The influence of temperature on leaf development and growth in potatoes in controlled environments

Three controlled environment experiments were conducted at different temperatures to determine the relation between temperature and leaf development and growth in the potato (cv. Maris Piper). Developmental stages are defined for the appearance and duration of leaf extension in the potato and comparisons made with other temperate zone crops. The rate of leaf appearance was linear over the temperature range (9–25°C) and above 25°C there was no further increase in the rate. The temperature coefficient for the rate of appearance of leaves was 0.032 leaves (degree days)^-1 using a base temperature of 0°C. The duration of extension of an individual leaf decreased with increase in temperature up to 25°C such that the thermal duration was constant at 170 degree days using a base temperature of 0°C for leaf positions 4–10 on the main stem. At higher leaf positions the thermal duration was similar or greater. The advantages and limitations of controlled environment work as a parallel to field experimentation are discussed.     

A thermal time model of post-initiation flower development in the shade plant, cineraria

Effects of temperature on flower development in cineraria cv. Cindy Blue were studied in controlled environment rooms and in glasshouses. The base, optimum and maximum temperatures respectively for progress to macroscopic flower appearance after flower initiation respectively were 1.6°C, 19.3°C and 39.8°C. From these cardinal temperatures, a thermal time requirement for flower appearance after flower initiation was calculated to be 130°Cd. The base, optimum and maximum temperatures for progress to anthesis after flower initiation were respectively 1.7°C, 22.3°C and 37.1°C and from these values, the thermal time required to reach anthesis after flower initiation was calculated to be 555°Cd. No significant difference was demonstrated between thermal times for flower development in plants grown in controlled environment growth rooms or under glasshouse conditions where irradiance and photoperiod varied markedly.     

The effect of flutter on the temperature of poplar leaves and its implications for carbon gain

The leaf temperatures of two poplar species (Populus tremuloides Michx. and P. fremontii Wats.) were characterized by attaching thermocouples to leaves that were either constrained to a fixed position or allowed to flutter naturally. There were no observed temperature differences between fluttering and constrained leaves in the lower canopy, but fluttering leaves at the top of the canopy were as much as 2–4°C cooler than constrained leaves. An increase in heat transfer, a decrease in light interception or both could account for these observed differences in the temperature of fluttering versus constrained leaves. Fluttering can increase the boundary-layer conductance to convective heat exchange by as much as 50 and 20% for laminar and turbulent flow, respectively. The benefit that these leaf temperature differences may provide to the carbon economy of a poplar canopy was dependent on the ambient temperature. Populus fremontii, which is frequently exposed to daytime temperatures exceeding 35°C during summer months in the central valley of California, USA, could show an increase in carbon gain as a result of lower upper canopy leaf temperatures. For aspen, the benefit would be much smaller and often negative because of much lower air temperatures. Lower leaf temperatures may also increase the water use efficiency of poplars. However, the maintenance of lower leaf temperatures may not be the primary adaptive significance of leaf flutter.     

The prediction of leaf canopy expansion in the leek from a simple model dependent on primordial development

In an analysis of leaf development of leek plants grown in the field in 1988, successive leaves initiated, appeared (tip and ligule) and senesced at equal intervals of accumulated temperature/thermal time. These intervals corresponded to a plastochron of 92°C days and phyllochrons of 135 (tip) and 233 (ligule) °C days. The rate of appearance of ligules was exactly equal to the rate of leaf senescence, with the result that the number of fully-expanded leaves per plant remained constant at 1.4. These data, which were compatible with results from previous seasons, were used to develop a model of the interrelationships between primordium initiation at the shoot apex and subsequent events in the development of individual leaves. Primordium initiation is considered to be the primary controlling event in the life of a leaf, and the processes of tip appearance, ligule appearance and death can be predicted from knowledge of the number of primordia which have been initiated, without reference to the environment. A model of canopy expansion, based on the central role of the shoot apex, was developed using the temperature relations of primordium initiation and additional data on leaf expansion and leaf dimensions. Leaf area indices computed in this way provided a satisfactory simulation of the thermal-time course of leaf area index observed in a previous season, 1985.     

