High Photosynthetic Photon Flux Research Articles

Afternoon inhibition of photosynthesis in maize. 1. Evidence, and relationship to stand density

Diurnal courses of net carbon dioxide uptake of maize ( Zea mays L.) leaves under field conditions at high photosynthetic photon flux density ( Q ) indicated constant or decreasing rates over the temperature range of 25–35°C. This was in contrast to short-term responses to temperature, in which photosynthetic rates at 35°C were 1.4 times those at 25°C. These results suggested an afternoon inhibition of photosynthesis. Photosynthetic rates of leaves kept at constant temperature at high Q decreased by 30–40% from morning to afternoon. The amount of afternoon inhibition of photosynthesis increased with increasing stand density over the range 4–20 plants per m 2 . Stomatal conductance did not decline during the afternoon inhibition of photosynthesis, and the inhibition was not prevented by maintaining the measured part of the leaf at elevated humidity.

Photosynthetic characteristics of Cymbidium plantlet in vitro

The photosynthetic characteristics of the Cymbidium plantlet in vitro cultured on Hyponex-agar medium with 2% sucrose were determined based on the measurements of CO2 concentration inside and outside of the culture vessels. The CO2 measurements were made with a gas chromatograph at a PPF (photosynthetic photon flux) of 35, 102 and 226 μmol m-2 s-1, a chamber air temperature of 15, 25 and 35°C and a CO2 concentration outside the vessel of approximately 350, 1100 and 3000 ppm. The net photosynthetic rates were determined on individual plantlets and were expressed on a dry weight basis. The steady-state CO2 concentration during the photoperiod was lower inside the vessel than outside the vessel at any PPF greater than 35 μmol m-2s-1 and at any chamber air temperature. The photosynthetic response curves relating the net photosynthetic rate, PPF, and CO2 concentration in the vessel and chamber air temperature were similar to those for Cymbidium plants grown outside and other C3 plants grown outside under shade. The results indicate that CO2 enrichment for the plantlets in vitro at a relatively high PPF would promote photosynthesis and hence the growth of chlorophyllous shoots/plantlets in vitro and that the plantlets in vitro would make photoautotrophic growth under environmental conditions favorable for photosynthesis.

Leaf Orientation of Soybean Seedlings. I. Effect of Water Potential and Photosynthetic Photon Flux Density on Paraheliotropism

Paraheliotropic (light avoiding) leaf movements can reduce transpirational water loss by lowering light interception by the leaf through action of the pulvinus. We investigated effects of plant water potential (ψw) and photosynthetic photon flux density (PPFD) on paraheliotropism in young seedlings of soybean [Glycine max (L.) Merr. cv. Northrup King S1346], The effect of paraheliotropism on leaf temperature, ψw, and stomatal conductance (ge) was determined. The angles of unifoliolate and lower trifoliolate leaves were measured for plants at a range of ψw values under different sources of illumination (sun, metal halide lamp, and fluorescent light bank) at PPFD ranging from 500 to 1600 μmol m‐2 s‐1. Leaf temperatures and gc were measured for selected plants, including those with'leaves restrained in a horizontal position. The angle between unifoliolate leaves, measured at the base of the leaves, was highly correlated with ψw. Both unifoliolate leaves and the terminal leaflets of trifoliolate leaves exhibited less paraheliotropism at a given ψw when PPFD was reduced. Paraheliotropism was associated with improved plant water status and lower leaf temperatures, but gc did not differ between paraheliotropic leaves and those restrained in a horizontal position. Paraheliotropic leaf movement and stomatal closure acted in parallel, commencing at approximately −0.4 MPa. Paraheliotropic leaf movements in soybean seedlings provide a mechanism that, with stomatal closure, can reduce transpiration under conditions of low ψw and high PPFD.

