The Control of Runner Development in the Strawberry Fragaria ananassa Duch

Factors controlling runnering of strawberry plants were studiedunder controlled and semi-controlled environments. Increasinglylong exposures to conditions favourable for runnering causeda subsequent increase in number of runners, their total length,number of daughters, and of dry matter produced by mother plants.Leaf and crown numbers of the mother plant showed no such parallelincrease. Temperature supplement to foliage, combined with alight interruption in the dark period, produced the greatestvegetative effect-except again on leaf number-when comparedto either factor individually, normal day extension for threehours by itself or combined with temperature supplement. Itwas suggested that the promotive effects of temperature andphotoperiod on runnering were due to increased activation ofvegetative buds on the rosette crown. Upon comparing constantand diurnally fluctuating temperatures under a constant longphoto-period in the phytotron it was found that, while all othermeasured vegetative criteria were closely similar, the totalrunner length produced by plants under fluctuating temperatureswas almost double that of those under constant temperatures.A temperature gradient from root to shoot stimulated vegetativegrowth in comparison to a gradient in the opposite directionand to lack of such gradient, irrespective of whether the temperaturecommon to both root and shoot was high or low. This was interpretedas resulting from either different temperature requirementsfor aerial and subterranean organs or from the occurrence oftranslocation gradients of substances which promote vegetativedevelopment of the shoots, e.g. kinins and gibberellin-likesubstances. The time interval between rooting of daughter plants and onsetof runnering was increased the later the rooting occurred, possiblydue to the advancing seasonal decline in conditions favourablefor vegetative development. The positional influence of theorder of the daughter along the runner chain, which was markedin flowering, was not found.     

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

Wheat plants were grown in columns of soil until early stem elongation at a wide range of constant root temperatures. Two light environments were imposed and three levels of nitrogen fertilizer added at sowing. Shoot and root development and growth were measured by destructive sampling to investigate the combined effects of temperature and changing nutrient and assimilate supply. Both mainstem leaf and root axis production were linearly related to thermal time above a base temperature of 0°C. Low irradiance affected the appearance of mainstem tillers and associated nodal root axes. Nitrogen had little effect on shoot or root development but increased shoot area between 6 and 8 mainstem leaves. Higher temperatures and supplementary light resulted in larger root systems when compared at equivalent times after sowing. Total root length and root dry weight increased exponentially with thermal time, based on the mean of 4 cm soil and 2 cm air temperatures, but no single relation existed for all temperature and light treatments. Total plant dry matter, root length and root dry weight increased linearly with accumulated, intercepted, photosynthetically active radiation. Root growth responded less than the shoot to supplementary light. Increasing temperature reduced the proportion of root weight to total plant weight.     

Mediation of high-temperature injury by roots and shoots during reproductive growth of wheat

Abstract Previous studies suggest that high temperature stress on wheat (Triticum aestivum L.) involves root processes and acceleration of monocarpic senescence. Physiological changes in wheat roots and shoots were investigated to elucidate their relationship to injury from elevated temperatures after anthesis. Plants were grown under uniform conditions until 10 d after anthesis, when shoot/root regimes of 25°C/25°C, 25°C/35°C, 35°C/25°C and 35°C/35°C were imposed. Growth and senescence of shoots and grain were influenced more by root temperatures than by shoot temperatures. High root temperatures increased activities of protease and RNasc enzymes, and loss of chlorophyll, protein and RNA from shoots, whereas low root temperatures had opposite effects. High root temperatures appeared to induce shoot senescence directly. High shoot temperatures probably disrupted root processes, including export of cytokinins, and induced high leaf protease activity, senescence and cessation of grain development. The authors concluded that responses of wheat to high temperatures, whether of roots or shoots, are manifested as acceleration of senescence and may be mediated by roots during grain development.     

Influence of Temperature on Sterol Biosynthesis in Triticum aestivum

Sitosterol, campesterol, stigmasterol, and cholesterol were isolated from green wheat (Triticium aestivum var. Monon) seedlings. Sitosterol was the predominant sterol extracted from the shoot, root, and crown tissue. Cholesterol accounted for less that 1% of sterol in shoot tissue with only trace amounts in the root. A temperature change from 10 to 1 C resulted in a general decrease in sitosterol, stigmasterol, and campesterol in the shoot tissue. The cholesterol level was not altered significantly by the temperature change. The sterols in the root responded in a manner very different from those in the shoots. With the reduction in temperature, sterols first decreased and then recovered over a period of 7 to 14 days to levels that were equal to or exceeded the original levels. From these experiments, it would appear that root tissue can acclimate to the lower temperatures and continue sterol synthesis at the normal rate. The level and response of sterols in the crown tissue were intermediate between the root and shoot tissue. At 10 C the crown response was similar to that of root tissue, whereas, at 1 C the response more closely resembled that of the shoot.     

