Moreira, M. Z. | bioRxiv Science

bioRxiv2024

Liming pasture soils in the Amazon region promotes low-affinity methane oxidation by type I and II methanotrophs

In the Amazon Forest region, cattle pastures are the main land use subsequent to deforestation. This land-use change affects the soil microbial community and methane fluxes, shifting the soil from a methane sink to a source. Soil physical and chemical attributes are changed due to slash-and-burn processes, including an increased soil pH after forest-to-pasture conversion. Without amendments, the pasture soils can become acidic again resulting in many cases in soil degradation. Liming is a standard management practice to increase soil pH while decreasing Al3+ availability. Liming is important to recover these degraded lands and increase soil fertility, but its impact on soil methane cycling in tropical soils is unknown. Here we investigated the role of soil pH on methane uptake under high concentrations of the gas. The top layer of forest (pH 4.1) and adjacent pasture soils (pH 4.8) from the Eastern Amazon were subjected to liming treatment (final pH 5.8) and incubated with [~]10,000 ppm of 13CH4 for 24 days to label DNA with 13C. Soil DNA was evaluated with Stable Isotopic Probing (SIP-DNA), methanotrophic abundance was quantified (pmoA gene), and high throughput sequencing of 16S rRNA was performed. Liming increased the methane uptake in both forest ([~]10%) and pasture ([~]25%) soils. Methanotrophs Methylocaldum sp. (type I) and Beijerinckaceae (type II) were identified to actively incorporate carbon from methane in limed pasture soils. In limed forest soils, Nitrososphaeraceae, Lysobacter sp., and Acidothermus sp. were identified as 13C-enriched taxa. The enrichment of the archaeal family Nitrososphaeraceae, known as ammonia oxidizers, is correlated with an increase of ammonia monooxygenase genes, which code for an enzyme complex with wide substrate specificity that can also perform methane oxidation. In conclusion, liming Amazonian pasture soils not only contributes to the fertility and recovery of degraded areas but also has the potential to improve the oxidation of methane at high concentrations of this gas.

ecology↗

bioRxiv2020

Prey choice of the common vampire bat on introduced species in an Atlantic forest land-bridge island

The proliferation of native, alien, invasive and domestic species provide novel and abundant food resources for the common vampire bat (Desmodus rotundus) that could alter its prey preference. Based on the analysis of carbon and nitrogen stable isotopes, we report the prey choice of D. rotundus on introduced mammals in an tropical land-bridge island where the domestic animals were removed and 100 individuals of 15 mammal species were intentionally introduced. Our analysis shows that, D. rotundus on Anchieta Island were more likely to prey upon species from open habitats (mean value of -14.8{per thousand}), i.e., animals with high {delta}13C values characterized by the consumption of C4 resources. As expected for a top predator species, {delta}15N values for D. rotundus were higher (mean value of 8.2{per thousand}) and overlapped the niche of the capybaras (Hydrochoerus hydrochaeris) from the Anchieta Island, while it was distant from coatis, and also from those potential prey from the preserved area in the mainland, including the capybaras, indicating that among all potential mammalian prey species, they fed exclusively on capybaras, the highest mammalian biomass on island. Based on previous information on human occupation, the domestic animals present on Anchieta island might be the main prey of D. rotundus and responsible for maintaining a viable population. As the capybaras were introduced only 36 years ago, this suggests a rapid prey shift due to anthropogenic disturbances, which has allowed common vampire bats to successfully exploit them. Literature records also show that common vampire bats were not captured in preserved areas of the mainland which are near Anchieta Island indicating that the percentage of capture of D. rotundus is usually low in natural forested habitats where potential prey are scattered. As three individuals of introduced capybaras were confirmed died from bat rabies viruses (RABV) in 2020, we suggest periodic monitoring of bat rabies viruses in common vampire bat populations on Anchieta Island and areas nearby, in order to quantify the magnitude of the outbreak area and develop strategies for controlling, especially considering that the island and areas nearby is frequently visited by tourists. We highlighted that this prey choice is context-dependent, and possibly influenced by the removal of domestic animals, the explosive population growth of introduced capybaras combined with their predictable foraging behavior.

ecology↗