Differences in N2O Fluxes and Denitrification Gene Abundance in the Wet and Dry Seasons Through Soil and Plant Residue Characteristics of Tropical Tree Crops

Abstract

The conversion of forest to agricultural soils is a widespread activity in tropical systems, and its link to nitrous oxide (N 2 O) fluxes and nitrogen cycling gene abundance is relevant to understand environmental drivers that may interact with climate change. A current challenge to estimating N 2 O emissions from land use conversion is an incomplete understanding of crop-specific impacts on denitrifier communities and the N 2 O fluxes driven by differences in the above-and below-ground inputs with crop type. To address this knowledge gap in tree crops, we evaluated N 2 O fluxes and denitrification gene abundance and their relationships with soil and plant residue characteristics in citrus and eucalyptus plantations in the field and in soil incubations. We found that the accumulated N 2 O fluxes from soil were lower for the two agricultural field sites than those for their adjacent forest sites in dry and wet seasons. The N 2 O fluxes were higher in the wet season, and this seasonal difference persisted even when the soils collected from both seasons were incubated under the same moisture and temperature conditions in the lab for 30 days. Increased N 2 O fluxes in the wet season were accompanied by an increase in soil nirK and nosZ gene abundance, the dissolved organic carbon (DOC) concentration, and the total soil carbon (C) and nitrogen (N) content. In turn, the abundance of denitrifiers, as indicated by nirK, nirS, and nosZ gene copy numbers, showed a low but significant positive correlation with soil bulk density. Our results suggest that soil moisture, leaf litter, and crop residues influence the seasonal differences in both N 2 O fluxes and abundance of denitrifiers in citrus-and eucalyptus-cultivated soils, likely through effects on soil physicochemical characteristics. These findings highlight the overwhelming role of environmental drivers that can make investigating microbial drivers difficult in the field and open the possibility for a better understanding of N cycling processes in tropical soils based on paired field-and incubation-based experimentation.

CO2, CH4 and N2O emissions after fertilizer application in banana plantations located in the Brazilian Atlantic Forest

“…Fruit orchard soils with fine texture are expected to promote N 2 O emissions; the banana plantations evaluated in this study presented higher clay contents than forest and the higher N 2 O emissions (Gu et al, 2019). As observed in several fruit orchards, our results suggested the seasonality as a factor influencing the differences in N 2 O fluxes by affecting soil moisture and temperature (Gu et al, 2019; Nishisaka et al, 2019; Zhu et al, 2015). Soil temperature was correlated with N 2 O fluxes in banana plantation scenarios, remaining high in the wet season and dropping in the dry season (averaged 28°C and 25°C, respectively).…”

Taxonomic and nitrogen-cycling microbial community functional profiles of sugarcane and adjacent forest soils in Southeast Brazil

“…These differences may be associated with the soil characteristics such as nutrient availability, moisture, and texture, which are also determinants to the microbiallymediated biogeochemical processes. 16…”

“…12 The shotgun metagenomic sequencing and bioinformatic analysis are important tools to quantify the abundance and distribution of microbial taxa at the community ecological level, gene families involved in soil microbial functions and nutrient metabolism belowground. 13 The size, composition, and function of these microbial communities are affected by land-use, 14,15 sazonality, 16 agricultural practices, 17,18 and others environmental changes. De Caceres, Legendre, and Moretti 19 consider that differential abundances in microbial taxa and functional genes can be used as potential bioindicators for environmental change.…”

Soil denitrification rates are more sensitive to hydrological changes than restoration approaches in a unique riparian zone

“…Hydrological change (i.e. altering flooding intensity and frequency) is a key determinant of denitrification in riparian ecosystems by changing redox conditions, given denitrification processes prefer the anoxic/anaerobic conditions (Gergel et al, 2005;Gu et al, 2012;Nishisaka et al, 2019;Shrestha et al, 2014;Ussiri & Lal, 2012;Venterink et al, 2002;Vidon et al, 2010). Frequent flooding enhances the reduction of N via coupled nitrification-denitrification (Bai et al, 2007), and flooded sites may act as denitrification hotspots with a short wetting and drying cycle (Tomasek et al, 2017(Tomasek et al, , 2019.…”