Effect of light and temperature on germination and early growth of Vochysia tucanorum Mart., Vochysiaceae, in cerrado and forest soil under different radiation levels

Efeito da luz e temperatura na germinação e crescimento inicial de Vochysia tucanorum Mart., Vochysiaceae, em solo de cerrado e mata sob diferentes níveis de radiação

Effect of light and temperature on germination and early growth of Vochysia tucanorum Mart., Vochysiaceae, in cerrado and forest soil under different radiation levels

ANDRÉA RODRIGUES BARBOSA¹, ², KIKYO YAMAMOTO² and IVANY F. M. VALIO³

(recebido em 06/11/98; aceito em 06/05/99)

ABSTRACT - (Effect of light and temperature on germination and early growth of Vochysia tucanorum Mart., Vochysiaceae, in cerrado and forest soil under different radiation levels). Vochysia tucanorum Mart. (Vochysiaceae) is a very widely distributed species in the cerrado and forests in Brazil, from the State of Bahia to Paraná. Its seed germination was analysed under eight treatments using different conditions of light and temperature. Up to 73 days, at least ca. 93% of the seeds germinated in all treatments, except under alternating temperatures of 35°/10°C (62%). Light enhanced germination, except under constant temperature of 25°C when seeds are not photoblastic. At this temperature, the highest percentage of germination was found. Initial vegetative growth was analysed by comparing the effects of shading, by means of different percentages of full daylight (100%, 45%, 10.6%, 4.8%), and soils from cerrado and forest. During 123 days, no mortality was recorded and cotyledons persisted on the seedlings of all treatments. In general, the seedlings of V. tucanorum were found to be more or less indifferent to the soil from cerrado or forest and shading seems to promote height increment. However, total dry mass was larger under a radiation of 45% full daylight and smaller under extreme conditions (100% or 4.8% full daylight).

RESUMO - (Efeito da luz e temperatura na germinação e crescimento inicial de Vochysia tucanorum Mart., Vochysiaceae, em solo de cerrado e mata sob diferentes níveis de radiação). Vochysia tucanorum Mart. (Vochysiaceae) é uma espécie amplamente distribuída em cerrado e florestas do Brasil, do estado da Bahia até o Paraná. Sua germinação foi analisada sob oito tratamentos usando diferentes condições de luz e temperatura. Até o 73 dia, pelo menos cerca de 93% das sementes germinaram em todos os tratamentos, exceto em alternância de temperaturas de 35°/10°C (62%). A luz favoreceu a germinação, exceto sob temperatura constante de 25°C, na qual as sementes não se mostraram fotoblásticas. Nesta temperatura, foi encontrada a maior porcentagem de germinação. O crescimento inicial foi analisado comparando-se os efeitos de diferentes porcentagens da luz do dia (100%, 45%, 10,6%, 4,8%), e do solo de cerrado e mata. Durante 123 dias não houve mortalidade e os cotilédones persistiram em plântulas de todos os tratamentos. Em geral, as plântulas de V. tucanorum foram indiferentes ao tipo de solo, sendo que o sombreamento parece ter promovido incremento na altura das plantas. Entretanto, a massa seca total foi maior sob a radiação de 45% da luz solar e menor sob as condições extremas utilizadas (100% ou 4,8% de pleno sol).

Key words - Germination, seedling growth, shading, Vochysia tucanorum, soil, cerrado

Introduction

Cerrado (savannah-like vegetation) and riparian forests present high diversity and extensive genetic variability which, due to human activities, has been degraded to undesirably high levels and now require urgent studies in order to establish criteria for its regeneration (Labouriau 1966, Nascimento & Saddi 1992). Several authors have studied the regenerative strategies involving seed germination and seedling growth of suitable species for different degraded areas (Ng 1976, Whitmore 1991, 1996, Almeida et al. 1994).

Although shade is not imposed by the physical environment it becomes very important in the initial establishment of seedlings. The effect of shading upon growth and morphogenesis of tropical tree species has been examined in a large number of species (Denslow 1980, Augspurger 1984, Swaine & Whitmore 1988). Rezende et al. (1998) studied the effect of shading on survival and growth pattern of seedlings of Cryptocaria aschersoniana Mez. with the specific aim of regeneration of degraded riparian forests.

