Testing estimates of year-to-year variation in global net primary production (NPP) poses some challenges. Large-scale, multiyear records of production are not readily available for natural systems but are for agricultural systems, We use records of agricultural yields at selected sites to test NPP estimates produced by CASA, a global-scale production model driven by both meteorological data and the satellite-derived normalized difference vegetation index (NDVI). We also test estimates produced by the Miami model, which has underlain several analyses of biosphere response to interannual changes in climate. In addition, we test estimates against tree ring data for one boreal site for which data from both coniferous and deciduous species were available. The agricultural tests demonstrate that CASA can reasonably estimate interannual variation in production. The Miami model estimates variation more poorly. However, differences in NDVI-processing algorithms substantially affect CASA's estimates of interannual variation. Of the four versions tested, the FASIR NDVI most closely reproduced yield data and showed the least correlation with changes in equatorial crossing time of the National Oceanic and Atmospheric Administration satellites, One issue raised is the source of the positive trends evident in CASA's NDVI-based estimates of global NPP. The existence of these trends is consistent with potential stimulation of terrestrial production by factors such as CO2 enrichment, N fertilization, or temperature warming, but the magnitude of the global trends seen is significantly greater than suggested by constraints imposed by atmospheric fluxes.

We present a detailed investigation of the gross C-12 and C-13 exchanges between the atmosphere and biosphere and their influence on the delta(13)C variations in the atmosphere. The photosynthetic discrimination Delta against C-13 is derived from a biophysical model coupled to a general circulation model [Sellers et al., 1996a], where stomatal conductance and carbon assimilation are determined simultaneously with the ambient climate, The delta(13)C of the respired carbon is calculated by a biogeochemical model [Potter et al., 1993; Randerson et al., 1996] as the sum of the contributions from compartments with varying ages, The global flux-weighted mean photosynthetic discrimination is 12-16 parts per thousand, which is lower than previous estimates. Factors that lower the discrimination are reduced stomatal conductance and C-4 photosynthesis. The decreasing atmospheric delta(13)C causes an isotopic disequilibrium between the outgoing and incoming fluxes; the disequilibrium is similar to 0.33 parts per thousand for 1988. The disequilibrium is higher than previous estimates because it accounts for the lifetime of trees and for the ages rather than turnover times of the biospheric pools. The atmospheric delta(13)C signature resulting from the biospheric fluxes is investigated using a three-dimensional atmospheric tracer model. The isotopic disequilibrium alone produces a hemispheric difference of similar to 0.02 parts per thousand, in atmospheric delta(13)C, comparable to the signal from a hypothetical carbon sink of 0.5 Gt C yr(-1) into the midlatitude northern hemisphere biosphere, However, the rectifier effect, due to the seasonal covariation of CO2 fluxes and height of the atmospheric boundary layer, yields a background delta(13)C gradient of the opposite sign. These effects nearly cancel thus favoring a stronger net biospheric uptake than without the background CO2 gradient. Our analysis of the globally averaged carbon budget for the decade of the 1980s indicates that the biospheric uptake of fossil fuel CO2 is likely to be greater than the oceanic uptake; the relative proportions of the sinks cannot be uniquely determined using C-12 and C-13 alone. The land-ocean sink partitioning requires in addition, information about the land use source, isotopic disequilibrium associated with gross oceanic exchanges, as well as the fractions of C-3 and C-4 vegetation involved in the biospheric uptake.

