Leaf Extension Research Articles

Effect of water stress on growth and biomass yield of contrasting genotypes of sugarcane (<i>Saccharum officinarum</i>)

Effect of water stress on expansive growth measured as leaf extension rate (LER) and plant height of five Selected lines of sugarcane (BD 83/019, BD 83/035, IB 85/43, USRI 86/4, and USRI 86/25) was investigated in a screenhouse trial at Unilorin Sugar Research Institute farm. The effect of water stress on biomass yield was also evaluated. Water stress was induced by differential watering intervals of daily, 4, and 10 days corresponding to 100 (no stress), 60 (moderate stress), and 25 per cent (severe stress) soil available water (determined gravimetrically). LER, hence leaf length and plant height, showed significant responses to water stress, decreasing when water is limiting. The results of this study also showed ontogenetic variations in the responses of leaves at different positions to water stress. Similarly, there were genotypic differences in leaf and plant height responses of the investigated lines to water stress, which were found to be related to the effect of water stress on biomass yields of the lines. Consequently, it was concluded that measurement of expansive growth could be very useful for distinguishing between genotypes in their responses to water stress; hence, a promising technique for screening for drought tolerance in sugarcane. The advantages of the techniques are also discussed. Ghana Jnl agric. Sci. Vol.31(1) 1998: 73-80

The thermal response of leaf extension rate in genotypes of the C4-grass Miscanthus: an important factor in determining the potential productivity of different genotypes

The thermal response of leaf extension rate in genotypes of the C4-grass Miscanthus: an important factor in determining the potential productivity of different genotypes

The thermal response of leaf extension rate in genotypes of the C4–grassMiscanthus: an important factor in determining the potential productivity of different genotypes

Thermal responses of plant extension rate are reported for 32 genotypes of the C4 grass Miscanthus. Displacement transducers were used to measure plant extension rate as temperatures were stepped between 20°C and 5°C. Leaf extension accounted for 83% of the plant extension. The Q10 between 10°C and 20°C for the genotypes varied from 3.0 to 4.7. The relationship between temperature (5-20 °C) and plant extension rate was found to be described adequately by fitting a third order polynomial. An estimate of the effect of differences in the thermal response of plant extension rate on the potential yield of the genotypes was calculated for Irish climatic conditions using a simple growth model. Potential yield varied between 3 and 23 t ha−1 year−1. This demonstrates the critical role which differences in leaf expansion rate can play in the selection of more productive genotypes. The significance of vapour pressure deficit on the estimates of thermal response of plant extension rate are discussed.

Maize Shoot and Root Response to Root Zone Saturation during Vegetative Growth

AbstractExcess water adversely affects 12% of the world's soils. In rainfed cropping areas, heavy rainfalls may produce transient soil saturation. Better understanding of plant growth under transient soil water saturation or high water tables is needed for effective simulation models. In particular, improved functions are needed to estimate maize (Zea mays L.) response to root zone saturation of various durations and at different stages of plant growth. This 2‐yr study was conducted in Michigan in a field facility where the water table could be independently managed on several 2.1‐ by 1.5‐m2 plots. Saturated conditions were imposed for 4 or 8 d in early (leaf tip 5–6) or late (leaf tip 10–12) vegetative growth. Shoot growth measurements included leaf extension, biomass, leaf area, leaf senescence, stomatal conductance, and photosynthesis. Roots were observed and counted at several soil depths, using minirhizotron tubes. Root zone saturation had a major impact on almost all aspects of plant growth and yield. Measured yield for the control was 153 g plant−1 in 1991. Plants exposed to root zone saturation yielded about half of the control yield, primarily because of a reduction in kernel number per ear. Biomass growth was reduced through reduced leaf area expansion, increased leaf senescence, and reduced photosynthesis. Root numbers at the 15‐ and 40‐cm depths decreased soon after soil saturation, but root growth increased rapidly about 10 d after the saturated treatments ended and final root numbers were about the same as the control by season's end. Loss of leaf area growth was never recovered, and green leaf area reduction due to senescence further decreased plant growth. Responses to early and late saturation were about the same. Doubling the saturation period reduced final biomass by only an additional 10%, showing the adaptive responses of maize for survival of saturation. Nonetheless, crop yields may be dramatically reduced.

