Vegetation Stress Research Articles

Stochastic Parsimonious Hydrologic Partitioning Model under East Asia Monsoon Climate and Its Application to Climate Change

A conceptual hydrologic partitioning model suitable for the East Asia monsoon climate region is constructed parsimoniously, and the variability of Horton index, which is the ratio of water vaporization and wetting in the watershed, is investigated. Numerical simulations in the study area show that the inter-annual variability of Horton index is reduced to around 60% of the inter-annual variability of annual precipitation, and there is a strong inverse correlation between Horton index and annual precipitation. Using cumulant expansion theory, the probability distribution function of soil water with various hydro-meteorological variables and watershed characteristics is derived. Using the steady-state soil water probability distribution function, the sensitivity of Horton index to hydro-meteorological variables such as precipitation occurrence probability, average rainfall depth at rainy days, and evapotranspiration rate and hydro-geophysical characteristics such as surface runoff coefficients, threshold soil water value to control vaporization, and exponent value to control groundwater recharge is analyzed. Looking at the future Horton index of the study area using a variety of future climate information ensemble, it is projected that the water stress of vegetation in the watershed is likely to increase due to fluctuations in precipitation patterns and increase in potential evapotranspiration even if annual precipitation increases.

Characterization of non-canonical G beta-like protein FvGbb2 and its relationship with heterotrimeric G proteins in Fusarium verticillioides.

Fusarium verticillioides is a fungal pathogen that is responsible for maize ear rot and stalk rot diseases worldwide. The fungus also produces carcinogenic mycotoxins, fumonisins on infested maize. Unfortunately, we still lack clear understanding of how the pathogen responds to host and environmental stimuli to trigger fumonisin biosynthesis. The heterotrimeric G protein complex, consisting of canonical Gα, Gβ and Gγ subunits, is involved in transducing signals from external stimuli to regulate downstream signal transduction pathways. Previously, we demonstrated that Gβ protein FvGbb1 directly impacts fumonisin regulation but not other physiological aspects in F. verticillioides. In this study, we identified and characterized a RACK1 (Receptor for Activated C Kinase 1) homolog FvGbb2 as a putative Gβ-like protein in F. verticillioides. The mutant exhibited severe defects not only in fumonisin biosynthesis but also vegetative growth and conidiation. FvGbb2 was positively associated with carbon source utilization and stress agents but negatively regulated general amino acid control. While FvGbb2 does not interact with canonical G protein subunits, it may associate with diverse proteins in the cytoplasm to regulate vegetative growth, virulence, fumonisin biosynthesis and stress response in F. verticillioides.

Assessment of the Forest Health Through Remote Sensing Techniques in Valea Roșie Natura 2000 Site, Bihor County, Romania

Abstract The present study deals with the estimation of the evolution tendency of the environmental stage of a protected habitat with predominant forest vegetation, during a short period of time, using techniques specific to remote sensing. Therefore, two important spectral indexes were tested while assessing the health of the forest ecosystems: i.e. the Normalized Difference Vegetation Index (NDVI) and the Structure Insensitive Pigment Index (SIPI). The period of time taken into consideration for the study was, 2013 - 2019, having used medium resolution satellite photos, Landsat 8 OLI, having initially undergone standard pre-processing operations (resize data, radiometric calibration, atmospheric correction). The satellite images modified according to the Top of Atmosphere Reflectance and corrected topographically resulted into getting values for the two before mentioned indexes. The quantity-spatial results obtained, correlated to the monthly values of the precipitations processed in order to obtain the SPI (Standardized Precipitation Index), mostly reveal, in what SIPI and also NDVI are concerned, a slight decrease in the quality of the forest on the analysed area in the sense that the vegetation stress is increased under meteorological factors, expressed differently depending on the morphometric and pedological parameters of the habitat.

Overexpression of ABA Receptor PYL10 Gene Confers Drought and Cold Tolerance to Indica Rice.

