Soil fungal communities and enzyme activities in a sandy, highly weathered tropical soil treated with biochemically contrasting organic inputs
Bhanudacha Kamolmanit, Patma Vityakon, Wanwipa Kaewpradit, Georg Cadisch, Frank Rasche
Department of Plant Science and Agricultural Resources, Khon Kaen University, Khon Kaen, Thailand.
The regulative effect of long-term application of biochemically contrasting organic inputs such as rice straw (4.7 g N; 6.5 g polyphenols), groundnut stover (22.8 gN; 12.9 g polyphenols) and leaf litter of tamarind (13.6 gN; 31.5 g polyphenols) and dipterocarp (5.7 gN; 64.9 g polyphenols) on fungal decomposers was studied in a tropical sandy soil. Fungal decomposers were assayed by 18S rRNA gene-based community profiling and were combined with measurements of selected enzyme activities. Dipterocarp residue application depressed fungal abundance, but promoted specialized decomposers (e.g., Aspergillus fumigatus and Anguillospora longissima) with increases in polyphenol oxidase activity. The degree of functional redundancy for invertase and B-glucosidase activities was induced after the addition of easily decomposable rice straw and groundnut stover. Higher N availability in the tamarind treatment increased, in contrast to low N rice straw, fungal abundance (i.e., Fusarium oxysporum, Myceliopthora thermophila, and Aspergillus versicolor) and promoted invertase and B-glucosidase activities, while peroxidase activity was depressed. In addition, N availability seemed to regulate not only decomposing soil fungi, but also the abundance of protozoan decomposers whose actual contribution to N turnover in soils is still poorly understood. Prospective research should thus consider apart from studying decomposing fungi also protozoa and bacteria to better understand the microbially mediated degradation of complex organic materials in soils.