GENERAL OVERVIEW

DECLARATION 2 PUBLICATIONS

1.4 GENERAL OVERVIEW

Germination requirements and germination rate are amongst the most important seed traits associated with plant fitness and are key components in the ecology and evolution of plant life histories (HARPER, 1977). The importance of seed germination as a plant trait leading to successful establishment and persistence of individual plants and populations is well discussed by VAN DER VALK (1992).

Germination is a complex process which is governed and influenced by many

factors and slight changes in the physical and chemical environment can lead to

different outcomes. Hence, it is often argued that germination ecology of species

cannot be fully understood by laboratory-based studies alone (BASKIN and

BASKIN, 1998). This notion partially holds true, as there are many more

unforeseen factors which influence germination

in situ. The reverse notion is also

available in that in plant communities, often slight differences in the physiological

characteristics and life history features of the species involved and the diverse

nature of successional environments can influence trends in succession

replacements (GRIME, 1979; TILMAN, 1988). Due to this fact, designing and

analysing ecological experiments in the field as tests of ecological theory are often

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viewed as insurmountable and challenging (VAN DER VALK, 1992). Hence, experimental laboratories are often used as instruments for investigating ecological questions not easily answered through the analysis of field data (HARPER, 1977;

GRIME, 1979; VAN DER VALK, 1992; BAZZAZ, 1996).

The research presented in this thesis brings together a variety of different laboratory, greenhouse and field-based studies related to the subject of “the role of fire and fire-related factors on germination and growth of grassland species”.

Although in some respects the experiments may seem unrelated, together they begin to provide some insight towards a greater understanding of the role of fire and smoke on germination and seedling growth of some representative grassland species which are currently used as livestock feed and/or directly or indirectly for human consumption.

Chapter 2 provides a comprehensive literature review on the topic of fire mediated vegetation changes and the role of smoke as a germination cue. This Chapter also attempts to cover the most recent advances in the role of smoke in different fields of science i.e. agriculture, horticulture and ecological studies. This Chapter concludes with a short discussion on the ecological significance of smoke- stimulated germination and some important considerations for vegetation ecology.

Chapter 3 presents results from the experiments conducted on the effects of plant- derived smoke solutions and the interaction with temperature on germination and seedling growth of six common grassland species from mesic grassland in South Africa. The results from this experiment showed that smoke solutions and its interaction with temperature significantly influence the germination and seedling growth of South African mesic grassland species which in the long-run can impact on grassland composition (GHEBREHIWOT, KULKARNI, KIRKMAN and VAN STADEN, 2009).

Chapter 4 provides results from an experiment which was conducted to test the

role of smoke solutions on germination and seedling vigour of Eragrostis tef (Zucc.)

Trotter under high temperature and low osmotic potential. The purpose of this

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study was to understand the mode of smoke action in facilitating germination. The results from this experiment demonstrate that smoke-water and butenolide treatment of Eragrostis tef seeds significantly improved germination and seedling growth. This study also revealed that smoke solutions play a significant role in facilitating water uptake by seeds (imbibition) and override stresses exerted from sub-optimal temperature and low osmotic potential. Importantly, this Chapter gives evidence that smoke-water and butenolide are able to widen the environmental range over which germination can occur (GHEBREHIWOT, KULKARNI, KIRKMAN and VAN STADEN, 2008).

Chapter 5 presents the results of the “lettuce seed bioassay” conducted to assess the effect of fire (burning) in altering the soil-smoke chemistry and the biological activity of burnt soil extracts on the germination of Grand Rapids Lettuce seeds.

The aim of this study was to examine the germination activity of smoke residue in soils following a fire event. Results from this experiment showed that fire (burning) affects the soil smoke chemistry with regards to the germination activity of smoke which can further influence the germination of seeds contained at a moderate depth in the soil seed bank. (GHEBREHIWOT, KULKARNI, LIGHT, KIRKMAN and VAN STADEN, 2010).

Chapter 6 presents the results of an experiment conducted to assess the role and interactive effect of smoke solutions of various dilution levels with soil macronutrients i.e. nitrogen (N), phosphorus (P) and potassium (K) on seedling growth of three grass species of contrasting response to smoke treatments.

Results showed that irrespective of nutrient (NPK) presence, the smoke solutions of various dilution levels enhanced seedling growth of Themeda triandra. Seedling growth in

Eragrostis curvula was more responsive to the presence or absence of

soil nutrients (mainly N). Seedling growth of

Panicum maximum was negatively

influenced by the interaction of the smoke solutions with soil macronutrients.

Findings from this study demonstrate that the interaction of plant-derived smoke

with soil nutrients is an important factor in species growth (KULKARNI,

GHEBREHIWOT, KIRKMAN and VAN STADEN, 2010).

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Chapter 7 provides the results of greenhouse experiment conducted to assess the effects of plant-derived smoke and heat on soil seed bank stimulation of mesic grassland in South Africa. Findings from this study highlight the potential role of plant-derived smoke in stimulating the soil seed bank of the mesic grassland and the potential use of plant-derived smoke in speedy restoration of degraded grasslands (GHEBREHIWOT, KULKARNI, KIRKMAN and VAN STADEN 2010).

Chapter 8 (General discussion and conclusion) and Chapter 9 (References) are

followed by three appendices compiled from the surveyed literature. Appendix 1

provides a list of Poaceae species which showed a positive germination response

to smoke treatments. In contrast, Appendix 2 provides a list of Poaceae species

which did not show a positive germination response to any type of smoke

treatment. Appendix 3 shows electro-microscopic photos of the grass seeds used

in this study. These electro-microscopic photos demonstrate the difference in size,

shape and the nature of the seed coat of the seeds used in this study.

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Literature review

״ Vegetation is the basic instrument the creator uses to set all of nature in motion "

Antoine-Laurent de Lavoisier (1743–1794)