Soil engineering by macroinvertebrates: controls on soil organic matter storage across land use change

Abstract

The Cerrado biome concentrates priority areas for sugarcane expansion in the coming years, making it a threatened ecosystem and an important focus to develop scientific studies. This research will evaluate the carbon stocks, aggregates stability and diversity of soil macrofauna influenced by land use change resultant from sugarcane expansion in Brazilian Cerrado. The strategy to achieve the proposed objective will be to evaluate the main land-use sequence used for ethanol production in Brazil, i.e., the conversion of native vegetation to pasture and them the conversion from pasture to sugarcane under green management (without straw burning). These conversions will be analyzed at three different locations in the Cerrado biome. We assumed that soil organic carbon stabilization is largely controlled by interactions between the soil organic matter dynamics, abundance and diversity of soil macrofauna and soil aggregation. Therefore, will be quantified changes promoted by cerrado-pasture-sugarcane succession on: (i) abundance (numbers of individuals per unit area), biomass (fresh weight per unit area) and taxonomic richness (number of taxa per monolith) of soil macrofauna (earthworms and termites); (ii) soil aggregate fractions separated by wet sieving, and macro-aggregates fractions; (iii) soil carbon and nitrogen stocks; and (iv) humification degree of soil organic matter using laser-induced fluorescence spectroscopy. The soil sampling scheme will be replicated 9 times per land use (native Cerrado, pasture and sugarcane) in three major locations in South Central Brazil (located at Goiás, São Paulo and Minas Gerais states). The diversity of soil organisms will be estimated for litter and soil layers considering the sampling scheme. In each evaluated monolith, the organisms larger than 2 mm will be manually separated from the litter and from the evaluated soil layers (0-10 cm, 10-20 cm and 20-30 cm) and preserved in ethanol for later identification. The changes in soil carbon stocks will be determined from composite samples consisting of 12 cores. At each sampling scheme soil will be sampled at 0-10 cm, 10-20 cm and 20-30 cm to determine carbon and nitrogen content. Samples for bulk density and water stable aggregation will be collected after monolith extraction at three mentioned layers. Aggregate-associated organic carbon and its humification degree will be determined from aggregates fraction samples to study the ability of the soils (and its individual fractions) to store SOM through physical protection. We also intend to evaluate possible correlations between all parameters measured through multivariate statistical methods.