Wednesday, June 20, 2012

Physiological ecology and plant functional types

As a physiological ecologist, the NGEE Arctic science question that is especially exciting to me is one related to plant functional types and the way climate models represent vegetation dynamics. We know that plant composition differs by position on the landscape, for example rims and troughs of low- and high-centered polygons, but the controls on this dynamic are unclear. Our team plans to address this question by focusing on water and nutrient acquisition strategies and by understanding how this translates to critical carbon cycle processes for plants and plant communities across the tundra.

It was, therefore, great to have Alistair Rogers (BNL) bring his photosynthesis system to Barrow this week. In a preliminary test of this apparatus, Alistair and Victoria Sloan gathered leaves from various plant species and subjected them to measurements of photosynthesis. Alistair targeted spot measurements of gas exchange, light response curves, and A/Ci curves. The latter provides mechanistic insights into the biochemical controls on gas exchange. Each of these three approaches provides unique information for models.

Over the summer, we will be taking many measurements of leaf gas exchange; and taking them on many plant species. We will relate these results to water and nutrient acquisition strategies and, over time, build new representations of plant functional types for models.

One of the several representations we will explore is that of relating nitrogen allocation and storage strategy to leaf CO2 uptake. We already have a nitrogen allocation model developed by Chonggang Xu at LANL that we will evaluate for this purpose. Chonggang just published his model in PLoS ONE, so we are ahead of the game in this regard. David McGuire and Eugenie Euskirchen, both from the University of Alaska Fairbanks, and Dan Hayes (ORNL) will be helpful as we begin to model these dynamic processes and incorporate them into models.

Alistair and Victoria will get new information over the next few days, and then we will formulate a plan forward in conjunction with our NGEE Arctic modelers .