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1.
D. C. E. Wurr Angela J. Hambidge G. P. Smith 《The Journal of Horticultural Science and Biotechnology》2013,88(3):415-426
SummaryThe effects of temperature, duration of temperature, growth stage, rate of cooling, daylength during raising, shading, seed quality, moisture stress and sowing date on blindness in calabrese cv. Marathon were investigated in eight experiments over three years. Of these only batches of plants raised throughout the winter produced appreciable levels of blindness. The incidence of the disorder varied from zero to 80% in plants which received no specific supplementary cold treatment. High levels of blindness were strongly associated with low solar radiation in the period just before plants went blind and were less well associated with low temperatures in the same period. However, it is not possible to separate effects of light and temperature in these data. There are suggestions that competition between leaves for limited assimilate may be responsible for switching off leaf production. 相似文献
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Water scarcity in the Mediterranean basin in addition to the extension of irrigated lands is one of the main factors limiting agricultural development. The need for supplementary irrigation of the Chemlali olive cultivar (Olea europaea L.) during summer and autumn periods was investigated. Leaf water content, gas exchange parameters, fruit development and yield in rain-fed and in irrigated plants have been monitored in 12-year-old olive trees grown under environmental conditions in semi arid regions characterized by high temperatures and high light intensity. Trees were subjected to three irrigation treatments, T0, T1 and T2 corresponding respectively to 0, 33 and 66% of crop evapotranspiration (ETc) by a drip irrigation system. The water deficit during the summer (from June to August) led to the decrease of soil moisture, leaf water content and gas exchange parameters. Irrigated trees showed the same slow activity in the three summer months as the rain-fed trees. For all treatments, net CO2 assimilation, stomatal conductance and transpiration rates were markedly decreased by environmental conditions (high air temperature and high light intensity) during the summer period. At the partial active growth phase of the Chemlali olive cultivar (September–November), a significant re-increase in all parameters was observed. However, net photosynthesis and stomatal conductance of control plants (T0) were, respectively, 57 and 40% lower than those of plants conducted under milder water contribution (T1). The decrease of physiological activity in irrigated plants during hot and dry (summer time) and cold (winter) seasons was a clear evidence that water supply during such periods will be without a great benefit for photosynthetic activity, and thus growth, if applied under critical conditions inducing the rest phase of the plant. The non-statistically significant slight differences as well in photosynthetic performances activities (Pn, Gs and E rates), as in olive production between the two irrigated treatments will not cover the expenses of water loss when applying irrigation at 66% of ETc especially in arid region characterized by scant and irregular rainfall. On the light of these results, we can conclude that the irrigation of this species during the vegetative growth phase (in spring and autumn), and stopping it during the olive rest phase (in summer and winter) could be recommended at least under the experimental conditions of this study; and that the contribution of 600 mm of water per year (33% of ETc) can respond to the needs of the Chemlali olive cultivar in a semi arid region without impairing photosynthetic activity and olive production. 相似文献
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To quantify the effects of climate change on fruit production in Germany, this study aimed at determining long-term trends in winter chill, as calculated with the Chilling Hours and Dynamic Models (Chill Portions). An idealized daily temperature curve was used to convert daily temperature records from 43 weather stations, taken throughout the twentieth and late nineteenth centuries, into an hourly dataset, which was then converted to units of winter chill. Besides exposing temporal trends in winter chill, the data could be spatially interpolated, yielding contiguous maps of typical winter chill in Germany around 2010, as well as chilling losses since 1950. Throughout Germany, winter chill varied between 1700 and 3000 Chilling Hours or 125 and 150 Chill Portions. The areas of highest winter chill were located in the northern parts of the country. For the whole of Germany, there were no significant temporal trends. The extent of interregional variation in winter chill depended on the chilling model used. While the Chilling Hours Model showed strong declines in winter chill for the areas around Dresden and Leipzig, as well as for the Lake Constance region, the Dynamic Model did not detect such dramatic changes. More than a decline in winter chill, increased heat during the winter months might become a challenge to German fruit growers. As already experienced during the extraordinarily warm winter of 2006/07, warm temperatures during the winter can cause fruit trees that fulfill their chilling requirements relatively early to bloom prematurely. This can then lead to elevated risk of frost damage and hamper the homogeneity of flowering. 相似文献
