Seminar: Ye Yuan

Soil organic matter (SOM) is the largest terrestrial carbon (C) pool and SOM can be functionally divided into two main fractions: mineral-associated organic matter (MAOM) and particulate organic matter (POM). MAOM is mainly formed by relatively low molecular weight (LMW) C substrates associating with the surfaces of slit- and clay-sized soil minerals, thus rendering organic compounds within MAOM less accessible to decomposers and their enzymes, so comparing to light, sand-sized POM, MAOM is regarded to be more persistent and has a longer turnover time, so understating MAOM formation process is quite necessary. Recent studies proposed that high-quality litter promotes MAOM formation and persistence by maximizing the synthesis of microbial products and residues that can form a substantial proportion of MAOM, however, it is still untested whether microbial residues will contribute more to MAOM formation than plant litters? The factors that influencing MAOM apart from substrate quality, mineral reactivity also plays a great role in MAOM formation, but how do mineral reactivity modify plant-derived and microbial-derived MAOM formation still remains ambiguous. In order to better understand the above two questions, we setup a one month incubation experiment including three substrates (bacterial residues, fungal residues and maize litter) with different qualities and three minerals (goethite, illite and quartz) with different reactivity. In our experiment, we found that both substrate quality and minerals influenced MAOM formation, changed enzymes, microbial biomass, carbon use efficiency, and shifted microbial composition. More detailly, maize litter had the highest MAOM formation efficiency, followed by fungal residues and bacterial residues, so there is no evidence for preferential stabilization of microbial derived over plant derived organic carbon on minerals. We also found that mineralas with higher reactivity reduced decomposition, increased MAOM formation (except for bacterial residues), increased enzyme activities, changed microbial biomass and community composition, but had no effect on CUE.