Taxonomic and functional turnover are decoupled in European peat bogs

In peatland ecosystems, plant communities mediate a globally significant carbon store. The effects of global environmental change on plant assemblages are expected to be a factor in determining how ecosystem functions such as carbon uptake will respond. Using vegetation data from 56 Sphagnum-dominated peat bogs across Europe, we show that in these ecosystems plant species aggregate into two major clusters that are each defined by shared response to environmental conditions. Across environmental gradients, we find significant taxonomic turnover in both clusters. However, functional identity and functional redundancy of the community as a whole remain unchanged. This strongly suggests that in peat bogs, species turnover across environmental gradients is restricted to functionally similar species. Our results demonstrate that plant taxonomic and functional turnover are decoupled, which may allow these peat bogs to maintain ecosystem functioning when subject to future environmental change

Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland

In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO(2) in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical variables. The analysis revealed a persistent and positive effect of elevated CO(2) on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO(2) mediated through increased litter C:N ratio. After eight years of treatment, however, the CO(2)-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term

Plant Identity Influences Decomposition through More Than One Mechanism

Plant litter decomposition is a critical ecosystem process representing a major pathway for carbon flux, but little is known about how it is affected by changes in plant composition and diversity. Single plant functional groups (graminoids, legumes, non-leguminous forbs) were removed from a grassland in northern Canada to examine the impacts of functional group identity on decomposition. Removals were conducted within two different environmental contexts (fertilization and fungicide application) to examine the context-dependency of these identity effects. We examined two different mechanisms by which the loss of plant functional groups may impact decomposition: effects of the living plant community on the decomposition microenvironment, and changes in the species composition of the decomposing litter, as well as the interaction between these mechanisms. We show that the identity of the plant functional group removed affects decomposition through both mechanisms. Removal of both graminoids and forbs slowed decomposition through changes in the decomposition microenvironment. We found non-additive effects of litter mixing, with both the direction and identity of the functional group responsible depending on year; in 2004 graminoids positively influenced decomposition whereas in 2006 forbs negatively influenced decomposition rate. Although these two mechanisms act independently, their effects may be additive if both mechanisms are considered simultaneously. It is essential to understand the variety of mechanisms through which even a single ecosystem property is affected if we are to predict the future consequences of biodiversity loss

Effect of the Phosphine Steric and Electronic Profile on the Rh-Promoted Dehydrocoupling of Phosphine-Boranes

[Image: see text] The electronic and steric effects in the stoichiometric dehydrocoupling of secondary and primary phosphine–boranes H(3)B·PR(2)H [R = 3,5-(CF(3))(2)C(6)H(3); p-(CF(3))C(6)H(4); p-(OMe)C(6)H(4); adamantyl, Ad] and H(3)B·PCyH(2) to form the metal-bound linear diboraphosphines H(3)B·PR(2)BH(2)·PR(2)H and H(3)B·PRHBH(2)·PRH(2), respectively, are reported. Reaction of [Rh(L)(η(6)-FC(6)H(5))][BAr(F)(4)] [L = Ph(2)P(CH(2))(3)PPh(2), Ar(F) = 3,5-(CF(3))(2)C(6)H(3)] with 2 equiv of H(3)B·PR(2)H affords [Rh(L)(H)(σ,η-PR(2)BH(3))(η(1)-H(3)B·PR(2)H)][BAr(F)(4)]. These complexes undergo dehydrocoupling to give the diboraphosphine complexes [Rh(L)(H)(σ,η(2)-PR(2)·BH(2)PR(2)·BH(3))][BAr(F)(4)]. With electron-withdrawing groups on the phosphine–borane there is the parallel formation of the products of B–P cleavage, [Rh(L)(PR(2)H)(2)][BAr(F)(4)], while with electron-donating groups no parallel product is formed. For the bulky, electron rich, H(3)B·P(Ad)(2)H no dehydrocoupling is observed, but an intermediate Rh(I) σ phosphine–borane complex is formed, [Rh(L){η(2)-H(3)B·P(Ad)(2)H}][BAr(F)(4)], that undergoes B–P bond cleavage to give [Rh(L){η(1)-H(3)B·P(Ad)(2)H}{P(Ad)(2)H}][BAr(F)(4)]. The relative rates of dehydrocoupling of H(3)B·PR(2)H (R = aryl) show that increasingly electron-withdrawing substituents result in faster dehydrocoupling, but also suffer from the formation of the parallel product resulting from P–B bond cleavage. H(3)B·PCyH(2) undergoes a similar dehydrocoupling process, and gives a mixture of stereoisomers of the resulting metal-bound diboraphosphine that arise from activation of the prochiral P–H bonds, with one stereoisomer favored. This diastereomeric mixture may also be biased by use of a chiral phosphine ligand. The selectivity and efficiencies of resulting catalytic dehydrocoupling processes are also briefly discussed

Palladium-Catalysed Carbon-Fluorine and Carbon-Hydrogen Bond Alumination of Fluoroarenes and Heteroarenes

Through serendipitous discovery, a palladium bis(phosphine) complex was identified as a catalyst for the selective transformation of sp2C−F and sp2C−H bonds of fluoroarenes and heteroarenes to sp2C−Al bonds (19 examples, 1 mol % Pd loading). The carbon–fluorine bond functionalization reaction is highly selective for the formation of organoaluminium products in preference to hydrodefluorination products (selectivity=4.4:1 to 27:1). Evidence is presented for a tandem catalytic process in which hydrodefluorination is followed by sp2C−H alumination

Room temperature catalytic carbon-hydrogen bond alumination of unactivated arenes: mechanism and selectivity

We report the first catalytic methods for the transformation of C–H bonds of unactivated arenes into C–Al bonds. The catalytic reactions occur at 25 °C (benzene, toluene and xylenes) with palladium loadings as low as 0.1 mol%. Remarkably, the C–H activation of toluene and xylenes proceeds with ortho- and meta-selectivity. This selectivity is highly unusual and complementary to both Friedel–Crafts and the majority of C–H borylation methods. Through a detailed mechanistic analysis (Eyring analysis, KIE, DFT, QTAIM) we show that unusual Pd–Al intermetallic complexes are on the catalytic cycle and that the selectivity is determined by weak attractive dispersion forces in the transition state for C–H bond breaking

Dehydrocoupling of phosphine-boranes using the [RhCp∗Me(PMe3)(CH2Cl2)][BArF 4] precatalyst: Stoichiometric and catalytic studies

We report a detailed, combined experimental and computational study on the fundamental B–H and P–H bond activation steps involved in the dehydrocoupling/dehydropolymerization of primary and secondary phosphine–boranes, H3B·PPhR′H (R = Ph, H), using [RhCp*(PMe3)Me(ClCH2Cl)][BArF4], to either form polyphosphino-boranes [H2B·PPhH]n (Mn ∼ 15 000 g mol−1, PDI = 2.2) or the linear diboraphosphine H3B·PPh2BH2·PPh2H. A likely polymer-growth pathway of reversible chain transfer step-growth is suggested for H3B·PPhH2. Using secondary phosphine–boranes as model substrates a combined synthesis, structural (X-ray crystallography), labelling and computational approach reveals: initial bond activation pathways (B–H activation precedes P–H activation); key intermediates (phosphido-boranes, α-B-agostic base-stabilized boryls); and a catalytic route to the primary diboraphosphine (H3B·PPhHBH2·PPhH2). It is also shown that by changing the substituent at phosphorus (Ph or Cy versustBu) different final products result (phosphido-borane or base stabilized phosphino-borane respectively). These studies provide detailed insight into the pathways that are operating during dehydropolymerization