Low Spring Temperatures Research Articles

Climate warming could shift the timing of seed germination in alpine plants

Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland. Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site. Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species. Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.

Establishing climatic constraints shaping the distribution of alien plant species along the elevation gradient in the Alps

In this work, we analyse the role of climatic constraints in shaping the distribution of alien plant species along the elevation gradient in the European Alps. Alien species occurrence was recorded in 278 plots located beside rivers, from 100 to 2,100 m a.s.l. Climate variables were calculated from the data recorded by 145 meteorological stations and interpolated by a multiple regression approach. Both richness and occurrence of aliens were modelled. In particular, relationships between the occurrence of alien plants and (1) elevation or (2) the climatic variables, were tested by applying generalised linear models and generalised linear mixed models; the model parameters obtained were used to estimate upper elevation limits of alien occurrence and their related climate values. Sixty-eight alien species were encountered, the majority (71%) invasive in Italy and worldwide. A steep decrease in alien species richness with elevation was found, with the probability of alien species occurrence decreasing by half for each 100 m increase in elevation. Minimal adequate models based on (1) non-transformed climatic variables and (2) derived PCA values, confirmed that occurrence of alien plant species along the elevation gradient was positively related to the minimum temperature, the mean temperature and the heat sum for the spring season, rather than to the incidence of absolute minimum temperature and frost days, as usually assumed. Although further experimental analyses are needed, these results support the hypothesis that, referring to climate factors, elevation limits along rivers are mainly established by low spring temperatures which operate at the level of population viability rather than plant survival.

Seed Dormancy and Adaptive Seedling Emergence Timing in Giant Ragweed (Ambrosia trifida)

Giant ragweed germination is delayed by both a physiological dormancy of the embryo (embryo dormancy) and an inhibitory influence of embryo-covering structures (covering structure-enforced [CSE] dormancy). To clarify the roles of embryo and CSE dormancy in giant ragweed seedling emergence timing, we conducted two experiments to address the following objectives: (1) determine changes in germinability for giant ragweed dispersal units (hereafter “involucres”) and their components under natural burial conditions, and (2) compare embryo and CSE dormancy alleviation and emergence periodicity between successional and agricultural populations. In Experiment 1, involucres were buried in crop fields at Columbus, OH, periodically excavated, and brought to the laboratory for dissection. Involucres, achenes, and embryos were then subjected to germination assays at 20 C. In Experiment 2, temporal patterns of seedling emergence were determined at a common burial site. Reductions in embryo and CSE dormancy were compared with controlled-environment stratification followed by germination assays at 12 and 20 C, temperatures representative of soil conditions in spring and summer. Results indicated that overwinter dormancy loss involved sequential reductions in embryo and CSE dormancy. CSE dormancy, which may limit potential for fatal germination during fall, was caused by the pericarp and/or embryo-covering structures within the pericarp. In Experiment 2, successional populations emerged synchronously in early spring, whereas agricultural populations emerged throughout the growing season. Levels of embryo dormancy were greater in the agricultural populations than the successional populations, but CSE dormancy levels were similar among populations. In 12 C germination assays, embryo dormancy levels were positively correlated with time required to reach 95% cumulative emergence (run 1:r= 0.81, P = 0.03; run 2:r= 0.76, P = 0.05). These results suggest that late-season emergence in giant ragweed involves high levels of embryo dormancy that prevent germination at low temperatures in spring.

Wetland drainage in the Canadian prairies: Nutrient, salt and bacteria characteristics

Intensification of agriculture has led to renewed efforts to drain wetlands throughout North American prairies. It is perceived to threaten downstream ecosystem health through enhancing nutrient, bacteria and salt loading. An experiment was conducted to determine temporal variations in wetland solute storage and export upon drainage. Water quality along seven ditches and five natural spills that form between wetlands was also compared. The experimental wetland acted as a solute storage zone prior to its drainage. Variations in salts and DOC were influenced by hydrological processes, whereas variations in nutrients and bacteria were also influenced by biotic and/or sorption processes. Wetland water quality was an important control of drainage water quality as the wetland ditch acted as a simple conduit. Concentrations of TDN, DOC, HCO 3 −, K +, and Ca 2+ were higher in ditches than spills. Minimal changes in water quality along ditches and spills occurred, likely due to low spring temperatures that can restrict biotic processing and sorption. Since ditches connect wetlands to streams, they have a greater potential to contribute to downstream solute loading than spills. Wetland drainage efficiency and wetland water quality were deemed the factors critical to determining solute exports via ditches.