Non-destructive assessment of the effects of elevated CO 2 on plant community structure in a calcareous grassland

Calcareous grassland was exposed to ambient or elevated CO 2 using a Screen-Aided CO 2 Control (SACC) system starting in March 1994. The effects of elevated CO 2 on plant community structure were studied using the point intercept method. Measurements were made in March 1994 prior to the start of CO 2 exposure and again in June 1994 at peak plant biomass. There were no significant differences in the initial structure of the communities based on their assigned CO 2 treatments in March. After 9 weeks of exposure of the community to elevated CO 2, the total number of intercepts per plot was not significantly different between CO 2 treatments; however, Carex flacca and Cirsium acaule had marginally significant (P=0.055 and P=0.06) increases in the % sward of the community at elevated CO 2 (number of intercepts for a single species divided by the total number of intercepts for all species). Measurements of leaf extension in Carex flacca showed that at least part of the increase in % sward at elevated CO 2 could be explained by greater leaf length per plant (P=0.02). These measurements and other experiments with calcareous grassland species and communities suggest that rising atmospheric CO 2 concentrations will probably alter the structure of calcareous grassland communities.

Controlled Grazing Studies on Molinia Grassland: Effects of Different Seasonal Patterns and Levels of Defoliation on Molinia growth and Responses of Swards to Controlled Grazing by cattle

Experiments were carried out at three sites in southern Scotland to determine the suitability of Molina grassland for sustained use in providing summer grazing for cattle, and to investigate grazing control as a tool to manipulate the species composition of hill pastures in Britain. Cutting experiments showed that frequency and severity of defoliation were more important than timing in their effects on Molinia. Weights of clippings declined in successive years only in response to treatments that involved repeated within-season cutting. Three years of repeated light defoliation (33% lamina length removed each June, July and August), compared with uncut controls, reduced leaf production in a fourth uninterrupted growing season by 40%, while repeated heavy defoliation (66% lamina removal) reduced it by 78%. Reductions in both the numbers and the size of tillers contributed to this result. Single annual cuts only reduced leaf production at 66% lamina removal when they took place late in the season. Plots grazed by cattle at two sites for 6 years compared treatments where 66% rather than 33% of the herbage was removed by grazing. The rates of leaf extension in Molinia were reduced at the higher level of use. In comparison with areas protected from grazing during the final year of treatment only, the biomass of Molinia and other grasses in areas open to grazing showed that the taller Molinia was utilized to a much greater extent than the other grasses. After 6 years of grazing, the biomass of Molinia at 33% utilization was reduced by 46-65% compared with ungrazed exclosures, while at 66% utilization it was reduced by 86%. Basal internode size was greatly reduced in the grazed plots compared with the ungrazed exclosures, with effects on tiller base size being more important than variation in concentrations in determining amounts of starch, total water soluble carbohydrates, N, P and K on a per tiller basis. Site x management interactions for concentrations could be interpreted in terms of variations in stage of maturity, potential for growth and plant/animal nutrient cycling pathways. Floristic diversity was increased on grazed compared with ungrazed areas. The cover of Molinia was decreased and that of other broad-leaved grasses increased by grazing. At 33% utilization, the cover of Molinia appeared to be levelling off (at around 60-65% after 3-5 years) while at 66% utilization a continued downward trend was evident. Species trends were also influenced by site factors, with exclusion of grazing leading to a reduced cover of Festuca ovina only where conditions were favourable for high yields of taller grasses. The responses of Molina to defoliation are discussed in relation to its pattern of growth and low rate of leaf and tiller turnover and to its responses to soil and climatic factors. The effects of grazing on nutrient cycling and sward canopy structure, in influencing competitive relationships with other species, are considered and the wider issues relevant to management protocols are outlined.

