Seasonal changes in carbon and nitrogen metabolism of Brachiaria decumbens in a long-term silvopastoral system

Abstract

Our objective was to quantify the metabolites involved in the carbon and nitrogen metabolism of leaf blades of Brachiaria decumbens grown under conditions of intense shade (69%) in the understory of a silvopastoral system (SPS) and compare them to B. decumbens leaf blades grown in an open pasture (OP) under full sunlight. Two treatments corresponding to the specific production system (SPS and OP) were evaluated over four seasons: Spring 2016, Summer 2017, Autumn 2017, and Winter 2017. In the SPS, we observed an increase in the levels of nitrogen-related metabolites (chlorophyll, nitrate, amino acids and total soluble proteins) and a reduction in carbon-related metabolites (total soluble carbohydrates, malate, fumarate, starch and sucrose) relative to those in the OP. This pattern of response was also influenced by the seasons, with higher levels of nitrogen-related metabolites present during seasons with a greater availability of growth resources. In contrast, most carbon-related metabolites were lower in the spring and summer and higher in the autumn and winter; only sucrose and starch were higher in the spring and winter. Our results demonstrated that intense light restriction in an SPS affects the productivity, longevity and nutritional value of the forage by reducing the levels of metabolites involved in carbon metabolism and increasing the metabolites involved in nitrogen metabolism.