Pollen limitation,species’ floral traits and pollinator visitation: different relationships in contrasting communities

Failures in the process of pollen transfer among conspecific plants can severely impact female reproductive success. Thus, pollen limitation can cause selection on plant mating systems and floral traits. The relationships between pollen limitation and floral traits might be partly mediated by the quantity and identity of pollinator visits. However, very little is known about the relationship between pollinator visits and pollen limitation. We examined the relationships between pollen limitation and floral traits at the community level to connect them to community ecology processes. We used 48 plant species from two contrasting communities: one species‐rich lowland community and one species‐poor alpine community. In addition, we calculated visitation rates and ecological pollination generalization for 38 of the species to examine the relationship between pollinator visitation and pollen limitation at the community level. We found low overall levels of pollen limitation that did not differ significantly between the alpine and the lowland community. In both communities, species with evolutionary specialized flowers were more pollen limited than species with unspecialized flowers. Species’ visitation rates and selfing capability were negatively related to pollen limitation in the alpine community, where pollinators are scarcer. However, flower size/number, ecological generalization of plants and flowering onset had greater effects on pollen limitation levels at the lowland community, indicating that the identity of the visitors and plant‐plant competitive interactions are more decisive for plant reproduction in this species‐rich community. There, pollen limitation increased with flower size and flowering onset, and decreased with ecological generalization, but only in species with evolutionary specialized flowers. Our study suggests that selection on plant mating system and floral traits may be idiosyncratic to each particular community and highlights the benefits of conducting community‐level studies for a better understanding of the processes underlying evolutionary responses to pollen limitation.     

Experimental simulations about the effects of overexploitation and habitat fragmentation on populations facing environmental warming

Populations of many species are dramatically declining worldwide, but the causal mechanism remains debated among different human-related threats. Coping with this uncertainty is critical to several issues about the conservation and future of biodiversity, but remains challenging due to difficulties associated with the experimental manipulation and/or isolation of the effects of such threats under field conditions. Using controlled microcosm populations, we quantified the individual and combined effects of environmental warming, overexploitation and habitat fragmentation on population persistence. Individually, each of these threats produced similar and significant population declines, which were accelerated to different degrees depending upon particular interactions. The interaction between habitat fragmentation and harvesting generated an additive decline in population size. However, both of these threats reduced population resistance causing synergistic declines in populations also facing environmental warming. Declines in population size were up to 50 times faster when all threats acted together. These results indicate that species may be facing risks of extinction higher than those anticipated from single threat analyses and suggest that all threats should be mitigated simultaneously, if current biodiversity declines are to be reversed.     

A sucrose-inducible promoter system for the intra- and extracellular protein production in Bacillus megaterium

A sucrose-inducible promoter system (P(sacB)) from Bacillus megaterium was identified using a secretome approach. It was successfully employed for the extracellular production of the homologous levansucrase SacB (4252.4 U l(-1)) and the heterologous green fluorescent protein GFP (7.9 mg g(CDW)(-1)). Mutational analysis of B. megaterium P(sacB) allowed the identification of important promoter elements. The sucrose-inducible promoter provides a useful alternative to the established xylose-inducible promoter system (P(xylA)) for recombinant gene expression in B. megaterium.     

D-mannitol production by resting state whole cell biotrans-formation of D-fructose by heterologous mannitol and formate dehydrogenase gene expression in Bacillus megaterium

An in vivo system was developed for the biotransformation of D-fructose into D-mannitol by the expression of the gene mdh encoding mannitol dehydrogenase (MDH) from Leuconostoc pseudomesenteroides ATCC12291 in Bacillus megaterium. The NADH reduction equivalents necessary for MDH activity were regenerated via the oxidation of formate to carbon dioxide by coexpression of the gene fdh encoding Mycobacterium vaccae N10 formate dehydrogenase (FDH). High-level protein production of MDH in B. megaterium required the adaptation of the corresponding ribosome binding site. The fdh gene was adapted to B. megaterium codon usage via complete chemical gene synthesis. Recombinant B. megaterium produced up to 10.60 g/L D-mannitol at the shaking flask scale. Whole cell biotransformation in a fed-batch bioreactor increased D-mannitol concentration to 22.00 g/L at a specific productivity of 0.32 g D-mannitol (gram cell dry weight)(-1) h(-1) and a D-mannitol yield of 0.91 mol/mol. The nicotinamide adenine dinucleotide (NAD(H)) pool of the B. megaterium producing D-mannitol remained stable during biotransformation. Intra- and extracellular pH adjusted itself to a value of 6.5 and remained constant during the process. Data integration revealed that substrate uptake was the limiting factor of the overall biotransformation. The information obtained identified B. megaterium as a useful production host for D-mannitol using a resting cell biotransformation approach.     

Long-term nitrogen deposition increases phosphorus limitation of bryophytes in an ombrotrophic bog

Here we investigate the effect of 4 years simulated atmospheric deposition of ammonium (NH₄) and nitrate (NO₃), applied alone or in combination with phosphorus and potassium (PK), on the surface phosphatase activities and nutrient acquisition behaviour of two species of moss (Sphagnum capillifolium and Hypnum jutlandicum) from an ombrotrophic peatland. Phosphatase activity was significantly enhanced by both the NH₄ and NO₃ treatments, particularly for Sphagnum, but the activity decreased when exposed to additions of PK. Regression analysis revealed that phosphatase activity on Sphagnum was positively related with tissue N and negatively related to tissue P concentrations. For Hypnum, a negative relationship between shoot P concentration and phosphatase activity was observed. Using a ³²P tracer, mosses removed from plots receiving PK in combination with NH₄ maintained their affinity for increased phosphorus uptake. These findings suggest that enhanced nutrient supply, even at modest doses, significantly alter the nutrient recycling behaviour of bryophytes.     

Leaf water 18O and 2H enrichment along vertical canopy profiles in a broadleaved and a conifer forest tree

Distinguishing meteorological and plant‐mediated drivers of leaf water isotopic enrichment is prerequisite for ecological interpretations of stable hydrogen and oxygen isotopes in plant tissue. We measured input and leaf water δ²H and δ¹⁸O as well as micrometeorological and leaf morpho‐physiological variables along a vertical gradient in a mature angiosperm (European beech) and gymnosperm (Douglas fir) tree. We used these variables and different enrichment models to quantify the influence of Péclet and non‐steady state effects and of the biophysical drivers on leaf water enrichment. The two‐pool model accurately described the diurnal variation of leaf water enrichment. The estimated unenriched water fraction was linked to leaf dry matter content across the canopy heights. Non‐steady state effects and reduced stomatal conductance caused a higher enrichment of Douglas fir compared to beech leaf water. A dynamic effect analyses revealed that the light‐induced vertical gradients of stomatal conductance and leaf temperature outbalanced each other in their effects on evaporative enrichment. We conclude that neither vertical canopy gradients nor the Péclet effect is important for estimates and interpretation of isotopic leaf water enrichment in hypostomatous trees. Contrarily, species‐specific non‐steady state effects and leaf temperatures as well as the water vapour isotope composition need careful consideration.     

Conformational stability of calreticulin

The conformational stability of calreticulin was investigated. Apparent unfolding temperatures (Tm) increased from 31 degrees C at pH 5 to 51 degrees C at pH 9, but electrophoretic analysis revealed that calreticulin oligomerized instead of unfolding. Structural analyses showed that the single C-terminal alpha-helix was of major importance to the conformational stability of calreticulin.