Clonal integration in Fragaria chiloensis differs between populations: ramets from grassland are selfish

In plants, only species with clonal growth are able to directly transfer resources between otherwise independent units of the same genetic individual. A simple conceptual model of plant performance as a function of internal resource supply and environmental resource availability suggests that resource sharing between ramets within clones is likely to be disadvantageous in uniform habitats and advantageous in patchy ones. It was therefore hypothesized that clones in populations from relatively uniform habitats will have been selected for low rates of resource sharing between ramets compared to clones in populations from patchier habitats. In coastal northern California, the clonal herb Fragaria chiloensis is common both in grasslands, where resources are relatively uniform, and on sand dunes, where resources are more patchy. It was predicted that clones from a grassland population of Fragaria would have “selfish” ramets with low rates of resource sharing compared to clones from an adjacent dune population. Ramets were subjected to contrasting light levels with and without connection between ramets. Patterns of biomass accumulation were consistent with the prediction. This appears to be the first report of genetically based variation in patterns of resource sharing in clonal plants. It supports the idea that these patterns are locally selected to increase plant performance in habitats with different patterns of resource availability. Received: 19 August 1998 / Accepted: 4 March 1999     

An analysis of the costs and benefits of physiological integration between ramets in the clonal perennial herb Glechoma hederacea

Summary The costs and benefits, measured in terms of dry weight, of physiological integration between clonal ramets, were analysed in two experiments conducted on the clonal herb Glechoma hederacea. Firstly, integration between consecutively-produced ramets was examined in an experiment in which stolons grew from one set of growing conditions (either unshaded or shaded and either nutrient-rich or nutrient-poor) into conditions in which light or nutrient level was altered. Comparisons were made between the dry weight of the parts of the clones produced before and after growing conditions were changed, and the dry weights of the corresponding part of control clones subjected to constant growing conditions. In a second experiment, integration between two distinct parts of G. hederacea clones was investigated. In this experiment clones were grown from two connected parent ramets and the parts of the clone produced by each parent ramet were subjected independently to either nutrient-rich or nutrient-poor conditions. Ramets in resource-rich conditions provided considerable physiological support to those in resource-poor conditions. This was measured as a dry weight gain compared with the weight of the corresponding part of the control clones growing in resource-poor conditions. However, when stolons grew from resource-poor conditions into resource-rich conditions, there was no similar evidence of the resourcepoor ramtes receiving support from resource-rich ramets. Physiological integration did not result in dry weight gains when this would have necessitated basipetal translocation of resources.Because of the predominantly acropedal direction of movement of translocates in G. hederacea, the structure of the clone was important in determining the effectiveness of integration between ramets. Where physiological integration was effective, the cost to the supporting ramets in terms of dry weight was insignificant. Physiological integration allows clones to maintain a presence in less favourable sites with insignificant cost to ramets in favourable sites, thereby reducing the probability of invasion by other plants, and providing the potential for rapid clonal growth if conditions improve. Integrated support of ramets in unfavourable conditions also enables the clone to grow through unfavourable sites, thus increasing the probability of encountering more favourable conditions by wider foraging.     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

Cell growth and nutritive value of the tropical benthic diatom, <Emphasis Type="Italic">Amphora</Emphasis> sp., at varying levels of nutrients and light intensity,and different culture locations

Two series of experiments were conducted to determine suitable growth factors for the mass propagation of the local algal isolate Amphora sp. A higher growth rate of 0.2 doubling (μ) day⁻¹ was attained at a lower photosynthetic photon flux density (PPFD; 11.4 μmol photon m⁻²s⁻¹) compared to cultures exposed to higher levels of PPFD (16.1 μmol photon m⁻²s⁻¹, −0.1 μ day ⁻¹; 31.3 μmol photon m⁻²s⁻¹, 0.0 μ day⁻¹). Cultures located inside the laboratory had a significantly higher cell density (133 × 10⁴ cells cm⁻²) and growth rate (0.3 μ day⁻¹) compared to those located outdoors (100 × 10⁴ cells cm⁻², 0.2 μ day⁻¹). A comparison of nutrient medium across two locations showed that lipid content was significantly higher in cultures enriched with F/2MTM (macronutrients + trace metals) and F/2MV (macronutrients + vitamins). Saturated fatty acids were also present in high concentrations in cultures enriched with F/2M (macronutrients only). Significantly higher amounts of saturated fatty acids were observed in cultures located outdoors (33.1%) compared to those located indoors (26.6%). The protein, carbohydrates and n-6 fatty acid content of Amphora sp. were influenced by the location and enrichment of the cultures. This study has identified growth conditions for mass culture of Amphora sp. and determined biochemical composition under those culture conditions. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Effect of CO2 and light on survival and growth of rice regenerants grownin vitro on sugar-free medium

