Partitioning the effects of algal species identity and richness on benthic marine primary production

Influential research in terrestrial habitats indicates that several ecosystem processes are related to plant biodiversity, yet these links remain poorly studied in marine ecosystems. We conducted one field and one mesocosm experiment to quantify the relative effects of macroalgal species identity and richness on primary production in coral reef macroalgal communities off the north coast of Jamaica. We measured production as the net accumulation of algal biomass in the absence of consumers and as photosynthetic rate using oxygen probes in sealed aquaria. We used two recently developed techniques to attribute deviations in expected relative yield to components associated with species identity or diversity and then to further partition diversity effects into mechanistic components based on dominance, trait-dependent complementarity, and trait-independent complementarity. Our results indicate that algal identity had far greater effects on absolute net growth and photosynthesis than richness. The most diverse mixture of macroalgae did not outperform the most productive monoculture or the average monoculture in either measure of primary production (i.e. we did not find evidence of either transgressive or non-transgressive overyielding). Trait-independent complementarity effects were positive but dominance and trait-dependent complementarity were both negative and became stronger when richness was increased. Thus the potentially positive influence of species interactions and niche partitioning on production were negated by dominance and other negative selection effects. These results demonstrate that the counteracting influence of component effects can diminish the net richness effects on production. This could explain frequently observed weak net richness effects in other aquatic and terrestrial systems and suggests that life history tradeoffs greatly reduce the potential for ecologically relevant plant biodiversity effects on ecosystem properties.     

The functional basis of a primary succession resolved by CSR classification

CSR classification aims to apply CSR theory to large numbers of plants in situ, thereby allowing the investigation of communities within a functional context. However, it has only ever been applied to British vegetation, during the development of the technique, and has not yet been used to investigate specific vegetation processes. Here, a vegetation primary succession on a glacier foreland (Rutor glacier, Aosta, Italy) was used as a 'test bed' for the hypothesis that CSR classification can distinguish functional shifts during this vegetation process. Morpho-functional traits were used to calculate CSR coordinates for 45 species throughout the glacier foreland. General functional similarities between species were verified using principal components analysis (PCA). CSR classification demonstrated a functional shift from broadly ruderal pioneers towards stress-tolerance in late succession. PCA 1 correlated with S and R strategies, confirming this gradient. Till deposited at the retreating glacier terminus provides a substrate that can support faster growing species (with high foliar N contents), but is only tenable to those that can avoid physical disturbance via rapid phenological development (i.e. ruderals). Stress-tolerance and lower N contents in late succession suggest selection for efficient nutrient use. CSR classification demonstrated that competitive traits were ubiquitous but of much lesser importance than stress-tolerance or ruderalism (also correlating with PCA 2 and 3). The detailed visualization provided by CSR classification, combined with its mechanistic explanation of community change, demonstrate the promise of this methodology as a quantitative tool for comparative community ecology.     

Nitrate-dependent control of root architecture and N nutrition are altered by a plant growth-promoting Phyllobacterium sp

Both root architecture and plant N nutrition are altered by inoculation with the plant growth-promoting rhizobacteria (PGPR) Phyllobacterium strain STM196. It is known that NO₃⁻ and N metabolites can act as regulatory signals on root development and N transporters. In this study, we investigate the possible interrelated effects on root development and N transport. We show that the inhibition of Arabidopsis lateral root growth by high external NO₃⁻ is overridden by Phyllobacterium inoculation. However, the leaf NO₃⁻ pool remained unchanged in inoculated plants. By contrast, the Gln root pool was reduced in inoculated plants. Unexpectedly, NO₃⁻ influx and the expression levels of AtNRT1.1 and AtNRT2.1 genes coding for root NO₃⁻ transporters were also decreased after 8 days of Phyllobacterium inoculation. Although the mechanisms by which PGPR exert their positive effects remain unknown, our data show that they can optimize plant development independently from N supply, thus alleviating the regulatory mechanisms that operate in axenic conditions. In addition, we found that Phyllobacterium sp. elicited a very strong induction of AtNRT2.5 and AtNRT2.6, both genes preferentially expressed in the shoots whose functions are unknown.     