Tillage and crop residue effects on rainfed wheat and maize production in northern China

Dryland farming in the dry semi-humid regions of northern China is dominated by mono-cropping systems with mainly maize (Zea mays L.) or wheat (Triticum aestivum), constrained by low and variable rainfall, and by improper management practices. Addressing these problems, field studies on tillage and residue management for winter wheat and spring maize were conducted at 4 sites in Linfen, Tunliu and Shouyang (Shanxi province) and Luoyang (Henan province). These studies (a.o.) explored the impacts of different tillage and residue application methods on soil physical conditions, water storage, water use, water use efficiency (WUE) and crop yields of wheat and maize. An analysis of the results of these studies is presented. Conservation tillage, comprising no-till as well as reduced tillage practices (subsoiling, deep ploughing) showed benefits which were more prominent in combination with residue application. Benefits compared to conventional tillage were found in the form of improved soil physical conditions, such as higher topsoil bulk densities but lower subsoil bulk densities. This resulted in a better water storage during the summer fallow or rainy season in winter wheat fields, and a better water conservation and soil protection in spring maize fields. Compared to conventional methods, reduced tillage gave yields around 13–16% higher in spring maize and round 9–37% higher in winter wheat. Yields under no-till were very close to those from conventional methods. Surface application of crop residue for maize was found to increase the risk for delayed seedling emergence, because of low temperatures, leading to a recommendation for incorporation of residue in combination with reduced tillage. For winter wheat, subsoiling in combination with straw mulching after harvest in summer every other two or three year, and no-till seeding is a promising practice for sandier soils and low rainfall conditions. For heavier clay loam soils, deep ploughing with straw mulching after wheat harvest in summer every other two or three year, and no-till seeding practice is recommended. For spring maize, deep ploughing with straw and fertilizers incorporation after harvest in fall, and no-till seeding practices are recommended. Subsoiling or no-till with residue mulching after harvest in fall, and no-till seeding practices in spring are also promising practices, the latter only in situations where low spring temperatures are not a problem. Continuous no-till is not recommended.

Biomass yield and heterosis of crosses within and between European winter cultivars of turnip rape (Brassica rapa L.)

Because of its high growth rate at low temperatures in early spring, there is renewed interest in Brassica rapa as a winter crop for biomass production in Europe. The available cultivars are not developed for this purpose however. An approach for breeding bioenergy cultivars of B. rapa could be to establish populations from two or more different cultivars with high combining ability. The objective of this study was to evaluate the heterosis for biomass yield in the European winter B. rapa genepool. The genetic variation and heterosis of the biomass parameters: dry matter content, fresh and dry biomass yields were investigated in three cultivars representing different eras of breeding by comparing full-sibs-within and full-sibs-between the cultivars. Field trials were performed at two locations in Germany in 2005–2006. Mean mid-parent heterosis was low with 2.5% in fresh and 3.0% in dry biomass yield in full-sibs-between cultivars. Mean values of individual crosses revealed a higher variation in mid-parent heterosis ranging from 14.6% to −7.5% in fresh biomass yield and from 19.7% to −12.7% in dry biomass yield. The low heterosis observed in hybrids between European winter cultivars can be explained by the low genetic variation between these cultivars as shown earlier with molecular markers. In conclusion, a B. rapa breeding program for biomass production in Europe should not only use European genetic resources, but should also utilize the much wider worldwide variation in this species.

