Productivity, physiology, community dynamics, and ecological impacts of a grassland agro-ecosystem: integrating field studies and ecosystem modeling

Feng, Xiaohui

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Description

Title

Productivity, physiology, community dynamics, and ecological impacts of a grassland agro-ecosystem: integrating field studies and ecosystem modeling

Author(s)

Feng, Xiaohui

Issue Date

2014-09-16

Director of Research (if dissertation) or Advisor (if thesis)

Dietze, Michael C.

Doctoral Committee Chair(s)

Ainsworth, Elizabeth A.

Committee Member(s)

• Dietze, Michael C.
• David, Mark B.
• Taft, John B.

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Grassland
• productivity
• biomass quality
• biomass moisture
• quantity-quality trade-off
• photosynthesis
• Bayesian model parameterization
• chlorophyll
• leaf ecophysiological traits
• leaf nitrogen
• specific leaf area
• Amax
• Vcmax
• community dynamics
• percent cover

Abstract

Grasslands are among the largest ecosystems in the world and provide numerous ecosystem services. These services include the ecosystem benefits important in an agricultural context such as biomass production and benefits from an ecological perspective such as mitigation of greenhouse gas emissions. My research has investigated the physiology, productivity and community dynamics of grassland ecosystems by combining field studies and modeling techniques. In an agriculture context, primary productivity is especially important. Therefore, the first part of my research addresses the optimal harvesting time of prairie biomass to achieve the maximum yield within one production cycle. Due to the biomass quantity-quality trade-off, the balance among yield, biomass quality, and impacts on environment needs to be carefully considered when harvesting prairie mixtures. Allowing grasses to completely senesce and recycle nutrients can reduce fertilizer requirements and improve feedstock quality by reducing biomass moisture and mineral content. But the trade-off is that a late harvest always results in less harvestable biomass. Effects of harvest time on biomass nitrogen concentration, moisture and yield of prairie production systems are rarely investigated. Therefore, I investigated responses of these factors to harvest time in prairie mixtures by conducting experiments in a restored tallgrass prairie in Urbana, IL. The results suggest that the optimal harvest time that maximizes expected net returns and balances feedstock quality and quantity is between November and January. Next, relationships between leaf traits and photosynthetic rates are commonly used to predict primary productivity at scales from the leaf to the globe. Hence, the second part of my dissertation focuses on investigating the variation in these relationships across taxonomic scales using a Bayesian parameterization of leaf photosynthesis models. Photosynthetic CO2 and light response curves and leaf ecophysiological traits of 25 grassland species were measured. The effects of leaf traits on photosynthetic capacity were quantified at different taxonomic scales through leaf photosynthesis model parameterization. I found that the effects of plant physiological traits on photosynthetic capacity and parameters varied among species and plant functional types. These results suggest that one broad-scale relationship is not sufficient to characterize ecosystem conditions and changes at multiple scales. The third part of my research builds on this foundation of leaf ecophysiology and aims to integrate the interaction between physiology, community and ecosystem functioning into a unified picture by testing the effects of photosynthesis on community dynamics. To test the relationship between photosynthesis and community composition, I measured species-level photosynthetic rate and abundance in a tallgrass prairie monthly across two growing seasons. Large portions of within-species and across-species variation in percent cover could be explained by seasonal changes in photosynthetic rate. My results suggest that photosynthesis influences community composition by affecting dominance of relatively common species in the prairie and establishes an important linkage between plant physiology and community which has been overlooked in previous studies.

Graduation Semester

2014-08

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Copyright and License Information

Copyright 2014 Xiaohui Feng. Portions of this dissertation have been published elsewhere: Copyright 2011 Aspects of Applied Biology Copyright 2013 John Wiley & Sons

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