Pinus afforestation in South Brazilian highlands: soil chemical attributes and organic matter composition

Abstract

In the last three decades, exotic tree species are being introduced in the natural pastures of the highlands located at the northeastern part of Rio Grande do Sul State (RS), Brazil. This alteration of land use may impart drastic changes in the soil attributes. In this context, this work aimed to evaluate the impact of Pinus taeda afforestation on soil chemical attributes and organic matter (SOM) composition in Leptosols from Campos de Cima da Serra, RS. Soil samples under eight year old (Pi8) and 30 year old (Pi30) Pinus plantations and under native pasture (NP) were studied. Contents of exchangeable cations and of micronutrients and soil pH were determined. The SOM composition was investigated by means of elemental analyses and FTIR spectroscopy. The soil under pasture had a higher content of nutrients and of SOM in comparison to Pinus soils, reflecting the higher input and decomposition rate of the below ground added residue in the grassland environment. The SOM in pasture soils showed a higher content of carbohydrate and of structures derived from microbial metabolism. Besides the depletion of nutrients and of SOM, Pinus afforestation affected the SOM quality: following afforestation, the proportion of chemically recalcitrant structures and of carboxylic groups increased, whereas N-containing groups decreased.

Distribution of chemical compartments of soil organic matter and c stocks of a cambisol from south Brazil as affected by Pinus afforestation

“…22,28 As expected, C and N contents of whole soil (C and N), in all three environments, increased after HF treatment (Table 4) indicating that the inorganic components were mostly dissolved. 7 The recovered mass (M R ) after HF treatment of whole soil ranged from between 21 and 33% and these results are related to the samples' sand (granulometric fraction with diameter < 53 μm) content which was around 40%. Quartz grains occurring in the sand fraction are more resistant to HF treatment and tend to remain in the sample; while the minerals contained in clay (< 2 μm) and silt (2-53 μm) fractions are preferentially dissolved.…”

“…The depths were considered as sub-treatments (sub-plots). 7,24 The stock results of the different SOM chemical compartments (C T , N T , C CO , N CO , C FA , C HA , C HUI , C HUH and C LMW ) and those of the C:N ratios were submitted to variance analyses (two-way ANOVA) to verify the differences between environments and soil depths and the occurrence of interactions among environments and soil depths. The mean values obtained were analysed by the Bonferroni test at a 5% significance level.…”

“…However, in subtropical highland soils under Pinus taeda plantation, both a rise in soil C stock in a Nitosol (SC, Brazil) after 20 years cultivation, 6 as well as a depletion after 30 years of plantation in a Leptosol (RS, Brazil), was observed. 2,7 Besides C stocks of whole soil, SOM chemical compartments may also serve as good indicators of the impact of afforestation on SOM dynamics. 8,9 Pinus plantation may decrease fulvic acid content, 10 while Eucaplyptus can promote an elevation.…”

“…In a recent study investigating the impact of Pinus introduction on SOM of a Leptosol located in South Brazil, an increase in the chemical recalcitrance and carboxylic groups in the SOM structure was observed in addition to a decrease in C stocks, after 30 years of plantation. 7 In order to complement the information about exotic species' influence on SOM chemical composition of highland soils, we carried out this work, aiming to evaluate the impact of the introduction of Pinus taeda monoculture on the stocks of the different chemical compartments of SOM in a South Brazilian Cambisol. Soil chemical attributes and exchangeable cations were also evaluated.…”

Atributos químicos e área superficial específica em Latossolo subtropical de altitude sob usos e manejos distintos

“…O pH indicou tendência de acidificação, sendo, em média, 0,2 unidades inferior ao do CN, similar ao verificado em FP com idades entre 8 e 30 anos (DICK et al, 2011;MAFRA et al, 2008). A acidificação e a redução de bases em FP nos CCS decorrem da intensa lixiviação, da absorção de cátions pelo pinus e da liberação de ácidos orgânicos pela decomposição das acículas (MAFRA et al, 2008).…”