Effects of lanthanum on dehydrogenase activity and carbon dioxide evolution in a Haplic Acrisol

Rare earth elements (REEs) are applied widely to increase crop production in China but less attention has been paid to the principle adverse effects of the accumulation of REEs in soils. In this paper we studied the effects of lanthanum (La) on two indicators of microbial activity: dehydrogenase activity and CO2 evolution. The soil was collected from crop land of the Chinese Academy of Sciences' Red Soil Ecological Experimental Station. Application of La decreased soil pH and there were significant negative correlations between soil pH and added La. Significant positive correlations were also observed between 0.05 M HCl extractable La and added La, indicating that exogenous La was highly available in soil. Additions of La decreased soil dehydrogenase activity and the recorded maximum decrease was 64% after 1 day of incubation with an application of 1000 mg La/kg dry soil. The inhibition of soil dehydrogenase activity by La was gradually alleviated on prolonged incubation time. Addition of La at low concentrations slightly increased soil CO2 evolution but decreased it if at greater concentrations. The recorded maximum decrease in soil CO2 evolution was 33% after 56 days of incubation with an application of 1000 mg La/kg dry soil. The results in this paper indicated that agricultural use of REEs such as La at excessive levels would produce harmful effects to soil microbial activity and microbially mediated soil function. It is likely that change in soil dehydrogenase activity can be used as a sensitive indicator in assessing the level of REEs pollution in soil.

Soil CO2 evolution in Florida slash pine plantations. II. Importance of root respiration

Respiration of live roots was the single largest contributor to soil CO2 evolution in two mature slash pine (Pinuselliottii) plantations. Root respiration accounted for 51% of soil CO2 evolution at the 9-year-old plantation and 62% at the 29-year-old plantation. Additional estimates, calculated from data recorded from two small trenched plot sites at the 29-year-old plantation and based on possible variations in initial root biomass and subsequent decomposition rates, also averaged 62% of soil CO2 evolution. Specific root respiration averaged 0.40 g•g−1•year−1, varying from 0.34 to 1.70 g•g−1•year−1. Plots with larger proportions of fine roots had faster soil CO2 evolution rates.