In vitro testing of strawberry resistance to Verticillium dahliae and Phytophthora cactorum

The effects of culture filtrates and homogenates of Verticillium dahliae and Phytophthora cactorum on in vitro growth and development of strawberry shoots of cvs. Elsanta, Real and Senga Sengana were investigated. The filtrates of fungal cultures as well as filtrates of homogenated mycelia did not affect strawberry shoot growth and development, whereas inoculation with mycelia of V. dahliae and P. cactorum resulted in leaf yellowing, growth inhibition, inhibition of root formation, and after several days, the death of infected plants. However, fungal growth on the media that were used was irregular and the infection rate of individual plants was very variable.Mycelial homogenates affected growth and development of strawberry shoots in a similar way to that of an intact mycelium. Because the homogenate was distributed evenly in the culturing medium, the effect was uniform and thus possible to quantitate. It was also possible to differentiate a pathogen’s inoculum potential by adequate dilution of the homogenate. The best effect was obtained with V. dahliae. Fungal homogenate inhibited root formation and shoot growth, caused leaf necrosis and death of the plants after 7–8 weeks. The reaction of the cultivars tested was similar to their sensitivity to verticillium wilt in the field.P. cactorum affected in vitro strawberry shoot growth and development in a similar way to V. dahliae, but the effect was not cultivar-dependent. Preliminary tests showed that the method developed is useful for selection of somaclonal variants resistant/tolerant to infection with these pathogens.     

Clay mineralogy,chemical weathering and landscape evolution in Arctic–Alpine Sweden

The purpose of this research was to: (1) characterize the clay mineralogy of soils in and adjacent to Kärkevagge, a recently deglaciated valley in Arctic Sweden, (2) document chemical weathering in a periglacial environment and (3) use the mineralogy to help explain landscape evolution. Soil samples were analyzed from 11 sites that differ in elevation, parent material, drainage, slope and vegetation. Parent materials include residuum, alluvium, colluvium and glaciofluvial material derived from garnet–mica–schist, plus, in one locality, a till of granitic origin. X-ray diffraction (XRD) was used to characterize the clay-size fraction (<2 μm). Muscovite, chlorite and mixed-layered (ML) minerals are the predominant soil minerals identified. ML minerals indicate chemical weathering and also act as tracers used to identify source areas of soil parent materials. High concentrations of ML minerals in the soils on the alpine ridges flanking Kärkevagge indicate in situ chemical weathering. At lower elevations within the valley, their distribution indicates that the ridges contributed sediments early on in the evolution of the landscape, but more recently the source has shifted towards ML-poor supply areas from lower elevations. Soil chemistry also supports this model; the alpine soils are base-poor while the valley soils are base-rich. The higher abundance of ML minerals in the alpine zone indicates either a long period of weathering or a greater period of development. The latter explanation supports the hypothesis that the ridge crests were covered by cold-based ice during the last glaciation; remnants of which still survive at the highest elevations. Cold-based ice preserved a pre-weathered landscape that was the primary source of the ML minerals in the soils in the valley.     

Influence of balsam poplar tannin fractions on carbon and nitrogen dynamics in Alaskan taiga floodplain soils

The feedbacks between plant and soil processes play an important role in driving forest succession. One poorly understood feedback mechanism is the interaction between plant secondary chemicals and soil microbes. In the Alaskan taiga, changes in nutrient cycling caused by balsam poplar (Populus balsamifera) secondary chemicals may affect the transition from alder (Alnus tenuifolia) to balsam poplar on river floodplains. We examined the effects of four poplar condensed tannin fractions on N cycling in alder and poplar soils. Tannins were added to forest floor samples from both poplar and alder sites. Samples were incubated for 1 month in the laboratory with soil respiration rates measured over the course of the incubation. At the end of the incubation we measured both net and gross nitrogen mineralization and nitrification, microbial biomass C and N, and the activity of various exoenzymes. In all soils, tannin additions reduced N availability, however, the mechanisms differed depending on the molecular weight of the tannin and the native soil microbial community. Low molecular weight tannin fractions served as a labile C source in poplar Oi, poplar Oe, and alder Oe horizons but were toxic to microbes in alder Oi. High molecular weight tannin fractions appeared to act primarily by binding extracellular substrates and thus limiting C and N mineralization, with the strongest effects observed in the alder soils.     

The influence of dietary nitrogen and phosphorus on Cd accumulation in the woodlouse Porcellio scaber Latr

Bioaccumulation of potentially toxic metals by litter-feeding invertebrates is determined not only by the concentration of metal in the diet, but also by the flux of food through the body. Nitrogen and phosphorus are the main elements regulating food consumption and so are expected to affect the bioaccumulation of trace elements such as cadmium. To test this idea, we applied a three-factor orthogonal experimental design to estimate the effects of nitrogen, phosphorus and cadmium additions to the food on cadmium accumulation by the terrestrial isopod Porcellio scaber. Cd, N and P were added to milled poplar litter in concentrations of 0, 10 and 20 μg g⁻¹ for cadmium, 0, 0.875 and 1.75% for nitrogen and 0, 0.2 and 0.4% for phosphorus. Observations were made for daily food consumption (estimated from faecal pellet production) and weekly Cd accumulation over a period of 4 weeks. Dietary Cd decreased consumption in the first 2 weeks of the experiment, but this effect disappeared later. Phosphorus had a significant positive effect on consumption in the second and the third week of the experiment. Accumulation of Cd was determined mainly by the Cd concentration in the food, but the effect was stimulated by P and diminished by N additions. Analysis of the data by regression using response surfaces confirmed that N and P had opposite influences on both Cd accumulation and food consumption. The data underline the importance of measuring consumption and food quality when conducting bioaccumulation and ecotoxicity experiments with soil invertebrates exposed through the diet.     

