Root depth and morphology in response to soil drought: comparing ecological groups along the secondary succession in a tropical dry forest

Abstract

Root growth and morphology may play a core role in species-niche partitioning in highly diverse communities, especially along gradients of drought risk, such as that created along the secondary succession of tropical dry forests. We experimentally tested whether root foraging capacity, especially at depth, decreases from early successional species to old-growth forest species. We also tested for a trade-off between two mechanisms for delaying desiccation, the capacity to forage deeper in the soil and the capacity to store water in tissues, and explored whether successional groups separate along such a trade-off. We examined the growth and morphology of roots in response to a controlled-vertical gradient of soil water, among seedlings of 23 woody species dominant along the secondary succession in a tropical dry forest of Mexico. As predicted, successional species developed deeper and longer root systems than old-growth forest species in response to soil drought. In addition, shallow root systems were associated with high plant water storage and high water content per unit of tissue in stems and roots, while deep roots exhibited the opposite traits, suggesting a trade-off between the capacities for vertical foraging and water storage. Our results suggest that an increased capacity of roots to forage deeper for water is a trait that enables successional species to establish under the warm-dry conditions of the secondary succession, while shallow roots, associated with a higher water storage capacity, are restricted to the old-growth forest. Overall, we found evidence that the root depth-water storage trade-off may constrain tree species distribution along secondary succession.

The Responses of Forest Fine Root Biomass/Necromass Ratio to Environmental Factors Depend on Mycorrhizal Type and Latitudinal Region

“…Although there was no difference on fine root B/N ratio between forests dominated by early (such as Betula , Pinus , and Populus ) and late successional genera (such as Fagus , Picea , and Quercus ) in this analysis (Table ), fine root B/N ratio of late‐ uccessional forests were closely aligned with climate, topography, and stand factors (Table ). These results are in accordance with many other studies that indicated that successional status strongly influence fine root dynamics and resource acquisition strategies (Paz et al, ; Yuan & Chen, ). Therefore, we conclude that aboveground variables such as stand density, tree age, and successional status should be included in large‐scale studies in order to improve usefulness of fine root biomass and necromass data.…”

Fine‐root exploitation strategies differ in tropical old growth and logged‐over forests in Ghana

“…Shade-tolerant (usually late-successional) species with high wood density are slow growing and may have lower nutrient requirements and, therefore, allocate less C to traits such as root length and surface area leading to lower root biomass (Xiang et al 2013). In addition, shade-tolerant species may increase nutrient uptake efficiency by producing roots with high SRL and SRA values (Xiang et al 2013, Paz et al 2015. On the other hand, shade-tolerant species may produce roots of low SRL and SRA as a conservative strategy to coexist with other species (Leuschner et al 2009, Xiang et al 2013, Reich 2014, Zangaro et al 2014, which is inconsistent with our results.…”

“…, Paz et al . ). On the other hand, shade‐tolerant species may produce roots of low SRL and SRA as a conservative strategy to coexist with other species (Leuschner et al .…”

“…Shade‐intolerant pioneer or light‐demanding species usually have high root length, surface area, and biomass, which allow for the rapid exploitation of soil resources necessary to sustain the high growth rate of such species (Paz et al . ). Alternatively, shade‐intolerant species may produce roots with high root length or surface area per dry mass investment as an adaptation to changes in soil resources after disturbance (Bauhus & Messier , Leuschner et al .…”

“…This significant flux of C to root systems and their symbionts may influence root biomass, architecture, and morphological patterns (Thaler & Pag es 1998, Bauhus & Messier 1999, with associated effects on uptake of soil resources and belowground functioning (Bardgett et al 2014). Plants employ a range of strategies to capture water and nutrient resources and to respond to changes in soil resources, mediated partly by root traits (i.e., biomass, architecture, and morphology) (Ostonen et al 2007a, Hodge 2009, Paz et al 2015.…”