Acorn Germination Research Articles

Irrigation is an effective strategy to assist cork oak (Quercus suber L.) regeneration in a semi-arid climate

ABSTRACT Irrigation can be a strategy to overcome the high mortality and declining vigour of cork oak trees facing increasing drought stress in the Mediterranean basin. Through a three-year irrigation experiment in a semi-arid Mediterranean region, which encompassed two sets of 100 planted individuals that had a 24-year age gap and the direct seeding of 100 acorns, we tested the influence of water irrigation on distinct stages of cork oak establishment and development, namely (1) acorn germination, (2) emerged seedling survival, (3) growth of planted seedlings, (4) vertical and (5) radial growth, and (6) the vigour of 28-year-old trees. Water irrigation significantly improved acorn germination and the growth of both cork oak seedlings and trees but did not affect the survival of emerged seedlings to the dry season. The vigour of 28-year-old trees (height-to-diameter ratio) showed no significant differences between the plants growing in watered and in controlled conditions.

Spicing up oak forest restoration: a preliminary report of the protective use of chili peppers in direct seeding of acorns

Direct sowing of acorns is a technique for oak forest restoration, however, high seed predation by mammals can occur and cost‐effective alternatives to protect acorns are therefore required. The present study evaluated the protection provided by chili peppers (Capsicum annuum and Capsicum pubescens) to acorns of Quercus germana, an endangered endemic oak tree of the cloud forests. Greenhouse and field experiments were established to evaluate the effect of chili peppers on acorn removal, germination, and seedling emergence. These processes were related to the prevalent microhabitat characteristics where the acorns were introduced, and the fauna that consumed chili peppers and acorns was identified using camera traps. In the greenhouse trial, more seedlings emerged from acorns covered by fruits of C. pubescens (65.71 ± 8.14) and C. annuum (57.14 ± 8.49%) compared to unprotected acorns (31.43 ± 7.96%). Contrary to expectation, acorn removal in the field was greater using C. pubescens than the unprotected acorns, particularly in microsites with lower tree cover and higher grass dominance. Acorn removal was similar among chili pepper treatments. These results are explained by the camera trap records, which showed bird species consuming Capsicum fruits, thus exposing the acorns to subsequent removal and/or consumption by rodents. The studied Capsicum fruits had no negative effect on acorn germination and seedling emergence under greenhouse conditions, and future practices could, therefore, involve the use of different techniques to prevent the discovery of chili peppers by birds; for example, using green chili peppers for camouflage, or hiding them under litter or herbaceous vegetation.

Plant hormones mediate the interaction between oak acorn germination and rodent hoarding behaviour.

The interaction between animals and plants for seed dispersal and predation has received much attention; however, the underlying physiological mechanisms driving the responses of both seeds and animals remain unclear. We conducted a series of behaviour and physiology experiments to examine the role of plant hormones in regulating seed germination and rodent hoarding behaviour in the Quercus variabilis and Leopoldamys edwardsi systems. We found that acorns that were partially consumed by rodents had increased gibberellin (GA) levels and shortened germination time. Rodents preferred scatter-hoarded abscisic acid (ABA)-treated and intact acorns but consumed germinated and GA-treated acorns; such treatment differences disappeared for inactivated acorns by boiling water. Moreover, we found that seven potential compounds may be linked to seed germination and rodent hoarding behaviour. Our results indicate that acorns of oak showed rapid germination when facing predation risk, while rodents could identify the germination status of seeds for hoarding; GA and ABA may play an important role in regulating seed germination of oak and hoarding behaviour of rodents.

Behavioral adaptation of sympatric rodents to early germination of oak acorns: radicle pruning and embryo excision.

