Short-term vs. Long-term Warming and Nitrogen Treatment Effects on Soil Carbon and Microbial Activity in a Temperate Old Field
Abstract
Climate warming and atmospheric nitrogen deposition, two elements of global change, are expected to exert strong effects on northern temperate ecosystems over the next century. I added new nitrogen addition and warming plots to a pre-existing nitrogen and warming field experiment in London, Ontario to compare the short-term (1-2 year; new plots) versus long-term (14-15 year; old plots) treatment effects on soil carbon and microbial activity. I used soil density fractionation and size fractionation to separate soil carbon fractions and analyzed carbon quality using Fourier-transform infrared spectroscopy (FTIR). I used extracellular enzyme assays to assess microbial activities. The soil organic matter free light fraction recovery increased with nitrogen addition in the old plots but decreased in the new plots. Interactions between warming and plot age were significant for some hydrolase enzymes. These results confirm short-term responses of soil carbon and microbial activity differed from long-term responses in this field experiment.