Relationships between microbial activity and soil physical and chemical properties in native and reforested Araucaria angustifolia forests in the state of São Paulo, Brazil

Rafael L. de F. Vasconcellos,Jamil de Morais Pereira,Dilmar Baretta,Elke Jurandy Bran Nogueira Cardoso,Daniel Bini

doi:10.1590/s0100-06832013000300003

Abstract

Araucaria angustifolia (Bert.) O. Kuntze is the main component of the Mixed Ombrophilous forest and, in the State of São Paulo, it is associated with a high diversity of soil organisms, essential for the maintenance of soil quality, making the conservation of this ecosystem a major and pressing challenge. The objective of this study was to identify the physical and chemical properties that are most closely correlated with dehydrogenase enzyme activity, basal respiration and microbial biomass under native (NF) and replanted (RF) Araucaria angustifolia forests in three regions of the state of São Paulo, in winter and summer. The main differentiating factors between the areas were also determined. Each forest was represented by three true replications; at each site, from around the araucaria trees, 15 soil samples (0-20 cm) were collected to evaluate the soil physical, chemical and microbiological properties. At the same points, forest litter was sampled to assess mass and chemical properties. The following microbiological properties were evaluated: microbial biomass carbon (MBC), basal respiration (CO2-C), metabolic quotient (Q: CO2), dehydrogenase enzyme activity (DHA) as well as the physical properties (moisture, bulk density, macroporosity and total porosity), soil chemical properties [pH, organic carbon (org-C), P, Ca, K, Mg, Al, H+Al], litter dry mass, and C, N and S contents. The data were subjected to analysis of variance (TWO-WAY: ANOVA). A Canonical Discriminant Analysis (CDA) and a Canonical Correlation Analysis (CCA) were also performed. In the soil under NF, the values of K, P, soil macroporosity, and litter dry mass were higher and Q: CO2 and DHA lower, regardless of the sampling period, and DHA was lower in winter. In the RF areas, the levels of moisture, porosity and Q: CO2 were higher in both sampling periods, and DHA was higher in winter. The MBC was only higher under NF in the summer, while the litter contents of C, N and S were greater in winter. In winter, CCA showed a high correlation of DHA with CO2-C, pH and H+Al, while in the summer org-C, moisture, Mg, pH and litter C were more associated with DHA and CO2-C. The CDA indicated H+Al, available P, total porosity, litter S content, and soil moisture as the most discriminating variables between NF and RF, but moisture was the most relevant, in both seasons and CO2-C only in winter. The combined analysis of CCA and CDA showed that the contribution of the microbiological variables to a differentiation of the areas was small at both samplings, which may indicate that the period after reforestation was long enough to allow an almost complete recovery of the microbial activity.

Highlights

The area of occurrence of Araucaria forests was formerly huge in the south and southeast of the country, but inadequate exploration led to a significant shrinkage of the original area, which once covered approximately 253,000 km2
Areas with native (NF) and reforested (RF) forests with Araucaria angustifolia were selected in three regions of the State (Figure 1)
There was a reduction in the available K and P levels, coinciding with higher soil moisture, which may have accelerated waste decomposition because of greater use of these elements by the biological community of the soil

Summary

Introduction

The area of occurrence of Araucaria forests was formerly huge in the south and southeast of the country, but inadequate exploration led to a significant shrinkage of the original area, which once covered approximately 253,000 km. There are only 32,021 km (12.6 %) left, of which 981 km are permanently preserved, representing only 0.39 % of the original forest area (Ribeiro et al, 2009). For the preservation of this forest, the presence of a high diversity of arbuscular mycorrhizal fungi (Moreira et al, 2009) and diazotrophic bacteria (Lammel et al, 2007), heterotrophic bacteria and archaebacteria (Maluche-Baretta, 2007; Bertini, 2010), and soil invertebrates (Merlim, 2005; Baretta et al, 2010) is fundamental. Conservation is an urgent issue that must be addressed without delay, since the soil quality is fundamental, for food, timber, fiber, and fuel production, and for the maintenance of biodiversity and environmental quality (Doran & Zeiss, 2000; Bastida et al, 2006; Kaschuk et al, 2010)

Objectives

Methods

Results

Conclusion