Growth and photosynthetic efficiency promotion of sugar beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.) by endophytic bacteria

Very little is known about the physiological interactions between plants and endophytic bacteria. We investigated the impact of three endophytic bacteria, Bacillus pumilus 2-1, Chryseobacterium indologene 2-2, and Acinetobacter johnsonii 3-1, on the photosynthetic capacity and growth of sugar beet. Endophyte-free plants were obtained first and infected with the bacteria. Measurements of total chlorophyll content revealed very significant differences between endophyte-free beet plants and some infected by endophytic bacteria. The maximum photochemical yield (Fv/Fm) was used to determine any photosynthetic effect on plants caused by biotic or abiotic factors. After 30 days of growth, there was significantly higher Fv/Fm for endophyte-infected than endophyte-free plants. The light response curves of beet showed that photosynthetic capacity was significantly increased in endophyte-infected plants. Photosynthesis of endophyte-free plants was saturated at 1,300 μmol m⁻² s⁻¹, whereas endophyte-infected plants were not saturated at the irradiance used. The effect seemed to be due to promotion of electron transport in the thylakoid membranes. Promotion of photosynthetic capacity in sugar beet was due to increased chlorophyll content, leading to a consequent increased carbohydrate synthesis. It is possible that the increased maximum yield of photosynthesis in sugar beet was promoted by phytohormones and produced by the bacteria.     

Characterization of novel diesel-degrading strains <Emphasis Type="Italic">Acinetobacter haemolyticus</Emphasis> MJ01 and <Emphasis Type="Italic">Acinetobacter johnsonii</Emphasis> MJ4 isolated from oil-contaminated soil

The diesel-degrading strains, designated as MJ01 and MJ4, were isolated from oil-contaminated soil in Daejeon (South Korea) and were taxonomically characterized using a polyphasic approach and their diesel oil degradation abilities were analyzed. The isolates MJ01 and MJ4 were identified as Acinetobacter haemolyticus and Acinetobacter johnsonii, respectively, based on their 16S rDNA gene sequences, DNA–DNA relatedness, fatty acid profiles and various physiological characteristics. Strains MJ01 and MJ4 were able to use diesel oil as the sole carbon and energy source. Both strains could degrade over 90% of diesel oil with an initial concentration of 20,000 mg/l after incubation for 7 days, the most significant degradation occurred during the first 3 days. To our knowledge, this is the first report on diesel oil-degrading microorganisms among bacterial strains belonging to A. haemolyticus and A. johnsonii.     

Solubilization of insoluble inorganic phosphates by a novel temperature-, pH-, and salt-tolerant yeast, <Emphasis Type="Italic">Rhodotorula</Emphasis> sp<Emphasis Type="Italic">.</Emphasis> PS4, isolated from seabuckthorn rhizosphere,growing in cold desert of Ladakh,India

The study was aimed to develop biofertilizer solubilizing inorganic phosphates for region experiencing temperature, pH and salt stressed conditions. A yeast strain PS4, which was temperature-, pH- and salt-tolerant and capable of solubilizing insoluble inorganic phosphate was isolated from rhizosphere of seabuckthorn (Hippophae rhamnoides L.), growing in the Indian Trans-Himalaya. Based on morphological, biochemical, whole cell FAME analysis and molecular characterization, strain PS4 was identified as Rhodotorula sp. The soluble phosphate production under optimal conditions at pH 7 and 30°C was 278.3 mg l⁻¹. Strain PS4 showed ability to solubilize insoluble phosphate under different stress conditions viz. 5–40°C temperature, 1–5% salt concentration and 3–11 pH range. Soluble phosphate production from Ca₃(PO₄)₂ under combined stress conditions at extreme values of temperature, pH and salt concentration showed 81.6–83.2% reduction as compare to optimal conditions after 5 days incubation. The strain solubilize Ca₃(PO₄)₂ to a great extent than FePO₄ and AlPO₄. The solubilization of insoluble phosphate was associated with drop in pH of the culture media. Inoculation of tomato seedling with the strain increased fruit yield, roots and shoot length. Rhodotorula sp. PS4 with phosphate-solubilizing ability under stress conditions appeared to be attractive for exploring their plant growth-promoting activity towards the development of microbial inoculants in stressed region.     

