Effect of temperature, irradiance and photoperiod on morphological characters of seedlings of contrasting white clover populations

Seedlings of 10 contrasting white clover populations differing in leaf size and origin were grown in a glasshouse in spring and autumn, and in controlled environments in which temperature (10°, 15°, 20°C), photoperiod ( 8 , 16-h) and irradiance ( 13, 47 , 57 Wm^-2) were varied. There were large effects of these environmental variables on a range of morphological characters. Population differences were closely related to classification of the populations by leaf size. Within the large leaf types there was also an effect of origin. In particular, Mediterranean types differed from those of northern origin. Rate of leaf appearance increased with temperature but was less affected by photoperiod. Population differences were greater at lower temperatures. Petiole length was more sensitive to temperature than was leaflet length, particularly in the range 10° to 15°C. Similarly, petiole length increased appreciably with photoperiod extension; smaller leaf types responded more than large leaf types with the result that there were no population differences in the 16-h photoperiod. Population differences in the other environments were closely related to leaf size classification. The onset of stolon production was delayed by lower temperatures and by short photoperiods but stolon number at the sixth leaf stage of development was not closely related to this character in the temperature environments since stolon numbers increased at lower temperatures. In low temperature and short day conditions the large leaf types including those of Mediterranean origin showed a desirable combination of long petioles and large leaves compared with the smaller leaf types. However, these differences between the two groups were eliminated for petiole length, and much reduced for leaflet length, by the greater response to temperature and photoperiod of the smaller leaf types. The implications of these responses for seasonal production are discussed. There were large effects of irradiance on the lengths of leaflets and petioles with longer ones at higher irradiance levels. There were also faster rates of leaf appearance at higher light levels. Stolon production was faster at 57 Wm^-2 than at 47 Wm^-2 while at 13 Wm^-2 no stolons were produced. After an extended period in the lowest light environment there was some plant mortality.     

Genetic differences in phosphorus absorption among white clover populations

Summary Eight semi-natural white clover populations and two cultivars were grown in culture solutions containing 10 ppm and 0.01 ppm phosphorus (P). The rate of P uptake by the intact plants was then measured in solutions containing 10 ppm P.Phosphorus uptake per unit root length was twice as great by plants previously grown at 0.01 ppm P than those grown at 10 ppm P. Large differences in total P uptake were found among populations regardless of the pretreatment; most of this variation was accounted for by differences in root length. Only small differences were found between populations for P uptake per unit root length, and then only after pretreatment with 10 ppm P; this variation was largely accounted for by relative growth rate and shoot %P.     

Yield and persistency of contrasting white clover populations grown in pure swards and in mixed swards with S.23 perennial ryegrass

Ten contrasting white clover populations were grown as spaced plants, in pure clover swards and in mixed swards with S.23 perennial ryegrass. Four of the populations were also tested for tolerance of low temperatures. In the establishment year, the autumn yields of populations were correlated with leaf size. However, during the severe winter which followed, populations with large leaves, particularly those of Mediterranean origin, suffered extensive stolon kill. This winter damage reduced the spring yields and total annual yields of populations with large leaves, so that leaf size and total annual yield were not correlated in the year after sowing. Stolon kill was positively correlated with autumn growth activity as measured by leaflet size and stolon internode length in October. Stolon kill during winter was correlated with cold tolerance of naturally-hardened stolon apices, assessed in artificial cold tests.     

Tradeoff between biomass and flavonoid accumulation in white clover reflects contrasting plant strategies

An outdoor study was conducted to examine relationships between plant productivity and stress-protective phenolic plant metabolites. Twenty-two populations of the pasture legume white clover were grown for 4½ months during spring and summer in Palmerston North, New Zealand. The major phenolic compounds identified and quantified by HPLC analysis were glycosides of the flavonoids quercetin and kaempferol. Multivariate analysis revealed a trade-off between flavonoid accumulation and plant productivity attributes. White clover populations with high biomass production, large leaves and thick tap roots showed low levels of quercetin glycoside accumulation and low quercetin:kaempferol ratios, while the opposite was true for less productive populations. The latter included stress-resistant ecotypes from Turkey and China, and the analysis also identified highly significant positive relationships of quercetin glycoside accumulation with plant morphology (root:shoot ratio). Importantly, a high degree of genetic variation was detected for most of the measured traits. These findings suggest merit for considering flavonoids such as quercetin as potential selection criteria in the genetic improvement of white clover and other crops.     

