Late Spring Freezes Research Articles

Physiological responses to a changing winter climate in an early spring-breeding amphibian.

Climate change is swiftly altering environmental winter conditions, leading to significant ecological impacts such as phenological shifts in many species. As a result, animals might face physiological mismatches due to longer or earlier activity periods and are at risk of being exposed to late spring freezes. Our study points for the first time to the complex physiological challenges that amphibians face as a result of changing thermal conditions due to winter climate change. We investigated the physiological responses to a period of warmer winter days and sudden spring freeze in the common toad (Bufo bufo) by acclimating them to 4°C or 8°C for 48 h or exposing them to 4°C or -2°C for 6 h, respectively. We assessed the daily energy demands, determined body condition and cold tolerance, explored the molecular responses to freezing through hepatic tissue transcriptome analysis, and measured blood glucose levels. Toads acclimated to higher temperatures showed a higher daily energy expenditure and a reduced cold tolerance suggesting faster depletion of energy stores and the loss of winter acclimation during warmer winters. Blood sugar levels were higher in frozen toads indicating the mobilization of cryoprotective glucose with freezing which was further supported by changed patterns in proteins related to glucose metabolism. Overall, our results emphasize that increased thermal variability incurs physiological costs that may reduce energy reserves and thus affect amphibian health and survival. This might pose a serious threat to breeding adults and may have subsequent effects at the population level.

Impacts of climate and weather on irrigation technology adoption and agricultural water use in the U.S. pacific northwest

AbstractIn this article, we model long‐run responses to climate expectations that are predetermined before the growing season and short‐run responses to weather realizations during the growing season. The model is applied to a climatically diverse region, the U.S. Pacific Northwest, and the most comprehensive dataset on irrigation in the United States to estimate the impact of extreme weather on irrigation technology adoption and agricultural water use. Impacts on agricultural water use were driven more by adjustments to irrigated acreage (extensive margin effects) than by adjustments to the water application rate (intensive margin effects). The model captures the two mechanisms for irrigation to mitigate freeze damage to crops: wetting the soil (heat retention) and over‐head sprinkler irrigation (latent heat). Realized late spring freeze caused water use for orchard/vineyard to increase by 3%, but this represents less than a 1% increase in total agricultural water use. Expected spring freeze variability encouraged adoption of sprinkler irrigation technology for some crops.

Climate Change and Internet of Things Technologies—Sustainable Premises of Extending the Culture of the Amurg Cultivar in Transylvania—A Use Case for Târnave Vineyard

Known for its dry and semi-dry white wine, the Târnave vineyard located in central Transylvania is challenged by the current climate change, which has resulted in an increase of the period of active vegetation by approximately 15–20 days, the average annual temperature by 1–1.5 °C and also the amount of useful temperatures (useful thermal balance for the grapevine). Furthermore, the frost periods have been reduced. Transylvania is an important Romanian region for grapevine cultivation. In this context, one can use the climatic changes to expand their wine assortment by cultivating an autochthonous grapevine variety called Amurg. Amurg is a red grape cultivar homologated at SCDVV Blaj, which also homologated 7 cultivars and 11 clones. Because viticulture depends on the stability of meteorological and hydrological parameters of the growing area, its foundations are challenged by climate change. Grapevine production is a long time investment, taking at least five years before the freshly planted vines produce the desired quality berries. We propose the implementation of a climate change-based precision viticulture turn-key solution for environmental monitoring in the Târnave vineyard. This solution aims to evaluate the grapevine’s micro-climate to extend the sustainable cultivation of the Amurg red grapes cultivar in Transylvania with the final goal of obtaining Protected Designation of Origin (PDO) rosé and red wines from this region. Worldwide, the changing conditions from the existing climate (a 30-year average), used in the past hundred years to dictate local standards, such as new and erratic trends of temperature and humidity regimes, late spring freezes, early fall frosts, storms, heatwaves, droughts, area wildfires, and insect infestations, would create dynamic problems for all farmers to thrive. These conditions will make it challenging to predict shifts in each of the components of seasonal weather conditions. Our proposed system also aims to give a solution that can be adapted to other vineyards as well.