Temperature effects on hydraulic conductance and water relations of Quercus robur L

The effects of temperature on root and shoot hydraulic conductances (g(shoot) and g(root)) were investigated for Quercus robur L. saplings. In a first experiment, conductances were measured with a High Pressure Flow Meter on excised shoots and detopped root systems. The g(root) and g(shoot) increased considerably with temperature from 0-50 degrees C. Between 15 degrees C and 35 degrees C, g(shoot) and g(root) varied with water viscosity. In a second experiment, the impact of temperature-induced changes in g(root) on sapling transpiration (E) and leaf water potential (psileaf) was assessed. Intact plants were placed in a growth cabinet with constant air and variable soil temperatures. E increased linearly with soil temperature but psileaf remained constant. As a consequence, a linear relationship was found between E and g(plant). The results illustrate the significance of g(plant) for the stomatal control of transpiration and the significance of temperature for tree water transport.     

The Influence of Temperature on Meloidogyne incognita on Soybean

The effects of temperature and initial inoculum density of Meloidogyne incognita on soybean growth and nematode reproduction were investigated in greenhouse temperature tanks and in controlled-growth chambers. The interactions of initial inoculum density (P_i) and soil temperature in effects on shoot growth were adequately described by multiple-regression models. At the highest temperatures (30 or 32/28 C), moderate to high inoculum killed many plants. A P_i of 27,000 eggs/15-cm-diam pot retarded shoot growth at 26 C. Only the greatest P_i (81,000 eggs/15-cm pot) suppressed shoot growth at 18, 22, or 20/16 C. Inoculation with 3,000 or 9,000 eggs/plant resulted in heavier root systems at all temperatures except 30 C. At that temperature, 9,000 eggs suppressed root growth. At 18 and 26 C, a Pi of 81,000 eggs was required to retard root growth. Nematode reproduction was related directly to temperature and P_i except at a density of 81,000 eggs/15-cm pot.     

Effects of Low Temperature on the Development and Morphology of Rye (Secale cereale) and Wheat (Triticum aestivum)

Seedlings of Secale cereale cv. Rheidol and Triticum aestivumcv. Mardler were grown at shoot/root temperatures of 20/20 °C,20/8 °C and 8/8 °C. During vegetative growth both cerealsproduced leaves, tillers and roots in a defined pattern, ata species-specific rate which was linearly related to the temperatureof the shoot meristem. Thus, plant development could be standardizedon a temperature x time (°C d) basis despite contrastinggrowth-temperature treatments. When compared at a similar developmentalstage, the cooling of whole plants or of plant roots resultedin an increase in the d. wt: f. wt ratio of both shoot and roottissues, a decrease in the length of both the longest shootand root, and the development of broader and thicker leaves.Although the effects of temperature on developmental characteristicscould be accurately predicted by an empirical relationship,the effects on morphological characteristics could not. Development, phyllochron, rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoides S. & H.): III. ROOT DEVELOPMENT

This paper examines the use of thermal time (accumulated temperature)to analyse the effects of temperature on the development ofpearl millet. The plants were grown in columns of soil withinstands of millet growing in controlled environment glasshouses.A range of almost constant soil temperatures was maintainedat a number of air temperatures that were allowed to vary sinusoidallythroughout the day. The number of root axes and lateral rootswere counted on several occasions for young plants by destructivesampling of the columns. The results show that root axis and lateral development is relatedto the thermal time measured at the shoot meristem using a basetemperature of 12 ° C. The shoot meristem temperature consistentlyproved to be more closely related to root development than soiltemperature at a depth of 5.0 cm. The difficulty of relating root development to temperature ata particular depth is discussed, together with the problemsof selecting an appropriate base temperature. For the conceptof thermal time to provide a clearer understanding of temperatureeffects on root development, it will be necessary to take accountof possible differences in the thermal response of differentparts of the root system and of other environmental factors,particularly soil water status. Key words: Pennisetum typhotdes, Temperature, Thermal time, Root development     

Partition of photosynthates between shoot and root in spring wheat (Triticum aestivum L.) as a function of soil water potential and root temperature

