CSIRO PUBLISHING
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The Rangeland Journal, 2007, 29, 133–137
Effect of seed treatment on the emergence of Cassia brewsteri and Lysiphyllum carronii seeds stored in soil S. M. ReichmanA,B,D , S. M. BellairsA,C and D. R. MulliganA A
Centre for Mined Land Rehabilitation, The University of Queensland, Brisbane, Qld 4072, Australia. Present address: Division of Agriculture and Life Sciences, Lincoln University, PO Box 84, Lincoln 7647, New Zealand. C Present address: School of Science and Primary Industries, Charles Darwin University, Darwin, NT 0815, Australia. D Corresponding author. Email:
[email protected] B
Abstract. Dormancy-breaking treatments are applied to seeds of many Australian species used for mine-site restoration in arid and semi-arid regions of Australia. Once seeds are sown, several months may pass before a rain event sufficient for germination. Therefore, it is important that treated seeds are able to survive in soil until conditions are hospitable for germination and growth. However, little is known about the effects of seed dormancy-breaking treatments on the longevity of seeds in soil. Two species that are potential candidates for use in mine site restoration programs in Queensland were trialed viz., Cassia brewsteri (F.Muell.) Benth and Lysiphyllum carronii (F.Muell.) Pedley. Untreated, boiled and acid treated seeds of the two species were sown in soil in a glasshouse. Seeds were watered immediately or kept dry for one or three months before watering and emergence was assessed. When applied to seeds incubated on filter paper in a germination cabinet, boiling and acid treatments were effective methods of breaking dormancy and increasing germination for both C. brewsteri and L. carronii seeds. However, in soil, seedling emergence from boiled seeds was the same or less than that of untreated seeds. Storage time in soil before watering had little effect on seedling emergence in the glasshouse, suggesting that most decreases in emergence compared with laboratory germination occurred after the input of water to the system. Treatments that promote germination in the laboratory can reduce seedling emergence in soil. Thus, treated seeds should be tested for survival in soil before use in mine-site restoration programs. Additional keywords: dormancy, germination, legume, mine rehabilitation, seed bed.
Introduction Long periods of time may elapse between rain events in arid and semi-arid environments. Plants endemic to these environments have evolved a variety of mechanisms to maximise survival under these conditions, including long-lived dormant seeds. In Australia, the germination of many plant species is regulated by seed dormancy mechanisms that maximise the chance of seeds germinating when the environment is favourable for establishment of the plant (Bell 1999; Adkins and Bellairs 2000). Environmental triggers that break dormancy may not necessarily occur in re-constructed environments, such as mine restoration sites. Thus, when seeds of Australian species are sown for restoration of post-mining landscapes, dormancybreaking treatments are regularly applied to seeds of hardseeded species before broadcasting to increase the chances of rapid germination and establishment of the desired species (Bell et al. 1990). Most of Australia has a variable and unpredictable climate and, thus, although sowing may be timed for periods when the probability of rain is high, in many regions, months may pass before a significant rain event (Bell 1984). Hence, it is important that treated seeds are able to survive © Australian Rangeland Society 2007
in the soil until sufficient rain occurs for germination and establishment. Seedling emergence in mine rehabilitation programs is often low irrespective of seed treatment, e.g. control > boiled. When the C. brewsteri Petri 100
Control Boiled Acid
80
Emergence (%)
134
60 40 20 0 Petri dish
0
1
3
Time to commencement of watering (months) Fig. 1. Effect of incubation conditions, emergence environment and seed pre-treatment on the germination of Cassia brewsteri. Germination was monitored in Petri dishes in a germination cabinet and emergence from soil was monitored in a glasshouse after storage in dry soil for 0, 1 or 3 months. Values are mean % (n = 50 × 4 replicates) of seeds sown ± s.e.
Impact of soil storage on emergence of seeds
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Table 1. Analysis of variance summary for the effects of seed treatment (control, boiled or acid) and time to commencement of watering (0, 1 or 3 months) on the emergence of Cassia brewsteri seeds stored in soil
at 0 or 3 months after sowing (l.s.d., P = 0.676) with emergence in both these treatments being significantly greater than when watering started at one month after sowing (l.s.d., P ≤ 0.025). When the Petri dish germination data (representing potential emergence) were included in the analysis for L. caronii, there were significant effects of seed treatment, emergence environment and seed treatment by emergence environment interactions on emergence (Table 4). Petri dish germination was greater than emergence following the corresponding treatment in soil for both acid treated and boiled seeds at all times of first watering (l.s.d., P < 0.001). However, germination in the Petri dish control treatment was not significantly different to the emergence of control seeds from soil where watering was immediate (l.s.d., P = 0.236) or delayed for 3 months (l.s.d., P = 0.117) and was only significantly greater than emergence where watering was delayed 1 month (l.s.d., P = 0.008). For seeds of both species in the germination cabinet, the boiled seeds were qualitatively more susceptible to fungal attack than the control and acid-treated seeds. For both species, when the various soil treatments were assessed, sparse fungal growth was noted on the soil that contained the boiled seeds but not in any other treatments.
Treatment
Discussion
dish germination data (representing potential emergence) were analysed along with the soil watering regimes as treatments of the factor ‘emergence environment’, there were significant effects of seed treatment, emergence environment and seed treatment by emergence environment on emergence (Table 2). Petri dish germination was greater than emergence from soil irrespective of the time to first watering (l.s.d., P < 0.01) and each seed treatment in the Petri dish treatment was significantly greater than the corresponding seed treatment in soil (l.s.d., P < 0.01). Lysiphyllum caronii emergence from soil (Fig. 2) was significantly affected by both seed treatment and the time to watering but there was no significant treatment by time interaction (Table 3). Acid treatment of seeds resulted in significantly greater emergence than both control and boiled seeds (l.s.d., P < 0.001) and there was no significant difference between the emergence of control and boiled seeds (l.s.d., P = 0.505). Emergence was highest when watering first started
Degrees of freedom
F
P
2 2 4 27
175.14 1.08 0.810 –