Rice (Oryza sativa L.) plantlets regenerated from callus (rice regenerants) were grownin vitro during the preparation stage either on a 1/4 strength N6 gellan gum (4 g l^-1) medium without sucrose (SFM) or with 30 g l^-1 sucrose (SCM), and under CO₂ concentrations of 0.4, 2, 10, 50 or 100 mmol mol^-1, a photoperiod of 24 h and a photosynthetic photon flux density (PPFD) of 125 mol m^-2 s^-1. Rice regenerants were also grownin vitro on SFM or SCM under CO₂ concentration of 50 mmol mol^-1, a photoperiod of 12 or 24 h and a PPFD of 80 or 125 mol m^-2 s^-1. All rice regenerants grew successfully on SFM under CO₂ concentrations of 50 or 100 mmol mol^-1. Increasing the CO₂ concentration increased the survival percentage, shoot length and shoot and root dry weights of rice regenerants grown on SFM. Increasing CO₂ concentration had no significant effect on the survival or growth of rice regenerants grown on SCM. Survival percentages of rice regenerants grown on SCM were less than 80% for each of the CO₂ concentrations. A photoperiod of 24 h under CO₂ enrichment improved the survival and growth of rice regenerants grown on SFM, and increased the survival percentage and shoot dry weight of rice regenerants grown on SCM.     

植株密度和氮素互作对垂穗披碱草生物量分配的影响

垂穗披碱草（Elymus nutans）是高寒地区建植和改良栽培草地的首选草种。虽然合理植株密度和氮素添加量是垂穗披碱草栽培草地稳产的关键因子,但两者之间是否存在最佳互作组合仍不清楚。采用盆栽试验,通过分析不同植株密度（58、102、146株/m²）和氮素添加量（0、200、400 mg/kg）组合状态下垂穗披碱草株高、单株分蘖数、地上生物量、地下生物量、根系体积和地上地下生物量比,以确定理论上是否存在植株密度和氮素添加量的最佳组合。结果表明：随植株密度增加,垂穗披碱草株高、地上生物量和地上地下生物量比值均先增加后降低,而单株分蘖数逐渐减小,根系体积和地下生物量先增加后保持相对稳定;随氮素添加量增加,垂穗披碱草单株分蘖数、地上生物量和地上地下生物量比值均表现为先增加后降低,地下生物量逐渐降低。植株密度与氮素添加量互作虽然对垂穗披碱草的根系体积和单株分蘖数没有显著影响,但两者互作显著影响了垂穗披碱草株高、地上生物量、地下生物量、地上地下生物量比（P<0.01）,这些指标与植株密度和氮素添加量的关系均表现为一个开口向下的抛物面。当植株密度为102株/m²和氮素添加量为200 mg/kg时,垂穗披碱草栽培草地产量最大,生物量分配最优。垂穗披碱草植株密度和氮素添加互作时理论上存在最佳组合,这为垂穗披碱草栽培草地的田间管理提供了理论依据。     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Long-term drought modifies the fundamental relationships between light exposure, leaf nitrogen content and photosynthetic capacity in leaves of the lychee tree (Litchi chinensis)

