Selective grazing modifies previously anticipated responses of plant community composition to elevated CO2 in a temperate grassland

Our limited understanding of terrestrial ecosystem responses to elevated CO₂ is a major constraint on predicting the impacts of climate change. A change in botanical composition has been identified as a key factor in the CO₂ response with profound implications for ecosystem services such as plant production and soil carbon storage. In temperate grasslands, there is a strong consensus that elevated CO₂ will result in a greater physiological stimulus to growth in legumes and to a lesser extent forbs, compared with C3 grasses, and the presumption this will lead in turn to a greater proportion of these functional groups in the plant community. However, this view is based on data mainly collected in experiments of three or less years in duration and not in experiments where defoliation has been by grazing animals. Grazing is, however, the most common management of grasslands and known in itself to influence botanical composition. In a long‐term Free Air Carbon Dioxide Enrichment (FACE) experiment in a temperate grassland managed with grazing animals (sheep), we found the response to elevated CO₂ in plant community composition in the first 5 years was consistent with the expectation of increased proportions of legumes and forbs. However, in the longer term, these differences diminished so that the proportions of grasses, legumes and forbs were the same under both ambient and elevated CO₂. Analysis of vegetation before and after each grazing event showed there was a sustained disproportionately greater removal (‘apparent selection’) of legumes and forbs by the grazing animals. This bias in removal was greater under elevated CO₂ than ambient CO₂. This is consistent with sustained faster growth rates of legumes and forbs under elevated CO₂ being countered by selective defoliation, and so leading to little difference in community composition.     

The rate of progression and stability of progressive nitrogen limitation at elevated atmospheric CO2 in a grazed grassland over 11 years of Free Air CO2 enrichment

A decline in the availability of nitrogen (N) for plant growth (progressive nitrogen limitation or PNL) is a feedback that could constrain terrestrial ecosystem responses to elevated atmospheric CO₂. Several long-term CO₂ enrichment experiments have measured changes in plant and soil pools and fluxes consistent with PNL but evidence for PNL in grasslands is limited. In an 11 year Free Air CO₂ Enrichment (FACE) experiment on grazed grassland we found the amount of N harvested in aboveground plant biomass was greater at elevated CO₂ but declined over time to be indistinguishable from ambient after 5 years. Re-wetting after a major drought resulted in a large input of N from mineralisation and a return to a higher N harvested under elevated CO₂ followed by a further decline. Over these two periods the amount of N in soil significantly increased at elevated CO₂. Data from mesocosms introduced into the rings at intervals, and therefore having different lengths of exposure to CO₂, showed plant N availability declined at elevated CO₂ reaching a new equilibrium after 6 years of exposure. We conclude that the availability of N for plants in this grassland is dynamic but the underlying trend at elevated CO₂ is for PNL.     

Determination of in-vivo cytoplasmic orthophosphate concentration in yeast

Summary To investigate in-vivo concentrations of cytoplasmic phosphate, especially during dynamic conditions, a method has been developed that enables reproducible determination of cytoplasmic phosphate from 5 M up to 30 M. The method involves fast sampling, spontaneous inactivation of cell metabolism and differential extraction procedure to gain porosity of the outer cell membrane exclusively. To determine very low cytoplasmic phosphate concentrations, an enzymatic assay was linked to a sensitive spectrophotometric cycling method to increase the detection limit.     

Anatomy and systematic position of Uldinia (Umbelliferae)

Vegetative, floral and fruit anatomy and morphology ofUldinia, a monotypic hydrocotyloid genus endemic to Australia, are described in detail. These observations, when compared to available reports for other genera of Hydrocotyloideae, indicate thatUldinia is most closely allied to members of Hydrocotyleae—Hydrocotylinae, and, in particular, toTrachymene. Similarities between these two genera include such anatomical and morphological characteristics as habit and leaf morphology, stem anatomy, trichome anatomy, inflorescence morphology, floral morphology, and several details of the floral venation pattern and fruit anatomy. Nevertheless, the nature and development of the fruit wings, the papillae and retrorse barbs of the fruit, the absence of a carpophore, the differences in floral venation at the commissure and in the upper portion of the mericarp, and the orientation of fibers in the endocarp, all provide a basis for the generic distinctness ofUldinia. These comparative studies also point to the need for a possible re-evaluation of relationships within the subtribes of Hydrocotyleae.     

Über den Bastard von Stieglitz und Kanarienvogel

Ohne Zusammenfassung     

The identification of genes involved in the stomatal response to reduced atmospheric relative humidity

Stomatal pores of higher plants close in response to decreases in atmospheric relative humidity (RH). This is believed to be a mechanism that prevents the plant from losing excess water when exposed to a dry atmosphere and as such is likely to have been of evolutionary significance during the colonization of terrestrial environments by the embryophytes. We have conducted a genetic screen, based on infrared thermal imaging, to identify Arabidopsis genes involved in the stomatal response to reduced RH. Here we report the characterization of two genes, identified during this screen, which are involved in the guard cell reduced RH signaling pathway. Both genes encode proteins known to be involved in guard cell ABA signaling. OST1 encodes a protein kinase involved in ABA-mediated stomatal closure while ABA2 encodes an enzyme involved in ABA biosynthesis. These results suggest, in contrast to previously published work, that ABA plays a role in the signal transduction pathway connecting decreases in RH to reductions in stomatal aperture. The identification of OST1 as a component required in stomatal RH and ABA signal transduction supports the proposition that guard cell signaling is organized as a network in which some intracellular signaling proteins are shared among different stimuli.