Diospyros texana Scheele (Ebenaceae) seed germination and seedling light requirements.
ABSTRACT. -- Germination of seeds of Diospyros texana Scheele (Ebenaceae, Texas or Mexican persimmon) were measured in 12 treatments in the dark at 20 to 25[degrees]C and in one light treatment. Growth of seedlings also was determined at seven light intensities. Highest germination was 52 percent in deionized water. Gibberellic acid did not have a significant effect on germination compared to the deionized water, whereas scarification with concentrated [H.sub.2]S[O.sub.4] for five to 45 minutes significantly reduced germination. Treatment of seeds with one percent Hg[Cl.sub.2], to reduce fungi, reduced germination. Incubation of seeds in high light and elevated temperature reduced germination to 26 percent and increased time required for the start of germination by two weeks. Growth of D. texana seedlings was greatest at light levels of approximately 1000 [micro]M * [m.sup.-2] * [sec.sup.-1]. Aboveground, belowground, and total dry weights did not change or were slightly reduced at higher light levels and reduced 50 percent at lower light levels. Diospyros texana plants do not appear to produce dormant seeds and seedlings grow as well in 50 percent shade as in full sunlight. Key words: Diospyros; germination; seedlings; light requirements; Texas.**********
Diospyros texana Scheele (Ebenaceae, Texas or Mexican persimmon) is a small tree or shrub, found throughout most of the western two-thirds of Texas, southeastern New Mexico, and south into Tamaulipas, Nueva Leon, and Coahuila, Mexico (Correll and Johnston, 1970). In south-central Texas, D. texana flowers in April and ripe fruit is present in late August and September. Fruits are black when ripe, sweet and edible, about two to three centimeters in diameter, with three to eight seeds per fruit.
Density of D. texana is 150 to 700 plants per hectare in various deciduous or evergreen woodlands of the southeastern Edwards Plateau (central Texas), with basal areas of 0.2 to 1.5 square meters per hectare with diameters at ground level between one and 10 centimeters per plant (Van Auken et al., 1979, 1981; Van Auken, 1988). Plant size distributions are skewed with 80 percent of all plants between one and five centimeters in diameter, indicating significant recruitment into the population (Van Auken et al., 1980).
Diospyros texana is a poor competitor in low nutrient soils compared to honey mesquite, Prosopis glandulosa Torr. (Van Auken and Bush, 1987). Seedlings of both D. texana and P. glandulosa had equal growth when alone, but if together, P. glandulosa had greater mean stem length, basal diameter, and total dry weight. Prosopis glandulosa is a legume, a colonizer, and nitrogen fixer, which may explain its better growth in low nitrogen soils (Felker and Clark, 1980; Johnson and Mayeux, 1990). Diospyros texana is a nonlegume, and as such is probably not a nitrogen fixer and seems to occur in mature communities, rather than being a colonizer (Van Auken et al., 1981).
Diospyros texana is one of the major species in many semiarid communities in southwestern Texas and other parts of southwestern North America, yet little is known about its seed germination, response to soil resources, response to light level, or responses to other biotic or abiotic factors. The purpose of this study was to determine if seeds of D. texana are dormant and if scarification or other treatments are necessary for germination. Additionally we were interested in knowing if fungal growth on seeds influenced seed germination or early seedling growth. Lastly, we measured seedling growth in a light gradient to determine light levels required for growth.
METHODS
Ripe fruits of Diospyros texana were collected from female plants in Juniper woodlands in the southern part of the Edwards Plateau, Bexar County, Texas (98[degrees]36'W and 29[degrees]37'N). Fruits were collected in August 1988 and 1989. Seeds were depulped by agitating by hand and forcing them through a 6.4 millimeter wire sieve, followed by washing in tap water and air drying. Clean, dry seeds were placed in a plastic bag and kept at 10[degrees]C until used.
