Glacial survival of boreal trees in northern Scandinavia

It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandinavia and with its highest frequency to the west-an area believed to sustain ice-free refugia during most of the last ice age. We further show the survival of DNA from this haplotype in lake sediments and pollen of Tr?ndelag in central Norway dating back ~10,300 years and chloroplast DNA of pine and spruce in lake sediments adjacent to the ice-free And?ya refugium in northwestern Norway as early as ~22,000 and 17,700 years ago, respectively. Our findings imply that conifer trees survived in ice-free refugia of Scandinavia during the last glaciation, challenging current views on survival and spread of trees as a response to climate changes.     

Enzymatic Activity of the Mycelium Compared with Oospore Development During Infection of Pea Roots by Aphanomyces euteiches

ABSTRACT To describe the disease cycle of the root pathogen Aphanomyces euteiches, enzymatic activity in the mycelium was compared with the development of oospores in pea roots. Plants were inoculated with two zoospore concentrations to achieve different disease levels. Hyphae were stained for fungal alkaline phosphatase activity in the roots. Additionally, enzyme activity was measured after electrophoresis of an A. euteiches-specific glucose-6-phosphate isozyme. Development of oospores in the roots was measured after staining the oospores with trypan blue. In plants inoculated with the higher zoospore concentration, the enzymatic activity of the pathogen mycelium peaked 10 to 14 days after inoculation, when oospore formation was initiated. Oospore formation was associated with a gradual increase in disease symptoms. At the last harvest, plants inoculated with the higher zoospore concentration had died. In these plants, oospores were found in 90% of the root length, while the enzymatic activity of the mycelium was low. This suggests that the pathogen mycelium is only active on living plants and does not grow saprophytically on dead plant material.     

Population genetics of Phytophthora infestans in Denmark reveals dominantly clonal populations and specific alleles linked to metalaxyl‐M resistance

Control of the potato late blight pathogen Phytophthora infestans relies heavily on chemicals. The fungicide metalaxyl‐M (Mefenoxam) has played an important role in controlling the disease, but insensitivity to the fungicide in certain isolates is now of major concern. A genetic basis for resistance to metalaxyl suggests the possibility for linking resistance phenotypes to specific population genetic markers, but in order to do this, the population genetic structure and mode of reproduction in a population must first be well described. The dynamics of metalaxyl‐M resistance in the Danish population of P. infestans was characterized over the course of the 2013 growing season, as was the population genetic structure, using simple sequence repeat (SSR) genotypes and single nucleotide polymorphism (SNP)‐based mitochondrial haplotyping of over 80 isolates. Both mating types A1 and A2 were present in most fields, but tests for recombination showed that clonal reproduction dominates in Danish populations. Genotype was not linked to haplotype and no differentiation was observed at the haplotype level, but rather between fields. Resistance phenotypes were linked to specific SSR alleles, demonstrating the potential for a more precise SNP‐based marker system for predicting resistance to metalaxyl‐M.     

Historical atmospheric deposition in a Swedish mining area traced by S isotope ratios in soils

Mining activities for almost thousand years have caused large S emissions in the Falun area, central Sweden. Since the beginning of the 20th century, the S deposition has decreased considerably. The soil S concentrations and S isotope compositions were analyzed for ΣS and adsorbed SO42- for three soil profiles close to the mining area in order to identify the soil S sources. The δ34S values were found to be different for ΣS and adsorbed SO42- and ranged from –3.7‰ to +2.6‰. In the B-horizon, the observed ΣS δ34S values (and hence calculated δ34S values for organic S) were mostly lower than those of the adsorbed SO42-. In the O-horizon, ΣS showed similar δ34S values as the adsorbed SO42- in the mineral soil. The adsorbed SO42- showed nearly constant δ34S values with depth. The δ34S values in the soils are interpreted to reflect a mixture of historical and modern deposition due to soil S circulation with no or negligible fractionation. The lower δ34S values of organic S in the B-horizon suggests preservation of acid deposition originating from mining activities back in time. The adsorbed SO42- in the mineral soil and the organic S in the O-horizon reflect a response to a new δ34S composition in the atmosphere due to fossil fuel burning during the 20th century.     

Physiological Response to Heat Stress During Seedling and Anthesis Stage in Tomato Genotypes Differing in Heat Tolerance