Daylength change and leaf appearance in winter wheat

Abstract In the field successive leaves of winter wheat appear at a rate which varies because it depends strongly upon temperature. When plotted against ‘thermal time’, however (temperature accumulated above a fixed base of 0°C), leaf appearance was a strictly linear function of temperature. The mean rate of leaf appearance in thermal time, R′, was faster for a spring sowing than for an autumn sowing. The variation in R′ between sowings was better correlated with the rate at which daylength was changing when the plants emerged than with the mean daylength while leaves were appearing.     

Environmental factors controlling seed germination and seedling recruitment of Stipa bungeana on the Loess Plateau of northwestern China

Germination studies are important for collecting information on field seedling recruitment, plant conservation and restoration. This study investigated the role of light, temperature, nitrogen, water stress and burial depth in controlling germination of Stipa bungeana seeds. S. bungeana seeds are photo-inhibited; light significantly decreased seed germination regardless of temperature and water conditions. Seeds germinated at 10–30° C, and the highest germination was 72 % and 88 % at 20° C in light and dark, respectively. Thermal model analysis showed that presence of light significantly increased average thermal requirement [θ _T (50)] from 105°Cd to 186°Cd at sub-optimal temperature, implying that light delays seed germination. Hydrotime model analysis showed that presence of light caused a shift in the median base water potential [Ψ _b(50)] from ?0.68 to ?0.26 MPa, which partly explains why light decreased both percentage and speed of germination, even at optimal conditions. As burial depth increased, seedling emergence initially increased and then decreased; the highest seedling emergence recruitment was 43 %, for seeds buried at a depth of 1 cm. Field observations showed that seedling emergence occurred primarily from July to September, and scarcely occurred from April to June. These results suggest that the light inhibitory effect is an adaptive mechanism that prevents S. bungeana seeds from germinating on the soil surface. To attain highest seedling establishment, seeds of S. bungeana should be sown at a soil depth of 1 cm prior to the rainy season, using seeds stored for 1 year.     

Genotypic variation in cold tolerance influences the yield of Miscanthus

When grown in Europe, Miscanthus genotypes often produce yields lower than their potential due to late emergence of shoots in the spring or to damage from late frosts when shoots emerge too early. Here, we investigate genotypic variation in the base temperature (T_b) for shoot emergence and in the lethal temperature for shoots (LT₅₀) in four Miscanthus genotypes. In all genotypes, lowering temperature increased the time to shoot emergence, with T_b ranging from 8.6°C in Sac‐5 to 6°C in Sin‐H9. Frost treatments below ?8°C resulted in a marked reduction in growth in all four genotypes. Sin‐H9 was the most frost tolerant with an LT₅₀ of ?9.3°C. There was little variation found in leaf osmotic potential, but leaf moisture content was significantly lower in Sin‐H9 than in the other genotypes. The lower thermal requirement for emergence and lower LT₅₀ seen in Sin‐H9 was incorporated into a model of Miscanthus production. The model showed an extended growing season that was predicted to increase yields by up to 25%.     

Influence of day length and temperature on number of main stem leaves and time to flowering in lupin

