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%.     

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.     

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.