Radiation Use Efficiency

The water balance and growth of Eucalyptus grandis hybrid plantations in Brazil are presented based on 6 years of intensive catchment hydrology, physiological and forest growthsurveying, and modelling. The results show a balance between water supply by precipitation and output through evapotranspiration (considered as canopy interception, soil evaporation and trees transpiration) and runoff. The annual average precipitation was 1147 mm

A field experiment was carried out to analyse the growth of lettuce, onion and red beet in terms of: (a) canopy architecture, radiation interception and absorption; (b) efficiency of conversion of absorbed radiation into biomass; and (c) dry matter partitioning. Growth analysis, total solar radiation interception, PAR interception and absorption by the crop canopy, ground cover, maintenance respiration of onion bulbs and red beet storage roots were measured. Models for different leaf angle distribution and ground cover were used to simulate light transmission by the crop canopy.The three crops are shown to have contrasting growth patterns from both a morphological and a physiological point of view. Lettuce showed very high light interception and growth after the early growth stages but, throughout the growth cycle, this leafy crop showed the lowest radiation use efficiency due to the respirational cost of the high leaf area. Onion showed a lower early relative growth rate than lettu...

Despite the recognized potential of forests as an important sink to sequester carbon, accurate estimates of the carbon sequestration potential of different ecosystems or their component species are lacking, especially for the different forest types present in Sri Lanka. The primary objective of the study is to determine the carbon sequestration potential of selected important natural forest ecosystems in the wet zone of Sri Lanka. In this study, completely non destructive approach, based on the basic physiology of biomass production process was used to estimate the carbon sequestration potential as a rate in ecosystem scale. Monteith (1972, 1977) showed that the rate of biomass production is directly proportionate to the amount of radiation intercepted by the foliage canopy. The above relationship can be given as: W = e R I , Where, W is the amount of total biomass (above and belowground biomass) produced and R I is the amount of radiation intercepted by canopy. The proportionality constant, e is termed as Radiation Use Efficiency (RUE). These two variables (R I and e) were determined explicitly for specific vegetation types using different approaches. R I values were estimated using hemispherical photographs obtained from 337 sampling points representing 44 transect covering four major vegetation types in wet zone in Sri Lanka. RUE values were derived by canopy level photosynthesis termed as photosynthetic RUE (PhRUE) (with generalized photosynthetic parameters) at selected locations and stand level PhRUE values were derived

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Variability of light interception and its derivatives are poorly understood at the field-scale in maize (Zea mays L.) and soybean [Glyine max (L.) Merr.]. Quantifying variability can provide reliable estimates of field-scale processes and reliable methodology. A field study was conducted during the 2005 growing season in a 31ha maize and 23ha soybean field rotated annually near Ames, IA to

Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance (‘PRI’, Photochemical Reflectance Index calculated as (R531− R570)/(R531+ R570)) as an indicator of efficiency of photosynthetic radiation use in seven species representing both C3 and CAM photosynthetic pathways. Leaves exposed to a dark-lighted ark transition in a steady-state laboratory gas exchange system exhibited nearly parallel changes in PRI and PS II quantum yield (ΔF/Fm′). Similar PRI and ΔF/Fm′ responses were seen in leaves exposed to diurnally changing sunlight levels outdoors. PRI was linearly related to ΔF/Fm′, and both ΔF/Fm′ and PRI were exponentially related to instantaneous efficiency of photosynthetic radiation-use in different species over a range of different field conditions. These results extend previous studies by indicating a functional relationship between PRI. ΔF/Fm′, and photosynthetic radiation-use efficiency. The narrow-band PRI index offers a simple, portable means of assessing PS II radiation-use efficiency, analogous to ΔF/Fm′, and with the potential for remote applications at scales larger than the leaf.

We explored simple and useful spectral indices for estimating photosynthetic variables (radiation use efficiency and photosynthetic capacity) at a canopy scale based on seasonal measurements of hyperspectral reflectance, ecosystem CO2 flux, and plant and micrometeorological variables. An experimental study was conducted over the simple and homogenous ecosystem of an irrigated rice field. Photosynthetically active radiation absorbed by the canopy (APAR),

The photochemical reflectance index (PRI), derived from narrow-band reflectance at 531 and 570 nm, was explored as an indicator of photosynthetic radiation use efficiency for 20 species representing three functional types: annual, deciduous perennial, and evergreen perennial. Across species, top-canopy leaves in full sun at midday exhibited a strong correlation between PRI and ΔF/Fm′, a fluorescence-based index of photosystem II (PSII)