Horwath, W. 1993. The dynamics of carbon, nitrogen, and soil organic matter in Populus plantations. Ph.D. Dissertation, Michigan State University, East Lansing, Michigan, USA.

Citable PDF link: https://lter.kbs.msu.edu/pub/2981

Short-rotation intensive-culture forestry is similar to agricultural systems requiring increased nutrient input and management. The expense and environmental concerns associated with fertilizers have raised questions about the sustainability of these ecosystems. Sustainability of production oriented ecosystems can be aided by understanding the mineralization-immobilization potential of the soil microbial biomass. The soil microbial biomass is central to a complex system of soil organic fractions that control soil fertility, production and environmental contamination.

The lack of root turnover studies has led to an inadequate understanding of the role of root turnover as substrate soil microbial biomass and organic matter formation. The current study was designed to determine: (i) the role of below-ground production and turnover in nutrient cycling processes; (ii) the contribution of leaf and root litter as substrate for the maintenance of soil organic matter; and (iii) relate soil microbial biomass and organic matter dynamics to plant carbon and nitrogen allocation patterns.

Two-year-old Populus euramericana cv. Eugenei trees were labeled with 14C and 15N in the field. The 15N was injected into the stem to label leaves and roots without labeling the soil. The 14C labeling was done in a Plexiglas chamber under ambient conditions. The tree-soil system was sampled for one year. Labeled leaf litter was placed onto unlabeled tree plots to differentiate the contribution of leaf and root derived carbon and nitrogen to soil over a two year period.

The 14C required two weeks to stabilize in the root system and averaged 20% of soil respiration. One year latter, 32% of applied 14C and 33% of the injected 15N was recovered. Reserves in the root system were sufficient to replace fine roots one and one half times. This represented significantly less C than leaf litter, yet similar amounts of 14C were found in soil from both litters. Leaf litter appeared to dominate N cycling since 15N was not detected in root labeled soil. Kinetic analysis of incubated soil showed a greater contribution of C and N to soil organic fractions from leaf litter. The turnover of labile soil 14C in both leaf and root litter labeled soil was 14-64 days. The 14C in pools of intermediate resistance had a turnover time of 2-16 years and increased with soil depth.Short-rotation intensive-culture forestry is similar to agricultural systems requiring increased nutrient input and management. The expense and environmental concerns associated with fertilizers have raised questions about the sustainability of these ecosystems. Sustainability of production oriented ecosystems can be aided by understanding the mineralization-immobilization potential of the soil microbial biomass. The soil microbial biomass is central to a complex system of soil organic fractions that control soil fertility, production and environmental contamination.

The lack of root turnover studies has led to an inadequate understanding of the role of root turnover as substrate soil microbial biomass and organic matter formation. The current study was designed to determine: (i) the role of below-ground production and turnover in nutrient cycling processes; (ii) the contribution of leaf and root litter as substrate for the maintenance of soil organic matter; and (iii) relate soil microbial biomass and organic matter dynamics to plant carbon and nitrogen allocation patterns.

Two-year-old Populus euramericana cv. Eugenei trees were labeled with 14C and 15N in the field. The 15N was injected into the stem to label leaves and roots without labeling the soil. The 14C labeling was done in a Plexiglas chamber under ambient conditions. The tree-soil system was sampled for one year. Labeled leaf litter was placed onto unlabeled tree plots to differentiate the contribution of leaf and root derived carbon and nitrogen to soil over a two year period.

The 14C required two weeks to stabilize in the root system and averaged 20% of soil respiration. One year latter, 32% of applied 14C and 33% of the injected 15N was recovered. Reserves in the root system were sufficient to replace fine roots one and one half times. This represented significantly less C than leaf litter, yet similar amounts of 14C were found in soil from both litters. Leaf litter appeared to dominate N cycling since 15N was not detected in root labeled soil. Kinetic analysis of incubated soil showed a greater contribution of C and N to soil organic fractions from leaf litter. The turnover of labile soil 14C in both leaf and root litter labeled soil was 14-64 days. The 14C in pools of intermediate resistance had a turnover time of 2-16 years and increased with soil depth.

Download citation to endnote bibtex

Sign in to download PDF back to index