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.     

The Effect of Temperature on the Growth of Individual Leaves of Vicia faba L. in the Field

The generalized logistic curve was used to describe the growthof individual leaves in crops of Vicia faba L. Durations of.expansionand mean absolute growth rates were derived from these curves.The duration of expansion was inversely related to temperatureaveraged over four days from unfolding. This relationship wasindependent of leaf position except for the lowest leaves. Theduration of expansion of a leaf was related to the rate of productionof new leaves, the number of expanding leaves remaining relativelyconstant. Absolute growth rates varied with leaf position upto leaf 10. At higher leaves, in the absence of water stress,absolute growth rate was a function of temperature and radiation. Vicia faba L., field bean, leaf growth, temperature     

Individual leaf development in Arabidopsis thaliana: a stable thermal-time-based programme

In crop species, the impact of temperature on plant development is classically modelled using thermal time. We examined whether this method could be used in a non-crop species, Arabidopsis thaliana, to analyse the response to temperature of leaf initiation rate and of the development of two leaves of the rosette. The results confirmed the large plant-to-plant variability in the studied isogenic line of the Columbia ecotype: 100-fold differences in leaf area among plants sown on the same date were commonly observed at a given date. These differences disappeared in mature leaves, suggesting that they were due to a variability in plant developmental stage. The whole population could therefore be represented by any group of synchronous plants labelled at the two-leaf stage and followed during their development. Leaf initiation rate, duration of leaf expansion and maximal relative leaf expansion rate varied considerably among experiments performed at different temperatures (from 6 to 26 degrees C) but they were linearly related to temperature in the range 6-26 degrees C, with a common x-intercept of 3 degrees C. Expressing time in thermal time with a threshold temperature of 3 degrees C unified the time courses of leaf initiation and of individual leaf development for plants grown at different temperatures and experimental conditions. The two leaves studied (leaf 2 and leaf 6) had a two-phase development, with an exponential phase followed by a phase with decreasing relative elongation rate. Both phases had constant durations for a given leaf position if expressed in thermal time. Changes in temperature caused changes in both the rate of development and in the expansion rate which mutually compensated such that they had no consequence on leaf area at a given thermal time. The resulting model of leaf development was applied to ten experiments carried out in a glasshouse or in a growth chamber, with plants grown in soil or hydroponically. Because it predicts accurately the stage of development and the relative expansion rate of any leaf of the rosette, this model facilitates precise planning of sampling procedures and the comparison of treatments in growth analyses.     

Differences between Indica and Japonica rice varieties in CO2 exchange rates in response to leaf nitrogen and temperature

Four Indica and five Japonica varieties of rice (Oryza sativa L.) were examined to elucidate their differences in photosynthetic activity and dark respiratory rate as influenced by leaf nitrogen levels and temperatures. The photosynthetic rates of single leaf showed correlations with total nitrogen and soluble protein contents in the leaves. Respiratory rate was also positively correlated with the leaf nitrogen content. When compared at the same level of leaf nitrogen or soluble protein content, the four Indica varieties and one of Japonica varieties, Tainung 67, which have some Indica genes derived from one of its parents, showed higher photosynthetic rates than the remaining four Japonica varieties. At the same photosynthetic rate, the Indica varieties showed lower respiratory rate than Japonica varieties. When the leaf temperature rose from 20°C to 30°C, the photosynthetic rate increased by 18 to 41%, whereas the respiratory rate increased by 100 to 150%. These increasing rates in response to temperature were higher in the Japonica than in the Indica varieties. In this respect, Tainung 67 showed the same behavior as of the other four Japonica varieties.Abbreviations 30/20 ratios the ratios of photosynthetic and respiratory rates at 30°C to those at 20°C     

