Foliage Water Research Articles

Feasibility study of forest wood-boring pest detection base on hyperspectral LiDAR

ABSTRACT Forest pests impose significant threats to tree productivity and ecosystem stability. Most studies focussed on foliage water, tree defoliate and mortality, which lag behind pest outbreak. To address this issue, we developed hyperspectral LiDAR (HSL) system based on an acousto-optic tunable filter (AOTF) to examine the echo intensity of tree trunks. First, we demonstrated the echo power of the cylindrical surface is approximately equivalent to that of the plate surface within 60° incidence angle, which provide the theoretical reference for trunk surface echo intensity calibration with a white panel. Second, we propose a two-step method to detect the attacked parts from barks. The first step is rapid pest detection conducted by the echo intensity ratio of damaged area and normal area. While the ratio is around one, the second step is pest detection based on support vector machine classifier with reflectance. When the reflectivity of five spectral channels is used as input parameters, 100% rapid detection accuracy of damage area is achieved. We also use the radiance under seven channels to achieve 100% classification of tree species and attack features. The results show that this HSL is effective in wood-boring pest detection and contributes to forest applications.

Priming Bean Seedlings to Boost Natural Plant Defenses Against Common Bacterial Wilt: Leaf Architecture, Leaf area, Foliage Water Content, and Plant Biomass Results (Part 3)

This greenhouse study evaluated the effects of two chemicals for priming kidney bean seedlings against bacterial wilt disease (Curtobacterium flaccumfaciens pv. Flaccumfaciens) (CFF). The premise of this study was that the oxidant properties of chlorine dioxide would mimic the signaling properties of radical oxygen species thereby initiating a cascade of molecular plant defenses. The factorial study included two levels for the foliar chlorine dioxide treatment, two levels for the bacterial wilt inoculation treatment, and two optional treatments. The biomass variables included oven dry total plant biomass, oven dry fruit biomass, and oven dry leaf biomass. Also, foliage and total plant water content data was collected, as well as total leaf area. Specific leaf area (SLA) was estimated from the leaf area and biomass data. The primers had equivalent leaf area, plant and fruit biomass as the water control for the CFF wilt inoculated plants. The EB 400 mg/l primer reduced SLA for the CFF inoculated plants. Both EB formulations increased aboveground water content in the CFF wilt inoculated plants. Multivariate tables revealed several significant correlations among leaf architecture, plant tissue water content, and biomass growth parameters for the EB primers and the water control treatment for the two CFF wilt treatments. Re-allocation of plant resources from plant growth to plant defenses due to chemical primers were estimated and discussed to determine the tradeoffs between plant yield and enhanced plant defenses. The three articles in this study show that chlorine dioxide primers can initiate a series of ROS and salicylic acid signals. This interplay of ROS signals and salicylic acid signals generated by the chlorine dioxide primers activates a long-term SAR response that protects plants against future pathogen attacks. In addition, interaction of the ROS and salicylic acid signals activates a suite of defense mechanisms that provide universal, multifaceted plant immunity that can be sustained across a crop season.

Experimental drier climates affect hydraulics and induce high mortality of seedlings of three northern conifer species

The future climate of northern temperate forests is projected to be drier and warmer by the end of this century. As a result, more drought-induced forest dieback events are anticipated in northeastern North America, and assessing the vulnerability of dominant tree species to drought is critical for understanding the future composition of these forests. In a greenhouse experiment, we exposed two-year-old seedlings of Picea glauca (Moench) Voss, Picea mariana (Mill.) B.S.P. and Pinus strobus L. to three future climate treatments for southern Quebec, Canada, and evaluated their mortality, growth, and foliage water status responses to soil water availability and atmospheric drought. Using a unique approach, climate treatments emulated droughts of different frequencies, durations, and intensities. Treatments closely simulated one growing season, with changes in air temperature and relative humidity every six hours and daily adjustment in the amount of water delivered to the seedlings. The three species experienced high mortality (75%) in all water-limited treatments compared to a control treatment that provided non-limiting soil moisture (0% mortality). The biomass of the seedlings that survived was 40% lower than that of control seedlings. Our results confirmed that the hydraulic safety margins, defined as the difference between seasonal minimum water potential and xylem water potential leading to 12, 50 and 88% of hydraulic conductivity loss, were good predictors of probability of tree mortality. Therefore, hydraulic safety margins are useful functional traits that can be used to compare the vulnerability of various species to drought and then provide crucial information to practitioners and policymakers to adjust forest management to climate change. We showed that three dominant conifer species of northern temperate forests were highly vulnerable to drought in future climates. Because drought is projected to be a significant threat to forests, understanding potentially adaptive physiological responses to drought, such as hydraulic safety margins of tree seedlings, is important for predicting the response of forest regeneration and composition in warmer and drier climates.