Cell wall composition of leaves of an inherently fast‐ and an inherently slow‐growing grass species

ABSTRACTDifferences in the relative growth rules of the inherently slow‐growing Deschampsia flexuosa L. and the inherently fast‐growing Holcus lanatus L. were reflected in cell wall synthesis in the elongation zone of the leaves. Leaf elongation rates depended on the size of the plant and ranged from 6 to 14 mm d−1 in Deschampsia and from 12 to 42 mm d−1 in Holcus. Anatomical data showed that the epidermis and vascular tissue are the important tissues controlling leaf extension. The cell wall polysaccharides of fully expanded leaves of the two species were identical in sugar composition. Enzymatic hydrolysis of polymeric sugars in the cell walls of the sheath and the lamina gave glucose (85%), arabinose (3.5%), fucose (0.5%), xylose (5.0%), mannose (0.5%), galaclose (0.8%) and galacturonic acid (3–4%). This composition applied throughout the blade and the sheath and did not change with ageing. Polysaccharides in the meristems of the two species showed identical sugar compositions with 51–55% glucose, 13–15% galactoronic acid and 13–14% arabinose as the main components. The extension zone was marked by a gradual increase of driselase‐digestable polymers (per mm tissue) and a concurrent shift in sugar composition. The massive increase of glucose in the cell wall polymers of the elongation zone is probably caused by cellulose synthesis. The rate of synthesis of cell wall polysaccharides in Holcus was twice as high as that in Deschampsia. The slower‐growing Deschampsia has more ferulic acid esterified with cell walls, which might contribute to the slowing of leaf growth. Lignin is not significantly deposited until growth has essentially ceased and is not responsible for the difference in growth rate.

Leaf morphogenesis and growth in Cyperus eragrostis (Cyperaoeae)

We identified the zones of leaf extension, cell division, cell elongation, and cell differentiation in developing leaves of a sedge species, Cyperus eragrostis Lam. (Cyperaceae). The zone of leaf extension was located by measuring the separation between pinhole markers and by observing the staining pattern of Calcofluor White after pulse-labelling growing leaves. These observations were supported by determining growth rates of control and punctured leaves and by scanning electron and light microscopy of developing leaves. The location of the zone of cell division was assessed by enumerating mitotic figures, and the zone of cell elongation was established by measuring lengths of epidermal cells in cleared leaves. These studies indicated that the zone of leaf elongation is within the basal 10–15 mm of a leaf and that cell divisions are restricted to the basal 0.2–1 mm. Radial enlargement of internal tissues begins in the basal half of the elongation zone and cells are fully differentiated within a short distance above it. Expanding leaves can be divided into three zones: zone 1, a basal meristematic zone where cell division and some cell elongation occur; zone 2, a zone above the base where cells are elongating but cell division has ceased; and zone 3, a zone where elongation is complete and cells have reached their final length. This pattern of leaf development is similar to, but more condensed than, feat found in the related monocotyledonous family, the Poaceae. Keywords: Cyperus eragrostis, leaf development, leaf extension zone, Cyperaceae, cell enlargement.

Controlled Grazing Studies on Nardus Grassland: Effects of Between-Tussock Sward Height and Species of Grazer on Nardus utilization and Floristic Composition in Two Fields in Scotland