Physiological Responses of Apple Trees to Supraoptimal Root Temperature

Ungrafted apple rootstocks were grown in sand cultures at constant root temperatures between 20°C to 40°C. Temperatures of 30°C and above reduced root and shoot growth. Serious damage to the leaves occurred at 35°C and above. The O₂ consumption, CO₂ evolution and respiratory quotient (RQ) of the roots showed maximum values at 35°C. Different rootstock cultivars varied greatly in their susceptibility to damage by supraoptimal root temperatures apparently due to anaerobic respiration. The more susceptible ones differed from resistant types in the larger amount of ethanol they accumulated in their roots at supraoptimal root temperature, and the more severe reduction in the malic acid content of the roots at such temperature. Acetaldehyde was also found in roots and leaves at supraoptimal root temperatures, whereas the organic acid content of the leaves tended to decrease. Supraoptimal root temperature also caused a reduction of cytokinins in both roots and leaves accompanied by a reduction in the leaf chlorophyll content. This could be prevented by the application of kinetin or benzyladenine to the leaves. In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C. The leaf water potential increased also with increasing root temperature. Leaf temperature increased with increasing root temperature, irrespective of increasing or decreasing transpiration rates.     

Relative growth rate of leaf biomass and leaf nitrogen content in several mediterranean woody species

In many plant species, herbivory is a major determinant of leaf mortality and it can cause a strong reduction in productive potential. Most predation occurs on young, expanding leaves. Thus, a rapid growth of the leaves can reduce the impact of predation. Furthermore, in cold Mediterranean climates the length of the growing season is constrained to a short period in spring and early summer owing both to low winter temperatures and drought stress in early summer. Therefore, a rapid deployment of leaf area and a high photosynthetic capacity during the spring and early summer might have important positive effects on the final carbon balance of the leaf population. Relative growth rates (RGR) of leaf biomass were measured in 19 woody species typical of Central Western Spain with deciduous and evergreen habits. Highly significant differences were detected in the leaf growth rate of the different species. The differences between species, however, did not correlate either with the mean leaf life-span of each of the species or with other leaf traits such as photosynthetic capacity, specific leaf area or nitrogen content. Leaf growth rate was positively correlated with time elapsed between leaf initiation and fruit maturation, so that species with fruit dispersal in spring and early summer in general had lower leaf growth rates than species with autumn fruit shedding. This relationship shows the effects of the concurrence between vegetative and reproductive organs for nutrients and other resources. Nitrogen concentration in the leaves was very high at the time of bud break, and declined during leaf expansion owing to the dilution associated with the increase in structural components. The rate of nitrogen dilution was, thus, positively related to the leaf growth rate. Relative growth rates calculated for nitrogen mass in leaves were very low compared to the growth in total mass. This suggests that most leaf nitrogen is translocated from the plant stores to the leaf biomass before the start of leaf expansion and that the contribution of root uptake during leaf expansion is comparatively low.     

Comparison of Leaf Plastochron Index and Allometric Analyses of Tooth Development in Arabidopsis thaliana

Abstract Two methods of analyses were used to investigate tooth development in serrate (se) mutant and wild-type Columbia-1 (Col-1) Arabidopsis thaliana leaves. There were almost twice as many teeth with deeper sinuses and two orders of toothing on the margins of serrate compared with Columbia-1 leaves. The main objective of this study was to test three hypotheses relative to the source of polymorphism in tooth development: (i) Teeth share similar growth rates and initial sizes, but the deeper teeth are initiated earlier in leaf development. (ii) Teeth share similar timing of initiation and growth rates, but the deeper teeth have a larger initial size. (iii) Teeth share similar timing of initiation and initial sizes, but the deeper teeth have a faster growth rate. Leaf plastochron index (LPI) was used as the time variable for leaf development. Results showed teeth in se were initiated at −27 LPI, 15 plastochrons earlier than those of Col-1. Serrate leaf expansion was biphasic, with the early phase expanding at half the relative plastochron rate of the later phase, which equaled the constant relative expansion rate of Col-1 leaves. Allometric analyses of tooth development obscured the interactions between time of tooth and leaf initiation and the early phase of leaf expansion characteristic of serrate leaves and teeth. Timing of developmental events that allometric analysis obscured can be readily detected with the LPI as a developmental index. Received 25 January 2000; accepted 17 March 2000     

Correlation between leaf growth variables suggest intrinsic and early controls of leaf size in Arabidopsis thaliana