A growth chamber experiment was carried out to investigate the influence of day length and temperature on the development of flowering in eight varieties of the three grain lupin species Lupinus albus (Wat and C3396), L. angustifolius (Gungurru, Polonez and W26) and L. luteus, (Juno, Radames and Teo). The plants were grown at two temperatures, 10°C and 18°C, in combination with five daylength regimes: 10, 14, 18, 24 h day at full light intensity and 10 h full light extended with 8 h low intensity light. Increased daylength decreased days from sowing to flowering in all varieties, but had little effect on thermal time to flowering in most varieties. However, C3396, W26 and Radames had a significantly longer thermal time to flowering at high, non‐vernalising temperature (18°C) at short daylengths. Low light intensity daylength extension did not significantly influence thermal time to flowering. For flower initiation, measured as number of leaves on the main stem three types of response were found. All varieties formed fewer leaves on the main stem at 10°C than at 18°C, although the two thermo‐neutral varieties of L. luteus, Juno and Teo, gave only a small response to temperature and daylength. In Polonez, Gungurru and Wat, low temperature decreased leaf number, but there was only a small response to changes in daylength. Three varieties, C3396, W26 and Radames, showed longer thermal time to flowering at 18°C with short daylengths. This could be explained by a greater number of main stem leaves formed at short daylength at non‐vernalising temperatures. Increased daylength decreased leaf number in these varieties, but never to a smaller number than for plants grown at 10°C. In these varieties, low intensity extension of the daylength had a similar (W26, Radames) or decreased (C3396) effect compared to full light extension. The hastening of time to flowering by long days could be separated into two effects: a high light energy effect hastened development by increasing the rate of leaf appearance in all varieties, while low light energy in thermo‐sensitive varieties was able to substitute for vernalisation by decreasing leaf number.     

Plant light interception can be explained via computed tomography scanning: demonstration with pyramidal cedar (Thuja occidentalis, Fastigiata)

BACKGROUND AND AIMS: Light interception by the leaf canopy is a key aspect of plant photosynthesis, which helps mitigate the greenhouse effect via atmospheric CO(2) recycling. The relationship between plant light interception and leaf area was traditionally modelled with the Beer-Lambert law, until the spatial distribution of leaves was incorporated through the fractal dimension of leafless plant structure photographed from the side allowing maximum appearance of branches and petioles. However, photographs of leafless plants are two-dimensional projections of three-dimensional structures, and sampled plants were cut at the stem base before leaf blades were detached manually, so canopy development could not be followed for individual plants. Therefore, a new measurement and modelling approach were developed to explain plant light interception more completely and precisely, based on appropriate processing of computed tomography (CT) scanning data collected for developing canopies. METHODS: Three-dimensional images of canopies were constructed from CT scanning data. Leaf volumes (LV) were evaluated from complete canopy images, and fractal dimensions (FD) were estimated from skeletonized leafless images. The experimental plant species is pyramidal cedar (Thuja occidentalis, Fastigiata). KEY RESULTS: The three-dimensional version of the Beer-Lambert law based on FD alone provided a much better explanation of plant light interception (R(2) = 0.858) than those using the product LV*FD (0.589) or LV alone (0.548). While values of all three regressors were found to increase over time, FD in the Beer-Lambert law followed the increase in light interception the most closely. The delayed increase of LV reflected the appearance of new leaves only after branches had lengthened and ramified. CONCLUSIONS: The very strong correlation obtained with FD demonstrates that CT scanning data contain fundamental information about the canopy architecture geometry. The model can be used to identify crops and plantation trees with improved light interception and productivity.     

Radiation Interception, Partitioning and Use in Grass -Clover Mixtures

Mixed swards of perennial ryegrass /white clover were grownin competition under controlled environmental conditions, attwo temperatures and with different inorganic nitrogen supplies.The swards were studied after canopy closure, from 800 to 1200°C d cumulative temperatures. Clover contents did not varysignificantly during the period. A simulation model of lightinterception was used to calculate light partitioning coefficientsand radiation use efficiencies for both components of the mixturein this controlled environment experiment. Additionally, thissame radiative transfer model was applied to the field datafrom Woledge (1988) (Annals of Applied Biology112: 175 –186)and from Woledge, Davidson and Dennis (1992) (Grass and ForageScience47: 230 –238). The measured and simulated valuesof light transmission, at different depths in the mixed canopy,were highly correlated (P<0.001) with more than 80% of thetotal variance explained. The daily average of photosyntheticallyactive radiation (PAR) interception in a natural environmentwas estimated from simulations, for the field and controlledenvironment data. Under these conditions, white clover capturedsignificantly more light per unit leaf area than perennial ryegrassat low, but not at high, nitrogen supply. In the controlled environment experiment, the radiation useefficiency of the legume was lower than that of its companiongrass. For both species, radiation use efficiency was negativelycorrelated with the mean irradiance of the leaf. The role ofa compensation between light interception and light use forstabilizing the botanical composition of dense grass –cloverswards is discussed. Light interception; radiation transfer model; growth analysis; radiation use efficiency; white clover; perennial ryegrass; Trifolium repensL.; Lolium perenneL.; grassland     

