Abstract
Extensive research efforts are devoted to understand fine root trait variation and to confirm the existence of a belowground root economics spectrum (RES) from acquisitive to conservative root strategies that is analogous to the leaf economics spectrum (LES). The economics spectrum implies a trade-off between maximizing resource acquisition and productivity or maximizing resource conservation and longevity; however, this theoretical framework still remains controversial for roots. We compiled a database of 320 Mediterranean woody and herbaceous species to critically assess if the classic economics spectrum theory can be broadly extended to roots. Fine roots displayed a wide diversity of forms and properties in Mediterranean vegetation, resulting in a multidimensional trait space. The main trend of variation in this multidimensional root space is analogous to the main axis of LES, while the second trend of variation is partially determined by an anatomical trade-off between tissue density and diameter. Specific root area (SRA) is the main trait explaining species distribution along the RES, regardless of the selected traits. We advocate for the need to unify and standardize the criteria and approaches used within the economics framework between leaves and roots, for the sake of theoretical consistency.
Highlights
Fine roots perform multiple essential functions, including acquisition and storage of soil resources (McCormack and Iversen, 2019)
The first principal component analyses (PCA) axis in our dataset represents a main trend of trait covariation with most of the total variance explained by this axis, showing a clear trade-off in the morphological structure of roots in Mediterranean species strongly dominated by mass-normalized traits that we can define as the root economics spectrum (RES)
Our findings highlight how the main trend of variation in this multidimensional root space is largely analogous to the main axis of the leaf economics spectrum
Summary
Fine roots perform multiple essential functions, including acquisition and storage of soil resources (McCormack and Iversen, 2019). Functional trait variation often represents different plant strategies or adaptations to a wide range of environmental conditions (Wright et al, 2004; Díaz et al, 2016), which usually respond to a trade-off between growth and survival (Reich, 2014) This implies that plants invest in their attributes to an overarching trade-off between maximizing resource acquisition and productivity or Frontiers in Plant Science | www.frontiersin.org de la Riva et al. RES Leads Mediterranean Plant Strategies maximizing resource conservation and longevity, the so-called “fast-slow” economics spectrum (Wright et al, 2004; Reich, 2014). This theoretical framework has been successfully linked to plant performance at the leaf level (Wright et al, 2004) but still remains controversial for roots (Freschet et al, 2021)
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