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Modular green roofs were investigated to better understand surface and membrane level temperature expectations of unirrigated green roofs during hot summer conditions in south-central Texas. We used three succulent monocultures, Sedum kamtschaticum, Delosperma cooperi, Talinum calycinum syn. Phemeranthus calycinus and one unplanted control module, each replicated 3 times. Media surface and below media temperatures were monitored, as well as soil water content and general weather conditions (RH, air temperature). Temperatures at the surface and below the media surface were compared with temperatures of a standard roof surface. We found that diurnal surface temperature reductions were very stable throughout the summer. Much larger temperature reductions were achieved below the modules than at the soil surface. Temperature reductions at the soil surface were predominantly driven by soil volumetric water content (VWC) and, to a lesser degree, air temperature while species and percent cover had small modifying effects through interactions with VWC and air temperature. Temperature reductions below the modules were driven by surface soil temperature, while increasing VWC led to a small decrease in temperature reductions at the membrane level. Mean daily temperature reductions achieved were 18.0 °C at the soil surface and 27.5 °C below the module, thus demonstrating that unirrigated, succulent-based green roofs can provide significant rooftop temperature reductions during hot, dry summer conditions. 相似文献
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This study investigated the weather effect on thermal performance of a retrofitted extensive green roof on a railway station in humid-subtropical Hong Kong. Absolute and relative (reduction magnitude) ambient and surface temperatures recorded for two years were compared amongst antecedent bare roof, green roof, and control bare roof. The impacts of solar radiation, relative humidity, soil moisture and wind speed were explored. The holistic green-roof effect reduced daily maximum tile surface temperature by 5.2 °C and air temperature at 10 cm height by 0.7 °C, with no significant effect at 160 cm. Green-roof passive cooling was enhanced by high solar radiation and low relative humidity typical of sunny summer days. High soil moisture supplemented by irrigation lowered air and vegetation surface temperature, and dampened diurnal temperature fluctuations. High wind speed increased evapotranspiration cooling of green roof, but concurrently cooled bare roof. Heat flux through green roof was also weather-dependent, with less heat gain and more heat loss on sunny days, but notable decline in both attributes on cloudy days. On rainy days, green roof assumed the energy conservation role with slight increase instead of reduction in cooling load. Daily cooling load was 0.9 kWh m?2 and 0.57 kWh m?2, respectively for sunny and cloudy summer days, with negligible effect on rainy days. The 484 m2 green roof brought potential air-conditioning energy saving of 2.80 × 104 kWh each summer, equivalent to electricity tariff saving of HK$2.56 × 104 and upstream avoidance of CO2 emission of 27.02 t at the power plant. The long-term environmental and energy benefits could justify the cost of green roof installation on public buildings. 相似文献
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The effect of various environmental factors on flowering of gladiolus. III. Temperature and moisture
Under conditions of low light intensity in winter, low temperatures (1–4°C) increase the occurrence of flower blasting. This chilling damage was observed at two developmental stages — immediately after planting and at the 7th leaf stage when spike emergence starts. Gladioli are extremely tolerant to high temperatures (up to 50 °C) as long as air humidity and soil moisture are at an optimum. The damaging effect of high temperature is generally indirect via its effect on plant water balance. Plants were directly damaged by high temperature during the period from planting to the first leaf stage. Decrease in soil moisture reduced flowering at most stages of development. The stages immediately after planting and just before spike emergence were the most sensitive. 相似文献
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Brownfield sites (e.g., wastelands, disused industrial grounds and power stations) are valuable refuges for urban birds during the breeding season. This owes to the presence of vegetation in different stages of succession, which provide a high diversity of food and breeding resources. However, insufficient research has explored their winter value, when temperatures are lower and food is scarcer. Accordingly, 342 bird and habitat surveys were conducted in brownfield sites, and other land-uses, across Greater Manchester. Bird density estimates were then calculated using Distance software and bird-habitat associations were analysed using Canonical Correspondence Analysis (CCA). Moreover, the impact of brownfield site development on winter bird density from 2000 to 2009 in Greater Manchester was explored using the bird density estimates, and historical image function in Google Earth. In brownfield sites, Pica pica had the highest density estimate (142 per km2), although four species had estimated densities > 100 per km2 (Turdus merula; Cyanistes caeruleus; Passer domesticus; Aegithalos caudatus). The CCA indicated that Aegithalos caudatus, Cyanistes caeruleus, Parus major, Prunella modularis were associated with Fagus sylvatica, Betula pendula, and Buddleja davidii on brownfield sites, which during the winter 1) produce seeds 2) support overwintering insects, providing a valuable food source. Nevertheless, across land-uses, most species favoured green space and pre-2000 housing. Brownfield sites were most replaced between 2000 and 2009, with 17.8 km2, 14.9 km2, and 12 km2 replaced by commercial, industrial, and post-2000 housing respectively. This is likely to have had a negative impact on the winter density of most bird species, owing to 1) the removal of brownfield site vegetation 2) increases in impervious land cover. Future declines in winter bird abundance could be mitigated by retaining brownfield site vegetation and setting aside brownfield sites in close proximity to green space and pre-2000 housing. 相似文献
