Genetic variation and ecosystem function in cottonwood forests

Understanding the effects of genes on ecosystems is important because it places ecosystem function in an evolutionary perspective and links processes from small to large scales. This dissertation consists of three studies which are among the first to examine how genes affect ecosystems through: (1) changes in plant water use and physiology; (2) genetic effects on root production; and (3) decoupling among the components of total belowground carbon allocation. Chapter two argues that genetics affect water use pathways in trees and this may represent an extended effect of genes on ecosystems. The third chapter introduces a novel hypothesis for plant defense, the Nutrient Cycling Feedback hypothesis (NCF), where fine root production and foliar condensed tannin are linked through genetic and ecological mechanisms. Chapter four examines the decoupling between fine root production and total belowground carbon allocation. This chapter introduces the Dynamic Belowground Allocation hypothesis (DBA) in which components of belowground carbon allocation are decoupled due to different controls at the plant and ecosystem level. These studies demonstrate the interconnectedness of ecosystems by placing difficult to measure ecosystem parameters in a genetic framework, and merging disparate fields in ecology.