Summary 1.A coordinated continental-scale field experiment across 31 sites was used to compare the biomass yield of monocultures and four species mixtures associated with intensively managed agricultural grassland systems. To increase complementarity in resource use, each of the four species in the experimental design represented a distinct functional type derived from two levels of each of two functional traits, nitrogen acquisition (N 2 -fixing legume or nonfixing grass) crossed with temporal development (fast-establishing or temporally persistent). Relative abundances of the four functional types in mixtures were systematically varied at sowing to vary the evenness of the same four species in mixture communities at each site and sown at two levels of seed density. 2. Across multiple years, the total yield (including weed biomass) of the mixtures exceeded that of the average monoculture in >97% of comparisons. It also exceeded that of the best monoculture (transgressive overyielding) in about 60% of sites, with a mean yield ratio of mixture to best-performing monoculture of 1Á07 across all sites. Analyses based on yield of sown species only (excluding weed biomass) demonstrated considerably greater transgressive overyielding (significant at about 70% of sites, ratio of mixture to best-performing monoculture = 1Á18).3. Mixtures maintained a resistance to weed invasion over at least 3 years. In mixtures, median values indicate <4% of weed biomass in total yield, whereas the median percentage of weeds in monocultures increased from 15% in year 1 to 32% in year 3. 4. Within each year, there was a highly significant relationship (P < 0Á0001) between sward evenness and the diversity effect (excess of mixture performance over that predicted from the monoculture performances of component species). At lower evenness values, increases in community evenness resulted in an increased diversity effect, but the diversity effect was not significantly different from the maximum diversity effect across a wide range of higher evenness values. The latter indicates the robustness of the diversity effect to changes in species' relative abundances. 5. Across sites with three complete years of data (24 of the 31 sites), the effect of interactions between the fast-establishing and temporal persistent trait levels of temporal development was highly significant and comparable in magnitude to effects of interactions between N 2 -fixing and nonfixing trait levels of nitrogen acquisition. 6. Synthesis and applications. The design of grassland mixtures is relevant to farm-level strategies to achieve sustainable intensification. Experimental evidence indicated significant yield benefits of four species agronomic mixtures which yielded more than the highest-yielding monoculture at most sites. The results are relevant for agricultural practice and show how grassland mixtures can be designed to improve resource complementarity, increase yields and reduce weed invasion. The yield benefits were robust to considerable changes in the relative propo...

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Summary Increased species diversity promotes ecosystem function; however, the dynamics of multi‐species grassland systems over time and their role in sustaining higher yields generated by increased diversity are still poorly understood. We investigated the development of species’ relative abundances in grassland mixtures over 3 years to identify drivers of diversity change and their links to yield diversity effects. A continental‐scale field experiment was conducted at 31 sites using 11 different four‐species mixtures each sown at two seed abundances. The four species consisted of two grasses and two legumes, of which one was fast establishing and the other temporally persistent. We modelled the dynamics of the four‐species mixtures, and tested associations with diversity effects on yield. We found that species’ dynamics were primarily driven by differences in the relative growth rates (RGRs) of competing species, and secondarily by density dependence and climate. The temporally persistent grass species typically had the highest RGRs and hence became dominant over time. Density dependence sometimes induced stabilising processes on the dominant species and inhibited shifts to monoculture. Legumes persisted at most sites at low or medium abundances and persistence was improved at sites with higher annual minimum temperature. Significant diversity effects were present at the majority of sites in all years and the strength of diversity effects was improved with higher legume abundance in the previous year. Observed diversity effects, when legumes had declined, may be due to (i) important effects of legumes even at low abundance, (ii) interaction between the two grass species or (iii) a store of N because of previous presence of legumes. Synthesis. Alongside major compositional changes driven by RGR differences, diversity effects were observed at most sites, albeit at reduced strength as legumes declined. This evidence strongly supports the sowing of multi‐species mixtures that include legumes over the long‐standing practice of sowing grass monocultures. Careful and strategic selection of the identity of the species used in mixtures is suggested to facilitate the maintenance of species diversity and especially persistence of legumes over time, and to preserve the strength of yield increases associated with diversity.

bIt was previously demonstrated that there are no indigenous strains of Bradyrhizobium japonicum forming nitrogen-fixing root nodule symbioses with soybean plants in arable field soils in Poland. However, bacteria currently classified within this species are present (together with Bradyrhizobium canariense) as indigenous populations of strains specific for nodulation of legumes in the Genisteae tribe. These rhizobia, infecting legumes such as lupins, are well established in Polish soils. The studies described here were based on soybean nodulation field experiments, established at the Poznań University of Life Sciences Experiment Station in Gorzyń , Poland, and initiated in the spring of 1994. Long-term research was then conducted in order to study the relation between B. japonicum USDA 110 and USDA 123, introduced together into the same location, where no soybean rhizobia were earlier detected, and nodulation and competitive success were followed over time. Here we report the extra-long-term saprophytic survival of B. japonicum strains nodulating soybeans that were introduced as inoculants 20 years earlier and where soybeans were not grown for the next 17 years. The strains remained viable and symbiotically competent, and molecular and immunochemical methods showed that the strains were undistinguishable from the original inoculum strains USDA 110 and USDA 123. We also show that the strains had balanced numbers and their mobility in soil was low. To our knowledge, this is the first report showing the extra-long-term persistence of soybean-nodulating strains introduced into Polish soils and the first analyzing the long-term competitive relations of USDA 110 and USDA 123 after the two strains, neither of which was native, were introduced into the environment almost 2 decades ago.