Retrieval of Harmonized LAI Product of Agricultural Crops from Landsat OLI and Sentinel-2 MSI Time Series

In this study, an approach for the harmonized calculation of the Leaf Area Indices (LAIs) for agronomic crops from Sentinel-2 MSI and Landsat OLI multispectral satellite data is proposed in order to obtain a dense seasonal trajectory. It was developed and tested on dominant crops grown in the Czech Republic, including winter wheat, spring barley, winter rapeseed, alfalfa, sugar beet, and corn. The two-step procedure harmonizing Sentinel-2 MSI and Landsat OLI spectral data began with deriving NDVI, MSAVI, and NDWI_1610 vegetation indices (VIs) as proxy indicators of green biomass and foliage water content, the parameters contributing most to a stand’s spectral response. Second, a simple linear transformation was applied to the resulting VI values. The regression model itself was built on an artificial neural network, then trained on PROSAIL simulations data. The LAI estimates were validated using an extensive dataset of in situ measurements collected during 2017 and 2018 in the lowlands of the Central Bohemia Region. Very strong agreement was observed between LAI estimates from both Sentinel-2 MSI and Landsat OLI data and independent ground-based measurements (r between 0.7 and 0.98). Very good results were also achieved in the mutual comparison of Sentinel-2 and Landsat-based LAI datasets (rRMSE < 20%, r between 0.75 and 0.99). Using data from all currently available Sentinel-2 (A/B) and Landsat (8/9) satellites, a dense harmonized LAI time series can be created with high potential for use in precision agriculture.

Competition and Niche Differentiation of Water and Nutrients between Broussonetia papyrifera and Platycladus orientalis under Prolonged Drought Stress

Little is known about the competition between and niche differentiation of water and nutrients between angiosperm and gymnosperm tree species under prolonged drought stress, especially in fragile environments. We imposed 21 d drought and competition treatments on Broussonetia papyrifera and Platycladus orientalis and measured water, N, and P contents, the isotopic composition of N and C, the activity of P assimilation enzymes, and stomatal conductance under solo planting and mixed planting to characterize resource diversity and competition in response to treatments. The N content, δ13C, δ15N, phosphomonoesterase, phosphodiesterase, gs, and foliage water content were significantly affected by the soil water content. The δ15N content in young leaves showed that N competition between these two plants could be alleviated through niche differentiation, but the changes in the PDE: PME ratio for these two plants indicated that they lost the niche differentiation of the P source under drought stress. Additionally, it was observed that foliage water content, WUE, N contents, and N and P sources were significantly affected by interspecific competition, and Broussonetia papyrifera benefited from water competition under moderate drought. Our results indicate that plants have different competition and niche differentiation modes to different nutrients under drought stress, and the effect of interspecific water competition should be seriously considered in mixed forests in semiarid areas.