1. The utilization of the tussock-forming grass Nardus stricta was investigated in controlled grazing experiments in which various sward heights of between-tussock grasses were maintained thoughout the growing season using either sheep, cattle or goats. 2. The utilization of Nardus increased as the height maintained for the between-tussock grasses was reduced. The relationship between sward height and level of utilization of Nardus, however, differed greatly among herbivore species. 3. Under similar sward conditions, cattle and goats utilized more Nardus than did sheep. Utilization of Nardus declined over successive seasons under grazing by sheep but was sustained under grazing by cattle or goats. 4. The severity of defoliation of Nardus achieved by cattle or goats when between-tussock grasses were maintained at 4.5 cm (mean sward surface height above ground) resulted in disappearance of tussocks from the sward and in reduced size, leaf extension growth and nutrient reserves of Nardus tillers. Under cattle grazing, the cover achieved by Nardus decreased from 55.4% to 30.0% over 5 years. 5. Under sheep grazing, both the biomass of individual Nardus tussocks and the cover of Nardus increased. Cover increased from 58% to over 86% at a between-tussock height of 4.5 cm, while at a height of 3.5 cm, after initially declining, it increased to reach 72%. 6. The broad-leaved grasses showed a trend towards increase in cover when between-tussock sward height was maintained at 4.5 cm whether grazing was by cattle or by sheep; the trend was not evident at 3.5 cm (sheep grazing only). 7. Changes in the floristic composition of the sward are discussed in relation to the roles of the inherent growth characteristics of the species present, to selective defoliation and uprooting of the shoots, to altered nutrient cycling pathways under grazing and to the nutrient status of sites.

Morphogenetic and structural characteristics of field-grown timothy cultivars differing in maturity

The leaf area development of grasses and, subsequently, radiation interception depends on morphogenetic processes such as leaf extension and appearance. No detailed studies of leaf extension and appearance of field-grown timothy (Phleum pratense L.) cultivars differing in maturity have been reported in the literature. Leaf extension and appearance of field-grown timothy cultivars differing in maturity and their impact on sward structural characteristics such as leaf size per tiller and tiller density were studied during primary growth in the spring of 1991 and 1992. The leaf extension rate of early-maturing cultivars was greater than that of late-maturing cultivars during primary growth of timothy. There were no differences in leaf appearance rates among cultivars Hence, individual tillers of early-maturing cultivars developed a larger leaf size than late-maturing cultivars. In 1992, late-maturing cultivars had a greater tiller density than early-maturing cultivars which compensated for the smaller leaf size. Different tiller density-tiller size characteristics of early and late-maturing timothy cultivars resulted in a similar outcome in terms of LAI. Key words:Phleum pratense L., timothy, leaf extension, leaf appearance, tillering

Response of the Tussock Grass Stipa tenacissima to Watering in a Semi-Arid Environment

1. Stipa tenacissima is a perennial tussock grass of arid and semi-arid zones around the Mediterranean basin that occupies extensive areas in south-eastern Spain. The environment of this region is extreme, with low irregular rainfall, high temperature and high irradiance, so that S. tenacissima tussocks are subjected to a high degree of environmental stress, especially during the summer months. 2. The ability of S. tenacissima to use a pulse of water applied in midsummer was tested in a field experiment in which extension growth and physiological performance of leaves of watered and unwatered plants were measured. 3. In unwatered plants, when leaf extension had ceased, leaf water potential, relative water content, leaf conductance and net photosynthetic rate were low and minimum fluorescence was high. 4. Leaf conductance and net photosynthetic rate doubled, leaf extension resumed, minimum fluorescence (F 0 ) fell and photosynthetic efficiency of photosystem II (F v /F m ) rose with watering. As the soil dried out again, values of these variables approached or equalled those of unwatered plants. 5. These changes in F 0 and F V /F m suggested that the photosynthetic apparatus had not been damaged permanently, i.e. that S. tenacissima has reversible photoprotective mechanisms. 6. We conclude that the decreased photosynthetic rate of unwatered plants in summer results from non-damaging photoinhibition and low leaf conductance. The latter is partly a consequence of the folding of leaves, which was inversely proportional to relative water content. 7. The arrested development of S. tenacissima leaves was apparently not due to summer dormancy because leaves responded opportunistically within days to an applied pulse of water.

