Consequences of forest conversion to pasture and fallow on soil microbial biomass and activity in the eastern Amazon

Abstract

The main change in soil use in Amazonia is, after slash and burn deforestation followed by annual crops, the establishment of pastures. This conversion of forest to pasture induces changes in the carbon cycle, modifies soil organic matter content and quality and affects biological activity responsible for numerous biochemical and biological processes essential to ecosystem functioning. The aim of this study was to assess changes in microbial biomass and activity in fallow and pasture soils after forest clearing. The study was performed in smallholder settlements of eastern Brazilian Amazonia. Soil samples from depths of 0–2, 2–5 and 5–10 cm were gathered in native forest, fallow land 8–10 yr old and pastures with ages of 1–2, 5–7 and 10–12 yr. Once fallow began, soil microbial biomass and its activity showed little change. In contrast, conversion to pasture modified soil microbial functioning significantly. Microbial biomass and its basal respiration decreased markedly after pasture establishment and continued to decrease with pasture age. The increase in metabolic quotient in the first years of pasture indicated a disturbance in soil functioning. Our study confirms that microbial biomass is a sensitive indicator of soil disturbance caused by land‐use change.

Effect of Water Availability on Soil Microbial Biomass in Secondary Forest in Eastern Amazonia

“…The values for SMBC and SMBN agreed with results of earlier studies conducted in the same region (Rangel-Vasconcelos et al, 2005;Sotta et al, 2008;Lopes et al, 2011;Melo et al, 2012). Bittencourt et al (2006) found a higher SMBN content in Amazonian soils under secondary vegetation in the rainy season.…”

“…The values of basal respiration were higher than those found by previous studies conducted in Amazonia: 0.81 μg g -1 h -1 of C-CO 2 (Luizão et al, 1992), 0.35 to 0.70 μg g -1 h -1 of C-CO 2 (Gama-Rodrigues et al, 1994), and 0.85 to 1.11 µg g -1 h -1 C-CO 2 (Melo et al, 2012). This may have been a result of soil-climatic differences, as well as differences between the methods used to determine basal respiration.…”

Factors explaining variability in woody above-ground biomass accumulation in restored tropical forest

“…Interestingly, in our study, duration of pasture use was not strongly correlated with any soil physical or chemical variables, although it is possible that there may be differences in compaction or soil nutrient concentrations at greater soil depths that were not analyzed. Another possibility is that long pasture usage affected microbial communities; increasing intensity of past land use can substantially affect biotic communities including microbes, mycorrhizae and potentially root herbivores (Carpenter et al, 2001;Melo et al, 2012;Araujo et al, 2013).…”

Indicadores de qualidade de Latossolo relacionados à degradação de pastagens

“…A atividade microbiana foi estatisticamente maior (p=0,012) em área de mata (68,56 mgC-CO 2 100 cm -3 ) do que no nível de degradação alto (41,9 mg C-CO 2 100cm -3 ). Melo et al (2012) também observaram maiores taxas de emissão de CO 2 , em Latossolo sob floresta, do que em pastagem de Urochloa. Segundo os autores, isso pode ocorrer em consequência da contínua adição de resíduos vegetais diversificados e mais lábeis, que estimulam os microrganismos heterotróficos e a ciclagem de nutrientes.…”