Phenotypic plasticity and stability of the size and number of adventitious roots of the climbing vine Monstera dubia Kunth (Engler & Krauze), Araceae

Abstract

Some 30% of Tropical Rainforests‟ plant species use roots for anchoring on trees, yet such root-bark interactions remain poorly studied. Hypothetically, bark-surface micro-sites differently offer resources to Monstera dubia roots altering roots‟ dry weight, length and number. I studied N=12 juvenile Monstera dubia individuals growing upon Anacardium excelsum while classifying Anacardium excelsum‟s bark micro-sites into plates, fissures, juxtapositions, sub-plates, and sub-juxtapositions. Since Monstera dubia grows as a series of segments from the ground to the canopy, I determined the relative age of Monstera dubia segments from the youngest to the oldest to explore age-related changes of roots‟ size and number. No Monstera dubia individual had enough segments for single-genotype tests of plasticity in response to micro-sites. Therefore, I ran Dunn‟s tests for classifying all Monstera dubia individuals having similar root weights (groups a-b), and lengths (groups a‟, b‟, and c‟). Segment-age had no-effect on the length and number of roots per segment (Linear regressions, p>0.35), and poorly explains root‟s weight (p<0.0001, r2=0.05). Heavier segments and inter-nodes had more roots than lighter segments (p<0.0001) but such a trend is weak (r2=0.24 for segment‟s weight; r2=0.08 for inter-node‟s weight). The same was valid for root length vs inter-node‟s weight (r2=0.06, p<0.0001), and for number of roots per segment vs inter-node‟s weight (r2=0.18, p<0.0001). For all Monstera dubia individuals, roots into host‟s fissures were lighter than in juxtapositions, sub-plates and sub-juxtapositions (KW, p<0.0001), and shorter than in all other micro-sites (KW; p<0.001). The later also occurred for groups a (p<0.001) and a‟ (p<0.0005), while roots into sub-juxtapositions were larger than in other micro-sites for group b‟ (p<0.005). Root numbers were similar on both left and right sides along M.dubia‟s body. All these suggest that root‟s size phenotypic plasticity, besides the stability of roots‟ number, evolved as part of one single anchoring strategy contributing to Monstera dubia‟s fitness.