A new hammer to crack an old nut : interspecific competitive resource capture by plants is regulated by nutrient supply, not climate

Peer reviewedPublisher PD

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes

Delhi, India, suffers from periods of very poor air quality, but little is known about the chemical production of secondary pollutants in this highly polluted environment. During the postmonsoon period in 2018, extremely high nighttime concentrations of NOx (NO and NO2) and volatile organic compounds (VOCs) were observed, with median NOx mixing ratios of ∼200 ppbV (maximum of ∼700 ppbV). A detailed chemical box model constrained to a comprehensive suite of speciated VOC and NOx measurements revealed very low nighttime concentrations of oxidants, NO3, O3, and OH, driven by high nighttime NO concentrations. This results in an atypical NO3 diel profile, not previously reported in other highly polluted urban environments, significantly perturbing nighttime radical oxidation chemistry. Low concentrations of oxidants and high nocturnal primary emissions coupled with a shallow boundary layer led to enhanced early morning photo-oxidation chemistry. This results in a temporal shift in peak O3 concentrations when compared to the premonsoon period (12:00 and 15:00 local time, respectively). This shift will likely have important implications on local air quality, and effective urban air quality management should consider the impacts of nighttime emission sources during the postmonsoon period

Optimising stand density and nitrogen fertiliser rates for seed production in the tetraploid italian ryegrass cultivar K29T

Tetraploid cultivars of Italian ryegrass have been developed and used as an alternative to diploid cultivars in an attempt to improve forage yield and quality. But, very often, production of tetraploid cultivars is reduced by unfavourable weather conditions. The objective of this research was to determine seed production stability of the tetraploid Italian ryegrass cultivar K29T in variable and contrasting environmental and meteorological conditions in Serbia. The study was conducted in four consecutive years and generations of seed multiplication. Every year, seed was harvested from the primary growth in the first production year after the year of establishment. Data of investigated traits (heading and harvest dates, tiller length, number of spikelets per spike, seed yield, dry herbage yield and 1,000 seed weight) were recorded for different management practices (stand densities and nitrogen applications). It was determined that seed yield, dry matter production and tiller length were presumably most affected by different environmental factors in different production years, and different management practice, especially different sowing densities. In contrast, number of spikelets per spike and 1,000 seed weight were less affected by management practice, except in the extremely arid 2003 year. Variation in seed yield was more related to variation in seed numbers than to variation in seed weight. In the first seed production year, the best density in this experiment was 15-20 kg ha−1 of seed sown at an interrow spacing of 60 cm without fertilizing or with only 50 kg ha−1 of N. Therefore, seed of tetraploid Italian ryegrass cv. K29T can be produced in diverse environmental conditions in Serbia, but lower stand densities allow for better plant tillering and the production of a greater volume of seed and, at the same time, good dry matter yield of the residual biomass

Annual Variations in Grass Pollen Seasons in London 1961-1990

The record of daily average grass pollen concentrations monitored at St Mary's Hospital, Paddington. London, U.K. since 1961 is the longest duration pollen data set in Europe. Analysis of the results identifies the trends and characteristics of grass pollen seasons over three decades. During this lime seasonal allergic rhinitis has increased significantly in Britain. The annual start dates, length of season and severity are examined in relation to the main meteorological variables of cumulated temperatures above 5-5°C and precipitation measured at one site within London and two in the surrounding rural areas. Land-use changes are also considered. Significant decreases have taken place in both the duration and severity of the seasons, particularly between the 1960s and the early 1970s but also through the last 20 yr. This is largely a result of a decrease in pollen abundance in the region. The decline in pollen counts has slowed in recent years due to the increase in flowering grasses caused by the seaside policy and by uncut verges. Grass pollen seasons have tended to start later over the last two decades, despite an increase in the cumulated temperature profiles during late winter and spring. Empirical models have been developed using multiple regressions to incorporate meteorological and pollen data for the last 20 yr in order to forecast the start dates. duration and severity of the grass pollen seasons. These models were applied successful using the data for 1991 and 1992. Predictions of the main characteristics on the pollen seasons can be obtained relatively early in the year through the use of these models by employing the monthly weather forecasts in conjunction with long-term average weather profiles