Rice Planting Increases Biological Nitrogen Fixation in Acidic Soil and the Influence of Light and Flood Layer Thickness
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ORIGINAL PAPER
Rice Planting Increases Biological Nitrogen Fixation in Acidic Soil and the Influence of Light and Flood Layer Thickness Hongliang Ma 1,2
&
Panpan Mao 1,2 & Shakeel Imran 3 & Taqi Raza 3 & Ren Gao 1,2 & Yanyu Lin 1,2
Received: 14 June 2020 / Accepted: 16 October 2020 # Sociedad Chilena de la Ciencia del Suelo 2020
Abstract Biological nitrogen fixation (BNF) varies in different soils and is impacted by rice planting. This study was conducted to investigate the extent of BNF in acidic soil planted with rice and to explore if the light and flood layer thickness affected the BNF. Soil and rice together were incubated in a 15N2-labeled closed chamber for whole growth period, and light and water depth effects were measured by labeling aboveground parts of rice plants in a plastic bag and labeling air in bottle without rice plants, respectively. The results showed that the total N fixation of soil and plant was 11.65 kg ha−1; nevertheless, it was only 2.11 kg ha−1 under fallow soil. In planted soil, plants and soil accounted for 25.1% and 74.9% of total 15N fixed, correspondingly. Soil NH4+-N concentration decreased due to uptake by the rice plants. There was higher available iron (Fe2+) in soil with rice plantings than in the fallow soil which was beneficial for BNF. Furthermore, 15N atom% in the roots was found higher than in the aboveground plant parts or leaves whether from experiment with whole rice-soil labeled in 15N2-enriched closed chamber or from that only rice aboveground parts labeled by 15N2, whereas water depth above the soil surface insignificantly influenced BNF without rice planting. Rice planting may significantly increase the amount of N fixation in acidic paddy soils. Further work regarding the role of rice plant and thickness of the water layer in BNF is highly important to gain an improved understanding of the N cycle in the rice ecosystem. Keywords Paddy soil . 15N2 labeling . Light . Flood layer
1 Introduction Nitrogen gas (N2) accounts for almost 80% of the volume of air. However, plants cannot use it directly, and it can only be absorbed and utilized by plants through biological or industrial fixation. The biological nitrogen fixation (BNF) and biological reduction of N2 to ammonium can merely be carried out by nitrogenase enzymes, which exist exclusively in prokaryotes (Canfield et al. 2010). The BNF can be symbiotic * Hongliang Ma [email protected] 1
State Key Laboratory for Subtropical Mountain Ecology of the Ministry of Science and Technology and Fujian Province, Fujian Normal University, Fuzhou 350007, China
2
School of Geographical Sciences, Fujian Normal University, 8# Shangsan Road, Cangshan District, Fuzhou 350007, Fujian, People’s Republic of China
3
University of Agriculture Faisalabad, UAF Sub-campus Burewala, Vehari 61010, Pakistan
when there are mutualistic associations between plant species and N fixing microorganisms (mainly rhizobia) or can be asymbiotic when it is carried out by free-living fixing microorganisms (do Figueiredo et al. 2013). Free-living N
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