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It is generally assumed that all bacteria must have at least one rRNA operon (rrn operon) on the chromosome, but some strains of the genera Aureimonas and Oecophyllibacter carry their sole rrn operon on a plasmid. However, other related strains and species have chromosomal rrn loci, suggesting that the exclusive presence of rrn operons on a plasmid is rare and unlikely to be stably maintained over long evolutionary periods. Here, we report the results of a systematic search for additional bacteria without chromosomal rrn operons. We find that at least four bacterial clades in the phyla Bacteroidota, Spirochaetota, and Pseudomonadota (Proteobacteria) lost chromosomal rrn operons independently. Remarkably, Persicobacteraceae have apparently maintained this peculiar genome organization for hundreds of millions of years. In our study, all the rrn-carrying plasmids in bacteria lacking chromosomal rrn loci possess replication initiator genes of the Rep_3 family. Furthermore, the lack of chromosomal rrn operons is associated with differences in copy numbers of rrn operons, plasmids, and chromosomal tRNA genes. Thus, our findings indicate that the absence of rrn loci in bacterial chromosomes can be stably maintained over long evolutionary periods. Bacteria usually have at least one rRNA operon on the chromosome, suggesting that the exclusive presence of rRNA operons on a plasmid is rare and unlikely to be stably maintained. Here, Anda et al. find that at least four bacterial clades in different phyla lost their chromosomal rRNA operons independently, and one of the clades has maintained this peculiar genome organization for hundreds of millions of years. [ABSTRACT FROM AUTHOR]

The effects of reduced water potential ( ψ) on seed germination at 25 and 15 °C in unprimed (UP) and primed (P) seeds of two cultivars of sweet sorghum (cv. Keller and cv. Makueni local), were analyzed through the hydrotime model. Six ψ (from 0 to −1.0 MPa) in polyethylene glycol 6000 (PEG) solutions were used for the tests. Seeds were primed in 250 g/L PEG solution at 15 °C for 48 h. Decreasing ψ of imbibition solution reduced and delayed germination. At 15 °C seeds germinated less and slower than at 25 °C at any ψ. Seeds of cv. Makueni local exhibited a greater sensitivity to water stress in terms of germination percentage, than seeds of cv. Keller, but they were faster in germination. Osmopriming was beneficial for seed germination, both in terms of final percentage and rate, at any temperature and ψ. The hydrotime analysis revealed that predicted θ constant was increased when temperature was reduced to 15 °C and at this temperature median base water potential [ ψ ] for germination was higher (less negative) than at 25 °C. Seed priming shifted ψ towards more negative values and reduced θ requirements for germination. At 25 °C the two cultivars behaved similarly while at 15 °C cv. Keller exhibited a ψ more negative but required a greater θ to germinate, indicating a greater water-stress tolerance but a slower germination, than cv. Makueni local. The application of the model allows to identify water stress tolerant cultivars during germination, to include into breeding programs for the selection of well-performing cultivars under stress conditions. [ABSTRACT FROM AUTHOR]

Soils of the Mediterranean area are subjected to erosion due to the cropping systems and crop managements adopted. This causes a loss of crop productivity that could be initially replaced with an increase of fertilizers, but in the end leads to land abandonment. The areas subjected to soil erosion in the Mediterranean area cover 1,309,000 km, equal to 15 % of the land of Mediterranean countries. In dry farming condition, the farmer's choices are often constrained by the prevailing climatic conditions. Rainfall amount and distribution represent the main constraints that lead farmers to choose annual autumn-winter crops. In this environment, the growing cycle of autumn-winter crops, such as durum wheat, determines a lack of soil covering during the first rains that occur in early autumn and winter. Soil losses by erosion also determine nutrient losses and affect soil organic matter content. All these aspects are evaluated by ongoing research started in 1996 in an area of the internal hills of Sicily (Italy) in the center of the Mediterranean basin. In this experimental site, on a 27 % slope, the effect of different cropping systems to determine surface runoff and soil losses was evaluated. In each plot, (40 × 8) m, a series of devices were installed in order to determine the amount of runoff and sediment: four covered trap channels were installed at the bottom of each plot, each channel drained into pipes which emptied into a tank to collect surface runoff and soil losses. After each erosive rainfall, the amount of water, of sediments, and the nitrate-nitrogen were measured. Soil organic matter was determined every fall at 0-30 and 31-60 cm depth. The highest annual values of soil losses were observed in the annual tilled crops, such as the typical Mediterranean crop rotation 'durum wheat-durum wheat-fallow' (11.2 t ha year). Very low soil losses were observed in the plots managed with perennial crops, alfalfa (0.34 t ha year), Italian ryegrass in pure stand and in mixtures with subterranean clover (3.2 t ha year), and subterranean clover (1.7 t ha year). The perennial giant miscanthus and moon trefoil reduced soil losses to 0.1 t ha year. The benefit of the cultivation of perennial crops instead of tilled crops was also highlighted in relation to organic matter content. The rotation 'giant miscanthus (from 1997 to 2001)-moon trefoil (from 2002 to 2015)' made it possible to increase soil organic matter from 1.03 to 2.51 % in the average of the first 60 cm soil depth. [ABSTRACT FROM AUTHOR]