Low soil water potential and low or high root temperatures are important stresses affecting carbon allocation in plants. This study examines the effects of these stresses on carbon allocation from the perspective of whole plant mass balance. Sixteen-day old spring wheat seedlings were placed in a growth room under precisely controlled root temperatures and soil water potentials. Five soil water potential treatments, from −0.03 MPa to −0.25 MPa, and six root temperature treatments, from 12 to 32°C were used. A mathematical model based on mass balance considerations was used, in combination with experimental measurements of rate of net photosynthesis, leaf area, and shoot/root dry masses to determine photosynthate allocation between shoot and root. Partitioning of photosynthates to roots was the lowest at 22–27°C root temperature regardless soil water potential, and increased at both lower and higher root temperatures. Partitioning of photosynthates to the roots increased with decreasing soil water potential. Under the most favourable conditions, i.e. at −0.03 MPa soil water potential and 27°C root temperature, the largest fraction, 57%, of photosynthates was allocated to the shoots. Under the most stressed conditions, i.e. at −0.25 MPa soil water potential and 32°C root temperature, the largest fraction, more than 80%, of photosynthates was allocated to roots.     

Development of Frost Tolerance in Winter Wheat as Modulated by Differential Root and Shoot Temperature

Abstract: Winter wheat plants ( Triticum aestivum L. cv. Urban), grown in nutrient solution, were exposed to differential shoot/root temperatures (i.e., 4/4, 4/20, 20/4 and 20/20 C) for six weeks. Leaves grown at 4C showed an increase in frost tolerance from - 4C down to - 11 C, irrespective of root temperature. In 4/20 C plants, high root temperature decreased the rate of hardening of the leaves, but did not influence the final level of frost tolerance. In roots grown at 4C frost tolerance increased from - 3 C down to - 4 C, independently of shoot temperature. An accumulation of soluble sugars in the leaves was only observed when both shoot and root were grown at 4C and was not correlated with final frost tolerance achieved. However, the rate of hardening was correlated with the soluble sugar concentration. An increase in root soluble sugar concentration was exclusively observed in roots exposed to a temperature of 4C, irrespective of shoot temperature. Proline concentration only increased in plant parts exposed to a temperature of 4C. The present results indicate that the importance of root temperature in low-temperature hardening of winter wheat is limited, even though exposure to differential root and shoot temperatures brought about pronounced changes in growth, soluble sugar concentration, insoluble sugar concentration and proline concentration in roots and leaves.     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Root contraction helps protect the "living rock" cactus Ariocarpus fissuratus from lethal high temperatures when growing in rocky soil

? Premise of the study: We investigated how the "living rock" cactus Ariocarpus fissuratus, like other low-growing desert plants, can endure potentially lethal high temperatures at the soil surface. Specifically, we examined how shoot descent by root contraction in the presence or absence of soil rocks influences shoot temperatures and transpiration. ? Methods: Root contraction was identified by measuring shoot descent and anatomical analysis. Temperatures and transpiration were measured for plants at two heights in sandy and rocky soil, and temperature tolerances were determined by vital staining. ? Key results: Plants embedded in rocky soil survived an extreme heat episode, unlike plants in sandy soil, though rocks did not moderate low temperatures. Root contraction occurred regardless of season and soil moisture. Xylem conduits (wide-band tracheids) formed a compressible lattice that decreased root length as rays enlarged the root base radially. Plant position in the soil did not affect transpiration. ? Conclusions: Contractile roots pulled plants of A. fissuratus into the soil at rates of 6-30 mm yr(-1). Maintaining shoots level with the soil surface kept plant temperatures below the high lethal temperature and improved survivorship in soil shaded by surface rocks.     

Root and shoot elongation of rhizotron-grown seedlings of Eucalyptus nitens and Eucalyptus globulus in relation to temperature

Information on the growth response of a crop plant in relation to temperature can be helpful in selecting genotypes to suit local environments, scheduling favourable time of planting and forecasting growth and yield. To determine the effects of varying temperature on root and shoot elongation of eucalypt seedlings, elongation rates of roots and shoots were measured in rhizotrons for two species (Eucalyptus nitens (Deane and Maiden) Maiden, and Eucalyptus globulus Labill.) at a temperature range of 5–23 °C. Within this range of temperatures, elongation rates of roots and shoots of both species increased with an increase in temperature. Roots of E. globulus were more sensitive and shoots less sensitive to temperature than those of E. nitens. However, the threshold temperature corresponding with zero elongation rate predicted from the regression of elongation rate against temperature was similar for the roots (∼5 °C) and shoots (∼0 °C) of both species. Hysteresis did not appear to have a significant influence on root or shoot elongation of both species during warming compared with cooling. Results are discussed highlighting the importance of the interaction between development and growth of plant components.     