The seed germination schedule is a key factor affecting the food-hoarding behavior of animals and the seedling regeneration of plants. However, little is known about the behavioral adaptation of rodents to the rapid germination of acorns. In this study, we provided Quercus variabilis acorns to several rodent species to investigate how food-hoarding animals respond to seed germination. We found that only Apodemus peninsulae adopted embryo excision behavior to counteract seed germination, which is the first report of embryo excision in nonsquirrel rodents. We speculated that this species may be at an early stage of the evolutionary response to seed perishability in rodents, given the low rate of embryo excision in this species. On the contrary, all rodent species preferred to prune the radicles of germinating acorns before caching, suggesting that radicle pruning is a stable and more general foraging behavior strategy for food-hoarding rodents. Furthermore, scatter-hoarding rodents preferred to scatter-hoard and prune more germinating acorns, whereas they consumed more nongerminating acorns. Acorns with embryos excised rather than radicles pruned were much less likely to germinate than intact acorns, suggesting a behavioral adaptation strategy by rodents to the rapid germination of recalcitrant seeds. This study provides insight into the impact of early seed germination on plant-animal interactions.

Simulated partial predation on the largest-seeded oak: Effects of seed morphology and size on early establishment

Plant recruitment is limited by seed predation. However, seeds that are only partially consumed can still contribute to regeneration provided the embryo remains viable. Seed size and shape are important traits that influence the relative location of the embryo, as well as its survival and further development. Yet, it is unclear whether the interaction of seed size and shape affects seed tolerance to partial damage and initial seedling performance. We evaluated the effects of simulated partial damage in three different acorn shapes (flattened, triangular and typical) on early seedling establishment in the threatened Quercus insignis, the largest-seeded oak species worldwide. We also distinguished between lateral acorn damage (pericarp damage only) and cotyledon damage (1/3 of the reserves), using acorn size as a covariate. For this, we recorded the germination, emergence and performance (total height, basal diameter, specific leaf area, total leaf area, above and belowground dry biomass) of each seedling after 110 days of growth.Seed shape influenced the rate and percentage of acorn germination, seedling emergence and performance. Typical-shaped acorns germinated at higher rates and produced more seedlings with higher performance. Simulated damage increased the rate and percentages of germination and emergence, but did not affect performance (except for specific leaf area). Seed size favored performance but not germination or emergence, and no significant interaction was found between acorn shape and seed size with respect to germination, emergence or performance, depending on each damage treatment. Our results suggest that acorn size allows tolerance to partial seed predation, since low to moderate acorn damage (<1/3 of cotyledon lost) had no negative effect on germination or emergence. Larger seed size could therefore not only support seedling performance, but also help to meet the nutritional requirements of small and mid-size predators without risking the integrity or development of the embryo. Acorn shape should therefore be considered in basic and applied oak ecology since seed morphology seems to influence not only germination and emergence, but also seedling performance. These results may have important eco-evolutionary implications in the context of seed-predator interactions, since certain shapes tolerate damage better than others and may thus benefit from the selection pressures exerted by seed foragers, both predators and dispersers. In addition to acorn size, managers should consider acorn shape and its relationship to early seedling establishment, as well as the potential for using partially damaged acorns in oak forest restoration projects.

Effects of exogenous bacterial quorum-sensing signal molecule/messenger N-hexanoyl-L-homoserine lactone (C-HSL) on acorn germination and plant growth of Quercus robur and Q. rubra (Fagaceae)

The effect of pre-sowing priming with N-hexanoyl-L-homoserine lactone (C6-HSL) solution (300 mg/L) on acorn germination and morpho-phenological characteristics of Quercus robur and Q. rubra was studied under laboratory conditions. After priming, 93.4% of Q. robur acorns germinated that exceeded the control by 32.2%, while the number of sprouted acorns of Q. rubra increased within error limits by 5% more than the control and amounted to 90%. According to morphological characteristics, the 47-day-old plants of Q. robur were divided into the following groups: germinated acorns, sprouts and seedlings with juvenile leaves, whereas among the plants of Q. rubra, sprouts and seedlings with true leaves were selected. A group of plants with juvenile leaves was detected only in the samples primed with C6-HSL. Priming induced differential changes in cotyledon biomass of both species and accelerated nutrient utilization by Q. robur seedlings. We observed a positive effect on the growth and biomass accumulation of Q. robur plants and a negative effect, except for plants of the third group, on those of Q. rubra. The dry weight of seedling roots of Q. robur and shoots of Q. rubra increased, respectively, by 103% and 153%. Priming of acorns with C6-HSL solution induced an increase in number, length, biomass and total area of leaves. These changes were more pronounced in Q. rubra seedlings. Alterations in the root system architecture towards formation of numerous additional lateral roots were recorded for both species. Thus, priming with C6-HSL solution activated acorn germination and stimulated growth of Q. robur plants and decelerated growth of plants of Q. rubra. Exogenous C6-HSL did not eliminate the syndrome of unfriendly seedlings of both studied oak species, but improved the viability of acorns and increased the number of seedlings.