Geographic variation in morphological and reproductive characters of coastal and tableland populations ofBlandfordia grandiflora (Liliaceae)

For tenBlandfordia grandiflora populations spanning about 90% of the species' range, univariate and multivariate analyses on 14 vegetative and reproductive characters separated plants into distinct coastal and tableland groups. Distinguishing characters were number of flowers and leaves, leaf length and width, and inflorescence stalk height and diameter; coastal plants were larger than tableland plants. In a transplant experiment, coastal and tableland plants retained their phenotypic distinctness, indicating that vegetative morphology was genetically determined. Coastal plants exhibited clinal variation with latitude. Compared to tableland plants, coastal plants had higher pollen: ovule ratios, and produced fewer but heavier seeds per flower. Tableland and coastal plants are phenotypically distinct, indicating that separate subspecific status is warranted.     

The inheritance of floral characters in white clover (Trifolium repens)

A diallel cross was carried out among seven varieties of white clover to investigate the inheritance of some of those characters which affect potential seed yield. Peduncle length and number of seeds/floret have low narrow-sense heritabilities, while peduncle length displays the added complications of heterozygosity and non-allelic interactions. Consequently, improvements in these characters will be difficult. Seed number m^-2 is a composite character which apparently exhibits heterozygosity. Higher seed yields will therefore be obtained by selection for its component characters, particularly floret number and floral density, both of which are apparently inherited in a comparatively straightforward manner. These results are discussed in the context of improving the potential seed yield of white clover.     

Effects of adaptation to winter stress on biomass production, growth and morphology of three contrasting white clover cultivars

Changes in biomass production and partitioning, together with morphology and growth of three white clover ( Trifolium repens L.) cultivars after exposure to winter stress were recorded in a controlled environment study. The cultivars used were Grasslands Huia (H, New Zealand), AberHerald (AH, bred in UK from material of Swiss origin) and Sandra (S, Sweden), sub-populations of these (survival populations), and a wild ecotype from the Uppsala area. The sub-populations were collected after 2 (with the exception of S) and 4 years of winter stress, respectively, at Uppsala (59°49' N, 17°39' E). In the controlled environment study the photoperiod was 12 h and there were two temperature regimes, namely 24/18 and 12/9°C (day/night), respectively. The experimental plants were cloned from eight different plants of each population. There were few interactions between populations and temperature regimes. Biomass production was lowest in the Swedish populations and in the surviving populations of the other cultivars collected after 4 years of exposure to winter stress. However, biomass partitioning, with the exception of allocation to branches, remained unaffected. Morphology differed significantly between cultivars, but, with the exception of internode length, was unaffected by exposure to winter stress. Internode length was significantly reduced in surviving populations of both H and AH after exposure to four winters, when its value was similar to that of the Swedish populations. The reduced internode length was a result of a greater reduction in the stolon extension rate than in the leaf appearance rate of survival populations compared with the original populations. It is hypothesised that reduced internode length would have implications for the carbon economy of the plant.     

Demographic variation in cycad populations inhabiting contrasting forest fragments

Reduced habitat quality after fragmentation can significantly affect population viability, but the effects of differing quality of the remaining habitat on population fitness are rarely evaluated. Here, I compared fragmented populations of the cycad Zamia melanorrhachis from habitats with different history and subject to contrasting levels of disturbance to explore potential demographic differences in populations across habitat patches that could differ in habitat quality. Secondary-forest fragments had a lower canopy cover and soil moisture than remnant-forest fragments, which may represent a harsh environment for this cycad. A smaller average plant size and lower population density in the secondary-forest fragments support the hypothesis that these fragments may be of lower quality, e.g., if plants have reduced survival and/or fecundity in these habitats. However, variation in the stage-structure of populations (i.e., the relative proportions of non-reproductive and reproductive plants) was associated with the area of the forest fragments rather than the type of habitat (remnant versus secondary forest). These results suggest that different demographic parameters may respond differently to habitat fragmentation, which may be explained if processes like adult survival and recruitment depend on different characteristics of the habitat, e.g., average light/water availability versus suitable area for plant establishment. This study shows that forest fragments may differ drastically in environmental conditions and can sustain populations that can vary in their demography. Understanding how forest fragments may represent different habitat types is relevant for evaluating population viability in a heterogeneous landscape and for designing conservation programs that account for this heterogeneity.     