Late spring freezes coupled with warming winters alter temperate tree phenology and growth.

Spring phenology is advancing with warming but late spring freezes may not advance at the same rate, potentially leading to an increase in freezes after trees initiate budburst. Research suggests warming winters may delay budburst through reduced chilling, which may cause plants to leafout more slowly, thus decreasing spring freeze tolerance. Here, we assessed the effects of late spring freezes and reduced over-winter chilling on sapling phenology, growth and tissue traits, across eight temperate tree and shrub species in a laboratory experiment. We found that spring freezes delayed leafout - extending the period of greatest risk for freeze damage - increased damage to the shoot apical meristem, and decreased leaf toughness and leaf thickness. Longer chilling accelerated budburst and leafout, even under spring freeze conditions. Thus, chilling compensated for the adverse effects of late spring freezes on phenology. Despite the effects of spring freezes and chilling on phenology, we did not see any major reordering in the sequence of species leafout. Our results suggest climate change may impact forest communities not through temporal reassembly, but rather through impacts on phenology and growth from the coupled effects of late spring freezes and decreased over-winter chilling under climate change.

Subseasonal prediction for bloom dates of tart cherries in Utah and Michigan, USA: merging phenological models with CFSv2 forecast.

Temperate fruit trees require chilling for rest completion, followed by sufficient heat accumulation for onset of growth and bloom. The application of phenological models to predict bloom dates has been widely used in orchard management. Examples of such application include selecting adapted cultivars less prone to early bloom, predicting needs for frost protection, and preventing damage from late spring freezes. This study merged the Utah (chill) and ASYMCUR (forcing) phenological models by combining chill units and heat units (measured in growing degree hours) to predict bloom dates of tart cherries (Prunus cerasus L.) in Utah and Michigan, the top producing states of the USA. It was found that the modified Utah model improves the estimation of chill units compared with the original one, while the original Utah model may still be suitable for use in the colder winter of Michigan (with its later bloom dates than Utah). The combined models were applied with the temperature predicted by the Climate Forecast System v2 (CFSv2) model. The prediction was applied twice a month, starting from 1 February to 1 May. The Utah-ASYMCUR model using the forecasted temperature from CFSv2 exhibits subseasonal performance in predicting the bloom dates for 6weeks in advance. The prediction can offer growers a way to mitigate extreme climate anomalies.

Rethinking false spring risk.

Temperate plants are at risk of being exposed to late spring freezes. These freeze events-often called false springs-are one of the strongest factors determining temperate plants species range limits and can impose high ecological and economic damage. As climate change may alter the prevalence and severity of false springs, our ability to forecast such events has become more critical, and it has led to a growing body of research. Many false spring studies largely simplify the myriad complexities involved in assessing false spring risks and damage. While these studies have helped advance the field and may provide useful estimates at large scales, studies at the individual to community levels must integrate more complexity for accurate predictions of plant damage from late spring freezes. Here, we review current metrics of false spring, and how, when, and where plants are most at risk of freeze damage. We highlight how life stage, functional group, species differences in morphology and phenology, and regional climatic differences contribute to the damage potential of false springs. More studies aimed at understanding relationships among species tolerance and avoidance strategies, climatic regimes, and the environmental cues that underlie spring phenology would improve predictions at all biological levels. An integrated approach to assessing past and future spring freeze damage would provide novel insights into fundamental plant biology and offer more robust predictions as climate change progresses, which are essential for mitigating the adverse ecological and economic effects of false springs.

Cell death point in flower organs of some apricot (Prunus armeniaca L.) cultivars at subzero temperatures