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A. C. Bunt 《The Journal of Horticultural Science and Biotechnology》2013,88(4):467-477
The effect of seasonal variation in the glasshouse environment on the initial growth rate of the carnation has been determined from the increase in dry weight of rooted cuttings of the cultivar White Sim grown for a 27-day period ; observations were repeated at 14-day intervals over a period of one year.Absolute growth rates varied over the season by a factor of ten, values ranging from approximately 0.01 g day-1 in winter to 0.1 g day-1 in summer. Growth rate was found to be a linear function of the mean daily radiation flux density during the growing period; shade-grown plants which received only 50% of the normal radiation showed a corresponding reduction in growth rates. The regression coefficients of absolute growth rate on radiation were similar for both full-light and shade-grown plants. Absolute growth rates showed a curvilinear relationship with respect to the glasshouse mean air temperature.Relative growth rates of plants grown under full radiation ranged from 1% per day in winter to 4.5% per day in summer. 相似文献
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Recent studies have emphasized the presence of microclimates in urban settings, but most do not have the high resolution observations necessary to understand the interactions taking place at a neighborhood scale. This study used a network of 10 identical weather stations and high resolution land cover data in Knoxville, Tennessee, to analyze the microclimates of a medium-sized city with a temperate climate. Two stations were installed in each of four urban neighborhoods in locations with varying localized tree cover, and two additional stations were installed in the center of downtown and in a nearby urban nature center. The intra-neighborhood results suggested that there is significant temperature variability within a single neighborhood based on the tree canopy density immediately surrounding a given weather station. However, the inter-neighborhood variability (differences between neighborhoods) was similar in magnitude, which suggests that the overall differences in neighborhood characteristics also have an effect on climate. Land cover at the neighborhood scale (in particular tree canopy percentages at the 500-m radii) had the highest correlation with the minimum daily temperature (Tmin) during the summer season. Maximum daily temperature (Tmax) relied most on the distance of each station from Downtown and the amount of impervious area in the 50 m surrounding each station. Tmax was also most influenced by surrounding land cover during dry conditions (a Dry Moderate air mass). Overall, highly localized impervious land cover percentages and larger-scale forested canopy were important in explaining temperature fluctuation, pointing to the importance of scale in microclimate assessments. Dry air masses enhanced the relationship between land cover and temperature during the day, while moist air masses did the same overnight. These data can be used to better inform planning strategies to build resiliency to extreme heat into urban environments by considering the influence of tree canopy. 相似文献
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G. I. Moss 《The Journal of Horticultural Science and Biotechnology》2013,88(4):549-558
Rose cvs Ilona, Mercedes and Sonia, budded onto R. multiflora rootstock, were grown using the nutrient film technique. A root-zone temperature of 25°C was compared with ambient root temperatures at three night-time air temperatures of 18°, 12° and ambient (9°C), and in two other experiments at 18°, 14° and 10°C. Bloom yield and stem length and diameter were recorded for a 22-week winter/spring period and for shorter periods in the following summer. In Experiment 1 Sonia responded to root zone warming (RZW) by giving 44% more blooms and a 26% increase in stem length compared with ambient root temperature. Ilona gave a yield response only at a night temperature of 12°C, but RZW resulted in 22% longer stems. Mercedes gave 22% more blooms from RZW. Plants from Experiment 1 were used for a second year in Experiment 2. Mercedes produced 113% more blooms from RZW, Sonia 61% and Ilona 42%. Stem lengths were all increased by 6-7%. Experiment 3 used first-year plants. The pattern of yield response to RZW was similar to the other experiments. Mercedes gave 61%, Sonia 24% and Ilona 18% more blooms. Ilona showed the largest increase in stem length (24%). RZW increased the amplitude of the growth flushes, but their frequency was unaffected. Yields during the subsequent summer, when temperature differences between RZW and ambient temperatures were small, indicated residual effects of the winter treatments. Sonia (Experiment 1), and Mercedes and Sonia (Experiment 2) gave significantly higher yields from the RZW treatments. There was no evidence for a decrease in yield caused by RZW, only Ilona in Experiment 3 giving a lower yield in the summer. 相似文献
12.