Photoinhibition and Recovery of Photosynthesis in psbA Gene-Inactivated Strains of Cyanobacterium Anacystis nidulans

The susceptibility of photosynthesis to photoinhibition and the rate of its recovery were studied in cyanobacterium Anacystis nidulans strain R2 and its two psbA gene-inactivated mutants R2S2C3 and R2K1. Changes in the fluorescence kinetics at 77K as well as the rate of O(2) evolution were measured when cells were exposed to high photosynthetic photon flux densities in the range of 0 to 2,000 micromoles per square meter per second. The R2S2C3 mutant has an active psbAI gene highly expressed under low and normal light intensities, whereas R2K1 possesses psbAII and psbAIII genes highly expressed under very high light intensities. The level of overall susceptibility of photosynthesis to photoinhibition was more pronounced in the wild type and the mutant R2S2C3 than in the mutant R2K1, especially at higher light intensities. In constrast, all three strains showed an increased but similar sensitivity to photoinhibition after addition of the translational inhibitor streptomycin; mutant R2K1 being slightly less sensitive at lower light intensities. The result is interpreted as demonstrating similar intrinsic susceptibility to photoinhibition of the two different forms of the D1 protein, form I and form II, encoded by the psbAI and psbAII/psbAIII genes, respectively. The increased resistance to photoinhibition of the R2K1 mutant was ascribed to an approximately 3 times higher rate of recovery than the wild type and the mutant R2S2C3. On the basis of our experiments we conclude that the susceptibilities to photoinhibition of the Anacystis nidulans psbA genes mutants studied are regulated mainly by modifying the rate of repair, i.e. the rate of turnover of the D1 protein.

Photosynthetic acclimation in a terrestrial CAM bromeliad, Bromelia humilis Jacq.

Photosynthetic acclimation of a terrestrial CAM bromeliad -Bromelia humilis Jacq. to irradiance and nitrogen supply during growth was investigated under controlled conditions. Considerable acclimation to shade was realized through an increase in total chlorophyll, accessory pigments, an increase in chloroplast size and appressed to non-appressed thylakoid membrane ratio, and a reduction in chlorophyll a/b ratio. A relatively high apparent photon yield in shade was associated with a low light-compensation point and low dark-respiration rate. Light saturation of integrated dark CO2 uptake occurred at a relatively low total daily photosynthetic photon flux density (PPFD) and was not influenced by growth PPFD level. Maximum photosynthetic capacity expressed per unit chlorophyll and nitrogen use efficiency were significantly higher in high-PPFD-grown plants. In addition, apparent photon yield was only slightly reduced in high-PPFD-grown plants with nitrogen, while maximum photosynthetic rate remained the same indicating radiationless dissipation of excess light. Very high levels of recycling of respiratory carbon were observed under nitrogen deficiency in plants grown in both high and low PPFD. The extensive photosynthetic acclimation of B. humilis is discussed in terms of contrasting exposure and limitations of its natural environment.

異なる培地基礎成分を用いて光独立栄養培養および混合栄養培養したカーネーション小植物体の生長

Plantlets ofDaianthus caryophyllusL. were cultured on a half strength MS basal medium (Murashige & Skoog, 1962) with 2% sucrose and an Enshi component of nutrient solution for hydroponics (Hori, 1966) without sucrose in vessels with different numbers of air exchanges per hour of vessels under different PPF (photosynthetic photon flux) conditions. Time courses of fresh and dry weights, number of leaves, plantlet shoot length, and CO2concentrations inside and outside the vessels were measured. The relative growth rate, net photosynthetic rate, and total chlorophyll content of the plantlets were estimated.The final fresh weight of the plantlets was the highest on sucrose-free Enshi medium with a high number of air exchange and high PPF, and was the lowest on the same medium with a low number of air exchange and low PPF.The results obtained in the present experiment suggest the need to develop a basal medium composition optimal for photoautotrophic tissue culture. Because, the optimal basal media for photoautotrophic and photomixotrophic growth appears to be different from those developed for heterotrophic growth of tissue or organ, such as MS basal medium.

Effect of increased light intensity on photosynthetic rate and ribulose 1,5-bisphosphate car☐ylase in bean leaves

