PROJECT PROFILE: Soil Warming and Hardwoods

By Sarah Gray

Here at the Harvard Forest, I am working on the effects of soil warming on various hardwoods. There has already been an experiment to test the effects of global warming on soil. The 20-year-long experiment found that with increased soil temperatures there was an increase in microbial activity. This increase in microbial activity led to more usable nitrogen in the system. Nitrogen is the limiting nutrient in tree growth; with more nitrate and ammonium availability, trees can continue to grow. Ammonium can easily be made into many amino acids, proteins, which the tree can use. However, nitrate, the other form of nitrogen, cannot be used to make proteins. Nitrate needs to be broken down into ammonium. Trees make this enzyme, called nitrate reductase, which reduces nitrate to ammonium. My project this summer is measuring the amount of nitrate reductase enzymes in Oak, Sugar Maple, Red Maple, and Birch. My mentors and I measure trees at Barre Woods where there are two twenty meter plots, one heated and one controlled. This summer we started measuring trees grown with different fertilizer treatments in the greenhouse. We measured both the roots and the leaves to compare nitrate reductase activity.

On a day-to-day basis, my activities vary between working in the lab to working in the field. It is the perfect mix for me since I am majoring in chemistry, but plants are my passion. In the lab, I measure the amount of nitrate reductase by using an indicator and a spectrophotometer. Out in the field, I collect samples and take soil cores. In the greenhouse, I fertilize, water, and deal with pests. In the beginning I did a lot of reading to formulate a protocol for testing roots since it had never been done before in the experiment.

The project is in its second year of testing. In future years they will continue to test nitrate reductase activity to see if there is any pattern between species or the different plots. There might be a competitive advantage among species if the tree is capable of using nitrate. For the rest of the summer, I will be analyzing the various data I have collected to see if there is any correlation.