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Relationships between fine root dynamics and nitrogen availability in Michigan northern hardwood forests
A J Burton1, K S Pregitzer1, R L Hendrick2
1School of Forestry and Wood Products, Michigan Technological University, Houghton, MI 49931, USA, USA.
Oecologia
|May 27, 2017
Summary
Nitrogen availability, not temperature, controls fine root lifespan in northern hardwood forests. Higher nitrogen levels lead to longer root lifespans and lower turnover rates, suggesting nutrient benefits outweigh carbon costs.
Area of Science:
- Forest Ecology
- Plant Physiology
- Soil Science
Background:
- Fine root dynamics are crucial for forest ecosystem function.
- Understanding factors influencing root longevity is key to predicting forest responses to environmental change.
- Previous research has focused on temperature, but nitrogen's role needs further investigation.
Purpose of the Study:
- To investigate the influence of soil temperature and nitrogen (N) availability on fine root production, mortality, and longevity in sugar maple forests.
- To determine whether latitudinal temperature gradients or N availability gradients drive fine root lifespan patterns.
Main Methods:
- Minirhizotrons were used to monitor fine root (≤1 mm) dynamics over two years in four northern hardwood forest sites.
- Sites were selected along a latitudinal temperature gradient and varied in N availability.
- Root longevity, production, mortality, N concentration, and respiration rates were measured.
Main Results:
- Fine root production peaked in early summer, while mortality was distributed evenly throughout the year.
- Median fine root lifespans ranged from 405 to 540 days, and fine root turnover rates were 0.50–0.68 year⁻¹.
- Root longevity and turnover patterns correlated with N availability, not temperature, with longer lifespans and lower turnover in higher N sites.
- Root N concentration and respiration rates were higher in N-rich sites.
Conclusions:
- Nitrogen availability, rather than temperature, is the primary driver of fine root lifespan and turnover in these northern hardwood forests.
- Longer root lifespans in N-rich soils suggest a strategy where nutrient acquisition benefits outweigh the carbon costs of root maintenance.
- Increased metabolic activity and carbohydrate allocation in N-rich zones may regulate root lifespan by altering root carbon sink strength.
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