Size‐correlated morpho‐physiology of the aroid vine Rhodospatha oblongata along a vertical gradient in a Brazilian rain forest

Abstract

In this work, we analyse morpho-physiological modifications presented during the allomorphic growth of the aroid vine Rhodospatha oblongata Poepp throughout its ascent into the forest canopy. We test the hypothesis that morphological modifications in the root, shoot and leaf are followed by a gradual improvement of the xylem vascular system in order to increase water acquisition and transport as body size increases. The characterisation of these structural modifications was based on 30-35 specimens divided into six size classes. The dimensions of shoots, leaves and roots were quantified and qualified. The transition from the terrestrial to the epiphytic phase was followed by a simultaneous increase of leaf number and lamina area, together with increased length and diameter of the petiole. Furthermore, as the plant grows, the shoot internodes become shorter and thicker. However, occurrence of aerial roots is the most important characteristic in the ascending phase. In taller individuals, the increase in number of roots with wider xylem vessels guarantees an increased theoretical xylem hydraulic conductance for this growth phase. Along an acropetal direction of the same shoot, the diameter of xylem vessels increased, while the number of vessels per stele area decreased, in contrast with such allometric models as that of West, Brown and Enquist, showing that xylem vessel number and diameter taper in a reverse manner along the same direction. Such structural changes of R. oblongata allow improved foraging for light and water, facilitating the survival of bigger-sized plants of this vine in the canopy.

Aerial root hydraulic conductivity increases with plant size for the aroid vine Rhodospatha oblongata (Araceae)

“…The adventitious root system of R. oblongata increases in size (length and external diameter) as long as this plant species ascends the host toward the canopy (Filartiga et al, 2014). Data presented herein show that this increment is followed by an increase in number and diameter of xylem vessels, improving the respective axial hydraulic conductivity of anchor and feeder roots with plant size.…”

“…When some of its branches reach the trunk of a host, the vine begins to grow vertically up to 8-10 m in height ( Figure 1). Along this ascent, stem diameter and leaf area increase, along with the simultaneous appearance of two types of aerial roots, anchor and feeder ( Figure 1), both of which increase in number and diameter with increasing plant size (Filartiga et al, 2014).…”

“…The influence of root size on the respective hydraulic conductivity of these root types was evaluated for 30 anchor roots and 30 feeder roots. Of these specimens, six samples (01 anchor and 01 feeder root per individual plant; 06 plants per size class) each were obtained from plants with different class sizes, according to Filartiga et al (2014): class I) plants with terrestrial habits (not analyzed owing to the absence of aerial roots); class II) plants with 0-1 m in height; III) plants with 1-2 m in height; class IV) plants with 2-3 m in height; class V) plants with 3-5 m in height; class VI) plants with 5-7 m in height. Each root was characterized by its external and stele diameters, total sum of xylem vessel diameters, and maximum axial hydraulic conductivity (Khmax).…”

“…However, no data were available for anchor roots since their size in this species is much reduced. When Rhodospatha oblongata ascends through the canopy, Filartiga et al (2014) described that both anchor and feeder roots become longer, wider and more numerous, presenting a wider stele composed of large xylem vessels. This increase of xylem vessel diameter was reported to positively influence plant hydraulic conductivity.…”

Mechanisms for minimizing height‐related stomatal conductance declines in tall vines

“…Yet, compared with trees, vines have a much lower sapwood area per unit of leaf area, which in trees has been associated with reduced water supply and carbon assimilation per leaf area (Ewers, Oren, Bohrer, & Lai, 2007;Phillips, Bond, McDowell, Ryan, & Schauer, 2003;Whitehead, Edwards, & Jarvis, 1984). Furthermore, compared with trees, the flow path along the stem of vines is much longer relative to the conducting stem cross-sectional area (Filartiga, Vieira, Mantovani, & Rennenberg, 2014;Rosell & Olson, 2014). Despite those restrictions to maximum water flow rates through long and narrow stems, vines can contribute a significant proportion of total evapotranspiration and carbon uptake in ecosystems (Restom & Nepstad, 2001).…”