Effects of interval between harvests and application of fertilizer N in spring on the growth of perennial ryegrass in a grass/white clover sward

AbstractA perennial ryegrass/white clover sward, which had been grazed for over 2 years, was cut at 1‐, 2‐, 3‐ or 6‐week intervals from 18 April to 28 November 1986. Two rates of fertilizer N application in spring, 0 and 66 kg N ha−1, were compared. Perennial ryegrass growth was studied in three 6‐week periods, beginning on 18 April, 18 July and 17 October. Clover growth was studied in the same three periods and described by Fisher and Wilman (1995) Grass and Forage Science, 50, 162–171.Applied N increased the number of ryegrass tillers m−2, the rate of leaf extension and the weight of new leaf produced tiller−1 and m−2per week. Increasing the interval between cuts reduced the number of ryegrass tillers m−2 and increased the rate of leaf extension, weight tiller−1and the weight of new leaf produced tiller−1week−1. Increasing the interval between cuts increased the weight of new ryegrass leaf produced m−2 where N had recently been applied, but otherwise had little effect on the weight of new leaf produced m−2. Applying N favoured the grass in competition with the clover in every respect, whereas increasing the interval between cuts only favoured the grass, compared with clover, where N had recently been applied; where N had not been applied, the ratio of ryegrass tillers to clover growing points in the sward was very little affected by the interval between cuts.

Contrasting CO2and temperature effects on leaf growth of perennial ryegrass in spring and summer

The effects of increased atmospheric carbon dioxide (CO 2 ) of 700 μmol mol -1 and increased air temperature of + 4°C were examined in Lolium perenne L. cv. Vigor, growing in semi-controlled greenhouses. Leaf growth, segmental elongation rates (SER), water relations, cell wall (tensiometric) extensibility (%P) and epidermal cell lengths (ECL) were measured in expanding leaves in spring and summer. In elevated CO 2 , shoot dry weight (SDW) increased in mid-summer. In both seasons, SDW decreased in elevated air temperatures with this reduction being greater in summer as compared to spring. Specific leaf area (SLA) decreased in elevated CO 2 and in CO 2 x temperature in both seasons. In spring, increased leaf extension and SER in elevated CO 2 were linked with increased ECL, %P and final leaf size whilst in summer all were reduced. In high temperature, leaf extension, SER, %P and final leaf size were reduced in both seasons. In elevated CO 2 x temperature, leaf extension, SER, %P, and ECL increased in spring, but final leaf size remained unaltered, whilst in summer all decreased. Mid-morning water potential did not differ with CO 2 or temperature treatments. Leaf turgor pressure increased in elevated CO 2 in spring and remained similar to the control in summer whilst solute potential decreased in spring and increased in summer. Contrasting seasonal growth responses of L. perenne in response to elevated CO 2 and temperature suggests pasture management may change in the future. The grazing season may be prolonged, but whole season productivity may become more variable than today.

Seasonal patterns of root, tiller and leaf production in a Grasslands Ruanui ryegrass sward

In a Grasslands Ruanui perennial ryegrass (Lofium perenne L.) sward at Palmerston North, root mass, root appearance, tiller population density, tiller appearance and death rates, and leaf extension and leaf appearance rates were measured at 2-monthly intervals over a 12-month period, commencing November 1988. Tiller appearance was lowest in November, but was also low in May, increasing to a peak in August. Root appearance showed a pronounced peak in August. Leaf extension and leaf appearance rates were low during the period of high root and tiller formation in August, but high in November when tiller and root formation were low, suggesting co-ordination of these processes, with sequential activation of tillering, root formation and leaf formation activity winter. Principal component analysis to gain an objective overview of these data indicated a primary peak of activity in August (spring), and a secondary peak in March (autumn). The seasonal patterns observed for Grasslands Ruanui ryegrass appear to be different from those reported in the literature for Ellett and Grasslands Nui cultivars. ---.----._- - - - Keywords: leaf extension rate, Lolium perenne, principal component analysis, root growth, tiller appearance

Diurnal variation in the simultaneous uptake and ‘sink’ allocation of NH4+and NO3-byLolium perennein flowing solution culture