T. W. Hegarty 《The Journal of Horticultural Science and Biotechnology》2013,88(1):133-146
Calabrese, carrot, onion and red beet seeds were sown at approximately weekly intervals throughout the spring and early summer of 1972–4. In a situation where soil tilth and seed placement in the soil were apparently non-limiting, regression analysis showed that in eight of the twelve crop × year combinations there were no significant relationships between seedling emergence and soil moisture or temperature at sowing. In 1972 emergence levels of beet and calabrese were depressed by either excess or lack of soil moisture at sowing, and calabrese emergence was positively related to temperature; in 1973 and 1974 onion emergence was negatively related to temperature at sowing. Rainfall occurring shortly after sowing was identified as a major factor causing emergence problems, apparently through the formation of a soil cap, but its effect varied with crop type, seed vigour and soil moisture content at the time of seedling emergence. The results suggest that low plant stands often found in agricultural practice may be due not to soil temperature or moisture, factors dependent largely upon the weather, but to soil tilth, fertilizer level, seed or soil infection, seed drill performance and seed vigour, over all of which except the last there is, theoretically, some control. 相似文献
13.
H. Jonkers 《Scientia Horticulturae》1979,10(2):149-154
In 2 experiments, apple and pear trees were grown in growth chambers and air conditioned greenhouses at a range of constant temperatures from 9 to 25° C during spring and summer. After the dormant buds had received a marginal chilling-period, bud break and leaf development were studied. A tendency was observed for the dormancy to be deeper when the temperature at which the buds were formed had been higher. The maximum retardation of bud break was observed in buds formed at 18 and 21° C. The hypothesis is put forward that the phenomenon of “delayed foliation” is not only due to insufficient chilling during winter but also to high temperatures during the preceding summer. 相似文献
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Plant selection for extensive green roofs has largely been based on cool, temperate climate research. However, as green roof implementation in hotter and drier climates increases, there is a need to evaluate plant performance under these climatic conditions. Succulents have been shown to be successful in hot and dry green roofs, although survival differs between species and the role of leaf succulence in survival has not been fully explored. For non-succulent plants, habitats with conditions similar to green roofs (‘habitat templates’) have been used to select plants, although few studies have discussed the performance of these selections under green roof conditions. Therefore, we evaluated establishment of 32 plant species on an unirrigated extensive (125 mm deep) green roof in Melbourne, Australia over a 42 week period (from winter through summer into autumn). Plants were selected on the basis of life-form, succulence, appropriate habitat templates and/or successful use on green roofs internationally. Climatic conditions during the experiment were often extreme, with evaporation regularly exceeding rainfall and a hot and dry summer (mean maximum air temperature 35 °C and 80.6 mm total rainfall), leading to roof temperatures of 65 °C. After 42 weeks, only succulent plants remained alive and only three of the succulent species had 100% survival. Survival was positively related to the degree of leaf succulence (g H2O leaf area cm−1) making this a useful trait for plant selection for unirrigated green roofs in hot, dry climates. The failure of most species, despite being chosen from appropriate habitats, demonstrates the need to evaluate potential plants on green roofs under extreme climatic conditions. Supplementary irrigation may be essential to sustain non-succulent species during extreme weather in hot and dry climates. 相似文献
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以‘寒富’苹果园为对象,研究不同覆盖方式包括冬季修剪枝条(粉碎枝条埋土(I)和成段枝条埋土(Ⅱ))和夏季修剪枝条(绿枝埋土(Ⅲ)和绿枝(Ⅳ))对果园土壤水分、养分和酶活性的影响。结果表明:苹果枝条覆盖能增加果园土壤水分含量,对土壤养分和土壤酶活性的影响不同。夏季修剪枝条覆盖土壤有机质、碱解氮、速效磷、速效钾含量以及土壤酶活性均高于冬季修剪枝条覆盖,总体上表现为绿枝覆盖>绿枝埋土覆盖>成段枝条覆盖>粉碎枝条埋土覆盖>清耕。因此,夏季修剪枝条可直接作为覆盖材料进行果园地表覆盖,冬季修剪的苹果枝条应剪成段埋土覆盖。 相似文献
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Context
Land-use legacies play an important role in shaping contemporary species distributions. However, land-use legacies are rarely considered in species distribution models (SDMs) that aim to model present-day species distributions across the landscape, even though they can lead to a species absence in suitable areas. SDMs that do not account for land-use legacies will likely result in biased predictions of species distributions.
