Effect of acclimation on heat-escape temperatures of two aphid species: Implications for estimating behavioral response of insects to climate warming

An aphid usually stays at one feeding site for a long time to achieve its development and reproduction, while high temperatures can make it decide to escape from heat stress. Climate warming increases daily high-temperature both in degree and time. However, it remains unknown whether such heat-escape behavior will be influenced by those daily temperature changes. In this study, a wheat-leaf temperature gradient was created based on field microhabitat temperatures. We defined a parameter, heat-escape temperature (HET) to describe the critical temperature at which an aphid turns back when it walks along the gradient from mild temperature to high temperatures. HET indicates behavioral responses of the aphids to heat stress. Two aphid species, Sitobion avenae and Rhopalosiphum padi, main economic pests in temperate areas were selected as test insects. Detailed studies were conducted on the temperature gradient to reveal effects of acclimation temperature, time, and condition (temperature×time) on HET of both species. Results showed that HET decreased non-linearly (S. avenae: 41.4-38.6°C, R. padi: 41.3-39.4°C), when acclimation temperature increased from 25 to 36°C. For both species, HET declined linearly (S. avenae: 40.1-38.0°C, R. padi: 41.3-38.5°C) as acclimation time increased from 0.5 to 6h at 35°C, whereas HET descended non-linearly with reduction of acclimation time at 10°C. HET for both species acclimated under constantly warm conditions (future daily temperature) were significantly lower than those acclimated under gradually warm conditions (current daily temperature). These results suggest that aphids' heat-escape behavior is significantly influenced by brief thermal history, implying that aphids make decision to avoid heat stress based on the combination of temperature and exposure time and escape before they were hurt by high temperatures under the conditions of climate warming. Avoiding high temperatures may cost a lot of time and resources of aphids and thus potentially reduced growth, development, and reproduction. Changes in insect behaviors caused by ongoing climate warming and their ecological consequences should be more concerned.     

Forecasting changes in population genetic structure of alpine plants in response to global warming

Species range shifts in response to climate and land use change are commonly forecasted with species distribution models based on species occurrence or abundance data. Although appealing, these models ignore the genetic structure of species, and the fact that different populations might respond in different ways because of adaptation to their environment. Here, we introduced ancestry distribution models, that is, statistical models of the spatial distribution of ancestry proportions, for forecasting intra-specific changes based on genetic admixture instead of species occurrence data. Using multi-locus genotypes and extensive geographic coverage of distribution data across the European Alps, we applied this approach to 20 alpine plant species considering a global increase in temperature from 0.25 to 4 °C. We forecasted the magnitudes of displacement of contact zones between plant populations potentially adapted to warmer environments and other populations. While a global trend of movement in a north-east direction was predicted, the magnitude of displacement was species-specific. For a temperature increase of 2 °C, contact zones were predicted to move by 92 km on average (minimum of 5 km, maximum of 212 km) and by 188 km for an increase of 4 °C (minimum of 11 km, maximum of 393 km). Intra-specific turnover-measuring the extent of change in global population genetic structure-was generally found to be moderate for 2 °C of temperature warming. For 4 °C of warming, however, the models indicated substantial intra-specific turnover for ten species. These results illustrate that, in spite of unavoidable simplifications, ancestry distribution models open new perspectives to forecast population genetic changes within species and complement more traditional distribution-based approaches.     

Developmental parameters and seasonal phenology of Calepitrimerus vitis (Acari: Eriophyidae) in wine grapes of western Oregon

Developmental parameters of protogyne Calepitrimerus vitis (Nalepa) (Acari: Eriophyidae) were determined at 12, 15, 17, 22, 25, 28, 31, and 34 °C to better understand seasonal activity, population growth, and ultimately more effectively manage pest mites in wine grapes. Net reproductive rate (R(o)) was greater than zero at all temperatures with the maximum R(o) (9.72) at 25 °C. The lowest estimated R(o) (0.001) occurred at 34 °C. There was a gradual decrease in mean generation time (T) as temperatures increased from 17 to 31 °C. The shortest and longest generation time was recorded at 31 °C (T = 5.5 d) and 17 °C (T = 17.5 d). Rates of natural increase were lowest at 17°C (0.035) and increased with increasing temperatures, respectively. The peak rate of natural increase value (0.141) was at 25 °C. Estimations for minimum and maximum developmental thresholds were 10.51 and 39.19 °C, respectively, while the optimum developmental temperature was 26.9 °C. The thermal constant for egg to adult development was estimated at 87.7DD. The highest fecundity was observed at 25 °C. These parameters indicated that mites begin feeding at the onset of shoot growth when tissue is most susceptible in spring. Historical weather data showed that vines are in this susceptible growth stage for longer periods in the cool Willamette Valley compared with warmer Umpqua and Applegate/Rogue Valley regions. Estimation of degree-days indicated when deutogyne mites move to overwintering refuge sites. Degree-day accumulations indicated up to 14 generations per growing season.     

