Impact of plant species evenness, dominant species identity and spatial arrangement on the structure and functioning of soil microbial communities in a model grassland.

Plant communities, through species richness and composition, strongly influence soil microorganisms and the ecosystem processes they drive. To test the effects of other plant community attributes, such as the identity of dominant plant species, evenness, and spatial arrangement, we set up a model mesocosm experiment that manipulated these three attributes in a full factorial design, using three grassland plant species (Anthoxanthum odoratum, Plantago lanceolata, and Lotus corniculatus). The impact of the three community attributes on the soil microbial community structure and functioning was evaluated after two growing seasons by ester-linked phospholipid fatty-acids analysis, substrate-induced respiration, basal respiration, and nitrogen mineralization and nitrification rates. Our results suggested that the dominant species identity had the most prevalent influence of the three community attributes, with significant effects on most of the measured aspects of microbial biomass, composition and functioning. Evenness had no effects on microbial community structure, but independently influenced basal respiration. Its effects on nitrogen cycling depended on the identity of the dominant plant species, indicating that interactions among species and their effects on functioning can vary with their relative abundance. Systems with an aggregated spatial arrangement had a different microbial community composition and a higher microbial biomass compared to those with a random spatial arrangement, but rarely differed in their functioning. Overall, it appears that dominant species identity was the main driver of soil microorganisms and functioning in these model grassland communities, but that other plant community attributes such as evenness and spatial arrangement can also be important.

Herbivory, litter and soil disturbance as determinants of vegetation dynamics during early old-field succession under set-aside.

Early-successional old fields are a major component of the European landscape. While a range of factors governing vegetation development in old fields has been identified, empirical and theoretical studies have tended to concentrate on plant competition as the dominant driving force behind succession. We studied the influence of three little researched, yet inter-related, factors on the early stages of an old-field succession: litter cover, soil disturbance and herbivory. Physical and chemical techniques were used to exclude large vertebrates and insects from experimental plots. These treatments had little effect on plant recruitment. A litter-removal experiment, nested within the exclusion treatments, revealed a significant inhibition of forb seedling germination by litter cover. However, the majority of seedlings died during the first month following emergence, whether or not litter was removed. A second experiment, involving the factorial combination of mollusc exclusion and soil disturbance, revealed that the response to disturbance was dependent on life-history characteristics of the plants. However, the dominant factor regulating community composition was seedling herbivory by molluscs. Molluscs caused high rates of forb seedling mortality and promoted the transition from a forb-dominated, to a grass-dominated community. Herbivory is often assumed to influence plant community dynamics through effects on competitive interactions. However, direct effects of herbivory, on the survival of seedlings, may be a significant factor structuring plant communities in ruderal, or other annual dominated systems.

Conservation implications of the link between biodiversity and ecosystem functioning.

The relationship between biodiversity and individual ecosystem processes is often asymptotic, saturating at relatively low levels, with some species contributing more strongly than others. This has cast doubt on arguments for conservation based on maintenance of the functioning of ecosystems. However, we argue that the link between biodiversity and ecosystem functioning is an important additional argument for conservation for several reasons. (1) Although species differ in importance to ecosystem processes, we do not believe that this argues for preservation of just a few species for two reasons: first, it is nearly impossible to identify all species important to the numerous systems and processes on which humans depend; second, the important species themselves may depend on an unknown number of other species in their communities. (2) Arguments for conservation based on ecosystem functioning are complementary to other utilitarian, ethical and aesthetic justifications. No single reason will convince all people or protect all species, however the combination produces a strong case for conservation of biodiversity. (3) Even if the relationship between biodiversity and ecosystem functioning is asymptotic at local spatial scales and in the short term, effects of biodiversity loss are likely to be important at larger temporal and spatial scales. (4) Initial arguments for the importance of biodiversity for ecosystem functioning were largely based on a precautionary approach (points 1-3). However, we are now moving to a scientific position based on accumulating experimental evidence. The future challenge is the integration of this scientific research with policy.

Impact of an environmentally-realistic intake of cadmium on calcium, magnesium, and phosphate metabolism in bank voles, Clethrionomys glareolus.