Aerial seed storage in <Emphasis Type="Italic">Melaleuca ericifolia</Emphasis> Sm. (Swamp Paperbark): environmental triggers for seed release

Aerial seed banks are potentially the main source of sexual recruitment for woody wetland plants. Whilst the importance of soil seed banks for the persistence and recruitment of wetland plants has been examined in many studies, the role of aerial seed banks has been largely neglected. We used seed traps and the seedling emergence technique to quantify the seed rain from aerial seed banks of the Swamp Paperbark Melaleuca ericifolia Sm. (Myrtaceae) in Dowd Morass, a Ramsar-listed, brackish-water wetland in south-eastern Australia. Nine plant species germinated from material collected in seed traps over 2004–2005, but emergents were dominated (80–97%) by M. ericifolia. The mean number of M. ericifolia emergents ranged from <1 to <100 seedlings m⁻² day⁻¹, and showed a peak in the summer–autumn period. Regression analysis showed a significant negative correlation (r ² = 0.738) between the number of M. ericifolia emergents and water depth. Water depth and salinity were negatively correlated (r ² = 0.819), and increases in the number of M. ericifolia emergents as water levels fell were also associated with high salinities. Increasing air temperature and vapour pressure deficit also stimulated seed release during periods of drying. This study is one of the first to demonstrate the importance of aerial seed banks for sexual recruitment in woody wetland plants and the release of seed in relation to environmental factors. Aerial seed banks warrant consideration alongside soil seed banks for the establishment and long-term survival of woody plants in wetlands. Handling editor: Luis Mauricio Bini     

Effects of plant competition,seed predation,and nutrient limitation on seedling survivorship of spotted knapweed (<Emphasis Type="Italic">Centaurea stoebe</Emphasis>)

We measured seed germination and seedling survivorship of spotted knapweed, Centaurea stoebe, in a series of laboratory and field experiments to evaluate the efficacy of seed limitation as a management focus. This work was initiated 6 years after introduction of several biological control agents. The soil seed bank of the site used in this study contained a mean density of 5,848 seeds/m² (ranging from 0 to 16,364 seeds/m²), and 92% of the seeds isolated from soils were shriveled, discolored, and/or partially decayed. Additionally, none of the intact seeds germinated, suggesting that the viable seed bank at our field study site has been exhausted. Centaurea stoebe seeds were planted into pots under a range of soil nitrogen (N) availability, with half of the pots containing a single density of previously established seedlings of a native cool-season grass, slender wheatgrass (Elymus trachycaulus). A watering regime mimicking local precipitation was applied. Spotted knapweed exhibited large biomass responses to N addition, but the presence of grasses suppressed the ability to exploit this N. Surprisingly, low soil N conditions improved knapweed survivorship in the presence of grasses. Nevertheless, recruitment and biomass were still far below the levels reached in the absence of competition. To evaluate the effect of density on successful recruitment, Centaurea stoebe seed was introduced into a meadow at three densities matching reduced levels of seed production under the constraints of seed predators. These densities were sown with or without a seed mixture of native species, into an existing plant community lacking C. stoebe, and seedling recruitment was recorded over 2.5 years. Across all plots and densities sown (568–2,272 seeds m⁻² year⁻¹), seedling recruitment was less than 1%. The invasion potential of spotted knapweed was greatly diminished when realistic levels of plant competition and biological control limit seed production. We therefore conclude that a combination of seed limitation and shortage of ‘safe sites’ within undisturbed vegetation can limit densities of C. stoebe.     

Biological control of root rot fungus <Emphasis Type="Italic">Macrophomina phaseolina</Emphasis> and growth enhancement of <Emphasis Type="Italic">Pinus roxburghii</Emphasis> (Sarg.) by rhizosphere competent <Emphasis Type="Italic">Bacillus subtilis</Emphasis> BN1