Development and survival of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) as a function of temperature: effect on the number of generations in tropical and subtropical regions

The diamondback moth, Plutella xylostella (L.), is the most important pest of brassicaceous crops worldwide. Since temperature is the major abiotic factor influencing insect development and thermal requirements may vary among insect populations, it is important to know the effect of temperature on development and survival of a subtropical strain of P. xylostella. Development and survival of the diamondback moth was evaluated under seven constant temperatures ranging from 10°C to 35°C. Development was completed between 10°C and 32.5°C, but at 35°C all individuals died in the larval stage. Data were fitted to one linear and five nonlinear models. Considering as criteria the goodness of fit and the ability to estimate parameters of biological significance, the models Briere-1 and Briere-2 were the most adequate to describe the relationship between temperature and development of P. xylostella. The linear model demonstrated that P. xylostella required 312.5 degree-days above a lower threshold of 6.3°C to complete development. The degree-day model showed that the number of diamondback moth generations in the tropical region of Brazil is nearly twice the number in the subtropical region of the country. This result explains, at least in part, the higher population levels of this species in the tropical region of Brazil, and also demonstrates that P. xylostella is tolerant to a wide range of temperatures (6.1-32.5°C). Therefore, temperature cannot be considered a limiting factor for the occurrence of diamondback moth throughout the year in most regions of Brazil.     

Embryonic developmental rates of northern grasshoppers (Orthoptera: Acrididae): implications for climate change and habitat management

Accurate models of temperature-dependent embryonic developmental rates are important to assess the effects of a changing climate on insect life cycles and to suggest methods of population management by habitat manipulation. Embryonic development determines the life cycle of many species of grasshoppers, which, in cold climates, spend two winters in the egg stage. Increasing temperatures associated with climate change in the subarctic could potentiate a switch to a univoltine life cycle. However, egg hatch could be delayed by maintaining a closed vegetative canopy, which would lower soil temperatures by shading the soil surface. Prediapause and postdiapause embryonic developmental rates were measured in the laboratory over a wide range of temperatures for Melanoplus borealis Fieber and Melanoplus sanguinipes F. (Orthoptera: Acrididae) A model was fit to the data and used to predict dates of egg hatch in the spring and prediapause development in the fall under different temperature regimens. Actual soil temperatures were recorded at several locations over 5 yr. To simulate climate warming, 2, 3, or 4°C was added to each hourly recorded temperature. Results suggest that a 2, 3, or 4°C increase in soil temperatures will result in eggs hatching ≈ 3, 5, or 7 d earlier, respectively. An increase of 3°C would be required to advance prediapause development enough to allow for a portion of the population to be univoltine in warmer years. To simulate shading, 2 and 4°C were subtracted from observed temperatures. A 4°C decrease in temperatures could potentially delay hatch by 8 d.     

Parasites do not adapt to elevated temperature,as evidenced from experimental evolution of a phytoplankton–fungus system

Global warming is predicted to impact the prevalence and severity of infectious diseases. However, empirical data supporting this statement usually stem from experiments in which parasite fitness and disease outcome are measured directly after temperature increase. This might exclude the possibility of parasite adaptation. To incorporate the adaptive response of parasites into predictions of disease severity in a warmer world, we undertook an experimental evolution assay in which a fungal parasite of phytoplankton was maintained at elevated or control temperatures for six months, corresponding to 100–200 parasite generations. Host cultures were maintained at the respective temperatures and provided as substrate, but were not under parasite pressure. A reciprocal infection experiment conducted after six-month serial passages revealed no evidence of parasite adaptation. In fact, parasite fitness at elevated temperatures was inferior in parasite populations reared at elevated temperatures compared with those maintained under control temperature. However, this effect was reversed after parasites were returned to control temperatures for a few (approx. 10) generations. The absence of parasite adaptation to elevated temperatures suggests that, in phytoplankton–fungus systems, disease outcome under global warming will be largely determined by both host and parasite thermal ecology.     

