Abstract
Plant root systems have a key role in ecology and agronomy. In spite of fast increase in root studies, still there is no classification that allows distinguishing among distinctive characteristics within the diversity of rooting strategies. Our hypothesis is that a multivariate approach for “plant functional type” identification in ecology can be applied to the classification of root systems. The classification method presented is based on a data-defined statistical procedure without a priori decision on the classifiers. The study demonstrates that principal component based rooting types provide efficient and meaningful multi-trait classifiers. The classification method is exemplified with simulated root architectures and morphological field data. Simulated root architectures showed that morphological attributes with spatial distribution parameters capture most distinctive features within root system diversity. While developmental type (tap vs. shoot-borne systems) is a strong, but coarse classifier, topological traits provide the most detailed differentiation among distinctive groups. Adequacy of commonly available morphologic traits for classification is supported by field data. Rooting types emerging from measured data, mainly distinguished by diameter/weight and density dominated types. Similarity of root systems within distinctive groups was the joint result of phylogenetic relation and environmental as well as human selection pressure. We concluded that the data-define classification is appropriate for integration of knowledge obtained with different root measurement methods and at various scales. Currently root morphology is the most promising basis for classification due to widely used common measurement protocols. To capture details of root diversity efforts in architectural measurement techniques are essential.
Highlights
The evolution of root systems1 is closely related to plant colonization of terrestrial ecosystems (Kenrick, 2002; Sperry, 2003) where plants require roots for anchorage, water, and nutrient acquisition
The present discussion paper is motivated by the increasing need to understand root system diversity and functioning in several fundamental and applied research disciplines
We suggest a data-defined procedure for functional root system classification and exemplify the approach with selected data sets
Summary
The evolution of root systems is closely related to plant colonization of terrestrial ecosystems (Kenrick, 2002; Sperry, 2003) where plants require roots for anchorage, water, and nutrient acquisition. Roots are a key organ for plant adaptation to variable environments and for biodiversity (Cornwell and Grubb, 2003), they have long been neglected in plant biology and agronomy. Root systems receive increasing attention as a key for a “second green revolution” (Lynch, 2007; Gewin, 2010) leading to more resource efficient plants. A classification scheme for root systems is needed. Most botanical textbooks do not go beyond a very general developmental distinction between tap and fibrous root systems, concentrating more on specialized morphological adaptations (e.g., haustorial roots, storage roots) that occur in certain species (Bresinsky et al, 2008)
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