Plants of Vochysiaceae, an important floristic and phytophysionomic family in South America, are frequent in cerrado areas. The four Brazilian non-amazonic genera of the family present some species considered to be characteristic elements of the cerrado vegetation of Brazil (Stafleu 1948, Oliveira & Gibbs 1994). Besides this importance, few studies have been carried out on the initial seedling growth of Vochysiaceae aimed at the regeneration of the cerrados (Godoy & Felippe 1992, Paulilo et al. 1993).

Vochysia tucanorum Mart. presents high competitive ability, high frequency and wide distribution in Brazil, from Bahia to Paraná and from Rio de Janeiro to Mato Grosso do Sul occurring in different types of forests (Stafleu 1948, Vianna 1980). This appears to favour this species in regenerative programs of degraded areas.

The main objectives of this research were to study the germination process of seeds of V. tucanorum, as well as the effect of shading and quality of soil on initial growth of its seedlings.

Material and methods

Germination - Seeds of Vochysia tucanorum Mart. were collected from dehiscent fruits of two trees in Rio Claro (SP), Brazil (22°20'82"S and 47°40'43"W). The seeds were randomized and stored in paper bags for 45 days under laboratory conditions until the beginning of the experiments. Material from the parental plants was dried and included in the UEC Herbarium (Rio Claro, I/1996, A.R.Barbosa 34188 and 34192).

Intact seeds were sterilized with 5% sodium hypochloride for 10 minutes, thoroughly washed and then placed in Petri-dishes on filter paper wetted with distilled water. The Petri-dishes were maintained in germinators under constant temperatures of 25°C or 30°C and continuous white fluorescent light or darkness and also alternate temperatures of 30°/15°C, 30°/10°C and 35°/10°C (12 hours of higher temperature in light and 12 hours of lower temperature in darkness). Three replicates of 15 seeds were used in each treatment. Protrusion of the radicle was the criterion used for a germinated seed. Germination index (GI) was calculated according Czabator (1962 apud Gonzalez J. & Fisher 1997) were GI = ADG x PV (ADG = average daily germination; PV = higher value of germination).

The viability of the apparently healthy non-germinated seeds was examined in all treatments through tetrazolium test (Delouche et al. 1962).

Seedling growth - Germinated seeds were transferred to trays with vermiculite in a humidifier in the glasshouse for 30 days until total expansion of the cotyledons. Uniform seedlings were then selected. Ten seedlings were harvested and dried at 80°C for 48 hours to obtain the T₀ dry mass. Other seedlings were transplanted in white plastic pots (0.5 l) filled with forest or cerrado soil. Forest soil was collected in the Mata de Santa Genebra, Campinas (SP) and cerrado soil in the cerrado region of Itirapina (SP). Soil samples were collected after removal of the litter to a depth of 10 cm. Seedlings were subjected to four photon flux densities (PPD) (PAR = 400 ­ 700 nm): treatment 1 = 1640 µmol.m^-2.s^-1 (full sunlight = 100% radiation); treatment 2 = 740 µmol.m^-2.s^-1 (glasshouse = 45% radiation); treatment 3 = 174 µmol.m^-2.s^-1 (glasshouse + one layer of black plastic screen = 10.6% radiation); treatment 4 = 80 µmol.m^-2.s^-1 (glasshouse + two layers of black plastic screen = 4.8% radiation). Radiation was measured on a clear day without clouds around midday using a line quantum sensor (LI191SA) attached to a datalogger (LI1000). Five seedlings per treatment were used in experiment 1 and 15 seedlings per treatment in the other experiments. Seedlings were watered every day. After 123 days seedling height and persistence of cotyledons were recorded. Seedlings were then carefully removed from the pots, roots thoroughly washed and separated into leaves, stems and roots before drying at 80°C for 48 hours. From the recorded data the following indices were calculated: root:aerial ratio; robustness index = stem dry mass:stem length (RI = SDM/SL) (Lee et al. 1996); allocation of photosynthates to leaves, stem and roots (% of total); relative growth rate [RGR = (lnM₁ ­ lnM₀)/(T₁ ­ T₀)] were M₀ is the total dry mass at the beginning of the experiment, T₀, and M₁ is the total dry mass at the end of the experiment, T₁ (Hunt 1982).