Germination of acorns and growth of one-year common oak seedlings in conditions of the Volga-Akhtuba floodplain, Astrakhan region

Seed germination and development of common oak ( Quercus robur L.) during the first year of growing under conditions of the Volga-Akhtuba floodplain, Astrakhan region, were studied in the research. Currently, the floodplain forests of the Astrakhan region are experiencing a very high load from the grazing of farm animals and wild tourism. Therefore, it is necessary to restore degraded forest phytocenoses to increase species diversity. The aim of the study was to study the effect of flooding duration on oak germination of in the soil and climatic conditions of the Volga-Akhtuba floodplain in the north of the Astrakhan region. Sowing seeds were carried out according to the Sukachev method (1961). According to the results of the three-year research (2019-2021), it was revealed: the germination of seeds (acorns) of common oak ( Quercus robur L.) averaged 31 % of the total sown seeds. In 2019 and 2021, germination of oak in non-flooded areas was 5 % higher compared to other variants of the experiment (short-term and long-term flooding), resulted from seed loss due to prolonged flooding. In 2020, as a result of short flooding period, germination had an insignificant difference in variants. The height of annual seedlings of common oak in the variant of prolonged flooding differed significantly (35 cm higher) from other variants.

Effect of priming with gibberellic acid on acorn germination and growth of plants of Quercus robur and Q. rubra (Fagaceae)

The effect of pre-sowing priming with gibberellic acid (GA3) solution (50 mg/L) on acorn germination and growth characteristics of 47-day-old plants of Quercus robur and Q. rubra was studied under laboratory conditions. The priming effect varied depending on the oak species and development phase of the plants. After priming, 86% of Q. robur acorns germinated that exceeded the control by 25%, while the number of sprouted acorns of Q. rubra was at the control level and amounted to 85%. The 47-day-old plants of Q. robur were divided into three groups: (1) sprouted acorns with cracked pericarp and main root; (2) seedlings with formed epicotyl and apical bud; (3) seedlings with unopened true leaves of juvenile type. The plants of Q. rubra were divided into two groups: (1) seedlings with formed epicotyl and apical bud; (2) seedlings with open true leaves. In plants of Q. robur, priming caused decrease of biomass in cotyledons, while no visible changes were found for those of Q. rubra. An increase in growth characteristics, fresh and dry biomass accumulation was noted for all Q. robur plants whereas thickening of shoots was observed only in seedlings of the second group. Instead, hormone treatment of acorns of Q. rubra led to inhibition of growth processes in plants of both groups. In general, priming with GA3 solution enhanced germination of acorns and stimulated growth of Q. robur plants and, conversely, slowed the growth of Q. rubra plants. Exogenous GA3 did not eliminate the syndrome of unfriendly seedlings of the studied oak species, but improved the viability of acorns and increased the number of seedlings/shoots.

Effects of substrate on the germination and seedling growth of Quercus suber L.

Abstract The seedling quality is one of the most important factors for the success of reforestation programs. In this sense, this work aimed to evaluate the effects of substrate on the germination of cork oak acorns from El Aouana forest, located in the Jijel region of north-eastern Algeria, and on the performance of seedlings, particularly their growth. The experiment was performed in the nursery of the Tlemcen Forest Conservation. For this purpose, five substrates were used: S1 (sand), S2 (topsoil), S3 (potting soil), S4 (1/2 sand + 1/2 topsoil) and S5 (1/3 sand + 1/3 topsoil + 1/3 potting soil). Germination and survival rates, and seedling morphological traits: average height of seedlings, average root collar diameter, stem height/root collar diameter ratio (H/D), average number of leaves per plant, leaf length, leaf width and leaf area, were evaluated. Results obtained after 16 months of monitoring in the nursery showed high germination rates of 91.4%, with an average survival rate of 89.5%, and significant differences were recorded between the substrates tested. In terms of growth, the best results were obtained with the potting soil substrate (S3) for all parameters. The lowest yields were recorded in seedlings grown on sand alone (S1).