We characterized decadal changes in the amplitude and shape of the seasonal cycle of atmospheric CO2 with three kinds of analysis. First, we calculated the trends in the seasonal cycle of measured atmospheric CO2 at observation stations in the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostic Laboratory network. Second, we assessed the impact of terrestrial ecosystems in various localities on the mean seasonal cycle of CO2 at observation stations using the Carnegie-Ames-Stanford Approach terrestrial biosphere model and the Goddard Institute for Space Studies (GISS) atmospheric tracer transport model, Third, we used the GISS tracer model to quantify the contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric CO2 for the period 1961-1990, specifically examining the effects of biomass burning, emissions from fossil fuel combustion, and regional increases in net primary production (NPP). Our analysis supports results from previous studies that indicate a significant positive increase in the amplitude of the seasonal cycle of CO2 at Arctic and subarctic observation stations. For stations north of 55 degrees N the amplitude increased at a mean rate of 0.66% yr(-1) from 1981 to 1995. From the analysis of ecosystem impacts on the mean seasonal cycle we find that tundra, boreal forest, and other northern ecosystems are responsible for most of the seasonal variation in CO2 at stations north of 55 degrees N. The effects of tropical biomass burning on trends in the seasonal cycle are minimal at these stations, probably because of strong vertical convection in equatorial regions. From 1981 to 1990, fossil fuel emissions contributed a trend of 0.20% yr(-1) to the seasonal cycle amplitude at Mauna Loa and less than 0.10% yr(-1) at stations north of 55 degrees N. To match the observed amplitude increases at Arctic and subarctic stations with NPP increases, we find that north of 30 degrees N a 1.7 Pg C yr(-1) terrestrial sink would be required. In contrast, over regions south of 30 degrees N, even large NPP increases and accompanying terrestrial sinks would be insufficient to account for the increase in high-latitude amplitudes.

To provide a common currency for model comparison, validation and manipulation, we suggest and describe the use of impulse response functions, a concept well-developed in other fields, but only partially developed for use in terrestrial carbon cycle modelling. In this paper, we describe the derivation of impulse response functions, and then examine (i) the dynamics of a simple five-box biosphere carbon model; (ii) the dynamics of the CASA biosphere model, a spatially explicit NPP and soil carbon biogeochemistry model; and (iii) various diagnostics of the two models, including the latitudinal distribution of mean age, mean residence time and turnover time. We also (i) deconvolve the past history of terrestrial NPP from an estimate of past carbon sequestration using a derived impulse response function to test the performance of impulse response functions during periods of historical climate change; (ii) convolve impulse response functions from both the simple five-box model and the CASA model against a historical record of atmospheric delta(13)C to estimate the size of the terrestrial C-13 isotopic disequilibrium; and (iii) convolve the same impulse response functions against a historical record of atmospheric C-14 to estimate the C-14 content and isotopic disequilibrium of the terrestrial biosphere at the 1 degrees x 1 degrees scale. Given their utility in model comparison, and the fact that they facilitate a number of numerical calculations that are difficult to perform with the complex carbon turnover models from which they are derived, we strongly urge the inclusion of impulse response functions as a diagnostic of the perturbation response of terrestrial carbon cycle models.

The residence times of carbon in plants, litter, and soils are required for partitioning land and ocean sinks using measurements of atmospheric delta(13)CO(2) and also for estimating terrestrial carbon storage in response to net primary production (NPP) stimulation by elevated levels of atmospheric CO2. While C-13-based calculations of the land sink decline with increasing estimates of terrestrial carbon residence times (through the fossil fuel-induced isotopic disequilibrium term in equations describing the global atmospheric budgets of (CO2)-C-13 and CO2), estimates of land sinks based on CO2 fertilization of plant growth are directly proportional to carbon residence times. Here we used a single model of terrestrial carbon turnover, the Carnegie Ames-Stanford Approach (CASA) biogeochemical model, to simultaneously estimate 1984-1990 terrestrial carbon storage using both approaches. Our goal was to identify the fraction of the (CO2)-C-13-based land sink attributable to CO2 fertilization. Uptake from CO2 fertilization was calculated using a beta factor of 0.46 to describe the response of NPP to increasing concentrations of atmospheric CO2 from 1765 to 1990. Given commonly used parameters in the C-13-based sink calculation and assuming a deforestation flux of 0.8 Pg C/yr, CO2 fertilization accounts for 54% of the missing terrestrial carbon sink from 1984 to 1990. CO2 fertilization can account for all of the missing terrestrial sink only when the terrestrial mean residence time (MRT) and the land isodisequilibrium forcing are greater than many recent estimates.

