The processes regulating nitrification in soils are not entirely understood. Here we provide evidence that nitrification rates in soil may be affected by complexed nitrate molecules and microbial volatile organic compounds (mVOCs) produced during nitrification. Experiments were carried out to elucidate the overall nature of mVOCs and biogenic nitrates produced by nitrifiers, and their effects on nitrification and redox metabolism. Soils were incubated at three levels of biogenic nitrate. Soils containing biogenic nitrate were compared with soils containing inorganic fertilizer nitrate (KNO 3 ) in terms of redox metabolism potential. Repeated NH 4 –N addition increased nitrification rates (mM NO 3 1- produced g -1 soil d -1 ) from 0.49 to 0.65. Soils with higher nitrification rates stimulated ( p < 0.01) abundances of 16S rRNA genes by about eight times, amoA genes of nitrifying bacteria by about 25 times, and amoA genes of nitrifying archaea by about 15 times. Soils with biogenic nitrate and KNO 3 were incubated under anoxic conditions to undergo anaerobic respiration. The maximum rates of different redox metabolisms (mM electron acceptors reduced g -1 soil d -1 ) in soil containing biogenic nitrate followed as: NO 3 1- reduction 4.01 ± 0.22, Fe 3+ reduction 5.37 ± 0.12, SO 4 2- reduction 9.56 ± 0.16, and CH 4 production (μg g -1 soil) 0.46 ± 0.05. Biogenic nitrate inhibited denitrificaton 1.4 times more strongly compared to mineral KNO 3 . Raman spectra indicated that aliphatic hydrocarbons increased in soil during nitrification, and these compounds probably bind to NO 3 to form biogenic nitrate. The mVOCs produced by nitrifiers enhanced ( p < 0.05) nitrification rates and abundances of nitrifying bacteria. Experiments suggest that biogenic nitrate and mVOCs affect nitrification and redox metabolism in soil.

Background: Nitrous oxide (N 2 O) emission from agriculture is increasing alarmingly due to intensive application of inorganic and organic fertilizers. Recently, biochar has been identified as a promising additive to improve agriculture by enhancing soil function and mitigate greenhouse gas emission. However, it is unclear how biochar of different size fractions influences N 2 O emission from agricultural soil. Aims:The current experiment aims to understand how the size of biochar (BC) and organic fertilizers interactively influence N 2 O emission from a tropical vertisol.Methods: BC was prepared using pigeon pea (Cajanus cajan) stalks and further processed to obtain two size fractions (<0.25 mm or 0.25-2.00 mm). Organic fertilizers (vermicompost [VC], poultry manure [PM], or farmyard manure [FYM]) and BC were added to soil to evaluate N 2 O emission potential. BC was added to soil at 10% (w/w), whereas the organic fertilizers were added at 80 kg N ha -1 . Emission of CO 2 and the abundance of 16S rRNA and amoA gene copies were estimated after incubation period. The interactive effect of BC size fractions and organic fertilizers were statistically evaluated.Results: Both BC and organic fertilizers stimulated N 2 O emission in soil. BC of larger size stimulated N 2 O emission (µg N 2 O produced g -1 soil day -1 ) more than smaller size.Of the three organic fertilizers, PM resulted highest N 2 O (0.380) emission followed by FYM (0.240) and VC (0.210). BC (0.25 mm) + PM produced least N 2 O. Abundance of heterotrophic bacterial 16S rRNA gene copies and ammonia-oxidizing bacterial (AOB) amoA gene copies were highest in PM + BC and lowest in control. Significant relation (p < 0.0001) existed among N 2 O emission, CO 2 emission, and microbial abundance.Conclusions: BC of small size fraction along with organic fertilizers can be an effective strategy to mitigate N 2 O emission from tropical vertisol.

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Apparently, climate change is observed in form of increased greenhouse gases (CH 4 , CO 2 , N 2 O, CFC), temperature (0.5-1°C), and UV radiations (UV B and UV C). It is affecting every aspect of ecosystem functioning; however, terrestrial crops are the most vulnerable group and crop productivity largely remains a challenge. Due to climate change, seed yield and nutrient depletion are inevitable in future scenarios. To overcome this problem microbial groups that exhibit plant growth promoting attributes and provide protection against environmental stress should be studied. One such group is the pink pigmented facultative methylotrophs (PPFMs) that can induce overall fitness to plants.PPFMs are involved in phosphorous mineralization, siderophore, ACC deaminase, phytohormone production, and assimilation of greenhouse gases. Additionally, these organisms can also resist harmful UV radiations effectively as they possess polyketide synthases that could serve as source of novel bioactives that can protect plant from abiotic stress. The review article comprehensively highlights the multifunctional traits of PPFMs and their role in mitigating climate change with an aim to use this important organism as microbial inoculants for sustainable agriculture under climate-changing scenarios.climate change, greenhouse gases, phyllosphere, pink pigmented facultative methylotrophs, terrestrial crops | INTRODUCTIONMethylotrophs belong to diverse classes of α, β, and γ proteobacteria group, they are gram-negative, rodshaped, strict aerobic microbes. Methylotrophy is also exhibited by members of Verrucomicrobia, Firmicutes, Flavobacterium, and Actinobacteria [1]. A small group of methylotrophs encompassing 51 species appear pink in color due to carotenoid pigments and are often referred as pink pigmented facultative methylotrophs (PPFMs) (http://www.bacterio.net/methylobacterium.html). Methylorubrum extorquens is the best-studied member of