Acorn germination and oak (Quercus brantii Lindl.) seedling development dramatically affected by spatial position of maternal trees from Ilam gas refinery, Iran

Air pollution from industrial areas is an environmental stress on trees that can seriously endanger the future of forests. Ancient Persian oak trees (Quercus brantii Lindl.) in the semi-arid forests of the Zagros are exposed to various environmental stresses such as air pollution from the Ilam gas refinery, which causes many challenges in forest regeneration and afforestation, thus jeopardizing forest sustainability or restoration. The aim of this study was to investigate the effect of toxic pollutants emitted from a gas refinery operation on seed germination and morphological characteristics of seedlings from maternal trees that are located at different distances (1000, 1500, 2000, 2500 and 10,000 m) and directions (east and west) from the facility. The results showed that oak seedlings grown from acorns collected at a distance of 10,000 m had the highest values in various seed germination and seedling developmental measures and morphological traits such as leaf and root mass, number and length compared to other distances of 1000, 1500, 2000 and 2500 m from the gas refinery. Highest values in seed germination, and seedling emergence and growth occurred at distances furthest from the refineries. Also, direction from the refinery significantly (p < 0.05) effected root growth, with larger seedlings occurring from acorn collected west of the refinery. The results of principal component analysis and discriminate analysis showed that, of the traits observed, various seed germination traits were most sensitive to gaseous toxic pollutants emitted from this source. Based on all studied traits, seedlings from acorns collected at 10,000 m from the facility were easily distinguished from seedlings of acorns collected at closer distances. It can be concluded that refinery toxic pollutants caused significant adverse changes in germination and seedling growth from acorns collected from oak trees located near (less than 10,000 m) to the source of air pollution. It is recommended that such pollution sources should be established far away from forest areas, and if constructed, be equipped with appropriate technologies such as flare gas recovery (FGR) to reduce emission of toxic pollutants and other emissions such as sulfur dioxide (SO2) and hydrogen sulfide (H2S) from the gas refinery. It is also strongly recommended that acorns collected for restoration measures come from maternal trees growing at a distance >10,000 m, and especially to the west of gas refineries.

Impact of Thermotherapy and Short-Term Storage on Quercus robur L. Acorn Mycobiota and Germination

When natural regeneration of Quercus robur stands is hampered by an insufficient acorn yield, human assisted sowing of acorns collected in non-affected stands and stored for some period of time is performed. To inhibit the development of fungi and acorn deterioration during storage, thermotherapy is usually applied by submerging acorns for 2.5 h in water heated to 41 °C. This research aimed to test the effect of four thermotherapy treatments of different durations and/or applied temperatures as well as short-term storage at −1 °C or 3 °C on acorn internal mycobiota and germination. Fungal presence in cotyledons was analyzed in 450 acorns by isolation of mycelia on artificial media, followed by a DNA-based identification. Germination of 2000 acorns was monitored in an open field trial. Thermotherapy significantly decreased fungal diversity, while storage at 3 °C increased the isolation frequency of several fungi, mainly Penicillium spp. The most frequently isolated fungi did not show a negative impact on acorn germination after short-term storage. The study confirmed the efficiency of thermotherapy in the eradication of a part of acorn internal mycobiota, but also its effect on the proliferation of fast-colonizing fungi during storage. However, the latter showed to be more stimulated by storage conditions, specifically by storage at 3 °C.

