- Email: [email protected]
Heat-stimulated germination in two Restionaceae species
175
S.AfrJ.Bot., 1991, 57(3)
Short Communication
Heat-stimulated germination in two Restionaceae species C.F. Musil and D.M. de Witt National Botanical Institute, Stress Ecology Unit, Private Bag X16, Rondebosch, 7700 Republic of South Africa Accepted 4 March 1991
Exposure of Staberoha distachya and Calopsis impolita seeds to temperatures of 80 0 G and above resulted in a significant improvement in their subsequent germination. Different exposure periods of up to 15 min in duration had no significant effect on subsequent germination when tested against the various temperatures applied. The highest temperature applied, viz. 120oG, which inhibits germination in other fynbos taxa, initiated a maximum germination response in both species. High-intensity fires may promote regeneration of these Restionaceae species. Blootstelling van Staberoha distachya en Calopsis impolita saad aan temperature van 80 G en hoer lei tot 'n betekenisvolle verhoging in hul daaropvolgende ontkieming. Verskillende blootstellingsperiodes van tot 15 min het geen beduidende effek op ontkieming by die onderskeie temperature gehad nie. Die hoogste temperatuur in hierdie ondersoek, naamlik 120oG, wat ontkieming in ander fynbos-taksa strem, het 'n maksimale ontkiemingsreaksie by albei spesies ten gevolg gehad. Brande met hoe intensiteite mag regenerasie van hierdie Restionaceae spesies bevorder. 0
Key words: Fire, fynbos, germination, Restionaceae, temperature
Intermittent fires, a natural phenomenon in fynbos vegetation of the South African mediterranean climatic zone, are generally considered beneficial for survival of most fynbos taxa (Kruger & Bigalke 1984). Reported beneficial effects of fire include fire-induced seed release in serotinous Proteaceae and the stimulation of germination of dormant soil-stored seed (Kruger 1983). In the ericoid component of fynbos (Taylor 1978), heat-stimulated germination has been demonstrated in members of the Asteraceae, Rutaceae, Rhamnaceae and Ericaceae (Blommaert 1972; Musil 1991; Levyns 1929; Van de Venter & Esterhuizen 1988), suggesting a direct response to high temperatures generated during fIres under natural conditions. Little is known of the effect of heat on seed germination in the restioid component of fynbos. Poor seed germination obtained in many Restionaceae species has been attributed mainly to immature seed resulting from incorrect time of seed harvest due to diffIculties in determining when seeds on plants are mature (Clegg 1980). This communication reports on improved germination in two Restionaceae species following seed exposure to high temperatures. Seeds were extracted from infructescences (spikelets) of Staberoha distachya (Rottb.) Kunth and Leptocarpus impolitus (Kunth) Pillans harvested during these species' seed release period (late spring) at the Fynbos Biome intensive study site at Pella (Jarman & Mustart 1988). Linder (1985) in his taxanomic revision of the Restionaceae
includes L. impo!itus in Calopsis impolita (Kunth) Linder comb. nov. In each species, plump seeds were separated from depauperate (incompletely developed) and predated forms under a stereo-dissecting microscope and grouped into 26 batches, each comprising 120 seeds. Batches of plump seeds on dry sand were exposed to different temperatures (40, 60, 80, 100, 120°C) of varying duration (3, 6, 9, 12, 15 min) in a thermostatically controlled forced-draft oven. Twenty-five different combinations of temperature and exposure period were applied to each species. Controls comprised plump seeds that were not subjected to heat treatment. Treatments and controls were replicated four times (30 seeds per replicate), randomized and incubated for 90 days in a growth chamber on moist sterile sand plain lowland fynbos soil, presieved through a 500-lJ.m mesh, contained in petri dishes. Benomyl (Benlate Du Pont) at a