Seeds were scarified in concentrated [H.sub.2]S[O.sub.4] with agitation for 0, 5, 15, 30, 45 or 60 minutes. Seeds were next washed thoroughly in tap water 25 seeds were placed on two layers of moist filter paper in plastic Petri plates that were 9.0 centimeters in diameter by 1.5 centimeters deep. The Petri plates were labeled and placed in cans in the dark at 20 to 25[degrees]C. Seeds were scored for germination on a daily basis. Because of fungal growth in preliminary experiments, a one percent Hg[Cl.sub.2] soak for 10 minutes, followed by rinsing in tap water was used as a treatment. This treatment was used alone and in conjunction with [H.sub.2]S[O.sub.4] scarification at the same times indicated above. Gibberellic acid is known to break dormancy in some seeds (Kahn, 1968; Van Auken and Lohstroh, 1990), consequently seeds of one treatment were soaked in five millimolar gibberellic acid for three hours and then rinsed in tap water prior to placement into Petri plates. An additional treatment included the gibberellic acid soak combined with the Hg[Cl.sub.2] treatment. Twenty-five seeds were used in each replication and there were three replications per treatment. The experiment was started on 7 September 1988 and completed on 23 September 1988. Seeds were considered germinated when radicles reached four millimeters in length; however, if seeds were overgrown with fungi and subsequently died or embryos were mechanically broken as they emerged from the seed coat, they were not counted as successful germinations. Statistical methods include a one way ANOVA with treatment as the main factor followed by the Scheffe multiple comparison test (Steel and Torrie, 1980; SAS Institute, 1982).
A second germination experiment was started on 4 October 1989 using fruit collected in August 1989 and depulped in the same way as described above. Cleaned seeds were placed in the bottom of plastic trays, nine centimeters deep, that were covered with two layers of moistened filter paper. Fourteen trays were used with 120 seeds per tray and 1680 seeds total. Trays were covered with thick plates (0.3 centimeter) of clear glass and kept in a fiberglass greenhouse with temperatures ranging from 23 to 38[degrees]C. Photosynthetically active photon flux density (PPFD) was 1264 [+ or -] 166 ([bar.x] [+ or -] SD [micro]M * [m.sup.-2] * [sec.sup.-1] at solar noon on 10 October 1990, which was 67 percent of the outside mean PPFD. Deionized water was added as needed to keep the filter paper moist. The experiment was terminated on 22 November 1989.
The third experiment utilized a light gradient. Seeds from the previous greenhouse germination study were selected for uniform size and transplanted into plastic pots that were 15 centimeters in diameter by 15 centimeters deep. Three seedlings were used per pot and each pot contained 1400 grams of native soil (upper 20 centimeters of a Patrick series clay-loam--Taylor et al., 1966). Pots were lined with plastic bags to prevent nutrient loss. They were randomized and four were placed in each of seven light treatments. Plants were watered as needed with deionized water, usually about 150 milliliters per day. Soil was supplemented with 0.15 gram nitrogen as N[H.sub.4]N[O.sub.3], 0.15 gram phosphorous as [Na.sub.2]HP[O.sub.4], 0.10 gram potassium as KCI, and 0.04 gram sulfur as MgS[O.sub.4] per pot at the beginning of the experiment (one-half the amounts used by Tiedemann and Klemmedson, 1986). Seedlings were transplanted into pots on 1 December 1989 and placed in shade treatments on 19 April 1990.
Shade chambers were constructed with commercial shade fabric, one by one millimeter mesh, to provide PPFDs of 1594 [+ or -] 124, 1265 [+ or -]126, 935 [+ or -] 111, 740 [+ or -] 73, 544 [+ or -] 45, 219 [+ or -] 24, and 117 [+ or -] 18 [micro]M * [m.sup.-2] * [sec.sup.-1] (with full sunlight at 2050 [+ or -] 213 [micro]M * [m.sup.-2] * [sec.sup.-1]). A fiberglass greenhouse was used with natural sunlight and daytime temperatures between 23[degrees]C and 38[degrees]C. No significant differences in air temperatures were detected among light treatments. Light levels were measured inside and outside the greenhouse with a Li-Cor[R] LI-188 integrating quantum sensor.
Stem length, basal diameter, number of leaves and stem, leaf and total aboveground dry weight were determined at the end of the experiment. All leaves larger than 0.5 centimeters were counted. Basal diameter, just above the cotyledon scars, was measured with a vernier caliper. Stem length was the distance from the cotyledon scars to the apical meristem plus the lengths of all secondary stems. Seedlings were harvested on 29 September 1990 by clipping at the cotyledon scars and aboveground dry weight was measured after drying to a constant weight at 100[degrees]C. Ash free dry weight (AFDW--Bohm, 1979) was determined for belowground tissue by washing the roots to remove soil, drying at 100[degrees]C to a constant weight, and ashing the samples at 550[degrees]C for three hours. Statistical analysis included a one-way ANOVA with light as the main factor followed by the Scheffe multiple comparison test (Steel and Torrie, 1980; SAS Institute, 1982).
RESULTS
Greatest germination was 52 percent in deionized water (Table 1). There were no significant differences between the deionized water, gibberellic acid, Hg[Cl.sub.2], five minutes--[H.sub.2]S[O.sub.4] or the Hg[Cl.sub.2] + five minutes--[H.sub.2]S[O.sub.4], although the last three treatments were much lower than the first two. The [H.sub.2]S[O.sub.4] scarification reduced germination significantly in six of eight treatments compared to deionized water. The longer the scarification, the lower the percent germination. Soaking the seeds in Hg[Cl.sub.2] protected them slightly from the effects of the acid. Increasing germination temperature and placing seeds in the light increased germination time by two weeks and reduced germination to 26 percent (Fig. 1). Twenty-three percent of the seeds germinated within 30 days, with only three percent germinating in the next three weeks.
[FIGURE 1 OMITTED]
In the light experiment, number of leaves increased from approximately 40 per pot in the lowest light treatment to 80 per pot in the 544 [micro]M * [m.sub.-2] * [sec.sup.-1] treatment, and remained constant at the higher light levels (Fig. 2A). Stem length increased from 25 to 40 centimeters in the two lowest light treatments, increased slightly to 50 centimeters in the 1265 [micro]M * [m.sup.-2] * [sec.sup.-1] treatment, and decreased to 25 centimeters in the highest light treatment. Basal diameter increased from 1.8 millimeters in the lowest light treatment to approximately 4.0 millimeters in the third light level, and remained unchanged through the highest light level. Total dry weight increased from 0.5 gram per pot in the lowest light level to 3.2 grams per pot in the 935 [micro]M * [m.sup.-2] * [sec.sup.-1] treatment, and remained constant through the highest level (Fig. 2B). Aboveground and belowground dry weight followed the same trend, except aboveground declined slightly in the highest light level and belowground increased.
[FIGURE 2 OMITTED]
DISCUSSION
Seeds of plants may be dormant or nondormant (Nikolaeva, 1977). Factors that appear to control seed dormancy include species, plant type (annual or perennial), time of seed maturation (spring, summer, autumn), local climatological conditions during and after seed dispersal, or a combination of these conditions. Seeds of certain species that mature in late summer or autumn may be nondormant, but germination may be suppressed by low winter temperature. Another possibility would be germination in autumn, but slow growth during winter because of low temperature. Many species that flower and set seed in spring or summer are dormant and require high followed by low temperature stratification to break dormancy (Baskin and Baskin, 1989). The above treatment would mimic summer and winter conditions prior to optimum conditions for germination and growth in early spring, but there are many varied strategies.
Germination of Diospyros virginiana L. (common persimmon) usually occurs in April or May, but low germination has been experienced (Olson and Barnes, 1974). Suspected dormancy was broken by stratification in sand or peat for 60 to 90 days at 3[degrees] to 10[degrees]C, but [H.sub.2]S[O.sub.4] scarification for two hours proved less effective (Olson and Barnes, 1974). We have not identified any studies of seed germination for D. texana. Acid treatment of D. texana seeds was detrimental, with 30 minutes of acid treatment reducing germination to zero. Results of acid treatment of seeds of D. virginiana appear to be similar, but mechanisms are uncertain, probably associated with acid entry into the seed, causing hydrolysis and death of the embryo.
Gibberellic acid treatment was ineffective in promoting germination of D. texana seeds, yielding the same number of germinations as deionized water. Other hormones might promote D. texana seed germination, but tests have not been attempted. Data showed maximum germination (52 [+ or -] 4 percent) in the deionized water treatment. It is possible all viable seeds germinated in the deionized water treatment. The only selection for fruits, was that they be ripe, black, and on the plant or recently fallen. After seeds were depulped and dried, removal of any that were flat, shriveled, or obviously not developed was completed. Less than one percent of the cleaned, dried seeds were discarded. Nongerminated seeds in both experiments were covered with fungi, seeds were soft and the endosperm had liquified. It appeared that all of these seeds were inviable at the end of the experiment. Use of Hg[Cl.sub.2] as a fungicide was not effective. In addition, we did not do initial tetrazolium tests to determine the number of viable seeds (Baskin and Baskin, 1989).
