Thermal de‐acclimation: how permanent are leaf phenotypes when cold‐acclimated plants experience warming?

We quantified a broad range of Arabidopsis thaliana (Col‐0) leaf phenotypes for initially warm‐grown (25/20 °C day/night) plants that were exposed to cold (5 °C) for periods of a few hours to 45 d before being transferred back to the warm, where leaves were allowed to mature. This allowed us to address the following questions: (1) For how long do warm‐grown plants have to experience cold before developing leaves become irreversibly cold acclimated? (2) To what extent is the de‐acclimation process associated with changes in leaf anatomy and physiology? We show that leaves that experience cold for extended periods during early development exhibit little plasticity in either photosynthesis or respiration, and they do not revert to a warm‐associated carbohydrate profile. The eventual expansion rate in the warm was inversely related to the duration of previous cold treatment. Moreover, cold exposure of immature/developing leaves for as little as 5 d resulted in irreversible changes in the morphology of leaves that subsequently matured in the warm, with 15 d cold being sufficient for a permanent alteration of leaf anatomy. Collectively, these results highlight the impact of transitory cold during early leaf development in determining the eventual phenotype of leaves that mature in the warm.     

Strong growth limitation of a floating plant (Lemna gibba) by the submerged macrophyte (Elodea nuttallii) under laboratory conditions

1. The asymmetric competition for light and nutrients between floating and submerged aquatic plants is thought to be key in explaining why dominance by either of these groups can be stable and difficult to change. 2. Although the shading effect of floating plants on submerged plants has been well documented, the impact of submerged plants on floating plants has been poorly explored hitherto. 3. Here, we used laboratory experiments to examine how submerged plant (Elodea nuttallii) alter nutrient conditions in the water column and how this affects the growth of floating plants (Lemna gibba). 4. We demonstrate that, at higher nutrient concentrations, Lemna is increasingly likely to outcompete Elodea. 5. Under low nutrient concentrations (0.1–2 mg N L^?1) Elodea can strongly reduce the growth of Lemna. Growth of floating plants virtually stopped in some of the experiments with Elodea. 6. Extremely reduced tissue N, Mn, chlorophyll and elongated roots indicated that the growth inhibition of Lemna by Elodea was predominantly caused by the latter’s impact on the nutrient conditions for floating plants. 7. These results strengthen the hypothesis that submerged plants can prevent colonization of a lake by floating plants.     

A simulation study of the feedback of phytoplankton on thermal structure via light extinction

1. A simulation study of the feedback of phytoplankton biomass on temperature stratification in the large, monomictic Lake Constance was undertaken. Phytoplankton biomass affects the light extinction coefficient (LEC) of the water and, in turn, the vertical distribution of short‐wave radiation, which shapes the temperature stratification in the lake. 2. A sensitivity study of the variation in LEC using the hydrodynamic model DYRESM showed that a high LEC is associated with stronger stratification, shallower thermoclines, higher surface temperatures and reduced heat content during the heating phase of the lake. During the cooling phase, a shallower thermocline at high LEC leads to a faster decrease in water temperature so that during autumn, a high LEC is associated with lower surface temperatures. Thermal structure was particularly sensitive to changes in LEC when its value was below 0.5 m^?1. 3. When LEC is simulated dynamically with the coupled hydrodynamic–ecological model DYRESM‐CAEDYM, its value is a function of phytoplankton dynamics that change vertically and temporally. Comparing simulations with and without dynamic LEC (i.e. with and without phytoplankton dynamics) produced a complex picture: during the vegetation period, we often found a warmer surface layer and colder water beneath in the simulations with dynamic LEC, as expected from the higher LEC when phytoplankton is abundant. However, since phytoplankton biomass (as LEC) fluctuates and because of occasional cooling phases, the patterns were comparatively weak and not consistent over the whole growing season. 4. The most obvious patterns emerged by comparing simulations of oligotrophic and eutrophic conditions. In the eutrophic state, with its higher LEC, stratification was stronger and characterized by higher surface water temperatures, a shallower thermocline and colder water temperatures between 5 and 10 m depth. 5. Statistical analysis of long‐term data of water temperatures in Lake Constance, corrected for external forcing by air temperature, revealed a significant tendency towards warmer temperatures at 7.5 and 10 m depths with decreasing LECs over the course of reoligotrophication. This finding is consistent with our model results.     