Abscisic acid (ABA) plays versatile functions in regulating plant development and tolerance to various biotic and abiotic stresses. Towards elucidating the functions of one of the ABA receptors (ABARs) in rice, OsPYL10 was cloned from drought tolerant rice cv. Nagina 22 and was overexpressed under stress inducible RD29A promoter in a mega rice variety MTU1010 by using Agrobacterium mediated genetic transformation. Four single copy transgenic lines selected based on Southern blot analysis were used for physiological and molecular analysis. PYL10 receptor appears to regulate its ligand ABA accumulation as PYL10 overexpressing transgenics accumulated 2–3.3-fold higher levels of ABA than that of WT in flag leaf at anthesis under non-stress conditions. The enhanced accumulation of ABA was associated with enhanced expression of genes for ABA biosynthesis viz., ZEP1, NCED1, NCED2, NCED3, and NCED4 in transgenics than in WT plants. At seedling stage, PYL10 transgenics showed significantly higher survival rate under cold stress as compared with WT plants. qRT-PCR analysis showed that expression levels of cold responsive genes viz., DREB1F, MYB3R2, TPP1, COR410, DEHYDRIN, and LEA3 were significantly higher in PYL10 overexpressing transgenic lines as compared to WT plants under cold stress. PYL10 transgenic and WT plants grown in the same pot were subjected to -80 kPa drought stress and recovery treatments at vegetative and reproductive stages. At vegetative stage drought stress, three overexpressing lines showed significantly higher grain yield (40–58%) and at reproductive stage drought stress one of these overexpression lines showed two-fold higher grain yield than that of WT plants. Excised leaf water loss analysis showed that PYL10 transgenic lost about 20% less water than WT plants. At reproductive stage, OsPYL10 transgenic maintained higher RWC, membrane stability index, chlorophyll content, and accumulated lower amount of MDA and H2O2 as compared with WT plants. qRT-PCR analysis showed that expression levels of RAB16, Dehydrin, LEA3, and ABA45 were higher in PYL10 transgenics as compared with WT plants under drought stress. Thus, overall results showed that OsPYL10 overexpression has potential to improve both drought and cold stress tolerance of indica rice.

A Small Horizontally Transferred Gene Cluster Contributes to the Sporulation of Alternaria alternata.

Horizontal gene transfer (HGT) has been identified as an important source of genomic innovation in fungi. However, how HGT drove the evolution of Alternaria alternata, a necrotrophic fungus which can be ubiquitously isolated from soil and various plants and decaying plant materials is largely known. In this study, we identified 12 protein-encoding genes that are likely acquired from lineages outside Pezizomycotina. Phylogenetic trees and approximately unbiased comparative topology tests strongly supported the evolutionary origin of these genes. According to their predicted functions, these HGT candidates are involved in nitrogen and carbohydrate metabolism. Especially, five genes of them were likely transferred as a physically linked cluster from Tremellales (Basidiomycota). Functionally knocking out the five-gene cluster in an A. alternata isolate causing citrus brown spot resulted in an 80% decrease in asexual spore production in the deletion mutant. We further knocked out each of these five genes in this cluster and the resultant single-gene deletion mutants exhibited a various degree of reduction in spore production. Except for conidiation, functions of these genes associated with vegetative growth, stress tolerance, and virulence are very limited. Our results provide new evidence that HGT has played important roles over the course of the evolution of filamentous fungi.

Identifying urban vegetation stress factors based on open access remote sensing imagery and field observations

Healthy vegetation in cities provides ecosystem services, which contribute to the overall well-being of urban populations, especially in times of climate change and increasing urbanization. More specifically, vegetation monitoring is needed in the context of intensifying and mitigating factors of the Urban Heat Island (UHI) effect. Therefore, fast and low-cost, but reliable approaches are needed for monitoring the status of urban greening. A satellite-based monitoring scheme based on freely available data could ensure the provision of key urban ecosystem services, and guide both policy maker and practitioners. Thus, the main objective of this paper is to investigate the impact of urbanization and urban green management on vegetation status of park trees during summer season in Bucharest, the capital city of Romania, using remote sensing. This city is known to be affected by air pollution and the UHI effect. Further, it is an example of a city with limited green spaces compared to other European cities. Hence, spatial data on vegetation status and potential impacts as a basis for management schemes are required to maintain a healthy urban green infrastructure. Vegetation indices related to chlorophyll, senescence, greenness and water stress were calculated from Sentinel-2 imagery as response variables to vegetation stress. Vegetation status was then predicted for each park using spatial environment factors (e.g. presence of irrigation systems) in a mixed model approach to account for heterogeneity among parks. The most important predictors of vegetation stress were irrigation systems, land surface temperature, distance to a lake and proximity to roads. However, the effect of these predictors on the vegetation status differed among parks. Therefore, a mixed effect model approach is suggested to quantify the effects of urbanization on green spaces in cities, and there is a high potential to use freely available satellite data for a spaceborne-monitoring service of urban green infrastructure.