After the transition of photosynthetic photon flux density (PPFD) from 700 μmol quanta m −2 sec −1 for one hour (step I) to 1400 μmol quanta m −2 sec −1 for one hour (step II) at air level of CO 2 and O 2, photosynthetic CO 2 fixation was suppressed to 60% in leaves of bean ( Phaseolus vulgaris). Under these conditions, a similar extent of decrease occurred in both initial and total activities, and RuBP-binding free site concentration of ribulose 1, 5-bisphosphate car☐ylase-oxygenase whose protein content remained constant. Catalytic analyses in vitro indicated no significant deterioration of activation state of ribulose 1,5-bisphosphate car☐ylases with respect to Mg 2+ and pH. Chloroplast metabolites including RUBP and 3- d-phosphoglycerate, whose stromal concentrations were slightly affected at step II, had a similar stimulatory and/or inhibitory effects on both activation and catalytic rates of ribulose 1,5-bisphosphate car☐ylases at steps I and II. Theoretical estimation does not totally account for the significant inhibition of RUBP car☐ylation reaction. The inhibition of photosynthetic rate, accompanied by a concomitant decrease in the free site concentration is considered to be due to a modified carbamylation state of the lysine residue at the active site, and a deteriorated activity of car☐yarabinitol 1-phosphate metabolism and RuBisCO activase, tightly related to a photosynthetic electron transport activity under a high PPFD for 1 hr in Phaseolus vulgaris leaves.

タバコ培養実生および培養小植物体の生長に及ぼす培養器内環境の影響

The effect of CO2enrichment in the culture room, photosynthetic photon flux (PPF), and the presence or absence of sucrose in the medium on the growth of tobacco seedlingsin vitroand plantletsin vitrowas investigated. Seedlings and explants were cultured on half strength MS medium in glass test tubes closed with relatively loose, formed plastic caps. All experiments were carried out under a 16 h photoperiod and a temperature of 25°C.The growth curves of seedlings and plantletsin vitrowere similar when cultured under the same environmental conditions. The dry weight increase of seedlings and plantletsin vitrowas greater in CO2enriched treatments than in CO2nonenriched treatments. In the CO2enriched treatments, the dry weight increase was greater in high PPF treatments than in low PPF treatments. The dry weight increase was greater in medium containing sugar than in sugar free medium both in low and high PPF treatments but the difference in dry weight was smaller in CO2enriched treatments than in CO2nonenriched treatments.Steady state CO2concentration during the photoperiod in the vessel closed with the plastic cap was between 100 and 200 ppm in CO2nonenriched treatments 30 days from the start of the experiment. Net photosynthetic rate per seedling and plantlet and net photosynthetic rate per leaf dry weight were greater in CO2enriched treatments than in CO2nonenriched treatments.The effect of thein vitroenvironment on the fresh weight, leaf area, relative growth rate and dark respiration rate of seedlings and plantlets is also discussed and some suggestions are made for further promotion of photoautotrophic growth.

The role of light and CO2 in optimising the conditions for shoot proliferation of Actinidia deliciosa in vitro

Proliferating cultures of Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson cv. Tomuri (♂) were grown under photosynthetic photon flux density (PPFD) rates ranging from 30 to 250 μmol m−2 s−1 in order to determine certain physiological parameters in vitro: CO2 evolution, photosynthesis at three CO2 atmospheric concentrations (330, 1450 and 4500 μl l−1), fresh and dry matter accumulation and proliferation rate.A proportional response in dry weight, dry/fresh weight ratios and PPFD was found. The proliferation rate increased up to 120 μmol m−2 s−1 but decreased at higher rates. At the highest PPFD, the CO2 released from cultures and accumulated in the vessels reached 200 μl l−1 of; at the lowest rate the CO2 concentration reached 10500 μl l−1 after 28 days of culture. The photosynthetic rate at 1450 and 4500 μl l−1 of CO2 was nearly 4 times higher than at the lowest concentration tested.

The influence of simulated shadelight and daylight on growth, development and photosynthesis of Pinus radiata, Agathis australis and Dacrydium cupressinum

Abstract. Juvenile seedlings, micropropagated plantlets, and adult rooted cuttings of Pinus radiata, together with seedlings of Agathis australis and Dacrydium cupressinum, were grown under either high (670/μmol m−2 s−1) or low (200 μmol m−2 s−1) photosynthetic photon flux density (PPFD) and, at low PPFD, under three red:far‐red (R/FR) conditions, approximately simulating canopy shadelight, daylight and one intermediate value. In all types of P. radiata, a shade‐intolerant species, stem height and diameter, stem and needle dry weight, and apical dominance were markedly increased by a reduction in R:FR ratio while fascicle density was decreased. In contrast, these increases were considerably less for the shade‐tolerant D. cupressinum and moderately tolerant A. australis. With the exception of the P. radiata seedlings, height growth was greatest in all species under high compared to low PPFD for daylight R:FR ratio conditions. Total shoot (or plant) dry weight was increased approximately two‐fold in all species and types by the higher PPFD. Shoot extension rates were negatively correlated with calculated phytochrome photoequilibrium with P. radiata, the most shade‐intolerant species, having the highest change in rate per unit change in photoequilibrium (i.e. very responsive), and D. cupressinum, the most shade tolerant species evaluated, having the smallest change (i.e. largely unresponsive). Within the spectral quality treatments at low PPFD, it is suggested that higher rates of dry matter accumulation under the low R:FR ratio were the result of reduced mutual shading of adjacent leaves as a consequence of photomorphogenically‐controlled internode lengths rather than of enhanced photosynthesis per se. The significance of the results is discussed in relation to planting stock management in nurseries, the management of forest canopies for understorey seedling growth, and to the construction of representative growth simulation models. Consequences for controlled environment lighting are also considered.

