Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controOled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO2 diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.Ultraviolet radiation in the 280 to 315 nm waveband, usually denoted as UV-B radiation, is readily absorbed by nucleic acid and protein chromophores (8) and effectively inhibits many plant processes (5), including photosynthesis (2, 22). Ultraviolet radiation of this waveband is of particular interest to photobiologists because this radiation occurs in normal sunlight and would be intensified if the atmospheric ozone layer were reduced (3,10). Although the action of intense 254 nm UV radiation on photosynthetic processes has been well studied (7), this radiation would not reach the Earth's surface even in the event of severe ozone radiation.The present study was initiated to evaluate effects of UV-B radiation on photosynthesis and aspects of the electron transport system, and to define morphological changes of chloroplasts in Pisum sativum L. plants exposed to Results of this study tend to support the hypothesis that photosynthetic processes primarily associated with PSII are affected by the levels of UV-B radiation tested in this study. MATERIALS AND METHODSP. sativum L. cv. Early Alaska plants were grown under greenhouse conditions with an approximate 14-hr photoperiod and PAR4 of about 400 ,ueinsteins m-2 sec-'. Studies of the effects of plant biomass were initiated when the seedlings were 7 days old. In all other experiments, the seedlings were 14 days old upon initiation of treatment.Spectral irradiance for the controlled environment studies was provided by the lamp filter system previously described (21). The PAR was 800 ,ueinsteins -m-2 -sec-1 with a 16-hr photoperiod. Temperatures were programmed to simulate a July day in northern Utah (13 to 37 C). Spectral irradiance for both the control and UV radiation treatments are illustrated in Figure 1.The biomass study was carried out i...

Appropriate specification of the error statistics for both observational data and short-term forecasts is necessary to produce an optimal analysis. Observation error stems from instrument error, forward model error, and error of representation. All sources of observation error, particularly error of representation, can lead to nonzero correlations. While correlated forecast error has been accounted for since the early days of atmospheric data assimilation, observation error has typically been treated as uncorrelated until relatively recently. Thinning, averaging, and/or inflation of the assigned observation error variance have been employed to compensate for unaccounted error correlations, especially for high-resolution satellite data. In this study, the benefits of accounting for nonzero vertical (interchannel) correlation for both the Advanced Technology Microwave Satellite (ATMS) and Infrared Atmospheric Sounding Interferometer (IASI) in the NRL Atmospheric Variational Data Assimilation System-Accelerated Representer (NAVDAS-AR) are assessed. The vertical observation error covariance matrix for the ATMS and IASI instruments was estimated using the Desroziers method. The results suggest lowering the assigned error variance and introducing strong correlations, especially in the moisture-sensitive channels. Strong positive impact on forecast skill (verified against both the ECMWF analyses and high-quality radiosonde data) is shown in both the ATMS and IASI instruments. Additionally, the convergence of the iterative solver in NAVDAS-AR can be improved by small modifications to the observation error covariance matrices, resulting in further reduction in RMS error.

A widely used observation space covariance localization method is shown to adversely affect satellite radiance assimilation in ensemble Kalman filters (EnKFs) when compared to model space covariance localization. The two principal problems are that distance and location are not well defined for integrated measurements, and that neighboring satellite channels typically have broad, overlapping weighting functions, which produce true, nonzero correlations that localization in radiance space can incorrectly eliminate. The limitations of the method are illustrated in a 1D conceptual model, consisting of three vertical levels and a two-channel satellite instrument. A more realistic 1D model is subsequently tested, using the 30 vertical levels from the Navy Operational Global Atmospheric Prediction System (NOGAPS), the Advanced Microwave Sounding Unit A (AMSU-A) weighting functions for channels 6-11, and the observation error variance and forecast error covariance from the NRL Atmospheric Variational Data Assimilation System (NAVDAS). Analyses from EnKFs using radiance space localization are compared with analyses from raw EnKFs, EnKFs using model space localization, and the optimal analyses using the NAVDAS forecast error covariance as a proxy for the true forecast error covariance. As measured by mean analysis error variance reduction, radiance space localization is inferior to model space localization for every ensemble size and meaningful observation error variance tested. Furthermore, given as many satellite channels as vertical levels, radiance space localization cannot recover the true temperature state with perfect observations, whereas model space localization can.

Coupled two/three‐dimensional variational (2D/3DVAR) assimilation of aerosol physical properties retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS), Multi‐angle Imaging Spectroradiometer (MISR) and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite‐borne instruments is described for the U. S. Navy Aerosol Analysis and Prediction System (NAAPS) global aerosol mass transport model. Coupled 2D/3DVAR assimilation for NAAPS is evaluated for 48‐hr forecast cycles, computed four times daily in six‐hour intervals, versus stand‐alone 2DVAR assimilation of MODIS and MISR aerosol optical depths (AOD). Both systems are validated against AERONET ground‐based sun photometer measurements of AOD. Despite a narrow nadir viewing swath and more than 2700 km of equatorial separation between orbits, satellite lidar data assimilation elicits a positive model response. Improvements in analysis and forecast AOD absolute errors are found over both land and maritime AERONET sites. The primary impact to the model from 3DVAR assimilation is the redistribution of aerosol mass into the boundary layer, though the process is sensitive to parameterization of vertical error correlation lengths.

To investigate the abscisic acid (ABA) production of tomato (Mill.) plants in response to diurnal stressful temperatures, five-week old seedlings were exposed to day/night temperatures of 10/5, 15/10, 25/15, 35/25, or 45/35 C. The daylength was 16 hours with a light intensity of approximately 400 microeinsteins per meter per second. Plant tops were sampled at 12, 24, 48, and 72 hours. Free, alkaline-hydrolyzable (conjugated), and total ABA quantities were measured using standard gas chromatographic techniques. AU temperature regimes significantly increased both free and conjugated ABA levels over concentrations in control plants (25/15 C). The highest ABA levels were observed in plants exposed to the coolest temperature of 10/5 C. Since normal water potentials were obtained in plants of al treatments, the observed ABA response was not due to temperature-induced water stress. Therefore, temperature stress, like several other environmental stresses, induces the plant to produce high levels of ABA. Because of the similar involvement of ABA in temperature-induced and other environmental stresses, ABA may be a common mediator for all plant stresses.ABA is a naturally occurring compound of major importance in regulating plant growth and development. It has been implicated in a variety of physiological processes (1,11,13,15) and is found in elevated levels under several stressful conditions (3,4,7,8,16,18,23 Samples for ABA determination were harvested at 0, 12, 24, 48, and 72 h. Zero sampling time (09:00 h) was 3 h after the lights came on; therefore, all samples, except those at 12 h, were harvested 3 h after the lights came on. The 12-h samples were taken 1 h before the end of the light period (2 1:00 h). At each harvest, three single plant replicates (exclusive of the root system) were immediately frozen on dry ice and stored in a freezer at -18 C until analyzed. A representative sample (1-3 g) of each frozen and crushed plant was weighed, homogenized in ice-cold 90% methanol (10 ml/g fresh tissue), and filtered. ABA was analyzed according to the method described by Seeley and Powell (21). The alkaline-hydrolyzable ABA (conjugated ABA) was determined by adjusting the pH of the remaining aqueous phase to 11.0 with KOH, heating it at 60 C for 45 min, and re-extracting with methylene chloride. Acidic fractions were derivatized by ethereal diazomethane. ABA was quantified with a Tracor 222 Gas Chromatograph equipped with a Ni3 electron capture detector. Column packing was 3% OV-25 on Gas Chrom Q (100 to 200 mesh support). Purified N2 at a flow rate of 80 ml/min was used as the carrier gas.