Root traits explain different foraging strategies between resprouting life histories

Susana Paula, Juli G. Pausas

Drought and fire are prevalent disturbances in Mediterranean ecosystems. Plant species able to regrow after severe disturbances (i.e. resprouter life history) have higher allocation to roots and higher water potential during the dry season than coexisting non-resprouting species. However, seedlings of non-resprouters have a higher survival rate after summer drought. We predict that, to counteract their shallow-rooting systems and to maximize seedling survival, non-resprouters have root traits that confer higher efficiency in soil resource acquisition than resprouters. We tested this prediction in seedlings of less than 1.5 months old. We select 13 coexisting woody species (including both resprouters and non-resprouters), grew them in a common garden and measured the following root traits: length, surface, average diameter, root tissue density (RTD), specific root length (SRL), surface:volume ratio (SVR), specific tip density (STD), tip distribution in depth, internal links ratio (ILR), and degree of branching. These root traits were compared between the two resprouting life histories using both standard cross-species and phylogenetic-informed analysis. Non-resprouters showed higher SRL and longer, thinner and more branched laterals, especially in the upper soil layers. The external links (i.e. the most absorptive root region) were also more abundant, longer, thinner and with higher SVR for non-resprouters. The results were supported by the phylogenetic-informed analysis for the root traits most strongly related to soil resource acquisition (SRL, SVR and branching pattern). The seedling root structure of non-resprouters species allows them to more efficiently explore the upper soil layer, whereas seedling roots of resprouters will permit both carbon storage and deep soil penetration.