Publications

Carbon© can be sequestered in the mineral soil after the conversion of intensively cropped agricultural fields to more extensive land uses such as afforested and natural succession ecosystems. Three land-use treatments from the long-term ecological research site at Kellogg biological station in Michigan were compared with a nearby deciduous forest. Treatments included a conventionally tilled cropland, a former cropland afforested with poplar for 10 years and an old field (10 years) succession. We used soil aggregate and soil organic matter fractionation techniques to isolate C pools that (1) have a high potential for C storage and (2) accumulate C at a fast rate during afforestation or succession. These fractions could serve as sensitive indicators for the total change in C content due to land-use changes. At the mineral soil surface (0-7 cm), afforesting significantly increased soil aggregation to levels similar to native forest. However, surface soil (0-7 cm) C did not follow this trend: soil C of the native forest site (22.9 t C ha(-1)) was still significantly greater than the afforested (12.6 t C ha(-1)) and succession (15.4 t C ha(-1)) treatments. However, when the 0-50 cm soil layer was considered, no differences in total soil C were observed between the cropland and the poplar afforested system, while the successional system increased total soil C (0-50 cm) at a rate of 0.786 t C ha(-1) yr(-1). Afforested soils sequestered C mainly in the fine intra-aggregate particulate organic matter (POM) (53-250 mum), whereas the successional soils sequestered C preferentially in the mineral-associated organic matter and fine intra-aggregate POM C pools.