Abiotic and biotic processes in lakes recovering from acidification: the relative roles of metal toxicity and fish predation as barriers to zooplankton re‐establishment

1. Recovery of acidified aquatic systems may be affected by both abiotic and biotic processes. However, the relative roles of these factors in regulating recovery may be difficult to determine. Lakes around the smelting complexes near Sudbury, Ontario, Canada, formerly affected by acidification and metal exploration, provide an excellent opportunity to examine the factors regulating the recovery of aquatic communities. 2. Substantial recovery of zooplankton communities has occurred in these lakes following declines in acidity and metal concentrations, although toxicity by residual metals still appears to limit survival for many species. Metal bioavailability, not simply total metal concentrations, was very important in determining effects on zooplankton and was associated with a decrease in the relative abundance of cyclopoids and Daphnia spp., resulting in communities dominated by Holopedium gibberum. 3. As chemical habitat quality has improved and fish, initially yellow perch and later piscivores (e.g. smallmouth bass, walleye), have invaded, biotic effects on the zooplankton are also becoming apparent. Simple fish assemblages dominated by perch appear to limit the survival of some zooplankton species, particularly Daphnia mendotae. 4. Both abiotic (residual metal contamination) and biotic (predation from planktivorous fish) processes have very important effects on zooplankton recovery. The re‐establishment of the zooplankton in lakes recovering from stress will require both improvements in habitat quality and the restoration of aquatic food webs.     

Method of predicting reference condition biota affects the performance and interpretation of ecological indices

1. The statistical rigour and interpretability of ecological assessments is strongly affected by how well we predict the biological assemblages expected to occur in the absence of human‐caused stress, i.e. the reference condition. In this study, we examined how the specific method used to predict the reference condition affected the performance of two commonly used types of ecological index: RIVPACS‐based O/E indices and multimetric indices (MMIs). 2. These two types of index have generally relied on different approaches to predicting the reference condition. For MMIs, some type of regionalisation is typically used to describe the range of metric values among reference sites and hence the expected range at assessed sites. For O/E indices, continuous modelling is used to predict how the biota varies among sites both among and within regions. Because the prediction method differs for these two types of index, it has been impossible to judge if differences in index performance (accuracy, precision, responsiveness and sensitivity) are caused by differences in the way reference condition biota are predicted or by differences in what the indices measure. 3. We used a common data set of 94 reference sites and 255 managed sites and the same potential set of predictor variables to compare the performance of five different MMIs and three O/E indices that were derived from different prediction methods: null models, multiple linear regression (MLR), classification and regression trees, Random Forests (RF) and linear discriminant functions models (LDM). We then calculated values of these indices for samples collected from the managed catchments as well as samples collected from 13 reference sites that were progressively altered in known ways by a simulation programme. 4. Both the type of predictor used and the type of index affected overall index performance. Modelled indices generally had the greatest sensitivity in assessing managed sites as biologically different from reference. Index sensitivity was determined by both an aspect of index precision (10th percentile of reference condition values) and responsiveness. The O/E indices showed the best scope of response to known biological alteration. All three O/E indices decreased linearly in response to simulated alteration in both overall assemblage structure (Bray‐Curtis dissimilarity) and taxa loss. The MMIs declined linearly from low to intermediate levels of assemblage alteration but were less responsive between intermediate and high levels of biological alteration. 5. Insights gained from simulations can aid in testing assumptions regarding index response to stress and help ensure that we select indices that are ecologically interpretable and most useful to resource managers.     

Hyperspectral Analysis of Columbia Spotted Frog Habitat

Abstract: Wildlife managers increasingly are using remotely sensed imagery to improve habitat delineations and sampling strategies. Advances in remote sensing technology, such as hyperspectral imagery, provide more information than previously was available with multispectral sensors. We evaluated accuracy of high-resolution hyperspectral image classifications to identify wetlands and wetland habitat features important for Columbia spotted frogs (Rana luteiventris) and compared the results to multispectral image classification and United States Geological Survey topographic maps. The study area spanned 3 lake basins in the Salmon River Mountains, Idaho, USA. Hyperspectral data were collected with an airborne sensor on 30 June 2002 and on 8 July 2006. A 12-year comprehensive ground survey of the study area for Columbia spotted frog reproduction served as validation for image classifications. Hyperspectral image classification accuracy of wetlands was high, with a producer's accuracy of 96% (44 wetlands) correctly classified with the 2002 data and 89% (41 wetlands) correctly classified with the 2006 data. We applied habitat-based rules to delineate breeding habitat from other wetlands, and successfully predicted 74% (14 wetlands) of known breeding wetlands for the Columbia spotted frog. Emergent sedge microhabitat classification showed promise for directly predicting Columbia spotted frog egg mass locations within a wetland by correctly identifying 72% (23 of 32) of known locations. Our study indicates hyperspectral imagery can be an effective tool for mapping spotted frog breeding habitat in the selected mountain basins. We conclude that this technique has potential for improving site selection for inventory and monitoring programs conducted across similar wetland habitat and can be a useful tool for delineating wildlife habitats.     