Burn Area Detection Using Landsat 8 OLI TIRS

Fires associated with land use conversion activities such as agricultural expansion, palm and pulp plantations, peat land alteration, and industrial deforestation are significant in Indonesia (Jerrod & Alex, 2015). Fires season in 2015 is one of the worst incident in Indonesia since 1997, it made Indonesia at the second position as an emitter country, at least 22 days in September 2015, and generated more than the daily average emission of U.S. economic activity. A study from the National Development Planning Agency (Bappenas) and Asian Development Bank (ADB) estimated that the amount of land affected by fires reaches 9.75 million hectares. It caused losses reached US$.4.861 or equivalent to IDR711 trillion or even more based on disruption of economic activities, transportation problems, and health problems. Head of Data Information and Public Relations of National Disaster Management Agency (BNPB), Sutopo Purwo Nugroho, said the economic impact of smog disasters occurring in several provinces in Indonesia in 2015 could exceed 20 trillion per province. The most widespread forest fire area occurred in South Sumatra Province. BNPB released that during 2015 in South Sumatera Province has 35.008 hotspots and the burnt area is 641.964 Ha. The most affected area is in Ogan Komering Ilir Regency. Landsat 8 OLI TIRS has a 30-meter spatial resolution for each band except TIRS band and panchromatic band (USGS, 2016). TIRS band has a 100-meter spatial resolution but are resampled to 30-meter that can be used to identify burned scars area. By using SWIR bands (TM bands 5 and 7 in Landsat 5 and 7 systems) as a NBR (Normalized burn ratio) composite, can be used to detecting and mapping burnt area. TIRS algorithm which was used to detect fire will be seen red and SWIR which was used to detect water stress in vegetation and burned vegetation will be seen green, both of them will become darker when burn happened. This method modifying dNBR (pre-NBR – post-NBR) composite, which only can be used in oil palm plantations area that has same commodities, so can be used in various type of landuse especially the area that has plantation adjoin with forest area.

Data Products, Quality and Validation of the DLR Earth Sensing Imaging Spectrometer (DESIS).

Imaging spectrometry from aerial or spaceborne platforms, also known as hyperspectral remote sensing, provides dense sampled and fine structured spectral information for each image pixel, allowing the user to identify and characterize Earth surface materials such as minerals in rocks and soils, vegetation types and stress indicators, and water constituents. The recently launched DLR Earth Sensing Imaging Spectrometer (DESIS) installed on the International Space Station (ISS) closes the long-term gap of sparsely available spaceborne imaging spectrometry data and will be part of the upcoming fleet of such new instruments in orbit. DESIS measures in the spectral range from 400 and 1000 nm with a spectral sampling distance of 2.55 nm and a Full Width Half Maximum (FWHM) of about 3.5 nm. The ground sample distance is 30 m with 1024 pixels across track. In this article, a detailed review is given on the applicability of DESIS data based on the specifics of the instrument, the characteristics of the ISS orbit, and the methods applied to generate products. The various DESIS data products available for users are described with the focus on specific processing steps. The results of the data quality and product validation studies show that top-of-atmosphere radiance, geometrically corrected, and bottom-of-atmosphere reflectance products meet the mission requirements. The limitations of the DESIS data products are also subject to a critical examination.

Effect of Dietary Red Meat on Colorectal Cancer Risk-A Review.