Bacterial isolates having antifungal and good plant growth-promoting attributes were isolated from chir-pine (Pinus roxburghii) rhizosphere. An isolate, Bacillus subtilis BN1 exhibited strong antagonistic activity against Macrophomina phaseolina, and other phytopathogens including Fusarium oxysporum and Rhizoctonia solani. It was characterized and selected for the present studies. BN1 resulted in vacuolation, hyphal squeezing, swelling, abnormal branching and lysis of mycelia. The cell-free culture filtrate of BN1 inhibited the growth of M. phaseolina. Pot trial study resulted in statistically significant increase in seedling biomass besides reduction in root rot symptoms in chir-pine seedlings. BN1 treatment resulted in 43.6% and 93.54% increases in root and shoot dry weights respectively, as compared to control. Also, 80–85% seed viability was recorded in treatments receiving BN1 either alone or in the presence of M. phaseolina, compared to 54.5% with M. phaseolina. Bioinoculant formulation study suggested that maximum viability of bacteria was in a sawdust-based carrier. B. subtilis BN1 produced lytic enzymes, chitinase and β-1,3-glucanase, which are known to cause hyphal degradation and digestion of the cell wall component of M. phaseolina. In the presence of M. phaseolina, population of B1 was 1.5 × 10⁴ c.f.u. g⁻¹ root after one month, which increased to 4.5 × 10⁴ c.f.u. g⁻¹ root in three months. Positive root colonization capability of B. subtilis BN1 proved it as a potent biocontrol agent.     

Habitat choice and seed–seedling conflict of Spartina alterniflora on the coast of China

To elucidate the seed–seedling conflict and the process of habitat choices during the expansion of S. alterniflora, densities of seeds and seedlings in three different habitats, foreland, Spartina meadow, and canopy gap patch, were measured. Statistical analyses of these measurements were performed to investigate the interaction between seeds or seedlings and environmental factors. Also, the process of habitat choice during the expansion of S. alterniflora was explored. The results show that, in the upper soil seed bank (0–5 cm), both the ratio of germinated seeds and the ratio of survival seedlings to total seeds do not differ significantly among the three habitats. However, in the lower soil seed bank (5–10 cm), these ratios differ significantly, suggesting the seed–seedling conflict of S. alterniflora generally occurs in the lower soil seed bank. The remarkable conflict occurs in the meadow habitat. Greenhouse experiments indicate that the germination rate decreases significantly and the mortality of pre-emerged seedlings increases significantly with increasing burial depth. The maximal burial depth of emerged seedlings varies with sediment types. Comparisons of burial depth effects on seedling height, mesocotyl length, coleoptile length, and root length show that the major responses of S. alterniflora pre-emerged seedlings to the burial treatments are the elongation of coleoptiles and mesocotyls, which favor seedling survival by enhancing aeration and accelerating emergence. These results suggest that burial treatment is a key selection factor, which leads to the seed–seedling conflict in recruitment of S. alterniflora population, and directly affects the expansion rate and the area infected by S. alterniflora. Handling editor: S. M. Thomaz Ziwang Deng: co-first author.     

Kinetics of styrene biodegradation by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. E-93486

The research into kinetics of styrene biodegradation by bacterial strain Pseudomonas sp. E-93486 coming from VTT Culture Collection (Finland) was presented in this work. Microbial growth tests in the presence of styrene as the sole carbon and energy source were performed both in batch and continuous cultures. Batch experiments were conducted for initial concentration of styrene in the liquid phase changed in the range of 5–90 g m⁻³. The Haldane model was found to be the best to fit the kinetic data, and the estimated constants of the equation were: μ _m = 0.1188 h⁻¹, K _S = 5.984 mg l⁻¹, and K _i = 156.6 mg l⁻¹. The yield coefficient mean value Y_\textxs^\textapp Y_{\text{xs}}^{\text{app}} for the batch culture was 0.72 g_{dry cells weight} (g_substrate)⁻¹. The experiments conducted in a chemostat at various dilution rates (D = 0.035–0.1 h⁻¹) made it possible to determine the value of the coefficient for maintenance metabolism m _d = 0.0165 h⁻¹ and the maximum yield coefficient value Y_\textxs^\textM = 0.913 Y_{\text{xs}}^{\text{M}} = 0.913 . Chemostat experiments confirmed the high value of yield coefficient Y_\textxs^\textapp Y_{\text{xs}}^{\text{app}} observed in the batch culture. The conducted experiments showed high activity of the examined strain in the styrene biodegradation process and a relatively low sensitivity to inhibition of its growth at higher concentrations of styrene in the solution. Such exceptional features of Pseudomonas sp. E-93486 make this bacterial strain the perfect candidate for technical applications.     

