The degree to which soil organic matter chemistry is linked to its rate of decomposition and soil microbial processes remains uncertain.  In this talk I will address several recent experiments in differently managed ecosystems examining whether: 1) organic matter chemistry is primarily controlled by plant C inputs or edaphic soil properties; 2) organic matter chemistry influences soil biological processes such as enzyme activities and fungal/bacterial ratios; and 3) feedbacks between soil organisms and organic matter structure influence C turnover dynamics and their response to agricultural disturbances. 

Results/Conclusions

Our results suggest that where edaphic soil properties vary considerably, vegetation and land use are poor predictors of soil organic matter chemistry.  Where land use varies but soil types are similar, management practices such as changing vegetation or the use of N or tillage can influence C structure.  Across agricultural and native sites there are close correlations between organic matter chemistry and biological processes.  The N content of soil organic matter is positively correlated with enzymes but negatively correlated with fungal/bacterial ratios; lignin, by contrast, shows the opposite relationships with enzymes and fungal/bacterial ratios.  Inorganic N use can have effects on enzyme activities that translate directly into changes in soil C chemistry.  Despite these patterns, predicting the sequence of changes in SOM chemistry during decomposition and the structure of stable C based on original inputs and soil biological processes remains difficult, likely because of organo-mineral interactions and the range of disturbances associated with agricultural production.