Does cropping modify the decomposition function and the diversity of the soil microbial community of tropical fallow soil?

Abstract

This study considers the relationship between microbial diversity and soil organic decomposition function of two soils whose microbial diversity was first established using molecular biology (DGGE) and in situ catabolic potential (ISCP). The soil used was a tropical ferruginous Oxisol, with samples taken from a 21-year fallow and a plot that had been cultivated for 4 years after lying fallow for 17 years. The samples from the 0–10 cm soil layer were incubated with or without the addition of Faidherbia albida litter under laboratory conditions (28 °C, 100% WHC) for 240 h. During incubation, the microorganism activity was measured (CO 2, mineral N, phosphatase, β-glucosidase and urease). In the unamended soil, the activity of the microorganisms was greater in the fallow soil which had a greater microbial diversity than that in the cultivated soil. However, other soil properties (carbon and organic nitrogen content, total microbial biomass) may also explain this result. For the amended soil, only the first 8 h of incubation showed a difference between the fallow and cultivated soil. During this period, the CO 2 respiration in the fallow soil was higher than that recorded in the cultivated soil. This difference should be compared with the catabolic microbial diversity, which was higher in the fallow soil than in the cultivated soil. After this initial phase, the microbial community in the cultivated soil seemed to acquire similar functions to those in the fallow soil. The phosphatase and β-glucosidase activities of the amended soils were higher in the fallow soil. This difference was maintained for the whole incubation period. The redundancy of microbial functions is discussed.