The apricots growing in different environments face the risk of frost in spring months. There is limited information about how floral organ structures of apricots are protected from frost injury during late spring frosts. As a solution related this matter, the cell death points (CDPs) of some apricot flower organs (pedicel, receptacle, petal, stamen and pistil) at different development phases (first white, first bloom and full bloom) were described for the first time using differential thermal analysis under temperature-controlled, laboratory-based freeze assays. The CDPs were clearly identified for the different apricot cultivars that were evaluated during all blooming phase. In order, from the most sensitive flower organs to the least sensitive on average, were the receptacle, pedicel, petal, stamen and pistil organs. Moreover, a significant cultivar effect was found on freeze damage to most of the flower parts. Under laboratory-based freeze assays, the CDP initially occurred in the receptacle of the apricot flower and ranged from -1.9 to -11.7 °C. The pistil, the most tolerant flower organs, however, remained tolerant of low temperatures range of -6.6 to -17.0 °C, the lowest temperature tested in the research. Overall, flowering organs of ‘Erzincan Tokaloglu’ was the most sensitive to freezing, whereas flowering organs of ‘Igdır Salak’ and ‘Sekerpare’ were the most freezing-tolerant. The DTA assays indicated that the receptacles are much less frost resistant than other flower organs, and especially in contrast to pistils, are not cold tolerant. The CDP of floral organs in apricot is an effective mechanism that protects developing offspring from possible cold injury result of episodic late spring freezing events. In conclusion, cultivar variability effects on frost tolerance of open apricot flowers were defined, which can be exploited in breeding programs to improve the cold hardiness.

The Role of Hydrogen Peroxide in Mediating the Mechanical Wounding-Induced Freezing Tolerance in Wheat.

Systemic wound response (SWR), a well-characterized systemic signaling response, plays crucial roles in plant defense responses. Progress in understanding of the SWR in abiotic stress has also been aided by the researchers. However, the function of SWR in freezing stress remains elusive. In this study, we showed that local mild mechanical wounding enhanced freezing tolerance in newly occurred systemic leaves of wheat plants (Triticum aestivum L.). Wounding significantly increased the maximal photochemical efficiency of photosystem II, net photosynthetic rate, and the activities of the antioxidant enzymes under freezing stress. Wounding also alleviated freezing-induced chlorophyll decomposition, electrolyte leakage, water lose, and membrane peroxidation. In addition, wounding-induced freezing stress mitigation was closely associated with the ratio between reduced glutathione (GSH) and oxidized glutathione (GSSG), and the ratio between ascorbate (AsA) and dehydroascorbate (DHA), as well as the contents of total soluble sugars and free amino acids. Importantly, pharmacological study showed that wounding-induced freezing tolerance was substantially arrested by pretreatment of wheat leaves with the scavenger of hydrogen peroxide (H2O2) or the inhibitor of NADPH oxidase (RBOH). These results support the hypothesis that local mechanical wounding-induced SWR in newly occurred leaves is largely attributed to RBOH-dependent H2O2 production, which may subsequently induce freezing tolerance in wheat plants. This mechanism may have a potential application to reduce the yield losses of wheat under late spring freezing conditions.Highlights:In our previous research, we found that local mechanical wounding could induce freezing tolerance in the upper systemic leaves of wheat plants. Surprisingly, in this paper, we further demonstrated that local mechanical wounding could also increase freezing resistance in newly occurred leaves of wheat plants. RBOH mediated H2O2 and ascorbate–glutathione cycle participate in this systemic wound response.

Preventing spring freeze injury on grapevines using multiple applications of Amigo Oil and naphthaleneacetic acid

‘Edelweiss’ is an important grape cultivar grown in the Midwestern part of the USA. It is one of the earliest cultivars in the vineyard to break bud, making it very susceptible to late spring freezes. ‘Edelweiss’ primary buds produce a significant amount of fruit, while unlike many other hybrids, the secondary and tertiary buds will have little to no yields, thus making it important to protect the primary buds from a late freeze. The objective of this research was to determine if multiple applications of Amigo Oil or naphthaleneacetic acid (NAA) achieve a greater bud delay when compared to single applications. ‘Edelweiss’ vines were treated in January, January and February or January, February and March. Amigo Oil was applied at 10% (v/v) and NAA at 1000 ppm with a custom built all-terrain vehicle (atv) sprayer. All treatments of oil led to a significant bud break delay ranging from 1 to 8 days as compared to the control. None of the treatments were phytotoxic to buds or negatively affected yield or fruit characteristics. Grape growers in climates with the potential of late spring freezes may consider the use of Amigo Oil or NAA as a potential means to protect their vines from freeze injury.

