Summer Frost Research Articles

A 4500-Year Tree-Ring Record of Extreme Climatic Events on the Yamal Peninsula

Based on the analysis of the frequency of anomalous anatomical structures in the wood of Siberian larch and Siberian spruce (frost rings, light rings, and false rings, as well as missing and narrow rings), we reconstructed a timeline of climatic extremes (summer frosts, sharp multiday decreases in air temperature during the growing season, and low average summer temperatures) in Yamal (Western Siberia) over the last 4500 years. In total, 229 years were determined to have experienced extreme events. The most significant temperature extremes were recorded in 2053, 1935, 1647, 1626, 1553, 1538, 1410, 1401, 982, 919, 883 BCE, 143, 404, 543, 640, 1209, 1440, 1453, 1466, 1481, 1601 and 1818 CE. These dates with extrema observed in Yamal corrobarated with tree ring data from other regions and revealed several coincidences. That is, in these years, the observed extremes appeared to have been on a global rather than a regional scale. Moreover, these dates coincided with traces of large volcanic eruptions found in ice cores from Greenland and Antarctica, dated to approximately the same years. Therefore, the cause of the extreme summer cooling on a global scale, in most cases, can be linked to large volcanic eruptions.

The climate downturns in China caused by volcanic eruptions in 535–40 CE and by Thera (Santorini) at the founding of the Shang dynasty (1562 BCE)

Abstract It is well known that ancient Chinese written records are an invaluable source of historical information on astronomy, technology, economy, and climate, dating back in some cases to the second millennium BCE. Numerous studies have established that the climatic consequences of the ejection of volcanic aerosols into the atmosphere can have a major impact on the climate worldwide. Here, the Chinese evidence of such a severe climatic anomaly during the decade of the 530s is first reviewed. A preponderance of the evidence from ice cores and tree rings worldwide points to more than one large volcanic eruption during the 530s, although which volcano was responsible has not yet been conclusively established. Even more severe than 1815, the “year without a summer,” due to the eruption of Tambora, in 536–537 summer frosts and snowfall occurred in China causing multi-year drought, crop failures, and catastrophic famine. Study of pre-imperial Chinese texts gives reason to believe that in mid-second millennium BCE a massive loading of the atmosphere with volcanic aerosols from the eruption of Thera (Santorini) may have been the cause of dramatic climatic downturn in the sixteenth century BCE. Dating of the events based on verifiable records of astronomical phenomena suggests that the long-remembered ancient calamity could have been caused by the eruption of Thera in the eastern Mediterranean. This benchmark date can be helpful in establishing a secure chronology of eastern Mediterranean kingdoms in the period.

High light-induced photoinhibition is not limiting seedling establishment at abrupt treeline ecotones in New Zealand.

Seedlings of New Zealand's treeline-forming Fuscospora cliffortioides (Hook.f.) perform poorly beyond the established canopy, limiting treeline advance. To test the long-standing assumption that photoinhibition impairs regeneration in the subalpine belt of New Zealand's Southern Alps, we assessed photosystem II (PSII) performance of seedling-sized individuals and microclimate variation. We performed diurnal, non-invasive chlorophyll-a-fluorescence measurements on exposed and canopy-sheltered individuals at two sites in New Zealand's Southern Alps during summer and winter. Diurnal recordings of the effective (ΦPSII) and optimal (Fv/Fm) photosynthetic quantum yield were supplemented with light response curves and micro-temperature recordings. ΦPSII returned to near-optimal values around 0.8 after 30min of shading, which rules out accumulative or long-term photoinhibition effects. The maximum electron transport rate derived from rapid light curves was significantly higher (+12%) in exposed compared with canopy-shaded individuals. Summer temperature fluctuated widely on the scree (-0.5 to 60.5°C) and near seedlings (-2 to 26.5°C). Our results revealed a remarkable level of light adaptation and contradict previous studies hinting at high light-induced photoinhibition as a treeline-limiting factor in the Southern Alps. By linking low ΦPSII on winter mornings, and large, sudden temperature drops in summer, we suspect that cold-induced photoinhibition might occur but the rapid recovery of ΦPSII seen across a wide temperature range makes lethal photo-oxidative damage rather unlikely. Given the demonstrably low summer frost tolerance of F. cliffortioides, cold-related damage resulting from frost events during the growing season or embolism induced by frost drought may offer more plausible explanations for the poor seedling establishment. Duration and frequency of these events could diminish with global warming, which may promote treeline advance.

