There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second description, based on the physics of electron fluids or 'Fermi liquids' states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave. It is at present unknown which view is appropriate at a 'quantum critical point' where the antiferromagnetic transition temperature vanishes. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu(6-x)Au(x), which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (x(c) = 0.1), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.

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The compensation heat pulse method (CHPM) is of limited value for measuring low rates of sap flow in woody plants. Recent application of the CHPM to woody roots has further illustrated some of the constraints of this technique. Here we present an improved heat pulse method, termed the heat ratio method (HRM), to measure low and reverse rates of sap flow in woody plants. The HRM has several important advantages over the CHPM, including improved measurement range and resolution, protocols to correct for physical and thermal errors in sensor deployment, and a simple linear function to describe wound effects. We describe the theory and methodological protocols of the HRM, provide wound correction coefficients, and validate the reliability and accuracy of the technique against gravimetric measurements of transpiration.

Plant roots transfer water between soil layers of different water potential thereby significantly affecting the distribution and availability of water in the soil profile. We used a modification of the heat pulse method to measure sap flow in roots of Grevillea robusta and Eucalyptus camaldulensis and demonstrated a redistribution of soil water from deeper in the profile to dry surface horizons by the root system. This phenomenon, termed "hydraulic lift" has been reported previously. However, we also demonstrated that after the surface soils were rewetted at the break of season, water was transported by roots from the surface to deeper soil horizons - the reverse of the "hydraulic lift" behaviour described for other woody species. We suggest that "hydraulic redistribution" of water in tree roots is significant in maintaining root viability, facilitating root growth in dry soils and modifying resource availability.

1077I.1078II.1079III.1080IV.1081V.1084VI.1087VII.10881089References1089 Summary The rate of CO2 assimilation by plants is directly influenced by the concentration of CO2 in the atmosphere, ca. As an environmental variable, ca also has a unique global and historic significance. Although relatively stable and uniform in the short term, global ca has varied substantially on the timescale of thousands to millions of years, and currently is increasing at seemingly an unprecedented rate. This may exert profound impacts on both climate and plant function. Here we utilise extensive datasets and models to develop an integrated, multi‐scale assessment of the impact of changing ca on plant carbon dioxide uptake and water use. We find that, overall, the sensitivity of plants to rising or falling ca is qualitatively similar across all scales considered. It is characterised by an adaptive feedback response that tends to maintain 1 − ci/ca, the relative gradient for CO2 diffusion into the leaf, relatively constant. This is achieved through predictable adjustments to stomatal anatomy and chloroplast biochemistry. Importantly, the long‐term response to changing ca can be described by simple equations rooted in the formulation of more commonly studied short‐term responses.

The stable C isotope composition (δC) of leaf and wood tissue has been used as an index of water availability at both the species and landscape level. However, the generality of this relationship across species has received little attention. We compiled literature data for a range of conifers and examined relationships among landscape and environmental variables (altitude, precipitation, evaporation) and δC. A significant component of the variation in δC was related to altitude (discrimination decreased with altitude in stemwood, 2.53‰ km altitude, r =0.49, and in foliage, 1.91‰ km, r =0.42), as has been noted previously. The decrease in discrimination with altitude was such that the gradient in CO partial pressure into the leaf (P -P) and altitude were generally unrelated. The ratio of precipitation to evaporation (P/E) explained significant variation in P -P of stemwood (r =0.45) and foliage (r=0.27), but only at low (<0.8) P/E. At greater P/E there was little or no relationship, and other influences on δC probably dominated the effect of water availability. We also examined the relationship between plant drought stress (Ψ) and δC within annual rings of stemwood from Pinus radiata and Pinus pinaster in south-western Australia. Differential thinning and fertiliser application produced large differences in the availability of water, nutrients and light to individual trees. At a density of 750 stems ha, Ψ and δC were less (more negative) than at 250 stems ha indicating greater drought stress and less efficient water use, contrary to what was expected in light of the general relationship between discrimination and P/E. The greater δC of trees from heavily thinned plots may well be related to an increased interception of radiation by individual trees and greater concentrations of nutrients in foliage - attributes that increase rates of photosynthesis, reduce P and increase δC. δC was thus modified to a greater extent by interception of radiation and by nutrient concentrations than by water availability and the δC-Ψ relationship varied between thinning treatments. Within treatments, the relationship between δC and Ψ was strong (0.38

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