Perennial ryegrass (Lolium perenne L.) was grown in flowing solution culture under artificial illumination with a 10 h light period. The diurnal fluctuations in the net uptake of NH4+ and NO3- from a 20 mmol m−3 NH4NO3 supply were measured (i) from the amounts of these ions supplied automatically to maintain concentrations in solution, and (ii) by 15N pulse-labelling throughout the diurnal cycle. Diurnal variation in leaf extension, translocation and allocation of assimilated C (14CO2 pulse-labelling) and N (15N pulse and steadystate labelling) were also followed. The apparent ‘sinkstrength’ of different organs for recently assimilated C and N was calculated from the concentration of label recovered in the tissues. Ammonium and NO3- showed qualitatively similar diurnal patterns of net uptake, with minimum and maximum rates, respectively, at the start and end of the photoperiod; but NH4+ uptake showed a proportionately steeper decline during the dark period. This trend was mirrored by the decrease in translocation of N from roots to shoots during the dark, concurrent with an increase in the relative allocation of NH4+-N to expanding leaves and young tillers, and in NO3--N to older expanded leaves. Overall the apparent ‘sink-strength’ of expanding leaves for N declined during the dark period. Pulse-chases of 14CO2 fed to the youngest fully expanded leaf at the start and end of the photoperiod showed that translocation of 14C to the roots continued throughout the dark period, but that the apparent rate was halved after 9 h of darkness. The results were interpreted as contrary to the ‘carbohydrate supply limitation’ hypothesis for the dark-related decline in N uptake, but compatible with regulation by ‘sink-strength’ for N.

The Net Orientation of Wall Microfibrils in the Outer Periclinal Epidermal Walls of Seedling Leaves of Wheat

Use of the dichroic stain chlor-zinc-iodine revealed that the net orientation of cellulose wall microfibrils in the outer paradermal wall of the epidermis of seedling wheat leaves is principally transverse in the extension zone. The net orientation of microfibrils changes abruptly to principally longitudinal at the end of cell elongation. The net angle of orientation of microfibrils in the extension zone was not a function of Rht-dosage (number of dwarfing alleles), and neither leaf extension rate nor estimated maximum relative elemental rate of elongation were functions of microfibril orientation. The results indicate that elongation rates are not regulated by the net angle of orientation of microfibrils and support the concept that leaf extension rate is regulated by the length of the extension zone.

Leaf growth of hybrid poplar following exposure to elevated CO2

summaryLeaf extension was stimulated following exposure of three interamerican hybrid poplar clones (Populus trichocarpa P. deltoides); ‘Unal’, ‘Boelare’, and ‘Beaupre’ and a euramerican clone ‘Primo’ (Populus nigra×P. deltoides) to elevated CO2, in controlled environment chambers. For all three interamerican clones the evidence suggests that this was the result of increased leaf cell expansion associated with enhanced cell wall extensibility (WEx), measured as tensiomerric increases in cell wall plasticity. For the interameriean clone ‘Boelare’, there was also a significant increase in cell wall elasticity following exposure to elevated CO2 (P⩽ 0.001). The effect of elevated CO2 in stimulating cell wall extensibility was confirmed in a detailed spatial analysis of extensibility made across the lamina of expanding leaves of the clone ‘Boelare’. For two of the interamerican hybrids, ‘Unal’ and ‘Beaupre’, both leaf cell water potential Ψ and turgor pressure (P) were lower in elevated than in ambient CO2. By contrast, no significant effects on the cell wall properties or leaf water relations for the euramerican hybrid ‘Primo’ were observed following exposure to elevated CO2. suggesting that the mechanism for increased leaf extension in elevated CO2, differed, depending on clone. The cumulative total length of leaves of ‘Boelare’ grown in elevated CO2, was significantly increased (P≤ 0.05) and since leaf number was not significantly increased in any inter‐american clone it is hypothesized that final leaf size was stimulated in elevated CO2 for these clones. By contrast, there was no significant effect of CO2 on cumulative total leaf length for the euramerican clone ‘Primo’, but leaf number was significantly increased by elevated CO2. The measurements suggest that total tree leaf area was stimulated for a range of poplar hybrids exposed to elevated CO2. Given the short rotation of a coppiced crop, it is likely that increased leaf areas will result in enhanced stemwood production when hybrid poplars are grown in the CO, concentrations predicted for the next century.