Spring Freeze Effect on Wheat Yield is Modulated by Winter Temperature Fluctuations: Evidence from Meta‐Analysis and Simulating Experiment

AbstractIncreasing climatic variability is projected to affect large‐scale atmospheric circulation, triggers and exacerbates more extreme weather events, including winter warming and more frequent extreme low temperatures in spring. Historical data from 1961–2000 indicate these temperature fluctuations may seriously affect grain yield of winter wheat crops. In this study, a field air temperature control system (FATC) was used to simulate the winter warming, spring cold and freezing events in the field experiment in 2010–2011 to explore their impacts on growth and yield of winter wheat. Eight elite wheat varieties released during 1961–2000 were included and four temperature scenarios were applied, including late spring freeze alone, winter warming + late spring freeze, early spring cold + late spring freeze and the normal temperature condition as control. Winter warming combined with late spring freeze significantly decreased tiller survival rate, leaf photosynthetic rate and leaf growth in wheat plants, and reduced the spike number and kernel number per spike, and the final grain yield. In contrast, the wheat plants experienced early spring cold had higher tiller survival rate, leaf photosynthetic capacity and sugar accumulation and improved tolerance to the late spring freeze, resulting in less yield loss, as compared with those without experiencing early spring cold. Both the meta‐analyses and the field experimental data demonstrated that the effects of later spring freeze stress on wheat yield were exacerbated by winter warming but were extenuated by early spring cold events. Therefore, it is important to consider the characteristics of temperature fluctuations during winter to spring for precise evaluation of climate change effects on wheat production.

Late Spring Freezes in Poland in Relation to Atmospheric Circulation

Abstract Late spring freeze events, a significant agroclimatic hazard, are investigated for Poland. Daily minimum air temperatures from 184 stations for the period 1951-2010 were used to analyze the frequency and conditional probability of late spring freezes. In addition, three classification schemes were employed to investigate the atmospheric circulation responsible for late spring freezes events. The findings suggest that knowledge of the airflow influencing late spring freezes can help to understand the complex historical trends and projected future changes in freeze risk for perennial crops

Spring patterns of freezing resistance and photosynthesis of two leaf phenotypes of Hedera helix

Subdominant evergreen broad-leaved plants occurring in deciduous forests throughout temperate zones have only a short window of optimum photoassimilation in spring before canopy closure. Yet increasing photosynthetic and metabolic activity occurs concurrently with reductions in freezing resistance, resulting in vulnerability of plant tissues to late spring freezing events. Our goal was to document the temporal patterns of photosynthesis versus freezing resistance during spring in adult and juvenile leaf phenotypes of Hedera helix in Switzerland. Freezing resistances in all leaves were well below long-term minimum temperatures experienced at the study site, with adult leaf phenotypes in the forest canopy being more freezing resistant than juvenile leaves occurring closer to the ground. Reductions in freezing resistance were followed by increases in leaf photosynthetic capacities, which appeared synchronized among leaf phenotypes. Adult canopy leaves maintained a higher freezing resistance but lower photosynthetic capacity than juvenile leaves through the end of winter and into early spring. However, shortly after the cessation of freezing temperatures, adult leaves greatly increased their photosynthetic capacity relative to juvenile leaves, yet maintained freezing resistances sufficient to resist late spring freezing events. These patterns highlight the importance of the tradeoff in H. helix between exposure to potentially damaging cold temperatures in late spring and the need for high photosynthetic carbon gains before full canopy closure.