Temperature and Photosynthetic Photon Flux Influence Chrysanthemum Shoot Development and Flower Initiation under Short-day Conditions

Abstract The effects of photosynthetic photon flux (PPF), day temperature (DT) and night temperature (NT) on leaf number, leaf unfolding rate and shoot length were determined for chrysanthemum (Dendranthema grandiflora Tzvelev. ‘Bright Golden Anne’) grown under short day (SD) conditions. A functional relationship was first developed to predict if flower bud appearance would occur within 100 SD under a given set of environmental conditions. All combinations of DT and NT in the range from 10° to 30°C were predicted to result in flower bud appearance at higher PPF than 10.8 mol·day−1·m−2. The number of leaves formed below the flower increased quadratically as DT and/or NT increased from 10° to 30°. As PPF increased from 1.8 to 21.6 mol·day−1·m−2, one to two fewer leaves were formed per shoot. Rate of leaf unfolding increased linearly with increasing average daily temperature from 0.2 leaves/day at 10° to 0.5 leaves/day at 30°. Internode length was highly correlated with the difference between DT and NT (DIF = DT – NT) such that increasing DIF from –12° to 12° resulted in progressively longer internodes.

Current and potential productivity of wheat for a controlled environment life support system

The productivity of higher plants is determined by the incident photosynthetic photon flux (PPF) and the efficiency of the following four physiological processes: absorption of PPF by photosynthetic tissue, carbon fixation (photosynthesis), carbon use (respiration), and carbon partitioning (harvest index). These constituent processes are analyzed to determine theoretical and potentially achievable productivity. The effects of optimal environmental and cultural factors on each of these four factors is also analyzed. Results indicate that an increase in the percentage of absorbed photons is responsible for most of the improvement in wheat yields in an optimal controlled environment. Several trials confirm that there is an almost linear increase in wheat yields with increasing PPF. An integrated PPF of 150 mol m −2 d −1 (2.5 times summer sunlight) has produced 60 g m −2 d −1 of grain. Apparently, yield would continue to increase with even higher PPF's. Energy efficiency increased with PPF to about 600 μmol m −2 s −1, then slowly decreased. We are now seeking to improve efficiency at intermediate PPF levels (1000 μmol m −2 s −1) before further exploring potential productivity. At intermediate and equal integrated daily PPF levels, photoperiod had little effect on yield per day or energy efficiency. Decreasing temperature from 23° to 17° increased yield per day by 20% but increased the life cycle from 62 to 89 days. We hope to achieve both high productivity and energy efficiency. ∗ ∗ Research reported in this paper was supported by the National Aeronautics and Space Administration Cooperative Agreement 2-139, administered through the Ames Research Center, Moffett Field, CA. Support was also received from the Utah Agricultural Experiment Station. This is Utah Agricultural Experiment Station paper no. 3653.

Endemism in Rock Outcrop Plant Communities of Unglaciated Eastern United States: An Evaluation of the Roles of the Edaphic, Genetic and Light Factors