Mesothelial cells lining the peritoneal cavity are the primary site of molecular exchange during peritoneal dialysis, a life support system for over 50 000 patients worldwide. In this study, techniques are described for the isolation and propagation in culture of peritoneal mesothelial cells from rats and rabbits. For comparison, mesothelial cells were also obtained from the serosal surface of human colonic tissue. By electron microscopy the cultured cells were found to exhibit microvilli, a well developed endoplasmic reticulum and golgi apparatus, micropinocytotic vesicles, and lipid-filled intracellular vesicles. Immunochemical probes revealed the expression by these cells in vitro of cytokeratin, fibronectin, vimentin, and keratin, but not von Willebrand factor. Mesothelial cells from rat, rabbit, and human exhibited contact inhibition, but differences in growth rates and dependence on supplements to the growth media. This work provides a multispecies comparison of the behavior of mesothelial cells in vitro for the purpose of developing an experimental system for the study of mesothelial cell biology and the role of these cells in peritoneal dialysis.

Genetic structure in field populations of Bradyrhizobium japonicum isolated in Poland was determined by using several complementary techniques. Of the 10 field sites examined, only 4 contained populations of indigenous B. japonicum strains. The Polish bradyrhizobia were divided into at least two major groups on the basis of protein profiles on polyacrylamide gels, serological reaction with polyclonal antisera, repetitive extragenic palindromic PCR fingerprints of genomic DNA, and Southern hybridization analyses with nif and nod gene probes. Serological analyses indicated that 87.5% of the Polish B. japonicum isolates tested were in serogroups 123 and 129, while seven (12.5%) of the isolates tested belonged to their own unique serogroup. These seven strains also could be grouped together on the basis of repetitive extragenic palindromic PCR fingerprints, protein profiles, and Southern hybridization analyses. Cluster analyses indicated that the seven serologically undefined isolates were genetically dissimilar from the majority of the Polish B. japonicum strains. Moreover, immuno-cross-adsorption studies indicated that although the Polish B. japonicum strains reacted with polyclonal antisera prepared against strain USDA123, the majority failed to react with serogroup 123-and 129-specific antisera, suggesting that Polish bradyrhizobia comprise a unique group of root nodule bacteria which have only a few antigens in common with strains USDA123 and USDA129. Nodulation studies indicated that members of the serologically distinct group were very competitive for nodulation of Glycine max cv. Nawiko. None of the Polish serogroup 123 or 129 isolates were restricted for nodulation by USDA123-and USDA129-restricting soybean plant introduction genotypes. Taken together, our results indicate that while genetically diverse B. japonicum strains were isolated from some Polish soils, the majority of field sites contained no soybean-nodulating bacteria. In addition, despite the lack of long-term soybean production in Poland, field populations of unique B. japonicum strains are present in some Polish soils and these strains are very competitive for nodulation of currently used Polish soybean varieties.

A new reagent, ethyl 4-azidobenzoylaminoacetimidate, was prepared in a four-step synthesis starting from 4-aminobenzoic acid. This compound was used to cross-link RNA with proteins within the Esclzerichiu coli 30-S ribosomal subunits. Following the reaction of the imidoester function with protein NH2 groups, photoactivation of the azide binds the other end of the reagent to RNA. The cross-linked proteins were labelled with 1251 and identified by bidimensional gel electrophoresis. Proteins S3, S4, SS, S7, S9, S17, S18 and, in a lower and more variable yield, S12, S13, S14 and S16 were bound to 16-S RNA. These results were confirmed by isolating cross-linked protein-oligonucleotide complexes from 30-S subunits containing 32P-labelled RNA.The spatial arrangement of biomolecules in Esclzerichiu coli ribosomes has been extensively studied by means of cross-linking methods. However, these investigations have so far concerned mostly the protein-protein neighborhood (for review, see [l]). Similar research on protein-RNA interactions has begun only recently and this field is at present much less developed. Several techniques have been used to cross-link RNA and proteins within the ribosome : (a) chemical approaches such as periodate oxidation of the 3'-terminal ribose of the 16-S RNA, followed by the formation of Schiff base with a protein amino group and stabilization by barohydride reduction [2 -41 ; (b) photochemical approaches (for bibliographical review, see [S]). Nevertheless, both types of approaches give limited results: Rinke and Brimacombe [6] discussed the limitations of the first technique; the use of direct ultraviolet irradiation of 30-S subunits only allowed protein S7 to be cross-linked to the 16-S RNA within the 30-S subunits at a significant yield [S,'7].Other methods were therefore necessary to progress in the research of localization of proteins on ribosomal RNA. Since chemical bifunctional reagents proved useful in establishing the protein-protein neighborhood in the particle, a similar approach is now Enzymes. T1 ribonuclease (EC 3.1.27.3); bovine pancreatic ribonuclease (EC 3.1.27.5).being developed for cross-linking ribosomal proteins with adjacent RNA. Thus, some new reagents suitable for this purpose have recently been synthesized and used to study the RNA-protein proximity in the ribosome [8-121. However this possibility is still far from being fully explored.In the present paper we describe the synthesis of a new reagent of this type, ethyl 4-azidobenzoylaminoacetimidate, its use to form RNA-protein crosslinks within the E. coli ribosomal 30-S subunit and the identification of the proteins cross-linked to 1 6 3 RNA. MATERIALS AND METHODS Syntlzesis qf the ReugenlThe reagent ethyl 4-azidobenzoylaminoacetimidate hydrochloride was obtained by the following fourstep synthesis.4-Azidohenzoic Acid. A solution of 2.76 g (0.04 mol) sodium nitrite in SO ml water was added dropwise to a stirred ice-cold mixture of 2.74 g (0.02 mol) 4-aminobenzoic acid, 100 ml water and 4ml 2 M HCl. Sodium azide (2.34 g,...

2018. The effect of tillage management and its interaction with site conditions and plant functional traits on plant species establishment during meadow restoration.