실내수조에서 인위적 수온자극이 참가리비 폐사에 미치는 영향

인위적 수온급변이 참가리비의 생존율에 미치는 영향을 조사하였다. 수온변화는 봄과 여름철에 동해안에서 나타나는 변화양상을 실험실 내 사육수조에서 인위적으로 유도하였다. 봄철 저수온 기간 중 수온 자극에 의한 참가리비의 생존율은 평균 51.6%를 보였고, 소형패 (85.82%) 와 대형패 (55.0%) 보다 중형패에서 4.4%로 가장 낮았다. 여름철 고수온 기간 중 수온 자극에 의한 참가리비의 생존율은 평균 43.3%를 보였으며, 중형패 (60.0%) 보다 소형패가 46.7%로 낮게 나타났다. 대체적으로 봄철보다 여름철에 생존율이 더 낮았다. 이와 같은 결과들은 참가리비의 폐사가 수온 변화와 밀접한 관련이 있음을 보여주고 있다. 봄철 중형패의 낮은 생존율은 충분한 영영 공급을 받는 소형패나 두 번의 겨울을 보내 수온변화에 적응한 대형패에 비해 충분히 성장하지 못한 상태에서 겨울을 보내기 때문에 나타나는 결과로 보인다. We examined the effect of an artificial change of water temperature on the survival rate of Korean Scallop, Patinopecten yessoensis. As for the change of water temperature, the aspects appearing on the eastern coast of Korea during spring and summer were artificially prepared in the rearing aquarium in the laboratory. The survival rate of Scallop, due to the stimulus of a low water temperature in spring, was an average of 51.6%. Medium-sized scallops averaged 4.4%, which is lower than that of small-sized ones (85.82%) and large-sized ones (55.0%). The survival rate of Scallop, due to the stimulus of water at a high temperature in summer, was an average of 43.3%. As for small-sized scallops, they averaged a 46.7% survival rate which is lower than that of medium-sized scallops (60.0%). In general, the survival rate was lower in summer than in spring. Such results show that the death of Scallop, has close relevance to the change of water temperature. The low survival rate of medium-sized ones. Alternatively, medium-sized scallops have to get through winter, even if they cannot grow enough compared with large-sized ones. This is because large-sized scallops have already been adapted to the change of water temperature by getting through winter twice.

Growth responses to climate and drought in silver fir (Abies alba) along an altitudinal gradient in southern Kosovo

This paper deals with the response of silver fir ( Abies alba Mill.) growth to climate, mainly drought, presenting data from southern Kosovo, for which only little information is available. Two cores from 55 dominant trees were extracted at two sites representing the limits of the natural distribution of silver fir. We built 80- and 112-year-long chronologies for each site. Comparison of both ring width chronologies showed that they were diverse. Pointer year analysis indicated that high spring temperatures and ample rainfall (1082 mm) influenced positively silver fir growth (wide ring), while low spring temperatures and scarce precipitation had an inverse effect. Bootstrapped response functions confirmed that April and May temperatures of the current growth year influenced positively silver fir growth at the low-elevation site, while the July precipitation of the previous growth year had a negative influence. At the high-elevation site, warm previous December temperatures had a positive influence on silver fir growth. Drought indices indicated two periods (1953–1961 and 1994–2001) with moderate drought. Correlation analysis between silver fir radial growth and drought indices revealed that the impact of drought on radial growth was significant at the time scale of 1.5 months during the summer months.

Rapid cold hardening increases cold and chilling tolerances more than acclimation in the adults of the sycamore lace bug, Corythucha ciliata (Say) (Hemiptera: Tingidae)

The sycamore lace bug, Corythucha ciliata is a new, invasive pest of Platanus trees in China. Although C. ciliata is often subjected to acute low temperatures in early winter and spring in northern and eastern China, the cold tolerance of C. ciliata has not been well studied. The objectives of this study were to determine whether adults of C. ciliata are capable of rapid cold hardening (RCH), and to compare the benefits of RCH vs. cold acclimation (ACC) in the laboratory. When the adult females incubated at 26 °C were transferred directly to the discriminating temperature (−12 °C) for 2 h, survival was only 22%. However, exposure to 0 °C for 4 h before transfer to −12 °C for 2 h induced RCH, i.e., increased survival to 68%. RCH could also be induced by gradual cooling of the insects at rates between 0.1 and 0.25 °C min −1. The protection against cold shock obtained through RCH at 0 °C for 4 h was lost within 1 h if the adults were returned to 26 °C before exposure to −12 °C. Survival at both −12 and −5 °C was greater for RCH-treated than for ACC-treated adults (for ACC, adults were kept at 15 °C for 5 days), and the lethal temperature (2 h exposure) was lower for RCH-treated than for ACC-treated adults. The results suggest that RCH may help C. ciliata survive the acute low temperatures that often occur in early winter and early spring in northern and eastern China.