Drought has dramatic negative effects on plants' growth and crop productivity. Although some of the responses and underlying mechanisms are still poorly understood, there is increasing evidence that drought may have a negative effect on photosynthetic capacity. Biochemical models of leaf photosynthesis coupled with models of radiation transfer have been widely used in ecophysiological studies, and, more recently, in global change modeling. They are based on two fundamental relationships at the scale of the leaf: (i) nitrogen content-light exposure and (ii) photosynthetic capacity-nitrogen content. Although drought is expected to increase in many places across the world, such models are not adapted to drought conditions. More specifically, the effects of drought on the two fundamental relationships are not well documented. The objective of our study was to investigate the effects of a long-term drought imposed slowly on the nitrogen content and photosynthetic capacity of leaves similarly exposed to light, from 3-year-old lychee trees cv. Kwa? Mi. Leaf nitrogen and non-structural carbohydrate concentrations were measured along with gas exchanges and the light-saturated rate of photosynthetic electron transport (J(max)) after a 5.5-month-long period of drought. Leaf nitrogen content on a mass basis remained stable, while the leaf mass-to-area ratio (LMA) increased with increasing water stress. Consequently, the leaf nitrogen content on an area basis (N(a)) increased in a non-linear fashion. The starch content decreased, while the soluble sugar content increased. Stomata closed and net assimilation decreased to zero, while J(max) and the ratio J(max)/N(a) decreased with increasing water stress. The drought-associated decrease in photosynthetic capacity can be attributed to downregulation of photosynthetic electron transport and to reallocation of leaf nitrogen content. It is concluded that modeling photosynthesis in drought conditions will require, first, the modeling of the effect of drought on LMA and J(max).     

Similarity of growth patterns between plantlets and seedlings of Brassica campestris L. under different in vitro environmental conditions

Explants and seeds of Brassica campestris L. were cultured on Murashige & Skoog (1962) medium with and without sucrose in a vessel with different numbers of air changes per hour under different PPF (photosynthetic photon flux) conditions. The growth and development of plantlets in the vessel were similar to those of seedlings when cultured under the same in vitro environmental conditions. The growth and development of seedlings when cultured under the same in vitro environmental conditions. The growth and development of plantlets/seedlings were greater for treatments with a higher number of air changes per hour and a higher PPF regardless of the sucrose concentration in the culture medium.The CO₂ concentration in the vessel with a lower number of air changes per hour decreased to approximately 100 ppm during the photoperiod on day 21 due to the photosynthetic activities of the plantlets/seedlings. The low CO₂ concentration, in turn, reduced the net photosynthetic rate of plantlets/seedlings in the vessel, and thus affected their growth and development.Abbreviations C_in CO₂ concentration in the culture vessel - C_out CO₂ concentration in the culture room - MS mineral composition of Murashige & Skoog (1962) medium - PPF photosynthetic photon flux     

Heritability of,and relationships between phosphorus and nitrogen concentration in shoot,stolon and root of white clover (Trifolium repens L.)

Ninety eight white clover genotypes were cloned and grown in pots at two levels of phosphorus (P) supply in soil. After harvest the nitrogen (N) and P content of shoot (leaf, petiole and unrooted stolon), stolon and root tissue was determined. Broad sense heritabilities for %N, %P, and proportion of total N or P in each tissue type were calculated. Heritabilities ranged from 0.22 to 0.68. They were generally higher for %P than %N; and higher in shoot and stolon tissue than root tissue for %P, %N, and proportion of N or P. Level of P in which plants were grown had little effect on heritability values. Genotypes from bred cultivars differed from those collected from hill country pastures for plant size, and partitioning of N and P to shoot, stolon and root. Relationships between plant characters were examined to determine the consequences of selection.     

云南文山石漠化区车桑子叶脉密度与叶氮含量关系对生境的响应

植物叶脉特征和叶氮含量的变化影响着叶片经济谱的形成,为验证叶片结构中叶脉网络构建提供了理论依据。该文以单位质量叶氮含量(N_mass)和单位面积叶氮含量(N_area)分别表示叶氮含量,采取主成分分析、线性回归分析的方法,研究了云南文山石漠化区旷地(Ⅰ)、林缘(Ⅱ)和林下(Ⅲ)3种自然生境下车桑子的叶脉密度(Vein density,VD)与N_mass和N_area的异速关系。结果表明:从乔灌群落的旷地到林下,车桑子的比叶面积、叶绿素总含量、光能利用率和N_mass逐渐增大,光饱和点、光补偿点、水分利用效率、VD、N_area逐渐减小,净光合速率、蒸腾速率、气孔导度呈先增大后减小的趋势。VD与叶氮含量呈不同程度的相关性,在生境I和III,VD与N_mass和N_area分别具有显著的负相关(P<0.05)和正相关(P<0.05);在生境Ⅱ,VD与N_mass和N_area分别...     

