Prediction of yield in the Rothamsted Park Grass Experiment by Ellenberg indicator values

Abstract. The Rothamsted Park Grass Experiment was established in 1856, with experimental plots subjected to annual applications of fertilizer and twice-yearly cutting of hay. There were two major responses to fertilizer, one reflecting high ammonium-nitrogen and increased acidity and the other reflecting high herbage yield without increased acidity. We calculated mean Ellenberg indicator values for N (nitrogen) and R (soil reaction) for the hay harvested between 1948 and 1975, using both unweighted and abundance-weighted means. Plot Ellenberg values were compared with herbage yield and with fertilizer application rates and published soil data. Annual yield of hay varied from 1.5 to 7.4 t/ha and was well predicted by the unweighted mean Ellenberg N-values (r = 0.91). Relatively large negative residuals from the relationship were found in plots whose soil combined low K and low pH. Soil pH was poorly predicted by the unweighted mean R-value, but showed a moderately good relation with weighted mean R (r = 0.73). The fact that Ellenberg N-values correlated better with yield than with applied nitrogen suggests that they might rather be called productivity values.     

Effects of additional illumination and fertilization on seasonal changes in fine-scale grassland community structure

Abstract. Fine-scale structure of a species-rich grassland was examined for seasonal changes caused by manipulated changes in the availability of above and below-ground resources (additional illumination with the help of mirrors and fertilization) in a field experiment. If changes induced by fertilization — which are expected to lead to a reduction in small-scale diversity —are due to intensified light competition, they should be compensated for by additional light input. Permanent plots of 40 cm × 40 cm were sampled by the point quadrat method at three angles (60°, 90° and 120° from the horizontal North-South direction), using a laser beam to position the quadrats, in early July and early September. The applied treatments did not cause apparent changes in plant leaf orientation. The degree of spatial aggregation of biomass increased seasonally in fertilized, non-illuminated plots: greater productivity at a constant light supply led to a faster growth rate of potentially dominant species, as compared to the subordinate ones. Additional illumination mitigated this effect of fertilization, indicating that the observed changes in biomass aggregation were due to increased light competition. There was a considerable seasonal decrease of variance ratio (ratio of observed variance of richness at a point and variance expected at random) in fertilized only and in illuminated only plots. In fertilized plots this was due to the positive relationship between biomass aggregation and expected variance of richness. Biomass constancy occurs to be inversely related to deficit in variance of richness. In illuminated plots, in contrast, only the observed variance of richness decreased seasonally, indicating a more uniform use of space by different species. Evidently, a deficit in variance of richness can be caused by drastically different processes, showing that the variance ratio statistic may not have a significant explanatory value in fine-scale community studies.     

A new sampler for extracting undisturbed surface peat cores for growth pot experiments

The sampler extracts uncompressed cores of 13·3 cm in diameter, up to 70 cm long, from the surface layers of peat. It has two close-fitting concentric cylindrical tubes, the outer one acting as a cutter and the inner one as a collector. As the outer tube is introduced by rotation into the peat, the cut core is collected in the inner tube which is maintained in a fixed position during the rotation phase and then pushed down stepwise. This limits friction between the peat core and the wall of the corer and prevents compression or distortion of the peat. These problems are also reduced by means of three skew cutters allowing the peat to be supported during the slicing action. Air can penetrate between the tubes to the lower end of the core, suppressing any suction effect during withdrawal. The sampler has been tested and has worked satisfactorily in many different peat types.     

Preadapted for invasiveness: do species traits or their plastic response to shading differ between invasive and non‐invasive plant species in their native range?

Aim Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non‐invasive species differ in presumably adaptive plasticity. Location Europe (for native species); the rest of the world and North America in particular (for alien species). Methods We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non‐shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance. Results Invasive species had higher shoot–root ratios, tended to have longer leaf‐blades, and produced more biomass than congeneric non‐invasive species both under shaded and non‐shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade‐induced responses, which are widely considered to be adaptive, did not differ between invasive and non‐invasive species. Main conclusions We conclude that high biomass production across different light environments pre‐adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured.     

Effects of ship‐induced waves on littoral benthic invertebrates

1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m^?2 was found for a structurally complex reed habitat, compared to 0.37 N m^?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h^?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance.     

Transfer of nitrogen from a tropical legume tree to an associated fodder grass via root exudation and common mycelial networks

Symbiotic dinitrogen fixation by legume trees represents a substantial N input in agroforestry systems, which may benefit the associated crops. Applying ¹⁵N labelling, we studied N transfer via common mycelial networks (CMN) and root exudation from the legume tree Gliricidia sepium to the associated fodder grass Dichantium aristatum . The plants were grown in greenhouse in shared pots in full interaction (treatment FI) or with their root systems separated with a fine mesh that allowed N transfer via CMN only (treatment MY). Tree root exudation was measured separately with hydroponics. Nitrogen transfer estimates were based on the isotopic signature of N ( δ ¹⁵N) transferred from the donor. We obtained a range for estimates by calculating transfer with δ ¹⁵N of tree roots and exudates. Nitrogen transfer was 3.7–14.0 and 0.7–2.5% of grass total N in treatments FI and MY, respectively. Root δ ¹⁵N gave the lower and exudate δ ¹⁵N the higher estimates. Transfer in FI probably occurred mainly via root exudation. Transfer in MY correlated negatively with grass root N concentration, implying that it was driven by source-sink relationships between the plants. The range of transfer estimates, depending on source δ ¹⁵N applied, indicates the need of understanding the transfer mechanisms as a basis for reliable estimates.     

On the PBB Designs for Multiresponse Experiments

We present the idea of using multiresponse incomplete block designs when not all responses can be observed in all experimental units. For a special class of such designs, in which partial designs are PBB designs, a method for estimating natural treatment contrast is given. We also consider the problem of testing the hypotheses concerning the natural and any estimable treatment contrasts. For testing this hypothesis the Wald statistics, being asymptotically chi-square distributed, is proposed.