Factors in the physical and biological environment affecting nodulation and nitrogen fixation by legumes

Summary The effects of root temperature on the four main stages of nodule formation and function are reviewed. Compared with results obtained under optimal conditions, lower root temperatures retard root hair infection more than they affect nodule initiation, nodule development (including bacteroid tissue development and degeneration), or nitrogen assimilation. Higher root temperatures upset the formation of bacteroid tissue and hasten its degeneration. Tropical and subtropical legumes have higher minimum temperatures for nodule formation than temperate species. Low and high shoot temperatures affect nodulation and nitrogen fixation, but the effect is less severe than that of similar root temperatures. Various approaches to minimise adverse environmental effects are considered. These include the selection of appropriate biological material (both host plants and bacterial strains) for the prevailing conditions, and the adoption of management practices designed to utilise the environment or to minimise its adverse effects. The importance of increase in bacteroid volume in relation to increase in rate of nitrogen fixation is considered, and the concept of compensation in nodule production and activity is examined. The limited information on defoliation effects on the nodulation of both temperate and tropical legumes is reviewed and aspects requiring examination are discussed.     

The Effect of Root and Shoot Temperatures on Growth of Ceanothus greggii Seedlings

The effect of varying independently nutrient solution temperature(5, 15, 25 C) and air temperature (10, 20, 30 C) on hydroponicallygrown Ceanothus greggii (Rhamnaceae) seedlings was studied.Increasing both air and solution temperatures caused higherroot and shoot biomass and larger root and leaf areas. Root/shootbiomass ratio increased with increasing solution temperatureand decreased with increasing air temperature. The surface areaof individual leaves decreased with higher air temperaturesbut did not change with solution temperatures. These resultsare opposite to what is predicted from Davidson's balanced rootand shoot activity model. We suggest that nutrient solutiontemperature directly affected root growth and that air temperaturedirectly affected shoot growth. Ceanothus greggii (Trel.) Jeps., root temperatures, soot temperature, plant growth, biomass allocation     

Interactive effects of soil temperature, atmospheric carbon dioxide and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth

Nutrient requirements for plant growth are expected to rise in response to the predicted changes in CO(2) and temperature. In this context, little attention has been paid to the effects of soil temperature, which limits plant growth at early stages in temperate regions. A factorial growth-room experiment was conducted with winter wheat, varying soil temperature (10 degrees C and 15 degrees C), atmospheric CO(2) concentration (360 and 700 ppm), and N supply (low and high). The hypothesis was that soil temperature would modify root development, biomass allocation and nutrient uptake during vegetative growth and that its effects would interact with atmospheric CO(2) and N availability. Soil temperature effects were confirmed for most of the variables measured and 3-factor interactions were observed for root development, plant biomass components, N-use efficiency, and shoot P content. Importantly, the soil temperature effects were manifest in the absence of any change in air temperature. Changes in root development, nutrient uptake and nutrient-use efficiencies were interpreted as counterbalancing mechanisms for meeting nutrient requirements for plant growth in each situation. Most variables responded to an increase in resource availability in the order: N supply >soil temperature >CO(2).     

Carbon and nitrogen assimilation and partitioning in soybeans exposed to low root temperatures

Low root temperature effects on vegetative growth of soybean (Harosoy 63 × Rhizobium japonicum USDA 16) were examined in 35 day old plants exposed to temperatures of 15°C (shoots at 25°C) for an 11 day period. Duing this period various aspects of C and N assimilation and partitioning were monitored including shoot night and nodulated root respiration, C and N partitioning to six plant parts, C₂H₂ reduction, H₂ evolution, leaf area, transpiration, net photosynthesis, and N₂ fixation. The low temperature treatment resulted in a decrease in the net rate of N₂ fixation but nitrogenase relative efficiency increased. In response, the plant retained N in the tissues of the nodulated root and decreased N partitioning to young shoot tissues, thereby inducing the remobilization of N from older leaves, and reducing leaf area development. The leaf area specific rate of net photosynthesis was not affected over the study period; however, shoot and nodulated root respiration declined. Consequently, C accumulated in mature leaves and stems, partly in the form of increased starch reserves. Three possibilities were considered for increasing low temperature tolerance in nodulated soybeans: (a) decrease in temperature optima for nitrogenase, (b) increased development of nodules and N₂ fixation capacity at low temperature, and (c) alterations in the pattern of C and N partitioning in response to low temperature conditions.     

