Document: CHR-3-58-16

Fine root dynamics of a developing forest in response to nitrogen.

BENO, C.C.* ¹, M.D.COLEMAN ² and A.L.FRIEND ³

University of Wisconsin-Stevens Point, Stevens Point, WI USA ¹
USDA Forest Service, New Ellenton, SC USA ²
Mississippi State University, Mississippi State University, MS USA ³

Abstract:
We examined the hypothesis that increasing soil N increases fine root production in an establishing forest. This hypothesis is pivotal to our understanding of environmental controls over belowground net primary production in forest ecosystems, and existing data on this question are ambiguous. A cottonwood plantation was established and plots within it received 0, 50, 100, and 200 kg N ha ^-1. Time-release fertilizer was used to prevent disturbance effects associated with large pulses of N. Root observation tubes (minirhizotrons) were used to follow production (sum of new root length), mortality (sum of missing root length), and standing crop (net amount of root length present). The study was maintained for two years. Fine root production and mortality increased from the first to the second year, irrespective of treatment, as the site became more completely exploited. Second year production was more than 40% higher and mortality tripled, which resulted in double the live-root standing crop compared to first year results. In support of the hypothesis, fertilized plots generally had high production and low mortality compared to the control plots. Initial results show that the 200 N treatment had the greatest amount of production and intermediate fertilizer levels had the lowest mortality rates resulting in a high final standing crop. The 0 N control had relatively low production and high levels of mortality, resulting in a low standing crop by the end of the second year. Consequently, preliminary results show that fertilized plots tended to have higher standing crops than the control. Because seedlings were planted in the first year, these results represent the response of young cottonwood in an intensively managed plantation and may differ from the response in mature forest stands.

Keywords: fine root turnover, nitrogen, cottonwood

This abstract is being presented at: 2:45 PM in session:
Oral Session #12: Roots.