In-vitro seed germination Trial for the population Terminalia ivorensis Collected from Benchi-Maji zone, south western Ethiopia

Tree seeds exhibit some degree of dormancy. Similarly, the seeds of Terminalia ivorensis germinate with great difficulties. To break the dormancy and improve the germination capability of seeds, different types of mechanical and physiological approaches can be followed. Accordingly, the seeds of T. ivorensis were subjected to two pre-sowing treatments (one is with seeds soaked in water for 24 hours and the other is with seeds soaked for 10 minutes in 80% concentrated H2SO4 then abundantly rinsed in running water for 20 minutes) in addition to the control one. So, a total of 100 seeds divided into 4 replications (25 seeds per tray) were tested for each treatment. Then, treated seeds were sown in sand tray to seed the germination characteristic of the different treatments. The sown seeds were followed up for 5 months with proper watering, and the germination record was taken accordingly. Analysis of the germination of the different treatments shows that seeds that were not treated exhibits better mean germination percentages (62%) followed by the one with seeds soaked for 24 hours (47%). However, seeds treated with 80% [H2SO4] for 10 minutes then abundantly rinsed in running water for 20 minutes showed no germination. So, both the 62% and 47% germination recorded are fairly accepted results considering the low germination capacity of T. ivorensis in laboratory and natural conditions. However, other possible pre-sowing treatment techniques can be studied and incorporated for increasing the seed germination of T. ivorensis in-vitro in addition to the records obtained in this trial.

The development of a surrogate soil to assist the revegetation and stabilisation of metal-mine tailings

Abandoned mines are considered among the most severe of environmental issues, and are a significant danger to environmental, animal, and human health (Mehta et al., 2020). To date, ~ 600,000 abandoned mines exist, the costly reclamation of which often falls to publicly funded bodies (Archer & Caldwell, 2004; Mayes et al., 2009). Traditional reclamation methods are financially unattainable at ~ £50 million per large mine (McKenna, 2002), and an alternative, lower-cost method is required (Garcia, 2008). One contemporary reclamation method found to be effective is that of capping mine waste with a soil cover (O’Kane & Ayres, 2012). In this research, an adhesive surrogate soil capping layer for the hydraulic application to steep-sided metal-mine tailings was developed at the cost of ~ £6 .m-² (at the time of writing). The surrogate soil was refined throughout a series of trials. A rainfall trial was conducted to develop an adhesive and erosion resistant soil material. A germination trial (N = 500) determined the soil materials which best assisted rapid plant establishment. The successful results of these laboratory-based trials guided a nine-month field trial on an abandoned Pb mine, Nantymwyn (UK) (N = 154). The field trial concluded that the surrogate soils effectively resisted erosion and supported the early (seven month) growth of metal-tolerant grass species. The grasses contained Pb, Zn, Cd and Cu concentrations at < 1% of the phytotoxic threshold. However, seasonal climatic events and a negative water balance ultimately led to complete grass mortality after nine months. Tailings bank destabilisation also influenced grass survival. The research revealed that the soil’s available water supply was of greater impact to plant survival than metal toxicity. The results indicated that should the soils water-holding capacity be improved, the application of a carefully designed surrogate soil has the potential to support vegetative cover on steep, bare metal-mine tailings.

Seed provenance determines germination responses of Rumex crispus (L.) under water stress and nutrient availability

Aims Seeds of Rumex crispus from six provenances were studied in relation to their germination under drought and presence of nitrogen in the germination and emergence media. We also investigated whether adaptation to soil increases the ability of the species to colonize and establish in contrasting environments along a longitudinal gradient in western Spain by means of a reciprocal transplantation experiment. Methods We conducted a germination trial in the lab to test for the germination responses to water scarcity along a polyethylene glycol gradient and to varying concentrations of nitrogen compounds. Simultaneously reciprocal transplantations experiment was conducted, where seeds from six provenances were grown in the soils from the very same provenances. Seedling emergence, survivorship and fitness-related variables were measured in all plots. Important Findings We found that R. crispus has a cold-stratification requirement that enhances its germination. Significant differences between the six provenances were detected for time-to-germination, total seedling emergence, plant mortality and reproductive effort in all the experiments. The differences between provenances with respect to germination were confirmed by the significant statistical analyses of the variance, thus providing evidence that seeds from parent plants grown in different environmental conditions have an intrinsically different abilities to germinate and establish. Soil nitrogen content where seed germination and seedlings establish also play an important role in their performance in terms of survivorship and reproduction, being the higher levels of inorganic nitrogen and of microbial biomass those that increased biomass production, enhanced inflorescence formation and reduced plant mortality. We conclude that one of the main reasons for the spread and maintenance of R. crispus would be the increased levels of nitrogen in agricultural soils.

