Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

Understanding plant physiological responses to high temperature is an important concern pertaining to climate change. However, compared with terrestrial plants, information about aquatic plants remains limited. Since the degree of midday depression of photosynthesis under high temperature depends on soil water conditions, it is expected that emergent aquatic plants, for which soil water conditions are always saturated, will show different patterns compared with terrestrial plants. We investigated the diurnal course of the photosynthetic light-response curve and incident light intensity for a freshwater emergent plant, buckbean (Menyanthes trifoliata L.; Menyanthaceae) in a cool temperate region. The effect of midday depression was observed only on a very hot day, but not on a moderately hot day, in summer. The diurnal course of photosynthetic light-response curves on this hot day showed that latent morning reduction of photosynthetic capacity started at dawn, preceding the apparent depression around the midday, in agreement with results reported in terrestrial plants. We concluded that (1) midday depression of emergent plants occurs when the stress intensity exceeds the species’ tolerance, and (2) measurements of not only photosynthetic rate under field conditions but also diurnal course of photosynthetic light-response curve are necessary to quantify the effect of midday depression.

The influence of cloudiness and atmospheric circulation on radiation balance and its components

The article contains an analysis of the influence of cloudiness and atmospheric circulation on the components of radiation balance (Q*) using the example of measurements taken in an extra-urban area of Koniczynka near Toruń (Central Poland) in the years 2011–2018. The average annual value of Q* was 1,818.5 MJ·m−2 with a maximum of 352.3 MJ·m−2 in June, and negative values from November to January (December: −27.4 MJ·m−2). The shortwave radiation balance (S*) amounted to 3,129.2 MJ·m−2 and the longwave radiation balance (L*) was ˗1,310.7 MJ·m−2. In June the average solar irradiance (S↓) at midday was 600 W·m−2. The natural annual and diurnal course of Q* components, determined by astronomical factors, is disturbed by changes in cloudiness and inflow of various air masses. It has been found that an increase in cloudiness causes the amount of incoming solar radiation (S↓) to fall, thus decreasing the S* balance. Moreover, clouds restrict longwave radiation balance (L*), in particular, downward atmospheric radiation (L↓) increases. The opposite relationships of S* and L* affect Q* in individual months. The components of Q* are influenced by atmospheric circulation; it has been observed that anticyclonic types, characterised by smaller cloud amounts, favour a greater influx of (S↓) and—at the same time—greater emittance (L↑); however, Q* is then greater than in the case of cyclonic circulation. A statistically significant trend of Q* and its components has not been ascertained. A notable great year-on-year variability of Q*, ranging from 1,640.4 MJ·m−2 (in 2011) to 2,081.6 MJ·m−2 (in 2018), affects the environment. The changes are related to the cloudiness and the frequency of occurrence of different atmospheric circulation types. The role of snow cover is also important as snow reflects solar radiation which leads to the decrease of S* and—as a result—to a negative value of Q* in winter.

Solar radiation variability at Koniczynka near Toruń (Central Poland) in the years 2003–2016

The paper presents the variability of global solar radiation (K↓) in the agriculture area (Koniczynka near Toruń) in the years 2003–2016. The variability of K↓ has been analysed with reference to atmospheric circulation. The mean yearly sum of K↓ in the analysed period was 3,816.0 MJ·m−2. In an annual course the highest mean values of K↓ occurred in June (608.3 MJ·m−2) and the smallest in December (69.0 MJ·m−2). The diurnal course of K↓ was symmetrical with respect to the solar noon. Only 44.7% of the solar energy on the top of atmosphere reaches the ground. The highest transmittance occurred in spring and summer, and the lowest in December. The observations revealed an increase in the amount of K↓ (trend 13.6 MJ·m−2·year−1) and its considerable day-to-day and year-to-year variability. Its increase has been attributed to reduced emissions of aerosols in Poland and Europe (global brightening). The changes of K↓ depend on atmospheric circulation (cyclonic and anticyclonic situations), cloudiness and the optical characteristics of incoming air masses.

Carotenoid biosynthesis of pak choi (Brassica rapassp.chinensis) sprouts grown under different light-emitting diodes during the diurnal course

This study highlights the impact of LEDs on the carotenoid biosynthesis in pak choi throughout the day.

Radiation balance diversity on NW Spitsbergen in 2010–2014

This article presents the results of observations of selected fluxes of the radiation balance in north-western Spitsbergen in the years from 2010 to 2014. Measurements were taken in Ny-Ålesund and in the area of Kaffiøyra, on different surface types occurring in the Polar zone: moraine, tundra, snow and ice. Substantial differences in the radiation balance among the various types of surface were observed. The observations carried out in the summer seasons of 2010–2014 in the area of Kaffiøyra demonstrated that the considerable reflection of solar radiation on the Waldemar Glacier (albedo 55%) resulted in a smaller solar energy net income. During the polar day, a diurnal course of the components of the radiation balance was apparently related to the solar elevation angle. When the sun was low over the horizon, the radiation balance became negative, especially on the glacier. Diurnal, annual and multi-annual variations in the radiation balance have a significant influence on the functioning of the environment in polar conditions.

Diurnal Course of Carbon Dioxide Mixing Ratios in the Urban Boundary Layer in Response to Surface Emissions

Observations of carbon dioxide (CO2) mixing ratios in the urban boundary layer (UBL) are rare, even though there is potential for such measurements to be used to monitor city-scale net CO2 emissions. This work presents a unique dataset of CO2 mixing ratios observed in the UBL above Vancouver, British Columbia, Canada, by means of a tethered balloon system over a continuous 24-h summertime period. Vertical profiles of CO2 mixing ratios are found to vary according to UBL thermal structure and mechanical dynamics (development of convective and nocturnal boundary layers, vertical mixing from mechanical turbulence, horizontal advection from land–sea thermal breezes, and vertical entrainment). A box model is applied to quantify net city-scale surface emissions to the UBL volume using the measured rate of change of UBL CO2 mixing ratios and estimated CO2 advection and entrainment fluxes. The diurnal course of city-scale net emissions predicted by the model is similar to simultaneous local-scale eddy-covariance CO2 flux measurements, although there are relatively large uncertainties in hourly model calculations of horizontal advection and vertical entrainment fluxes due to inputs of regional background CO2 mixing ratios. Daily city-scale emissions totals predicted by the model (20.2 gC m−2 day−1) are 35% larger than those measured simultaneously on an urban local-scale eddy-covariance flux tower and are within 32% of a spatially scaled municipal greenhouse gas inventory. However, these methods are not expected to agree exactly because they represent different spatial source areas and include different CO2 source and sink processes.