Heme iron overload has been implicated as the main cause of the increased risk of cancer due to the consumption of red meat. However, fish and shellfish, teas, and spices contain up to five times more iron than red meat. There is insufficient evidence that iron intake in dietary red meat is the primary causal factor for colorectal cancer. In addition, harmful substances produced during the preparation of red meat, including heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs), N-nitroso compounds, and acrylamide, are extrinsic factors that increase carcinogenicity. HCAs are produced during the cooking of red meat, poultry meat, and fish. PAHs may also be produced during the cooking of diverse food groups, such as dairy products, fruits, vegetables, and cereals. The average daily intake of red meat among Korean individuals is 62 g; the amount of PAHs entering the body via red meat is less than the average amount of PAHs the body is exposed to in the air. Therefore, it is difficult to conclude that dietary red meat is the main cause of colorectal cancer. Rather, there may be an intricate influence of multiple factors, including fruit and vegetable intake, alcohol consumption, smoking, overweight, obesity, and stress.

2D Numerical Modeling on the Transformation Mechanism of the Braided Channel

This paper investigates the transformation mechanism between different channel patterns. A developed 2D depth-averaged numerical model is improved to take into account a bank vegetation stress term in the momentum conservation equation of flow. Then, the extended 2D model is applied to duplicate the evolution of channel pattern with variations in flow discharge, sediment supply and bank vegetation. Complex interaction among the flow discharge, sediment supply and bank vegetation leads to a transition from the braided pattern to the meandering one. Analysis of the simulation process indicates that (1) a decrease in the flow discharge and sediment supply can lead to the transition and (2) the riparian vegetation helps stabilize the cut bank and bar surface, but is not a key in the transition. The results are in agreement with the criterion proposed in the previous research, confirming the 2D numerical model’s potential in predicting the transition between different channel patterns and improving understanding of the fluvial process.

Adaptation of vegetation in high-rate constructed wetland using artificial carriers for bacterial growth: Assessment using phytopathological indicators

A variant of constructed wetland using artificial carriers for bacterial growth as support medium (High Rate Constructed Wetlands (HRCW)) has been developed to depurate high organic loads (45 g BOD5 m−2 d-1). The metabolic state of vegetation in this phytodepuration system affects the treatment processes; therefore, its optimum adaptation is necessary. A comparative study, in mesocosms scale, was undertaken to test the capacity of adaptation of three plant species (Cyperus alternifolius, Heliconia burleana, and Zantedeschia aethiopica) in HRCW. 25 units of each species were planted in three lines of HRCW (one species per line), named for ease of understanding as L1, L2, L3 respectively, and monitored during the start-up phase of the system under climatic conditions of intersection between dry tropical forest and premontane sub-humid. Quantitative epidemiology was used to determine incidence, infection rate, and the relative area under the disease progress curve for each type of plant. The relationship between these epidemiology variables and the environmental conditions was determined. Vegetative stress was observed in all species, followed by a phase of high phytopathology, with infection rates of 0.0049-0.0183; 0.1085-0.1821; 0.0911-0.1158 (units/day) for L1, L2, and L3, respectively. The combination between the high organic load, water volume (94% v/v), and weather conditions favoured this behaviour. This study indicated that Cyperus alternifolius is a type of plant suitable for HRCW; highlighted the importance of studies on plant adaptation in CW with particular conditions; and showed epidemiological analysis as a tool for performing this selection in a low cost and user-friendly way.

Variations in Persistence and Regenerative Zones in Coastal Forests Triggered by Sea Level Rise and Storms

Retreat of coastal forests in relation to sea level rise has been widely documented. Recent work indicates that coastal forests on the Delmarva Peninsula, United States, can be differentiated into persistence and regenerative zones as a function of sea-level rise and storm events. In the lower persistence zone trees cannot regenerate because of frequent flooding and high soil salinity. This study aims to verify the existence of these zones using spectral remote sensing data, and determine whether the effect of large storm events that cause damage to these forests can be detected from satellite images. Spectral analysis confirms a significant difference in average Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) values in the proposed persistence and regenerative zones. Both NDVI and NDWI indexes decrease after storms triggering a surge above 1.3 m with respect to the North American Vertical Datum of 1988 (NAVD88). NDWI values decrease more, suggesting that this index is better suited to detect the effect of hurricanes on coastal forests. In the regenerative zone, both NDVI and NDWI values recover three years after a storm, while in the persistence zone the NDVI and NDWI values keep decreasing, possibly due to sea level rise causing vegetation stress. As a result, the forest resilience to storms in the persistence zone is lower than in the regenerative zone. Our findings corroborate the ecological ratchet model of coastal forest disturbance.