concentration of 0.02% active ingredient was added to each petri dish to prevent fungal contamination. Diurnal temperature range during incubation was 20°C/5°C with an 8-h photoperiod corresponding with the higher temperature. Germinants were recorded at 3-weekly intervals. A radicle which exceeded twice the maximum seed diameter was used as an arbritary criterion for distinguishing germination. Percentage germination data obtained for the two species over their entire incubation period following heat treatments were tested for non-normality in distribution, ranked and subjected to a non-parametric 2-way ANOVA (Friedman test). Both the Friedman statistic (X,.) and the ConoverFriedman statistic (Tz) using an F approximation were computed to test for significant effects of different temperatures against exposure period and vice versa on subsequent germination (Sachs 1982). A multiple comparisons test on all rank sums was conducted where the Friedman and Conover-Friedman statistic probabilities were less than 0.05 (Sachs 1982). In both species, germination was significantly (P < 0.01) enhanced following seed exposure to temperatures of 80°C and above (Table 1). Different exposure periods had no significant (P > 0.05) effect on subsequent germination when tested against the various temperatures applied. In S. distachya, maximum germination (45.0%) was attained following seed exposure to a temperature of 120°C of 3 min. duration (Figure lA). In C. impolita, maximum germination (27.5%) was also attained following seed exposure to a temperature of 120°C, but of 6 min duration (Figure IB). This temperature is higher than that (ca. 80 100°C) required to initiate a maximum germination response in other fynbos taxa (Musil 1991). Their germination, like many seeds of sclerophyllous vegetation in other mediterranean-type ecosystems (Wright 1931; Sampson 1944; Stone & Juren 1952; Quick & Quick 1961; Keeleyet al. 1985), is usually inhibited following seed exposure to a temperature of 120°C (Musil 1991). Data suggest that highintensity fires may promote regeneration of Restionaceae from their dormant soil-stored seed reserves, at least in the two species studied. However, a correlation between postfire seedling population densities or numbers of nondormant seeds present in soils after fire and fire intensity levels needs to be demonstrated to validate this suggestion.
176
S.-Afr.Tydskr.Plantk., 1991, 57(3)
Table 1 A 2-way ANOVA (Friedman test) of germination data following seed exposure of two Restionaceae species to heat (25 diferrent combinations of temperature and exposure period)· Species/ Treatment
Slaberoha dislachya Temperature COC) Germination % Exposure period (min) Germination %
40 2 1.3 a 3 27.0a
60 21.7a 6 27.3a
SO 27.0b 9 2S.3a
100 27.Sb 12 24.7a
120 33 .Sb IS 26.7a
Ca/opsis impo/ilus Temperature COC) Germination % Exposure period (min) Germination %
40 6.0a 3 1O.Sa
60 S.2a 6 12.5a
SO I1.Sb 9 14.2a
100 22.Oc 12 13.3a
120 21.Oc IS 14.Sa
Friedman test statistic X" DFt = 4
Conover-Friedman test statistic T2 DFt = 4, 76
14.S30t
4.69S t
1.190
0.312
49.33~
34.624$
S.240
1.491
• Values with any letter in common are not significantly different at P < O.OS. t DF, degrees of freedom. t Significantly different at P < 0.01. $ Significantly different at P < 0.001 .
A
50 X
40
Z 0
j::
30
i~ .... tl
20
z-<
10 0 C(Ps)
TEMPERATURE
°c
B
30 X Z
25
0
20
j::
-<
Z
i .... '"tl
10 10
5 0
C(PS)
40
80
60
TEMPERATURE
100
120
°c
Figure 1 Percentage germination (means of four replicates) of (A) S. dislachya and (B) C. impolilus plump seeds following heat treatment (25 different combinations of temperature and exposure period). Controls [CCPS)] comprised plump seeds not subjected to heat treatment.
Acknowledgements Dr. M.e. Rutherford and various anonymous referees are thanked for their comments on an earlier draft of the manuscript.
References BLOMMAERT, K.LJ. 1972. Buchu seed germination. I/. S. Afr. Bot. 38: 237 - 239.