Foliar summer frost resistance measured via electrolyte leakage approach as related to plant distribution, community composition and plant traits

AbstractFrost resistance (FR) is a fundamental process determining various aspects of plant life. Measurements of FR remain challenging as existing methods are time‐ and labour‐intensive.Here, we test the applicability of foliar summer FR measured via the ‘electrolyte leakage’ approach (FRPEL), a simple and inexpensive technique so far underused in ecological research to estimate FR. We tested the ability of this trait to predict (a) species occurrence, (b) community composition along an elevation gradient and (c) analysed its relationship with nine other traits (SLA, Cmass, Nmass, Pmass, Camass, Mgmass, Kmass, canopy height and the ability to form rosettes) related to plant performance. We studied 183 vascular species occurring at 37 sites, which we also analysed in terms of species composition along an elevation gradient from 656 to 2,363 m a.s.l. in the Bavarian Alps, Germany.Species' FRPELvalues correlated significantly with the species occurrence along the elevation gradient. However, this relationship was weak as it explained only 10% in the variation of the Landolt indicator values, a proxy for species geographic ranges. We found a strong positive relationship between community‐weighted FRPELvalues and elevation suggesting a strong environmental filtering of this trait that removes species with low FR from the local species pool at high elevations. The community functional diversity of FRPELsignificantly increased with increasing elevation suggesting a higher trait divergence in harsher climates. We found significant negative relationships between FRPELand SLA, canopy height and the ability to form leaf rosettes, indicating a trade‐off in plants between the investment in conservative strategies, in our case FR, and fast resource acquisition.Our study highlights the potential of using FRPELmore frequently in ecological research as we were able to reconfirm three patterns inferred by more precise yet time‐consuming and labour‐intensive approaches. We demonstrate that FRPELcan be used to predict species occurrence and infer assembly rules along elevation gradients. Furthermore, we found that FRPELis linked to plant functional traits associated with plant performance and morphological features of the plants. However, the trait's predictive power varied greatly among the study objectives and levels.A freePlain Language Summarycan be found within the Supporting Information of this article.

Annual and perennial high-Andes species have a contrasting freezing-resistance mechanism to cope with summer frosts

In high-mountain habitats, summer frosts have negative consequences for plant fitness, therefore high-mountain plants have developed mechanisms of avoidance and tolerance to cope with freezing temperatures. Various hypotheses have been proposed to explain the prevalence of one freezing-resistance mechanism over another, focusing on thermal conditions without a consensus. We hypothesize that the prevalence of a freezing-resistance mechanism depends on the life-history strategy of the species, and is probably the consequence of a trade-off between growth/reproduction and the cost of the mechanism. Specifically, short-lived annual species should be freezing avoidant, whereas perennial long-lived species should be freezing tolerant. We used thermal analysis to determine the mechanism of freezing resistance of leaves and flowers for 10 annual and 14 perennial herb species from an alpine ecosystem in the Central Chilean Andes. We found that 70% of the annual species, their flowers and leaves were freezing avoidant, indicating that avoidance was their predominant freezing-resistance mechanism. In the case of perennial species, both mechanisms were almost equally represented in flowers and leaves. Overall, our results showed that a species freezing-resistance mechanism depends on its life-history strategy, and that leaves and flowers of single species exhibit the same freezing resistance mechanism, suggesting a common whole plant strategy. Further, freezing resistance strategies were not found to be mutually exclusive. In some cases, a specific combination of phenological, structural, and functional strategies may determine how freezing resistant vegetative and reproductive organs are to freezing during the growing season.

Does the life-history strategy determine the freezing resistance of flowers and leaves of alpine herbaceous species?

