Do improved pastures affect enzymatic activity and C and N dynamics in soils of the montado system?

Abstract

A B S T R A C TVast montado areas are threatened by degradation, as the result of a long history of land use changes. Since improved pastures have been installed aiming soil quality improvement and system sustainability, it is crucial to evaluate the effects of these management changes on soil organic matter status and soil biological activity, as soil quality indicators. Therefore, a 35-yr old improved pasture and a natural pasture were studied, considering areas beneath tree canopy and in the open. Total organic C, total N, hot water soluble (HWS) and particulate (POM) C, microbial biomass C (MBC) and N (MBN), C mineralization rate (CMR) and net N mineralization rate (NMR) were determined. In addition, for a 1-yr period, soil β-glucosidase, urease, proteases and acid phosphomonoesterase were periodically determined. Improved pasture promoted the increase of soil C and N through POM-C increment, particularly beneath the trees canopies. The two study pastures did not show differences regarding soil microbial biomass, but variations in CMR, HWS-C and N availability (proteases and urease activities) suggest divergent soil microbial communities. Tree regulator role on C, N and P transformation processes in soil was confirmed.Keywords: C and N mineralization rates; evergreen oak woodland management; organic matter fractions; soil enzymes; soil microbial biomass. R E S U M OMuitas áreas de montado estão em risco de degradação como resultado de um longo historial de modificações de uso. Nalgumas áreas foram instaladas pastagens melhoradas, visando melhoria da qualidade do solo e a sustentabilidade do sistema. Os efeitos desta alteração de gestão foram avaliados comparando uma pastagem melhorada com 35 anos e uma pastagem natural, considerando-se áreas sob e fora da influência das copas. Determinaram-se os teores de C orgâncio e N total, de C das fracções solúvel em água quente (HWS) e particulada (POM) e de C e de N na biomassa microbiana (MBC e MBN), e as taxas de mineralização de C e N (CMR e NMR). Determinaram-se ainda periodicamente as actividades das enzimas β-glucosidase, urease, proteases e fosfomonoesterase ácida do solo. A pastagem melhorada promoveu o aumento de C e N do solo através do aumento do C da POM, principalmente em áreas sob a copa das árvores. A biomassa microbiana do solo não distinguiu as duas pastagens, mas diferenças na CMR, no HWS-C e na disponibilização de N (actividade das proteases e da urease) sugerem comunidades microbianas do solo divergentes. Confirmou-se o papel regulador das árvores sobre os processos de transformação do C, do N e do P no solo.Palavras-chave: biomassa microbiana do solo; enzimas do solo; fracções de matéria orgânica; gestão do montado; taxas de mineralização de C e N.

Following the Turnover of Soil Bioavailable Phosphate in Mediterranean Savanna by Oxygen Stable Isotopes

“…We expect that the soil phosphate δ 18 O P values will be affected by the soil microbial biomass, as found by previous studies (Angert et al, ; Gross & Angert, ; Tamburini et al, ). In the current study, we are interested in exploring how the P turnover by the microbiota (P microbial turnover rate) will change under N and P fertilizer treatments, and under tree canopies (in which the carbon, soil moisture, and nutrient content are higher; Rodrigues et al, ), and in comparing the result of this study to P turnover rates estimated by the same method in tropical soils (Gross, Turner, et al, ).…”