Jean W. Wooten

An examination of the phytotoxicity of the water shield, Brasenia schreberi

Antialgal, antibacterial, and allelopathic properties of the submersed, aquatic, dicotyledonous water shield,Brasenia schreberi Gmelin (Cabombaceae), were examined. Extracts ofB. schreberi were found to inhibit the eukaryotic alga,Chlorella pyrenoidosa, and the prokaryotic alga,Anabena flosaqua, as well as nine different bacteria. Lettuce seedling bioassay showedB. schreberi to be allelopathic. These phytotoxic properties probably contribute to the observed dominance ofB. schreberi in aquatic environments and also make it a promising candidate for allelopathic plant management of aquatic weeds.

Variations in leaf characteristics of six species of Sagittaria (alismataceae) caused by various water levels

Abstract Plants grown from seeds of Sagittaria falcata, S. lancifolia, S. platyphylla, S. rigida, S. isoetiformis and S. papillosa were grown in water-saturated soil or soil submerged to 4.5, 12, 19.5 or 27 cm. Length and width of leaves and petiole lengths were measured at anthesis of the first flower on the first inflorescence produced by each plant. In general, leaf width and length were decreased by submergence, and petiole length increased. The species × water depth interaction was significant for emersed leaf width, leaf length and petiole length except for S. lancifolia leaf length and S. papillosa leaf length and width. These trends indicate genetic differences among, and variability within, taxa. Leaf width, leaf length and petiole length of plants growing in seed source populations were measured. The means from these measurements, when compared to those from experimental plants, indicate that both groups of plants respond similarly to variations in water depth.

Allelopathic potential ofnuphar lutea (L.) Sibth. & Sm. (Nymphaeaceae).

Aqueous extracts ofNuphar lutea (L.) Sibth. & Sm. leaves (blades plus petioles) and roots plus rhizomes were tested for allelopathic activity using lettuce seedling andLemna minor L. assay systems. The 12.5, 25, 125, and 250 parts per thousand (ppt) treatments of both extracts killed the lettuce seedlings. At 2.5 ppt of extract, radicle growth of lettuce was 29% of the control for leaves and 31% of the control for roots plus rhizomes.Lemna minor frond number was reduced to 34% of the control by the 25 ppt leaf extract and to 43% of the control by the 25 ppt roots plus rhizomes extract.L. minor was killed by concentrations of 125 ppt and above of both plant part extracts. As expected, the frond number and total chlorophyll content measured by theL. minor assay were highly correlated. Osmotic potentials below 143 mOsmol/kg had no influence onL. minor growth. Neither the osmotic potential nor the pH of the undiluted extracts ofN. lutea were in the range known to influence the growth of either lettuce seedlings orL. minor. Nuphar lutea extracts were many times more inhibitory than 16 other hydrophytes we previously examined.

Edaphic factors associated with eleven species of Sagittaria (Alismataceae)

Abstract Soil from 69 populations of Sagittaria falcata, S. lancifolia, S. platyphylla, S. rigida, S. isoetiformis, S. papillosa, S. stagnorum, S. fasciculata, S. cristata, S. kurziana and S. subulata were analyzed for pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and organic matter (OM). Significant intercorrelations were found between Ca, Mg and OM. Significant differences between means of one or more measured parameters were associated with differences in the distribution of all the taxa, suggesting a specificity for certain soils.

Effects of photoperiod, light intensity, and stage of development on flower initiation in Sagittaria graminea Michx. (Alismataceae)

Heterophyllous plants of Sagittaria graminea Michx. do not normally flower until non-phyllodial leaves have emerged from the water. Effects of photoperiod, light intensity, and excision of non-phyllodial leaves on growth and flower initiation by plants developing from submerged seedlings were tested in controlled environments. Light quality and irradiance were measured as function of water depth. Plants flowered at all tested daylengths (7–15 hours per day). In light of high irradiance (ca. 3000 μW cm−2 at soil surface) plants without emergent leaves (i.e. bearing only phyllodia) flowered when grown in shallow water (5 cm). When grown in deeper water (17.5 cm), they flowered only after leaves had emerged. A low irradiance (ca. 600 μW cm−2) sufficed for leaf emergence and flower formation at this depth; higher irradiances resulted in faster growth and earlier flowering. An hypothesis involving phytochrome is presented to explain the depth-dependence of the morphogenetic sequence.

Observations of inflorescence patterns and flower sex in a population of Sagittaria papillosa Buch. (Alismataceae)

Abstract Sagittaria papillosa Buch. is monoecious with unisexual flowers, pistillate below, staminate above, typically with an unbranched scape. A large population with unusual numbers of staminate and bisexual flowers on the lowest whorl of the inflorescence and many particles was quantitatively evaluated. First-formed inflorescences had more staminate and bisexual flowers than those produced later. Branched scapes were predominantly found to be the second inflorescence produced by a given plant. Genetic crosses between flowers on recemes and panicles produced no branched inflorescences. When grown under greenhouse conditions all tested plants had racemes with pistillate flowers in the lower whorls and staminate ones above. Data from soil parameters, daylengths and air temperatures are compared to reported information on modification of flower sexuality by these factors.