Gregory G. Ksander

Field Evaluation of Degree-Day Based Equations for Predicting Sprouting of Hydrilla (Hydrilla verticillata) Turions and Tubers

ABSTRACT The ability to predict sprouting of aquatic macrophyte vegetative propagules is an important step in understanding their temporal distribution and abundance and in developing long-range management strategies. We examined the ability of degree-day based equations to predict monoecious hydrilla (Hydrilla verticillata L. f. Royle) tuber and turion sprouting in Clear Lake, California using sediment and water temperatures measured in the lake. Sediment temperature data were used to calculate accumulated degree-days. Sprouting of turions and tubers was estimated using previously developed equations relating sprouting to accumulated degree-days. There was good agreement between sprouting predictions and field data on the presence of hydrilla in weed rake samples. Small differences among water temperatures at the five sites and strong relationships between water and sediment temperatures indicate that sprouting should be similar in hydrilla beds found along the western and southern shores of upper Clear Lake. These results can be used to estimate optimal timing for surveys of hydrilla abundance and the application of hydrilla management techniques.

Phenolic Acids and Nutrient Content for Aquatic Macrophytes from Fall River, California

Abstract We compared seasonal changes in tissue C, tissue N, C:N ratio, and total phenolic acids for five species of submersed plants from Fall River, California. Mean tissue C differed among the five species and was between 35 and 40%, except for Ranunculus aquatilis, which was 26%. Mean tissue N differed among species; Ranunculus aquatilis had the lowest mean value (2.71%) and Zannichellia palustris had the highest (3.74%). Mean C:N ratio was between 9.7 and 12.7. Among the five species examined, mean phenolic acid content was greatest for Myriophyllum sibiricum and it was nearly seven times that for the species with the lowest phenolic acid content, Elodea canadensis. Regression analysis indicated positive relationships between phenolic acid content and tissue C for two species, Callitriche hermaphroditica and Ranunculus aquatilis. Regression equations relating phenolic acid content to tissue N were not statistically significant. For Elodea canadensis, the equation describing phenolic acid content as a...

Root Size and Depth Distributions for Three Species of Submersed Aquatic Plants Grown Alone or in Mixtures: Evidence for Nutrient Competition

ABSTRACT We hypothesized that if aquatic plants were competing for nutrients then the spatial distribution and sizes of roots should change when competitors were present. Stukenia pectinatus, Potamogeton nodosus, and Hydrilla verticillata (monoecious type) were grown in either monocultures or mixtures in polyvinylchloride containers. Four 5 cm diameter minirhizotrons were mounted horizontally across the containers so that they were 2.5, 12.5, 22.5, or 32.5 cm below the surface of the sediment, and we inserted a specialized video camera in each minirhizotron tube and recorded root images at 21 locations in each tube. For two of three cases, adding plants of another species changed the root depth distribution and increased the volume of soil occupied by roots compared to monocultures. Additionally, smaller diameter roots were more abundant when competitors were present. This implies that the plants adjusted to the presence of competitors by producing more roots capable of nutrient uptake. These results imply that competition for sediment-based nutrients occurred in these systems.

Nutrient Limitation of Zannichellia palustris and Elodea canadensis Growing in Sediments from Fall River, California

ABSTRACT Predicting aquatic plant growth based on sediment nutrients is problematic. Two experiments with sandy or silty sediments from Fall River, California were performed to identify the limiting nutrient for two abundant species of submersed plants in the river. Growth of Zannichellia palustris L. or Elodea canadensis Rich, was significantly enhanced by the addition of N or a combination of N and P to sandy sediments but not those that were silty. Root shoot ratios declined for plants growing with added nutrients. Plant tissue N concentrations increased as well. Tissue N:P ratios indicated that N rather than P limited growth. Results support the literature hypothesis that sediment N availability may limit growth and distribution of submersed rooted aquatic plants.