Plant ecophysiology

Water and CO2 fluxes during leaf gas exchange
With partial support from the Fulbright Research Scholars program and in collaboration with the EcoFun team at INRA Bordeaux-Aquitaine and Bernard Genty at CNRS-CEA-Université Aix-Marseilles we are utilizing laser spectrometry and other tools to better constrain uncertainties in CO2 exchange with leaves and the interactions of CO2 with leaf water during photosynthesis and respiration. We are currently focusing on internal conductance to CO2, patterns of leaf water enrichment in 18O, and the role of carbonic anhydrase.

Deep rooting
A new project led by PhD student Rachel Roenfeldt seeks to explore the role of deep rooting in woody plants and to close key gaps in our understanding of this potentially important phenomenon. The project is focused on the degree to which climate, species characteristics and regional geology interact to affect the occurrence of deep rooting, as well as the dependence on deep water sources during dry periods. We're taking advantage of access to deep roots in caves located in Texas and Mexico and are developing new field experimental approaches to assess dependence directly.

Caatinga biogeochemistry
A collaborative project in the fascinating Caatinga of northeastern Brazil is ongoing, including the PhD project of Cynthia Wright who is focusing on key ecohydrologic processes. The Caatinga is a contiguous semiarid shrubland in northeastern Brazil that covers some 90,000 km2 or 12% of the country. From a socioeconomic standpoint it is of enormous importance—being home to a population of some 20 million people, many of whom are impoverished. The environmental conditions of the Caatinga are quite harsh; rainfall is generally low, the soils are poor, and droughts are frequent. In addition, the population of the region is continuing to increase.The goal of our project is to elucidate the fundamental ecophysiological, ecohydrological and biogeochemical processes that characterize Caatinga landscapes. We are collaborating in this effort with Brad Wilcox and several faculty at the Universidade Federal de Pernambuco and the Universidade Federal Rural de Pernambuco.

Isoscapes - scaling ecophysiological processes

Isoscapes capacity building
Isoscapes are maps of spatio-temporal variation in isotope ratios and are typically gridded products of spatially explicit modeling. Isotopes modeled can be stable (e.g., 18O) or radioactive (e.g., 14C) and include radiogenic isotopes such as 87Sr. Our group is interested primarily in the stable isotope ratios of the "light" elements : carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H), and oxygen (δ18O) and their utility in understanding a range of questions and systems.
In a collaboration with Gabriel Bowen and colleagues at Purdue, we developed web-based cyberinfrastructure for isoscapes

products and modeling, including access to necessary data sets and interactive data and model sharing. The IsoMAP project web page containing more in-depth description of the project may be found here. This project was funded through a grant from the National Science Foundation Division of Biological Infrastructure (0743543-DBI).

Ongoing work focuses on the degree to which spatial variation in precipitation and hydrologic processes interact with plant biophysical processes to affect the H and O isotope ratios of organic matter. Much of this work is collaborative and is designed to permit better interpretations of lipid H isotope ratios derived from sediments (e.g., from river systems in the Alps and Himalayas), but it also includes interpretation of tree rings and other paleo-records. Key collaborators here include Ansgar Kahmen and Dirk Sachse and their students and postdocs, and more recently Greg Goldsmith and Rolf Siegwolf working on a large-scale dataset on Swiss trees.

Vegetation and C & N cycle impacts

In a collaboration with Jason Vogel, Jean-Christophe Domec, Carol Loopstra, Claudio Casola, and many other collaborators across the network, we are studying the carbon cycle response to climate change and management in the PINEMAP Project. PINEMAP is one of three Coordinated Agriculture Projects (CAP) recently awarded by the USDA National Institute of Food and Agriculture (NIFA). The purpose of these CAPs is to encourage agriculture and forestry producers to increase carbon sequestration and adapt practices to reduce the impact of climate variation. PINEMAP, a 5-year, $20 million project, focuses on planted pine forests in the Atlantic and Gulf coastal states from Virginia to Texas, plus Arkansas and Oklahoma, that are managed by industrial and non-industrial private landowners.

Savanna alternative stable states
The effects of anthropogenic activity (woody plant removal) on vegetation structure and its consequences for the vertical movement of water through the critical zone is the focus of a project funded by the Wintergarden Groundwater Conservation District. The field sites for this work are located primarily on the Chaparrosa Ranch over the recharge zone of the Carrizo-Wilcox aquifer in southwestern Texas in areas that initially had significant densities of woody vegetation. Mechanical/chemical treatments here include roller chopping, cutting/stump herbicide, and no treatment combined with the effect of fire. All mechanical/chemical treatments were completed in the winter of 2010/2011 and the controlled burns will occur when fuel loads permit. The team's efforts have yielded insights to how vegetation and other aspects of ecosystem structure respond to these anthropogenic manipulations, as well as how changes in vegetation water use and soil characteristics drive changes in soil moisture and potential aquifer recharge. This effort is a collaboration with Bill Rogers (Texas A&M University) and Bob Lyons (Texas AgriLife Extension, Uvalde) and was the focus of graduate studies completed by April Mattox and Carissa Wonkka.

An extenstion of this work seeks to understand how these vegetation changes affect soil trace gas fluxes, in particular N2O. The project seeks to improve our understanding of the biogeochemical changes that accompany woody plant encroachment. The project builds on significant previous efforts to understand the drivers and consequences of this global phenomenon at La Copita Ranch and the Sonora Research Center.

Global environmental change
There is a continuing interest in the effects of global environmental change on terrestrial ecosystem function in the lab. This includes atmospheric and climatic changes and the effects of anthropogenic modification of the land surface. Postdoctoral work at the University of Minnesota on a large global change experiment at Cedar Creek known as BioCON (from its three primary experimental manipulations: Biodiversity, atmospheric CO2, and N deposition) targeted key aspects of the responses of grassland soil nitrogen cycling. More information on this experiment can be found on the BioCON website. Ongoing efforts focus on the use of 15N as a tracer of alterations of N cycling in response to these important global changes. Future work will target the interactions between biodiversity, plant function and landscape-scale processes, including hydrologic fluxes, and nitrogen and carbon cycling.

Gas exchange on loblolly pine in greenhouse