Seed germination in a southern Australian temperate seagrass

Abstract

In a series of experiments, seeds from a temperate seagrass species, Zostera nigricaulis collected in Port Phillip Bay, Victoria, Australia were exposed to a range of salinities (20 PSU pulse/no pulse, 25 PSU, 30 PSU, 35 PSU), temperatures (13 °C, 17 °C, 22 °C), burial depths (0 cm, 1 cm, 2 cm) and site specific sediment characteristics (fine, medium, coarse) to quantify their impacts on germination rate and maximum overall germination. In southern Australia the seagrass Z. nigricaulis is a common subtidal species; however, little is known about the factors that affect seed germination which is a potential limiting factor in meadow resilience to natural and anthropogenic disturbances. Overall seed germination was low (<20%) with germination decreasing to <10% when seeds were placed in the sediment. When germination of Z. nigricaulis seeds was observed, it was enhanced (greater overall germination and shorter time to germination) when seeds were exposed to a 20 PSU pulse for 24 h, maintained at salinity of 25 PSU, temperatures <13 °C, in sediments with fine or medium grain sand and buried at a depth of <1 cm. These results indicate that germination of Z. nigricaulis seeds under in situ conditions may be seasonally limited by temperatures in southern Australia. Seed germination may be further restricted by salinity as freshwater pulses reaching 20 PSU are typically only observed in Port Phillip Bay following large scale rainfall events. As a result, these populations may be particularly susceptible to disturbance with only a seasonally limited capacity for recovery.

Germination Data Analysis by Time-to-Event Approaches

“…McNair et al [17] reviewed exhaustively non-parametric and semi-parametric models applied to germination data, whereas Onofri et al [18] considered a range of AFT models to describe germination responses for different weed species. Other authors applied these methods to their research, more precisely non-parametric and semi-parametric models [19][20][21][22][23][24][25][26][27] and AFT model [28,29].…”

Mutualistic relationships in marine angiosperms: Enhanced germination of seeds by mega‐herbivores

“…This suggests that Z. muelleri seeds which have been dropped by the plant may need to undergo some type of stress to break dormancy (Orth et al, 2000(Orth et al, , 2006, and that temperature does not act as a germination cue for Z. muelleri in the tropics. This is unlike temperate regions where Z. muelleri is also found, and for other Zostera species (Abe et al, 2008;Brenchley & Probert, 1998;Cumming et al, 2017). Seeds which have passed through a marine mega-herbivore appear to have already undergone a form of dormancy break, and temperature stress had no additional germination benefits.…”

“…To reduce confounding issues, the germination experiment concentrated on one environmental factor (temperature) (Cumming et al, 2017; Fernández‐Torquemada & Sánchez‐Lizaso, 2013; Jarvis & Moore, 2008; Stafford‐Bell et al, 2016; Xu et al, 2016) in conjunction with a seed deposition treatment (passed through a herbivores gut or dropped from the plants). To assess the effect of temperature on germination success, we exposed seeds to three temperature treatments: low (19°C ± 1), medium (26°C ± 1), and high (32°C ± 1).…”

“…Reduced temperatures, low oxygen, freshwater pulses, burial depth, light, and scarification are known germination cues for seagrass species (Brenchley & Probert, 1998;Cumming et al, 2017;Harrison, 1991;Jarvis & Moore, 2015;Kawasaki, 1993;Loques et al, 1990;Moore et al, 1993;Stafford-Bell et al, 2016;Wu et al, 2016). Scarification of seagrass seed coatings has been observed in over 60% of the seeds found in marine mega-herbivore feces (Tol et al, 2017).…”

Seagrass Restoration Is Possible: Insights and Lessons From Australia and New Zealand

“…There is now a growing emphasis on seed-based restoration, largely due to the lower impact it has on existing meadows (i.e., removal of large numbers of fragments or cores in shoot-based restoration), and its potential for upscaling (Orth et al, 2006). To facilitate the growing area of seed-based restoration, more information is required on how flowering and seed production varies within and across species, and the environmental factors that trigger reproduction and germination (Cumming et al, 2017). Substantial inter-annual and small-scale spatial variability in sexual reproduction has been reported from studies in Western Australia, New South Wales, Victoria, and New Zealand, with results suggesting that the timing and intensity of flowering are influenced by processes occurring across a range of spatial scales (Dos Santos and Matheson, 2016;Smith et al, 2016;Sherman et al, 2018).…”