Long-term effects of water stress on hyperspectral remote sensing indicators in young radiata pine

The development of methods to spatially describe long-term water stress in plantations is going to become increasingly important as drought events increase in frequency under climate change. Despite this we are unaware of any research that has used hyperspectral imagery to describe long-term water stress for the most widely established exotic pine species, Pinus radiata D. Don (radiata pine). Hyperspectral imagery and foliage water content were repeatedly sampled over a five month period in one-year old radiata pine that were allocated to well-watered and drought treatments. These data were used to (i) determine how rapidly equivalent water thickness (EWT) and leaf fresh weight (LWCF) change in response to drought and (ii) identify the key hyperspectral indicators associated with changes in EWT and LWCF.Both EWT and LWCF exhibited little treatment variation until 91 days after treatment (DAT) but diverged strongly after this time. By 108 DAT, mean values in the control exceeded the droughted treatment by 41.3% for EWT (0.0175 vs. 0.0124 g cm−2, P < 0.001) and 17.2% for LWCF (67.7 vs. 57.8%, P < 0.001). Using hyperspectral data captured 108 DAT, highly significant treatment differences (P < 0.001) in reflectance were found in the SWIR region with the most significant differences occurring between 1139 and 2497 nm.There were strong correlations between a wide range of water indices and both measures of water stress using data captured 108 DAT. The indices that were most strongly correlated with EWT were found to be GVMI, NDWI1640 and SIWSI with R2 values ranging from 0.86 to 0.87. Indices that had the strongest correlations with LWCF were SRWI1, GVMI and MSI with R2 values ranging from 0.89 to 0.90. Water indices were more strongly related to both measures of water stress than the physiological index PRI which was moderately correlated to both EWT (R2 = 0.47) and LWCF (R2 = 0.62). A wide range of structural and chlorophyll indices were less well correlated with both measures of water content and long-term water stress than either PRI or the water indices.

Estimation of phloem carbon translocation belowground at stand level in a hinoki cypress stand.

At stand level, carbon translocation in tree stems has to match canopy photosynthesis and carbohydrate requirements to sustain growth and the physiological activities of belowground sinks. This study applied the Hagen-Poiseuille equation to the pressure-flow hypothesis to estimate phloem carbon translocation and evaluate what percentage of canopy photosynthate can be transported belowground in a hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc.) stand. An anatomical study revealed that, in contrast to sieve cell density, conductive phloem thickness and sieve cell hydraulic diameter at 1.3 m in height increased with increasing tree diameter, as did the concentration of soluble sugars in the phloem sap. At tree level, hydraulic conductivity increased by two orders of magnitude from the smallest to the largest trees in the stand, resulting in a stand-level hydraulic conductance of 1.7 × 10-15 m Pa-1 s-1. The osmotic potential of the sap extracted from the inner bark was -0.75 MPa. Assuming that phloem water potential equalled foliage water potential at predawn, the turgor pressure in the phloem at 1.3 m in height was estimated at 0.22 MPa, 0.59 MPa lower than values estimated in the foliage. With this maximal turgor pressure gradient, which would be lower during day-time when foliage water potential drops, the estimated stand-level rate of carbon translocation was 2.0 gC m-2 day-1 (30% of daily gross canopy photosynthesis), at a time of the year when aboveground growth and related respiration is thought to consume a large fraction of photosynthate, at the expense of belowground activity. Despite relying on some assumptions and approximations, this approach, when coupled with measurements of canopy photosynthesis, may further be used to provide qualitative insight into the seasonal dynamics of belowground carbon allocation.

A multiple time scale modeling investigation of leaf water isotope enrichment in a temperate grassland ecosystem

Understanding the controls on temporal variation in plant leaf δ2H and δ18O values is important for understanding carbon–water dynamics of the biosphere and interpreting a wide range of proxies for past environments. Explaining the enrichment mechanisms under field conditions is challenging. To clarify the leaf water isotopic enrichment process at the ecosystem scale, four models with a range of complexities that were previously conducted at the leaf scale have been tested to simulate canopy foliage water in a multispecies grassland ecosystem. Although the exact importance of considering non-steady-state or/and isotopic diffusion in bulk leaf isotopic simulations has been reported in previous studies, our findings suggested that the steady-state assumption (SSA) is practically acceptable as a first-order approximation. The SSA two-pool model was the best option for reproducing seasonality of the bulk-leaf-water isotopic ratio for a grassland ecosystem. Relative humidity at canopy layer as the most controlling factor for canopy foliage water stable isotope composition because of its high sensitivity and variation. The results highlighted that canopy foliage water was a well-behaved property that was predictable for a multispecies grassland ecosystem at hourly or daily time-scales.

