Trees modify the dynamics of soil CO2 efflux in coffee agroforestry systems

Abstract

Agroforestry systems may help significantly reduce atmospheric carbon levels in forthcoming years through photosynthesis and regulation of soil CO2 efflux. This study aimed to characterise the soil CO2 efflux dynamics of coffee plants cultivated under agroforestry and full-sun production systems and identify the factors that regulate this process. The study was carried out in agroforestry and full-sun coffee systems on three family farms in Minas Gerais, the Atlantic Forest Biome, Brazil during three consective days on each farm. Twenty 1-m^2 sampling areas (10 for each system), each separated by a distance of 5 × 5 m and located between coffee plant rows, were selected on each farm. Soil physical and chemical attributes, air temperature and humidity, soil temperature and moisture, the percentage of canopy cover, and soil CO2 efflux were measured at each sampling area in the two systems. The air and soil temperature in the agroforestry systems were lower and soil moisture was higher than in the full-sun systems. Soil CO2 efflux showed different dynamics in the two systems. Daytime soil CO2 efflux was more stable (i.e. from morning to midday) in the agroforestry system (average 15% increase) compared to the full-sun system (average 49.1% increase). Soil CO2 efflux was regulated by labile carbon and total nitrogen variation in the agroforestry systems, and by soil temperature variation at a depth of 10 cm in the full-sun systems. A principal components analysis with data from all grouped systems showed that soil CO2 efflux was generally positively correlated with soil temperature at 5 and 10 cm depths, and negatively correlated with soil moisture. In conclusion, agroforestry systems promote microclimate stability and decrease soil CO2 efflux variability compared to full-sun systems.