Title : High, medium and low cover gradient of vallisneria spiralis in association with plant species diversity and phenology of five tropical ponds near kolkata, India
Vallisneria spiralis, a widespread but least concern aquatic macrophyte as per red list of IUCN (2019). The species is well known oxygenator plant in our aquarium. V. Spiralis is reported to be more acceptable rosette forming type than canopy forming ones in respect to rampant public uses specially of our rural and peri-urban tropical ponds. To date, risk assessment of this plant invasion in temperate lakes reported no major threats on native biodiversity and ecosystem functional services. Only presence of V. Spiralis in clear water of Indian ponds had been observed and recorded but abundance, phenology of associated species was poorly studied. Co-existence and phenology of aquatic plant species including their major growth forms were investigated to collect baseline data in five selected eutrophic ponds (total nitrogen: 7 to 9 mgl-1; total phosphorus: 0.1 to 0.2 mgl-1) around Kolkata (India), used for bathing, washing and cleaning of utensils. Ponds were selected on the basis of gradient of Vallisneria spiralis coverage [high (70%): two ponds, medium (45%): one pond and low (6%): two ponds] for fifty-one months, in order to gain an idea about species biology, their diversity strategy and utility. Total of twenty hydrophytic species including dominant (≥50% occurrence) angiosperms, less-dominant (≤50% occurrence) ferns and macro-algae were recorded during the study period. Average number of less-dominant species presence was observed to be greater in high cover ponds. Nymphaea pubescens, a locally threatened species, Rotala rotundifolia, an uncommon species of the area and Azolla pinnata, a useful biofertilizer species were found to be present. More than half of total recorded plant list was noted to be useful/economic from different aspect of utilization by rural communities for their livelihood subsistance. Significant associations (P≤0.05) with invasive (Alternanthera philoxeroides in all ponds and Eichhornia crassipes in medium as well as low cover ponds) and non-invasive [Nymphoides hydrophylla and Marsilea minuta (dominant form) in high cover ponds, Ludwigia adscendens in medium and low cover ponds] were observed according to Jaccard Similarity Coefficient. Implications of these results have been discussed in light of conservation of local species and management of invasive macrophytes. When growth-form was considered, species in same categories of ponds pooled together for representative samples. Highest monthly occurrence for Emergent species, record of reproductive structures in nearly 60% of survival period of floating types and dense pond area infestation for almost half of the presence of submerged form were unique features of high cover ponds. Thus baseline data showed particular mode of phenological trait should be studied for a specific type of growth form in ponds with rich V. Spiralis.