Estimating fine root longevity in a temperate Norway spruce forest using three independent methods

Area of Science:

• Forest ecology
• Soil science
• Biogeochemistry

Background:

• Fine root longevity significantly influences forest carbon (C) cycling.
• Understanding root lifespan is key to accurately modeling forest ecosystem processes.

Purpose of the Study:

• To investigate fine root longevity in a Norway spruce forest using multiple methods.
• To assess the influence of root diameter, C/N ratio, and soil depth on fine root lifespan.
• To compare the effectiveness of radiocarbon analysis, sequential soil coring, and minirhizotron observations for estimating root longevity.

Main Methods:

• Radiocarbon (¹⁴C) analysis of fine roots.
• Sequential soil coring.
• Minirhizotron observations.
• Analysis of root diameter and C/N ratios across soil depths.

Main Results:

• Mean radiocarbon age of fine root carbon increased with soil depth (5 years in organic layer to 13 years in mineral soil).
• Fine root C/N ratios increased with soil depth.
• Larger roots (>0.5 mm diameter) exhibited longer longevity.
• Radiocarbon analysis yielded significantly higher longevity estimates (5.4 years) compared to sequential coring (0.9 years) and minirhizotrons (0.7 years).

Conclusions:

• Sequential soil coring and minirhizotron methods likely underestimate mean fine root longevity.
• Radiocarbon analysis may overestimate mean fine root longevity.
• Methodological choice critically impacts estimates of fine root lifespan and subsequent carbon cycling assessments.