Canopy architecture and leaf type as traits of heat resistance in pea

Pea (Pisum sativum L.) is sensitive to heat stress, and thus traits of heat resistance are desirable to minimize crop damage and maintain yield stability in improved cultivars. Crop research has focused on flowering and pollination success for heat resistant traits and vegetative structure is usually overlooked. The plant canopy, through leaf shape, plant habit and resistance to lodging, may offer additional sources of heat resistance in many crops. In pea, commercial cultivars have upright or vining plant habits, and either normal leaves comprised of stipules, leaflets and tendrils or semileafless leaves lacking leaflets. To determine the best canopy architecture and leaf traits associated with heat resistance, 24 diverse pea cultivars were tested in field trials across six environments in western Canada during 2014 to 2016. Compared to control conditions, heat stress increased canopy temperature from 24.9 °C to 27.8 °C and reduced reproductive stem length by 37% (17 cm), flowering duration by 21% (4.7 days), pod number by 30% (3 pods plant−1), and seed yield by 16% (54 g m-2). Pea cultivars had differential responses for measured traits; under heat stress conditions, semileafless cultivars with the upright habit had cooler canopies and greater seed yield, pod number and pod to node ratio than normal leafed vining cultivars. Lodging was associated with increased canopy temperature, a novel finding, implying greater heat stress. In contrast, growth and yield-related traits were greater in control environments for normal leaf, indeterminate and vining cultivars. Overall, the semileafless leaf and upright plant habit were superior traits that not only reduced lodging but maintained lower canopy temperatures in heat and drought stress environments. Therefore, vegetative heat stress can be avoided by management options that resist lodging and by selecting traits in plant breeding that can keep a cultivar upright.

Wildland fire potential outlooks for Portugal using meteorological indices of fire danger

Abstract. Portugal is recurrently affected by large wildfire events that have serious impacts at the socio-economic and environmental levels and dramatic consequences associated with the loss of lives and the destruction of the landscape. Accordingly, seasonal forecasts are required to assist fire managers, thus contributing to alter the historically based purely reactive response. In this context, we present and discuss a statistical model to estimate the probability that the total burned area during summer will exceed a given threshold. The statistical model uses meteorological information that rates the accumulation of thermal and vegetation stress. Outlooks for the 39-year study period (1980–2018) show that, when the statistical model is applied from 26 May to 30 June, out of the six severe years, only one year is not anticipated as potentially severe and, out of the six weak years, only one is not anticipated as potentially weak. The availability of outlooks of wildfire potential with an anticipation of up to 1 month before the starting of the fire season, such as the one proposed here, may serve to provide clear directions for the fire community when planning prevention and combating fire events.

Análisis de anomalías geobotánicas a partir del procesamiento e interpretación de productos de sensores remotos, estudio de caso: occidente de Boyacá (Colombia)

This work presents the boundaries of a new area of interest for the detailed exploration of emeralds in Colombia, identified through the interpretation of geobotanical anomalies in areas of dense vegetation. A methodology was designed in which fifteen vegetation indices were calculated. The anomalies correlated most with the lineaments detected from the interpretation of a shaded-relief model generated from a digital terrain model (DTM) were selected. A detailed spectral analysis in the mineralized zones of the area with the highest correlation showed a halo of vegetative stress in all studied cases; moreover, the analysis corroborated a direct relationship between the albitization present in the mineralized zones, the lineaments and the degree of vegetative stress. A sector between the Coscuez mine and the La Pita mine was identified as a target for detailed exploration, where the vegetation indexes indicate less vegetative stress and correlate better with the natural terrain lineaments. It was found that the proposed methodology based on geobotanical anomalies yields consistent results and can be used as a tool for emerald exploration.

