By pairing high-resolution chemical imaging analysis with a long-term litter decomposition experiment under field conditions, the researchers discovered that litter decomposition is tightly coupled to redox cycling of Mn. The researchers discovered why Mn exerts such a strong control on litter decomposition rates and the mechanism of the underlying biogeochemical process, observing molecular changes within the litter as it decomposed over the years and probing structural changes within the very large biomolecules present in litter that frequently are not directly detectable by other means. This tunable technique also allowed the scientists to selectively ionize different biopolymers present in the litter, such as lignin, which is an important biopolymer because it lends rigidity to plant cell walls and protects litter from microbial decay.
In microenvironments within the litter, microbes actively cycle Mn as they colonize and break down the litter, and research indicates that biogeochemical constraints on bioavailability, mobility, and Mn reactivity in the plant-soil system may have a profound impact on litter decomposition rates. Understanding more about the mobility and reactivity of Mn in the plant-soil system also helps researchers improve their ability to accurately predict carbon cycling trends in ecosystems, contributing to greater insights into climate change patterns.
Keiluweit, M.. et al. “Long-Term Litter Decomposition Controlled by Manganese Redox Cycling,” PNAS 12(38), E5253–E5260 (2015). [DOI:10.1073/pnas.1508945112].
Instruments and Facilities Used: Beamlines 10.3.2 (X-ray microprobe capabilities) and 1.4.3 (Fourier transform infrared spectromicroscopy) at Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory; beamline 4-3 at Stanford Synchrotron Radiation Light Source (SSRLS).