Upper temperature limits of tropical marine ectotherms: global warming implications

Animal physiology, ecology and evolution are affected by temperature and it is expected that community structure will be strongly influenced by global warming. This is particularly relevant in the tropics, where organisms are already living close to their upper temperature limits and hence are highly vulnerable to rising temperature. Here we present data on upper temperature limits of 34 tropical marine ectotherm species from seven phyla living in intertidal and subtidal habitats. Short term thermal tolerances and vertical distributions were correlated, i.e., upper shore animals have higher thermal tolerance than lower shore and subtidal animals; however, animals, despite their respective tidal height, were susceptible to the same temperature in the long term. When temperatures were raised by 1°C hour(-1), the upper lethal temperature range of intertidal ectotherms was 41-52°C, but this range was narrower and reduced to 37-41°C in subtidal animals. The rate of temperature change, however, affected intertidal and subtidal animals differently. In chronic heating experiments when temperature was raised weekly or monthly instead of every hour, upper temperature limits of subtidal species decreased from 40°C to 35.4°C, while the decrease was more than 10°C in high shore organisms. Hence in the long term, activity and survival of tropical marine organisms could be compromised just 2-3°C above present seawater temperatures. Differences between animals from environments that experience different levels of temperature variability suggest that the physiological mechanisms underlying thermal sensitivity may vary at different rates of warming.     

气候变暖对昆虫影响研究进展

"全球气候变化"已成为国内外最受关注的环境问题。气候变化中以温度升高为特征的气候变暖对变温动物昆虫自身及其所在的生物群落产生直接或间接影响。从研究内容与研究方法2个方面综述了气候变暖对昆虫影响研究的国内外进展。气候变暖导致昆虫发生期提前,地理分布向更高纬度和海拔地区扩散,低温适生种种群密度下降,高温适生种种群密度增加。气候变暖改变寄主植物—害虫—天敌的物候同步性和昆虫原有种间互作关系,影响植食性昆虫的寄主植物范围和取食为害程度。长期的气候变暖带来的强烈的选择性压力引起某些昆虫种群的基因组发生变异。以日均温升高、日最高气温升高和昼夜温差变化等为主要特征气候变暖对昆虫发育、繁殖及存活等生态学指标产生重要影响。研究方法上主要是利用野外直接观察法、回归预测模型、有效积温模型、CLIMEX和GIS等生态风险评估软件、生物化石比较技术、人工气候下生态试验、检测标记基因频率变化等方法来研究气候变暖对昆虫的影响。最后简要评述了已有研究的不足并指出未来的研究方向:(1)气候变暖情景下开展昆虫种间互作研究并拓展研究对象;(2)高温下昆虫适应性研究;(3)建立完善人工模拟气候下的实验方法;(4)构建昆虫有效生态机理模型。     

陆地生态系统野外增温控制实验的技术与方法

由于人类活动导致的碳排放急剧增加, 工业革命以来全球地表温度显著增加约1 ℃, 未来全球气候还将持续变暖, 到21世纪末最高可升温4 ℃。这种前所未有的气候变化不仅影响陆地植被的适应策略, 也深刻影响生态系统的结构和功能。其中陆地生态系统碳收支对全球变暖的反馈, 是决定未来气候变化强度的关键因素, 因此全球已经开展了大量的生态系统尺度的野外增温控制实验, 研究生态系统碳收支对气温升高的响应, 从而提高地球系统模型的预测精度。然而由于增温技术和方法的不同, 不同研究的结果之间难以进行比较。该文系统总结了常见的野外增温技术和方法, 包括主动增温和被动增温, 阐述了其优缺点、适用对象以及相关研究成果。同时简要介绍了野外增温控制实验的前沿研究方向——新一代野外增温技术(包括全土壤剖面增温和全生态系统增温)和基于新一代增温技术开展的野外增温联网实验。     

Thermal acclimation of interactions: differential responses to temperature change alter predator-prey relationship

