Interplay of inorganic fertilizers on the relative abundance of effective microorganisms and methane emission in wetland soil

Abstract

The heterogeneity in fertilization (single or integrated) in paddy fields and wetland soil leads to dynamic unconformity in soil physicochemical properties, plant biomass, microbial community ecology, and their underlying physiological behavior, and enzymatic mechanisms. Paddy ecosystems comprise 11% of our arable land and are greatly influenced by composite environmental perturbations. The interplay among environmental factors and microbial community ecology is quite challenging and needs to be addressed via a contemporary perspective to attain sustainable ecosystems and agriculture practice. The current study was devised to investigate the fluctuating influence of inorganic (NPK) and organic (rice straw) fertilizers in a single and integrated fashion on the soil physicochemical attributes, plant biomass, effective microbial community, and functional metabolic predictions. It employs microcosm-based experiments with agricultural paddy soil with rice plants (Oryza sativa var. Super basmati) and subsequent supplementation of NPK in three doses. Single and integrated supplementation of nitrogen (N) as C(H2N)2O, phosphorus (P) and potassium (K) as KH2PO4, K as KCl, and rice straw (Rs) with concentrations equivalent to 160 kg N ha−1, 60 kg P ha−1, 130 kg K ha−1 , and 1% respectively were made to make at least 16 different combinations (18 including two controls). Soil physicochemical properties i.e., gravimetric water content (GWC), pH, electrical conductivity (EC), total nitrogen (TN), total carbon (TC), soil organic matter (SOM), available K (AK), and total extractable P (TEP) were accessed. The microbial community structure was apprehended by 16S rRNA high throughput sequencing (HTS) and phospholipid fatty acid (PLFA) profiling. Using 16S rRNA HTS data, alpha diversity (Pielou’s E and Abstract xvii Shannon) and beta diversity (Jaccard, Bray-Curtis) indices were reported. Furthermore, functional predictions were made employing phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) at different levels. Activities of acid phosphatase (AP), carbohydrate hydrolases i.e. β-glucosidase (GLU) and N-acetyl-β-glucosaminidase (NAG), and plant biomass variations were also studied. Additionally, methane production potential (MPP) of supplemented soils samples was measured. Moreover, in another experiment, Potential methane oxidation (PMO) rates were also monitored in flooded and non-flooded conditions against the different concentrations of (NH4)2SO4 in wetland soil. Our results indicated GWC, pH, TN, TC, C/N, and SOC to be the most influential indicators of microbial community ecology. HTS and PLFA analysis also revealed bacteria and archaea being more responsive compared to fungi. The outcomes revealed enhancement of community richness and diversity in all supplemented treatments compared to controls. Proteobacteria, Actinobacteria, and Firmicutes were the highly prominent phyla among bacteria. In different combinations, Chloroflexi, Bacteroidetes, and Verrucomicrobia showed positive while Actinobacteria, Acidobacteria, and Gemmatimonadetes showed negative tendencies contracted to controls. Thaumarchaeota and Euryarchaeota were dominant archaeal phyla and exhibited increasing and decreasing trends, respectively. The methanogenic genera i.e., Methanobrevibacter, methaosaeta, and methanomassiliicoccus showed a significant increase while methanosphaerula and methanocella showed decreasing trend. Overall, a discouraged methanogenic population was observed in U, K, UK, and UKRs which signifies the negative role of U and K in methane emission. The PICRUSt indicated microbial community shifts significantly towards amino acid, carbohydrate, energy, Abstract xviii and lipid metabolism while less towards glycan biosynthesis, synthesis of secondary metabolites, terpenoids, and biodegradation. Significantly enhanced activity of β glucosidase (GLU) and urease was observed in a majority of treatments compared to acid phosphatase (AP) and N-acetyl-β-glucosaminidase (NAG). The principal component analysis (PCA) signified microcosms with mixed combinations of fertilizer and controls as the most crucial variable regarding community structure. pH, C/N, SOM, and AK are identified as key factors in shaping bacterial and fungal abundance in different treatments. Our results inferred more disparity in the bacterial community than fungal. The effect of integrated fertilization especially UP and UPK was more promising regarding community ecology, methane metabolism, and plant growth. Keywords: NPK fertilizers, paddy soil microcosms, high throughput sequencing, PICRUSt, methane metabolism, enzyme activities