INTRODUCING THE OUT-OF-SEASON ARTICHOKE PRODUCTION IN THE PIEDMONT REGION

Artichoke reaches the fresh market in Italy from October to May. During summer, many fresh vegetables are available, while fresh artichoke is not present despite consumer appreciation for its organoleptic quality and freshness. During summer, in the typical Mediterranean growing areas of artichoke, high temperature limits head formation, while the species cultivated in North France are commercialized in Italy in September. In North of Italy there are traditional and small plantations in some areas of the Piedmont Region, producing head artichokes for the summer, although serving a narrow local market only. The major agronomic issue is to overcome the winter freezing temperatures and late spring freeze. A two-year project aimed at the introduction of out-of-season artichoke production took place, testing two F1 hybrids (Opal, Concerto), two weed control strategies (mulching, no-mulching), two transplanting dates (April, May), two covering strategies for late spring freeze (plastic cover, no cover). Gibberellins were applied for flowering to obtain heads in the first year. Harvest occurred in August and September, in the first year, and in June and July, in the second year. During the first year, Opal, early planting and covering enhanced yield, although total production was very limited (0.12 kg/plant). During the second year, early planting only increased production, however, yield was greater than in the first year (0.43 kg/plant). Early planting gave 45% more yield in the second year than late planting. In general, Opal produced more than Concerto, while heavier and greater heads were obtained with Concerto. Opal was thus more adapted for processing than Concerto, and it was tested as canned artichoke. Both hybrids were resistant to freezing winter temperatures, although during summer plant protection was a serious problem, especially due to downy mildew (Bremia lactucae) and European corn borer (Ostrinia nubilalis) attacks, both due to close by growing areas of lettuce and corn, respectively.

DORMANT APPLICATIONS OF A SOYBEAN OIL ADJUVANT PLUS ETHEPHON REDUCE PEACH FLOWER BUD SURVIVAL

Early removal of flower buds, flowers or small fruitlets increases peach fruit size and commercial value. Due to the lack of labeled or consistent thinning chemicals, peach growers usually wait approximately 30 days after bloom before hand-thinning fruit, which decreases fruit growth potential. Experiments were conducted near Seneca, South Carolina to determine the efficacy of combining Vegetoil (VO), an emulsified soybean oil adjuvant (93% soybean oil), with Ethrel (E) (a.i. 21.7% Ethephon) for pre-bloom killing of peach flower buds. ‘Contender’, ‘Cresthaven’ and ‘Rubyprince’ peach trees were sprayed once in January 2008 with 10% VO containing Ethephon concentrations of 25 (only ‘Rubyprince’), 50 or 75 ppm. Dormant oil (DO) at 3% and VO at 10% were the control treatments. In 2009, 10% VO with 75 ppm Ethephon was sprayed on ‘Cresthaven’ and ‘Rubyprince’ trees on either 1 of 5 different dates ranging from 12 January to 16 February. In 2008, Vegetoil reduced ‘Contender’, ‘Cresthaven’ and ‘Rubyprince’ flower bud survival by 10, 20 and 30%, respectively compared to the DO control and by 20-25, 50-60, and 45-55%, respectively when VO was combined with different Ethephon concentrations. The VO plus E treatments reduced fruit yield by 25-35% in ‘Cresthaven’ and 45-60% in ‘Rubyprince’ compared to the DO control. ‘Rubyprince’ yield was also significantly affected (i.e., reduced) because of a late spring freeze. ‘Contender’ fruit yield was only slightly reduced by the Vegetoil plus Ethephon treatments. Mean fruit size increased 10-15% with the VO and E treatments. The 2009 flower bud survival, fruit set and yield were significantly reduced by the VO plus E treatments for all application times. The earliest application date was the most effective in thinning flower buds for both cultivars.

Leaf phenology and freeze tolerance of the invasive shrub Amur honeysuckle and potential native competitors

The non-native invasive deciduous shrub Lonicera maackii causes a reduction in plant growth and species diversity under its canopy. The mechanisms of these effects are not fully understood, but an apparent difference between L. maackii and native shrub species is its extended leaf duration. We tested the hypothesis that L. maackii has a longer leaf duration than native shrub species found in the same habitats. Leaf phenology of L. maackii and the native deciduous shrubs Asimina triloba and Lindera benzoin was observed at four sites in central Kentucky (USA) from March until December, 2007. Additionally, a late spring freeze allowed for examination of freeze tolerance among the three test species. Lonicera maackii leaf development was two to three weeks earlier than the natives in March and early April. A hard freeze in early April caused significant (P < 0.05) leaf mortality to both of the native species (60–100% leaf mortality at 3 of 4 sites) while L. maackii showed no observable damage. L. maackii had a later transition to fall color and leaf abscission than the native species, which were at a significantly later stage of development (closer to leaf abscission) for a period of four to six weeks. These data suggest two advantages for L. maackii over potential native competitors: 1) greater access to carbon via a longer leaf duration, and 2) a greater capacity to withstand freezing temperatures.

