Germination characteristics of Zannichellia palustris from a northern California spring-fed river

Authors: Bytnerowicz, Thomas; Carruthers, Raymond

Submitted to: Aquatic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2014
Publication Date: 6/30/2014
Publication URL: http://doi.org/10.1016/j.aquabot.2014.06.013
Citation: Bytnerowicz, T.A., Carruthers, R.I. 2014. Germination characteristics of Zannichellia palustris from a northern California spring-fed river. Aquatic Botany. 119:44-50.

Interpretive Summary: Horned pondweed, Zannichellia palustris, is a common native plant species that grows in many lakes and streams throughout North America and the world. It is a key natural component of the vegetation in the Fall River of Northern California where it serves as one of the primary producers that acts as the bases of a complex food chain that supports a world-famous trout fishery in the area. The Fall River runs through an extensive agricultural area that draws water from this tributary and in recent years has been invaded by exotic plants such as Eurasian watermilfoil. Efforts to reduce milfoil growth and displace it with more highly desired species such as Z. palustris have required detailed biological studies on many different aspects of this native species life cycle, including its germination characteristics and dynamics. This current study experimentally assessed Z. palutris seed germination in conjunction with differing temperature conditions that are critical in determining the magnitude and timing of seed germination and establishment in the Fall River and elsewhere. Studies determined that the time to germination is highly temperature dependent and the seed germination is highest between 25-30 degrees C. Temperatures beyond 35 degree C highly limit seed germination and no seeds germinate over 40 degree C. Colder temperature highly extend the germination time, however, seeds at all temperature showed a high degree of variability in germination time, causing Z. palustris to have a very extended time of reseeding. This is advantageous to the plant in that some seeds are nearly always in a state of ready germination when habitats are opened through ecological disturbances.

Technical Abstract: The germination characteristics of Zannichellia palustris seeds collected from the spring-fed Fall River of Northern California were investigated across a range of constant temperatures from 4.2 to 40.8 ºC. Germination experiments were conducted on freshly produced and collected seeds. Seeds germinated at all temperatures except 40.8 ºC, with the maximum germination fraction observed at 24.4 and 29.5 ºC with 69 ± 5 and 73 ± 3 % total germination, respectively. Germination rates (1/time) were also highest at 24.4 and 29.5 ºC where median germination periods were observed to be 9 d. At 4.2 ºC, the lowest experimental temperature, 45 ± 7 % of seeds germinated over a span of over 200 days with a median germination time of 133 d. The cumulative spread in germination over time was determined to be log-normally distributed through modeling comparisons made using a probit function for both individual temperatures and for temperature data that was converted to thermal units, through linear regressions of subpopulations. Findings suggest that Z. palustris seeds from cold-water systems, such as the Fall River, will germinate at high percentages over a range of temperatures below 30 ºC, and that rates are lowest and germination spread greater at lower water temperatures (such as 5 ºC), while rates are greatest and germination spread at its lowest at the optimal temperatures that are between 20 and 30 ºC. These data are useful in predicting germination and establishment times in conjunction with other measured environmental parameters in natural waterways.