Assessing the effects of the clumping phenomenon on BRDF of a maize crop based on 3D numerical scenes using DART model

Inverting radiative transfer (R-T) models against remote sensing observations to retrieve key biogeophysical parameters such as leaf area index (LAI) is a common approach. Even if new inversion techniques allow the use of three-dimensional (3D) models for that purpose, one-dimensional (1D) models are still widely used because of their ease of implementation and computational efficiency. Nevertheless, they assume a random distribution of foliage elements whereas most canopies show a clumped organization. Due to that crude simplification in the representation of the canopy structure, sizeable discrepancies can occur between 1D simulations and real canopy reflectance, which may further lead to false LAI values. The present investigation aims to appraise to which extent the incorporation of a clumping index (noted λ) into 1D R-T model could improve the simulations of Bidirectional Reflectance Distribution Function (BRDF). Canopy BRDF is simulated here for three growth stages of a maize crop with the Discrete Anisotropic Radiative Transfer (DART) model in the visible and near infrared spectral bands, for two contrasted soil types (dark and bright) and different levels of heterogeneity to represent the canopy structure. 3D numerical scenes are based on in-situ structural measurements and associated BRDF simulations are thus considered as references. 1D scenarios assume either that leaves are randomly distributed (λ = 1) or clumped (λ < 1). If BRDF simulations seem globally reliable under the assumption of a random distribution in near infrared, it can also lead to relative errors on the total BRDF up to 30% in the red spectral band. It comes out that the use of a clumping index in a 1D reflectance model generally improves BRDF simulations in the red considering a bright soil, which seems relatively independent of LAI. In the near infrared, best results are usually obtained with homogeneous canopies, except with the dark soil. Clearly, influent factors are mainly the LAI and the spectral contrast between soil and leaves.     

BMC ecology image competition 2017: the winning images

For the fifth year, BMC Ecology is proud to present the winning images from our annual image competition. The 2017 edition received entries by talented shutterbug-ecologists from across the world, showcasing research that is increasing our understanding of ecosystems worldwide and the beauty and diversity of life on our planet. In this editorial we showcase the winning images, as chosen by our Editorial Board and guest judge Chris Darimont, as well as our selection of highly commended images. Enjoy!     

Coexisting invasive gobies reveal no evidence for temporal and trophic niche differentiation in the sublittoral habitat of Lake Erhai,China

Niche differentiation facilitates the coexistence of species within a community through avoidance of competition via mechanisms involving spatial, temporal and/or trophic dimensions. Where invasive species coexist in their non‐native range, niche differentiation could allow their persistence at higher levels of abundance. Here, we tested whether there was temporal and/or trophic niche differentiation between two congeneric invasive goby species (Rhinogobius cliffordpopei and Rhinogobius giurinus) in the sublittoral habitat of Lake Erhai (south‐west China) through quantifying their diel and seasonal rhythm of locomotion activities, feeding activities and diet composition. Both species displayed two similar diel peaks in activity and two main feeding periods (6:00–10:00 and 18:00–22:00), with rhythms of locomotion and feeding activity not differing significantly between the species in each season. Their diets had a high degree of overlap, being primarily composed of macrozooplankton, aquatic insects and shrimp larvae, with no diel changes across the seasons. Thus, in this habitat, there was no clear temporal or trophic niche differentiation between the invasive congeners, indicating their coexistence with high temporal and trophic overlap. In conjunction with data from the littoral and profundal habitats, the gobies revealed different strategies across the habitats (e.g. spatial segregation, trophic niche differentiation) that minimised their competitive interactions and promoted their coexistence. This suggests that the interactions of invasive fishes during the integration into native communities can be context dependent, varying according to factors including habitat and the availability of food resources.     

Occurrence and genetic diversity of hemoplasmas in beef cattle from the Brazilian Pantanal,an endemic area for bovine trypanosomiasis in South America

Hemotropic mycoplasmas (hemoplasmas) are Gram-negative bacteria that parasitize the erythrocyte surface of a wide variety of mammals. The present study aimed at investigating the occurrence of hemoplasmas in beef cattle in the Brazilian Pantanal, an area endemic for bovine trypanosomiasis in South America. Additionally, the objective of this study was to characterize molecularly the genotypes of the found hemoplasmas. For this purpose, blood and serum samples of 400 beef cattle were collected from five properties in Corumbá, Nhecolândia sub-region, Mato Grosso do Sul, in Midwest Brazil. Blood samples underwent DNA extraction and standard 16S rRNA gene-based PCR assays for hemoplasmas. The sequences obtained were submitted to phylogenetic inferences, distance analysis, and genotype diversity. The Indirect Enzyme-Linked Immunoabsorbent Assay (iELISA) indicated the presence of anti-Trypanosoma vivax IgG antibodies in 89.75% of the animals sampled, confirming the endemicity of said agent in the studied region. Among the 400 bovine blood samples tested, 2.25% (9/400) were positive for hemoplasmas in cPCR. The phylogenetic analysis of the obtained sequences confirmed the presence of 'Candidatus Mycoplasma haemobos' and Mycoplasma wenyonii DNA in 0.5% (2/400) and 1.75% (7/400) animals, respectively. Five genotypes of M. wenyonii and one of 'Candidatus M. haemobos' were detected among the sequenced amplicons. The present study showed low molecular occurrence of haemoplasmas in beef cattle sampled in the Brazilian Pantanal, an area endemic for bovine trypanosomiasis. Despite of the conservation of the 16S rRNA gene, there was considerable diversity of hemoplasma genotypes infecting the sampled beef cattle.