Long-term Effects of Pre-harvest Burning and Nitrogen and Vinasse Applications on Yield of Sugar Cane and Soil Carbon and Nitrogen Stocks on a Plantation in Pernambuco, N.E. Brazil

Since the 1970s the area under sugarcane in Brazil has increased from 2 million to over 5 million ha (M ha), and it is expected to pass the 7 M ha mark in 2007. More than half of the cane is harvested to produce bioethanol as a fuel for light vehicles. The distilleries produce approximately 13 L of distillery waste (vinasse) for each litre of ethanol produced. In the 1980s there was considerable concern over the long-term effects of the disposal of this material (containing about 1% carbon and high in K) on cane yields if it was applied to the field. At the same time there was a growing movement to abandon the practice of pre-harvest burning and some research was showing that some Brazilian varieties of sugar cane were able to obtain significant contributions of N from plant-associated biological nitrogen fixation (BNF). For these reasons an experiment was installed on a cane plantation in the state of Pernambuco, NE Brazil to investigate the long-term effects of vinasse and N fertiliser additions and the practice of pre-harvest burning on crop and sugar yield, soil fertility parameters, N balance and soil C stocks. The results showed that over a 16-year period, trash conservation (abandonment of burning) increased cane yields by 25% from a mean of 46 to 58 Mg ha⁻¹. Vinasse applications (80 m³ ha⁻¹ crop⁻¹) increased mean cane and sugar yield by 12 to 13% and the application of 80 kg N ha⁻¹ as urea increased cane yields by 9%, but total sugar yield by less than 6% (from 7.0 to 7.4 Mg ha⁻¹ crop⁻¹). The total N balance for the soil/plant system when only the surface 20 cm of the soil was considered was positive in plots where no N fertiliser was added. However, the data indicated that during the 16 years of the study considerable quantities of soil organic matter were accumulated below 20 cm depth such that the N balance considering the soil to 60 cm depth was strongly positive, except where N fertiliser was added. The data indicated that there were considerable BNF inputs to the system, which was consistent with its low response to N fertiliser and low N fertiliser-use-efficiency. There were no significant effects of vinasse or urea addition, or trash conservation on soil C stocks, although the higher yields proportioned by trash conservation had potentially significant benefits for increased mitigation of CO₂ emissions where the main use of the cane was for bioethanol production.     

Diversity of wild and cultivated pearl millet accessions (Pennisetum glaucum [L.] R. Br.) in Niger assessed by microsatellite markers

Genetic diversity of crop species in sub-Sahelian Africa is still poorly documented. Among such crops, pearl millet is one of the most important staple species. In Niger, pearl millet covers more than 65% of the total cultivated area. Analyzing pearl millet genetic diversity, its origin and its dynamics is important for in situ and ex situ germplasm conservation and to increase knowledge useful for breeding programs. We developed new genetic markers and a high-throughput technique for the genetic analysis of pearl millet. Using 25 microsatellite markers, we analyzed genetic diversity in 46 wild and 421 cultivated accessions of pearl millet in Niger. We showed a significantly lower number of alleles and lower gene diversity in cultivated pearl millet accessions than in wild accessions. This result contrasts with a previous study using iso-enzyme markers showing similar genetic diversity between cultivated and wild pearl millet populations. We found a strong differentiation between the cultivated and wild groups in Niger. Analyses of introgressions between cultivated and wild accessions showed modest but statistically supported evidence of introgressions. Wild accessions in the central region of Niger showed introgressions of cultivated alleles. Accessions of cultivated pearl millet showed introgressions of wild alleles in the western, central, and eastern parts of Niger.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.Cedric Mariac and Viviane Luong have contributed equally to this work.     

Preliminar evaluation of cytokines in the hepatitis C-schistosomiasis co-infection

Evaluation of hepatic fibrosis is usually performed by histopathological examination of biopsies. However, this is an invasive and potentially dangerous procedure. Several studies have proposed serum biological markers of hepatic fibrosis. This communication evaluates the use of serum cytokines as markers of hepatic fibrosis in hepatitis C, schistosomiasis, and co-infection.     

Nucleosome dynamics

In the 30 years since the discovery of the nucleosome, our picture of it has come into sharp focus. The recent high-resolution structures have provided a wealth of insight into the function of the nucleosome, but they are inherently static. Our current knowledge of how nucleosomes can be reconfigured dynamically is at a much earlier stage. Here, recent advances in the understanding of chromatin structure and dynamics are highlighted. The ways in which different modes of nucleosome reconfiguration are likely to influence each other are discussed, and some of the factors likely to regulate the dynamic properties of nucleosomes are considered.