Different species respond differently to environmental change so that species interactions cannot be predicted from single-species performance curves. We tested the hypothesis that interspecific difference in the capacity for thermal acclimation modulates predator-prey interactions. Acclimation of locomotor performance in a predator (Australian bass, Macquaria novemaculeata) was qualitatively different to that of its prey (eastern mosquitofish, Gambusia holbrooki). Warm (25°C) acclimated bass made more attacks than cold (15°C) acclimated fish regardless of acute test temperatures (10-30°C), and greater frequency of attacks was associated with increased prey capture success. However, the number of attacks declined at the highest test temperature (30°C). Interestingly, escape speeds of mosquitofish during predation trials were greater than burst speeds measured in a swimming arena, whereas attack speeds of bass were lower than burst speeds. As a result, escape speeds of mosquitofish were greater at warm temperatures (25°C and 30°C) than attack speeds of bass. The decline in the number of attacks and the increase in escape speed of prey means that predation pressure decreases at high temperatures. We show that differential thermal responses affect species interactions even at temperatures that are within thermal tolerance ranges. This thermal sensitivity of predator-prey interactions can be a mechanism by which global warming affects ecological communities.     

Grazing alters warming effects on leaf photosynthesis and respiration in Gentiana straminea,an alpine forb species

Aims Vast grasslands on the Tibetan Plateau are almost all under livestock grazing. It is unclear, however, what is the role that the grazing will play in carbon cycle of the grassland under future climate warming. We found in our previous study that experimental warming can shift the optimum temperature of saturated photosynthetic rate into higher temperature in alpine plants. In this study, we proposed and tested the hypothesis that livestock grazing would alter the warming effect on photosynthetic and respiration through changing physical environments of grassland plants.Methods Experimental warming was carried by using an infrared heating system to increase the air temperature by 1.2 and 1.7°C during the day and night, respectively. The warming and ambient temperature treatments were crossed over to the two grazing treatments, grazing and un-grazed treatments, respectively. To assess the effects of grazing and warming, we examined photosynthesis, dark respiration, maximum rates of the photosynthetic electron transport (J max), RuBP carboxylation (V cmax) and temperature sensitivity of respiration Q 10 in Gentiana straminea, an alpine species widely distributed on the Tibetan grassland. Leaf morphological and chemical properties were also examined to understand the physiological responses.Important findings 1) Light-saturated photosynthetic rate (A max) of G. straminea showed similar temperature optimum at around 16°C in plants from all experimental conditions. Experimental warming increased A max at all measuring temperatures from 10 to 25°C, but the positive effect of the warming occurred only in plants grown under the un-grazed conditions. Under the same measuring temperature, A max was significantly higher in plants from the grazed than the un-grazed condition. 2) There was significant crossing effect of warming and grazing on the temperature sensitivity (Q 10) of leaf dark respiration. Under the un-grazed condition, plants from the warming treatment showed lower respiration rate but similar Q 10 in comparison with plants from the ambient temperature treatment. However, under the grazed condition Q 10 was significantly lower in plants from the warming than the ambient treatment. 3) The results indicate that livestock grazing can alter the warming effects on leaf photosynthesis and temperature sensitivity of leaf dark respiration through changing physical environment of the grassland plants. The study suggests for the first time that grazing effects should be taken into account in predicting global warming effects on photosynthesis and respiration of plants in those grasslands with livestock grazing.     

Walking speed adaptation ability of Myzus persicae to different temperature conditions

Walking speeds were calculated for nine clones of the peach potato aphid Myzus persicae collected from three countries along a latitudinal cline of its European distribution from Sweden to Spain (Sweden, UK and Spain), and the effects of collection origin and intra and intergenerational acclimation were investigated. Walking speeds declined with decreasing temperature, with maximum performance at temperatures closest to acclimation temperature (fastest median walking speed of 5.8 cm min(-1) was recorded for clone UK 3, collected from the UK, at 25°C after acclimating to 25°C for one generation). Following acclimation at both 20°C and 25°C, walking ceased (as indicated by median walking speeds of 0.0 cm min(-1)) at temperatures as high as 7.5°C and 12.5°C. However, acclimation at 10°C enabled mobility to occur to temperatures as low as 0°C. There was no relationship between mobility and latitude of collection, suggesting that large scale mixing of aphids may occur across Europe. However, clonal variation was suggested, with clone UK 3 outperforming the majority of other clones across all temperatures at which mobility was maintained following acclimation at 10°C for one and three generations and at 25°C for one generation. The Scandinavian clones consistently outperformed their temperate and Mediterranean counterparts at the majority of temperatures following acclimation for three generations at 25°C.     