Petenaeaceae,a new angiosperm family in Huerteales with a distant relationship to Gerrardina (Gerrardinaceae)

Petenaea cordata (from northern Central America) was first described in Elaeocarpaceae and later placed in Tiliaceae, but most authors have been uncertain about its familial affinities. It was considered a taxon incertae sedis in the Angiosperm Phylogeny Group classification (APG III). A recent collection was made in Guatemala, and analysis of both rbcL and atpB in the large Soltis et al. angiosperm matrix, the most completely sampled study published to date, indicated a moderately supported relationship to Tapiscia (Tapisciaceae, the only member of the newly recognized order Huerteales in this matrix; 81% bootstrap support). We then conducted a more restricted analysis using the Bayer et al. rbcL/atpB matrix for Malvales supplemented with the other genera of Huerteales from published studies. Our results indicate a distant, weakly supported sister‐group relationship to the African genus Gerrardina (Gerrardinaceae; Huerteales). After comparison of the characters cited in the literature and an examination of herbarium material of both genera, we could find no obvious synapomorphies for Gerrardina and Petenaea or any other relationship of the latter, and we therefore propose the new monogeneric family, Petenaeaceae. The polymorphic order Huerteales now comprises four small families: Dipentodontaceae, Gerrardinaceae, Petenaeaceae and Tapisciaceae. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 16–25.     

The microbe–mineral environment and gypsum neogenesis in a weathered polar evaporite

Evaporitic deposits are a globally widespread habitat for micro‐organisms. The microbe–mineral environment in weathered and remobilized gypsum from exposed mid‐Ordovician marine evaporite beds in the polar desert of Devon Island, Nunavut, Canadian High Arctic was examined. The gypsum is characterized by internal green zones of cyanobacterial colonization (dominated by Gloeocapsa/Aphanothece and Chroococcidiopsis spp. morphotypes) and abundant black zones, visible from the surface, that contain pigmented cyanobacteria and fungi. Bioessential elements in the gypsum are primarily provided by allochthonous material from the present‐day polar desert. The disruption, uplift and rotation of the evaporite beds by the Haughton meteorite impact 39 Ma have facilitated gypsum weathering and its accessibility as a habitat. No cultured cyanobacteria, bacteria and fungi were halophilic consistent with the expectation that halophily is not required to persist in gypsum habitats. Heterotrophic bacteria from the evaporite were slightly or moderately halotolerant, as were heterotrophs isolated from soil near the gypsum outcrop showing that halotolerance is common in arctic bacteria in this location. Psychrotolerant Arthrobacter species were isolated. No psychrophilic organisms were isolated. Two Arthrobacter isolates from the evaporite were used to mediate gypsum neogenesis in the laboratory, demonstrating a potential role for microbial biomineralization processes in polar environments.     

Stagonospora nodorum: cause of stagonospora nodorum blotch of wheat

Stagonospora nodorum is an important pathogen of wheat and related cereals, causing both a leaf and glume blotch. This review summarizes recent advances in our understanding of taxonomy, control and pathogenicity of this species.
Taxonomy:   Stagonospora (syn. Septoria ) nodorum (Berk.) Castell. and Germano [teleomorph: Phaeosphaeria (syn. Leptosphaeria ) nodorum (Müll.) Hedjar.], kingdom Fungi, phylum Ascomycota, subphylum Euascomycota, class Dothideomycetes, order Pleosporales, family Phaeosphaeriaceae, genus Phaeosphaeria , species nodorum .
Host range:   Wheat, Triticum aestivum , T. durum , Triticale, are the main hosts but other cereals and wild grasses have been reported to harbour S. nodorum. Disease symptoms are lens-shaped necrotic lesions on leaves, girdling necrosis on stems (especially the nodes, hence ' nodorum ') and lesions on glumes. Mature lesions produce pycnidia scattered throughout the lesions, especially as tissue senesces.
Useful websites:   http://ocid.nacse.org/research/deephyphae/htmls/asco_taxlist_spat.html (taxonomic information), http://ohioline.osu.edu/ac-fact/0002.html (disease information), http://wwwacnfp.murdoch.edu.au/  (ACNFP homepage), http://www.broad.mit.edu/annotation/fungi/stagonospora_nodorum/index.html (genome sequence homepage), http://cogeme.ex.ac.uk/efungi/ (genome sequence annotation and analysis).