitioning of pho-
tosynthates in the underground plant parts (Daepp et al., 2000), which
results in higher root exudates (Bhattacharyya et al., 2014) and
* Corresponding author.
E-mail address: aknayak20@yahoo.com (A.K. Nayak).
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Agriculture, Ecosystems and Environment
journal homepage: www.elsevier.com/locate/agee
https://doi.org/10.1016/j.agee.2020.107268
Received 18 July 2020; Received in revised form 22 November 2020; Accepted 23 November 2020