Growth, Photosynthesis, and Respiration of the Aquatic Floating Fern Salvinia minima

Salvinia minima is a relatively small, floating aquatic leptosporangiate fern in the family Salviniaceae. It is widely distributed in the horticultural trade as an ornamental plant for aquaria and aquatic gardens. Consequently, it has escaped into the natural environment where it produces large, dense mats of branching ramets that are often deleterious to other aquatic biota, particularly in tropical and mild temperate regions. This is a report of a laboratory experimental study of the growth, photosynthesis and dark respiration of S. minima, particularly addressing the variables in a way that is potentially relevant for environmental and ecological research applications. Photosynthetic carbon assimilation rates are inversely related to the leaf area of the ramets, and approximates a second-order polynomial function defined by non-linear regression analysis (p < 0.01); namely, A = 6.3761 - 0.3381 (*) L +0.005 * L-2, where A is CO2 assimilation rate (mu mol m(-2) s(-1)) and L is leaf area of the ramets (cm(2)). Data are also presented on the quantum yield efficiency (F-v/F-m) and electron transfer (ET0/RC) for ramet leaves of different sizes, indicating that low quantum yield efficiency most likely accounts for lower CO2 assimilation rates in more mature ramets with larger leaves. The dark respiration is approximately equivalent to 30% of the net photosynthesis CO2 assimilation rate. The relative growth rate (RGR) is 0.03 accounting for about a 4% gain in weight per day relative to the initial weight of the S. minima ramets.