Impacts of increasing fine fuel loads on acorn germination and early growth of oak seedlings

BackgroundPrescribed fire is increasingly used to restore and maintain upland oak (Quercus L. spp.) ecosystems in the central and eastern US. However, little is known about how prescribed fire affects recently fallen acorns under different fine fuel loads, which can vary with stand composition and basal area, burn season, and fire frequency. We conducted plot-level (1 m2) burns in an upland oak stand in northern Mississippi, USA, during December 2018, using single (i.e., ambient), double, and triple fine fuel loads, representative of those in nearby unburned and recently fire-treated, closed-canopy stands. Pre burn, we placed 30 acorns each of white oak (Quercus alba L.) and Shumard oak (Quercus shumardii Buckley) ~1 cm below the litter surface in five plots of each fuel treatment. Immediately post burn, we planted unburned and burned acorns in a greenhouse. After ~50% of each species’ unburned acorns germinated, we measured percent germination and height, basal diameter, and leaf number of germinating seedlings weekly for 11 weeks. Then, we harvested seedlings to determine above- and belowground biomass.ResultsThe single fuel treatment reduced acorn germination rates of both species to ~40% compared to ~88% in unburned acorns. When burned in double and triple fuel loads, acorns of both species had a <5% germination rate. There was no difference in basal diameter, leaf number, or biomass of seedlings from burned versus unburned acorns for either species. However, seedlings originating from burned acorns of both species were ~11% shorter than those from unburned acorns. Thus, both species responded similarly to fuel load treatments.ConclusionsAcorns of both species exhibited greater survival with lower fine fuel loads, and consequently lower percent fuel consumption. Acorns germinating post fire generally produced seedlings with growth patterns similar to seedlings originating from unburned acorns. These findings indicate that regular, repeated prescribed fires or canopy reductions that limit fine fuel accumulation and create heterogeneous fuel beds are likely to increase acorn germination rates relative to unburned sites or those with recently introduced fire.

Effect of acorn size on survival and growth of Quercus suber L. seedlings under water stress

While the effects of seed size on survival and early seedling growth have been demonstrated in Quercus spp., there is a knowledge gap regarding these effects under water limiting conditions. To address this need, we studied cork oak (Quercus suber L.) seedling development among treatments including three acorn classes (small: < 4 g, intermediate: 4–6 g), and large: ≥ 6 g) and two water regimes (well-watered versus water stressed). The following hypotheses were proposed: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), the seedling-size effect (larger seeds produce larger seedlings), and that plant tolerance to water stress increases with increasing seed size. Acorn size had no effect on duration and rate of acorn germination nor on seedling survival, but it significantly affected almost all growth parameters, excepting the number of growth unit and leaves and leaf area. Seedlings coming from large acorns always showed the highest values for the affected growth parameters, followed by those coming from acorns of intermediate size; seedlings coming from small acorns always exhibited the lowest values. Water stress significantly affected survival rate (88.2% for well-watered seedlings versus 64.7% for water stressed seedlings) and biomass of fine roots and stems, but independently of acorn size. Our results are in line with both hypothesizes of the reserve effect and seedling-size effect, but not for the metabolic effect nor the plant tolerance to water stress increases with increasing seed size hypotheses. In general, our results show that large acorns had no advantage in survival or seedling growth under water stress comparatively to intermediate or small acorns, at least under the conditions of our experiment.

Direct seeding for restoration of mixed oak forests: Influence of distance to forest edge, predator-derived repellent and acorn size on seed removal by granivorous rodents