TWO WAVELENGTHS METHODS FOR DETERMINATION LEVEL OF CONTAMINATION OF SOIL WITH CRUDE OIL HYDROCARBONS USING REFLECTION SPECTRUM OF VEGETATION

The questions on determination level of contamination of soil with crude oil hydrocarbons using vegetations reflection spectrum are considered. The close link between concentration of pigments in vegetation and its reflection properties make it possible to use the reflection spectroscopy as an indicator to predict the vegetation stress occur due to spill of different types of crude oil. The reason is that light types of oil have a more effect on vegetation in comparison with heavy ones. The heavy types of oil have a predominant high molecular heavy components which are hardly transported and distributed within vegetation. The light oil is less viscose’s and well filtered through soil and roots of vegetation. The stressed condition occurred due to effect of oil is mainly reasoned by its such toxic components as aromatic compounds. The carried out analysis of reflection spectrums reveals the double polarity of differences of spectral signals formed by subtraction of reflection spectrums of oil of light and heavy types from controlled reflection spectrum. It causes uncertainty in estimation of contamination of oil using single wavelength method. The question on utilization in practices the inverse type interrelations for diminishing errors of measurements inherent for single wavelength method by transition to two wavelength regime of measurements. It is shown that presence of above said inverse interrelations allows to reach following prevalence’s upon use of two wavelength measurements. 1. Incrtease of dynamic range of measurements; 2. Decrease of random errors. Two variants of two wavelengths methods allowing to determine the level of contamination of soil with crude oil hydrocarbons are developed. The general methodic for determination of level of soil pollution with oil is suggested.

THE POTENTIAL OF DUAL-WAVELENGTH TERRESTRIAL LASER SCANNING IN 3D CANOPY FUEL MOISTURE CONTENT MAPPING

Abstract. Terrestrial laser scanning (TLS) instruments have been widely utilized in measuring vegetation canopy structural parameters, being capable of providing high density point clouds. However, less attention has been paid to using TLS intensity data in estimating vegetation biochemical attributes, and calculating water status metrics, that can help in early detection of vegetation stress and risk of wildfire. Water status metrics, such as the leaf Equivalent Water Thickness (EWT) and the Fuel Moisture Content (FMC), are being commonly estimated from optical remote sensing data. However, such estimates mainly reflect the water status of canopy top and ignore the vertical heterogeneity of water content distribution within the canopy. The estimates are also affected by canopy structure and understory reflectance. Such limitations can potentially be addressed using TLS intensity data, as observations are performed in three dimensions (3D). This study therefore investigated the potential of using dual-wavelength TLS intensity data to estimate FMC in 3D. The calculated Normalized Difference Index (NDI) of 808 nm near infrared and 1550 nm shortwave infrared wavelengths was found to be correlated to FMC at leaf level for four different tree species. The correlation was moderate, and the relationships were not consistent between species. NDI was subsequently used to estimate FMC at canopy level in seven trees in a small tree plot with an average error < 5 %. The 3D estimates of FMC revealed vertical heterogeneity in all trees measured, which varied between species and also between trees from the same species.

Multiple Health Risk Behaviors in Young Adult Smokers: Stages of Change and Stability over Time.

