# Sclerified Cork Outperforms the Exodermis: Root Water Permeability Decreases in the Soil‐To‐Canopy Transition of the Aroid Vine Epipremnum aureum

## TL;DR

Aroid vines adapt to canopy life by replacing root coverings to reduce water loss, enabling survival in atmospheric conditions.

## Contribution

The study reveals that sclerified cork replaces exodermis in aerial roots of Epipremnum aureum, reducing water permeability during canopy transition.

## Key findings

- Aerial roots of Epipremnum aureum develop a sclerified cork, reducing water loss compared to terrestrial roots.
- Exodermis is replaced by cork in non-contact regions of aerial roots, while contact regions retain exodermis and root hairs.
- Ligno-suberized tissues in aerial roots show structural differences between host-contact and atmospheric regions.

## Abstract

The aroid vine
Epipremnum aureum
undergoes changes in habitat and growth axis direction from terrestrial (plagiotropic) to canopy (orthotropic) conditions. Since aerial roots connected to the forest soil are vital for water and nutrient uptake in these vines, we hypothesize that morphophysiological acclimation occurs, enabling root survival under atmospheric conditions. Root morpho‐anatomy, water balance, water absorption assayed via fluorescent tracer, and photochemical activity measured by chlorophyll fluorescence were analyzed. Gentle mechanical abrasion was applied to remove root coverings and compare water retention capacity in intact versus abraded roots. During the soil‐to‐canopy transitions, the root surface shifted from smooth, light brown in terrestrial roots to rough, dark brown surface in aerial roots, a change resulting from exodermis replacement by a sclerified cork in aerial regions. Small host‐contacting regions of aerial roots retained exodermis and epidermal hairs instead of developing a cork, establishing spatial–dimorphism. Intact aerial roots with sclerified cork presented lower water‐loss permeance than terrestrial roots with exodermis; this difference disappeared after abrasion, confirming the functional role of tissue replacement. Optical and fluorescence microscopy identified a ligno‐suberized nature for the covering tissues, differing in structure and size between host‐contact versus atmospheric regions of the aerial roots. While water absorption through root hairs was confirmed in host‐contact, chlorophyll fluorescence suggests minimal photosynthetic capacity in atmospheric region. We propose that exodermis replacement by a sclerified cork is induced by steeper water potential gradients under atmospheric conditions. This anatomical novelty mitigates water loss in aerial roots, enabling
E. aureum
to thrive in the canopy habitat.