In high-mountain habitats, summer frost events can have negative consequences for plant fitness. Despite this, most studies have evaluated the consequences of frosts for vegetative structures of perennial plants, and neither for leaves nor for flowers of annual plants. We hypothesize that the degree of freezing resistance of flowers and leaves of a species depends on its life-history strategy (LHS), and is probably the consequence of a trade-off between growth/reproduction and the cost of the freezing resistance. Specifically, flowers and leaves of short-lived annual species should be less freezing resistant than those of perennial plant species. We compared the freezing resistance of flowers and leaves of 10 annual and 12 perennial plant species from the Andes of central Chile using the electrolyte leakage method. Temperature damage for 50% tissue (LT50) of annual species was − 9.6 °C in flowers and − 11.9 °C in leaves. In perennial species, LT50 was similar in flowers (− 12.3 °C) and leaves (− 12.5 °C). Despite that, these differences were not significant (except the flowers of annual species), we found remarkable differences between LHS when freezing resistance was analyzed species by species. Like this, 58% and 83% of perennial species resist temperatures ≤ − 10 °C in their flowers and leaves, respectively, compared with only 30% and 40% of annual species. Additionally, in most of the species, the freezing resistance of leaves was greater than that of flowers, with this proportion being greater in annual (58%) than in perennial species (43%). Thus, we concluded that the degree of freezing resistance depends on the LHS, such that annual species, which are less freezing resistant than perennial species, have an infrequent occurrence and a distribution restricted to low elevation in high-mountain habitats.

Low temperatures at higher elevations require plants to exhibit increased freezing resistance throughout the summer months

The frequency and severity of night frosts increase during the summer in the alpine environment as elevation increases. Intra-specific, temporal, and elevational variability in the freezing resistance (FR) of alpine plants during the active growing period has not been documented, especially in regards to the intra-specific distribution of plants at their upper elevational limits of growth.The FR of leaves of 13 species was investigated at regular intervals from June through August, 2017 at elevations between 600 and 3200 m. The examined species have different lower and upper elevational range limits, and either grow exclusively in alpine sites or extend into the subalpine life zone. Each species was sampled twice, close to its upper and lower range limit.For most of the species, leaves exhibited a higher FR (−0,17 K/100 m) at the upper elevational range limit. The intra-specific FR was substantial, covering an amplitude of 7–15 K (>15 K in Pinus). Fully-expanded leaves had a lower level of FR in June. Evergreen leaves had a higher FR than deciduous leaves throughout the summer. Frost hardening in evergreen and a decrease in FR in deciduous leaves was observed in August; whereas, deciduous leaves at that time had already begun to senesce.Ecotypes growing at their upper elevation limit were more frost hardy than individuals of the same species growing near the lower level of their elevation range. The most severe summer frosts occurred in June when leaves were fully expanded and their FR was lowest. Thus, the highest risk of frost damage to plants at alpine sites occurs in June, even though the most frost-susceptible phase of leaf expansion may have already passed.

Frost sensitivity of leaves and flowers of subalpine plants is related to tissue type and phenology

Summary Harsh abiotic conditions – such as low temperatures that lead to spring and summer frost events in high‐elevation and high‐latitude ecosystems – can have strong negative consequences for plant growth, survival and reproduction. Despite the predicted increase in episodic frost events under continued climate change in some ecosystems, our general understanding of the factors associated with frost sensitivity of reproductive and vegetative plant structures in natural plant communities is limited. The timing of growth and reproduction may be an important strategy by which plants can avoid frost. In this study, we experimentally investigated the frost sensitivity of eight long‐lived perennial herbaceous plant species from a subalpine ecosystem in the Colorado Rocky Mountains, USA. The study taxa represent four congeneric pairs from four flowering plant families; within each pair, there is a species with early and late growth and reproductive phenology. Thus, we control for evolutionary history – and therefore additional traits shared through common ancestry – to some degree, while examining the influence of phenology on frost sensitivity. Specifically, we compared frost sensitivity of vegetative and reproductive structures for each species and asked whether frost sensitivity was similar between species within congeneric pairs or, instead, was related to phenology (i.e. differences in the timing of growth and reproduction). For most species (6 of 8), flowers were more sensitive to frost than leaves. Within most congeneric pairs (3 of 4), the leaves of species with later phenology were significantly more sensitive to frost than the leaves of species with earlier phenology. For flowers, the later flowering species were more sensitive in two of the four congeneric pairs. Synthesis. This study contributes to our general understanding of factors related to interspecific differences in plant sensitivity to episodic frost events of naturally occurring species. The increased frost sensitivity of reproductive structures compared to vegetative structures may be a widespread pattern for long‐lived perennial plants. Furthermore, we find evidence for a trade‐off between phenology and frost sensitivity, whereby species with later phenology exhibit higher frost sensitivity compared to species with earlier phenology. These results have implications for plant populations, species interactions and ecological communities.