A general obstacle to the development of perennial grasses is the relatively high cost of propagation and planting. The objective of the present study was to investigate new propagation and planting methods of giant reed ( Arundo donax L.), miscanthus ( Miscanthus x giganteus Greef et Deuter) and switchgrass ( Panicum virgatum L.). Field and open-air pot trials were carried out in four different locations across Europe: hydro-seeding of switchgrass was tested in field trials at the experimental farm of the University of Bologna, Italy; stem propagation and bud activation methods of miscanthus were evaluated in field experiments in Péteri, Hungary; giant reed rhizome and stem propagations were compared in a field trial in Aliartos, Greece; finally, an open-air pot trial was carried out in Catania, Italy, using single-node stem cuttings of giant reed. Hydro-seeding emerged as a feasible and promising technique for switchgrass to ensure prompt seed emergence and weed control during plant establishment. Direct stem plantings of miscanthus were successful, and activated stem-buds were able to sprout in field conditions; however, timely stem transplant was determinant for shoot density and biomass yield. In giant reed, rhizome propagation showed a higher stem density and biomass yield than stem propagation; however, the yield gap was not significant from the second year onwards. Single-node rooting was mainly driven by air temperature. Nodes from basal stems showed higher rooting rates than median and apical ones. Growth regulator pretreatments enhanced rooting rate only at transplanting times under suboptimal air temperatures. In general, these experiments provided insights into propagation strategies aimed at enhancing the establishment phase of perennial grasses. [ABSTRACT FROM AUTHOR]

Uncertainty in predictions of long-term yields of perennial grasses makes business plans untenable in the short run. Long-term data across varied environments, including marginal lands, will help in preventing uncertainty while providing farmers and entrepreneurs with sound information to estimate reliable and affordable strategies on what, where, and how long to grow perennial grasses. In the present study, the long-term yields (11 to 22 years) of switchgrass ( Panicum virgatum L.), miscanthus ( Miscanthus × giganteus Greef et Deuter), and giant reed ( Arundo donax L.) grown in northern and southern Mediterranean environments are reported. Switchgrass was grown in Greece and northern Italy, giant reed in southern and northern Italy, and miscanthus in southern Italy. Furthermore, lowland and upland switchgrass ecotypes were compared in Greece. Despite similar biomass productions (9.8 and 10.0 Mg DM ha for uplands and lowlands, respectively), the upland ecotypes showed a significantly higher yield stability (CV of 24 and 32 % for uplands and lowlands, respectively) over a 17-year period. Biomass yield varied considerably across years and locations; giant reed outperformed switchgrass under northern Italy environment (21.2 and 13.6 Mg DM ha for giant reed and switchgrass, respectively). Annual yield of switchgrass was 30 % higher in the north than south Mediterranean; miscanthus showed intermediate production compared to giant reed and switchgrass (average of 22 years) and a CV similar to switchgrass. In summary, these results evidence that multi-location, long-term trials are strongly needed to reduce uncertainties on crop yield variability and provide more accurate data from which optimized socio-economic and environmental predictions can be achieved. [ABSTRACT FROM AUTHOR]

Giant reed ( Arundo donax) and Miscanthus spp. were tested to evaluate their tolerance and phytoremediation capacity in soils contaminated with heavy metals. Giant reed was tested under 450 and 900 mg Zn kg, 300 and 600 mg Cr kg, and 450 and 900 mg Pb kg contaminated soils, while the Miscanthus genotypes M. × giganteus, M. sinensis, and M. floridulus were tested on 450 and 900 mg Zn kg contaminated soils, along 2 years. Giant reed biomass production was negatively affected by the contamination; however, yield reduction was only significant under 600 mg Cr kg soil. Zn contamination reduced significantly M. × giganteus production but not M. sinensis or M. floridulus yields. Yet, M. × giganteus was also the most productive. Both grasses can be considered as indicators, once metal concentration in the biomass reflected soil metal concentration. Regarding giant reed experiments, higher modified bioconcentration factors (mBCFs, 0.3-0.6) and translocation factors (TFs, 1.0-1.1) were obtained for Zn, in the contaminated soils, followed by Cr (mBCFs, 0.2-0.4, belowground organs; TFs, 0.2-0.4) and Pb (mBCFs, 0.06-0.07, belowground organs; TFs, 0.2-0.4). Metal accumulation also followed the same pattern Zn > Cr > Pb. Miscanthus genotypes showed different phytoremediation potential facing similar soil conditions. mBCFs (0.3-0.9) and TFs (0.7-1.5) were similar among species, but highest zinc accumulation was observed with M. × giganteus due to the higher biomass production. Giant reed and M. × giganteus can be considered as interesting candidates for Zn phytoextraction, favored by the metal accumulation observed and the high biomass produced. A. donax and Miscanthus genotypes showed to be well suited for phytostabilization of heavy metal contamination as these grasses prevented the leaching of heavy metal and groundwater contamination. [ABSTRACT FROM AUTHOR]

In this work, ultrathin amorphous Ge films (2 to 30 nm in thickness) embedded in SiO2 layers were grown by magnetron sputtering and employed as proficient light sensitizer in photodetector devices. A noteworthy modification of the visible photon absorption is evidenced due to quantum confinement effects which cause both a blueshift (from 0.8 to 1.8 eV) in the bandgap and an enhancement (up to three times) in the optical oscillator strength of confined carriers. The reported quantum confinement effects have been exploited to enhance light detection by Ge quantum wells, as demonstrated by photodetectors with an internal quantum efficiency of 70%. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the editor discusses various reports published within the special issue including one by Elena Sanchez and colleagues on the impact of salinity and water stress on biomass production, another by Luciano Cosentino and colleagues on reducing erosion by cultivating miscanthus and giant reed and a paper by Ana Luisa Fernando on environmental impacts of new potential agro-energy systems.