The Automated Planet Finder (APF) is a facility purpose-built for the discovery and characterization of extrasolar planets through high-cadence Doppler velocimetry of the reflex barycentric accelerations of their host stars. Located atop Mount Hamilton, the APF facility consists of a 2.4 m telescope and its Levy spectrometer, an optical echelle spectrometer optimized for precision Doppler velocimetry. APP features a fixed-forivat spectral range from 374-970 nm, and delivers a "throughput" (resolution x slit width product) of 114,000", with spectral resolutions up to 150,000. Overall system efficiency (fraction of photons incident on the primary mirror that are detected by the science CCD) on blaze at 560 nm in planet-hunting mode is 15%. First-light tests on the radial-velocity (RV) standard stars HD 185144 and HD 9407 demonstrate sub-meter-per-second precision (rms per observation) held over a 3 month period. This paper reviews the basic features of the telescope, dome, and spectrometer, and gives a brief summary of first-light performance.

The architecture of the branched root system of plants is a major determinant of vigor. Water availability is known to impact root physiology and growth; however, the spatial scale at which this stimulus influences root architecture is poorly understood. Here we reveal that differences in the availability of water across the circumferential axis of the root create spatial cues that determine the position of lateral root branches. We show that roots of several plant species can distinguish between a wet surface and air environments and that this also impacts the patterning of root hairs, anthocyanins, and aerenchyma in a phenomenon we describe as hydropatterning. This environmental response is distinct from a touch response and requires available water to induce lateral roots along a contacted surface. X-ray microscale computed tomography and 3D reconstruction of soil-grown root systems demonstrate that such responses also occur under physiologically relevant conditions. Using early-stage lateral root markers, we show that hydropatterning acts before the initiation stage and likely determines the circumferential position at which lateral root founder cells are specified. Hydro-patterning is independent of endogenous abscisic acid signaling, distinguishing it from a classic water-stress response. Higher water availability induces the biosynthesis and transport of the lateral root-inductive signal auxin through local regulation of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 and PIN-FORMED 3, both of which are necessary for normal hydropatterning. Our work suggests that water availability is sensed and interpreted at the suborgan level and locally patterns a wide variety of developmental processes in the root.

Northwest Africa (NWA) 869 is the largest sample of chondritic regolith breccia, making it an ideal source for research on accretionary processes and primordial chemical mixing. One such process can be seen in detail through the first identification of a eucrite impactor clast in an L chondrite breccia. The similar to 7 mm diameter clast has oxygen isotope compositions (Delta O-17 = -0.240, -0.258 parts per thousand) and pigeonite and augite compositions typical for eucrites, but with high areal abundance of silica (9.5%) and ilmenite (1.5%). The rim around the clast is a mixture of breccia and igneous phases, the latter due to either impactor-triggered melting or later metamorphism. The rim has an oxygen isotope composition falling on a mixing line between known eucrite and L chondrite compositions (Delta O-17 = 0.326 parts per thousand) and, coincidentally, on the Mars fractionation line. Pyroxene grains from the melt component in the rim have compositions that fall on a mixing line between the average eucrite pyroxene composition and equilibrated L chondrite composition. The margins of chondritic olivine crystal clasts in the rim are enriched in Fe as a result of diffusion from the Fe-rich melt and suggest cooling on the scale of hours. The textures and chemical mixing observed provide evidence for an unconsolidated L chondrite target material, differing from the current state of NWA 869 material. The heterogeneity of oxygen isotope and chemical signatures at this small length scale serve as a cautionary note when extrapolating from small volumes of materials to deduce planetesimal source characteristics.

The organic-inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley-Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (up to 70% to similar to 100% increase) under mild pressures at similar to 0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon-electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance.