ECOLOGICAL LIFE CYCLE OF
TREPOCARPUS AETHUSAE (APIACEAE)
Carol C. Baskin1,2,3, Jerry M. Baskin1,3, and Edward W. Chester3
1
School of Biological Sciences, University of Kentucky, Lexington, KY 40506ABSTRACT. In western Kentucky, seeds of the state-endangered species Trepocarpus aethusae mature in mid- to late August and early September and germinate from late September through November. Plants overwinter as rosettes and flower the following June and July. Vernalization was not required for flowering, and plants flowered faster under long days (night interruption) than under short days. Plants died after producing seeds, thus the species is a late-flowering winter annual. Seeds have underdeveloped (small, but differentiated) linear embryos that are physiologically dormant, thus they have morphophysiological dormancy. None of the freshly-matured seeds placed at 12 h/12 h alternating temperature regimes of 15/6, 20/10, 25/15, 30/15, or 35/20EC in light (14 h daily photoperiod) or in continuous darkness for 2 wk germinated. Experiments showed that embryos do not grow until after physiological dormancy is broken. Physiological dormancy was broken in a portion of the freshly-matured seeds by 4 to 6 wk of incubation on moist sand at the simulated September (30/15EC) temperature regime. After incubation for 6 wk at 30/15EC, embryo growth and germination occurred within 2 wk in 69, 73, and 56% of the seeds incubated in light at 15/6, 20/10, and 25/15EC, respectively, and in 40, 45, and 54% of those incubated in darkness, respectively. Few or no seeds germinated in light or in darkness at 30/15EC or at 35/20EC. Thus, physiological dormancy is broken in the field in Kentucky during the relatively warm days of September, and embryo growth and germination occur in October and November. Seeds sown on soil in a nonheated greenhouse in Lexington, Kentucky, in early September germinated from mid-October to early December, with the peak occurring in late October and early November. In spite of the lack of a light requirement for embryo growth and germination, seeds of T. aethusae have the potential to form a long-lived ($5 yr) persistent seed bank. Germination of seeds sown on soil and of those in soil seed bank samples collected in a population site in Trigg County, Kentucky, was monitored for 10 years in the nonheated greenhouse. A few of the seeds sown on soil did not germinate until the 10th year, and the last seedlings to appear in the soil samples was in the 8th year. Six weeks of cold stratification at 5EC did not cause a significant number of seeds to re-enter physiological dormancy. Since seeds of T. aethusae do not have a light requirement for embryo growth and germination, those that come out of physiological dormancy in early autumn germinate that autumn; no seeds germinated in the nonheated greenhouse in spring. Thus, the persistent seed bank in this species is attributed to a delay (of several years in some seeds) in loss of physiological dormancy and not to dormancy cycling. The dormancy/germination strategy of T. aethusae differs from that of another native winter annual species of Apiaceae, Chaerophyllum tainturieri, whose seeds also have morphophysiological dormancy. In C. tainturieri, the seeds have a light requirement for embryo growth and germination, and they exhibit dormancy cycling (J. and C. Baskin. 1990. Journal of Ecology 78:993-1004).
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TAXONOMIC AND ECOLOGICAL DIVERSITY OF THE OAKS
OF LAND BETWEEN THE LAKES: A REVIEW
Richard J. Jensen
Department of Biology, Saint Mary’s College, Notre Dame, IN 46556
ABSTRACT. At least 18 of the 22 species of oaks native to Kentucky and Tennessee are known to occur in the Land Between The Lakes (LBL). This taxonomic diversity is unusual for such a relatively small geographic area and is undoubtedly related to the diversity of ecological habitats documented for LBL. Oaks dominate the moderately mesic to dry forests in LBL, with as many as seven species co-occurring in a single community type, and are encountered regularly, albeit infrequently, in wetter habitats (e.g., ravines and bottomlands). The patterns of co-occurrence of species provide support for the hypothesis that co-occurring species are more likely to belong to different sections of the genus (red and black oaks versus white and chestnut oaks) than to the same section. Despite this, there is ample evidence of hybridization among a number of species. In particular, the xeric slope and ridge forests above Ginger Bay and the forests in and adjacent to Wrangler’s Camp contain a high proportion of trees of apparent hybrid origin. These, and other, cases of putative hybridization involve species of red and black oaks. While no specimens of hybrids among the white and chestnut oaks have been recorded, there is every reason to believe that such hybrids also occur in LBL.
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SEED DORMANCY IN ARISTOLOCHIA TOMENTOSA
(ARISTOLOCHIACEAE)
Christopher A. Adams1, Jerry M. Baskin1,3, Carol C.
Baskin1,2,3,
and Edward W. Chester3
1
School of Biological Sciences, University of Kentucky, Lexington, KY 40506 ABSTRACT. Aristolochia tomentosa Sims (Aristolochiaceae) is a woody
vine found primarily in riparian areas and wet alluvial woods from southern
Indiana and Illinois, west to southern Kansas, south to eastern Texas, and east
to southwest Georgia and the Florida panhandle. Flowering occurs from mid to
late May through June, and seeds are dispersed from October to early November.
The purpose of this study was to investigate the seed dormancy-breaking and
germination requirements of A. tomentosa. This species is part of a
comparative study of seed dormancy that also includes two of its close
relatives, the California endemic A. californica and the Appalachian
endemic A. macrophylla. These three species, along with the eastern Asian
species A. manshuriensis, are part of a monophyletic group
(subgenus Siphisia). The primary objective of the larger study is to
determine if dormancy-breaking requirements have evolved (diverged) in different
directions since these three closely-related species became geographically
separated, presumably in the mid to late Tertiary. Efforts are underway to
obtain seeds of A. manshuriensis so that this species can be included in
the comparative study.
Embryos of freshly-matured A. tomentosa seeds are 2.35 ±
0.5 mm (mean ± SE) long, and they must grow to more than twice this length
before germination can occur. Thus, fresh seeds have morphological dormancy
(MD). Seeds incubated in light (14 hr photoperiod) at five 12hr/12hr
thermoperiods (35/20, 30/15, 25/15, 20/10, 15/6EC)
germinated to 68, 54, 69, 35, and 2%, respectively, after 30 days, and to 84,
56, 74, 51, and 63%, respectively, after 90 days. Embryos in nongerminated seeds
removed from each of the five thermoperiods did not grow during a 12-wk cold (5EC)
stratification treatment. However, cumulative germination of these
cold-stratified seeds after an additional incubation of 30 days was 95, 100, 90,
100, and 95%, respectively. Thus, a portion of these seeds also has a
physiological component to dormancy; they have morphophysiological dormancy (MPD).
To determine length of cold period needed to break MPD, fresh seeds were
given 4, 8, or 12 wk of cold stratification in light (simulating natural field
conditions in winter) and then moved to the five thermoperiods. After 30 days,
seeds cold-stratified for 4 wk germinated to 98, 100, 98, 99, and 76%,
respectively, and those stratified for 8 wk germinated to 98, 100, 99, 99, and
96%, respectively. Seeds cold-stratified for 12 wk germinated to 97, 100, 100,
100, and 97%, respectively, after only 18 days. Seeds stratified for 12 wk
germinated at a faster rate at all five thermoperiods than those stratified for
4 or 8 wk.
Fresh seeds incubated in darkness over the range of thermoperiods germinated
to 64, 52, 42, 48, and 38%, respectively, after 30 days, and to 72, 63, 68, 53,
and 42%, respectively, after 90 days. Cumulative germination increased to 86,
70, 72, 58, and 65%, respectively, after the seeds subsequently were incubated
in light for 60 days. Thus, a portion of seeds in the population has a light
requirement for germination. Seeds given 12 wk of cold stratification in dark
and then incubated at the five thermoperiods in dark for 60 days germinated to
100, 96, 100, 98, and 94%, respectively. Thus, cold stratification overcomes the
light requirement in seeds that initially will not germinate in darkness
Like seeds of A. macrophylla [Adams, C.A., J.M. Baskin, and C.C.
Baskin. 2000. Amer. J. Bot. 87 (suppl. to No. 6): 38-39 (abstract).], those of A.
tomentosa require a cold stratification pretreatment to germinate to highest
percentages over the 35/20-15/6EC
temperature range. In contrast, seeds of A. californica do not germinate
at the higher (e.g. 30/15, 25/15EC)
thermoperiods and, further, they require exposure to a period of
warm-stratifying temperatures (e.g. 30/15, 25/15EC)
to germinate at low (15/6EC)
temperatures. Thus, preliminary results of this comparative study indicate that
dormancy-breaking requirements in these three species have diverged since their
separation, presumably from a common ancestor in the Tertiary.
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A COMPARATIVE GERMINATION STUDY OF AN
EASTERN AND A WESTERN NORTH AMERICAN
HEUCHERA SPECIES (SAXIFRAGACEAE)
Siti N. Hidayati and Jeffrey L. Walck
Department of Biology, Middle Tennessee State University,
Murfreesboro, TN 37132
ABSTRACT. Heuchera parviflora Bartl. var. parviflora occurs primarily in southeastern North America and H. cylindrica Dougl. var. cylindrica in northwestern North America. Both species are herbaceous perennials that grow in rocky habitats. Seeds of H. parviflora, collected in eastern Kentucky in November 1995 and 1996, and those of H. cylindrica, collected in western Washington in August 1996, were used to test temperature and light requirements for dormancy-break and germination, and germination phenology. Fresh seeds of H. parviflora germinated to 2-64% during 2 wk of incubation in light at alternating temperature regimes of 15/6, 20/10, 25/15, 30/15, and 35/20oC, with highest germination at 25/15oC; none of them germinated in darkness. Dry storage under laboratory conditions for up to 52 wk was not effective in overcoming dormancy. However, seeds given a 12 wk cold stratification period at 5oC in light germinated to 76-96% in light and those given cold stratification in darkness germinated to only 0-1% in darkness over the range of thermoperiods. Peak germination of H. parviflora seeds sown in mid-November 1996 in a nonheated greenhouse occurred in early March 1997, when mean weekly maximum and minimum temperatures were 14.8 and 8.7oC, respectively. On the other hand, fresh seeds of H. cylindrica germinated to 0-37% during 2 wk of incubation in light at 15/6-35/20oC, with highest germination at 15/6 and 20/10oC, and none germinated in darkness. Seeds continued germinating to $76% at 15/6-20/10oC during 4-12 wk of incubation in light. Neither dry storage for up to 52 wk nor cold stratification at 5oC for 9 wk was effective in overcoming dormancy. Peak germination of seeds sown in the greenhouse in early September 1996 occurred in late October 1996, when mean weekly maximum and minimum temperatures were 20.7 and 11.9oC, respectively.
84
GENETIC ALTERATION OF SEED GERMINATION TRAITS IN
EUPATORIUM RUGOSUM
David L. Robinson1 and Joann M. Lau2
1
Department of Biology, Bellarmine University, Louisville, KY 40205 ABSTRACT. We are attempting to examine the physiological basis of seed
dormancy and germination in white snakeroot (Eupatorium rugosum
Houtt [Ageratina altissima (L.) King & Robinson]) by carrying
out a recurrent selection program for individual plants producing seeds with
either high or low levels of dormancy.
In May 1998, 2000 seeds (achenes), collected from a single population of
white snakeroot growing in Louisville, KY, were planted onto a single tray lined
with moist germination paper. Most (77%) of the seed germinated within 17 d when
kept at a 21oC. The first seeds to sprout (4 d after sowing) were
transplanted into pots and grown to maturity in a nursery. At 17 d after sowing,
the ungerminated seeds were given a cold treatment (56 h) followed by another
long incubation at 21oC. Thirty-four seeds (2% of total) germinated
after this stratification treatment and were transplanted. This procedure was
continued ten additional cycles. In each cycle seeds were given adequate time to
germinate after cold-treatment, and were transplanted upon germination, with
unsprouted seeds receiving another cold-treatment. The last seed to germinate
(Cycle 9) did so 83 d after imbibition. Transplanted seedlings were grown to
maturity in the same environment, and allowed to set seed.
In the spring/summer of 1999, seed from these individual selections were
planted onto separate Petri dishes lined with moist filter paper and allowed to
germinate with the same alternating cycles of cold and warm. As a group, there
were no statistical difference in rates of germination for the seed from the
non-dormant lines when compared to seed from plants that had shown some
dormancy. There were obvious differences between individual selections, however.
Individual seedlings exhibiting the appropriate germination patterns were
transplanted and grown up in the same nursery for the next round of seed
production.
In the spring/summer of 2000, the seeds from plants that had undergone two
cycles of recurrent selection were again compared. These progeny expressed the
desired phenotype much more strongly than what was observed after the first
cycle of selection. While 74% of the seed from the non-dormant population
germinated during the first 10 d of the study, only 17% of the seed germinated
from plants that had been selected for cold-requirement during the same period.
This difference was statistically significant (P=0.001).
The constant-temperature population continued to show small amounts of
germination after exposure to one, two, three, or four cycles of cold
treatments, but the quantities declined steadily after each treatment. The
dormancy-selected progeny, however, showed more germination after the first and
second cold treatments than before. The differences in how these two populations
responded to cold treatment was statistically significant (P=0.002).
Therefore, it appears that we have identified white snakeroot plants which
produce seeds that respond to the environment in very different ways. It is
hoped that this germplasm will be a valuable resource in examining the
morphological and physiological features of seed dormancy and germination in
this species.
85
THE ECOLOGICAL LIFE CYCLE OF
CRYPTOTAENIA CANADENSIS (APIACEAE) WITH SPECIAL
REFERENCE TO BIOMASS ALLOCATION
Tracy S. Hawkins1,2, Jerry M. Baskin1, and Carol C. Baskin1,3
1 School of
Biological Sciences, University of Kentucky, Lexington, KY 40506
2 Hazard Community College, Jackson, KY 41339
3Department of Agronomy, University of Kentucky,
Lexington, KY 40546
ABSTRACT. Cryptotaenia canadensis is an herbaceous plant species of mesic and wet-mesic deciduous forests of eastern North America. This species reproduces sexually, flowering and fruiting during early to mid-summer, and asexually via monocarpic ramets produced at the base of the stem. Plants of C. canadensis growing in Robinson Forest, Breathitt County, Kentucky are being observed and sampled to construct a detailed life cycle model and document biomass allocation. Preliminary results of this research, which was initiated in August 1999, indicate that under field conditions, plants produced from seeds have a biennial life cycle, thus requiring two growing seasons to reproduce (sexually and asexually). Ramets behave as annuals and reproduce (sexually and asexually) after one growing season. Throughout the active growing stages of the asexual life cycle, relative percent biomass allocation to roots decreases, whereas total biomass of all plant parts (roots, stem, leaves, and umbels) increases throughout the annual growth cycle, until death of the entire parent plant following reproduction. Further, percent biomass (mean ± SE) allocated to sexual reproduction (19.7 ± 2.0) is less than that of the sympatric biennial Apiaceae Sanicula canadensis (32.7 ± 1.7) and S. trifoliata (26.8 ± 1.8) and greater than that of the sympatric perennial Apiaceae Osmorhiza claytonii (5.2 ± 0.7), S. gregaria (13.1 ± 1.5), and Thaspium barbinode (10.4 ± 1.2). Based on current results of this research, a graphical model of the ecological life cycle and pattern of biomass allocation for C. canadensis will be presented.
86
A COMPARISON OF GROWTH AND REPRODUCTIVE CHARACTERISTICS OF THE
INVASIVE
LIGUSTRUM SINENSE AND THE NATIVE FORESTIERA LIGUSTRINA (OLEACEAE)
Lorna L. Morris and Jeffrey L. Walck
Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132
ABSTRACT. Ligustrum sinense Lour. is an invasive shrub in southeastern United States that was introduced from China. In middle Tennessee, the species grows with the shrub Forestiera ligustrina (Michx.) Pour., native to southeastern United States, in the redcedar and/or hardwood forests surrounding cedar (limestone) glades. The goal of our research was to compare the growth and reproduction of the two species, and identify aspects that might influence the invasiveness of L. sinense. Plants of both species were sampled along the woodland edges of cedar glades (1362.0 ± 78.8 mmol m-2 s-1 on a clear day at noon in late August) and in the (primarily) redcedar forest (111.6 ± 12.9 mmol m-2 s-1) at Stones River National Battlefield, Rutherford County, Tennessee between March 2000 and February 2001. Multivariate analyses of variances (MANOVAs, P # 0.05), analyzing all variables simultaneously, indicated significant differences between the species. Regardless of the habitat, L. sinense had higher stem elongation rate, leaf weight ratio (investment in leaf biomass), leaf area ratio (leafiness), and number of fruits per branch, and lower leaf abscission rate and percentage of damaged leaves (by insects) than F. ligustrina. Leaf area expansion rate, leaf area, and height of L. sinense plants growing in the woods were greater than those of L. sinense plants growing along the edge and were greater than those of F. ligustrina plants growing in both habitats. Branch architecture based on branch length and orientation and on bifurcation ratio was similar between the species. However, leaves of L. sinense were oriented at 98-107E from vertical in both the woods and edge, whereas those of F. ligustrina were oriented at 107E in the woods but at 132E along the edge. The results suggest that L. sinense has a competitive advantage due to its greater ability to spatially and temporally capture light, greater adjustment of growth responses to the light environment, and higher fruit production than F. ligustrina.
87
DORMANCY-BREAK AND GERMINATION REQUIREMENTS OF
TWO EVENING PRIMROSES: OENOTHERA MACROCARPA
AND O. TRILOBA (ONAGRACEAE)
Jeffrey L. Walck and Siti N. Hidayati
Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132
ABSTRACT. Temperature and light requirements for dormancy-break and germination were determined for seeds of two Oenothera species collected in Rutherford County, Tennessee: O. macrocarpa Nutt. and O. triloba Nutt. Oenothera macrocarpa is a herbaceous perennial that occurs in central North America and is disjunct to middle Tennessee. Oenothera triloba is described as a winter annual, a biennial, or a short-lived perennial, and it grows in eastern and central North America. Fresh seeds of O. macrocarpa collected in mid-July 2000 germinated to 1-3% during 2 wk of incubation at alternating temperature regimes of 15/6, 20/10, 25/15, 30/15, and 35/20oC in light and in darkness. Seeds given a 12-wk warm stratification period at 25/15oC in light germinated to 4-11% over the range of thermoperiods in light, and those given warm stratification in darkness germinated to 0-4% in darkness. On the other hand, seeds given a 12-wk cold stratification period at 5oC in light germinated to 6% at 15/6oC and 93-100% at 20/10-35/20oC in light, and those given cold stratification in darkness germinated to 0-14% at 15/6-35/20oC in darkness. Seeds collected in mid-September 2000 and in mid-November 2000 germinated to 0-8% during 2 wk of incubation over the range of thermoperiods in light and in darkness, whereas those collected in mid-January 2001 germinated to 0% at 15/6oC and 83-100% at 20/10-35/20oC in light and to 0% at 15/6oC and 32-45% at 20/10-35/20oC in darkness. In contrast, fresh seeds of O. triloba collected in mid-July 2000 germinated to 1% at 15/6oC and 95-100% at 20/10-35/20oC in light and to 0-9% at 15/6-35/20oC in darkness during 2 wk of incubation. Seeds collected at monthly intervals between August 2000 and January 2001 germinated to 0-16% at 15/6oC and 61-100% at 20/10-35/20oC in light and to 0-16% at all thermoperiods in darkness during 2 wk of incubation. Thus, whereas seeds of O. triloba are nondormant at maturity, those of O. macrocarpa are dormant and require low (winter) temperatures to become nondormant.
88
VEGETATION STRUCTURE MONITORING IN A MANAGEMENT
CONTEXT, ARNOLD AIR FORCE BASE, TENNESSEE
Kevin C. Fitch
Arnold Air Force Base, Tullahoma, TN 37388
ABSTRACT. Vegetation monitoring is used to track management impacts in
sites included in a Barrens Restoration Demonstration Project at Arnold Air
Force Base, TN. The goal of the Barrens Restoration Demonstration Project is to
assess the effectiveness of various management methods for restoring or
maintaining a range of barrens habitats. The range of targeted Barrens habitats
includes: grassland, shrub-grassland, oak savanna, and oak woodland. Management
goals describing a range of desired vegetation structure, and monitoring
objectives were designated for each demonstration site prior to management
implementation. The management goal for grassland sites is to use biannual
prescribed fire or annual mowing to maintain the grassland community (i.e.,
graminoid and forb cover) and minimize abundance of oaks and other woody
species. The management goal for the shrub-grassland site is to use prescribed
fire to convert shrublands to shrub-grasslands. The management goal for the oak
savanna site and the oak woodland site is to use prescribed fire to change the
vegetation structure from oak forest to a more open-canopy structure with a
substantial ground cover dominated by graminoids and forbs. Monitoring
objectives include estimating mean tree density, percent canopy cover, percent
ground cover of functional groups (i.e., graminoids and forbs) below 1 meter,
percent cover of woody species at 1-3 meters above the ground, and basal area.
Vegetation structure within the restoration sites has responded favorably to
management. Biannual prescribed fire and annual mowing are adequate management
tools for grassland maintenance. Prescribed fire is an adequate management tool
for shrub-grassland restoration and has reduced tree density in some size
classes within the oak savanna and oak woodland sites. However, the canopy cover
management threshold has not been met. Continued management will likely decrease
the canopy cover within the oak savanna and oak woodland sites to desirable
levels. Mechanical thinning may be considered as a tool for reducing canopy and
minimizing impacts from a high frequency fire regime.
89
THE ROLE OF DISTURBANCE AND STRESS
ON SPECIES DISTRIBUTION ACROSS A KENTUCKY LAKE MUDFLAT
Kari M. Foster and William E. Spencer
Department of Biological Sciences, Murray State University, Murray, KY 42071
ABSTRACT. Water-level fluctuations in Kentucky Lake create disturbed and stressed habitats within the mudflat community. Flooding destroys vegetation at lower elevations; water-saturated soils stress growth at upper elevations. Plant community parameters were measured at four zones, and seedbanks were germinated in a greenhouse under flooded or moist-soil treatments. Flowering date, population density, flower number, and seed number were determined. Plants (germinated from upper and lower elevation mudflat-collected seed) of Rorippa sessiliflora were grown under flooded or moist-soil treatments. Chlorophyll fluorescence, flowering date, and seedpod number estimated stress. At the lower elevation annuals composed 100% of species, while at higher elevations annuals were only 33%. Population density was 400/m2 at higher elevations compared to 2,758/m2 at lower elevations. Average height was 52.5 cm at higher elevations compared to 2.7 cm at lower elevations. Individuals from upper elevations initially exhibited greater stress (reduced photosynthetic yield) than individuals from lower elevations. Lower elevation individuals flowered sooner in both soil treatments than upper elevation individuals. Both low and high elevation individuals exhibited greater seedpod production under flooding. Disturbance appears to determine species composition at lower elevations. Levels of stress tolerance appear to vary among individuals within the same species.
90