Germination and emergence of Sorghum bicolor. genotypic and environmentally induced variation in the response to temperature and depth of sowing

Abstract The germination of Sorghum bicolor seeds of 9 genotypes was tested at temperatures between 8°C and 48°C on a thermal gradient plate. Samples were tested from three regions of the panicle expected to differ in temperature during grain filling. Seeds of a tenth genotype, SPV 354, produced in controlled-environment glasshouses at different panicle temperatures, were tested similarly. In addition, the emergence of SPV 354 was measured from planting depths of 2 and 5 cm at mean soil temperatures of 15, 20 and 25°C. Four methods of calculating mean germination rate for the nine genotypes were compared. Germination characters like base, optimum and maximum temperature (T_b, T_o, T_m), thermal time (θ)and the germination rate at T_o(R_max showed only small differences between methods. There was a range of genotypic variation in all characters: T_b 8.5–11.9°C; T_o, 33.2–37.5°C; T_m, 46.8–49.2°C; θ, 23.4–38.0°Cd; R_max, 0.69–1.14-d_-1. In contrast, mean germinability (G) was between 90% and 100% over the temperature range 13–40°C. Panicle temperature had no effect on any germination character in SPV 354. However, deeper burial increased θ for emergence and decreased G, irrespective of soil temperature except at 5 cm. Increasing panicle temperature, by reducing seed size, reduced G and increased θ by about 10% only at 15°C and 5 cm depth.     

Trees tolerate an extreme heatwave via sustained transpirational cooling and increased leaf thermal tolerance

Heatwaves are likely to increase in frequency and intensity with climate change, which may impair tree function and forest C uptake. However, we have little information regarding the impact of extreme heatwaves on the physiological performance of large trees in the field. Here, we grew Eucalyptus parramattensis trees for 1 year with experimental warming (+3°C) in a field setting, until they were greater than 6 m tall. We withheld irrigation for 1 month to dry the surface soils and then implemented an extreme heatwave treatment of 4 consecutive days with air temperatures exceeding 43°C, while monitoring whole‐canopy exchange of CO₂ and H₂O, leaf temperatures, leaf thermal tolerance, and leaf and branch hydraulic status. The heatwave reduced midday canopy photosynthesis to near zero but transpiration persisted, maintaining canopy cooling. A standard photosynthetic model was unable to capture the observed decoupling between photosynthesis and transpiration at high temperatures, suggesting that climate models may underestimate a moderating feedback of vegetation on heatwave intensity. The heatwave also triggered a rapid increase in leaf thermal tolerance, such that leaf temperatures observed during the heatwave were maintained within the thermal limits of leaf function. All responses were equivalent for trees with a prior history of ambient and warmed (+3°C) temperatures, indicating that climate warming conferred no added tolerance of heatwaves expected in the future. This coordinated physiological response utilizing latent cooling and adjustment of thermal thresholds has implications for tree tolerance of future climate extremes as well as model predictions of future heatwave intensity at landscape and global scales.     

An analysis of leaf growth in sugar beet.

The responses of leaf appearance and expansion to temperature in sugar beet were measured under controlled conditions, using ruler and auxanometers, to establish a basis for a subsequent analysis of leaf growth in field crops. The studies showed that leaf appearance rate responded linearly to temperature above 1°C, that leaf expansion rate responded likewise above 3°C and that both rates were zero below these base temperatures. Auxanometer measurements of leaf extension showed that daily rates of expansion of leaf area increased linearly with the daily integral of temperature. However, hourly rates of extension in length alternated with those in width during each 24 h cycle in patterns that were not clearly related to hourly changes of temperature or to the day/night sequence.     

