Effect of land use and seasonality on nematode faunal structure and ecosystem functions in the Caatinga dry forest

Abstract

Seasonally dry tropical forests are strongly affected by anthropogenic disturbance and climate changes, which represent the main threats to soil biodiversity, affecting the activity and functional composition of soil communities that provide crucial ecosystem functions and services. However, the effects of these factors and their interactions on soil nematodes, which are bioindicators of soil quality and health, remain poorly understood in the seasonally dry tropical forests. Thus, we investigated the effects of land use and seasonality on the structure and function of nematode components of the soil food web in Caatinga dry forest, north-eastern Brazil. The study was conducted in Catimbau National Park, Pernambuco State, which covers 607 km2 of Caatinga vegetation. Soil samples were collected in dry and rainy seasons in three types of land use: mature forest, agricultural areas, and secondary forest. We quantified the abundance, biomass carbon and metabolic footprint of each functional guild of nematodes. In this study, a total of 104 and 115 nematode genera were identified in the dry and rainy season, respectively. The biomass carbon and metabolic footprints of the total nematode assemblage, and of bacterivores, fungivores and omnivore-predators, were affected by types of land use and seasons. The soil organic carbon and metabolic footprints of nematodes were lower in agricultural areas than in mature forest and secondary forest, and lower in the dry season than in the rainy season. In all types of land use and in both seasons, we verified that most resource assimilation into the soil food web was via the bacterial channel. The enrichment footprint was positively related to the level of soil organic carbon and the structure footprint to the enrichment footprint. In turn, the interactive effect between types of land use and seasonality was observed only for soil organic carbon, biomass carbon of omnivore-predators and the fungal footprint. In general, the differences between types of land use became more significant during the rainy season. In general, our study indicates that change of land use and rainfall in the Caatinga affect the magnitudes of ecosystem functions of functional guilds of nematodes.