My past and ongoing research is centered around two major themes: 1) improving mechanistic understanding of the biotic and abiotic drivers of belowground carbon (C) and nutrient cycling and 2) applying the knowledge of spatial soil heterogeneity to better understand ecosystem functions. In particular, I am interested in the responses of biogeochemical processes to human disturbance and natural environmental change, and how these responses shape the ecosystem at a landscape scale. I use multidisciplinary approaches in my research, ranging from manipulative field and laboratory experiments, to advanced spectroscopic methods, and ecosystem and landscape modeling.
My Ph.D. dissertation research focused on understanding the underlying mechanisms of photodegradation, a novel decomposition process through which solar radiation degrades plant litter and soil organic matter. Using field and laboratory experiments and advanced spectroscopic techniques, I demonstrated how ultraviolet radiation interacts with microbial decomposers to break down plant litter. My research helps to establish photodegradation as a significant biogeochemical process in terrestrial ecosystems and advances our understanding of the chemical mechanisms underlying photodegradation.
Another focus of my past research was to improve current understanding of spatial soil heterogeneity and its response to land management. For example, my M.Sc. thesis examined the effects of sheep grazing on the spatial patterns of soil organic matter and aboveground productivity in a Chinese desert steppe. Using spatially explicit experiments, I found that high-intensity grazing decreased the occurrence of “hot spots” of soil water and organic matter at a fine spatial scale (1-18 meters). I also found that high-intensity grazing strongly fragmented vegetation patches using remote sensing techniques. These results demonstrate that spatial patterns of soil and vegetation can be used as indicators of grazing disturbance. In another project, I found that subsoil thickness explained over 80% of the variability in soil C storage on the hillslopes of a California grassland. I also identified landscape concavity and aspect as the main predictors of subsoil thickness and soil C storage on these hillslopes. This work helps to achieve accurate mapping of soil C at a regional scale in similar landscapes.
I am currently studying the impacts of iron (Fe)-redox cycling on the decomposition of soil organic matter in tropical forest soils. My research focuses on quantifying the roles of two novel decomposition pathways: the C mineralization coupled to abiotic Fe oxidation via Fenton reactions and the stimulation of C decomposition from increased acidity driven by Fe oxidation. In a series of laboratory experiments, I am altering the redox conditions of soils from different landscape positions to simulate Fe oxidation and reduction processes. Meanwhile, I am correlating the changes in soil pH, Fe speciation, and soil oxidative activity with the soil C loss measured by the production of CO2 and dissolved organic C. Early results show that Fe oxidation explained approximately 40% of the variability in soil CO2 production from a slope position, which covers over 65% of the landscape. To examine the roles of Fe-redox cycling on soil C at a landscape scale, I am extrapolating the Fe-C relationships observed from the laboratory to a digital elevation model with the help of a large-scale field sensor array in the watershed.
Soil C stabilization and sequestration is another focal area of my current research. It is well documented that nutrient deposition increases above- and below-ground productivity in many grassland ecosystems. However, it is unclear how soil C storage responds to elevated nutrient availability. By taking advantage of a long-term, cross-site experiment (the Nutrient Network), I am studying the impacts of enhanced nutrient availability on soil C storage at four California grassland sites.
I plan to continue my research in the areas of soil biogeochemistry and spatial soil heterogeneity. The long-term goal of my research program is to quantify and predict changes in soil biogeochemical processes in response to future climate and human disturbance. Some avenues I plan to pursue in the next several years include:
Investigating the responses of trace gas fluxes and soil C storage and stability to environmental change.
Advancing the understanding of the spatial controls of soil biogeochemical processes.
Investigating the consequences of land management on soil biogeochemical processes. There is great potential to improve soil health and other ecosystem services by adopting sustainable land management practices.