Available Forms of Nitrogen for Tundra Plants and Microbes…

Yesterday was a productive day for all NGEE Arctic teams working on the tundra. Today our group left the Herman House apartment with a couple of goals. One was to complete surface and pore water sampling for geochemistry; another was to continue vegetation resurveys for the purpose of fine-scale mapping of plant functional types (PFTs) across polygons. Mallory and I also wanted to finish sampling of soils that she began two days ago for analysis of nitrogen availability. While Mallory has not yet developed the full scope of her PhD studies, she is interested in better understanding the interplay between soil organic matter decomposition and the forms of nitrogen ultimately made available for plants and microbes. More specifically Mallory would like to combined advanced analytical methods with some aspect of plant and microbial biology, and therein characterize the pool size and diversity of low molecular weight (LMW) nitrogenous compounds in soils. There is a considerable amount of published literature on nitrate and ammonium availability in tundra soils, but LMW compounds that can be used by plants and microbes as a source of nitrogen are also important. However, they have not been fully characterized. Working with Bob Hettich and Rich Norby at ORNL and as a student through the Bredesen Center for Interdisciplinary Studies and Graduate Education, Mallory has the opportunity to merge powerful mass spectroscopic approaches (MALDI and electrospray ionization sources) and field ecology, into a single program of study. But before she can do this, Mallory needed to obtain a range of samples from the Barrow Environmental Observatory (BEO) so she could conduct preliminary studies to refine her techniques and then, equally important, the questions that Mallory would like to tackle will also need to be developed. She identified plots within low- and high-center polygons and excavated a small monolith of soil from the upper active layer. She did this at a number of locations making sure that she had adequate replicates and samples for areas that supported the growth of several different plant species. This way Mallory can assess her early work in terms of variation in nitrogenous compounds due to topographic location and species composition. Once samples were collected they were labeled, placed in plastic bags, packed into a cooler, and will be shipped to ORNL later this evening. Mallory will be busy during the coming months and it will be interesting to see how her research develops both with regards to fundamental science and integration of that knowledge into models.