Effects of meteorological factors and global warming on rice insect pests in Korea

We examined the occurrence patterns of insect pests in paddy fields using a self-organizing map (SOM) and the influence of meteorological factors on these patterns. Data for nine insect pests and three meteorological factors were collected on the Korean nationwide scale from 1992 to 2008. The SOM analysis was based on annual mean densities of each pest species in eight regions. We classified the samples into five clusters (I–V) to display the spatial and temporal changes in the insect pests' occurrences. Clusters I and II included samples collected before 2000; clusters III and IV included samples collected after 2000. The density of Scotinophara lurida was in the lowest range in clusters I and II, and Lissorhoptrus oryzophilus exhibited higher densities in clusters III and IV. Seasonal temperature, humidity, and precipitation were significantly different among clusters, indicating that these factors play a key role in population dynamics and the occurrence of insect pests. The occurrence area of the insect pests was expected to increase with elevated air temperature influenced by global warming based on the IPCC (Intergovernmental Panel on Climate Change) A1B scenario. This study suggests that gathering data on temporal and spatial variations in pest populations and changes in occurrence rate under the effects of global warming can provide insight into the factors governing the population-environment relationships, as well as the information needed for future pest management.     

Effects of adaptation, chance, and history on the evolution of the toxic dinoflagellate Alexandrium minutum under selection of increased temperature and acidification

The roles of adaptation, chance, and history on evolution of the toxic dinoflagellate Alexandrium minutum Halim, under selective conditions simulating global change, have been addressed. Two toxic strains (AL1V and AL2V), previously acclimated for two years at pH 8.0 and 20°C, were transferred to selective conditions: pH 7.5 to simulate acidification and 25°C. Cultures under selective conditions were propagated until growth rate and toxin cell quota achieved an invariant mean value at 720 days (ca. 250 and ca. 180 generations for strains AL1V and AL2V, respectively). Historical contingencies strongly constrained the evolution of growth rate and toxin cell quota, but the forces involved in the evolution were not the same for both traits. Growth rate was 1.5-1.6 times higher than the one measured in ancestral conditions. Genetic adaptation explained two-thirds of total adaptation while one-third was a consequence of physiological adaptation. On the other hand, the evolution of toxin cell quota showed a pattern attributable to neutral mutations because the final variances were significantly higher than those measured at the start of the experiment. It has been hypothesized that harmful algal blooms will increase under the future scenario of global change. Although this study might be considered an oversimplification of the reality, it can be hypothesized that toxic blooms will increase but no predictions can be advanced about toxicity.     

Changes in fine root biomass of Picea abies forests: predicting the potential impacts of climate change

Aims The impact of global warming on belowground processes, especially on fine root production, is poorly understood in comparison with its aboveground counterpart.Methods Here, we compiled 227 measurements to assess the influence of temperature and precipitation on fine root biomass of Norway spruce (Picea abies [L.] Karst) forest ecosystems in the Eurasia boreal region.Important findings We found that fine root biomass decreased significantly with latitudes. There was a biomass increase of 0.63 Mg ha^-1 and 0.32 Mg ha^-1 for fine roots <2 and <1 mm in diameter, respectively, with 1°C increase of mean annual temperature. There was an increase of 0.5 and 0.1 Mg ha^-1 per 100 mm year^-1 precipitation for the two size classes of fine roots. If the adaption of root production can match the pace of global warming and water is not a limiting factor for plant growth, fine root biomass would be expected to increase by 40–140% in response to the predicted increase in temperature (3–10°C) over the next century. Our analyses highlighted the strongly positive influences of temperature and precipitation on belowground function, suggesting that predicted future climate change could substantially enhance belowground biomass in the boreal region where the greatest warming is anticipated. This potential increase of belowground biomass, coupled with aboveground biomass, may provide a better understanding of climate–ecosystem feedbacks.     

Predicting impacts of global warming on population dynamics and distribution of arthropods in Japan

The mean surface temperature rose by 1.0°C over the last 40 years in Japan. Changes in the pest status, distribution range, winter mortality, and the synchronization in phenology were examined. The increase in the number of annual generations of each taxon was predicted based on the lower developmental threshold and the thermal constant. Increasing damage due to rice- and fruit-infesting bugs, their simultaneous outbreaks and the poleward geographic spread observed for six species may be triggered by global warming. The winter mortality of adults of Nezara viridula and Halyomorpha halys is predicted to be reduced by 15% by each rise of 1°C. More than 50 species of butterflies showed northward range expansions and ten species of previously migrant butterflies established on Nansei Islands during 1966–1987. Global warming may be responsible for the recent decline in abundance of Plutella xylostella and the increase in Helicoverpa armigera and Trichoplusia ni. In general, global warming may work in favour of natural enemies (except for spiders) by increasing the number of generations more than in their host species. Biological control utilizing native natural enemies is expected to become a more important control tactic in the future. Greenhouse culture may provide a model of a temperate agroecosystem after global warming. The increasing occurrence of alien species of tropical origin in association with the increase in pesticide applications might be expected. Interception of alien pests by plant quarantine followed by integrated pest management is needed.     