Drought Impact on Phenology and Green Biomass Production of Alpine Mountain Forest—Case Study of South Tyrol 2001–2012 Inspected with MODIS Time Series

Ecological balance and biodiversity of the alpine forest is endangered by global and local climatic extremes. It spurs a need for comprehensive forest monitoring, including in depth analyses of drought impact on the alpine woodland ecosystems. Addressing an arising knowledge gap, we identified and analyzed 2002–2012 aridity related responses within the alpine mountain forest of South Tyrol. The study exploited a S-mode PCA (Principal Component Analysis) based synergy between meteorological conditions rendered by the scPDSI (self-calibrated Palmer Drought Severity Index) and forest status approximated through MODIS (Moderate Resolution Imaging Spectroradiometer) derived NDVI (Normalized Difference Vegetation Index) and NDII7 (Normalized Difference Infrared Index based on MODIS band 7) time series. Besides characterizing predominant forest temporal response to drought, we identified corresponding spatial footprints of drought impact, as well as examined aridity-related changes in forest phenology and biomass production. The latter was further evaluated in relation to forest type, elevation, aspect and slope. Recognized meteorological conditions highlighted: prolonged 2003–2007 mild to extreme drought, and overall regional drying tendencies. Arising remotely sensed forest responses accounted on localized decline in foliage water content and/or photosynthetic activity, but also indicated regions where forest condition improved despite the meteorological stress. Perceived variability in the forest response to drought conditions was governed by geographic location, species structure, elevation and exposition, and featured complexity of the alpine forest ecosystem. Among the inspected biophysical factors elevation had the strongest influence on forest phenology and green biomass production under meteorological stress conditions. Stands growing above 1400 m a.s.l. demonstrated initial increase in annual biomass growth at the beginning of the dry spell in 2003. Conversely, woodlands at lower altitudes comprising considerable share of hardwood species were more prone to biomass decline in 2003, but experienced an overall upturn in biomass production during the following years of the dry spell. Aspect showed moderate effect on drought-related phenology and green biomass production responses. Diverse forest ecosystem responses identified in this study were in line with known local and regional analyses, but also shed some new light on drought induced alternation of forest status.

Response of Sugar Beet Yield to Deficit Irrigation under Drip Irrigation System

A field experiment of drip-irrigated sugar beet (Beta vulgaris, L.)was conducted at the research field of the Nubaria Agricultural Research Station, Egypt at 30° 54' 21'' N, 29° 52' 15'' E and 11.0 m altitude above mean sea level during 2011/2012 growing season.The aim of the present study was to evaluate the impact of deficit irrigation on sugar beet productivity, and quantitative and qualitative characteristics of sugar beet root yield under drip irrigation. The sugar beet (Beta vulgaris, L) variety Gloria (polygerm) was planted on 13 October 2011. Sugar beet plants were thinned to one plant at distance of about 0.3 m on the rows at the 4th week after planting. After emergence, the plots were irrigated by the drip irrigation method.The present study consisted of 5 treatments. The irrigation treatments were based on replenishment of soil water depletion according to reference evapotranspiration (ET0). The irrigation treatments were: Irrigation at 40, 60, 80, 100 and 120% of ET0. Sugar beet vegetative growth, sugar beet yield and yield components, and juice quality and impurities content were determined. The results clearly indicated a significant effect of different irrigation regimes on all sugar beet growth characters except leaf area per plant and foliage water content as compared with control (100% of ET0). The results alsoclearly indicated a significant effect of irrigation regimes on sugar beet yield and yield components. Irrigation at 40% of ET0 gave a highest value of root length (32.7cm) and root diameter (13.0 cm), but 60 % of ET0 gave the highest values of average root fresh weight (1500 g/plant) and root gross yield (100.0 ton/ha). The highest value of root/top ratio (1.31) was attained at irrigation with 120% of ET0. The percent increase of root gross yield of sugar beet at 60% of ET0 was account as 49.99%, for gross sugar yield was 45.66% and for white sugar yield was 44.16% over the common treatment (100% of ET0). The different irrigation regimes significantly affected the juice quality and impurities contents of sugar beet. Irrigation at 40 and 60% of ET0 gave the highest value of TSS (total soluble solids), 23.0%, white sugar yield (13.71 ton/ha), gross sugar yield (16.97 ton/ha) and loss sugar yield (3.26 ton/ha) were attained at 60% of ET0. The highest values of polarity or sucrose content (17.76 %), effective polarimetric assay of sugar (15.46%),thick purity juice, TPJ (90.66%), white sugar content (14.94%) and juice purity (84.13%) were attained at 60% of ET0. The increase in sugar yield was due to both increase in sugar content and root yield in which sugar yield was adversely affected by water deficit. Increasing the impurities in the root of stressed plants decreased extraction of white sugar. So, deficit irrigation improved sugar beet quality by reducing these impurities. The findings in this study strongly recommend that up to 60% deficit irrigation of sugar beet would be advantage if the farmers target is to maximize root and white sugar yield. But if the target is to put more area into production under limited water supply, irrigation at 40% of reference evapotranspiration in sugar beet may be feasible.