CLEGG, A.D. 1980. Restionaceae - their potential. Veld & Flora 66:16-17. JARMAN, M.L. & MUSTART, P. 1988. Introduction. In: A Description of the Fynbos Biome Project Intensive Study Site at Pella, ed. Jarman, M.L., S.A. Nat. Sci. Prog. Report, 33, pp. 1 - 9, CSIR, Pretoria. KEELEY, J.E., MORTON, B.A., PEDROSA, A. & TROTTER, P. 1985. Role of allelopathy, heat and charred wood in the germination of chaparral herbs and suffrutescents. 1. Ecol. 73: 445 - 458 . KRUGER, FJ. 1983 . Plant community diversity and dynamics in relation to fire. In: Mediterranean-type Ecosystems: the Role of Nutrients, eds. Kruger, FJ., Mitchell, D.T. & Jarvis, J.U.M., Ecological Studies Vol. 43, pp. 447 - 442, Springer-Verlag, Berlin. KRUGER, F.I. & BIGALKE, R.C. 1984. Fire in fynbos . In: Ecological Effects of Fire in South African Ecosystems, eds. Booysen, P.de V. & Tainton, N.M., pp. 67 - 114, SpringerVerlag, Berlin. LEVYNS, M.R. 1929. Veld burning experiments at Ida's Valley, Stellenbosch. Trans. R . Soc. S. Afr. 17: 61 - 92. LINDER, H.P. 1985. Conspectus of the African species of Restionaceae. Bothalia 15 : 387 - 503. MUSIL, c.P. 1991. Seed bank dynamics in sand plain lowland fynbos . S. Afr. f. Bot. 57: 131 - 142. QUICK, C.R. & QUICK, A.S. 1961. Germination of Ceanothus seeds. Madrono 16: 23 - 30. SACHS, L. 1982. Applied Statistics a Handbook of Techniques. Springer Verlag, New York. SAMPSON, A.W. 1944. Plant succession and burned chaparral lands in northern California. Univ . Calif. Agric. Exp. Sta. Bull., No. 685, 144 pp. STONE, E.C. & JUREN, G. 1952. The effect of fire on germination of the seed of Rhus ovata Wats. Am. f. BOI. 38: 368 - 372. TA YLOR, H.C . 1978. Capensis. In: The Biogeography and Ecology of Southern Africa, ed. Werger, M.J.A., pp. 171 229. Junk, The Hague. VAN DE VENTER, H.A. & ESTERHUIZEN, A.D. 1986. The effects of factors associated with fIre on seed germination of Erica sessiliflora and E . hebecalyx (Ericaceae). S. Afr. f. Bot. 54: 301 - 304. WRIGHT, E. 1931. The effect of high temperature on seed germination. f. Forestry 29: 679 - 687 .
S.AfrJ.Bot., 1991, 57(3)
Short Communication
Heat-stimulated germination in two Restionaceae species C.F. Musil and D.M. de Witt National Botanical Institute, Stress Ecology Unit, Private Bag X16, Rondebosch, 7700 Republic of South Africa Accepted 4 March 1991
Exposure of Staberoha distachya and Calopsis impolita seeds to temperatures of 80 0 G and above resulted in a significant improvement in their subsequent germination. Different exposure periods of up to 15 min in duration had no significant effect on subsequent germination when tested against the various temperatures applied. The highest temperature applied, viz. 120oG, which inhibits germination in other fynbos taxa, initiated a maximum germination response in both species. High-intensity fires may promote regeneration of these Restionaceae species. Blootstelling van Staberoha distachya en Calopsis impolita saad aan temperature van 80 G en hoer lei tot 'n betekenisvolle verhoging in hul daaropvolgende ontkieming. Verskillende blootstellingsperiodes van tot 15 min het geen beduidende effek op ontkieming by die onderskeie temperature gehad nie. Die hoogste temperatuur in hierdie ondersoek, naamlik 120oG, wat ontkieming in ander fynbos-taksa strem, het 'n maksimale ontkiemingsreaksie by albei spesies ten gevolg gehad. Brande met hoe intensiteite mag regenerasie van hierdie Restionaceae spesies bevorder. 0
Key words: Fire, fynbos, germination, Restionaceae, temperature
Intermittent fires, a natural phenomenon in fynbos vegetation of the South African mediterranean climatic zone, are generally considered beneficial for survival of most fynbos taxa (Kruger & Bigalke 1984). Reported beneficial effects of fire include fire-induced seed release in serotinous Proteaceae and the stimulation of germination of dormant soil-stored seed (Kruger 1983). In the ericoid component of fynbos (Taylor 1978), heat-stimulated germination has been demonstrated in members of the Asteraceae, Rutaceae, Rhamnaceae and Ericaceae (Blommaert 1972; Musil 1991; Levyns 1929; Van de Venter & Esterhuizen 1988), suggesting a direct