Within the unglaciated eastern United States, where the natural vegetation is mostly deciduous forest, edaphically-controlled herbaceous plant communities occur on unshaded rock outcrops in shallow soil developed from serpentine, shale, granite, limestone, dolomite, sandstone, chert, rhyolite and other rock types. The most distinctive features of the flora of these communities are their endemic taxa. Many of the endemics are not restricted to a single geological substratum, and they grow equally well, or better, in non-outcrop as in outcrop soil. Thus, it seems unlikely that they are restricted to the outcrops because of a require- ment for some chemical, physical or biological element found there but nowhere else. Several of the endemics exhibit intraspecific variability in one or more of the following characteristics: morphology, physiology, breeding system, flower colour and enzyme pattern. Thus, it is unlikely that lack of genetic variation per se is the cause of endemism. ' A requirement that the endemics have in common for growth and survival is a high photosynthetic photon flux density. The obligate nature of the high light requirement is supported by: (1) field observations that the endemics grow on well-lighted portions of the outcrops but not in adjacent forests, (2) studies which show that growth and photosynthetic rates are maximal in high light but are severely inhibited at low light levels, and (3) field and glasshouse experiments which show that the endemics are shade intolerant and that they compete poorly with taller plants. Thus, of the three hypotheses examined to account for the proximal causes of endemism in the rock outcrop endemics, the requirement for a high level of light is the most important.

Growth and yield characteristics of ‘Waldmann's Green’ leaf lettuce under different photon fluxes from metal halide or incandescent + fluorescent radiation

‘Waldmanns' Green’ leaf lettuce ( Lactuca sativa L.) was grown either under 84% irradiance from incandescent (In) + 16% from fluorescent (Fl) lamps, or 100% from metal halide (MH) lamps, both at 392 μmol s −1 m −2 of photosynthetically active radiation (400–700 nm) from 11 to 19 days after seeding. No differences in leaf dry weight, leaf area, relative growth rate (RGR) or photosynthesis (Pn) occurred after 8 days of exposure to these radiation treatments for 20 h day −1. However, a 23% reduction in root dry weight, a 123% increase in stem length and a 61% increase in stem dry weight were found with In + Fl relative to MH radiation. A photosynthetic photon flux (PPF) of 920 μmol s −1 m −2 from the In + Fl source increased leaf dry weight by 13% and RGR by 21% relative to those at 460 μmol s −1 m −2 from the same source. From 4 to 8 days of treatment, high PPF did not lower shoot dry weight gain, but did lower RGR. Photosynthesis and net assimilation rate were lower while leaf area ratio was higher at 460 than at 920 μmol s −1 m −2 over the 8-day treatment period. When PPF from MH lamps was 400 μmol s −1 m −2, leaf dry weight was 20% greater than if PPF was 805 μmol s −1 m −2 after 4 days of treatment, but no differences were detected after 8 days. Relative growth rate increased by 11% during the first 4 days, but declined by 12% during the second 4 days under high-relative to low-PPF MH radiation. Lettuce productivity was stimulated by high PPF from either lamp type from Day 11 to Day 14, but not from Day 15 to Day 19 after seeding.

Influence of Light and Heated Medium on Rooting and Shoot Growth of Two Foliage Plant Species

Abstract Ficus benjamina and Codiaeum variegatum ‘Gold Dust’ stem tip cuttings were rooted in a mist bed at 290 or 90 µmols·m–2 Photosynthetic photon flux (PPF) with or without 28° ± 1°C medium heating and then potted. Number of roots in C. variegatum was unaffected by either PPF or medium heating; however, both factors enhanced root elongation. Forty days after potting, cuttings rooted under 290 µmol·s–1·m–2 had more lateral shoots than those rooted under 90 µmol·s-1·m–2 PPF. Although cuttings rooted in heated medium under the lower PPF had roots more than twice as long as those on cuttings rooted in unheated medium under the high PPF, it had little effect on subsequent shoot growth. F. benjamina rooting was improved in heated medium and was not affected by PPF. Unheated cuttings rooted better under high than low PPF. Shoot growth 10 weeks after transplanting was unaffected by the initial differences in root grade.

Effects of boundary layer conductance on substomatal pressures of carbon dioxide

Abstract. Gas exchange measurements were made on single leaves of three C3 and one C4 species at air speeds of 0.4 and 4.0 m s−1 to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m−2 s−1 at the lower air speed, and 1.2 to 1.5 mol m−2 s−1 at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C3 species, and about 3 Pa lower in the C4 species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C3 species. The commonly reported values of substomatal carbon dioxide pressure for C3 and C4 species were found to occur only when measurements were made at the higher air speed.

Effects of CO2 and photosynthetic photon flux on yield, gas exchange and growth rate of Lactuca sativa L. 'Waldmann's Green.'