Effects of temperature on the development and growth of winter wheat roots

Winter wheat was sown on 2 dates with 3 levels of nitrogen fiertiliser (0, 50 and 200 kg N ha⁻¹) in one year and on 2 sites in a followign season. Shoot and root development and growth were measured between emergence and anthesis in the first season and emergence and 7 mainstem leaves in the second. Differences in temperature and light regime led to significant differences in shoot and root development and growth between sowing dates. A thermal time-scale, based on soil surface or air temperatures, with a base of 0°C, adequately described the production of mainstem leaves and nodal root axes over all treatments. Autumn applied nitrogen had little effect on development. Shoot growth and green area index increased exponentially with thermal time prior to spring nitrogen application and the completion of canopy development. Early-sown crops had larger root systems than late-sown crops prior to winter and this divergence was retained until anthesis. The relationship between root growth and thermal time was little better than with days after sowing and was not improved by either varying the site of temperature measurement or the base temperature used for calculation. Differences in soil texture and drainage, between sites, led to significant changes in root length distribution. Although spring applied nitrogen generally increased root length, its effects were inconsistent. There was a curvilinear relation between root length and the amount of photosynthetically active radiation (PAR) intercepted; this relation was unaffected by sowing date or nitrogen treatment. The amount of root produced per unit PAR decreased as the season progressed, reflecting the decrease in the proportion of total dry matter partitioned to the root system.     

Field Studies of Cereal Leaf Growth: I. INITIATION AND EXPANSION IN RELATION TO TEMPERATURE AND ONTOGENY

Measurements of leaf initiation, appearance, and expansion arepresented for winter wheat and spring barley crops. For winterwheat, these processes occurred during periods of several weekswhen fluctuating temperatures influenced process rates. Analysisof these measurements was facilitated by plotting variablesagainst the time integral of temperature above an appropriatebase temperature (O °C), here called thermal time with unitsof °C d. Leaf primordial number and appearance stage increasedlinearly with thermal time for both winter wheat and springbarley which initiated 12 and 9 leaves respectively. When plottedagainst thermal time 90% of laminar and leaf length growth and80% of laminar width growth was satisfactorily described bya straight line for both species. This enabled an average extensionrate and duration of linear growth to be defined for each leaf.When expressed in thermal time, wheat leaves had a similar durationof linear growth (210 °C d; s.d. 30 °C d) with insolationexerting a negligible influence. The first seven barley leaveshad a shorter duration of linear growth (151 °C d; s.d.8 °C d). For wheat, final leaf length and laminar widthincreased with leaf number and were not apparently associatedwith changes in apical development stage. Changes of barleyleaf dimensions with leaf number were more complex.     

Co-ordination between leaf initiation and leaf appearance in field-grown maize (Zea mays): genotypic differences in response of rates to temperature

BACKGROUND AND AIMS: In maize (Zea mays), early flowering date, which is a valuable trait for several cropping systems, is associated with the number of leaves per plant and the leaf appearance rate. Final leaf number depends upon the rate and duration of leaf initiation. The aims of this study were to analyse the genotypic variation in the response to temperature of leaf appearance rate and leaf initiation rate, and to investigate the co-ordination between these processes under field conditions. METHODS: Sixteen hybrids of different origins were grown under six contrasting environmental conditions. The number of appeared leaves was measured twice a week to estimate leaf appearance rate (leaves d(-1)). Plants were dissected at four sampling dates to determine the number of initiated leaves and estimate leaf initiation rate (leaves d(-1)). A co-ordination model was fitted between the number of initiated leaves and the number of appeared leaves. This model was validated using two independent data sets. KEY RESULTS: Significant (P < 0.05) differences were found among hybrids in the response to temperature of leaf initiation rate (plastochron) and leaf appearance rate (phyllochron). Plastochron ranged between 24.3 and 36.4 degree days (degrees Cd), with a base temperature (Tb) between 4.0 and 8.2 degrees C. Phyllochron ranged between 48.6 and 65.5 degrees Cd, with a Tb between 2.9 and 5.0 degrees C. A single co-ordination model was fitted between the two processes for all hybrids and environments (r2= 0.96, P < 0.0001), and was successfully validated (coefficient of variation < 9 %). CONCLUSIONS: This work has established the existence of genotypic variability in leaf initiation rate and leaf appearance rate in response to temperature, which is a promising result for maize breeding; and the interdependence between these processes from seedling emergence up to floral initiation.     