Response of ‘Desirable’ and ‘Kiowa’ Pecan to a Late-spring Freeze

This study was established to assess the effects of a severe late spring freeze on flowering, shoot growth, leaf nutrient status, and the retention of fruit developing from secondary buds of pecan [Carya illinoinensis (Wangenh.) K.Koch]. Freeze damage appears to have a significant influence on pecan physiology and fruit retention. ‘Desirable’ produced a crop of pistillate flowers from secondary buds after the freeze; however, many of these flowers were abnormal in appearance. Freeze-damaged ‘Desirable’ trees exhibited shorter shoots, reduced flower and fruit retention, a lower chlorophyll index, and decreased leaf nitrogen concentration compared with nondamaged trees. Leaf zinc concentration was higher in freeze-injured ‘Desirable’ trees than in nondamaged trees. Freeze-damaged ‘Kiowa’ trees had longer shoots and failed to produce a crop of pistillate flowers from secondary buds on most shoots. Freeze damage led to the appearance of mouse-ear leaf symptoms and reduced leaf chlorophyll index, leaf nitrogen, and leaf magnesium concentrations in ‘Kiowa’. Leaf phosphorous and leaf potassium concentrations were higher in freeze-injured ‘Kiowa’ trees than in nondamaged trees. These observations provide insight into the potential response of bearing orchard trees injured by a late spring freeze.

RECENT USDA–ARS BLUEBERRY CULTIVAR RELEASES

Two new southern highbush blueberry cultivars, `Dixieblue' and `Gupton', will provide growers with new blueberry cultivars having excellent fruit quality that ripen relatively early in the season, during the profitable early fresh-market window. Berries of `Dixieblue' are light blue, medium in size, and their flat shape makes them most attractive. `Gupton' is very productive and berry quality is also excellent. The performance of these cultivars represent an improvement over most currently available southern highbush blueberry cultivars due to 1) their durability and performance on both upland and sandy soils endemic to the Gulf Coast and 2) consistent production of high quality fruit that will meet the demand for early ripening fresh-market blueberries. The new rabbiteye blueberry cultivar, `DeSoto', represents an improvement over currently available rabbiteye blueberry cultivars for late-season production. `DeSoto' produces medium-to-large fruit having excellent color, flavor, and firmness Plants of `DeSoto' are productive, vigorous but semi-dwarf, upright and spreading. It's semi-dwarf growth habit, which is unique among currently grown rabbiteye blueberries, results in bushes that attain a maximum height of about 2 meters upon maturity, reducing the necessity of top-pruning that is required for all other cultivars. `DeSoto' blooms two to three weeks later than early-to-mid season cultivars such as `Climax' and `Tifblue', providing insurance against late-spring freezes. Similarly, its fruit mature 21 to 14 days or more, respectively after these same cultivars. `DeSoto' will provide niche market blueberry growers with a new cultivar having productivity, plant vigor, fruit quality, and very late ripening period that will extend their marketing season. The new evergreen ornamental blueberry, `Native Blue', is low growing, compact and finely branched with small glaucous leaves, traits that are quite typical of V. darowii. `Native Blue' has beautiful foliage that changes color in different seasons. Mature leaves are darker green while newer growth exhibits a light pinkish hue that changes to a bluish green. Other desirable characteristics of `Native Blue' are its dwarf growth habit, hardy and vigorous growth, and its capacity for a high level of fruit production that serves as an attractant to birds and other wildlife. `Native Blue' will provide southeastern U.S. nurserymen, landscapers, and homeowners with a novel and beautiful new ornamental shrub that will complement plantings of azaleas, camellias, crepe myrtles, etc.

