Terrestrial vegetation in the Earth system

Nicholas G Smith, Purdue University

Abstract

The Earth is going through a period of unprecedented, exponential change, resulting in abiotic conditions that many species, including humans, have never experienced. There is a strong demand of the scientific community to understand and project the trajectory of these changes. One of the primary drivers of these global changes is the anthropogenic emission of CO2 . Because terrestrial plants constitute the largest sink for CO 2 on Earth, the response of the world’s flora to these unprecedented changes will be a major determinant of the rate of future CO2 increases and global change. Therefore, it is imperative to properly understand and model these responses. In this dissertation, I present five studies performed during my graduate tenure that were designed to improve the way in which plant species are represented in the models used to project future global change. The first three chapters tackle the issue of plant responses to temperature and temperature acclimation of plant carbon exchange in particular. In the first of these chapters, I review the state of the science on temperature acclimation prior to 2013. I find that, while temperature acclimation has been heavily studied by the empirical community, model incorporation of this response is lacking. The second chapter assesses the impact of acclimation on global models and finds that acclimation improves model performance and leads to increased projected carbon uptake by the land surface in the future. The third chapter examines acclimation responses in a global subset of species to explore plant traits that may predict a plant’s capacity to acclimate to changes in temperature. In it, I find that plant capacity to acclimate varies by plant type, indicating that evolutionary pressures may influence acclimation capacity. The following two chapters switch to examining terrestrial responses to precipitation change. In the first of these, I review the empirical and quantitative understanding of these responses. I find that, in many cases, model representation of terrestrial responses to precipitation is much simpler than what is seen in experimental studies, but that experimental studies are not well positioned for improving models. In the second chapter, I use a manipulative field experiment to examine plant community responses to altered precipitation and find that increased precipitation variability favors less conservative species leading to reduced plant community diversity when combined with experimental nitrogen fertilization. The five main chapters are bookended by introductory and concluding chapters. The work performed during this dissertation highlights the importance of studying plants in an Earth system framework and it is my hope that the chapters presented will lead to improve model projections. Nonetheless, these chapters also demonstrate the challenge of trying to integrate biological complexity into large-scale predictive models. There is a great deal of interdisciplinary work to be done in this domain and I look forward to helping lead those studies in the future.

Degree

Ph.D.

Advisors

Dukes, Purdue University.

Subject Area

Ecology|Climate Change|Environmental science

COinS