Differences between maize and wheat in growth-related nutrient demand and uptake of potassium and phosphorus at suboptimal root zone temperatures

The effects of low root zone temperatures (RZT) on nutrient demand for growth and the capacity for nutrient acquisition were compared in maize and wheat growing in nutrient solution. To differentiate between direct temperature effects on nutrient uptake and indirect effects via an altered ratio of shoot to root growth, the plants were grown with their shoot base including apical shoot meristem either within the root zone (low SB), i.e. at RZT (12°, 16°, or 20°C) or, above the root zone (high SB), i.e. at uniformly high air temperature (20°/16° day/night).At low SB, suboptimal RZT reduced shoot growth more than root growth in wheat, whereas the opposite was true in maize. However, in both species the shoot growth rate per unit weight of roots, which was taken as parameter for the shoot demand for mineral nutrients per unit of roots, decreased at low RZT. Accordingly, the concentrations of potassium (K) and phosphorus (P) remained constant or even increased at low RZT despite reduced uptake rates.At high SB, shoot growth at low RZT in both species was higher than at low SB, whereas root growth was not increased. At high SB, the shoot demand per unit of roots was similar for all RZT in wheat, but increased with decreasing RZT in maize. Uptake rates of K at high SB and low RZT adapted to shoot demand within four days, and were even higher in maize than in wheat. Uptake rates of P adapted more slowly to shoot demand in both species, resulting in reduced concentrations of P in the shoot, particularly in maize.In conclusion, the two species did not markedly differ in their physiological capacity for uptake of K and P at low RZT. However, maize had a lower ability than wheat to adapt morphologically to suboptimal RZT by increasing biomass allocation towards the roots. This may cause a greater susceptibility of maize to nutrient deficiency, particularly if the temperatures around the shoot base are high and uptake is limited by nutrient transport processes in the soil towards the roots.     

Clouds homogenize shoot temperatures,transpiration, and photosynthesis within crowns of <Emphasis Type="Italic">Abies fraseri</Emphasis> (Pursh.) Poiret

Multiple studies have examined the effects of clouds on shoot and canopy-level microclimate and physiological processes; none have yet done so on the scale of individual plant crowns. We compared incident photosynthetically active radiation (PAR), leaf temperatures, chlorophyll fluorescence, and photosynthetic gas exchange of shoots in three different spatial locations of Abies fraseri crowns on sunny (clear to partly cloudy) versus overcast days. The field site was a Fraser fir farm (1038 m elevation) in the Appalachian mountains, USA. Ten saplings of the same age class were marked and revisited for all measurements. Sunny conditions corresponded with 5–10× greater sunlight incidence on south-facing outer shoots compared to south-facing inner and north-facing outer shoots, which were shaded and received only indirect (diffuse) sunlight. Differences in spatial distribution of irradiance were mirrored in differences in shoot temperatures, photosynthesis, and transpiration, which were all greater in south-facing outer shoots compared to more shaded crown locations. In contrast, overcast conditions corresponded with more homogeneous sunlight distribution between north and south-facing outer shoots, and similar shoot temperatures, chlorophyll fluorescence (ΦPSII), photosynthesis, and transpiration; these effects were observed in south-facing inner shoots as well, but to a lesser extent. There was no significant difference in conductance between different crown locations on sunny or overcast days, indicating spatial differences in transpiration under sunny conditions were likely driven by leaf temperature differences. We conclude that clouds can affect spatial distribution of sunlight and associated physiological parameters not only within forest communities, but within individual crowns as well.     

Biology and Pathogenicity of Pratylenchus neglectus on Alfalfa

Pratylenchus neglectus reduced the growth of alfalfa cultivars in greenhouse and growth chamber studies. Inocula (1,000, 5,000 and 10,000 nematodes per plant) reduced shoot dry weights of Ranger by 16, 27, and 40%, of Lahontan by 16, 32, and 40%, and of Nevada Synthetic XX (Nev Syn XX) by 18, 26, and 37%, respectively, at 26 ñ 2 C. Pratylenchus neglectus at 1,000 nematodes per plant reduced Ranger shoot dry weights by 5, 12, 18, and 27%, at 15, 20, 25, and 30 C, respectively, whereas 5,000 nematodes per plant reduced shoot dry weights by 12, 17, 26, and 38%, respectively, at similar temperatures. Reductions in dry root weights were directly related to reductions in shoot growth. At 1,000 nematodes per plant, Ranger root dry weights were reduced by 3, 14, 40, and 40%, whereas 5,000 nematodes per plant reduced root dry weight by 25, 31, 59, and 63%, respectively, at similar temperatures. Similar results were observed on Lahontan and Nev Syn XX at the same inoculum levels and soil temperatures. Nematode reproductive indices (final nematode population per plant divided by initial nematode inoculum per plant) were higher at 1,000 nematodes per plant than at 5,000 nematodes per plant, were positively correlated with temperature, and were unaffected by cultivar.