Temperature Effects on Phenological Development and Yield of Muskmelon

Our goal was to construct a simple muskmelon phenology modelthat could be run with easily obtainable weather station dataand used by growers to quantify phenological development andaid in projecting harvest dates. A growth chamber experimentwas conducted with two cultivars of muskmelon (‘Gold Rush’and ‘Mission’) to determine how main vine leaf appearancerates responded to temperature. We identified three cardinaltemperatures for leaf appearance rate: the base temperature(10 °C) at which leaf appearance rate was zero; an optimumtemperature (34 °C) at which the rate of leaf appearancewas maximal; and an upper threshold temperature (45 °C)at which leaf appearance rate returned to zero. Using thesethree cardinal temperatures, we constructed a simplified thermalunit accumulator for hourly measurements of air temperature.Main vine plastochron interval (PI), thermal time to harvest,and final yield were determined for three cultivars of muskmelon(‘Explorer’, ‘Gold Rush’ and ‘Mission’)grown in the field at Overton, TX, USA, over six transplantingdates from March to June 1998. PI was calculated for each cultivarx transplanting date combination as the reciprocal of the slopeof main vine node number vs. accumulated hourly thermal units(     

The Influence of Temperature and Soil Water Deficit on the Development and Morphology of Groundnut (Arachis hypogaea L.)

The rate/temperature relation of several developmental processesin groundnut was examined in a suite of temperature-controlledglasshouses maintained at mean air temperatures of 19, 22, 25,28 and 31 °C. The sensitivity of the various processes tosoil water deficit was also examined. When the relation between rate and temperature was linear, measurementswere analysed in terms of thermal time (°Cd) and an extrapolatedbase temperature (T_b) at which the rate was zero. T_b was conservative(10 °C) for leaf appearance, branching, flowering, peggingand podding. A higher value of T_b for seedling emergence (16°C) was probably an artifact caused by soil pathogens. Leafappearance and branching were more sensitive to soil water deficitthan the other processes examined. Key words: Temperature, Soil water deficit, Development, Groundnut     

Thermal sensitivity of a Neotropical amphibian (Engystomops pustulosus) and its vulnerability to climate change

A species’ thermal sensitivity and its exposure to climate variation are key components in the prediction of its vulnerability to climate change. We tested the thermal sensitivity of a tropical amphibian that lives in a mild constant climate in which the thermal tolerance range is expected to closely match the experienced environmental temperature. The air temperature that this species is exposed to varies between 21.9 and 31.6°C with an annual mean of 27.2°C. We estimated the microhabitat water temperature variation under vegetation shade, which buffers the temperature by 1.8°C in relation to that of the air, and with open canopy, where the water was 1.9°C warmer than the air temperature. With broods of tadpoles split into five treatments (15°C, 21°C, 28°C, 31°C, and 33°C), we estimated the critical thermal maximum (CTMax) and critical thermal minimum (CTMin) after at least 7 days of acclimation. Both CTMax (42.3°C) and CTMin (11.8°C) were more extreme than the temperature range estimated for the field. We estimated the optimum temperature (T_o = 28.8°C) and the thermal performance breadth (range: 23.3–34.1°C) based on growth rate (g/day). The animals were able to acclimate more extensively to cold than to warm temperatures. These performance curve traits closely matched the air temperature. The estimated vulnerability varied according to the microhabitat prediction model used. The combination of tadpole data on thermal sensitivity and macro‐ and microhabitat variation provides a necessary framework to understand the effects of climate change on tropical amphibians.