Soil Organic Matter Responses to Anthropogenic Forest Disturbance and Land Use Change in the Eastern Brazilian Amazon

Abstract

Anthropogenic forest disturbance and land use change (LUC) in the Amazon region is the main source of greenhouse gas emissions to the atmosphere in Brazil, due to the carbon (C) and nitrogen (N) emitted from vegetation clearance. Land use conversion associated with management practices plays a key role in the distribution and origin of C in different soil organic matter (SOM) fractions. Here, we show how changing land use systems have influenced soil C and N stocks, SOM physical fractions, and the origin of SOM in the Santarém region of the eastern Brazilian Amazon. Soil C and N stocks were calculated for the surface layer of 0-30 cm. Anthropogenic disturbances to the standing forest, such as selective logging and wildfires, led to significant declines in soil C and N stocks. However, in the long-term, the conversion of the Amazon forest to pasture did not have a noticeable effect on soil C and N stocks, presumably because of additional inputs from pasture grasses. However, the conversion to cropland did lead to reductions in soil C and N content. According to the physical fractionation of SOM, LUC altered SOM quality, but silt and clay remained the combined fraction that contributed the most to soil C storage. Our results emphasize the importance of implementing more sustainable forest management systems, whilst also calling further attention to the need for fire monitoring systems, helping to ensure the resilience of C and N stocks and sequestration in forest soils; thereby contributing towards urgently needed ongoing efforts to mitigate climate change.

Hydraulic redistribution affects modeled carbon cycling via soil microbial activity and suppressed fire

“…Durigan et al. () measured ~4,500 gN/m 2 in surface soil (0–30 cm) in undisturbed forest, Santarem, Brazil; CLM4.5 output from BR‐Sa1 (also in Santarem) was 1,245 gN/m 2 (for 0–39 cm soil depth). For US‐Wrc, Binkley, Sollins, Bell, Sachs, and Myrold () estimated annual conifer nitrogen uptake at the Wind River Experimental Forest to be in the range of 5 kg ha −1 year −1 (based on estimates of annual biomass production and the nitrogen concentration of various tissue types), translating to 0.2 × 10 −7 gN m −2 s −1 .…”

Active rehabilitation of Amazonian sand mines converges soils, plant communities and environmental status to their predisturbance levels

“…With a mean temperature of approximately 25 C and an annual precipitation between 1,900 and 2,000 mm (Piló, Auler, & Martins, 2015), the climate of the region is tropical warm with rainy summers and dry winters; Aw in the Köppen classification (Alvares, Stape, Sentelhas, De Moraes Gonçalves, & Sparovek, 2013). The dominant vegetation types are evergreen dense or seasonal (semi)deciduous forests, and the main soils are oxisols and inceptisols (Aragão et al, 2009;Durigan et al, 2017).…”

Soil Carbon Dynamics in Soybean Cropland and Forests in Mato Grosso, Brazil

“…Soil texture controls C storage capacity (Desjardins et al, 2004;Feller & Beare, 1997;Parton et al, 1987;Six et al, 2002), with fine-textured soils having greater C capacity (Angers et al, 2011), but coarse-textured soils had slightly greater C increases with pasture use in the Amazon (Desjardins et al, 2004). Crop-based agricultural use in the Amazon has in some cases led to C losses, particularly under frequent tilling which can enhance decomposition by breaking up aggregates and mixing surface soil C into deeper soil layers (Carvalho et al, 2010;Durigan et al, 2017;Maia et al, 2010;Rittl et al, 2017). Less is known about changes in deep soil C after conversion to intensive agriculture at the scale of that in the southern Amazon, and deep soils are a focus of the work described here.…”