Oral intake of cadmium can disrupt calcium metabolism in laboratory rodents. If this occurs in free-living wild rodents, reproductive potential, growth, and survival could be adversely affected. This study investigated whether an environmentally-realistic intake of cadmium (1.5-1.7 mg/kg BW/24h) by bank voles, Clethrionomys glareolus, affected uptake and assimilation of calcium and also that of magnesium and phosphorus, two elements metabolized in close association with calcium. Mineral metabolism was monitored in bank voles fed four different diets; two diets were relatively low (0.12%) in calcium and also contained either no cadmium (HC) or cadmium (LCCd), while the remainder were relatively high (0.74%) in calcium and also contained either no cadmium (HC) or cadmium (HCCd). Dietary calcium levels were varied because calcium can affect gut absorption of cadmium, and calcium levels in natural forage vary with habitat soil type. Cadmium had a significant effect on voles fed a low calcium diet. Animals given LCCd diet had significantly poorer calcium net gut absorption efficiency than animals fed the corresponding control (LC) diet and were in negative calcium balance, losing approximately 0.5-1% of body calcium reserves each day. In contrast, calcium inputs matched total outputs in animals fed the LC diet. Cadmium had no effect on net gut absorption of magnesium and phosphorus, but renal reabsorption and subsequent assimilation of these elements was greater in animals fed the LCCd diet than in those given the LC diet. Cadmium had no clear effect on macroelement metabolism in bank voles fed a diet relatively high in calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Extreme chromosomal heterogeneity in a small-island population of Rumex acetosa.

Chromosome analyses of 227 mature plants of the dioecious species Rumex acetosa collected on the small island of Skomer have revealed an extremely high level of unique and polymorphic variation. The three common polymorphisms in this species--supernumerary segments on chromosomes 1 and 6, and B-chromosomes--are widespread on the island and the frequency of supernumerary segment 1 is higher than in all 37 mainland populations previously studied. Novel variants, unknown elsewhere, occur in each polymorphism. Fourteen different chromosome rearrangements are unique to the island, and eleven of these were detected in 67 plants from a small area which had undergone a population crash in 1977. It is argued that the genome of R. acetosa is undergoing rapid reorganisation on this small island which may be associated with an enforced shift towards inbreeding in this dioecious species.

Mendelian and non-Mendelian inheritance of newly-arisen chromosome rearrangements.

Seven centric shifts and three reciprocal interchanges, all newly-arisen in natural populations, have been tested for their inheritance in the dioecious flowering plant Rumex acetosa. In backcrosses between the heterozygote and standard plants transmissions ranged from 0.36 to 0.85 per gamete for the novel chromosome. The inheritance of only four rearrangements correspond to Mendelian expectations while others exhibited either drive or drag. Drive was observed both through the egg and through the pollen indicating heterogeneity of mechanisms in the generation of non-Mendelian patterns of inheritance. This suggests that accumulation may play a significant role in the establishment of chromosomal variants in natural populations.

The effect of synthetic analogues of chymostatin upon protein degradation in isolated skeletal muscle.

A series of peptides based on the structure of the proteinase inhibitor chymostatin were tested for their toxicity and ability to suppress protein degradation in the isolated mouse diaphragm. The inhibitory activities of the analogues were very similar, in marked contrast to their disparate abilities as inhibitors of chymotrypsin. Toxicity was determined by measurement of the rates of protein synthesis and of leakage of lactate dehydrogenase into the incubation medium. No significant toxicity was measurable at concentrations of inhibitor that were effective at suppressing proteolysis. The structural features of the chymostatin molecule may be less than optimal for suppression of proteolysis in muscle.

Synthetic analogues of the proteinase inhibitor: chymostatin.

Putative proteinase inhibitors with the general structure Z. Arg. X.Phe.H (where X = Leu, Ile or Val) were prepared by solution synthesis using semicarbazone protection for the aldehyde function. These inhibitors showed strong activity towards chymotrypsin whereas the semicarbazones and dipeptides aldehydes showed considerably reduced activity. The structural requirements for inhibition would seem to mimic those of the natural chymotrypsin inhibitor chymostatin.

Inhibition of hepatic protein degradation by synthetic analogues of chymostatin.

Analogues of the microbial proteinase inhibitor chymostatin have been synthesized. The two most promising analogues were tested on protein turnover in isolated rat hepatocytes. Their effect is much similar to the effect of chymostatin, but the analogues are even more powerful inhibitors, probably due to an increased effect on lysosomal thiol proteinases. The analogues blocked most of the lysosomal (i.e. methylamine-sensitive) degradation of endogenous protein and caused a 50% inhibition of the non-lysosomal degradation; the effect occurred rapidly and was reversed upon washing the cells. One of the analogues, Z-Arg-Leu-Phe(H), is the most potent inhibitor of hepatic protein degradation so far found.