An Invasive Succulent Plant (Kalanchoe daigremontiana) Influences Soil Carbon and Nitrogen Mineralization in a Neotropical Semiarid Zone

It has long been recognized that plant invasions may alter carbon(C) and nitrogen(N) cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant,Kalanchoe daigremontiana(Crassulaceae), on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes(C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease) between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall,our results showed that C mineralization and transformation of organic compounds to NH_4^+ were favored at sites colonized by K.daigremontiana. With this species, we found the highest cumulative amounts of NH_4^+-N and C and the lowest mineralization time.These results could be explained by higher activities of urease and glucosaminidase in soils under the influence of K. daigremontiana.In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion,invasion of Neotropical semiarid zones by K. daigremontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.

It has long been recognized that plant invasions may alter carbon （C） and nitrogen （N） cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant, Kalanchoe daigrernontiana （Crassulaceae）, on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes （C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease） between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall, our results showed that C mineralization and transformation of organic compounds to NH4^＋ were favored at sites colonized by K. daigrernontiana. With this species, we found the highest cumulative amounts of NH4^＋-N and C and the lowest mineralization time. These results could be explained by higher activities of urease and glueosaminidase in soils under the influence of K. daigremontiana. In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion, invasion of Neotropical semiarid zones by K. daigrernontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.