Environmental and microbial factors influencing methane and nitrous oxide fluxes in Mediterranean cork oak woodlands: trees make a difference

Abstract

Cork oak woodlands (montado) are agroforestry systems distributed all over the Mediterranean basin with a very important social, economic and ecological value. A generalized cork oak decline has been occurring in the last decades jeopardizing its future sustainability. It is unknown how loss of tree cover affects microbial processes that are consuming greenhouse gases in the montado ecosystem. The study was conducted under two different conditions in the natural understory of a cork oak woodland in center Portugal: under tree canopy (UC) and open areas without trees (OA). Fluxes of methane and nitrous oxide were measured with a static chamber technique. In order to quantify methanotrophs and bacteria capable of nitrous oxide consumption, we used quantitative real-time PCR targeting the pmoA and nosZ genes encoding the subunit of particulate methane mono-oxygenase and catalytic subunit of the nitrous oxide reductase, respectively. A significant seasonal effect was found on CH4 and N2O fluxes and pmoA and nosZ gene abundance. Tree cover had no effect on methane fluxes; conversely, whereas the UC plots were net emitters of nitrous oxide, the loss of tree cover resulted in a shift in the emission pattern such that the OA plots were a net sink for nitrous oxide. In a seasonal time scale, the UC had higher gene abundance of Type I methanotrophs. Methane flux correlated negatively with abundance of Type I methanotrophs in the UC plots. Nitrous oxide flux correlated negatively with nosZ gene abundance at the OA plots in contrast to that at the UC plots. In the UC soil, soil organic matter had a positive effect on soil extracellular enzyme activities, which correlated positively with the N2O flux. Our results demonstrated that tree cover affects soil properties, key enzyme activities and abundance of microorganisms and, consequently net CH4 and N2O exchange.

Drivers of Plot-Scale Variability of CH4 Consumption in a Well-Aerated Pine Forest Soil

“…Considering the entire un-stratified plot, spatial variability (evaluated as coefficient of variation CV) of the standardized CO2 and CH4 fluxes and non-standardized N2O flux was highest for N2O and similar for CO2 and CH4 (Tab. 1) and agrees well with data from literature [14,49]. Since the vegetation strata could explain some of the spatial variability of the soil gas fluxes at our site, our stratification approach reduced the CV for CH4 substantially, from 38% to 24% (Tab.…”

“…Few studies though could stratify or explain spatial variability of GHG fluxes on the plot scale. Shvaleva et al [49] showed that tree cover had an effect on net N 2 O fluxes and that CH 4 fluxes were affected by soil organic carbon content. Darenova et al [14] identified litter thickness and local soil moisture as important factors affecting CO 2 fluxes on the plots scale within a forest and grassland.…”

“…Studies comparing plots of different vegetation could show that tree species can affect CH 4 consumptions by soils [25,26,49,53,54]. Menyailo et al [26] observed that tree species had an effect on methanotrophic activity in an afforestation, but that the composition of high affinity methantrophs was not altered.…”

The superior effect of nature based solutions in land management for enhancing ecosystem services

“…Similarly, montado systems have a higher density and richness of ectomycorrhizal (ECM) fungal communities than regions with denser tree and shrub cover, due to lower competition; this can increase the resilience of the managed system due to improved nutrient acquisition, drought tolerance and pathogen resistance (Azul et al, 2010). The montado landscape has also been shown to have other effects such as lowering land surface temperature (Godinho et al, 2016) or affecting soil microbiology (Shvaleva et al, 2015) and soil fauna (Martins da Silva et al, 2015).…”

Atmospheric impact of nitrous oxide uptake by boreal forest soils can be comparable to that of methane uptake

“…Upland forest soils, even when well-aerated, can also act as a sink for atmospheric N 2 O. Periodic N 2 O uptake has been observed during dry periods in temperate Norway spruce forests (Bowden et al 1991;Klemedtsson et al 1997;Butterbach-Bahl et al 1998;Goldberg and Gebauer 2009), during spring and autumn in temperate Red pine (Bowden et al 1990) and Scots pine forests (Butterbach-Bahl et al 2002) and boreal pine dominated forest (Machakova et al 2019), in deciduous forests (Dong et al 1998;Goossens et al 2001), as well as in Mediterranean pine (Rosenkranz et al 2006) and oak forests (Shvaleva et al 2015). According to the best of our knowledge, data on N 2 O uptake from boreal spruce forests, an important coniferous forest type in the boreal region, is currently lacking.…”