Effects of constant and changing temperature conditions on diapause induction in Helicoverpa armigera (Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.     

Experiments with duckweed–moth systems suggest that global warming may reduce rather than promote herbivory

1. Wilf & Labandeira (1999) suggested that increased temperatures because of global warming will cause an increase in herbivory by insects. This conclusion was based on the supposed effect of temperature on herbivores but did not consider an effect of temperature on plant growth. 2. We studied the effect of temperature on grazing pressure by the small China‐mark moth (Cataclysta lemnata L.) on Lemna minor L. in laboratory experiments. 3. Between temperatures of 15 and 24 °C we found a sigmoidal increase in C. lemnata grazing rates, and an approximately linear increase in L. minor growth rates. Therefore, an increase in temperature did not always result in higher grazing pressure by this insect as the regrowth of Lemna changes also. 4. At temperatures below 18.7 °C, Lemna benefited more than Cataclysta from an increase in temperature, causing a decrease in grazing pressure. 5. In the context of global warming, we conclude that rising temperatures will not necessarily increase grazing pressure by herbivorous insects.     

Effect of temperature on pollen tube kinetics and dynamics in sweet cherry, Prunus avium (Rosaceae)

Prevailing ambient temperature during the reproductive phase is one of several important factors for seed and fruit set in different plant species, and its consequences on reproductive success may increase with global warming. The effect of temperature on pollen performance was evaluated in sweet cherry (Prunus avium L.), comparing as pollen donors two cultivars that differ in their adaptation to temperature. 'Sunburst' is a cultivar that originated in Canada with a pedigree of cultivars from Northern Europe, while 'Cristobalina' is a cultivar native to southeast Spain, adapted to warmer conditions. Temperature effects were tested either in controlled-temperature chambers or in the field in a plastic cage. In both genotypes, an increase in temperature reduced pollen germination, but accelerated pollen tube growth. However, a different genotypic response, which reflected the overall adaptation of the pollen donor, was obtained for pollen tube dynamics, expressed as the census of the microgametophyte population that successfully reached the base of the style. While both cultivars performed similarly at 20°C, the microgametophyte population was reduced at 30°C for Sunburst and at 10°C for Cristobalina. These results indicate a differential genotypic response to temperature during the reproductive phase, which could be important in terms of the time needed for a plant species to adapt to rapid temperature changes.     

Temperature-induced increase in methane release from peat bogs: a mesocosm experiment

Peat bogs are primarily situated at mid to high latitudes and future climatic change projections indicate that these areas may become increasingly wetter and warmer. Methane emissions from peat bogs are reduced by symbiotic methane oxidizing bacteria (methanotrophs). Higher temperatures and increasing water levels will enhance methane production, but also methane oxidation. To unravel the temperature effect on methane and carbon cycling, a set of mesocosm experiments were executed, where intact peat cores containing actively growing Sphagnum were incubated at 5, 10, 15, 20, and 25°C. After two months of incubation, methane flux measurements indicated that, at increasing temperatures, methanotrophs are not able to fully compensate for the increasing methane production by methanogens. Net methane fluxes showed a strong temperature-dependence, with higher methane fluxes at higher temperatures. After removal of Sphagnum, methane fluxes were higher, increasing with increasing temperature. This indicates that the methanotrophs associated with Sphagnum plants play an important role in limiting the net methane flux from peat. Methanotrophs appear to consume almost all methane transported through diffusion between 5 and 15°C. Still, even though methane consumption increased with increasing temperature, the higher fluxes from the methane producing microbes could not be balanced by methanotrophic activity. The efficiency of the Sphagnum-methanotroph consortium as a filter for methane escape thus decreases with increasing temperature. Whereas 98% of the produced methane is retained at 5°C, this drops to approximately 50% at 25°C. This implies that warming at the mid to high latitudes may be enhanced through increased methane release from peat bogs.