Distribution of hydrocarbons in the estuarine area of the Northern Dvina River during seasonal flood

Heavy contaminant load released into the Northern Dvina River during flooding increased the concentrations of aliphatic (AHC) and polcyclic aromatic (PAH) hydrocarbons in water and bottom sediments. The composition of hydrocarbons was different from that of the summer low flow season. The concentrations of dissolved and particulate AHC ranged from 12 to 106 and from 192 to 599 μg/l, respectively, and bottom sediments contained from 26.2 to 329 μg/g AHC and 4 to 1785 ng/g PAH. As the transformation of AHC occurred at low spring temperatures, the alkane composition was shown to be dominated by terrigenous compounds, whereas more stable PAH showed elevated contents of petrogenic and pyrogenic compounds. It was also shown that the Northern Dvina-Dvina Bay geochemical barrier prevents contaminant input into the White Sea, i.e., acts as a marginal filter.

Fish recruitment in a large, temperate floodplain: the importance of annual flooding, temperature and habitat complexity

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young-of-the-year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006–2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species–environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature

Interdependent effects of habitat quality and climate on population growth of an endangered plant

Summary 1. To predict the viability of populations, it is essential to clarify how performance depends both on large-scale environmental changes, such as climate warming, and on the local habitat. However, in spite of their potential importance, effects of interactions between large-scale environmental changes and the local environment on population viability have rarely been examined. 2. We investigated how population dynamics of the endangered alpine plant Dracocephalum austriacum depend on local habitat quality and climatic variation, as well as how effects of climate depend on local habitat. We used lasso regression shrinkage and integral projection models to identify effects on vital rates and population growth rates in seven populations over seven annual transitions. 3. Populations on steeper slopes had lower survival and stochastic population growth rate than populations on more gentle slopes. In years with low spring temperatures and high summer temperatures, survival and population growth rate were lower. In addition, the negative effects of high summer temperatures did depend on local habitat quality, being more negative in populations on steeper slopes. 4. Combining the net positive effects of high spring temperature and the net negative effects of high summer temperature on plant vital rates with predicted climate change over the next 30 years suggested that effects on D. austriacum would be relatively small. 5. Synthesis. Our results show that different aspects of a warmer climate may have opposing effects on populations, and that climatic effects may depend on local habitat quality. Such interactive effects should be accounted for when determining effects of large-scale environmental changes on population and community dynamics.

Microclimate and the Zoonotic Cycle of Tick-Borne Encephalitis Virus in Switzerland

The focal distribution of tick-borne encephalitis virus (TBEV; Flaviviridae, Flavivirus) appears to depend mainly on cofeeding transmission between infected Ixodes ricinus L. nymphs and uninfected larvae. To better understand the role of cofeeding ticks in the transmission of TBEV, we investigated tick infestation of rodents and the influence of microclimate on the seasonality of questing I. ricinus ticks. A 3-yr study was carried out at four sites, including two confirmed TBEV foci. Free-living ticks and rodents were collected monthly, and microclimatic data were recorded. A decrease in questing nymph density was observed in 2007, associated with low relative humidity and high temperatures in spring. One site, Thun, did not show this decrease, probably because of microclimatic conditions in spring that favored the questing nymph population. During the same year, the proportion of rodents carrying cofeeding ticks was lower at sites where the questing nymph density decreased, although the proportion of infested hosts was similar among years. TBEV was detected in 0.1% of questing ticks, and in 8.6 and 50.0% of larval ticks feeding on two rodents. TBEV was detected at all but one site, where the proportion of hosts with cofeeding ticks was the lowest. The proportion of hosts with cofeeding ticks seemed to be one of the factors that distinguished a TBEV focus from a non-TBEV focus. The enzootic cycle of TBEV might be disrupted when dry and hot springs occur during consecutive years.

Crops that feed the world 3. Investing in lentil improvement toward a food secure world

Lentils play a major role in the food and nutritional security of millions, particularly among low-income Asian families, because of the high protein content of their seed. As is the case for many pulses, lentils play an important role as a rotation crop, enhancing soil fertility and providing other environmental services in production systems. While its production has risen globally at 8.6 kg/ha/year from 1961 to 2008, the major challenge is to increase investment in lentil improvement (both research and outreach) in countries where the crop is part of the production system. Where currently grown the major abiotic stresses are low moisture availability and high temperatures in spring, and winter cold at high elevations. Among biotic stresses, rust, and vascular wilt are key, and resistance has resulted in improvements in performance. Additional production constraints include the agronomic problems of pod loss, lodging and poor crop management. Adequate variability for most genetic constraints exists within the gene pool allowing breeding. However, several key traits, such as biomass yield, pod shed, nitrogen fixation and resistance to aphids are not currently addressable by breeding because of insufficient variation. Among lentil-producing developing countries, policies have not yet focused on lentil development needs to enhance food security and provide a remunerative rotation crop for cereals. Looking towards a future in which there is likely to be less water available to agriculture, climate change, food insecurity, rising costs for inorganic nitrogen fertilizer, and an increasingly nutrition-conscious society—collectively these give a bright future for a highly nutritious food produced by a nitrogen-fixing crop such as lentil adapted to the farming systems of marginal lands.