Tomato cultivars differ in their sensitivity to heat stress, and the sensitivity depends on the developmental stage of the plants. It is less known how heat stress affects tomato at the anthesis stage in terms of leaf physiology and fruit set and whether the ability of tomato to tolerate heat at different developmental stages is linked. To investigate photosynthetic gas exchange characteristics, carbohydrate content and fruit set during heat stress, a thermo‐tolerant cultivar (‘LA1994’) and a thermo‐sensitive cultivar (‘Aromata’) were studied at the seedling and anthesis stage. The photosynthetic parameters, maximum quantum efficiency of photosystem II (F_v/F_m), chlorophyll content, carbohydrate content and fruit set were determined in plants grown at 26/18 °C (control) and 36/28 °C (heat stress). The physiological responses including net photosynthetic rate (P_N), chlorophyll content and F_v/F_m decreased in ‘Aromata’ at both developmental stages during heat stress, whereas they were unaltered in ‘LA1994’ during heat stress as compared to the respective control. This was accompanied by lower contents of glucose and fructose in mature leaves of ‘Aromata’ at the seedling stage under heat stress. In contrast, the glucose content increased while the fructose content was unaltered in mature leaves of ‘LA1994’ at the seedling stage under heat stress. High temperature induced a similar change in carbohydrate content in the young leaves of both cultivars at anthesis. The fructose and sucrose content were unaffected in the mature leaves of ‘Aromata’ but significantly increased in ‘LA1994’ under heat stress at anthesis. The heat stress treatment decreased pollen viability and inhibited fruit set due to flower wilting and abnormal abscission in ‘Aromata’, whereas fruit set was not inhibited in ‘LA1994’. A decrease in chlorophyll content, photosynthesis and carbohydrate content in the mature leaves of tomato could be related to fruit set failure at high temperature. The results show that physiological responses to heat stress at the seedling stage correspond with the responses at the anthesis stage, demonstrating that screening for heat stress sensitivity can be carried out in young plants.     

Seasonal reproductive cycle of Waigieu seaperch (Psammoperca waigiensis)

Predictive and reliable parameters of reproductive status are integral aspects of sustainable fisheries and aquaculture management. These parameters are also important for an accurate evaluation of the effects of different treatments on sexual maturation in fish farming. In the present study, we have characterized the seasonal reproduction profile and described changes in sex steroids in relation to gonadal maturation and development in female and male Waigieu seaperch (Psammoperca waigiensis). The experimental period covered a full calendar year (January–December). In males and females, we observed that plasma sex steroid hormones [oestradiol‐17β (E2), testosterone (T), 11‐ketotestosterone (11‐KT) and progesterone (P)] levels showed monthly fluctuations during the spawning period. Particularly, plasma steroid hormone levels were positively associated with gonadosomatic index values. In addition, high levels of plasma steroid coincided with recruitment of oocytes into yolk accumulation in females. The main spawning period occurred between April and October in females, and between March and November in males. The non‐aromatizable androgen, 11‐KT is generally believed to be the active male‐specific androgen in teleosts, and is associated with the process of spermiation, development of secondary sexual characteristics and regulation of male reproductive behaviour in most teleost species. In this study, we found relatively high amounts of 11‐KT in females between May and December, suggesting an integral role in the maturation process, also for the females. A rapid peak in plasma P level was observed in November and suggests significant roles during post‐spawning and/or resting periods in both female and male fish. Furthermore, all oocyte developmental stages were present within the same sampling month and also within the spawning period, demonstrating the gamete group asynchronous developmental strategy. Overall, Waigieu seaperch showed strong seasonality in reproductive development with corresponding sex steroid patterns. The data presented in this study may contribute to the understanding of the reproductive endocrinology of a tropical marine finfish with increasing industrial prospects and sustainable aquaculture of this species in a developing country, such as Vietnam.     

Nitrex: The timing of response of coniferous forest ecosystems to experimentally-changed nitrogen deposition

In large regions of Europe and eastern North America atmospheric deposition of inorganic nitrogen (N) compounds has greatly increased the natural external supply to forest ecosystems. This leads to N saturation, in which availability of inorganic N is in excess of biological demand and the ecosystem is unable to retain all incoming N. The large-scale experiments of the NITREX project (NITRogen saturation EXperiments) are designed to provide information regarding the patterns and rates of responses of coniferous forest ecosystems to increases in N deposition and the reversibility and recovery of impacted ecosystems following reductions in N deposition.The timing of ecosystem response generally followed a hypothesized cascade of response. In all sites N outputs have responded markedly but to very different degrees within the first three years of treatment. Within this time significant effects on soil processes and on vegetation have only been detected at two sites. This delayed response is explained by the large capacity of the soil system to buffer the increased N supply by microbial immobilization and adsorption. We believe that this concept provides a framework for the evaluation and prediction of the ecosystem response to environmental change.     

Bacterial dynamics during decomposition of alder litter

Different groups of aerobic and anaerobic bacteria were enumerated in decomposing alder litter (Alnus glutinosa) and the underlying soil. Unspecific media with soil extract were used for total counts and media with single carbon compounds or different nitrogen compounds for specific functional groups.The numbers of aerobic, amylolytic and proteolytic bacteria were high after litter fall and decreased towards the end of decomposition. The fluctuations in the anaerobic groups of organisms were mainly influenced by moisture. The numbers of denitrifiers in the soil were highest during decomposition of litter in the winter, while the numbers of ammonifiers in litter were always high.     

The challenge of reproducing remote sensing data from satellites and unmanned aerial vehicles (UAVs) in the context of management zones and precision agriculture

Precision Agriculture - Mapping the within-field variability of crop status is of great importance in precision agriculture, which seeks to balance agronomic inputs with spatial crop demands....