response to high temperatures generated during fIres under natural conditions. Little is known of the effect of heat on seed germination in the restioid component of fynbos. Poor seed germination obtained in many Restionaceae species has been attributed mainly to immature seed resulting from incorrect time of seed harvest due to diffIculties in determining when seeds on plants are mature (Clegg 1980). This communication reports on improved germination in two Restionaceae species following seed exposure to high temperatures. Seeds were extracted from infructescences (spikelets) of Staberoha distachya (Rottb.) Kunth and Leptocarpus impolitus (Kunth) Pillans harvested during these species' seed release period (late spring) at the Fynbos Biome intensive study site at Pella (Jarman & Mustart 1988). Linder (1985) in his taxanomic revision of the Restionaceae
includes L. impo!itus in Calopsis impolita (Kunth) Linder comb. nov. In each species, plump seeds were separated from depauperate (incompletely developed) and predated forms under a stereo-dissecting microscope and grouped into 26 batches, each comprising 120 seeds. Batches of plump seeds on dry sand were exposed to different temperatures (40, 60, 80, 100, 120°C) of varying duration (3, 6, 9, 12, 15 min) in a thermostatically controlled forced-draft oven. Twenty-five different combinations of temperature and exposure period were applied to each species. Controls comprised plump seeds that were not subjected to heat treatment. Treatments and controls were replicated four times (30 seeds per replicate), randomized and incubated for 90 days in a growth chamber on moist sterile sand plain lowland fynbos soil, presieved through a 500-lJ.m mesh, contained in petri dishes. Benomyl (Benlate Du Pont) at a concentration of 0.02% active ingredient was added to each petri dish to prevent fungal contamination. Diurnal temperature range during incubation was 20°C/5°C with an 8-h photoperiod corresponding with the higher temperature. Germinants were recorded at 3-weekly intervals. A radicle which exceeded twice the maximum seed diameter was used as an arbritary criterion for distinguishing germination. Percentage germination data obtained for the two species over their entire incubation period following heat treatments were tested for non-normality in distribution, ranked and subjected to a non-parametric 2-way ANOVA (Friedman test). Both the Friedman statistic (X,.) and the ConoverFriedman statistic (Tz) using an F approximation were computed to test for significant effects of different temperatures against exposure period and vice versa on subsequent germination (Sachs 1982). A multiple comparisons test on all rank sums was conducted where the Friedman and Conover-Friedman statistic probabilities were less than 0.05 (Sachs 1982). In both species, germination was significantly (P < 0.01) enhanced following seed exposure to temperatures of 80°C and above (Table 1). Different exposure periods had no significant (P > 0.05) effect on subsequent germination when tested against the various temperatures applied. In S. distachya, maximum germination (45.0%) was attained following seed exposure to a temperature of 120°C of 3 min. duration (Figure lA). In C. impolita, maximum germination (27.5%) was also attained following seed exposure to a temperature of 120°C, but of 6 min duration (Figure IB). This temperature is higher than that (ca. 80 100°C) required to initiate a maximum germination response in other fynbos taxa (Musil 1991). Their germination, like many seeds of sclerophyllous vegetation in other mediterranean-type ecosystems (Wright 1931; Sampson 1944; Stone & Juren 1952; Quick & Quick 1961; Keeleyet al. 1985), is usually inhibited following seed exposure to a temperature of 120°C (Musil 1991). Data suggest that highintensity fires may promote regeneration of Restionaceae from their dormant soil-stored seed reserves, at least in the two species studied. However, a correlation between postfire seedling population densities or numbers of nondormant seeds present in soils after fire and fire intensity levels needs to be demonstrated to validate this suggestion.