Leaf development is affected by both internal (genetic) and external (environmental) regulatory factors. The aim of this work was to investigate how leaf growth variables are related to one another in a range of environments. The leaf growth variables of wild-type Arabidopsis thaliana and leaf development mutants (ang4, ron2-1, elo1, elo2 and elo4) were studied under different incident light treatments (light and shade). The leaves studied were altered in various leaf development variables, such as the duration of expansion, relative and absolute expansion rates, epidermal cell size, epidermal cell number and initiation rate. Final leaf area was correlated to maximal absolute leaf expansion rate and cell number, but not to duration of leaf expansion or cell size. These relationships were common to all studied genotypes and light conditions, suggesting that leaf size is determined early in development. In addition, the early variables involved in leaf development were correlated to one another, and initial relative expansion rate was negatively correlated to the duration of expansion. These relationships between the leaf development variables were used to construct a conceptual model of leaf size control.     

Bean Leaf Expansion in Relation to Temperature

When dwarf Phaseolus vulgaris plants were grown in a controlledenvironment at 20, 25, 30, and 35° C, expansion of the primaryleaves occurred in two phases with an intermediate lag. Varyingrates and duration of expansion were involved, leading to greatestfinal areas at the two intermediate temperatures. Dry weightsof the leaves and leaf areas were similary influenced by temperature,except that the initial rates of increase continued for a longerperiod for weights than for areas. The rates of cell divisionand final numbers of cells were similar from 25 to 35° C,but both were decreased at 20° C. Final cell sizes were,on the other hand, decreased only at the highest temperature.The time trends of cell expansion varied greatly with temperature. Leaf expansion is discussed as a possible consequence of substratesupply, which may be determined by temperature in a number ofways. Cell division and cell expansion are not considered tobe joint direct determinants of leaf expansion. Temperatureinfluences division, with two consequences; the rate interactswith substrate supply to determine size of cells, and finalcell number affects potential leaf area. Cell size is regardedas being secondary to numbers of cells and total material available,although some factors can vary cell size independently of substrate,e.g. water status. An important control of leaf growth, until the attainment ofabout half the final area, may be exercised by way of the leaf.Subsequently, intra-plant competition is likely to dominate.     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): kinematic analysis of leaf elongation

Wheat leaves (Triticum aestivum L.) elongated 50% more slowlywhen plants were grown in soils with high mechanical resistanceto penetration (R_s. The profiles of epidermal cell lengths alongthe growth zone of expanding leaves and the locations of newlyformed walls were recorded in order to compare the kineticsof elongation and partitioning of both meristematic and non-meristematiccells. In leaf 5, which completely developed under stress, highR_s, did not affect the flux of mature cells through the elongationzone; leaf elongation was reduced only because these cells wereshorter. This reduced size reflected a reduction in cell lengthat partitioning, associated with shorter cycling time. The relativerates of cell elongation before and after partitioning wereunchanged. Cell fluxes were similar because the population ofmeristematic cells was reduced, offsetting their increased partitioningrate. In contrast, in leaf 1, high R_s, had no effect on thenumber of dividing cells; elongation rate was reduced becauseof slower relative cell expansion rate and slower cell partitioningrate. These differences could reflect differences in the stageat which successive leaves perceived root stress and also time-dependentchanges in the responsiveness of leaf development to stress-inducedroot signals or in the nature of these signals. The data reveal that cell cycling time may in fact be decreasedby unfavourable growth conditions and is not directly relatedto cell expansion rates; they also show that the elongationrate of meristematic cells is partly independently controlledfrom that of non-meristematic cells. Key words: Wheat, kinematics of leaf expansion, cell partitioning, cell elongation, root impedance     

Growth and Senescence of the Successive Grass Leaves on a Tiller. Ontogenic Development and Effect of Temperature

The tiller characteristics (length and age of laminae, numberof leaves per tiller) which depend on morphogenetic characterssuch as leaf appearance and expansion rates, leaf growth durationand leaf lifespan were studied in the field over four growingseasons to gain a better understanding of the progressive changesin leaf digestibility over time, and to facilitate the developmentof predictive mathematical models. We show that, for a givenregrowth, only the number of leaves per tiller and the laminaexpansion rate remain constant throughout growth. In other words,the length of successive laminae, their growth duration andlifespan increased while their rate of appearance decreasedin such a way that the lamina expansion rate at the tiller levelremained constant. These changes were associated with an increasein sheath length which governs both the lamina appearance rateand its growth duration. As temperature increased, the averagelamina expansion rate and the number of laminae which grew bothincreased simultaneously. Therefore, high temperature acceleratesthe changes in tiller characteristics which occur as growthprogresses. Copyright 2000 Annals of Botany Company Leaf, senescence, phyllochron, lifespan, digestibility, temperature, cocksfoot, Dactylis glomerata L     

