Intrinsic and Extrinsic Controls of Fine Root Life Span

Abstract

Although fine roots play an integral role in biogeochemical cycling and supporting plant function, fundamental understanding of the mechanisms that control fine root life span is limited. Based on literature, we examined how intrinsic plant characteristics including root diameter, root branching order, rooting depth, and mycorrhizal symbiosis affect fine root life span, and how fine root life span differs with plant life form and foliar habit and between early versus late seral species. We also examined how soil nitrogen and water availability, temperature, and atmospheric carbon dioxide concentration influence fine root life span. We focused on evidence from rhizotron and minirhizotron observations which allow for individual roots to be directly monitored in situ. Fine root life span increased with increasing root diameter, was shorter for more distal than proximal roots, and increased with increasing rooting depth, but was not influenced by mycorrhizal symbiosis. Trees had the longest fine root life spans of all the plant life forms, followed by grasses, lianas, shrubs, and forbs. Among trees, deciduous species had shorter fine root life spans than evergreen species. Fine root life span appears to decrease with increasing temperature and increase with soil water availability, whereas the effects of soil nitrogen availability and atmospheric carbon dioxide concentration on fine root life span were highly inconsistent among studies. Our findings indicate that root morphological characteristics and plant traits are useful predictors of fine root life span. However, environmental influences on fine root life span remain poorly understood due to the limited number of respective studies. Future studies of root demographic processes are needed to better understand environmental controls of fine root life span. It is also critical that research continues into developing more direct and less invasive techniques for studying root demographics.

Keywords:

• atmospheric CO₂ concentration
• fine root lifespan
• fine root longevity
• mycorrhizal symbiosis
• rhizotrons and minirhizotrons
• root diameter and branching order
• rooting depth
• soil nitrogen and water availability
• temperature

ACKNOWLEDGMENTS

We thank Zhiyou Yuan, Samuel Bartels, Amber Brant, and anonymous reviewers for their valuable comments on an early version of the paper. Financial support from the Natural Sciences and Engineering Research Council of Canada (DG283336-09 and SPG281886), the Sustainable Forest Management Network Centre of Excellence of Canada, the Government of Ontario for an Ontario Graduate Scholarship and the Early Researcher Award from the Ontario Ministry of Research and Innovation is gratefully acknowledged.

Both authors contributed equally.