Effects of ridge and conventional tillage systems on soil properties and cotton growth

Cotton (Gossypium hirsutum L.) seeds are susceptible to low temperature and excess moisture in soil during seed emergence in years with high rainfall and low temperature in spring. Therefore, a two-year field experiment was carried out to evaluate effects of ridge tillage formed in autumn (RT-I), ridge tillage formed about a month before planting (RT-II) and flat conventional tillage (CT) cultivation systems on physical properties of soil and cotton growth. The RT-I and RT-II resulted in higher soil temperature and lower soil penetration resistance than CT at all depths. The RT-II gave highest emergence, earliest maturity and greatest seed cotton yield. In conclusion, ridge tillage formed a month before planting may be considered a good agronomic practice because it can provide favorable physical conditions in soil, while also improving growth and yield of cotton under weather conditions in spring in South East Anatolia Region of Turkey.

Habitat selection as the mechanism for thermoregulation in a northern population of massasauga rattlesnakes (Sistrurus catenatus)

Although temperature is recognized as an important barrier to reptile distribution, the mechanisms of this limitation are poorly understood. We investigated the association between temperature, habitat selection, and thermoregulation in a population of massasauga rattlesnakes (Sistrurus catenatus) near their northern range limit, where low temperatures are likely an important constraint. Movement data indicated that the lower limit of the massasauga's performance range (i.e., ≥ 50% of optimal) was 19.9 °C. Operative environmental temperatures were almost always below the massasauga's preferred range (30.0–33.6 °C) and frequently below its performance range in spring and fall. Massasaugas differed from other northern snakes by thermoregulating primarily by microhabitat selection and not by macrohabitat selection. Massasaugas thermoregulated more effectively as their visibility increased and forest cover decreased. Gravid females increased thermoregulatory behaviour in response to low temperatures in spring and summer. Male and nongravid female massasaugas did not take full advantage of thermoregulatory opportunities in the spring and fall, and as a consequence were often too cool to perform essential functions such as prey capture. Our results are consistent with the hypothesis that temperature limits massasauga distribution primarily via effects on gestation and hence juvenile recruitment.

Municipal Biosolids as an Alternative Nutrient Source for Bioenergy Crops: II. Decomposition and Organic Nitrogen Mineralization

High‐yielding biomass crops remove significant quantities of soil nutrients, and nutrient replacement using inorganic fertilizers may not be sustainable. Municipal biosolids (MBS) are an alternative nutrient source. Organic N is the primary N form in MBS, and patterns of N mineralization can determine the effectiveness of MBS as an N source. The objectives of this experiment were to: (i) determine the effect of season of application on organic N mineralization rate and dry matter (DM) decomposition of Class A MBS measured in the field with litter bags and (ii) compare N mineralization measured using a field‐based technique with that predicted from the DECOMPOSITION model. Treatments were season of MBS application (spring and summer) during 2 yr. Organic N mineralization measured using litter bags followed the same pattern and arrived at a similar endpoint as predicted by the DECOMPOSITION model in three of four seasons. Lower spring temperatures and rainfall were associated with lower rates of N mineralization and DM decomposition during the 50 d following spring vs. summer application of MBS. When MBS were applied in summer, organic N mineralization leveled off approximately 50 d after application compared with 150 to 250 d following spring application. Seasonal weather conditions and N mineralization patterns should be considered when determining whether to apply MBS as the source of N, the timing of MBS application, and if single or split applications are best.