Flowering Performance of 21 Hydrangea macrophylla Cultivars

Abstract The flowering performance of 21 Hydrangea macrophylla cultivars was evaluated for three years at two locations. Ten plants of each cultivar were planted during 1997 in field plots at McMinnville, TN (USDA hardiness Zone 6b), and New Franklin, MO (USDA hardiness Zone 5b). The number of inflorescences was recorded every two weeks from May through September in 1999, 2000 and 2001. Daily maximum and minimum temperatures were recorded from October 1998 through September 2001. Differences among cultivars were found all three years at McMinnville and in 1999 and 2000 in New Franklin. While rankings of cultivars for number of inflorescences differed among years and locations, ‘All Summer Beauty’ and ‘Nikko Blue’ were consistently among the best performing cultivars. ‘Blauer Prinz’, ‘Blue Wave’, ‘Mariesii’ and ‘Todi’ flowered poorly all 3 years at both locations. No cultivar flowered reliably all three years of the study. Although some cultivars flowered sporadically throughout the summer, no remontant cultivars were identified. Poor flowering performance during the study appeared to be related to damage to aboveground portions of plants from a combination of early fall freezes, low winter temperatures and late spring freezes.

In situ Effects of Elevated Atmospheric CO2on Leaf Freezing Resistance and Carbohydrates in a Native Temperate Grassland

The objectives of this study were to quantify changes in leaf freezing resistance and carbohydrate concentrations caused by long-term (6 years) exposure to elevated CO2(ambient: 360μll−1, elevated: 600μll−1) in five dominant plant species growing in situ in a native temperate grassland. Across all five species tested from three functional groups, the mean temperature at which all leaves were damaged (T100) significantly (P=0.016) increased from −9.6 to −8.5°C under elevated CO2, and a similar marginally significant (P=0.079) reduction was observed for the mean temperature that caused 50% leaf damage (T50), from −6.7 to −6.0°C. The mean temperature at which initial leaf damage was observed (T0) was not significantly influenced by elevated CO2. Although concentrations of soluble sugars (+25%,P=0.042), starch (+53%, P<0.001), and total non-structural carbohydrates (TNC, +40%, P<0.001) were significantly higher under elevated CO2, leaf freezing resistance actually decreased under elevated CO2. Concentrations of soluble sugars were positively correlated with freezing resistance when viewed across all five community dominants, but within any individual species, no such relationships were found. We also found no evidence for our original hypothesis that increased concentrations of soluble sugars increase freezing resistance. Thus, future atmospheric CO2levels may instead increase the risk of late spring freezing damage. Furthermore, the strong differences in freezing resistance observed among the species, along with decreased freezing resistance, may increase the risk of losing species that have inherently weak freezing resistances from the plant community.

575 Effect Of AVG and Dormant Oils on Bloom Delay In `Redhaven' Peach

Peach production is significantly reduced and severely limited by frost injury in regions frequently exposed to late spring freeze conditions. Peach flower buds become increasingly susceptible to low-temperature damage from the period of completion of rest through fruit set. Delaying dehardening and/or flower bud development is an effective way to avoid frost damage. Bio-regulator applications, affecting dormancy or bud development, can delay flowering and dehardening of the buds and can help in avoiding spring freeze injury. Spring applications of AVG and dormant oils on 8-year-old `Redhaven' peach trees were evaluated. AVG applications effectively delayed bloom by 2 to 5 days. The most effective treatment was two applications of 2000 ppm AVG, which delayed bloom by almost 5 days. Repeat applications of AVG were more effective than the single dosage treatments. The 1000 ppm, repeat application delayed bloom by 4 days. A single application of 5000 ppm AVG resulted in severe phytotoxicity. The wetting agent levels were also varied and AVG applications were most effective in combination with 0.2% `Sylgard'. AVG, apparently, delayed bloom by delaying bud development following the completion of rest. The dormant oil sprays were ineffective in achieving bloom delay. The specific leaf weight characteristics of the treated trees were not affected except for the 5000-ppm AVG application, which reduced SLW. Fruit characteristics such as maturity, weight, and soluble sugar concentration were not affected by any of the spring applications (except for the 5000-ppm AVG application, which was phytotoxic). Our studies indicate that AVG is effective in delaying bloom in peaches by up to 5 days. This has the potential to substantially increase peach yields in years with a late spring freeze.