Результаты испытаний препарата Biodux на рост и развитие растений пиона

В статье представлены результаты изучения влияния нового регулятора роста Biodux на биоморфологические показатели и семенную продуктивность некоторых представителей рода Paeonia L., культивируемых в Башкирском Предуралье. Показано, что обработка растений водным раствором препарата способствует увеличению их биоморфологических показателей и семенной продуктивности. В климатическом отношении район исследований (Уфа, Башкирское Предуралье) характеризуется большой амплитудой колебаний температуры в ее годовом ходе, быстрым переходом от суровой зимы к жаркому лету, поздними весенними и ранними осенними заморозками. Опыты проводили в 2012 – 2014 гг. на базе Ботанического сада-института Уфимского научного центра РАН. В качестве объектов исследования использованы четыре вида рода Paeonia: P. anomala L., P. hybrida Pall., P. lactiflora Pall. и P. tenuifolia L. — 8-летние кусты в фазе бутонизации, выращиваемые на коллекционных участках Ботанического сада-института в открытом грунте. Ежегодно (в течение трех лет) в каждой повторности обрабатывали по 10 растений. Повторность опыта трехкратная. Обрабатывали в конце второй декады апреля (фаза весеннего отрастания) опрыскиванием кустов водными растворами препарата в концентрациях, рекомендованных производителями. Основные биоморфологические параметры замеряли в фазе массового цветения; семенную продуктивность определяли в фазе полной спелости семян; сбор семян начинали, когда вскрывались плоды (листовки), а семена приобретали светло-коричневую или темно-синюю окраску. Статистическая обработка данных выполнена в программе MS Excel с использованием стандартных показателей. Достоверность различий определяли по критерию Стьюдента при P = 0,95.

Ice barriers promote supercooling and prevent frost injury in reproductive buds, flowers and fruits of alpine dwarf shrubs throughout the summer

Over-wintering reproductive buds of many woody plants survive frost by supercooling. The bud tissues are isolated from acropetally advancing ice by the presence of ice barriers that restrict ice growth. Plants living in alpine environments also face the risk of ice formation in summer months. Little knowledge exists, how reproductive structures of woody alpine plants are protected from frost injury during episodic summer frosts. In order to address this question, frost resistance of three common dwarf shrubs, Calluna vulgaris, Empetrum hermaphroditum and Loiseleuria procumbens was measured and ice formation and propagation were monitored in twigs bearing reproductive shoots during various stages of reproductive development (bud, anthesis, and fruit) throughout the alpine summer. Results indicated that, in the investigated species, ice barriers were present at all reproductive stages, isolating the reproductive shoots from ice advancing from the subtending vegetative shoot. Additionally, in the reproductive stems ice nucleating agents that are active at warm, sub-zero temperatures, were absent. The ice barriers were 100% effective, with the exception of L. procumbens, where in 13% of the total observations, the ice barrier failed. The ice barriers were localized at the base of the pedicel, at the anatomical junction of the vegetative and reproductive shoot. There, structural aspects of the tissue impede or prevent ice from advancing from the frozen stem into the pedicel of the reproductive shoot. Under the experimental conditions used in this study, ice nucleation initially occurred in the stem of the vegetative shoot at species-specific mean temperatures in the range of −4.7 to −5.8°C. Reproductive shoots, however, remained supercooled and ice free down to a range of −7.2 to −18.2°C or even below −22°C, the lowest temperature applied in the study. This level of supercooling is sufficient to prevent freezing of reproductive structures at the lowest air temperature occurring at the altitude of the upper distribution boundary of the natural habitat of the investigated species which is between −8 and −10°C in summer. Frost resistance assays indicated that reproductive shoots are much less frost resistant than vegetative stems, and in contrast to vegetative shoots, are not ice tolerant. Supercooling of reproductive shoots in alpine, woody plant species is an effective mechanism that protects developing offspring from potential frost damage resulting from episodic summer freezing events.

