Enzymatic activity in relation to carbon cycling in temperate forest soils.

Abstract

Large amounts of carbon (C) are stored in soil organic matter, thus soils are a key component of the global C budget. Decomposition of organic matter occurs when microorganisms release enzymes which catalyze the breakdown of these carbon bonds. Four enzymes were tested in four different manipulated soil treatments. The four different treatments included a plot with double the amount of leaf litter on the soil surface, a plot with a normal amount of leaf litter on the surface, a plot where all leaf litter was removed from the surface and a plot where fertilizer was added to an area with normal amount of leaf litter. With the varying amounts and quality of litter inputs, relative enzymatic activity trends were observed. The four different soil treatments tested were replicated in three different blocks allowing for twelve different soil samples. Inverse relations between Cellulase activity and Phenol Oxidase activity suggest soil C storage is a function of microbial metabolism. Cellobiohydrolase, B-Glucosidase, Phosphatase and Phenol Oxidase are the four enzymes examined in each of the soil plots. The amount of activity calculated was compared to the amount of CO2 flux measured, carbon to nitrogen ratio, pH and root biomass. A one way analysis of variance showed that p values approach significant readings for %C, %N, CN, CO2 and trends are observed for Phenol Oxidase. In the presence of increased organic matter in the Double Litter plots, Phenol activity decreased. This is due to the surplus of energy rich cellulose found in the litter which makes phenol degradation unfavorable. Similarly, fertilizer plots provide a larger amount of Nitrogen which is another key microbial nutrient. Control plots have fewer nutrients than both Double Litter and Fertilizer plots. This makes phenol degradation more of a necessity; therefore, increased Phenol Oxidase activity was seen in the control plots. Organic matter is not present in the No Litter plots which explain the very small Phenol Oxidase activity observed. Enzymatic activity will be less efficient if global warming continues to the point that soil environments are raised temperatures and pH outside the optimum.