Trade‐off between root porosity and mechanical strength in species with different types of aerenchyma

Abstract

The objective of this work was to study the existence of a trade-off between aerenchyma formation and root mechanical strength. To this end, relationships among root anatomical traits and mechanical properties were analysed in plant species with contrasting root structural types: Paspalidium geminatum (graminaceous type), Cyperus eragrostis (cyperaceous type), Rumex crispus (Rumex type) and Plantago lanceolata (Apium type). Variations in anatomical traits and mechanical strength were assessed as a function of root diameter by exposing plants to 0, 7, 15 and 30 d of control and flooded conditions. For each species, the proportion of root cortex was positively associated with the increment of root diameter, contributing to the increase in root porosity under both control and flooded conditions. Moreover, cell lysis produced an additional increase in root porosity in most species under flooded conditions (except R. crispus). Both structural types that presented a uniseriate layer (epidermis) to cope with compression (Rumex and Apium types) were progressively weakened as root porosity increased. This effect was significant even when the increment of root porosity was solely because of increased root diameter (R. crispus), as when both processes (root diameter and cell lysis) added porosity to the roots (P. lanceolata). Conversely, structural types that presented a multiseriate ring of cells in the outer cortex (graminaceous and cyperaceous types) maintained mechanical strength over the whole range of porosity, in spite of lysogenic processes registered in the inner cortex. In conclusion, our study demonstrates a strong trade-off between aerenchyma formation and mechanical strength in root structural types that lacked a multiseriate ring of tissue for mechanical protection in the outer cortex. The results suggest that this ring of tissue plays a significant role in maintaining the mechanical strength of roots when flooding induces the generation of additional aerenchyma tissue in the root cortex.

Large Root Cortical Cell Size Improves Drought Tolerance in Maize

“…The reduced variation and smaller cells in outer and inner bands could be related to their functions: the inner band represents highly specialized cells with important functions for the regulation of radial transport in the roots, and the outer band provides protection against pathogen entry. In addition, the multiseriate epidermal band cells have been associated with root mechanical strength (Striker et al, 2007). Root CCS was correlated with the size of cells of the mesocotyl cortex and leaf midrib parenchyma.…”

Root Cortical Aerenchyma Enhances Nitrogen Acquisition from Low-Nitrogen Soils in Maize

“…RCA formation may reduce mycorrhizal symbiosis, which requires living cortical tissue. RCA may also affect the mechanical strength of roots, especially in plant species that lack a structural support in the outer part of the cortex, although maize was not in that category in a study of resistance to radial compression (Striker et al, 2007). The cost/benefit of RCA and its interactions with other root traits are likely to be complex and may differ in different environments.…”

Morpho-Anatomical Traits for Plant Adaptation to Drought

“…Recently, it has been also speculated that the presence of cortical lacunae is beneficial under drought conditions because it reduces root metabolic costs by transforming living cortical cells in air volume (Zhu et al 2010). However, the formation of cortical lacunae can weaken root mechanical strength, making it more vulnerable in soils prone to swelling-shrinkage cycles consequent to frequent fluctuations in water availability (Striker et al 2007). This weakening of root strength can be counterbalanced by the general finding of increased development of lignified tissues with cells characterised by thicker walls in various structures (e.g.…”