Modeling biophysical controls on canopy foliage water 18O enrichment in wheat and corn

AbstractLeaf water 18O enrichment is an important factor controlling the H218O, C18OO, and O18O exchanges between the biosphere and the atmosphere. At present, there is limited capacity to explain the enrichment mechanisms in field conditions. In this study, three models of varying complexity were used to simulate the leaf water 18O enrichment at the canopy scale. Comparisons were made among the models and with high‐frequency isotopic measurements of ecosystem water pools in wheat and corn. The results show that the steady state assumption was a better approximation for ecosystems with lower canopy resistance, that it is important to consider the effect of leaf water turnover in modeling the enrichment and not necessary to deal with time changes in leaf water content, and that the leaf‐scale Péclet effect was incompatible with the big‐leaf modeling framework for canopy‐air interactions. After turbulent diffusion has been accounted for in an apparent kinetic factor parameterization, the mean 18O composition of the canopy foliage water was a well‐behaved property predictable according to the principles established by leaf‐scale studies, despite substantial variations in the leaf water enrichment with leaf and canopy positions. In the online supplement we provided a discussion on the observed variability of leaf water 18O composition with leaf and canopy positions and on the procedure for correcting isotopic measurements for organic contamination.

Efectos de extractos acuosos de la maleza Cyperus rotundus L. (Cyperaceae) sobre la germinación de semillas y crecimiento de plántulas de maíz ( Zea mays L.) cv. Pioneer 3031

La investigación tuvo por fi nalidad determinar los efectos de extractos acuosos del follaje de Cyperus rotundus L. sobre la germinación de semillas y el crecimiento de plántulas de maíz ( Zea mays L.) cv. Pioneer 3031. Un primer extracto al 15% p/v fue preparado con el follaje de plantas mays L.) cv . Pioneer 3031. Un primer extracto al 15% p/v fue preparado con el follaje de plantas mays de C. rotundus de 15 días, se dejó reposar por 48 h y luego se obtuvo por dilución extractos al 0; 2,0; 4,0 y 6,0% p/v evaluándoseles pH y conductividad eléctrica (S.cm -1 ). Para la siembra se utilizaron bandejas cubiertas con una doble capa de papel absorbente sobre la que se colocó 20 semillas/bandeja, tapadas con dos hojas más de papel y regadas tres veces al día con los extrac- tos foliares. El tratamiento control recibió agua corriente. El diseño estadístico fue bloques al azar con cuatro concentraciones de extracto y cinco repeticiones. A los 12 días después de la siembra se determinaron los diferentes parámetros de germinación y crecimiento. Se práctico un análisis de varianza y regresión para los parámetros estudiados. El pH disminuyó y la CE incrementó al aumentar la concentración del extracto. La germinación, altura de las plántulas, longitud de las radículas, peso seco del vástago y relación peso seco del vástago/peso seco de la radícula dismi- nuyeron proporcionalmente al aumento de la concentración de extracto, contrariamente, el peso seco de la radícula incrementó. La relación altura de la plántula/longitud de la radícula no presentó diferencias signifi cativas en las fuentes de variación.

