Root morphophysiology changes during the habitat transition from soil to canopy of the aroid vine Rhodospatha oblongata

Abstract

Background and Aims The aroid vine Rhodospatha oblongata is characterized by a habitat change from terrestrial to canopy, relying on aerial roots at maturity to obtain water and nutrients from the forest soil. We hypothesize that morpho-physiological acclimation occurs in roots as they grow under atmospheric conditions. These changes would guarantee the whole plant survival of aroid vines in the new and potentially stressful habitat of the canopy. Methods Terrestrial and aerial roots were compared on a morpho-physiological basis. Root anatomy, water balance, water absorption capacity via fluorescent tracer, and photochemical activity via chlorophyll fluorescence were measured. Key Results While thin fasciculate roots occur on terrestrial crawling individuals, two clearly distinct aerial roots (anchor and feeder) are produced on canopy individuals, which are both adhered to the host trunk. The color of both aerial roots change during development from red and brownish to striped and green at maturity. Color changes are induced by the replacement of epidermis, exodermis, and outer cortex by an inner layer of lignified cork on the root region exposed to the atmosphere. In the root region that is in contact with the host, covering substitutions do not occur and both exodermis and lignified cork, along with several epidermal hairs, appear. Water retention capacity was higher in green roots than in other root types. Rehydration capacity via water absorption by hairs of aerial roots was confirmed by fluorescence. Chlorophyll fluorescence data indicated low levels of photosynthetic capacity in both root types. Conclusions Plants should evolve strategies to survive stress situations. The transition from soil to canopy imposes abiotic changes and potentially stressful situations to R. oblongata. We conclude that the morpho-physiological changes observed represent an important strategy that permits the maintenance of aroid roots and the survival of R. oblongata in the canopy.

Putting vascular epiphytes on the traits map

“…Whether their roots are less effective in absorption than those of tank bromeliads and if epiphyte roots in general have anatomical adaptations for greater mechanical strength and differ from ground roots is not known, but could easily be investigated (Liz Filartiga et al, 2020). Roots have been included rather late into the plant functional trait spectrum, but are important to understand plant strategies (Laliberté, 2017) and the lack of root data leaves a substantial gap in understanding epiphyte adaptations and their trait spectrum.…”

Maize plants and the brace roots that support them

“…Perhaps we can learn from other aerial roots. For example, the aerial feeder roots of the monocot Rhodospatha oblongata exhibit cell death of the exterior cell layers, but also death of the epidermis, exodermis and outer cortex layers (Filartiga et al ., 2021). These outermost layers are replaced by a lignified cork, which is a rare occurrence in monocots, and the acquisition of a green color (Filartiga et al ., 2021).…”

“…For example, the aerial feeder roots of the monocot Rhodospatha oblongata exhibit cell death of the exterior cell layers, but also death of the epidermis, exodermis and outer cortex layers (Filartiga et al ., 2021). These outermost layers are replaced by a lignified cork, which is a rare occurrence in monocots, and the acquisition of a green color (Filartiga et al ., 2021). In their study, the authors propose that these changes are adaptations to the aerial growth environment and improve water retention and provide small photosynthetic capacities (Filartiga et al ., 2021).…”

“…These outermost layers are replaced by a lignified cork, which is a rare occurrence in monocots, and the acquisition of a green color (Filartiga et al ., 2021). In their study, the authors propose that these changes are adaptations to the aerial growth environment and improve water retention and provide small photosynthetic capacities (Filartiga et al ., 2021). By contrast, orchid aerial roots have a specialized outer layer called the velamen radicum, which consists of layers of dead cells that act to absorb water from the air (Hauber et al ., 2020).…”

Microbiota-mediated nitrogen fixation and homeostasis in aerial root-mucilage

“…Plant aerial roots have distinct functions from underground roots such as anchorage, oxygen absorption (Shekhar et al, 2019), water uptake, photosynthesis (Zotz and Winkler 2013), and support (Eskov et al, 2016, Liz Filartiga et al, 2020. Most aerial roots require to enter the soil or cling to other support to perform above function.…”