Date of Award:

5-2022

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

John M. Stark

Committee

John M. Stark

Committee

Bonnie G. Waring

Committee

Jeanette M. Norton

Committee

Andrew Kulmatiski

Committee

William D. Pearse

Abstract

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.

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