Suitability of the ESS laboratory method to determine the equilibrium soil solution composition of agricultural soils,and suggestions for simplification of the experimental procedure

The proper selection of the background electrolyte is of special importance studying element availability and mobility in the laboratory. The determination of the background solution composition can be done with the equilibrium soil solution method ESS (Matschonat and Vogt, 1997). The ESS method is a procedure to find out a salt solution of major cations and anions that does not undergo changes in its composition when brought into contact with a specific soil sample. This composition is experimentally approximated in an iterative procedure until certain quality criteria are fulfilled. We tested if the ESS method, which was developed for forest soils, can successfully be applied also to agricultural soils. The solution composition was confirmed by an independent method. We used samples of a glasshouse and an arable loess soil. Because the ESS method is relatively time and work consuming, we tested modifications which should simplify the procedure: the use of dried and frozen samples instead of field fresh soil, an approximation according to the solution's electric conductivity only, and the modeling of cation exchange to omit iteration steps. The ESS method caused slight overestimation (10–25 %) in cation concentrations, but in general, these were well met. Individual anion concentrations, however, were not buffered in this soil and could not unequivocally be determined. We recommend to adjust the anion concentrations in the ESS procedure according to their proportions in an initial water extract. As ion concentrations are functions of the soil : solution ratio, any method based on addition of water to the soil, like the so‐called soil saturation extract (Germany: Bodensättigungsextrakt), runs a risk to seriously underestimate ion concentrations at field conditions. The ESS method may therefore be especially well suited for soils with a low water content. The use of frozen soil gave good results and the omission of iteration steps by cation exchange modeling was promising and will be explored with the aim to operationalize it in forthcoming work.     

Translocation of cave fish (Poecilia mexicana) within and between natural habitats along a toxicity gradient

During ecological speciation, diverging taxa have the potential to remain in close spatial proximity (i.e., sympatry or micro‐allopatry) theoretically allowing for continued contact and gene flow. In a system where incipient speciation of populations of the Atlantic molly (Poecilia mexicana) appears to be driven by abiotic factors, we investigated whether one of these factors, hydrogen sulphide (H₂S) toxicity, also constitutes an effective barrier to slow migration within and between habitats. We addressed this experimentally by translocating individuals from high toxicity to lower toxicity within a toxic cave and by translocating individuals from the toxic cave to a nontoxic surface habitat. Using a stepwise‐backwards Cox regression, we found that overall mortality was low, but statistically significant mortality occurred when individuals were transferred from higher toxicity to lower toxicity. In addition, only males were negatively affected by being transferred from low levels of toxicity to nontoxic, surface waters. This indicates that in addition to abiotic factors, other mechanisms, like predation and sexual selection, must be important in maintaining population separation.     

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of ¹³C labelled rye residues (δ¹³C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO₂, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.     

Quantitative trait loci mapping of forage agronomic traits in six mapping populations derived from European elite maize germplasm

Four agronomic traits were analysed including dry matter concentration (DMC) and dry matter yield (DMY) for stover, plant height (PHT) and days from planting to silking (DPS). We mapped quantitative trait loci (QTL) in three populations with doubled haploid lines (DHL), one RIL population and two testcross (TC) populations derived from crosses between two of the four populations mentioned above to elite tester lines, based on field phenotyping at multiple locations and years for each; 146–168 SSRs were used for genotyping of the four mapping populations. Significant high phenotypic and genotypic correlations were found for all traits at two locations, while DMC was negatively correlated with the other traits. A total of 42, 41, 54, and 45 QTL were identified for DMC, DMY, PHT, and DPS, respectively, with 9, 7, 12, and 7 major QTL for each trait. Most detected QTL displayed significant interactions with environment. Major QTL detected in more than two populations will contribute to marker‐assisted breeding and also to fine mapping candidate genes associated with maize agronomic traits.     

Environmental threats and conservation implications for Atlantic salmon and brown trout during their critical freshwater phases of spawning,egg development and juvenile emergence

Atlantic salmon Salmo salar L. and brown trout Salmo trutta fario L. are species of high socio-economic and ecological value. Declining populations make them target species of fisheries management. This paper reviews the direct effects of deficient longitudinal connectivity, changes in discharge, high water temperatures, oxygen depletion, changes in water chemistry and increasing loads of fine sediment on the critical life stages of spawning, egg incubation and emergence. It further provides an overview about the basic autecological requirements of Atlantic salmon and brown trout and summarises important thresholds of physico-chemical tolerances. This collection of information provides important baselines for assessing historical, ongoing and new threats relevant for the management of both species in fresh waters. Critical early-life stages of both species are almost identical, creating synergies in conservation and restoration. Seaward-migrating forms are exposed to further stressors, but improving starting conditions can also greatly improve their resilience.     

