Effect of Diurnally Fluctuating vs. Constant Temperatures on Flower Induction and Sex Expression in the Olive (Olea europaea)

Olive trees must be exposed to a period of winter chilling temperatures in order to form inflorescences the following spring. The effects of diurnally fluctuating and constant temperatures on flower induction and sex expression in the olive were compared under controlled environment conditions. The effect on flowering of diurnally fluctuating temperatures depends upon the length of time at the higher temperatures. While daily exposure to the high temperatures (21° to 26°C) for a short period (four hours) intensified the effectiveness of the low temperatures (7° to 12.5°C), when the high temperature duration was 12 hours it counteracted the low temperature action. Possibly, daily low temperatures act to stimulate reactions leading to floral hormone synthesis, while daily short exposures to high temperatures act to maintain metabolic activity, promote energy-yielding reactions, and possibly stimulate cell-division activity. In the olive, an intermediate constant temperature (12.5°C) favors both types of reactions and induces flowering; however, in this case, the pistils fail to develop. The olive has very specific temperature requirements for flowering and neither the mean temperature nor the accumulated number of hours below a given value, e.g. 7°C, adequately characterizes these requirements.     

Long‐term experimental manipulation of climate alters the ectomycorrhizal community of Betula nana in Arctic tundra

Climate warming is leading to shrub expansion in Arctic tundra. Shrubs form ectomycorrhizal (ECM) associations with soil fungi that are central to ecosystem carbon balance as determinants of plant community structure and as decomposers of soil organic matter. To assess potential climate change impacts on ECM communities, we analysed fungal internal transcribed spacer sequences from ECM root tips of the dominant tundra shrub Betula nana growing in treatments plots that had received long‐term warming by greenhouses and/or fertilization as part of the Arctic Long‐Term Ecological Research experiment at Toolik Lake Alaska, USA. We demonstrate opposing effects of long‐term warming and fertilization treatments on ECM fungal diversity; with warming increasing and fertilization reducing the diversity of ECM communities. We show that warming leads to a significant increase in high biomass fungi with proteolytic capacity, especially Cortinarius spp., and a reduction of fungi with high affinities for labile N, especially Russula spp. In contrast, fertilization treatments led to relatively small changes in the composition of the ECM community, but increased the abundance of saprotrophs. Our data suggest that warming profoundly alters nutrient cycling in tundra, and may facilitate the expansion of B. nana through the formation of mycorrhizal networks of larger size.     

Will a 385 million year‐struggle for light become a struggle for water and for carbon? – How trees may cope with more frequent climate change‐type drought events

Trees are exceptional organisms that have evolved over some 385 million years and have overtaken other plants in order to harvest light first. However, this advantage comes with a cost: trees must transport water all the way up to their crowns and inherent physical limitations make them vulnerable to water deficits. Because climate change scenarios predict more frequent extreme drought events, trees will increasingly need to cope with water stress. Recent occurrences of climate change‐type droughts have had severe impacts on several forest ecosystems. Initial experimental studies have been undertaken and show that stomatal control of water loss hinders carbon assimilation and could lead to starvation during droughts. Other mechanisms of drought‐induced mortality are catastrophic xylem dysfunction, impeded long‐distance transport of carbohydrates (translocation) and also symplastic failure (cellular breakdown). However, direct empirical support is absent for either hypothesis. More experimental studies are necessary to increase our understanding of these processes and to resolve the mystery of drought‐related tree mortality. Instead of testing the validity of particular hypothesis as mechanisms of drought‐induced tree mortality, future research should aim at revealing the temporal dynamics of these mechanisms in different species and over a gradient of environmental conditions. Only such studies will reveal whether the struggle for light will become a struggle for water and/or for carbon in drought‐affected areas.     

Water deprivation tolerance and humidity response in a larval dragonfly: a possible adaptation for survival in drying ponds

Abstract.  Water deprivation tolerance is investigated in the last larval stadium of Libellula depressa under various conditions of relative humidity (60–100% relative humidity; RH). Most of the larvae maintained at 100% RH emerge and, at lower RH levels show some resistance to dehydration because they die after a mean period ranging from 1.4 days at 60% RH up to 6.7 days at 90% RH. In dual-choice chambers with humidity gradients from 63–74% RH and from 68–84% RH, larvae spend most of the time in the moist side of the chamber. In a Y-tube olfactometer, the larvae reveal a positive hygrotaxis to two airstreams carrying different amounts of water vapour (98% vs. 50%) and spend most of their time in the 'humid' arm. The ecological significance of desiccation tolerance and hygropositive response in the last larval stadium of L. depressa is discussed in relation to the presence of hygroreceptors in dragonfly larvae.     

Environmental features influencing Carabid beetle (Coleoptera) assemblages along a recently deglaciated area in the Alpine region

Abstract.  1. The spatio-temporal approach was used to evaluate the environmental features influencing carabid beetle assemblages along a chronosequence of an Italian Alpine glacier foreland. The influence of environmental variables on species richness, morphology (wing and body length), and distribution along the chronosequence was tested.
2. Species richness was found to be a poor indicator of habitat due to weak influences by environmental variables. It seems that the neighbouring habitats of a glacier foreland are not able to determine significant changes in carabid species richness.
3. Instead it appears that history (age since deglaciation) and habitat architecture of a glacier foreland are strongly correlated to species adaptive morphological traits, such as wing morphology and body length. Assemblages characterised by species with reduced wing size are linked to the older stages of the chronosequence, where habitat is more structured. Assemblages characterised by the largest species are linked to the younger sites near the glacier. These morphological differentiations are explained in detail.
4. Habitat age can therefore be considered the main force determining assemblage composition. On the basis of the relationship between morphological traits and environmental variables, it seems likely that age since deglaciation is the main variable influencing habitat structure (primary effect) on the Forni foreland. The strong relationship between carabid assemblages and habitat type indicates that site age has but a secondary effect on carabid assemblages. This may be utilised to interpret potential changes in assemblages linked to future glacier retreat.