Fine root dynamics in the Boreal Forest of northern Saskatchewan, Canada
The study of fine roots (FR) (roots < 2 mm in diameter) in the boreal forests has become a focus of many forest researchers in the past decade in an effort to better understand belowground processes and improve current carbon (C) models to better predict possible C sinks and sources. The objectives of this study were: 1) to determine the inter-annual variability in FR C production in relation to C cycling and other fluxes for four Saskatchewan boreal sites during a four year period, 2) to determine if minirhizotron (MR) estimates of root biomass were similar to root coring estimates, 3) to determine how root production, mortality, turnover, and longevity vary with root diameter class and soil depth, and 4) to determine if image collection orientation influenced estimates of FR biomass and production. Four Saskatchewan boreal sites including aspen (Populus tremuloides) (OA), black spruce (Picea mariana) (OBS), and two jack pine (Pinus banksiana) (mature – OJP, young – HJP94) stands were selected and MR were installed in July of 2002. Minirhizotron images were collected monthly from the end of May through September from 2003 to 2006. Total ecosystem C was estimated to be 47.5, 78.1, 163.1, and 450.5 Mg ha-1 for HJP94, OJP, OA, and OBS, respectively. The FR component of the ecosystem carbon storage ranged from 0.7 Mg ha-1 (1%) at HJP94 to 1.2 Mg ha-1 (< 1%) at OBS. Fine roots were found to contribute a very large portion of C production with estimates of 1.0, 0.6, 1.2, and 1.5 Mg ha-1 yr-1 accounting for 47, 27, 25, and 54% of total ecosystem C production at HJP94, OJP, OA, and OBS, respectively. In a one time comparison of MR and soil cores, FR biomass estimates were found to be similar at OJP, OA, and OBS, with MR estimates being significantly greater at HJP94. Approximately 85, 90, 96, and 96% of FR measured in this study were found to be less than 0.5 mm in diameter with median diameters of 0.250 ± 0.237, 0.225 ± 0.208, 0.175 ± 0.149 and 0.150 ± 0.149 (median ± SD) mm at HJP94, OJP, OA, and OBS, respectively. Fine root longevity was found to increase with increasing diameter and soil depth while turnover decreased. In many cases, it was found that even within a diameter interval of < 0.1 mm, differences in biomass, production, turnover, and longevity were detectable. This brings into question the use of the traditional 2 mm diameter class in FR studies. Fine root data, such as presented in this thesis, help to fill in some of the gaps in the knowledge base, enabling researchers to better understand the underground processes of the boreal forest and develop more complex and accurate C models.
minirhizotron, turnover, longevity, productivity, Fine roots, biomass
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