Nitrogen supply and the control of expansive growth and function in leaves and roots

In plants which have acclimatized to limiting supplies of nitrogen (steady-state nutrition), leaf expansion (numbers and sizes of leaves and cells) is under tight control. Over a wide range of nitrogen supplies, the control of leaf growth is associated with a narrow band of photosynthetic rate per leaf area (measured at the growth climate) and, at limiting supplies, a carbon uptake which is in excess of immediate carbon usage in structural growth.For every increment of nitrogen absorbed, root extension is greater at limited nitrate supply, but V_max values (per root dry weight) for nitrate absorption are typically less. However, the capacity of the whole root system for nitrate uptake at limited supply is sufficient to allow for maximum growth, should nitrate supply be increased.It is concluded that a better understanding at the cellular level of the mechanisms which result in a greater inhibition of the expansion of single leaves than of root extension would contribute to an understanding of differences in carbon sink strength among plant organs. This may be a crucial step towards a more physiologically-based appreciation of plant dry matter distribution among organs in plants experiencing different nitrogen supplies.     

A global meta‐analysis of exotic versus native leaf decay in stream ecosystems

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From individual leaf elongation to whole shoot leaf area expansion: a comparison of three Aegilops and two Triticum species

BACKGROUND AND AIMS: Rapid leaf area expansion is a desirable trait in the early growth stages of cereal crops grown in low-rainfall areas. In this study, the traits associated with inherent variation in early leaf area expansion rates have been investigated in two wheat species (Triticum aestivum and T. durum) and three of its wild relatives (Aegilops umbellulata, A. caudata and A. tauschii) to find out whether the Aegilops species have a faster leaf area expansion in their early developmental stage than some of the current wheat species. METHODS: Growth of individual leaves, biomass allocation, and gas exchange were measured on hydroponically grown plants for 4 weeks. KEY RESULTS: Leaf elongation rate (LER) was strongly and positively correlated with leaf width but not with leaf elongation duration (LED). The species with more rapidly elongating leaves showed a faster increase with leaf position in LER, leaf width and leaf area, higher relative leaf area expansion rates, and more biomass allocation to leaf sheaths and less to roots. No differences in leaf appearance rate were found amongst the species. CONCLUSIONS: Aegilops tauschii was the only wild species with rapid leaf expansion rates similar to those of wheat, and it achieved the highest photosynthetic rates, making it an interesting species for further study.     

Leaf area partitioning as an important factor in growth

Despite continuing efforts to correlate unit area rates of photosynthesis of crop varieties with growth rates, there has been little or no success. It is reasonable to assume that partitioning of photosynthate into new leaf area is an important component of growth. Accordingly, an expression was developed to measure leaf area partitioning. Using growth analysis techniques, relative growth rates were compared to net assimilation rates, partitioning of daily weight gain into new leaf area, and partitioning of daily weight gain into new leaf weight of nine species grown in growth chambers under three temperature regimes. Day/night temperatures of 21/10, 32/21, and 38/27 C caused large differences in relative growth rates. Relative growth rates were closely correlated with leaf area partitioning in seven of the nine species, but were inversely correlated with leaf weight partitioning for six of the nine species. Relative growth rates were poorly correlated with net assimilation rates for five of the nine species. The product of net assimilation rate times leaf area partitioning is shown to be equal to the relative leaf area expansion rate.     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): composition, number and size of epidermal cells in mature blades

