Coarse root biomass and architecture of hybrid aspen ‘Crandon’ (Populus alba L. × P. grandidenta Michx.) grown in an agroforestry system in central Iowa, USA

ABSTRACT

In this study, we evaluated ‘Crandon’ coarse root biomass and architecture grown at different topographic positions and fertilizer rates. Complete excavations were conducted on a subset of trees after the first growing season and showed that root biomass was strongly related to stem biomass (R² = 0.93), but not topographic position or fertilizer rate. After the third growing season, subsamples of roots were collected from another subset of trees and showed coarse root architecture variables to be strongly related to several metrics of the tree and root size (R² = 0.61 to 0.82), while also differing by topographic position. Equations relating root biomass to stem biomass were derived from both methodologies (complete excavation v. subsampling for architecture measurements), and comparison of the equations indicated no difference in slopes (p = 0.59) or intercepts (p = 0.90), although the subsampling approach had a weaker model fit. Our results suggest ‘Crandon’ roots (i) adhere to strong allometric relationships with stem biomass, (ii) alter their architecture within the constraints of this allometric relationship according to site conditions, and (iii) can be subsampled to estimate root biomass from root architecture parameters with similar accuracy (but less precision) compared to complete excavations.

KEYWORDS:

• Biomass allocation
• fertilizer
• pipe theory
• root geometry
• topography

Acknowledgments

We would like to dedicate this paper to the memory of our dear friend and co-author Rick Hall, who passed away in September 2016. We would also like to thank ArborGen, Inc. (Ridgeville SC), for supplying a portion of the long-term study trees, ISU Horticulture Research Station for the use of their tree spade, and Ed Bauer and Austin Himes for providing helpful comments on an earlier draft of the manuscript.

Additional information

Funding

Funding and other support for this research was provided by the Leopold Center for Sustainable Agriculture (Project E2008-24), USDA Agriculture and Food Research Initiative (Project IOW5249), USDA National Institute of Food and Agriculture (McIntire Stennis Project 1009221), Iowa State University College of Agriculture and Life Sciences, and USDA Forest Service Northern Research Station Institute for Applied Ecosystem Studies.