176
S.-Afr.Tydskr.Plantk., 1991, 57(3)
Table 1 A 2-way ANOVA (Friedman test) of germination data following seed exposure of two Restionaceae species to heat (25 diferrent combinations of temperature and exposure period)· Species/ Treatment
Slaberoha dislachya Temperature COC) Germination % Exposure period (min) Germination %
40 2 1.3 a 3 27.0a
60 21.7a 6 27.3a
SO 27.0b 9 2S.3a
100 27.Sb 12 24.7a
120 33 .Sb IS 26.7a
Ca/opsis impo/ilus Temperature COC) Germination % Exposure period (min) Germination %
40 6.0a 3 1O.Sa
60 S.2a 6 12.5a
SO I1.Sb 9 14.2a
100 22.Oc 12 13.3a
120 21.Oc IS 14.Sa
Friedman test statistic X" DFt = 4
Conover-Friedman test statistic T2 DFt = 4, 76
14.S30t
4.69S t
1.190
0.312
49.33~
34.624$
S.240
1.491
• Values with any letter in common are not significantly different at P < O.OS. t DF, degrees of freedom. t Significantly different at P < 0.01. $ Significantly different at P < 0.001 .
A
50 X
40
Z 0
j::
30
i~ .... tl
20
z-<
10 0 C(Ps)
TEMPERATURE
°c
B
30 X Z
25
0
20
j::
-<
Z
i .... '"tl
10 10
5 0
C(PS)
40
80
60
TEMPERATURE
100
120
°c
Figure 1 Percentage germination (means of four replicates) of (A) S. dislachya and (B) C. impolilus plump seeds following heat treatment (25 different combinations of temperature and exposure period). Controls [CCPS)] comprised plump seeds not subjected to heat treatment.
Acknowledgements Dr. M.e. Rutherford and various anonymous referees are thanked for their comments on an earlier draft of the manuscript.
References BLOMMAERT, K.LJ. 1972. Buchu seed germination. I/. S. Afr. Bot. 38: 237 - 239.
CLEGG, A.D. 1980. Restionaceae - their potential. Veld & Flora 66:16-17. JARMAN, M.L. & MUSTART, P. 1988. Introduction. In: A Description of the Fynbos Biome Project Intensive Study Site at Pella, ed. Jarman, M.L., S.A. Nat. Sci. Prog. Report, 33, pp. 1 - 9, CSIR, Pretoria. KEELEY, J.E., MORTON, B.A., PEDROSA, A. & TROTTER, P. 1985. Role of allelopathy, heat and charred wood in the germination of chaparral herbs and suffrutescents. 1. Ecol. 73: 445 - 458 . KRUGER, FJ. 1983 . Plant community diversity and dynamics in relation to fire. In: Mediterranean-type Ecosystems: the Role of Nutrients, eds. Kruger, FJ., Mitchell, D.T. & Jarvis, J.U.M., Ecological Studies Vol. 43, pp. 447 - 442, Springer-Verlag, Berlin. KRUGER, F.I. & BIGALKE, R.C. 1984. Fire in fynbos . In: Ecological Effects of Fire in South African Ecosystems, eds. Booysen, P.de V. & Tainton, N.M., pp. 67 - 114, SpringerVerlag, Berlin. LEVYNS, M.R. 1929. Veld burning experiments at Ida's Valley, Stellenbosch. Trans. R . Soc. S. Afr. 17: 61 - 92. LINDER, H.P. 1985. Conspectus of the African species of Restionaceae. Bothalia 15 : 387 - 503. MUSIL, c.P. 1991. Seed bank dynamics in sand plain lowland fynbos . S. Afr. f. Bot. 57: 131 - 142. QUICK, C.R. & QUICK, A.S. 1961. Germination of Ceanothus seeds. Madrono 16: 23 - 30. SACHS, L. 1982. Applied Statistics a Handbook of Techniques. Springer Verlag, New York. SAMPSON, A.W. 1944. Plant succession and burned chaparral lands in northern California. Univ . Calif. Agric. Exp. Sta. Bull., No. 685, 144 pp. STONE, E.C. & JUREN, G. 1952. The effect of fire on germination of the seed of Rhus ovata Wats. Am. f. BOI. 38: 368 - 372. TA YLOR, H.C . 1978. Capensis. In: The Biogeography and Ecology of Southern Africa, ed. Werger, M.J.A., pp. 171 229. Junk, The Hague. VAN DE VENTER, H.A. & ESTERHUIZEN, A.D. 1986. The effects of factors associated with fIre on seed germination of Erica sessiliflora and E . hebecalyx (Ericaceae). S. Afr. f. Bot. 54: 301 - 304. WRIGHT, E. 1931. The effect of high temperature on seed germination. f. Forestry 29: 679 - 687 .