Abstract
Due to their relatively small sizes, temperate forest vernal pools are less studied than other wetlands, despite being potential biogeochemical hotspots in landscapes. We investigated spatial and temporal factors driving N2O and CH4 emission rates from vernal pools in a temperate forest. We determined higher N2O (3.66 ± 0.53 × 10−6, μg N2O/m2/h) and CH4 (2.10 ± 0.7 × 10−3, μg N2O/m2/h) rates in spring relative to fall (~50% and 77% lower for N2O and CH4 rates, respectively) and winter (~70% and 94% lower for N2O and CH4 rates, respectively). Soil organic matter, nitrate content and bacterial 16S rDNA, nirS, and norB gene abundances emerged as significant drivers of N2O rates, whereas, soil pH, organic matter content and mcrA abundance were significant drivers of CH4 rates. Denitrification gene abundances were negatively correlated with N2O rates, whereas mcrA abundance correlated positively with CH4 rates. Results suggest that CH4 rates may be directly coupled to methanogen abundance, whereas N2O rates may be directly impacted by a variety of abiotic variables and indirectly coupled to the abundance of potential denitrifier assemblages. Overall, additional studies examining these dynamics over extended periods are needed to provide more insights into their control.
Highlights
Vernal pools are ephemeral wetlands formed in relatively small permanent basins/depressions that experience periodic inundation and drying (Zedler 2003)
Biogeochemical processes in wetlands depend on the presence, composition, and activity of microbial populations that are capable of responding to seasonal changes in abiotic factors (Butterbach-Bahl et al 2013; Capps et al 2014)
N2O emission rates in bottomland (BL) vernal pools was ~35% higher relative to upland (UL) vernal pools in fall and winter; rates were higher in BL vernal pools (~ 46%) than in UL vernal pools in winter (P = 0.01), but not in fall (Fig. 1a)
Summary
Vernal pools are ephemeral wetlands formed in relatively small permanent basins/depressions (less than 2 m deep) that experience periodic inundation and drying (Zedler 2003). Biogeochemical processes in wetlands depend on the presence, composition, and activity of microbial populations that are capable of responding to seasonal changes in abiotic factors (Butterbach-Bahl et al 2013; Capps et al 2014). These microbial assemblages are Wetlands (2020) 40:721–731 crucial for the maintenance of ecosystem processes under fluctuating conditions (Allison and Martiny 2008). The uncertainty around this is because microbial diversity and abundances of functional populations vary spatially and seasonally, and the effects of changing environmental variables on functional groups within these assemblages are complex and not well-understood (Braker et al 2010; Dandie et al 2011; Hallin et al 2012; Chen et al 2015; Saarenheimo et al 2015)
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