The effect of environmental factors and root system on CO2 efflux in different types of soil and land uses

Carbon dioxide (CO2) efflux from 0-5 cm topsoil layer in conventional tillage plots, in grassland and forest Retisol (in West Lithuania in a hilly terrain) and Cambisol (in Central Lithuania in a plane terrain) was investigated using a closed chamber method. The soil CO2 efflux was measured six times per growing season from April to August in 2018. Soil temperature and the volumetric water content were recorded at 5 cm depth at the same time as soil CO2 efflux measurements. Small soil monoliths were collected for the measurements of plant root parameters within 0-10 cm layer and were investigated later in the laboratory. In Cambisol, the efflux values ranged from 0.20 to 2.67 mu mol CO2 m(-2) s(-1) under conventional tillage, from 1.10 to 3.41 mu mol CO2 m(-2) s(-1) in grassland and from 0.89 to 2.28 mu mol CO2 m(-2) s(-1) in forestland. In Retisol, the efflux values varied from 0.81 to 3.54 mu mol CO2 m(-2) s(-1) under conventional tillage, from 1.23 to 2.69 mu mol CO2 m(-2) s(-1) in grassland and from 0.88 to 2.06 mu mol CO2 m(-2) s(-1) in forestland. The soil temperature varied from 11.5 degrees C to 33.6 degrees C during the experimental period and averaged 22.8 degrees C and 21.1 degrees C at 5 cm depth in Cambisol and Retisol, respectively. The volumetric water content at 5 cm depth averaged 18.7% and 23.9% in Cambisol and Retisol, respectively. The volumetric water content in Cambisol was markedly lower than in Retisol during the whole experimental period. The maximum root volume within 0-10 cm depth was determined in grassland Retisol. Root volume under conventional tillage in Cambisol was 6.2-fold lower, in Retisol - 5.1-fold lower, in forest Retisol - 1.9-fold lower, in forest Cambisol - 1.4-fold lower and in grassland Cambisol - 1.1-fold lower compared to grassland Retisol. Average CO2 efflux from Retisol was 12% lower than that from Cambisol. Soil CO2 emission decreased in the following order: Cambisol - grassland > forestland > conventional tillage plots and Retisol - grassland > conventional tillage plots > forestland. Volumetric water content was found to increase soil CO2 efflux; however, at the content higher than 20%, efflux decreased. A soil temperature of up to 25 degrees C increased soil CO2 emission. However, with a further increase in soil temperature, soil respiration decreased in both soil types investigated. The decrease in root volume and root length density depended on the land use: grassland > forestland > conventional tillage plots.