Grassland Soil Science and Fungal-Bacterial Interactions

Fungal-Bacterial Interactions: Bridging Soil Niches in Regulating Carbon and Nitrogen Processes


Grasslands play a vital role in the nutrient cycling process of both carbon and nitrogen. The state of California is home to perennial and annual grasslands, distinguished from one another by their growth patterns. Annual grasses complete their growth cycle in a single season, whereas perennial grasses exhibit persistent growth throughout the year. Perennial grasses often develop extensive root systems that provide a more stable mechanism for long term carbon storage than their annual counterparts. Historically, three disturbances contributed to the  conversion of California's former native perennial grasses to its current annual-dominated status: European colonization, fire-suppression, and drought. 


Oak-woodland adjacent annual grasslands here in Hopland offer a distinctive seasonal rhythm. The growth season of this grass begins when rainfall is hearty enough to germinate grass seeds, typically during the late fall/winter. While characterized by herbaceous vegetation, the structure of these grasslands depends greatly on local weather and livestock grazing patterns. Because the life cycle of annual grass is limited to a single growing season, there is less time for it to contribute to long-term carbon storage. This means that the nutrient cycling process in an annual grassland ecosystem is primarily the job of biotic reactions between fungi and bacteria below the surface of the grass, in its soil. The Hopland Research and Extension Center (HREC) and soil microbial ecologist Dr. Mengting “Maggie” Yuan from UC Berkeley's Firestone Lab have teamed up to better understand how these biotic interactions in soil are affected by reduced precipitation conditions associated with climate change. 


Dr. Mengting “Maggie” Yuan in the UC Berkeley Firestone Lab

Oxford Tract, Berkeley CA


Dr. Yuan's interest in natural resources began when her family would spend time walking together outside. This time spent in nature inspired her to think about the complexities of a much smaller biotic world. What kind of systems contribute to the function of smaller microbial ecosystems? She asked herself. This curiosity eventually led her to study environmental engineering in university. In 2011, she earned her Bachelor's degree in Environmental Engineering from Tsinghua University in Beijing. After which, she moved to the United States to earn her Ph.D. in Microbiology from the University of Oklahoma in 2017. 


In the world of ecology, specifically soil microbial ecology, there exists promising opportunities for innovation and scientific advancement. Dr. Yuan points out that there is no standardized model for measuring the Biological Fertility Index (BFI) of soil, because scientists don't understand on a fundamental level the heterogeneity of the soil. The analytical methods scientists use currently to measure soil fertility point more to a soil's habitat than its biotic function. 


“A scoop of soil contains, on a more microscopic level, mineral surfaces and pore space” says Dr. Yuan. “It's important that future research considers the spatial difference instead of potential.” She admits that understanding soil on a spatial level is a challenging facet of soil microbial ecology. She calls this her “lifelong challenge.” Still, she hopes to work towards projects like these that create well defined frameworks for describing the probability of microbes to be able to interact with the environment and other microbes.


Fungal ingrowth cores, used to allow fungal hyphae into soil core samples

Oxford Tract, Berkeley CA



Spectrometer equipment, owned by Lawrence Livermore National Laboratory

Oxford Tract, Berkeley CA

When it comes to staying up to date with advancements in microbial soil ecology, Dr. Yuan relies on her undergraduate researchers just as much as her postdoctoral colleagues. She cites collaboration as the mechanism of understanding what's going on in both her scientific community, and the greater academic community at UC Berkeley. She loves talking to undergraduates one-on-one to get a better understanding of their struggles and motivations for pursuing a career in natural resource science. Dr. Yuan says that, from her personal experience at UC Berkeley, “Students nowadays have a more developed understanding of their passion for climate action” and “bring to the table a valuable skill set missing from current climate solutions”. She is optimistic that undergraduate eagerness to participate in climate action research is indicative of a larger generational interest. 


It was collaboration, flexibility, and the opportunity to connect with people on a national scale that encouraged Dr. Yuan to work on projects like these at UC Berkeley. She feels grateful that working in academia has allowed her the freedom to try and pose solutions to some of the state's most complex natural resource issues. Her work on this project holds profound implications for agriculture, environmental sustainability, and our understanding of climate change adaptation. The study's relevance extends far beyond the confines of HREC, as its findings will offer valuable insights applicable to other annual grassland areas in California, ultimately guiding land conservation and management strategies all around the state.