Litter quality, decomposition rate, and N mineralization are strongly connected and control nutrient availability over time scales of 0-5 y. However, little is known about species effects on soil humus turnover (turnover time >10 y). Ecosystem simulation models show that the humus fraction contains the largest pool of N and controls N availability over longer time scales (>10 y). This project will test whether species differences in litter quality and quantity influence the turnover of humus. Specifically, these investigators will address (1) whether litter quality and quantity alter the physical protection of SOM and the turnover rate of humus fractions, and (2) whether species influence labile SOM (turnover time < 5 y) and if this could change humus mineralization rate. These questions will be addressed at sites where only species differences have modified SOM characteristics. Long-term laboratory incubations will be used to assess species effects on C and N mineralization kinetics. Species differences in litter quality and quantity will then be related to characteristics of the different humus fractions. This project will show whether species modify humus turnover and whether this influences long-term soil fertility.