A comparative study of the thermal ranges of three germination criteria of a tropical tree with bioeconomic interest: Carapa surinamensis Miq. (Meliaceae)

Species of the Carapa spp. complex, occurring in the Neotropics, Africa and India, have multiple uses, including timber, with the seed oil being used in phyto-pharmaceutical products and cosmetics. This study aimed to determine the thermal ranges of the germination process, comparing germination criteria used by seed physiologists and seed technologists, and to suggest recommendations for seed quality assessment. Germination was assessed at constant temperatures between 10 ─ 40 °C using three germination criteria: (1) radicle length ≥ 0.5 cm (physiological criterion); (2) epicotyl length ≥ 1 cm; and (3) epicotyl length ≥ 5 cm (criterion for seed quality tests). The base temperature was similar for the three criteria and ranged between 10 ─ 2 °C. The Maguire’s Speed Index indicated 30 °C as most adequate. However, the upper temperature limit differed: for radicle protrusion it was above 40 ºC; and for both epicotyl lengths, it was between 35 ─ 40 °C. Seed coat removal accelerated the germination process of these recalcitrant seeds, and is recommended for seed quality assessment, which allows completion of the germination trial in approximately one month.

Evaluation of Pseudoraphis spinescens (Poaceae) seed bank from Barmah Forest floodplain

Use of environmental water allocations to conserve floodplain and wetland plants is becoming an increasingly common management tool. In south-eastern Australia, Pseudoraphis spinescens (R.Br.) Vickery has historically covered extensive areas within Barmah Forest where it is deemed to be ecologically significant and of high conservation value. The areal extent of P. spinescens significantly declined throughout the forest during the Millennium drought (1996–2010). Natural flooding (2010–2012) failed to elicit an expected increase in the extent of P. spinescens, suggesting that this species may not have a viable long-lived seed bank. We investigated the presence and viability of the seed bank of P. spinescens by (1) germination trials, (2) identification of seeds within the sediment and (3) estimates of seed viability. No plants were identified as P. spinescens during the germination trial. Seeds of P. spinescens were identified as present in the sediment, but the majority (98%) were not viable. In contrast, 16% of seeds collected from mature seed heads were found to be viable. The present study demonstrated the absence of a persistent long-lived seed bank of P. spinescens in Barmah Forest.

Seed germination and unusual serotiny in two species of Conospermum from fire-prone vegetation in Western Australia

Serotiny is a mechanism for storing propagules on plants, so that seed dispersal can be maximised after the death of aerial parts of plants or to take advantage of conditions beneficial to establishment. In fire-prone vegetation, regeneration of new plants after fire is mostly from seeds that are stored in the soil or on the plant. These traits are generally consistent within a genus. However, in Conospermum, a genus of shrubs that mostly occur in fire-prone vegetation and in which most species have soil-stored seeds, two species exhibit an unusual serotinous structure. We examined the morphology and anatomy of inflorescences and infructescences of C. capitatum and C. petiolare that were collected from natural vegetation in south-western Western Australia. Inflorescence and infructescence axes were sectioned and examined microscopically, fresh infructescences were heated in an oven to various temperatures for 2 min and the fruits from them sown in a germination trial. Some fruits were also treated with smoke chemicals. Both species have a low, dense growth form and retain the seed-like fruits in a serotinous structure formed by enlargement of the cortical cells of the inflorescence axis after flowering. The fruits can be effectively released from the plant only if the foliage is removed by a fire. For both species, the infructescence protects the fruits from heat up to 200°C for 2 min and this is similar to protection afforded by woody cones in other serotinous species. C. capitatum requires either heat or smoke to cue germination, whereas C. petiolare requires no cue, as is found in most other serotinous species. A combination of morphological modification associated with allometry of the whole plant body and physiological changes to germination requirements shows that a series of complex changes may be needed to develop serotiny from non-serotinous antecedents.

Habitat Segregation by Serotinous Shrubs in Heaths: Post-fire Emergence and Seedling Survival

Seeds of two serotinous shrub species generally restricted to the drier edges, and two serotinous shrub species commonly confined to the wetter drainage channels of upland sedge–heaths were assessed for germinability and used in manipulative field experiments. In post-fire field experiments the effects of habitat and manipulated soil moisture were examined to test if the distribution of adult plants was influenced by soil moisture at seed germination. The effects of habitat on seedling survival for 11 months were also assessed. One species from the edge zone, Banksia marginata Cav., and one from the channel zone, Hakea microcarpa R.Br., had germination preferences corresponding to the distribution of adult plants. The other edge species, Hakea dactyloides (Gaertner) Cav., did not show a significant preference for either zone. The second channel species, Callistemon pityoides F.Muell., did not germinate in the field or in a laboratory germination trial. Some evidence for soil-stored dormancy related to temperature and or waterlogging was found in both Hakea species. Overall the results suggest that for two species habitat segregation occurs when seeds are incorporated into the seed-bed and germination occurs. No differential survival effects across habitats were found in the first year of growth.