Wheat seedlings {Triticum aestivum L.) were grown on soils withcontrasted resistances to root penetration (measured as penetrometerresistance, R_s. High R_s reduced the rates of leaf appearanceand expansion. Although the duration of expansion was increased,mature leaves were smaller. Underlying changes in leaf anatomywere investigated on cleared mature leaves, focusing on theepidermes. Three leaves were analysed: leaves 1 and 3 whichstarted their development in the embryo, and leaf 5 which wasinitiated on the seedling, after imposition of contrasted soilconditions. In all leaves, high R_s, caused a reduction in maturecell sizes, lengths and widths, and a shift in the relativeproportions of functionally different cell types, with a decreasein the relative proportions of stomata and associated cell types(interstomatal and sister cells) and an increase in the proportionsof unspecialized elongated epidermal cells and of trichomes.In leaves 3 and 5 the number of cellular files across the bladewas also reduced, while in leaf 1 it was similar at the twoR_s. These differences between leaves are attributed to differencesin their developmental stage when root stress was first perceived.Remarkably, R_s had no effect (leaf 1) or relatively small effects(leaves 3 and 5) on the total number of cells per file, suggestingthat this parameter is either largely insensitive to variationin root environment, or is programmed at the outset before stresswas perceived at the apex. Key words: Wheat, anatomy, mature epidermis, root impedance     

Importance of adventitious roots to growth of floodedPlatanus occidentalis seedlings

Summary Flooding of soil with standing water for 50 or 110 days drastically reduced growth of 178-day-oldPlatanus occidentalis seedlings, with growth inhibited more as the duration of flooding was increased. Flooding reduced the rate of height and diameter growth, leaf initiation and expansion, and dry weight increment and relative growth rates of leaves, stems, and roots. Flooding also induced leaf epinasty, leaf necrosis, and formation of hypertrophied lenticels and many adventitious roots on submerged portions of stems. Severing of adventitious roots after 50 and 95 days from the submerged portions of stems of continuously flooded seedlings reduced several growth parameters including height and stem diameter growth and relative growth rates of leaves and roots. Evidence for the physiological importance of flood induced adventitious roots is discussed.Research supported by College of Agricultural and Life Sciences, University of Wisconsin, Madison and by Yamagata University, Tsuruoka, Japan. The technical assistance of John Shanklin is appreciated.     

Is thermal time adequate for expressing the effects of temperature on sunflower leaf development?

We have tested whether the effects of temperature on sunflower leaf growth could be documented by using thermal time. The rates of leaf expansion and of cell division were analysed in leaves located at two positions on the stem, and a spatial analysis of expansion rate was carried out. Experiments were performed in growth chamber (stable conditions), in the field or in a greenhouse (fluctuating conditions). We compared three methods for characterizing the rate and the duration of expansion. Responses to leaf temperature were consistent only when expansion was characterized as a two-phase process — a period of exponential expansion (constant relative expansion rate, RER ) followed by a decrease in RER . RER and relative cell division rate ( RDR ) responded linearly to temperature with a common response curve for all studied conditions. This response curve was also common to all studied zones within a leaf and to leaves at two positions on the stem. The reciprocals of the durations of the periods of exponential expansion, non-zero expansion and non-zero division were also linearly related to leaf temperature with common response curves in a given leaf zone. The x -intercepts of all these response curves and of the response curve of leaf initiation rate to temperature did not significantly differ in an analysis of covariance, with a common value of 4·8 °C. The expression of time in cumulative degree days, with a base temperature of 4·8 °C, resulted in a unique time course of RER and cell division rate regardless of temperature. These results suggest that a powerful 'program' of leaf development exists in a sunflower plant.     

Net Photosynthesis and Early Growth Trends of a Dominant White Oak (Quercus alba L.)

Examination of the relationship between photosynthesis and growth of a dominant white oak (Quercus alba L.) tree has shown that most growth processes were either completed or well underway before the establishment of significant positive rates of net photosynthesis. Growth was initiated first in the root system (March 3), followed by stem cambial growth (March 26) and later by flower, leaf, and branch growth (April 10). During the period of rapid leaf and branch growth, root and cambial growth ceased and then resumed as the leaves approached maturity. The rapid rate of leaf maturation, the early appearance of positive rates of net photosynthesis in leaves (15% of final size) and the CO₂-refixing capability of elongating branch tissue reduced the period of time that this white oak tree was dependent on stored reserves. Lower temperature optima and compensation points in developing leaves and stems indicated that the growth-temperature response was optimized for the lower seasonal temperatures observed during the spring. This temperature adaptation further reduced the time that this tree was dependent on stored reserves.