Quorum Sensing Contributes to Seed‐to‐Seedling Transmission of Acidovorax citrulli on Watermelon

Based on the observation that Acidovorax citrulli switches from saprobic to pathogenic growth for seed‐to‐seedling transmission of bacterial fruit blotch of cucurbits (BFB), we hypothesized that quorum sensing (QS) was involved in the regulation of this process. Using aacI (luxI homologue) and aacR (luxR homologue) mutants of AAC00‐1, we investigated the role of QS in watermelon seed colonization and seed‐to‐seedling transmission of BFB. aacR and aacI mutants of AAC00‐1 colonized germinating watermelon seed at wild‐type levels; however, BFB seed‐to‐seedling transmission was affected in a cell density‐dependent manner. There were no significant differences in BFB seedling transmission between watermelon seed infiltrated with approximately 1 × 10⁶ CFU of AAC00‐1, the aacR or aacI deletion mutants (95.2, 94.9 and 98.3% BFB incidence, respectively). In contrast, when seed inoculum was reduced to approximately 1 × 10³ CFU/seed, BFB seed‐to‐seedling transmission declined to 34.3% for the aacI mutant, which was significantly less than the wild type (78.6%). Interestingly, BFB seed‐to‐seedling transmission for the aacR mutant was not significantly different to the wild‐type strain. These data suggest that QS plays a role in regulation of genes involved in seed‐to‐seedling transmission of BFB.     

<Emphasis Type="Italic">Nocardiopsis terrae</Emphasis> sp. nov., a halophilic actinomycete isolated from saline soil

A Gram-positive, moderately halophilic, facultatively alkaliphilic, catalase- and oxidase-positive, obligately aerobic, filamentous actinomycete strain, designated YIM 90022^T, was isolated from saline soil collected from the Qaidam Basin, north-west China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate was a member of the genus Nocardiopsis and the sequence similarities between the isolate and the type strains of members of the genus Nocardiopsis were in the range of 95.1–98.7%. Phenotypic and chemotaxonomic properties of this organism also indicated that strain YIM 90022^T was a member of the genus Nocardiopsis. The strain grew well on most of the media tested, producing yellow-white to deep brown substrate mycelium and white aerial mycelium. Light gray to deep brown diffusible pigments were produced. The substrate mycelium was well developed and fragmented with age; the aerial mycelium produced long, straight to flexuous spore chains with non-motile, smooth-surfaced, rod-shaped spores on them. The strain grew in the presence of 1–15% (w/v) total salts (optimum, 3–5%) and at pH 6.0–10.5 (optimum, pH 8.5) and 10–45°C (optimum, 30°C). Whole-cell hydrolysates of strain YIM 90022^T contained meso-diaminopimelic acid and no diagnostic sugars. The predominant menaquinones were MK-10(H₄), MK-9(H₈), MK-10(H₆) and MK-10(H₈). Polar lipids comprised diphosphatidylglycerol, phosphatidylcholine, phosphatidylglycerol and phosphatidylmethylethanolamine. The major cellular fatty acids were iso-C_16:0, anteiso-C_17:0, 10-methyl-C_18:0 and 10-methyl-C_17:0. The DNA G + C content of strain YIM 90022^T was 71.5 mol%. The combination of phylogenetic analysis, DNA–DNA relatedness data, phenotypic characteristics and chemotaxonomic data supported the suggestion that strain YIM 90022^T represents a new species of the genus Nocardiopsis, for which the name Nocardiopsis terrae sp. nov. is proposed. The type strain is YIM 90022^T (=CCTCC AA 208011^T =KCTC 19431^T).     

Degradation of methamidophos by <Emphasis Type="Italic">Hyphomicrobium</Emphasis> species MAP-1 and the biochemical degradation pathway

Methamidophos is one of the most widely used organophosphorus insecticides usually detectable in the environment. A facultative methylotroph, Hyphomicrobium sp. MAP-1, capable of high efficiently degrading methamidophos, was isolated from methamidophos-contaminated soil in China. It was found that the addition of methanol significantly promoted the growth of strain MAP-1 and enhanced its degradation of methamidophos. Further, this strain could utilize methamidophos as its sole carbon, nitrogen and phosphorus source for growth and could completely degrade 3,000 mg l⁻¹ methamidophos in 84 h under optimal conditions (pH 7.0, 30°C). The enzyme responsible for methamidophos degradation was mainly located on the cell inner membrane (90.4%). During methamidophos degradation, three metabolites were detected and identified based on tandem mass spectrometry (MS/MS) and gas chromatography-mass spectrometry (GC–MS) analysis. Using this information, a biochemical degradation pathway of methamidophos by Hyphomicrobium sp. MAP-1 was proposed for the first time. Methamidophos is first cleaved at the P–N bond to form O,S-dimethyl hydrogen thiophosphate and NH₃. Subsequently, O,S-dimethyl hydrogen thiophosphate is hydrolyzed at the P–O bond to release –OCH₃ and form S-methyl dihydrogen thiophosphate. O,S-dimethyl hydrogen thiophosphate can also be hydrolyzed at the P–S bond to release –SCH₃ and form methyl dihydrogen phosphate. Finally, S-methyl dihydrogen thiophosphate and methyl dihydrogen phosphate are likely transformed into phosphoric acid.     