Statistical analyses - In the germination experiments the main factors were temperature (°C), light (light or darkness, continuous or alternate each 12 hours) and time (days). The variable response was the proportion of germinated seed. For each time, one factor ANOVA was applied to test the effect of light at the temperatures of 25°C, 30°C, and 30°/15°C. In the seedling growth experiments, the main factors were type of soil (forest or cerrado) and radiation (PPD - % of radiation). The variable responses (height, dry mass) were transformed into log₁₀. To each radiation level one factor ANOVA was applied to test the effect of treatments. Multiple comparisons were obtained from ANOVA using the Duncan test at 5% level of significance. All analyses were carried out using the General Linear Models (GLM) of the Statistical Analysis System (SAS Institute 1986).

Results and Discussion

Germination - Fruiting of V. tucanorum is abundant with a massive production of uniform seeds, not light and dark coloured as it occurs in Qualea cordata Spreng. seeds (Godoy & Felippe 1992) and Q. grandiflora Mart. (Felippe 1990). The seeds with 1.3-2.8 x 0.4-0.7 cm bear a lateral wing consisting of interlaced trichomes inserted in the coat. The beginning of germination of intact seeds takes ca. 13 days. Removal of seed coat reduces this time to half.

The most efficient treatment in promoting germination was 25°C, under continuous light or darkness, showing that the seeds are not photoblastic at this temperature. Arasaki & Felippe (1987) found similar result in Dalbergia violacea (Vog.) Malme (= D. miscolobium Benth., Carvalho 1989 apud Sassaki 1995), a common tree species from cerrado. Some degree of photoblastism was observed in all remaining treatments (figures ¹A, ¹B, ²A). Among them, constant 30°C and continuous light produced the best results. Until up to ca. 2-4 weeks, the percentage of germination were smaller under alternate temperatures of 30°/10°C or 30°/15°C and alternate light and darkness. Furthermore, the germination delayed for 20 days under continuous darkness and alternate temperatures of 30°/15°C. When temperatures are alternated, lower temperatures of 10°C or 15°C produced no significant differences. When the constant or the highest temperature is 30°C, light enhances germination (figure ¹B). But at last, more than 93% of germination was attained in all these treatments.

Figure 1. Germination of seeds of V. tucanorum: A - germination under different temperatures and light conditions; B - germination under temperature and constant and alternate light. Vertical comparison by Duncan's test (a = 0,05): same letters are not statistically different. L = light; D = darkness. Treatments: 25°C L (¨), 25°C D (à), 30°C L (D), 30°C D (X), 30/15°C D (m), 30/15°C L/D (–), 30/10°C L/D (_*), 35/10°C L/D (+).

Under 35°/10°C, the maximum germination percentage after 73 days was as low as 62%, the remaining 38% of the seeds being completely deteriorated by this time (figure ²B). This result may be due to the increase of 5°C in the highest temperature, from 30°C to 35°C, which may probably caused protein denaturation to an irreversible stage, as found by Bewley & Black (1994) and Heydecker (apud Dell'Aquilla & Spada 1994).

Figure 2. Germination of seeds of V. tucanorum: A - under alternate light and temperature and alternate temperature under continuous darkness; B - under constant light and temperature and alternate ligh and temperature. Vertical comparison by Duncan's test (a = 0,05): same letters are not statistically different. L = light; D = darkness. Treatments: 30°C L (D), 30/15°C D (m), 30/15°C L/D (–), 30/10°C L/D (_*), 35/10°C L/D (+).

Therefore, the seeds of V. tucanorum germinate under a wide range of temperature (10 to 35°C), a characteristic shared with other species of cerrado (Arasaki & Felippe 1987). Photoblastism was detected by means of a delay or a lower germination percentage during the earlier 2-4 weeks when the constant or the highest temperature in alternate conditions was 30°C. In these cases, light enhances germination. It may be seen by the highest germination index (GI) found under continuous light at constant 30°C, at least up to 20^th day of the experiments. After ca. 48 days, this index was not high only in the 30°/15°C and 30°C continuous darkness treatments. In these treatments germination lasted 73 days (figure ³).