Ethnobotanical knowledge of Philippine lowland farmers and its application in agroforestry

Complex agroforestry systems that mimic local forest structure, so-called ‘analogs’, are assumed to be of specific value to rural people as well as the environment. The objective of this study was to document and evaluate the utilization of plant resources by Philippine lowland farmers to identify native species suitable for integration in such a system. The interviewed farmers maintain a comprehensive ethnobotanical knowledge. They reported using 122 plant species for 77 purposes. Eighty species have medicinal value, 35 provide food, and 32 serve other uses. About 64% of the identified species are Philippine natives. The life form composition of these species is dominated by trees but also includes herbs, lianas, and graminoids, thus providing the structural elements required in analog systems. Nevertheless, only a few of the species seem to be promising for cultivation. Many of them are ubiquitous in the vicinity of villages. Some species are also not much appreciated but act as staple food only during food shortage. Even though several of the species have proven market value, such as rattan (e.g. Calamus merrillii), or are reputed medicines, such as ‘Philippine ginseng’ (Sarcandra glabra), no cultivation could be observed. This shows that usefulness in itself cannot be the only criterion to promote species but that it requires a careful analysis of the marketability of the respective species. In this context we suggest the following three species that are of proven medicinal value for in-depth study: the liana Tinospora crispa (Menispermaceae), the tree Picrasma javanica (Simaroubaceae), and the herb Sarcandra glabra (Chloranthaceae). They represent three different life form strategies and would thus fit well in vertically structured agroforestry systems.     

Regulation of integrin adhesions by varying the density of substrate-bound epidermal growth factor

Substrates coated with specific bioactive ligands are important for tissue engineering, enabling the local presentation of extracellular stimulants at controlled positions and densities. In this study, we examined the cross-talk between integrin and epidermal growth factor (EGF) receptors following their interaction with surface-immobilized Arg-Gly-Asp (RGD) and EGF ligands, respectively. Surfaces of glass coverslips, modified with biotinylated silane-polyethylene glycol, were functionalized by either biotinylated RGD or EGF (or both) via the biotin-NeutrAvidin interaction. Fluorescent labeling of the adhering A431 epidermoid carcinoma cells for zyxin or actin indicated that EGF had a dual effect on focal adhesions (FA) and stress fibers: at low concentrations (0.1; 1 ng/ml), it stimulated their growth; whereas at higher concentrations, on surfaces with low to intermediate RGD densities, it induced their disassembly, leading to cell detachment. The EGF-dependent dissociation of FAs was, however, attenuated on higher RGD density surfaces. Simultaneous stimulation by both immobilized RGD and EGF suggest a strong synergy between integrin and EGFR signaling, in FA induction and cell spreading. A critical threshold level of EGF was required to induce significant variation in cell adhesion; beyond this critical density, the immobilized molecule had a considerably stronger effect on cell adhesion than did soluble EGF. The mechanisms underlying this synergy between the adhesion ligand and EGF are discussed.     

Tree and stand structure of the non-native Pinus contorta in relation to native Pinus sylvestris and Picea abies in young managed forests in boreal Sweden

Managed forest stands are typically younger and structurally less diverse than natural forests. Introduction of non-native tree species might increase the structural changes to managed forest stands, but detailed analyses of tree- and stand-structures of native and non-native managed forests are often lacking. Improved knowledge of non-native forest structure could help clarify their multiple values (e.g. habitat for native biodiversity, bioenergy opportunities). We studied the structural differences between the introduced, non-native Pinus contorta and the native Pinus sylvestris and Picea abies over young forest stand ages (13–34 years old) in managed forests in northern Sweden. We found that P. contorta stands had greater mean basal areas, tree heights, diameters at breast height, and surface area of living branches than the two native species in young stands. The surface area of dead attached branches was also greater in P. contorta than P. abies. Although this indicates greater habitat availability for branch-living organisms, it also contributes to the overall more shaded conditions in stands of P. contorta. Only one older 87 years old P. contorta stand was available, and future studies will tell how structural differences between P. contorta and native tree species develop over the full forestry cycle.