Mode of action of chlorsulfuron in a sensitive wheat (Triticum aestivum) cultivar: primary and secondary effects on nitrogen assimilation

SummaryChlorsulfuron (15 g a.i. ha‐1) inhibited growth of wheat (Triticurn aestivum L. cv. Rongotea) especially on high nitrate (NO3) supply. Decreased growth at high NO‐3 was associated with higher concentrations of reduced nitrogen (N) and NO‐3 in the shoots. Seven days after spraying (DAS), shoot dry weight (dry wt) of sprayed plants was similar with NO‐3 or branched chain amino acids as main N supply but 28 DAS, shoot dry wt was greater with the amino acid treatment.One DAS, chlorsulfuron caused substantial decreases in extension of the youngest leaf and acetolactate synthase activity and valine content of shoots of plants supplied with NO‐3 or branched chain amino acids. Total amino acid content of shoots was greater in sprayed plants than in unsprayed plants 1 DAS. Acetolactate synthase activity of sprayed plants supplied low NO‐3 returned to normal 14–21 DAS. For sprayed plants transferred from low to high NO‐3 supply 7, 14 or 21 DAS, shoot dry wt 50 DAS increased with increased time of transfer to high NO‐3 while shoot NO‐3 content decreased. Shoot NO3 content of sprayed plants transferred to high NO‐3 supply 7 or 14 DAS was similar to that in unsprayed plants at applied NO‐3 concentrations which inhibited growth. It is concluded that inhibition of acetolactate synthase is likely to be the primary mode of action of chlorsulfuron in this wheat cultivar; data are consistent with the proposal that subsequent NO‐3 accumulation can also inhibit growth.

Growth response ofFestuca altaica,Festuca hallii, andFestuca campestristo temperature

In Alberta, the rough fescue complex consists of Festuca altaica Trin., Festuca hallii (Vasey) Piper, and Festuca campestris Rydb. The potential commercial value of these species for grazing, and their ecological significance, necessitates an increased understanding of their environmental adaptation. This study compared the growth response of the three species at five temperature regimes of 7:3, 12:8, 17:13, 22:18, and 27:23 °C (light:dark; 18-h photoperiod). Seedlings were established and grew for 10 weeks at 18 °C before being trimmed to a height of 3.5 cm and randomly assigned (36 pots of each species) to the growing environments. Growth was followed for 12 weeks. Temperature had a significant effect on most plant variables but the response differed among species. The optimal temperature for dry matter accumulation was 17:13 °C, and for tillering 12:8 to 17:13 °C. Festuca hallii and F. campestris exhibited a faster tillering rate than F. altaica, which had the heaviest tillers and highest leaf extension rate. The root to shoot ratio declined at temperatures above 17:13 °C. The significance of these observations to the geographical distribution of the species is discussed. Key words: rough fescue, defoliation, yield, growth analysis, adaptation.

Temperature sensitivities of Festuca arundinacea Schreb. and Dactylis glomerata L. ecotypes

summaryThe thermal responses of leaf growth and senescence were measured in four populations of Festuca arundinacea Schreb. and three of Dactylis glomerata L. with a range of geographical origins. Leaf extension was quantified by fitting logistic curves to lengths measured for up to 120 d in controlled environments at 20 °C or after transfer to 5 °C at emergence of the fourth leaf. Electronic position transducers were employed to observe rapid adjustments in leaf elongation rate in response to changes in the temperature experienced by the growing zone. Leaf segments were incubated in darkness on a thermal gradient bar giving a range of temperatures between 0 and 20 °C, and chlorophyll and protein were determined after 4 d of senescence. For each process, temperature sensitivities were determined as 010, to give a profile of thermal response for each ecotype. Correlations between processes across ecotypes enabled possible relationships between temperature perception mechanisms to be identified. In their responses to chilling temperatures, mean extension rates measured over a period of one or more plastochrons were not closely related to short‐term rates. There was a significant negative correlation between chlorophyll stability in excised leaf tissue and mean long‐term extension rates. In general, ecotypes from the coldest habitats were the most sensitive to low temperature inhibition.