Spatial and temporal variations in the photosynthesis-nitrogen relationship in a Japanese cedar (Cryptomeria japonica D. Don) canopy

Spatial and temporal variations in light-saturated photosynthetic capacity and needle nitrogen (N) content were investigated in one 8 m tall Japanese cedar (Cryptomeria japonica D. Don) canopy for a full year. The photosynthetic capacity and needle N content in various layers of the canopy were measured every month. Temporal variations in photosynthetic capacity and needle N content expressed on a projected-area basis (Parea, Narea) were similar. Furthermore, both Parea and Narea decreased with increasing depth from the top of the canopy on each sampling date. As a consequence, a significant correlation was observed between Narea and Parea. Temporal variations in photosynthetic capacity and needle N content expressed on a mass basis (Pmass, Nmass) were also similar. Pmass also decreased with increasing canopy depth. However, in contrast to Narea, there was only a slight decrease in Nmass with increasing canopy depth. Hence, the correlation between Nmass and Pmass was lower than the projected-area value. Because Narea was highly correlated with the needle mass per projected-area (NMA), the spatial variation in Narea (and therefore Parea) in the canopy is attributed to the variation in NMA, which decreases as the depth from the top of the canopy increases. Furthermore, the slope of the linear regression between Narea and NMA differed between sampling dates, indicating that the temporal variations in Narea (and therefore Parea) are strongly influenced by Nmass. For most of the sampling dates, a linear regression between Narea and Parea tends to converge into a single line segment. However, on several sampling dates, there was a pronounced decline in Parea below this line segment. This reduction in Parea, which does not accompany a reduction in Narea, seems to be attributable to stomatal limitations induced by the low soil temperature in winter and early spring.

Effects of open-top chambers on physical properties of air and soil at post-disturbance sites in northwestern Quebec

Ecosystem responses to current global climate change can be predicted through experimental climate simulations. One such simulation method is the open-top chamber (OTC). The effects of OTCs on environmental factors are potentially complex, and recognizing the numerous interactions among these factors is crucial for the proper use of chambers. We studied the effects of OTCs on microclimatic factors including ambient temperature, relative humidity, soil temperature, and soil moisture. Plant abundance responses were also assessed. Our study involved the construction of 20 OTCs (1 m in diameter and 0.75 m in height; made of clear acrylic plastic) and 20 control plots on substrates with and without Sphagnum moss, at post-fire and logging sites of the transitional mixedwood-boreal forest in the southern part of James Bay region, Quebec. Experimental trials were also conducted to test the effects of OTCs on snowmelt in the Montreal region. Our results suggest that OTC treatment is most evident in terms of increased daytime maximum temperatures (2°C to 3°C), and cooler (up to ∼2.4°C), drier (up to 10% volumetric moisture content) soils. Advanced thawing of the insulating snow cover and exposure of soil in the OTCs to low spring temperatures appeared to prolong soil freeze and result in cooler soils. Earlier snowmelt probably also led to earlier onset and overall increased evaporation of meltwater in the OTCs, leading to drier soils. Plant abundance responses to OTC treatment differed depending on plant species. Overall, open-top chambers provide an effective and simple method of climate change simulation, but it is highly advisable that the complex interactive effects, both desired and undesired, are well understood and appreciated before using OTCs for experimental climate simulation.

The earliest daily barometric pressure readings in Italy: Pisa AD 1657-1658 and Modena AD 1694, and the weather over Europe

The earliest daily barometric pressure readings were taken during the Maunder Minimum of Solar activity (1645—1715). In Italy, observations were made at Pisa over the years 1657—1658 by V. Viviani and A. Borelli, and at Modena during the year 1694 by B. Ramazzini. These readings have been recovered, corrected and adjusted to modern units. The early instruments used and their problems have been thoroughly discussed. Barometer observations recorded by John Locke in Essex (UK) during the year 1694 have also been recovered and corrected. Daily observations were recorded during the same period in Paris by L. Morin; these have previously been published by Legrand and Le Goff (1992: Les observations météorologiques de Louis Morin. Monographie No. 6, Direction de la Météorologie Nationale, Ministère de l’Equipement, de Logement et des Transports, 41 pp.). However, cross-comparisons with the Locke and Ramazzini data have shown that the Paris series needed a further correction to take into account instrumental error. Using these three corrected series, it has been possible to reconstruct the atmospheric circulation over Europe for the year 1694. An indication of the state of the atmospheric circulation can also be made by using the earlier observations recorded in Italy. A common feature of the two periods studied (1657—1658 and 1694) is that winters were characterized by higher pressure compared with the reference period 1961—1990, while the summers generally experienced lower pressure. This latter conclusion indicates that the Azores High was late or not well developed, favouring low temperature and frequent rain in the late spring and early summer.