Effect of Albizia julibrissin Water Extracts on Low-Density Lipoprotein Oxidization

High-value phytochemicals could be extracted from biomass prior to the current cellulosic pretreatment technologies (i.e., lime, ammonia, dilute acid, or pressurized hot water treatments) provided that the extraction is performed with a solvent that is compatible with the pretreatment. This work reports on the extraction of flavonoids from Albizia julibrissin biomass. While extracting A. julibrissin foliage with 50 degrees C water, 2.227 mg/g of hyperoside and 8.134 mg/g quercitrin were obtained, which is in the realm of what was obtained with 60% methanol. A. julibrissin foliage, flower, and whole plant extracts were tested in terms of their potential to inhibit low-density lipoprotein (LDL) oxidization. The highest inhibition was obtained with foliage water extracts, which were standardized at 2.5 microM of flavonoids. Also, the 2.5 microM foliage water extract resulted in a reduction from 43% to only 1% of the observed monocyte adherence. To have commercial application, A. julibrissin water extracts should be devoid of toxicity. The A. julibrissin foliage, flower, and whole plant water extracts were not toxic to Vero 76 cells. In summary, A. julibrissin biomass can be extracted with 50 degrees C water to yield an antioxidant stream, showing that it may be possible to couple extraction of valuable phytochemicals to the cellulosic pretreatment step.

Nocturnal stomatal conductance effects on the 18O signatures of foliage gas exchange observed in two forest ecosystems

We report field observations of oxygen isotope ((18)O) discrimination during nocturnal foliage respiration ((18)Delta(R)) in branch chambers in two forest ecosystems: a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation in Scotland; and a beech (Fagus sylvatica L.) forest in Germany. We used observations and modeling to examine the impact of nocturnal stomatal conductance on the (18)O/(16)O (delta(18)O) signatures of foliage gas exchange at night. We found that nocturnal stomatal conductance can influence the delta(18)O signature by affecting: (1) the bidirectional diffusion of CO(2) into and out of the leaf (with isotopic equilibration); and (2) the (18)O enrichment of the foliage water with which the CO(2) equilibrates. Both effects were manifest in high apparent (18)Delta(R) values and enriched delta(18)O signatures of foliage water at night. The effects were more pronounced for Sitka spruce because of its higher nocturnal stomatal conductance and higher specific leaf water content compared to beech. We found that taking the effects of nocturnal stomatal conductance into account may change the sign of the delta(18)O signature of nocturnal foliage respiration, generally thought to decrease the delta(18)O of atmospheric CO(2). We conclude that nocturnal stomatal exchange can have a profound effect on isotopic exchange depending on species and environmental conditions. These effects can be important when using delta(18)O signatures of canopy CO(2) to distinguish foliage and soil respiration, and when modeling the delta(18)O signature of CO(2) exchanged between ecosystems and the atmosphere.

Non‐steady state effects in diurnal 18O discrimination by Picea sitchensis branches in the field

We report diurnal variations in 18O discrimination (18 delta) during photosynthesis (18 delta A) and respiration (18 delta R) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18 delta (18 delta pred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the Delta 18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18 delta pred and observed 18 delta (18 delta obs) compared with the assumption of isotopic steady state (ISS) for the Delta 18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18 delta values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of delta 18O of CO2.

Radiative transfer modeling within a heterogeneous canopy for estimation of forest fire fuel properties

Imaging spectrometer data were acquired over conifer stands to retrieve spatially distributed information on canopy structure and foliage water content, which may be used to assess fire risk and to manage the impact of forest fires. The study relied on a comprehensive field campaign using stratified systematic unaligned sampling ranging from full spectroradiometric characterization of the canopy to conventional measurements of biochemical and biophysical variables. Airborne imaging spectrometer data (DAIS7915 and ROSIS) were acquired parallel to the ground measurements, describing the canopy reflectance of the observed forest. Coniferous canopies are highly heterogeneous and thus the transfer of incident radiation within the canopy is dominated by its structure. We demonstrated the viability of radiative transfer representation and compared the performance of two hybrid canopy reflectance models, GeoSAIL and FLIGHT, within this heterogeneous medium. Despite the different nature and canopy representation of these models, they yielded similar results. Subsequently, the inversion of a hyperspectral GeoSAIL version demonstrated the feasibility of estimating structure and foliage water content of a coniferous canopy based on radiative transfer modeling. Estimates of the canopy variables showed reasonably accurate results and were validated through ground measurements.

