Wild pigs mediate far-reaching agricultural impacts on tropical forest soil microbial communities

Edge effects, the altered abiotic and biotic conditions on the borders of natural areas, rarely extend more than a few hundred meters. Edge effects have rarely been linked to altered soil biota, which shape ecosystem processes including carbon storage, biogeochemical cycling, and plant performance. Here, we investigated if agriculturally-mediated increased wildlife populations affect soil biotic communities at a distance well over that of estimated edge effects when they move between agriculture and natural habitats using a 22-year fenced exclusion experiment in a primary rainforest in Peninsular Malaysia. We found that the presence of wildlife (mainly native pigs (Sus scrofa) that crop-raid in nearby oil palm plantations) was associated with higher bacterial diversity, and an altered community composition (mediated by changes in soil pH), and reduced abundances of symbiotic ectomycorrhizal fungi compared to soil in exclosures. There were only minor effects of pigs on soil chemistry or microclimate, so we suggest that changes in soil communities are driven by pigs' leaf litter removal and alterations to plant composition. Our study highlights that indirect effects from agriculture can be transferred by wildlife >1 km into protected areas and this could have important repercussions for ecosystem processes and plant-soil feedbacks.

Analysis of canopy structural and functional properties of tropical forests in a fertilisation experiment by Sentinel-2 images

<p>Tropical forests such as Amazon is repository of ecological services. Understanding how tropical forest responds to the climate helps to improve ecosystem modeling and declining the uncertainty in calculation of carbon balance. Nowadays, the availability of very high resolution satellite imagery such as Sentinel-2 are powerful tools for analyzing the canopy structural and functional shifts over time, especially for tropical forest.</p><p>In this study, we examined the effect of the nutrient availability (nitrogen (N) and phosphorus (P)) on canopy and structural properties in tropical forest of French Guiana. In situ observations of canopy structure and functioning (i.e. photosynthesis, leaf N, chlorophyll content) were collected at two experimental sites (Paracou and Nouragues). Three topographical positions in each site were considered (top of the hills, middle and bottom end of the slope) and four plots were manipulated with different level of fertilization (Control, N, P, NP) in September 2016. Statistical analysis were conducted to analyze how the fertilization affect the forest canopy seasonality and if differences between sites and across positions existed. Furthermore, we tested whether Sentinel-2 data could help or not to describe the canopy changes observed in the field. Therefore, all Sentinel-2 images available before the start of the experiment, which date represent the natural situation, and two years after the intensive and repeated fertilization were collected. Greenness, chlorophyll and N, P related indicators were calculated from Sentinel-2 images.</p><p>Key words: Sentinel-2, Tropical forest, soil fertilization, topographical position.</p>

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Soil organic carbon (SOC) dynamics represent a persisting uncertainty in our understanding of the global carbon cycle. SOC storage is strongly linked to plant inputs via the formation of soil organic matter, but soil geochemistry also plays a critical role. In tropical soils with rapid SOC turnover, the association of organic matter with soil minerals is particularly important for stabilising SOC but projected increases in tropical forest productivity could trigger feedbacks that stimulate the release of stored SOC. Here, we demonstrate limited additional SOC storage after 13–15 years of experimentally doubled aboveground litter inputs in a lowland tropical forest. We combined biological, physical, and chemical methods to characterise SOC along a gradient of bioavailability. After 13 years of monthly litter addition treatments, most of the additional SOC was readily bioavailable and we observed no increase in mineral-associated SOC. Importantly, SOC with weak association to soil minerals declined in response to long-term litter addition, suggesting that increased plant inputs could modify the formation of organo-mineral complexes in tropical soils. Hence, we demonstrate the limited capacity of tropical soils to sequester additional C inputs and provide insights into potential underlying mechanisms.