Apparently D. texana produces nondormant seeds. Thus, seeds could germinate at anytime after fruit-ripening in August and September, providing soils are wet. Rainfall over much of the eastern part of the range of D. texana is bimodal, with spring and autumn peaks coupled with an east-to-west gradient (Arbingast et al., 1976). In the eastern part of the Edwards Plateau, Texas, rainfall is approximately 762 millimeters per year, whereas in the extreme western part of Texas, near El Paso, it is 203 millimeters per year and falls mainly in summer. Rainfall is highly variable in the region, from month to month and year to year.
Germination of D. texana seeds could occur in autumn after fruit ripening in wet years, followed by slow growth over the winter, with increased growth the following spring during or after rains. However, low rainfall could reduce germination until spring, prior to summer drought. Establishment would probably be below an adult D. texana or other woody species because the severity of environmental conditions would be modified (Tiedemann and Klemmedson, 1973a, 1973b, 1986; Bush and Van Auken, 1986a). Growth of D. texana would be just as high below a canopy as in full sunlight. Increasing shade up to approximately 50 percent caused little change in growth compared to full sunlight. This suggests that D. texana is a shade plant and growth would be similar to Celtis laevigata Willd. (Texas sugarberry), which shows a similar pattern of lack of growth stimulation in full sunlight (Bush and Van Auken, 1986b; Van Auken and Lohstroh, 1990).
Little information is available concerning where and when seedlings of D. texana establish. Significant numbers of mature plants were found below woodland canopies on the Edwards Plateau of central Texas (Van Auken et al., 1981), suggesting germination occurred there in the past. Demographic studies suggest new additions to the population (Van Auken et al., 1980). Lack of seed dormancy and shade tolerance suggests maximum use of available microsites and resources, or both, when resources are available.
TABLE 1. Mean percent germination of Diospyros texana seeds ([+ or -] SD) in 12 treatments after 15 days in the dark at 25[degrees]C. There were three replicates of 25 seeds each. Mean values followed by the same letter are not significantly different (ANOVA, Scheffe multiple comparison test P > 0.05). Treatment Percent germination Deionized Water 52 [+ or -] 4 a Gibberellic Acid 49 [+ or -] 8 a [H.sub.2]S[O.sub.4]--5 min 24 [+ or -] 17 ae [H.sub.2]S[O.sub.4]--15 min 7 [+ or -] 2 be [H.sub.2]S[O.sub.4]--30 min 0 [+ or -] 0 be [H.sub.2]S[O.sub.4]--45 min 0 [+ or -] 0 be Hg[Cl.sub.2] 39 [+ or -] 6 ac Hg[Cl.sub.2] + [H.sub.2]S[O.sub.4]--5 min 39 [+ or -] 13 ad Hg[Cl.sub.2] + [H.sub.2]S[O.sub.4]--15 min 16 [+ or -] 4 bcde Hg[Cl.sub.2] + [H.sub.2]S[O.sub.4]--30 min 3 [+ or -] 2 be Hg[Cl.sub.2] + [H.sub.2]S[O.sub.4]--45 min 0 [+ or -] 0 be Hg[Cl.sub.2] + Gibberellic Acid 17 [+ or -] 8 bcde
LITERATURE CITED
Arbingast, S. A., L. G. Kennamer, R. H. Ryan, J. B. Buchanan, W. L. Hezlep, L. T. Ellis, T. G. Jordan, C. T. Granger, and C. P. Zlatkovich. 1976. Atlas of Texas. Bureau of Business Research, Univ. Texas, Austin, 179 pp.
Baskin, J. M., and C. C. Baskin. 1989. Seed germination ecophysiology of Jeffersonia diphylla, a perennial herb of mesic deciduous forests. Amer. J. Bot., 76:1073-1080.
BOHM, W. 1979. Methods of studying root systems. Ecological studies (W. D. Billings, F. Golley, O. L. Lange, and J. S. Olson, eds.), Springer-Verlag, New York, 33:1-188.