Managing Potato Biodiversity to Cope with Frost Risk in the High Andes: A Modeling Perspective

Austral summer frosts in the Andean highlands are ubiquitous throughout the crop cycle, causing yield losses. In spite of the existing warming trend, climate change models forecast high variability, including freezing temperatures. As the potato center of origin, the region has a rich biodiversity which includes a set of frost resistant genotypes. Four contrasting potato genotypes –representing genetic variability- were considered in the present study: two species of frost resistant native potatoes (the bitter Solanum juzepczukii, var. Luki, and the non-bitter Solanum ajanhuiri, var. Ajanhuiri) and two commercial frost susceptible genotypes (Solanum tuberosum ssp. tuberosum var. Alpha and Solanum tuberosum ssp. andigenum var. Gendarme). The objective of the study was to conduct a comparative growth analysis of four genotypes and modeling their agronomic response under frost events. It included assessing their performance under Andean contrasting agroecological conditions. Independent subsets of data from four field experiments were used to parameterize, calibrate and validate a potato growth model. The validated model was used to ascertain the importance of biodiversity, represented by the four genotypes tested, as constituents of germplasm mixtures in single plots used by local farmers, a coping strategy in the face of climate variability. Also scenarios with a frost routine incorporated in the model were constructed. Luki and Ajanhuiri were the most frost resistant varieties whereas Alpha was the most susceptible. Luki and Ajanhuiri, as monoculture, outperformed the yield obtained with the mixtures under severe frosts. These results highlight the role played by local frost tolerant varieties, and featured the management importance –e.g. clean seed, strategic watering- to attain the yields reported in our experiments. The mixtures of local and introduced potatoes can thus not only provide the products demanded by the markets but also reduce the impact of frosts and thus the vulnerability of the system to abiotic stressors.

How endangered is sexual reproduction of high-mountain plants by summer frosts? Frost resistance, frequency of frost events and risk assessment.

In temperate-zone mountains, summer frosts usually occur during unpredictable cold spells with snow-falls. Earlier studies have shown that vegetative aboveground organs of most high-mountain plants tolerate extracellular ice in the active state. However, little is known about the impact of frost on reproductive development and reproductive success. In common plant species from the European Alps (Cerastium uniflorum, Loiseleuria procumbens, Ranunculus glacialis, Rhododendron ferrugineum, Saxifraga bryoides, S. moschata, S. caesia), differing in growth form, altitudinal distribution and phenology, frost resistance of reproductive and vegetative shoots was assessed in different reproductive stages. Intact plants were exposed to simulated night frosts between −2 and −14 °C in temperature-controlled freezers. Nucleation temperatures, freezing damage and subsequent reproductive success (fruit and seed set, seed germination) were determined. During all reproductive stages, reproductive shoots were significantly less frost resistant than vegetative shoots (mean difference for LT50 −4.2 ± 2.7 K). In most species, reproductive shoots were ice tolerant before bolting and during fruiting (mean LT50 −7 and −5.7 °C), but were ice sensitive during bolting and anthesis (mean LT50 around −4 °C). Only R. glacialis remained ice tolerant during all reproductive stages. Frost injury in reproductive shoots usually led to full fruit loss. Reproductive success of frost-treated but undamaged shoots did not differ significantly from control values. Assessing the frost damage risk on the basis of summer frost frequency and frost resistance shows that, in the alpine zone, low-statured species are rarely endangered as long as they are protected by snow. The situation is different in the subnival and nival zone, where frost-sensitive reproductive shoots may become frost damaged even when covered by snow. Unprotected individuals are at high risk of suffering from frost damage, particularly at higher elevations. It appears that ice tolerance in reproductive structures is an advantage but not an absolute precondition for colonizing high altitudes with frequent frost events.

