Systematic assessment of terrestrial biogeochemistry in coupled climate–carbon models

With representation of the global carbon cycle becoming increasingly complex in climate models, it is important to develop ways to quantitatively evaluate model performance against in situ and remote sensing observations. Here we present a systematic framework, the Carbon‐LAnd Model Intercomparison Project (C‐LAMP), for assessing terrestrial biogeochemistry models coupled to climate models using observations that span a wide range of temporal and spatial scales. As an example of the value of such comparisons, we used this framework to evaluate two biogeochemistry models that are integrated within the Community Climate System Model (CCSM) – Carnegie‐Ames‐Stanford Approach′ (CASA′) and carbon–nitrogen (CN). Both models underestimated the magnitude of net carbon uptake during the growing season in temperate and boreal forest ecosystems, based on comparison with atmospheric CO₂ measurements and eddy covariance measurements of net ecosystem exchange. Comparison with MODerate Resolution Imaging Spectroradiometer (MODIS) measurements show that this low bias in model fluxes was caused, at least in part, by 1–3 month delays in the timing of maximum leaf area. In the tropics, the models overestimated carbon storage in woody biomass based on comparison with datasets from the Amazon. Reducing this model bias will probably weaken the sensitivity of terrestrial carbon fluxes to both atmospheric CO₂ and climate. Global carbon sinks during the 1990s differed by a factor of two (2.4 Pg C yr^?1 for CASA′ vs. 1.2 Pg C yr^?1 for CN), with fluxes from both models compatible with the atmospheric budget given uncertainties in other terms. The models captured some of the timing of interannual global terrestrial carbon exchange during 1988–2004 based on comparison with atmospheric inversion results from TRANSCOM (r=0.66 for CASA′ and r=0.73 for CN). Adding (CASA′) or improving (CN) the representation of deforestation fires may further increase agreement with the atmospheric record. Information from C‐LAMP has enhanced model performance within CCSM and serves as a benchmark for future development. We propose that an open source, community‐wide platform for model‐data intercomparison is needed to speed model development and to strengthen ties between modeling and measurement communities. Important next steps include the design and analysis of land use change simulations (in both uncoupled and coupled modes), and the entrainment of additional ecological and earth system observations. Model results from C‐LAMP are publicly available on the Earth System Grid.     

Analysis of growth during geotropic curvature in seedling hypocotyls

Abstract. The patterns of growth in organs curving under the influence of gravity were analysed by time-lapse photography of cress and cucumber hypocotyls which were delimited into 1 mm zones by ion-exchange beads. Geotropic curvature resulted from changes in growth rate on both sides of the organ. Growth inhibition of varying degrees of intensity occurred in all the previously growing zones of the upper (concave) side. An absolute reduction in length due to compression frequently occurred in some zones. Also, in both species growth stimulation was observed on the lower (convex) side. The disparity in growth rate between the upper and lower surfaces varied with time, being more apparent in the subapical region in the first hour of curvature. A later promotion of growth rate on the lower surface subsequently increased the curvature of the more basal zones. Autotropic straightening occurred as a consequence of growth changes, both inhibitory and stimulatory, in the apical zones. These events indicate a polarity of response in which apical zones have precedence over basal zones.     

Anti-Auxin Activity of Xyloglucan Oligosaccharides: the R?le of Groups other than the Terminal {alpha}-L-Fucose Residue

The quantitatively major nonasaccharide (XG9) derived from xyloglucanby digestion with cellulase exhibits anti-auxin activity inthe pea stem segment straight-growth bioassay; the most effectiveconcentration of XG9 is c. 10^–9 M. Previous work had shownthat XG9 owes its biological activity to the presence of a terminal-L-fucopyranose residue. In order to investigate to what extentthe remainder of the XG9 molecule is essential for activity,several fucose-containing compounds were tested for their abilityto mimic the anti-auxin effect of XG9. A fucose-containing pentasaccharideof xyloglucan (XG5; probable structure FucGalXylGlcGlc) was,at 10^–8 M, about as effective an anti-auxin as 10^–9M XG9; unlike XG9, XG5 did not diminish in effectiveness at10^–7 M. The human milk trisaccharide, 2'-fucosyl-lactose[L-fucopyranosyl--(12)-D-galactopyranosyl-ß-(14)-D-glucose],whose FucGal unit is identical with that of XG9, inhibited auxin-inducedelongation over a wide range of concentrations centred on about10^–8 M. 2'-Fucosyl-lactose at 10^–8 M was about aseffective an anti-auxin as 10^–9 M XG9. Free L-fucose andmethyl--L-fucopyranoside were unable to inhibit auxin-inducedgrowth at any concentration tested (10^–10 M to 10^–6M) and neither compound interfered with the inhibition causedby 10^–9 M XG9 when co-incubated at concentrations up to10^–4 M. The results confirm the essential r?le of an -linkedterminal fucose residue in the anti-auxin activity of XG9 andshow that the sub-terminal galactose residue may also be required.Possible reasons why high concentrations of XG9 fail to antagonizeauxin-induced growth while high concentrations of XG5 and 2'-fucosyl-lactosecontinue to do so are discussed. Key words: Anti-auxin, oligosaccharin, fucose     

Effects of growth retardants on bulbil production by Narcissus twin-scales

Narcissus twin-scale propagules, cut from various positions in the parent bulb, were incubated with gibberellic acid (GA₃) or growth retardants. Bulbil production was inhibited in all cases by GA₃ at 10–100 mg/litre. Chlormequat chloride, chlorphonium chloride and paclobutrazol also inhibited bulbil production; in the case of paclobutrazol, outer twin-scales were more sensitive to lower concentrations of the retardant than inner ones. Ancymidol enhanced bulbil production (in numbers by up to 15%) in the outermost twin-scales, and had no stimulatory effect on the inner twin-scales. Treatments affected bulbil numbers and bulbil lengths about equally.     

Evaluation of Harmonic Direction-Finding Systems for Detecting Locomotor Activity

Abstract: We conducted a physical simulation experiment to test the efficacy of harmonic direction finding for remotely detecting locomotor activity in animals. The ability to remotely detect movement helps to avoid disturbing natural movement behavior. Remote detection implies that the observer can sense only a change in signal bearing. In our simulated movements, small changes in bearing (<5.7°) were routinely undetectable. Detectability improved progressively with the size of the simulated animal movement. The average (±SD) of reflector tag movements correctly detected for 5 observers was 93.9 ± 12.8% when the tag was moved ≥11.5°; most observers correctly detected tag movements ≥20.1°. Given our data, one can assess whether the technique will be effective for detecting movements at an observation distance appropriate for the study organism. We recommend that both habitat and behavior of the organism be taken into consideration when contemplating use of this technique for detecting locomotion.     

The effect of the CpTi gene in strawberry against attack by vine weevil (Otiorhynchus sulcatus F. Coleoptera: Curculionidae)

The degree of protection against insect feeding conferred upon transgenic strawberry lines expressing the Cowpea trypsin inhibitor was evaluated under glasshouse conditions. Insect bioassays were carried out using vine weevil (Otiorhynchus sulcatus) in two experiments and in both experiments there was a highly significant reduction in damage by weevil larvae on the transgenic lines.