Plasticity in R/S ratio, morphology and fitness-related traits in response to reciprocal patchiness of light and nutrients in the stoloniferous herb, Glechoma longituba L

Clonal fragments of the stoloniferous herb Glechoma longituba were subjected to a complementary patchiness of light and soil nutrients including two spatially homogeneous treatments (SR–SR and IP–IP) and two spatially heterogeneous treatments (IP–SR and SR–IP). SR and IP indicate patches (shaded, rich) with low light intensity (shaded, S), high nutrient availability (rich, R) and patches (illuminated, poor) with high light intensity (illuminated, I) and low nutrient availability (poor, P), respectively. Plasticity of the species in root–shoot ratio, fitness-related traits (biomass, number of ramets and dry weight per ramet) and clonal morphological traits (length and specific length of stolon internodes, area and specific area of laminae, length and specific length of petioles) were experimentally examined. The aim is to understand adaptation of G. longituba to the environment with reciprocal patches of light and soil nutrients by plasticities both in root–shoot ratio and in (clonal) morphology. Our experiment revealed performance of the clonal fragments growing from patches with high light intensity and low soil nutrient availability into the adjacent opposite patches was increased in terms of the fitness-related characters. R/S ratio and clonal morphology were plastic. Meanwhile, the capture of light resource from the light-rich patches was enhanced while the capture of soil nutrients from either the nutrient-rich or the nutrient-poor patches was not. Analysis of cost and benefit disclosed positive effects of clonal integration on biomass production of ramets in the patches with low light intensity and high soil nutrient availability. These results suggest an existence of reciprocal translocation of assimilates and nutrients between the interconnected ramets. The reinforced performance of the clonal fragments seems to be related with specialization of clonal morphology in the species.     

Control of cytochrome b6f at low and high light intensity and cyclic electron transport in leaves

The light-dependent control of photosynthetic electron transport from plastoquinol (PQH₂) through the cytochrome b₆f complex (Cyt b₆f) to plastocyanin (PC) and P700 (the donor pigment of Photosystem I, PSI) was investigated in laboratory-grown Helianthus annuus L., Nicotiana tabaccum L., and naturally-grown Solidago virgaurea L., Betula pendula Roth, and Tilia cordata P. Mill. leaves. Steady-state illumination was interrupted (light-dark transient) or a high-intensity 10 ms light pulse was applied to reduce PQ and oxidise PC and P700 (pulse-dark transient) and the following re-reduction of P700⁺ and PC⁺ was recorded as leaf transmission measured differentially at 810-950 nm. The signal was deconvoluted into PC⁺ and P700⁺ components by oxidative (far-red) titration (V. Oja et al., Photosynth. Res. 78 (2003) 1-15) and the PSI density was determined by reductive titration using single-turnover flashes (V. Oja et al., Biochim. Biophys. Acta 1658 (2004) 225-234). These innovations allowed the definition of the full light response curves of electron transport rate through Cyt b₆f to the PSI donors. A significant down-regulation of Cyt b₆f maximum turnover rate was discovered at low light intensities, which relaxed at medium light intensities, and strengthened again at saturating irradiances. We explain the low-light regulation of Cyt b₆f in terms of inactivation of carbon reduction cycle enzymes which increases flux resistance. Cyclic electron transport around PSI was measured as the difference between PSI electron transport (determined from the light-dark transient) and PSII electron transport determined from chlorophyll fluorescence. Cyclic e⁻ transport was not detected at limiting light intensities. At saturating light the cyclic electron transport was present in some, but not all, leaves. We explain variations in the magnitude of cyclic electron flow around PSI as resulting from the variable rate of non-photosynthetic ATP-consuming processes in the chloroplast, not as a principle process that corrects imbalances in ATP/NADPH stoichiometry during photosynthesis.