Seed size, germination and seedling growth of Australian species of the desert and halophytic plant genus Frankenia. By Lyndlee C. Easton, Molly A. Whalen and Duncan A. Mackay

Seed size and number Seed size is an important component in plant life histories; –is a measure of amount of resources invested in an individual offspring by parent plant. Maternal resources for producing seeds are limited; –compromise between selection to produce more offspring (many small seeds) & selection favouring greater allocation of maternal resources to each offspring (large seeds). Thus alternate reproductive strategies.

Advantages of multiple small seeds per fruit. Greater number of seeds can be produced; –more chance of some finding suitable site, –often associated with colonizing species.

Advantages of a single large seed per fruit. Larger seeds produce larger seedlings; –better provisioned. Longer roots & taller shoots = increased access to light/soil resources; –competition –shaded environments –burial –survive defoliation –high risk of drought.

Drought risk is a significant factor to life history strategies of arid zone flora. Studies have suggested that larger seeds in arid zones impart some kind of advantage. However; most research to date compares these strategies using seeds from different plant families.

Frankenia (Frankeniaceae) What are frankenias ? –small shrubs, sub-shrubs, herbs –halophytes - salt pans, salt lakes, salt marshes –habit arid desert & coastal regions –specialized soils ie gypsum Characteristics. –white, pink or purple 4- or 5-petalled flowers –salt glands –revolute leaves

Distribution Globally -Mediterranean coastal & desert regions including Europe, the Americas & Middle East Australia - WA, SA, SW Qld, western NSW, NW Vic, southern NT & Bass Strait Islands.

What is the significance of Frankenia in the seed size/number studies? Frankenia include several suites of species that vary in seed size & number although occurring within the same region. Overall study is investigating microhabitats to search for possible reasons for alternate strategies.

Aims Studies have suggested that large seed size provides an advantage for seedling establishment in arid zones. Hypothesis - “Large seeds germinate sooner and at higher percentage of overall numbers than small seeds”.. Seed size is correlated to seedling size ie. large seeds produce large seedlings. Compare germination rates of seeds of various Frankenia species to test germination success using size as a predictor of germination rates.

Aims Arid zones have unpredictable rainfall events. Frankenia more commonly occur in winter rainfall zones but rain can occur at any time -thus temperature may make a difference. Added the variable of temperature.

Methods Compared rates of germination of large seeded species and small seeded species at three temperatures:- 16 o, 24 o and 30 o. Thirteen species with up to 3 populations per species. Five large seeded species - size range >0.5 mg. Eight small seeded species - size range <0.1 mg.

Methods Grown in germination vials for 30 days. Four replicates of 15 seeds per treatment. Scored for germination and removed at 2-day intervals. Germination recorded with emergence of the radicle

Results - Did large seeds germinate faster? Individual species Large seeds vs. small seeds

Results – Was the overall percentage of large seeds that germinated by day 30 higher than small seeds? *Higher germination rates overall at low temperatures. *Small seeded species showed more variable responses at all three temperatures. *Decline in germination at high temperature greater in small seeds.

Results % germinated by day 30 per temperature * Note gap in size range. Small seeds - greater variation between species

Discussion - Seed germination summary. * Larger seeds tended to germinate more rapidly. * Both large and small seeded species exhibited higher germination percentages at cooler temperatures. *Decline in germination percentages at higher temperatures more pronounced for smaller species. * At highest temperatures, variability in final germination was greater amongst smaller seeded species.

Discussion – What are the possible advantages of large seeded species? *Grow quickly after a rainfall event. *Prefer cooler conditions (winter rainfall zone) but can germinate at high temperatures thus utilise any rainfall event for germination. *Advantageous in an unpredictable rainfall zone.

Seedling size and salinity Extent of rainfall event unknown. If only light or of short duration, new seedlings will need to cope will increasing salinity levels as ground water content decreases. Hypothesis - “Large seedlings have longer roots to keep track with receding water levels.” Do seedlings of small seeded species cope with higher salinity levels?

Preliminary salinity trials - Methods Seedlings germinated and grown for 3 weeks in standardized conditions. Subjected to 33%, 66% and 100% salinity of seawater. Watered every second day for one month. Dry weights, height, number of nodes recorded.

Preliminary results.

Preliminary results – Salinity tolerance. 1 plant only Greater root mass at 33% 1 plant only 0%33%66%100% Small10 53 Large9810 Number alive at day 30. Ten plants per treatment.

Conclusions * Do large seeded species germinate faster and at greater percentages than small seeded species? Yes - Advantageous to unpredictable rainfall events. *Do seedlings of small seeded species tolerate higher salinity levels? Yes – Advantageous to smaller seedlings growing in highly saline areas eg adjacent to salt pans. Further work – Adding more species to the trials. Include droughting experiments. Include drought/salinity experiments.

Acknowledgments This study is part of PhD research undertaken at Flinders University, SA. This project is partially funded by; Australian Flora Foundation Research Grant Nature Foundation SA Inc. Mark Mitchell Research Foundation