Decomposition of macrophytes and dynamics of enzyme activities in subalpine marshes in Lake Tahoe basin, U.S.A.

Abstract

To reveal the environmental and substrate quality effects on decomposition process and enzyme activities, litterbag experiments containing Nuphar and Carex leaves, Nuphar rhizome, and Ranunculus shoot, were carried in five-subalpine marshes in Lake Tahoe basin, USA. Alkaline phosphatase, β-glucosidase, and β-xylosidase activities were determined by a fluorogenic method using methyumbelliferyl substrates. Carex leaves, Nuphar rhizome and leaves, and Ranunculus shoots lost, respectively, 33, 67, 82 and 93% of original dry weight over 268 days. Decay rates were different among substrates but not among marshes. Nitrogen and carbon contents increased during the first 58 days and subsequently remained stable. Phosphorus content was stable during the experimental period except for a decrease in the first 16 days in Nuphar shoots. Enzyme activities in decomposing Carex and Nuphar leaves in four marshes were not significantly affected by environmental conditions. β-glucosidase and β-xylosidase activities in decomposing Carex leaves increased with time, but in other plant tissue these enzyme activities remained stable during experimental period. Enzyme activities were significantly different among decomposing substrates. Alkaline phosphatase activity was highest in Nuphar leaves (ca. 1286 µ-mole h−1 g DW −1) but lower and similar in other plant tissues (ca. 100 and 10 µ-mole h −1 g DW −1, respectively). This study showed differences in decay rates and enzyme activities rely on substrate and not the environment conditions of the study area. Decomposition rates in the early stage of decomposition were related to cumulative enzyme activities.