Health risk behaviors (HRBs) are common, yet not well understood in young adult smokers. We examined HRB profiles over 12 months in young adult smokers participating in a Facebook smoking cessation intervention clinical trial. Participants (N = 500; age M = 20.9 years; 54.6% women) were recruited online and randomized to receive either a 3-month Facebook smoking cessation intervention or referral to Smokefree.gov (control). A Health Risk Assessment determined risk for 10 behaviors at baseline and 3, 6, and 12 months. Latent class analysis (LCA) and latent transition analysis (LTA) were used to identify patterns of HRBs and changes over time. At baseline, participants reported an average of 5.4 (standard deviation [SD] = 1.7) risk behaviors, including smoking (100%), high-fat diet (84.8%), poor sleep hygiene (71.6%), and low fruit and vegetable intake (69.4%). A 3-class model fit the data best at baseline and all follow-up time points: low risk (28.8% at baseline) with low likelihood of risk on all behaviors except smoking, substance use risk (14.0% at baseline) characterized by heavy episodic drinking, cannabis use, and other illicit drug use, and metabolic risk (57.2% at baseline), with a high percentage of members at risk for a low fruit and vegetable intake, high-fat diet, inactivity, stress, and poor sleep hygiene. Classes were very stable at 3, 6, and 12 months, with few participants transitioning between classes. Most young adult smokers engaged in multiple risk behaviors, with meaningful clustering of behaviors, and demonstrated stability over a year's time. In addition to smoking, targets for intervention are co-occurring substance use and metabolic risk behaviors. NCT02207036.

Isotopic constraint on the twentieth-century increase in tropospheric ozone.

Tropospheric ozone (O3) is a key component of air pollution and an important anthropogenic greenhouse gas1. During the twentieth century, the proliferation of the internal combustion engine, rapid industrialization and land-use change led to a global-scale increase in O3 concentrations2,3; however, the magnitude of this increase is uncertain. Atmospheric chemistry models typically predict4-7 an increase in the tropospheric O3 burden of between 25 and 50 per cent since 1900, whereas direct measurements made in the late nineteenth century indicate that surface O3 mixing ratios increased by up to 300 per cent8-10 over that time period. However, the accuracy and diagnostic power of these measurements remains controversial2. Here we use a record of the clumped-isotope composition of molecular oxygen (18O18O in O2) trapped in polar firn and ice from 1590 to 2016 AD, as well as atmospheric chemistry model simulations, to constrain changes in tropospheric O3 concentrations. We find that during the second half of the twentieth century, the proportion of 18O18O in O2 decreased by 0.03±0.02 parts per thousand (95 per cent confidence interval) below its 1590-1958 AD mean, which implies that tropospheric O3 increased by less than 40 per cent during that time. These results corroborate model predictions of global-scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O3 precursors4,5,11. We also estimate thatthe radiative forcing of tropospheric O3 since 1850 AD is probably less than +0.4 watts per square metre, consistent with results from recent climate modelling studies12.

Water relations and productivity of two lines of pearl millet grown on lysimeter with two different soil types

Crop water productivity is one of the important aspects of water use of crop, most especially where water is a limiting factor. This study was carried out to assess and compare water relations and productivity of two lines of pearl millet grown on lysimeters with two soil types. The study was carried out at the lysimeter unit of the Department of Soil, Crop and Climate Sciences Experimental Farm, Kenilworth, University of the Free State, Bloemfontein. One row of the unit contains a Clovelly soil and the other row, Bainsvlei soil. The two lines of pearl millet used for the study were GCI 17, improved variety and Monyaloti, a local variety. Irrigation treatments were applied such that water was withheld at the beginning of different growth stages of the crop to impose water stress. These treatments were well-watered (WW), vegetative stage stress (VS), reproductive stage stress (RS), and grain-filling stage stress (GS). The treatments were replicated two times per line of pearl millet per soil type. The results show that the lowest leaf water potential was observed in the GS stress plants for both lines of pearl millet on Bainsvlei soil form. The highest stomatal conductance observed on Clovelly soil was around 400 mmol m−2 s−1 while it was around 300 mmol m−2 s-1 on Bainsvlei soil for the two lines of pearl millet. The highest and lowest grain yields for GCI 17 were from Clovelly soil. The highest grain yield for Monyaloti was 10.74 t ha-1from the WW found on Clovelly soil type while the lowest was 3.93 t ha-1 from GS found on Bainsvlei soil type. The mean water productivity for biomass (WPbm) of GCI 17 was 0.036 t ha−1 mm−1for both soil types while Monyaloti had WPbm of 0.037 and 0.035 t ha−1 mm−1 on Bainsvlei and Clovelly respectively. Clovelly soil type proved to exhibit high water productivity for grain yield production of pearl millet.