Enrichment of CO2 to 46 mmol m-3 (1000 mm3 dm-3) at a moderate photosynthetic photon flux (PPF) of 450 micromoles m-2 s-1 stimulated fresh and dry weight gain of lettuce leaves 39% to 75% relative to plants at 16 mmol m-3 CO2 (350 mm3 dm-3). Relative growth rate (RGR) was stimulated only during the first several days of exponential growth. Elevating CO2 above 46 mmol m-3 at moderate PPF had no further benefit. However, high PPF of 880-900 micromoles m-2 s-1 gave further, substantial increases in growth, RGR, net assimilation rate (NAR) and photosynthetic rate (Pn), but a decrease in leaf area ratio (LAR), at 46 or 69 mmol m-3 (1000 or 1500 mm3 dm-3) CO2, the differences being greater at the higher CO2 level. Enrichment of CO2 to a supraoptimal level of 92 mmol m-3 (2000 mm3 dm-3) at high PPF increased leaf area and LAR, decreased specific leaf weight, NAR and Pn and had no effect on leaf, stem and root dry weight or RGR relative to plants grown at 69 mmol m-3 CO2 after 8 d of treatment. The results of the study indicate that leaf lettuce growth is most responsive to a combination of high PPF and CO2 enrichment to 69 mmol m-3 for several days at the onset of exponential growth, after which optimizing resources might be conserved.

Response of Sonia roses to continuous daytime CO2 supplementation under controlled environment conditions

Rose plants (Rosa hybrida cv. Sonia, Syn. Sweet Promise) were placed in growth chambers under conditions resembling winter in a controlled environment greenhouse in the desert: mild temperatures, high incident photosynthetic photon flux density (PPFD), high air humidity and 10.5 h daylenght. Concentrations of CO2 in the air were maintained throughout the day at 320, 600 or 1200 8l l-1 with approximately 350 8l l-1 at night. Plant growth (length, fresh and gry weight), development (breaks, blindness), flower yield and flower quality (flower bud diameter, fresh weight and cane length) indices were monitored throughout three consecutive flowering cycles. CO2 supplementation caused an increase in leaf resistance to water vapour diffusion, accompanied by a reduction in the rate of transpiration per unit leaf area, Total leaf area increased at higher CO2 concentrations. Water use per plant did not change. Plant water potentials increased with rising CO2 concentrations. Growth, development, flower yield and flower quality were greatly enahnced in the CO2-enriched atmosphere. The response of growth and development to CO2 supplementation tended to decrease slightly with time when calculated per branch, but increased when calculated per plant. Flower yield and qualtiy did not change with time. The highest CO2 treatment resulted in a sustained, approximately 50% increase in yield, and doubling of the above quality indices throughout the three growth cycles.

Growth and Morphological Responses to Irradiance in Three Forest Understory Species of the C4Grass Genus Muhlenbergia

Three species of the C4 grass genus Muhlenbergia-M. frondosa, M. sobolifera, and M. schreberi-were collected from forest understory sites in northeastern Kansas and grown in a growth chamber at 1,500, 150, and 15-25 μmol m-2 s-1 photosynthetic photon flux density (PPFD). Leaf, stem, root, and total biomasses and several morphological and anatomical characteristics were measured after 35-38 days. Results were compared with similar measurements for M. cuspidata collected from exposed prairie sites. Although all species grew maximally at the highest PPFD, M. sobolifera grew equally well at medium PPFD. Few anatomical changes were correlated with changes in PPFD except leaf thickness, which increased with increasing PPFD. The results indicate that, while the understory species of Muhlenbergia can adjust morphologically to some extent to shaded environments, they produce more biomass at higher PPFD.

Biennal behaviour of Cirsium palustre in ash coppice

In the first years after coppicing, Cirsium palustre is abundant in Dutch ash coppice woodlands and in the second year, it flowers abundantly. In later years the species is nearly absent. In contrast to its behaviour in meadow and spring communities, the species typically behaves as a true biennial in this system. Despite fairly high mortality, the plants flowering in their second year produce enough seeds to replenish the seed bank. It is suggested that the persistence of the species in this system depends on Its ability to form a longlived seed bank and on a nutrient availability high enough to enable some rosettes to exploit the high photosynthetic photon flux density (PPFD) in the first year after coppicing and thus to reach the critical size needed for flowering in the second year. Rosettes persisting to the third year generally do not flower and ultimately die because shading by the tree canopy has become too severe.