Restoration of mixed oak forest in northern temperate regions is important for biodiversity and for adaptation of forest management to climate change. Direct seeding has been considered as a cost-effective method for the assisted regeneration of oaks. However, removal of acorns by granivorous rodents hinders its application. Patterns of acorn removal can vary with habitat type, presence of predators, and acorn size. In this field study, we tested the effects of distance to forest edge, predator excrement as a repellent, and acorn size on the performance of direct-seeded oak in southern Sweden. The experiment was carried out at two different sites. Our hypotheses were: (i) in clear-cuts, acorn removal is higher closer to the forest edge compared to open areas, (ii) treatment with predator excrement reduces acorn removal without affecting germination, and (iii) larger acorns will be removed more readily than smaller acorns. Finally, we also investigated if seedlings from larger acorns survive better and grow taller compared to smaller acorns in relation to habitat structure and predator excrement as repellent. Acorn removal differed at the two sites. At Skrylle (older clear-cut), no forest edge effects were found. At Klåveröd (new clear-cut site), our results suggest that removal of acorns was higher in the open clear-cut due to the presence of large slash piles. Less vegetation coverage correlated with lower rates of acorn removal, except near slash piles. Our results therefore suggest that forest managers should reduce understory vegetation and avoid slash piles during direct seeding of oak. Mink excrement failed to protect acorns against removal, but did not reduce acorn germination. Bigger acorns produced taller seedlings but did not enhance overall woodland establishment due to their higher removal rate. Our results further suggest a potential food satiation effect due to an extra supply of additional food. Satiation manipulation might potentially be a method of mitigating the impact of seed predation by granivorous rodents during the direct seeding of oak, but such an approach requires further research before it could be recommended.

Dormancy break and germination requirements in acorns of two bottomlandQuercusspecies (Sect.Lobatae) of the eastern United States with references to ecology and phylogeny

AbstractQuercusspecies are ecologically and economically important components of deciduous forests of the eastern United States. However, knowledge pertinent to a thorough understanding of acorn germination dynamics for these species is lacking. The objectives of this research were to determine dormancy break and germination requirements for acorns of two eastern United States bottomland species,Quercus nigraandQuercus phellos(SectionLobatae), and to present results within ecological and phylogenetic contexts. Three replicates of 50 acorns of each species received 0 (control), 6, 12 or 18 weeks of cold stratification, followed by incubation in alternating temperature regimes of 15/6, 20/10, 25/15 and 30/20°C. Eighteen weeks of cold stratification were not sufficient for dormancy break inQ. nigraacorns. Cumulative germination percentages at 4 weeks of incubation were ≥77%, but only in incubation temperatures of 25/15 and 30/20°C. Dormancy break inQ. phellosacorns was achieved with 18 weeks of cold stratification, and cumulative germination percentages were ≥87% at 4 weeks of incubation in all test temperature regimes. Gibberellic acid solutions were not an effective substitute for cold stratification in either species. Phylogenetically,Q. nigraandQ. phellosare closely related species and, ecologically, both grow in the same habitat. Acorns of both species possess deep physiological dormancy (PD), but dormancy break and germination requirements differ in acorns of these twoQuercusspecies.

Surface sterilization of English oak (Quercus robur L.) acorns using wet water steam

Effective and environmentally friendly methods of protection to reduce seed contamination from fungi are constantly sought. The use of thermal impulses of 100 °C wet water steam to reduce fungal contamination has not been sufficiently investigated, and the potential of this physical approach has not been estimated.The aim of the study was to investigate what impact 100 °C wet water steam with different time durations had on acorn contamination with fungi, acorn germination and biometric indicators of English oak (Quercus robur) seedlings during the first year of growth. Different treatment durations with wet water steam were used: 2, 4, 6, 8, 10, 12 and 14 s.Research showed that 6 seconds impact of wet steam on the surface of the oak acorn destroyed Alternaria spp., 8 seconds impact destroyed Penicillium spp. and 14 seconds impact destroyed Mucor spp. Using 14 seconds water steam treatment Penicillium, Alternaria and Mucor spp. fungi were eliminated.Wet water steam treatment for 2 - 4 seconds not only stimulated the acorns germination by 4.0 - 7.6%, but also had positive influence on the root collar diameter of seedlings. Wet water steam treatment for 2 - 12 seconds had a positive effect on the root development of oak seedlings, however, high temperature environment had a suppressive effect on the oak seedling height.&#x0D; Keywords: biological control, wet water steam, fungi, oak acorns, seedling production

Exclusion of interspecific competition reduces scatter-hoarding of Siberian chipmunk Tamias sibiricus: A field study.