ObjectiveWe examine the importance of land-use legacies for modeling present-day distributions of tree species at a regional scale, assessing how the addition of land-use legacy variables improves predictive power of SDMs.
MethodsWe generated land-use legacy variables using raster layers of reconstructed historical agricultural land use and 3310 inventory plots. SDMs were developed for six forest tree species based on climatic, edaphic, and topographic variables, and with (SDMLU) and without (SDMBase) land-use legacy variables. We compared the predictive power between SDMLU and SDMBase models and then quantified the local importance of land-use legacy variables relative to other abiotic variables.
ResultsOur results show that the importance of land-use legacy variables for present-day species distributions and the improvement on the predictive power of SDMs is species-specific. The inclusion of land-use legacy variables improved SDMs primarily by lowering errors of commission and increasing the overall accuracy of prediction.
ConclusionThe influence of land-use legacies on SDMs suggests that, for some tree species, incorporating land-use legacies can accurately identify suitable areas that are not occupied by the species due to land-use legacies, and advance our understanding of their present-day distributions.
相似文献19.
Wei-Hai Yang Xiao-Chuan Zhu Si-Cong Deng Hui-Cong Wang Gui-Bing Hu Hong Wu Xu-Ming Huang 《Scientia Horticulturae》2010
Fruit development was investigated in the field in over-winter off-season (bloomed in late November) and on-season (bloomed in mid April) longans (Dimocarpus longan Lour. cv. Chuliang) in 2004–2005 and 2007–2008 crops, and in potted trees grown in phytotrons set at cold (15/10 °C, day/night, simulating winter) or warm temperatures (28/23 °C, day/night) in 2008. Development of fruit in both on-season and off-season longans could be divided into two stages based on the pattern of fresh weight increase. Stage I was characterized by the slow fruit growth, and Stage II by rapid fruit growth with aril expansion. Off-season longan had a longer period of fruit development than on-season longan, chiefly due to a longer Stage I. The development of off-season fruit, especially in Stage I, was exposed to low and abruptly fluctuating temperatures. In contrast, the temperatures during on-season fruit growth were warmer and less fluctuating. Off-season fruit were smaller with a significantly higher fruit drop. Intensive fruit drop did not occur during cold period until temperature had risen. Fruit cracking in off-season longan was severe (27.6%) in 2004–2005 with a dry and cold winter, but negligible in 2007–2008 with a wet and cold winter. In phytotron experiment, trees exposed to the cold temperature regime during early fruit development produced significantly smaller fruit compared to those exposed to the warm temperature regime (6.2 g vs 7.3 g), while there was no significant difference in fruit drop rate and cracking incidence. The results suggested temperatures lower than 15 °C were stressful for the growth of young fruit and reduced the growth potential and thus fruit size. Severe fruit drop in over-winter off-season longan might be associated with stressful cold plus abrupt temperature fluctuations, while severe fruit cracking in over-winter off-season longan might be related to cold and dry weather in the winter. 相似文献
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Plant florogenesis is determined by the interaction between the genetics of the individual plant and environmental factors. Flower initiation and development of many studied plant species require low temperatures. However, some geophytes form flowers within the bulb during the summer quiescence period and do not require low temperatures for florogenesis. Narcissus tazetta was employed to study, in detail, the stages of flower development during the summer period, with special emphasis on the effect of temperature on inflorescence initiation. The sequence of morphological processes occurring during floral initiation and development was observed by SEM. During 3 years, the bulbs were subjected to different storage temperatures during the summer, and records were taken of the percentage of apical meristems that shifted from vegetative to reproductive development. Flowering and inflorescence quality were recorded after planting. It was concluded that, under natural conditions, the temperature increase in June, during the growth of the mother plant, leads to the transition of the apical meristem to the reproductive stage. Floral initiation and reproductive development in N. tazetta is promoted by high temperatures with an optimum of 25 °C. Sub- and supra-optimal temperatures (20 and 30 °C) delayed differentiation, while lower temperatures (12 °C) inhibited florogenesis completely. 相似文献