Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

John M. Stark


John M. Stark


Bonnie G. Waring


Jeanette M. Norton


Andrew Kulmatiski


William D. Pearse


Since terrestrial ecosystems store approximately 3 times more carbon (C) than the atmosphere, they have a significant effect on the atmospheric CO2 concentration. Although many studies have been conducted to determine global change effects on C cycling in terrestrial ecosystems, the underlying mechanisms remain uncertain. To address this knowledge gap, I utilized meta-analysis, laboratory experiments, and soil microbial community analysis.

In chapter 2, I conducted a meta-analysis to examine whether effects of long-term N addition on plant productivity can shift over time. I found that 44% of studies showed a marked trend (increase or decrease) in the strength of N impacts over time. The temporal trend of N impacts on plant productivity was mainly explained by climate variables (e.g. mean annual temperature and precipitation). This chapter suggests that, to estimate N impacts on terrestrial ecosystem more accurately, not only the magnitude of N impacts on plant productivity, but also their temporal pattern should be considered in future studies.

In chapter 3, I determined the responses of dryland soil C cycling to multiple global change factors (e.g. previous warming, C availability, soil moisture content, and soil moisture variability) by conducting a laboratory incubation experiment. I found that interactive effects of multiple global change factors were ubiquitous in drylands. For example, effects of soil moisture and previous warming on soil respiration were insignificant without C addition. However, higher soil respiration was found under high soil moisture and prior warming in soils with C additions. This chapter indicates that future experiments should include multiple global change factors to assess their interactive effects on soil C cycling and to unravel underlying mechanisms.

In chapter 4, I quantified roles of plant-microbe-soil interactions in soil C cycling by utilizing synthetic root/soil systems. The treatments consisted of C input quality, root exudates, soil minerology, and soil microbial community composition. I found that the root exudates-soil minerology interaction was dominant in regulating soil C cycling. More specifically, the positive effect of root exudates on soil respiration decreased with increasing soil clay activity. This chapter suggests that plant-soil interactions play a great role in soil C formation and loss.