Causes of Decreases in Residual Carbohydrase Activity in Soil During Old-Field Succession

Abstract

Previous work demonstrated that activities of residual carbohydrases in soil decrease during ol—field succession. We hypothesized that this decrease in carbohydrase activity might be due to a decrease in the carbohydrate: lighnin ratio of plant material added to the soil during succession. The carbohydrate: lignin ratio of randomly collected underground material was found to decrease from a high in the first stage to a low in the climax prairie. This was not true, however, of the tops. When plant material was added to climax soil, the highest average numbers of actinomycetes, bacteria, and fungi occurred in soil to which Stage 1 tops or underground material was added, with 1 exception. Relative effects of Stage 2 and climax materials were not clear even after 6 mo. Soil amended with tops or underground plant material from the first successional stage yielded the highest number of species of fungi (41) and the lowest number of species occurred in soil ammended with Stage 2 material (33). Ten of the 51 species isolated never occurred in soil ammended with Stage 1 plant materials, 18 never occurred in soil amended with Stage 2 materials, and 17 never occurred in soil amended with climax materials. Thus, the type of successional plant material added to climax soil markedly affected kinds of microorganisms as well as numbers. Stage 1 underground materials resulted in significantly higher activities of invertase and amylase than did Stage 2 and climax underground materials. In the case of cellulase, Stage 1 and climax underground material had simiar effects and both had significantly greater effects than did Stage 2 materials. In contrast to effects of undergound materials, climax tops elicited the highest activities of amylase and cellulase. In the case of invertase, Stage 1 and the climax tops resulted in similar activities. Our hypothesis was not well supported because invertase activity was the only carbohydrase activity significantly correlated with the carbohydrate:lignin ratio of added plant material, based on polynomial regression. Our data did clearly demonstrate that the decrease in activities of invertase, amylase, and cellulase during old—field succession results from the quality of plant material added during each stage. Clearly, this is the underground material which has the chief influence on activities of the carbohydrases. No single chemical constituent of the added material appears to be chiefly responsible for the decline in activity of the carbohydrases during old—field succession.