ПОТЕНЦИАЛ ХОЛОДОУСТОЙЧИВОСТИ ЛЕТНИХ НАСЕКОМЫХ НА ПРИМЕРЕ UPIS CERAMBOIDES (COLEOPTERA: TENEBRIONIDAE), ОБИТАЮЩЕГО В ЦЕНТРАЛЬНОЙ ЯКУТ

Ability of Upis ceramboides imago was studied to be resisted to the different ranges of freezing temperatures during hot summer period in Yakutia . It was shown that Upis ceramboides are tolerant to multiply cycles of freezing-thawing at their SCP (supercooling point) and even more, they survived over at least three cycles of freezing-thawing at –15....–17°C, if they were pre-incubated during 14 days at +4°C before laboratory testing. According to the study, one of the reasons of elevating of the insect resistance to such temperature conditions is a deep cleansing of body from occasional ice nucleators appearing in the intestine. It is suggested that in the case of summer frost, the cold tolerance of these species would be based on gut clearing.

Frost as a limiting factor for recruitment and establishment of early development stages in an alpine glacier foreland?

AbstractQuestionsHow frost resistant are the early development stages (seeds, seedlings, plantlets and juveniles) of alpine plant species? Do summer frosts impair establishment of plant species typical of different successional stages on a central alpine glacier foreland?LocationRotmoos glacier foreland, Austrian Central Alps (Obergurgl, Tyrol, Austria).MethodsSeeds of 12 species typical of different successional stages were collected in the glacier foreland and either sown directly in the field or in a growth chamber (25/10 °C, 16/8 h) and grown to the investigated development stages. Frost resistance of the early development and adult stages was determined by exposing them to a set of freezing temperatures and assessing viability with the tetrazolium test (LT 50, i.e. 50% of samples being lethally frost damaged).ResultsDry seeds had the highest frost resistance (LT 50: −19 °C), followed by wet seeds after imbibition (LT 50: −8 °C). With the onset of germination, frost resistance decreased rapidly. While germinated seeds tolerated a mean of −3.2 °C, seedlings and juveniles were less frost resistant (LT 50: −2.5 °C). Along the primary succession, seedlings of pioneer species were significantly less frost resistant than early‐ and late‐successional species. However, field grown seedlings, mainly of pioneer species, showed higher frost resistance (mean: −5 °C) than the growth chamber seedlings (mean: −3 °C), indicating that frost hardening (transition from a lower to a higher level of frost resistance) is already possible during these early stages of development.ConclusionsThe low frost resistance during and after germination may not suffice to survive summer frosts and may at least in certain years explain the high seedling mortality rates recognized in the glacier foreland.

Impact of climate change, seedling type and provenance on the risk of damage to Norway spruce (Picea abies (L.) Karst.) seedlings in Sweden due to early summer frosts

A model including site-specific microclimate-affecting properties of a forest regeneration area together with seedling characteristics was used to evaluate the accumulated risk of frost damage to Norway spruce (Picea abies (L.) Karst.) seedlings. Climate change in Sweden was simulated on the basis of the regional climate model RCA3. The daily average temperature, the driving factor for bud burst in the model, was adjusted using the difference between the mean of the climate model data for the years 1961–1990 and 2036–2065. The model was run for a highly frost prone, clear-cut site in which bare-rooted Norway spruce seedlings of mid-Swedish provenance were planted. Alternate runs were conducted with data for containerized seedlings and seedlings of Belarusian origin. The study showed that bud burst will occur at earlier dates throughout Sweden in the period 2036–2065 if the climate changes according to either of the climate scenarios examined, compared to the reference period 1961–1990. Furthermore, the risk of damage to Norway spruce seedlings as a result of frost events during summer will increase in southern Sweden and be unaffected or decrease in northern Sweden. The risk of frost damage was exacerbated in containerized seedlings, while the risk was lower for the seedlings of Belarusian provenance when compared with bare-rooted seedlings or seedlings of mid-Swedish origin.

