Phosphorus-limited Conditions Research Articles

The nutritional ecology of Cyperus esculentus, an emergent aquatic plant, grown on different sediments

In a greenhouse investigation, Cyperus esculentus L. was grown from tubers on sediments obtained from different shoreline regions of the Great Lakes, U.S.A. The sediments were predominantly fine textures, but differed greatly in organic and nutrient contents. A wide range of biomass was obtained after 3 months of growth. Concurrent sand culture experiments with Cyperus under nitrogen- and phosphorus-limiting conditions provided critical concentrations of nitrogen and phosphorus, which were used to evaluate the supply of these elements to Cyperus grown on the different sediments. Differences in plant growth and biomass distribution were related to sediment fertility. Nitrogen was demonstrated to limit the growth of Cyperus on 10 of the 11 sediments examined. Ratios of belowground to aboveground biomass were negatively correlated with plant growth. The allocation of biomass to both aboveground and belowground portions of Cyperus is discussed in relation to the degree of nutrient limitation and other metabolic stresses.

Algal growth prediction using growth kinetic constants

The growth kinetics under conditions of phosphorus limitation of Selenastrum capricornutum Printz, a green alga specified for use in algal bioassays, were used to predict growth in batch cultures for varied specific conditions of time and phosphorus concentration. These predictions compared very well with actual batch culture growth studies. The predicted maximum cell concentration for two different levels of phosphorus lay within values obtained in different laboratories. The predicted maximum specific growth rates ( μ ̄ ) were either close to or just above actual laboratory data. The determination of growth kinetics thus allows accurate prediction of the growth of planktonic algae, a benefit in either algal bioassays or the solution of practical eutrophication problems. The growth kinetic constants of specific algae important in eutrophication problems need to be determined in order to utilize potentialities of prediction in the rational solution of these problems.