An optimized fine root sampling methodology balancing accuracy and time investment
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Tree roots are spatially highly heterogeneous and it thus requires large numbers of samples to detect statistically significant changes in root biomass. The objectives of this study were to understand and quantify the sources of error in the assessment of fine root biomass (<2 mm) during the second year of a high-density Populus plantation.
Soil cores were collected in winter (n = 35) and in summer (n = 20), and fine roots were picked by hand for varying lengths of time: 1, 2, 5, 20, 40, and 60 min. The root biomass data were used to identify the best combination of the time spent for root picking and the number of samples collected, that minimizes the overall uncertainty (i.e. the combination of the spatial error due to the incomplete sampling and the temporal error due to the incomplete core processing).
On average, 25 min was enough time to pick 90 % of the fine root biomass in winter, while in summer only 10 min were needed. In winter fewer samples were needed, but more time for picking was necessary as compared to summer when root biomass was higher.
Fine root sampling can be optimized by minimizing the uncertainty of the biomass estimates and simultaneously decreasing root sampling time investment.
KeywordsAuger sampling Sampling time Root picking time Spatial error Temporal error
This research has received funding from the European Research Council under the European Commission’s Seventh Framework Programme (FP7/2007–2013) as ERC Advanced Grant agreement # 233366 (POPFULL), as well as from the Flemish Hercules Foundation as Infrastructure contract ZW09-06. Further funding was provided by the Flemish Methusalem Programme and by the Research Council of the University of Antwerp. GB holds a grant from the Erasmus-Mundus External Cooperation, Consortium EADIC – Window Lot 16 financed by the European Union Mobility Programme # 2009-1655/001-001. JSK was supported as a visiting professor at the University of Antwerp by the International Francqui Foundation and by the US State Department Commission for Educational Exchange Fulbright Program. We gratefully acknowledge the excellent technical support of Joris Cools, the field management of Kristof Mouton, the logistic support of the POPFULL team including Nadine Calluy, as well as the generous assistance of Jonas Lembrechts, Alexander Vandesompele and Maud Lampaert for tedious fine root picking.
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