Earliest documented report of Scleroderris canker in North America: damage believed until now to be caused by summer frost

In 1934, over 200,000 red pine (Pinus resinosa) seedlings were planted at Valcartier, near Quebec City. By 1939, more than 28% of these pines were dead. Fifteen years after plantation, red pine mortality reached 93% and the plantation was considered a total loss. Summer frost was thought to be the cause of red pine mortality, while white pine (Pinus strobus) trees planted at the same time were killed by white pine blister rust (Cronartium ribicola), without any trace of frost damage. However, while summer frost was not listed in insect and disease survey reports published from 1953 to 1993, it was reported in the Valcartier area. Analysis of archival documents and publications shows that Scleroderris canker caused by Gremmeniella abietina was responsible for this mortality. This disease was not known in Canada before 1960. Our diagnosis is based on the description of signs and symptoms, on photographs of damage and on samples collected on site. Gremmeniella abietina, North American race, was isolated and identified. The age of the trees confirms the identity of the plantation; the age of the cankers on residual pines shows that the disease reached the trunks around 1945. High snow depth - not frost - in topographic depressions created conditions conducive to the development of the disease at the epidemic level. This is the earliest documented report of Scleroderris canker in North America.

RELATIVE RESPONSE OF FORAGE AND SEED YIELD OF ALFALFA TO SULFUR, PHOSPHORUS, AND POTASSIUM FERTILIZATION

A field experiment was conducted from 2000 to 2007 on three-year old alfalfa stand near Star City in northeastern Saskatchewan to determine the influence of balanced application of sulfur (S), phosphorus (P), or potassium (K) fertilizers on forage dry matter yield (DMY) and seed yield, protein concentration (PC) in forage, concentration and uptake of total nitrogen (N), P, K, S, and boron (B) in forage and seed, and residual soil extractable P, exchangeable K and sulfate-S. Appropriate application of S, P, or K fertilizer nutrients was required to obtain optimum yield, PC, and nutrient concentration and uptake, especially when alfalfa was grown for hay production. Yield response to fertilization was much more frequent and much higher when alfalfa was managed as hay compared to when managed for seed production. The results suggest the importance of proper fertilization in increasing longevity of alfalfa stands. Under both hay and seed plots, there was only a small increase in residual sulfate-S from S fertilization, but significant accumulation of extractable P mainly in the 0–15 soil layer from P application. There was relatively higher concentration of exchangeable K in soil in the seed plots than in hay plots. In hay plots, concentrations of residual exchangeable K in soil were negatively related to DMY, especially in 2007. The findings suggest that when a soil is testing low (or deficient) in a nutrient and alfalfa growth is reduced, then alfalfa producers should consider applying fertilizers to supply adequate amounts of nutrients that are lacking in the soil, especially for optimum forage production. However, it is still difficult to predict accurately if a profitable alfalfa seed yield response to fertilization would occur, particularly when soils are testing marginal in some nutrient levels and yields are negatively affected by abnormal weather conditions (drought soil moisture conditions reducing plant growth, wet, cloudy and cool weather conditions decreasing pollination activity and late summer and/or early autumn frost damage to seed formation) that often occur in the growing season in this region.

