Adaptations of strangler figs to life in the rainforest canopy

Abstract

Figs are rainforest keystone species. Non-strangler figs establish on the forest floor; strangler figs establish epiphytically, followed by a dramatic transition from epiphyte to free-standing tree that kills its hosts. Free-standing figs display vigorous growth and resource demand suggesting that epiphytic strangler figs require special adaptations to deal with resource limitations imposed by the epiphytic environment. We studied epiphytic and free-standing strangler figs, and non-strangler figs in tropical rainforest and in cultivation, as well as strangler figs in controlled conditions. We investigated whether the transition from epiphyte to free-standing tree is characterised by morphological and physiological plasticity. Epiphyte substrate had higher levels of plant-available ammonium and phosphate, and similar levels of nitrate compared with rainforest soil, suggesting that N and P are initially not limiting resources. A relationship was found between taxonomic groups and plant N physiology; strangler figs, all members of subgenus Urostigma, had mostly low foliar nitrate assimilation rates whereas non-strangler figs, in subgenera Pharmacocycea, Sycidium, Sycomorus or Synoecia, had moderate to high rates. Nitrate is an energetically expensive N source, and low nitrate use may be an adaptation of strangler figs for conserving energy during epiphytic growth. Interestingly, significant amounts of nitrate were stored in fleshy taproot tubers of epiphytic stranglers. Supporting the concept of plasticity, leaves of epiphytic Ficus benjamina L. had lower N and C content per unit leaf area, lower stomatal density and 80% greater specific leaf area than leaves of conspecific free-standing trees. Similarly, glasshouse-grown stranglers strongly increased biomass allocation to roots under water limitation. Epiphytic and free-standing F. benjamina had similar average foliar δ 13 C, but epiphytes had more extreme values; this indicates that both groups of plants use the C 3 pathway of CO 2 fixation but that water availability is highly variable for epiphytes. We hypothesise that epiphytic figs use fleshy stem tubers to avoid water stress, and that nitrate acts as an osmotic compound in tubers. We conclude that strangler figs are a unique experimental system for studying the transition from rainforest epiphyte to tree, and the genetic and environmental triggers involved.

Hemiepiphytic figs kill their host trees: acquiring phosphorus is a driving factor

“…Adaptive strategy of hemiepiphytic figs in changing habitats. These supplementary adaptive strategies of hemiepiphytic figs are reported by Putz & Holbrook (1989); Holbrook & Putz (1996); Schmidt & Tracey (2006); Guevara & Lopez (2007); Hao et al . (2010); Hao et al .…”

“…But once in the canopy, hemiepiphytic figs face drought stress and adjust to the relatively dry environment by modifying their hydraulic traits (Holbrook & Putz, 1996; Hao et al ., 2011; Liu et al ., 2014). For their germination and seedling growth, hemiepiphytic figs must rely on the nutrient and water conditions of microsites provided by host trees (Laman, 1995; Athreya, 1999) and economically use nitrogen (N) at their epiphytic stage (Schmidt & Tracey, 2006). As epiphytic seedlings grow downward from the canopy, corresponding shifts in habitat conditions (e.g.…”

“…S1), these figs are better known as ‘stranglers’, could be a reason for why their host trees die prematurely (Berg & Corner, 2005; Zotz et al ., 2021). But knowledge gaps persist regarding the competition between hemiepiphytic figs and their hosts, fitness advantages gained by the former when the latter die, and adaptive strategies of hemiepiphytes through different growth phases (Lawton & Williams‐Linera, 1996; Schmidt & Tracey, 2006; Machado et al ., 2018). Previous studies have inferred that acquiring light and escaping mortality risks (e.g.…”

Diversity and distribution of fig (Ficus spp) in University of Sumatera Utara (USU) green space

“…Seeds that fall on the host tree's canopy grow and produce roots that proliferate downward until they reach the ground and surround the host. allowing it to grow larger [27].…”

Epiphytic Weeds Control by Root Infusion Method in Oil Palm

“…Epiphytic plants (banyan) are strangling plants whose roots are wrapped around the stem of the main plant. The roots grow towards the soil to absorb water and nutrients (Schmidt & Tracey, 2006). Epiphytic weed control with the root infusion method has advantages over the spray method in terms of safety for the applicator.…”