Bush, J. K., and O. W. Van Auken. 1986a. Changes in nitrogen, carbon, and other surface soil properties during secondary succession. Soil Sci. Soc. Amer. J., 50:1597-1601.
______. 1986b. Light requirements of Acacia smallii and Celtis laevigata in relation to secondary succession on floodplains of south Texas. Amer. Midland Nat., 115:118-122.
Correll, D. S., and M. C. Johnston. 1970. Manual of the vascular plants of Texas. Texas Research Foundation, Renner, Texas, 1881 pp.
Felker, P., and P. R. Clark. 1980. Nitrogen fixation (acetylene reduction) and cross inoculation in 12 Prosopis (mesquite) species. Plant Soil., 57:177-186.
Johnson, H. B., and H. S. Mayeux, Jr. 1990. Prosopis glandulosa and the nitrogen balance of rangelands: extent and occurrence of nodulation. Oecologia, 84:176-185.
Kahn, A. A. 1968. Inhibition of gibberellic acid-induced germination by abscisic acid and reversed by cytokinins. Plant Physiol., 43:1463-1465.
Nikolaeva, M. G. 1977. Factors controlling the seed dormancy pattern. Pp. 51-74, in The physiology and biochemistry of seed dormancy and germination (A. A. Kahn, ed.), North-Holland Publ. Co., Amsterdam and New York.
Olson, D. F., Jr., and R. L. Barnes. 1974. Diospyros virginiana L. common persimmon. Pp. 373-375, in Seeds of woody plants in the United States (C. S. Schopmeyer, ed.), Agric. Handbook, Forest Service, USDA, Washington, D. C., 450:1-883.
SAS Institute. 1982. SAS user's guide. SAS Institute Inc., Cary, North Carolina, 584 pp.
Steel, R. G. D., and J. H. Torrie. 1980. Principles and procedures of statistics: a biometric approach. McGraw-Hill, New York, 633 pp.
Taylor, F. B., R. B. Hailey, and D. L. Richmond. 1966. Soil survey of Bexar County, Texas. USDA, Soil Conserv. Serv., Washington, D. C., 126 pp.
Tiedemann, A. R., and J. O. Klemmedson. 1973a. Nutrient availability in direct grassland soils under mesquite (Prosopis glandulosa) trees and adjacent open areas. Soil Sci. Soc. Amer. Proc., 37:107-111.
______. 1973b. Effects of mesquite on physical and chemical properties of the soil. J. Range Manag., 26:27-29.
______. 1986. Long-term effects of mesquite removal on soil characteristics. I. Nutrients and bulk density. Soil Sci. Soc. Amer. J., 50:472-475.
Van Auken, O. W. 1988. Woody vegetation of the Southeastern escarpment and plateau. Pp. 43-55, in Edwards Plateau vegetation: plant ecological studies in central Texas (B. B. Amos and F. R. Gehlbach, eds.), Baylor Univ. Press, Waco, Texas, viii + 144 pp.
Van Auken, O. W. and J. K. Bush. 1987. Interspecific competition between Prosopis glandulosa Torr. (honey mesquite) and Diospyros texana Scheele (Texas persimmon). Amer. Midland Nat., 118:385-392.
Van Auken, O. W., and R. J. Lohstroh. 1990. Importance of canopy position for growth of Celtis laevigata seedlings. Texas J. Sci., 42:83-89.
Van Auken, O. W., A. L. Ford, and J. L. Allen. 1981. An ecological comparison of upland deciduous and evergreen forests of central Texas. Amer. J. Bot., 68:1249-1256.
Van Auken, O. W., A. L. Ford, and A. Stein. 1979. A comparison of some woody upland and riparian plant communities of the southern Edwards Plateau. Southwestern Nat., 24:165-180.
Van Auken, O. W., A. L. Ford, A. Stein, and A. G. Stein. 1980. Woody vegetation of upland plant communities in the southern Edwards Plateau. Texas J. Sci., 32:23-35.
O. W. VAN AUKEN AND J. K. BUSH
Division of Life Sciences, The University of Texas at San Antonio, San Antonio, Texas 78249
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| Author: | Van Auken, O.W.; Bush, J.K. |
|---|---|
| Publication: | The Texas Journal of Science |
| Geographic Code: | 1USA |
| Date: | May 1, 1992 |
| Words: | 3502 |
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