<Emphasis Type="Italic">Halomonas sediminis</Emphasis> sp. nov., a new halophilic bacterium isolated from salt-lake sediment in China

A novel Gram-negative, slightly halophilic, catalase- and oxidase-positive, obligately aerobic bacterium, strain YIM-C248^T, was isolated from a sediment sample collected from a salt-lake in the Qaidam Basin in Qinghai, north-west China. Cells were non-sporulating short rods, occurring singly or as doublets, motile with peritrichous flagella. Growth occurred with 1–15% (w/v) NaCl [optimum 2–4% (w/v) NaCl], at pH 6.0–10.0 (optimum pH 7.5) and at 4–35°C (optimum 25–30°C). The major cellular fatty acids were C_18:1 ω7c, C_12:0 3-OH, cyclo C_19:0 ω8c, C_16:0 and C_16:1. The predominant respiratory quinone was Q-9 and the genomic DNA G + C content was 58.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YIM-C248^T should be assigned to the genus Halomonas. The sequence similarities between the isolate and the type strains of members of the genus Halomonas were in the range of 92.5–97.5%. The combination of phylogenetic analysis, DNA–DNA hybridization data, phenotypic characteristics and chemotaxonomic differences supported the view that strain YIM-C248^T represents a new species of the genus Halomonas, for which the name Halomonas sediminis sp. nov. is proposed, with YIM-C248^T (=CCTCC AA 207031 = KCTC 22167) as the type strain. The GenBank/EMBL/DBBJ accession number for the 16S rRNA gene sequence of strain YIM-C248^T is EU135707.     

Genetic transformation of <Emphasis Type="Italic">Harpagophytum procumbens</Emphasis> by <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>: iridoid and phenylethanoid glycoside accumulation in hairy root cultures

A genetic transformation method using Agrobacterium rhizogenes was developed for Harpagophytum procumbens. The influence of three factors on hairy root formation was tested: bacterial strains (A4 and ATCC 15834), various types of explants and acetosyringone (AS) (200 μM). The highest frequency of transformation (over 50% of explants forming roots at the infected sites after 6 weeks of culture on Lloyd and McCown (WP) medium) was achieved using a combination of nodal stem explants and A. rhizogenes strain A4. The addition of 200 μM AS to root induction medium was found to enhance hairy root induction but its effect varied depending on bacterial strain and explant type. Three of the most vigorously growing hairy root clones of H. procumbens were chosen and analyzed for accumulation of iridoid and phenylethanoid glycosides. The transgenic nature of these root clones was confirmed by PCR amplification; they were positive for rolB and rolC genes. Harpagoside, verbascoside and isoverbascoside were identified by HPLC and LC–ESI-MS as the major compounds from all analyzed hairy root clones. The Hp-3 root clone showed the higher harpagoside content (0.32 mg g⁻¹ dry wt.) compared with other analyzed transformed and non-tuberized untransformed roots of H. procumbens. However, the level of the compound in the hairy root clone was lower than that detected in a sample of commercially available root tubers of H. procumbens. The Hp-3 root clone also produced high amounts of verbascoside and isoverbascoside (8.12 mg g⁻¹ dry wt. and 9.97 mg g⁻¹ dry wt., respectively) comparable to those found in root tubers.     

