Degree Of Self-shading Research Articles

Optimization of the distance between the rows in solar collectors’ arrays

The article presents some results of the analysis of the influence of the distance between the collectors’ rows in thermal solar systems on the degree of self-shading. For the purposes of the study, the dimensionless ratio Ks between the required minimum distance between the rows, guaranteeing the absence of self-shading, and the height of the collectors, was used. A simulation study was performed for specific climatic conditions and the annual solar radiation incident on the collectors’ array at different degrees of self-shading was determined. Its annual financial equivalent for various alternative heat sources (electricity, natural gas, wood pellets, district heating and gas oil) was assessed, as well as the necessary investment costs for construction of the solar system. A regression relationship between the coefficient of net present value NPVQ and Ks was derived and its optimal values were established, which ensure the achievement of maximum economic efficiency of the system operation for the considered replaced heat sources.

A high resolution green area index for modelling the seasonal dynamics of CO2 exchange in peatland vascular plant communities

We studied vegetation dynamics at peatlands, differing in their climate, land use management history and vegetation community in Ireland and Finland over a two-year period. Our aim was to develop a species-specific method to be used to (1) describe the seasonal dynamics of green (photosynthetic) area (GA) of the vegetation and (2) incorporate these changes into CO2 exchange models. The extent of temporal and spatial variation between and within communities indicated the need for a two-step calculation approach for each community. Firstly, at biweekly to monthly intervals, GA of all species within a range of vascular plant communities was estimated by non-destructive field measurements. Gaussian or log-normal models were fitted to describe the seasonal dynamics of each species. Secondly, an estimate of community vascular green area (VGA) was obtained by summing the modelled daily GA of all species within the community. The highest values of VGA (2.1–6.0 m2 m−2) occurred within the reed communities at the rewetted cutaway peatland in Ireland and the lowest at the ombrotrophic lawn communities in Finland (0.5–1.0 m2 m−2). The relationship between light saturated gross photosynthesis (PG) and VGA was either linear or hyperbolic depending on the degree of self-shading that occurred within each community. The addition of the VGA term into PG models improved the explaining power of the model by 57.6, 24.5 and 23% within the Typha latifolia, Phalaris arundinacea and Eriophorum angustifolium/Carex rostrata communities, respectively. VGA proved useful in recording the seasonal development of a wide range of peatland vascular plant communities over geographically and climatically different regions.

Abrupt change in primary productivity in a littoral zone of Lake Biwa with the development of a filamentous green‐algal community

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.2. Pmax (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a−1 h−1) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a−1 h−1). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.3. Relatively high Ik values (150–200 μmol photon m−2 s−1) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.

PLANT SPACING EFFECTS ON LIGHT INTERCEPTION BY GREENHOUSE TOMATOES

The effect of six equidistant spacings (23, 30, 38, 45, 53, 60 cm) on interception of photosynthetically active radiation (PAR) by four-row plantings of greenhouse tomato (Lycopersicon esculentum Mill. ’Jumbo’ and ’CR-6’) was studied. A silicon cell sensor was used to measure PAR in and around the test plant canopies. These observations were used to construct canopy profiles of PAR absorption, as affected by plant spacing and cultivar. Measurements under both clear and overcast skies revealed no major differences in the pattern of PAR interception within a canopy due to the presence or absence of direct light over the sampling period. The proportion of available PAR intercepted increased with closer plant spacing, but PAR penetration increased and distribution improved with increasing plant spacing. An increasing degree of self-shading of the central and north parts of the canopies was evident with closer planting. Plant spacing also had a large effect on the quality of canopy transmitted light. The ratios of blue:far-red, red:far-red and blue:red light transmitted through the four-row canopies of both cultivars decreased with decreases in plant spacing and in general were lower under the canopies of CR-6, than under the canopies of Jumbo.Key words: Tomato, Lycopersicon esculentum Mill., plant spacing, light interception

Bunchgrass architecture, light interception, and water-use efficiency: assessment by fiber optic point quadrats and gas exchange.

The bunchgrass growth form, which is very prominent in water-limited environments, can result in considerable self-shading of photosynthetically active foliage. The consequences of this growth form for light interception and water-use efficiency (photosynthesis/transpiration, P/T) were investigated for two Agropyron species which differ in tussock density and degree of self-shading. During the period of most active gas exchange, the tussocks were very compact and photosynthesis of shaded foliage was markedly light-limited. Stomatal control of older shaded foliage was poorly attuned for water-use efficiency. At low light, P/T decreased and intercellular CO2 concentrations increased. Despite differences in architecture and amount of shaded foliage, P/T of whole tussocks under ambient field conditions did not differ between these species. Partial defoliation decreased, rather than increased, P/T, primarily as a result of the poor photosynthetic light harvesting by the remaining foliage. Despite self-shading, the architecture of widely-spaced bunchgrasses provides for interception of as much direct beam solar radiation as is calculated for a rhizomatous grass occupying an area six-fold greater than the ground area underneath the canopy of these bunchgrasses.