Although food availability and the abundance of seed predators have been postulated to affect seed dispersal, it is not clear how seed-eating animals modify their scatter-hoarding strategies in response to different levels of interspecific competition. We placed paired germinated and ungerminated acorns of Quercus mongolica on 30-cm high platforms to exclude potential interspecific competition of the predominant larder hoarders Apodemus peninsulae and Myodes rufocanus, to investigate seed dispersal by a predominant scatter-hoarder, Tamias sibiricus, in the field in north-eastern China. Our results showed that T. sibiricus ate more acorns in situ in the absence of interspecific competition. In the presence of interspecific competition of A. peninsulae and C. rufocanus, however, more acorns were scatter-hoarded by T. sibiricus. Regardless of interspecific competition, germination of acorns showed no significant effects on seed dispersal patterns, inconsistent with the "seed perishability hypothesis" that animals avoid hoarding seeds with high perishability. Exclusion of interspecific competition, though relatively increasing the per capita seed abundance, appears to reduce seed dispersal, scatter-hoarding and seedling establishment. Therefore, we propose that moderate interspecific competition rather than competition exclusion may benefit seed scatter-hoarding and seedling establishment.

Effects of titanium dioxide nanoparticles on germination and growth indices of oak acorns under drought stress

Effects of titanium dioxide nanoparticles on germination and growth indices of oak acorns under drought stress

Variation in seed traits among Mediterranean oaks in Tunisia and their ecological significance.

Oaks are the foundation and dominant tree species of most Mediterranean forests. As climate models predict dramatic changes in the Mediterranean basin, a better understanding of the ecophysiology of seed persistence and germination in oaks could help define their regeneration niches. Tunisian oaks occupy distinct geographical areas, which differ in their rainfall and temperature regimes, and are thus a valuable model to investigate relationships between seed traits and species ecological requirements. Seed morphological traits, desiccation sensitivity level, lethal freezing temperature, embryonic axis and cotyledon sugar and lipid composition, and seed and acorn germination rates at various constant temperatures were measured in Quercus canariensis, Q. coccifera, Q. ilex and Q. suber, using seeds sampled in 22 Tunisian woodlands. Only faint differences were observed for desiccation sensitivity in the oak species studied. By contrast, the species differed significantly in sensitivity to freezing, germination rates at low temperature and base temperature. Quercus ilex and Q. canariensis, which occur at high elevations where frost events are frequent, showed the lowest freezing sensitivity. A significant correlation was found between hexose contents in the embryonic axis and freezing tolerance. Significant interspecific differences in the time for seeds to germinate and the time for the radicle to pierce the pericarp were observed. The ratio of pericarp mass to acorn mass differed significantly among the species and was negatively correlated with the acorn germination rate. Quercus coccifera, which is frequent in warm and arid environments, showed the highest acorn germination rate and synchrony. Seed lethal temperature, seed germination time at low temperatures, the ratio of pericarp mass to acorn mass and the embryonic axis hexose content appeared to be key functional traits that may influence the geographical ranges and ecological requirements of Mediterranean oaks in Tunisia.

The Influence of Dormancy Break Requirements on Germination and Viability Responses to Winter Submergence in Acorns of Three Bottomland Red Oak (Sect. Lobatae) Species

Abstract The objective of this study was to examine the relation of dormancy break requirements to winter submergence effects on germination and viability in cherrybark, willow, and Nuttall oak acorns. Acorns were submerged in a greentree reservoir and received 0, 21, 42, 63, or 84 days of winter submergence, followed by 8 weeks of incubation in four temperature regimes (15/6°, 20/10°, 25/15°, and 30/20° C). Winter submergence substituted for cold stratification requirements of cherrybark oak acorns, and dormancy break was achieved with 63 days of submergence. Although winter submergence exerted a positive effect on germination in Nuttall and willow oak acorns, dormancy break was not achieved in acorns of either species. Germination percentages were highest in the 30/20° C incubation temperature—cherrybark oak acorns (75–83 percent), followed by Nuttall oak (33–55 percent) and willow oak (14–52 percent). Among treatment combinations, all willow oak nongerminants were viable. Viability loss in cherrybark and Nuttall oak acorns was greatest in the 63- and 84-day treatments. The dynamics of acorn germination in response to winter hydrologic regime is influenced by submergence duration that may, or may not, satisfy dormancy break requirements in acorns of these red oak species.