Dr. Jeffrey Bird, Assistant Professor of Soil Biogeochemistry
School of Earth and Environmental Sciences
Queens College, CUNY

Seminar Abstract: While soil microorganisms are known to mediate plant litter decomposition and transformation into soil organic matter, little quantitative information exists on the functional roles of the main microbial groups involved in soil C cycling. Consequently, ecosystem C models can consider only the activity of the entire belowground microbial community despite large differences in community structures found in temperate and tropical ecosystems. Using two temperate ecosystems in California, Dr. Bird will present findings on C utilization preferences and succession of broad microbial groups including soil fungi, actinobacteria, gram (+) bacteria, gram (-) bacteria and protozoa during the decomposition of above- and belowground plant C inputs. Dr. Bird will emphasize his recent work examining the microorganisms involved in soil C priming due to the presence of living roots. In these studies, Dr. Bird used stable isotope (13C and 15N) labeled soil organic matter, plant roots and Ponderosa pine needles in conjunction with microbial biomarkers (phospholipids fatty acids) to quantify the flux of C through the microbial community in situ. Despite large differences in microbial community structures, broad microbial groups had distinct preferences in C type. Gram (-) bacteria and soil fungi preferred labile C compounds released during the initial decomposition of litters and root exudates. In contrast, gram (+) bacteria and actinobacteria were preferred more recalcitrant C compounds present after a significant period of decomposition and native soil organic matter. Soil C priming due to living plant roots was found to be due to the activity of gram (+) bacteria and actinobacteria. The effect of soil C priming was relieved by additions of inorganic N. These overall function roles of soil microbial groups provide a critical roadmap for C flow through soil microbial communities. In addition, this approach helped to explain an important mechanism for soil C priming events.

Research Interests: Dr. Bird's primary research interests address the underlying soil processes that drive biogeochemical dynamics in terrestrial ecosystems with an emphasis on the movement of carbon, nitrogen, phosphorous, and water. His work aims to advance our understanding of how biological, chemical, and physical factors interact and control the flux of these fundamental building blocks of life on process and ecosystem levels. Dr. Bird's lab is currently focusing on the ways soil microbial communities mediate the turnover and stabilization of carbon and nitrogen in temperate and tropical ecosystems.

IES host: Dr. William Schlesinger