半夏种内居群形态变异的模糊聚类分析

在同一栽培条件下,对主要引自长江中下游地区的１５个半夏〔Ｐｉｎｅｌｉａｔｅｒｎａｔａ（Ｔｈｕｎｂ．）Ｂｒｅｉｔ．〕居群的１６个主要形态性状进行模糊聚类分析,在置信水平λ＝０．６７６４时,将１５个居群划分成４个类型：（１）双珠芽类型：主要形态特征为叶柄上均具双珠芽,但叶型和块茎形状变异较小;（２）普通类型：主要形态特征为叶柄上均只着生单珠芽,但叶型和块茎形状变异较大;（３）长茎类型：主要形态特征为叶柄上具单珠芽,但着生位置较低,块茎呈矩圆形;（４）复合类型：主要形态特征为叶柄上具单珠芽,但居群内常有双珠芽个体出现。     

Flowering of contrasting white clover varieties in relation to daylength in controlled environments and in the field

The effect of 12 , 14 and 16 h photoperiods, given consecutively, on flower production in 10 varieties of white clover (Trifolium repens) in controlled environments, is described. The effect of natural daylengths from September to July on the same plants in the field was also studied in the following year. Relationships between morphological and physiological traits and flowering were examined. In controlled environments most plants flowered under the longest days, three times as many in the 16 h daylength as in the 12 h. Larger leaved types had a higher proportion of reproductive plants than did smaller leaved types. Floral initiation was not observed in the field until daylengths were in excess of 15 h. Increasing daylength increased flower production, floret and ovule numbers but did not appear to increase nectar production significantly.     

硃砂根(Ardisia crenata)居群的形态特征变异及聚类分析

以分布于福建(漳平永福、漳平官田和武平东留)、江西(会昌永隆和大余庾岭)和广西(南宁宾阳)的6个野生硃砂根(Ardisia crenata Sims)居群的144个单株为研究对象,对植株形态特征(株高、干高、干径、分枝数、枝下高和冠径)、叶部性状(叶色、叶数、叶长、叶宽和叶柄长)和整体观赏性(果穗数、果穗长、每穗果数、果径、果穗柄长、果柄长、果实百粒重、果色和观赏性)3个方面的20个形态性状及其变异幅度进行了比较分析,在此基础上采用欧氏距离进行UPGMA聚类分析.结果表明:不同居群间硃砂根的分枝数、枝下高、叶数、叶色、果穗数和果色等性状的变异幅度较大,总变异系数分别为38.66%、37.19%、42.48%、42.57%、50.36%和52.34%;叶长、叶宽、果实百粒重和果径的变异幅度较小,总变异系数均小于15%.在不同居群间,分枝数、枝下高、叶色、果穗数和果色等性状有极显著差异(P＜0.01),冠径和每穗果数差异显著(P＜0.05),其余性状均无显著差异.在欧氏距离30处可将所有单株划分为A、B、C、D、E和F共6个表征群,同一居群的大部分单株基本被聚在同一个表征群中,其中,武平东留和漳平官田居群的所有单株分别被聚在C和D中,E和F则分别由会昌永隆居群的3个单株和南宁宾阳居群的8个单株组成.在欧氏距离26处可将表征群A、C、D和F进一步划分为14个亚表征群,其中,A、C和F均可划分出4个亚表征群,D可划分出2个亚表征群;亚表征群C1所包含的单株分别归属于4个居群,另外13个亚表征群所包含的单株则分别归属于1～3个居群.研究结果显示,不同居群硃砂根植株的形态特征表现出较明显的地理分化特性,不同居群间的形态分化程度较高,且其形态分化不仅存在于居群间,也存在于居群内.     

Tests for resistance to white clover mosaic virus in red and white clover

A range of red and white clover cultivars was tested for immunity to white clover mosaic virus. All plants became infected although some showed no symptoms. Enzyme-linked immunosorbent assay (ELISA) and immunosorbent electron microscopy (ISEM) revealed significant differences in virus concentration between red clover cultivars and between clones of white clover artificially infected with the virus. These differences could not, however, be related to relative yield losses.     

Detection of selection in populations of white clover (Trifolium repens L.)

Seed populations of white clover polymorphic for the presence/absence of both ovariogenic glucosides and the hydrolysing enzyme linamarase, were introduced into three natural populations. Over the first six months of life a significant increase in the frequency of linamarase containing individuals occurred. Estimated selection coefficients against plants lacking linamarase were in the region of 0.3. This result may have been due to selection at the enzyme locus alone, or to selection favouring cyanogenic individuals which possess both cyanogenic glucosides and enzyme.     