Inflorescences of alpine cushion plants freeze autonomously and may survive subzero temperatures by supercooling

Freezing patterns in the high alpine cushion plants Saxifraga bryoides, Saxifraga caesia, Saxifraga moschata and Silene acaulis were studied by infrared thermography at three reproductive stages (bud, anthesis, fruit development). The single reproductive shoots of a cushion froze independently in all four species at every reproductive stage. Ice formation caused lethal damage to the respective inflorescence. After ice nucleation, which occurred mainly in the stalk or the base of the reproductive shoot, ice propagated throughout that entire shoot, but not into neighboring shoots. However, anatomical ice barriers within cushions were not detected. The naturally occurring temperature gradient within the cushion appeared to interrupt ice propagation thermally. Consequently, every reproductive shoot needed an autonomous ice nucleation event to initiate freezing. Ice nucleation was not only influenced by minimum temperatures but also by the duration of exposure. At moderate subzero exposure temperatures (−4.3 to −7.7°C) the number of frozen inflorescences increased exponentially. Due to efficient supercooling, single reproductive shoots remained unfrozen down to −17.4°C (cooling rate 6Kh−1). Hence, the observed freezing pattern may be advantageous for frost survival of individual inflorescences and reproductive success of high alpine cushion plants, when during episodic summer frosts damage can be avoided by supercooling.

DEVELOPMENT OF AN EFFICIENT REGENERATION SYSTEM FOR EGYPTIAN CULTIVAR(S) OF BARLEY (Hordeum vulgare L.)

Cultivated barley (Hordeum vulgare L.) belongs to the Triticeae in the grass family, Poaceae. Barley ranks as the world’s fourth most important cereal crop after wheat, maize and rice. It is grown over a wide environmental range than any other cereal crop. It is more tolerant to drought, summer frosts, saline and alkaline soils than other cereals; the grain is used for human food, animal feed and malt (FAO, 1998). Although barley is an important member of the cereal crops, it lags behind in gene transfer technology with regard to the introduction of elite agronomic traits such as disease and herbicide resistance. Non-sexual transfer of DNA to cereal species such as Hordeum vulgare L. has historically been problematic, chiefly because of problems encountered during attempts to regenerate cultured transgenic cells. Frequently, few or no plants can be recovered following selection for transformed cells, or only albino can be recovered (Lemaux et al., 1999). The recovery of fertile plants from transgenic callus is a critical component of many cereal transformation systems (Bregitzer et al., 1998; Hussein et al., 2004; Assem et al., 2008). Efficient regeneration of plants from transformed embryogenic callus is often limited to specific genotypes that exhibit vigorous plant regeneration (Bregitzer et al., 1998). Improved plant regeneration from elite barley cultivars will facilitate their genetic transformation. The media composition is an important key factor influencing the regeneration ability of different genotypes. Different media compositions have been applied by Bregitzer (1992) and Hussein et al. (2004). Therefore, it is necessary to optimize the regeneration conditions for the Egyptian cultivars. The objectives of the present investigation were: to establish an efficient regeneration system for some Egyptian barley genotypes using immature embryos as explants, and to evaluate the effect of different media composition on the embryogenic response and regeneration ability of the barley genotypes.

Planted stock performance 10 years after partial cutting in west-central British Columbia

Mature lodgepole pine (Pinus contorta) forests were harvested using group selection (GS) (0.02-ha openings) and irregular group shelterwood (IGS) (0.05-ha openings) systems to maintain arboreal and terrestrial lichens in the winter range of northern woodland caribou (Rangifer tarandus caribou). Ten years after planting, lodgepole pine showed excellent survival, but were smaller in the partial cut openings compared to the clearcuts. Pine grew less in the Sub-Boreal Pine–Spruce biogeoclimatic subzone (SBPSxc) than in the Montane Spruce subzone (MSxv), and trees were smaller in the GS versus IGS treatment within the MSxv subzone. Interior spruce (Picea glauca × engelmannii) grew best in the MSxv and partial cut treatments, but was significantly affected by summer frost in the clearcuts. In an operational-scale Adaptive Management trial, openings were enlarged to 0.15 ha, and both pine and spruce showed excellent survival, minimal frost damage, and 10-year size similar to clearcut conditions. This study suggests that lodgepole pine and interior spruce can be successfully regenerated in partial cut openings with acceptable growth in gaps of 0.15 ha. Key words: caribou, group selection, interior spruce, irregular group shelterwood, light level, lodgepole pine, Montane Spruce zone, partial harvest, soil moisture, soil temperature, Sub-Boreal Pine Spruce zone, summer frost