Contrasting soil respiration in young and old‐growth ponderosa pine forests

AbstractThree years of fully automated and manual measurements of soil CO2 efflux, soil moisture and temperature were used to explore the diel, seasonal and inter‐annual patterns of soil efflux in an old‐growth (250‐year‐old, O site) and recently regenerating (14‐year‐old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO2 efflux at both sites showed large inter‐annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO2 efflux at the O site showed a strong positive correlation between diel mean soil CO2 efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site‐specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO2 efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m−2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes.

Air and vegetated ground interactions in air quality diagnosis for emergency response

The land-surface parameterization scheme BATS was incorporated into a diagnostic atmospheric modeling system, using an unstructured prismatic grid, to investigate the capability of a diagnostic tool, designed for emergency response, to assign the land-cover impact on the boundary layer structure and pollutant dispersion. In this framework, two applications were made over a complex alpine region with 14 different landuses. In the first application (case A), the effects of the snow and vegetation processes on the ground-atmosphere heat exchanges (such as snow melt, fractional ground shading, vegetation and snow-cover-dependent albedo, existence of transpiring plant surfaces, plant water budget including foliage and stem water storage, transpiration limitations by stomatal resistance and soil dryness) were taken into account, while in the second (case B), they were omitted. The results were compared with data from the TRANSALP experiment. Considerable differences were found between cases A and B concerning the sensible heat flux, the atmospheric stability and the mixing layer height while the pollutant concentration maxima were significantly underestimated in the second case. The localization of these effects by a diagnostic modeling system, with a minor increase in the computing time, is considered significantly important for the improvement of the accuracy and reliability of the results in case of emergency response.

Dew and Spray Volume Effect on Glyphosate Efficacy1

The influence of three simulated dew levels and 150, 300, and 450 L/ha spray volume on glyphosate control of oat plants was determined from pot experiments. Results showed that the effect of dew level on glyphosate efficacy was related to application volume. Glyphosate efficacy at the low and medium application volume (150 and 300 L/ha) was not affected by dew level. However, glyphosate efficacy decreased when applied at the high spray volume (450 L/ha), regardless of dew level. However, high dew level reduced efficacy only when glyphosate was applied at 450 L/ha.Nomenclature: Glyphosate; oat, Avena sativa L.Additional index words: Application volume, glyphosate activity, foliage water retention, foliage free water.Abbreviations: DAE, days after emergence; HDA, homogeneous dew area.

Xylem acoustic emissions and water relations of Calluna vulgaris L. at two climatological regions of Britain.

The acoustic emission rate (as a result of xylem cavitation), stem water content, stomatal conductance, and leaf water potential of heather (Calluna vulgaris L. Hull) were compared over a period of 18 months at two contrasting sites in Britain. The sites were Thursely Common in south-east England, and Flanders Moss in central Scotland (average rainfall of 600 mm per year and 1500 mm per year, respectively). In the first year of study (1992) the natural difference between the sites was amplified by a severe drought affecting south-east England. The relative water content of the xylem (RWC) did not differ between the sites, and did not fluctuate seasonally, despite the drought at Thursely. Acoustic emissions were detected at both sites, but the incidence was low. The same range of foliage water potential and stomatal conductance was found at both sites. The leaf area to sapwood area ratio at the dry site was half that at the wet site, and it is suggested that this adjustment of the transpiring area relative to the water conducting area facilitates the close physiological state of the plants at the two sites. The possible occurrence of aerial refilling and freezing induced xylem cavitation is also discussed.