Allometric scaling laws linking biomass and rooting depth vary across ontogeny and functional groups in tropical dry forest lianas and trees

Abstract

Summary There are two theories about how allocation of metabolic products occurs. The allometric biomass partitioning theory (APT) suggests that all plants follow common allometric scaling rules. The optimal partitioning theory (OPT) predicts that plants allocate more biomass to the organ capturing the most limiting resource. Whole‐plant harvests of mature and juvenile tropical deciduous trees, evergreen trees, and lianas and model simulations were used to address the following knowledge gaps: (1) Do mature lianas comply with the APT scaling laws or do they invest less biomass in stems compared to trees? (2) Do juveniles follow the same allocation patterns as mature individuals? (3) Is either leaf phenology or life form a predictor of rooting depth? It was found that: (1) mature lianas followed the same allometric scaling laws as trees; (2) juveniles and mature individuals do not follow the same allocation patterns; and (3) mature lianas had shallowest coarse roots and evergreen trees had the deepest. It was demonstrated that: (1) mature lianas invested proportionally similar biomass to stems as trees and not less, as expected; (2) lianas were not deeper‐rooted than trees as had been previously proposed; and (3) evergreen trees had the deepest roots, which is necessary to maintain canopy during simulated dry seasons.

Digging deeper? Biomass allocation patterns in trees and lianas in tropical seasonal forests

“…It was hypothesized that because lianas use trees as support to grow, they would allocate less biomass to stems and potentially invest their resources in leaves to reach the canopy and also in roots to provide anchorage and to explore deeper soils in search for water and nutrients, especially during dry periods (Selaya et al , ; van der Heijden et al , ). Contrary to the general belief, Smith‐Martin et al found that mature lianas do not invest less in stem biomass and do not display deeper root systems when compared to deciduous and evergreen mature trees in a tropical dry forest. Their model simulations indicate coordination between belowground allocation and aboveground phenology, mainly related to water supply, where evergreen trees invest in deeper roots to sustain leaves for longer periods than deciduous trees and lianas, since the latter display shallower root systems.…”

“…714–726) dug deep into these questions by bringing together results from fieldwork, a common‐garden experiment, and also by incorporating their results in an individual‐based terrestrial biosphere model to test the effects of changing biomass allocation and the rules behind such patterns. While Smith‐Martin et al confirm some of the expectations regarding biomass allocation of lianas and trees in tropical dry forests, they also find surprising and important trends that contradict prevailing wisdom.…”

“…Due to the increasing dominance of lianas growing in tropical forests and their potential role in decreasing carbon accumulation in forests by intensifying tree mortality (van der Heijden et al , ), understanding how co‐occurring trees and lianas share the same space and allocate carbon aboveground and belowground becomes crucial. In this issue of New Phytologist , Smith‐Martin et al . (2020; pp. 714–726) dug deep into these questions by bringing together results from fieldwork, a common‐garden experiment, and also by incorporating their results in an individual‐based terrestrial biosphere model to test the effects of changing biomass allocation and the rules behind such patterns.…”

“…Owing to the high species diversity, sometimes not so welcoming environmental conditions, and remote access, working in tropical forests is a major challenge that becomes even harder when harvesting whole mature trees and lianas in situ . Nonetheless, by using shovels and picks, Smith‐Martin et al shone a needed spotlight on ecological concepts that have been studied since the 19 th century (Kny, ), proving that we may need to revisit some theories before generalizing them across biomes and life forms. It was hypothesized that because lianas use trees as support to grow, they would allocate less biomass to stems and potentially invest their resources in leaves to reach the canopy and also in roots to provide anchorage and to explore deeper soils in search for water and nutrients, especially during dry periods (Selaya et al , ; van der Heijden et al , ).…”

Conceptualising the Global Forest Response to Liana Proliferation

“…Liana physical advantages also extend belowground, potentially including deeper, more extensive root systems and faster capillary flow than trees (Ewers et al, 1991;Restom and Nepstad, 2001). However, recent data from Costa Rica suggest that liana roots extend no deeper than trees (Smith-Martin et al, 2019). Further liana advantages among some species also include increased tolerance to herbivores (Ashton and Lerdau, 2008) and release of allelopathic chemicals (Ladwig et al, 2012).…”