Figure 3. Germination Index (G.I.) of seeds of V. tucanorum under different temperatures and light conditions. L = light; D = darkness. Treatments: 25°C L (o), 25°C D (à), 30°C L (D), 30°C D (X), 30/15°C D (m),30/15°C L/D (–), 30/10°C L/D (_*), 35/10°C L/D (+).

Early growth of seedlings - V. tucanorum shows epigeal germination with leafy cotyledons that persisted until the end of the treatments (123 days), when no mortality was recorded. Cotyledon longevity was already observed in seedlings of other Vochysiaceae (Paulilo et al. 1993, Almeida et al. 1994). According to Fenner (1985), this kind of seedling is partly light dependent during the beginning of growth, due to the paucity of reserves. In this way, the persistent cotyledons may be important as a source of photosynthates.

The soil of cerrado is less fertile (highly acidic with high concentration of Al and reduced availability of P, K, Ca and Mg) than that from the forest floor (table ¹). Radiation level was found to affect growth parameters, sometimes in a different way according to the soil type (table ²).

The lowest gain in biomass was found under full sunlight (radiation of 100%) or strong shading (radiation of 4.8%). The lowest and the highest increment in height were respectively observed under radiation levels of 100% and 10.6% or lower (table ³). Under full sunlight, similar values of growth parameters were found in forest and in cerrado soils. Under radiation of 4.8%, the thinnest seedlings with similar and very low values of RI in the two soil types were observed. RGR under radiation levels of 100% and 4.8% are the lowest of the experiment and close to each other (table ⁴).

High values of R:A ratio (root:aerial) and robustness index (RI) were obtained in seedlings grown in forest soil under 45% radiation (table ⁴). These results appear to be opposite to those of Kozlowski et al. (1991) where seedlings growing in unfertile soils allocate a higher proportion of photosynthates to the roots. Nevertheless, Godoy & Felippe (1992) reported that in some species of cerrado, higher allocation of photosynthates to the roots of seedlings occurs only after four months.

In general, the radiation of 45% appeared to be the best condition for seedling growth, very closely followed by that of 10.6%, because these conditions produced higher increase in total biomass with a higher investment in leaf mass (table ³), enlarging potentially the photosynthetic capacity of the seedling. Highest RGR were also found under these radiation levels in the two soil types (table ⁴). According to Paulilo et al. (1993), RGR varies from 0.003 to 0.086 mg.mg^-1.d^-1 in tropical forest tree species, and from 0.014 to 0.040 mg.mg^-1.d^-1 in cerrado tree species. Under the radiation levels of 45% and 10.6%, the RGR of V. tucanorum ranged respectively from 0.026 to 0.028 mg.mg^-1.d^-1 and from0.024 to 0.027 mg.mg^-1.d^-1. These values are close to that found for Q. grandiflora (0.025 mg.mg^-1.d^-1), a tree species found in dense cerrados (Paulilo et al. 1993), but lower than that found for Q. cordata (0.038 mg.mg^-1.d^-1), a common tree species of cerrado (Godoy & Felippe 1992).

These results agree with the ecological characteristics of V. tucanorum in nature. This is a very frequent and widely distributed species, mostly in the cerrado domain, in environments with intermediate radiation levels, such as small forest gaps or edges or other places reached by the sunshine only part of the day (A.R. Barbosa, personal observation). These sites provide adequate conditions regarding the requirements for germination (highest or constant temperature around 25-30°C, light preference but not dependence) and seedling growth, since this species appeared to be well adapted to unfertile soils and is shade tolerant.

Acknowledgements - The authors thank Arício Xavier Linhares, for advice in statistical analyses and Ladaslav Sodek for assistance with the manuscript. The first author was supported by CAPES' scholarship as Master Student of the Curso de Pós-Graduação em Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, SP, Brazil.

2. Departamento de Botânica, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970 Campinas, SP, Brasil.

3. Departamento de Fisiologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970 Campinas, SP, Brasil.

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1. Pós-Graduação em Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas; Bolsista CAPES-DS.

Pós-Graduação em Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas; Bolsista CAPES-DS.

Publication Dates

• Publication in this collection
  22 Feb 2000
• Date of issue
  Oct 1999

History

• Accepted
  06 May 1999
• Received
  06 Nov 1998