BVPaP-3, a T7-Like Lytic Phage of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>: Its Isolation and Characterisation

The increasing emergence of antibiotic-resistant bacteria has produced a growing interest among scientists in bacteriophages as alternative antimicrobial agents. This article reports a lytic phage against an antibiotic-resistant strain of Pseudomonas aeruginosa. Phage BVPaP-3 is a member of the Podoviridae family and morphologically similar to the T7-like phage gh-1. The phage has a hexagonal head of 58–59 nm in diameter and a short tail of 10 × 8 nm. It is stable at a wide range of pH (6–10) and temperatures (4–40°C). Its optimal growth temperature is 37°C and the adsorption rate constant is 1.19 × 10⁻⁹. Latent and eclipse periods are 20 and 15 min, respectively, and the burst size is 44 after 35 min at 37°C. The phage has a DNA size of 41.31 kb and a proteome of 11 proteins. The major protein is 33 kDa in size.     

Variation in response to heavy metals during vegetative growth in <Emphasis Type="Italic">Dorycnium pentaphyllum</Emphasis> Scop.

Seeds, young plants and adult plants of the perennial Mediterranean leguminous shrub Dorycnium pentaphyllum Scop. were exposed to Cd (1–100 μM) or Zn (10–10,000 μM) on nutrient solution. This species is resistant to Cd and Zn at different phenological stages. The lowest doses of Zn and Cd improved seed germination and young seedling growth, while only the highest doses of both heavy metals inhibited germination and decreased growth. High doses of Cd reduced seed imbibition and young seedling water content, while Zn did not. Osmotic adjustment was more efficient in Zn-treated young plants than in Cd-treated ones, while chlorophyll concentrations decreased in the former but not in the latter. Those differences were not observed anymore in adult plants. Exclusion processes were more efficient at the adult stage than at the young seedling stage and were more marked in response to Zn than to Cd. It is concluded that D. pentaphyllum could be used for phytostabilization of heavy metal-contaminated areas. The physiological strategies of tolerance, however, differ according to the age of the plants and the nature of the metal.     

Anchorage of GFP fusion on the cell surface of <Emphasis Type="Italic">Pseudomonas putida</Emphasis>

Here we report the cell surface display of organophosphorus hydrolase (OPH) and green fluorescent protein (GFP) fusion by employing the N- and C-terminal domains of ice nucleation protein (INPNC) as an anchoring motif. An E. coli–Pseudomonas shuttle vector, pNOG33, coding for INPNC–OPH–GFP was constructed for targeting the fusion onto the cell surface of p-nitrophenol (PNP)-degrading P. putida JS444. The surface localization of INPNC–OPH–GFP was verified by cell fractionation, Western blot, proteinase accessibility, and immunofluorescence microscopy. Furthermore, the functionality of the surface-exposed OPH–GFP was demonstrated by OPH assays and fluorescence measurements. Surface display of macromolecular OPH–GFP fusion (63 kDa) neither inhibited cell growth nor affected cell viability. These results suggest that INP is an useful tool for the presentation of heterologous proteins on cell surfaces of indigenous microbes. The engineered P. putida JS444 degraded organophosphates (OPs) as well as PNP rapidly and could be easily monitored by fluorescence. Parathion (100 mg kg⁻¹) could be degraded completely within 15 days in soil inoculated with the engineered strain. These merits make this engineered strain an ideal biocatalyst for in situ bioremediation of OP-contaminated soil.     

Biennial cycling caused by demographic delays in a fire-adapted annual plant

We explored models explaining population cycling in the annual Warea carteri. We modeled the life cycle of W. carteri and compared projected trajectories to independently observed trajectories (up to 16 years) of plants in 74 patches in three populations. We built matrix models with an annual time step for two populations, including four stages, (recently produced seeds, seeds in the seed bank, seedlings, and adults) and five vital rates, summarized in seven transitions. Fluctuations of both observed and modeled populations were evaluated using power spectra, autocorrelation, amplitude, and damping. Observed populations had two point cycling. Observed amplitude was higher in frequently burned populations, reached its maximum 1 year after fire, and then dampened. Asymptotic transition and vital rate elasticities showed that seedling survival was the most important factor for long-term population growth, but transient elasticities showed that recruitment from the seed bank was important during the first years post-fire. Deterministic modeling and elasticity analyses indicated that delayed germination (for 1 year) may explain biennial population cycling. Stochastic models created similar cycling with slower damping than deterministic models, but still had lower amplitudes (especially 1–3 years post-fire) than observed populations. The biennial cycle in W. carteri is likely caused by the delay in seed germination, which creates two overlapping cohorts of plants, much like a strict biennial. Fire initiates the cycle by killing aboveground individuals and promoting seedling recruitment in the first post-fire year.