Variation in growth attributes of contrasting populations of Trifolium repens

A range of growth attributes was measured in seedlings of 10 Trifolium repens populations, differing in leaf size and origin, grown in three temperature and two glasshouse environments. Growth rates of large leaf types of Mediterranean origin were higher than those of smaller leaf types at 10°C. However, the greater temperature response of the smaller leaf types resulted in higher growth rates for S.100 and S.184 than for a large leaf type from Israel at 20°C. The increase of growth rate with temperature was associated with changes in leaf area ratio and net assimilation rate between 10° and 15°C but only with changes in net assimilation rate between 15° and 20°C. Within each temperature environment, population differences in growth rate were related to differences in net assimilation rate rather than leaf expansion. At low temperature a greater proportion of dry matter was distributed to leaf tissue in large leaf types particularly those of Mediterranean origin but they showed a proportionately smaller increase in allocation to leaves with increasing temperature compared with small leaf types. In the glasshouse environments growth rates in spring were more than double those in the autumn. This difference was associated with net assimilation rates which were about five times greater in the spring environment. However, leaf area ratios in the spring were only half those in the autumn. These differences in leaf area ratio between the glasshouse environments were closely related to differences in specific leaf area but not to differences in distribution of dry matter to leaf tissue which was greater in the spring environment.     

Variation in flooding-induced morphological traits in natural populations of white clover (Trifolium repens) and their effects on plant performance during soil flooding

Background and Aims

Soil flooding leads to low soil oxygen concentrations and thereby negatively affects plant growth. Differences in flooding tolerance have been explained by the variation among species in the extent to which traits related to acclimation were expressed. However, our knowledge of variation within natural species (i.e. among individual genotypes) in traits related to flooding tolerance is very limited. Such data could tell us on which traits selection might have taken place, and will take place in future. The aim of the present study was to show that variation in flooding-tolerance-related traits is present among genotypes of the same species, and that both the constitutive variation and the plastic variation in flooding-induced changes in trait expression affect the performance of genotypes during soil flooding.

Methods

Clones of Trifolium repens originating from a river foreland were subjected to either drained, control conditions or to soil flooding. Constitutive expression of morphological traits was recorded on control plants, and flooding-induced changes in expression were compared with these constitutive expression levels. Moreover, the effect of both constitutive and flooding-induced trait expression on plant performance was determined.

Key Results

Constitutive and plastic variation of several morphological traits significantly affected plant performance. Even relatively small increases in root porosity and petiole length contributed to better performance during soil flooding. High specific leaf area, by contrast, was negatively correlated with performance during flooding.

Conclusions

The data show that different genotypes responded differently to soil flooding, which could be linked to variation in morphological trait expression. As flooded and drained conditions exerted different selection pressures on trait expression, the optimal value for constitutive and plastic traits will depend on the frequency and duration of flooding. These data will help us understanding the mechanisms affecting short- and long-term dynamics in flooding-prone ecosystems.Key words: Secondary roots, aerenchyma, genotypic variation, petiole length, plant performance, root porosity, selection, soil flooding, specific leaf area (SLA), Trifolium repens, white clover     

Translocation of phosphorus from nodal roots in two contrasting genotypes of white clover (Trifolium repens)

Patterns of translocation of recently-assimilated phosphorus (P) exported from'young' source roots (located 3–4 nodes from the stolon apex) and 'old' source roots (located near the base of the stolon) on the primary stolon of clonal plants of the forage legume white clover ( Trifolium repens L.) were determined using ³²P. Plants of a small-leaved genotype and of a large-leaved genotype were grown in sand culture at two notionally limiting or near-limiting rates of P supply and one non-limiting rate of supply. The small-leaved genotype showed little response in growth rate to the full range of P treatments whereas growth of the large-leaved genotype at the non-limiting rate of P supply was 2. 4 times greater than at the two low rates of P supply. Source roots of both genotypes exported only 26–30% of the P they acquired to the shoot within 24 h when P supply was limited whereas at the high-P rate 54% of recently-assimilated P was exported. Patterns of translocation of exported P to specific sinks differed little between the genotypes and the P treatments; branches were the main sink, accounting for nearly 80% of the estimated amounts of P (μg day⁻¹) exported from young and old roots combined. Translocation patterns from individual roots were determined largely by the modular structure of plants and by the location of the root relative to the major sinks, and were therefore consistent with the same source-sink principles which govern carbohydrate translocation in clonally-growing species. There were strong suggestions that storage of P in stolons and roots played a much greater role in the growth of the small-leaved plants than of the large-leaved plants.