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Photosynthetic Active Radiation (photosynthetic + active_radiation)
Selected AbstractsMonoterpene emissions from rubber trees (Hevea brasiliensis) in a changing landscape and climate: chemical speciation and environmental controlGLOBAL CHANGE BIOLOGY, Issue 11 2007YONG-FENG WANG Abstract Emissions of biogenic volatile organic compounds (VOCs) have important roles in ecophysiology and atmospheric chemistry at a wide range of spatial and temporal scales. Tropical regions are a major global source of VOC emissions and magnitude and chemical speciation of VOC emissions are highly plant-species specific. Therefore it is important to study emissions from dominant species in tropical regions undergoing large-scale land-use change, for example, rubber plantations in South East Asia. Rubber trees (Hevea brasiliensis) are strong emitters of light-dependent monoterpenes. Measurements of emissions from leaves were made in the dry season in February 2003 and at the beginning of the wet season in May 2005. Major emitted compounds were sabinene, , -pinene and , -pinene, but , -ocimene and linalool also contributed significantly at low temperature and light. Cis -ocimene was emitted with a circadian course independent of photosynthetic active radiation (PAR) and temperature changes with a maximum in the middle of the day. Total isoprenoid VOC emission potential at the beginning of the wet season (94 ,g gdw,1 h,1) was almost two orders of magnitude higher than measured in the dry season (2 ,g g dw,1 h,1). Composition of total emissions changed with increasing temperature or PAR ramps imposed throughout a day. As well as light and temperature, there was evidence that assimilation rate was also a factor contributing to seasonal regulating emission potential of monoterpenes from rubber trees. Results presented here contribute to a better understanding of an important source of biogenic VOC associated with land-use change in tropical South East Asia. [source] Remote sensing of protected areas to derive baseline vegetation functioning characteristicsJOURNAL OF VEGETATION SCIENCE, Issue 5 2004Martín F. Garbulsky Abstract: Question: How can we derive baseline/reference situations to evaluate the impact of global change on terrestrial ecosystem functioning? Location: Main biomes (steppes to rain forests) of Argentina. Methods: We used AVHRR/NOAA satellite data to characterize vegetation functioning. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of the photosynthetic active radiation intercepted by vegetation (fPAR), and the surface temperature (Ts), for the period 1981,1993. We extracted the following indices: NDVI integral (NDVI -I), NDVI relative range (Rrel), NDVI maximum value (Vmax), date of maximum NDVI (Dmax) and actual evapotranspiration. Results: fPAR varied from 2 to 80%, in relation to changes in net primary production (NPP) from 83 to 1700 g.m- 2.yr -1. NDVI -I, Vmax and fPAR had positive, curvilinear relationships to mean annual precipitation (MAP), NPP was linearly related to MAP. Tropical and subtropical biomes had a significantly lower seasonality (Rrel) than temperate ones. Dmax was not correlated with the defined environmental gradients. Evapotranspiration ranged from 100 to 1100 mm.yr -1. Interannual variability of NDVI attributes varied across the temperature and precipitation gradients. Conclusions: Our results may be used to represent baseline conditions in evaluating the impact of land use changes across environmental gradients. The relationships between functional attributes and environmental variables provide a way to extrapolate ecological patterns from protected areas across modified habitats and to generate maps of ecosystem functioning. [source] A model of stomatal conductance to quantify the relationship between leaf transpiration, microclimate and soil water stressPLANT CELL & ENVIRONMENT, Issue 11 2002Q. Gao Abstract A model of stomatal conductance was developed to relate plant transpiration rate to photosynthetic active radiation (PAR), vapour pressure deficit and soil water potential. Parameters of the model include sensitivity of osmotic potential of guard cells to photosynthetic active radiation, elastic modulus of guard cell structure, soil-to-leaf conductance and osmotic potential of guard cells at zero PAR. The model was applied to field observations on three functional types that include 11 species in subtropical southern China. Non-linear statistical regression was used to obtain parameters of the model. The result indicated that the model was capable of predicting stomatal conductance of all the 11 species and three functional types under wide ranges of environmental conditions. Major conclusions included that coniferous trees and shrubs were more tolerant for and resistant to soil water stress than broad-leaf trees due to their lower osmotic potential, lignified guard cell walls, and sunken and suspended guard cell structure under subsidiary epidermal cells. Mid-day depression in transpiration and photosynthesis of pines may be explained by decreased stomatal conductance under a large vapour pressure deficit. Stomatal conductance of pine trees was more strongly affected by vapour pressure deficit than that of other species because of their small soil-to-leaf conductance, which is explainable in terms of xylem tracheids in conifer trees. Tracheids transport water by means of small pit-pairs in their side walls, and are much less efficient than the end-perforated vessel members in broad-leaf xylem systems. These conclusions remain hypothetical until direct measurements of these parameters are available. [source] Temporal and spatial patterns of ecosystem functioning in protected arid areas in southeastern SpainAPPLIED VEGETATION SCIENCE, Issue 1 2005José M. Paruelo Abstract We characterized the spatial variability and temporal dynamics of the photosynthetic active radiation absorbed (APAR) by the canopy, a descriptor of ecosystem functioning, in Cabo de Gata , Níjar Natural Park (CGNNP) (Spain). Ecosystem functioning was characterized for five landscape classes using the Normalized Difference Vegetation Index (NDVI) derived from NOAA/AVHRR LAC (1 km × 1 km) images. We also used a 19-year time series of NDVI PAL data (8 km × 8 km) to analyse the relationship APAR-precipitation inside and outside the park. The vegetation of CGNNP absorbed less than 20% of the incoming radiation. Plains intercepted 37% and hills 14% less photosynthetic active radiation than mountains, the most productive landscape of the park. CGNNP showed a well-defined growing season with a unique peak of APAR. Plains and piedmont, covered by annual vegetation displayed an earlier development of the leaf area index than the shrublands and grasslands typical of the other landscapes. APAR had a significant relationship with the sum of the precipitation of the current and two previous growing seasons, except for the plains. We found that the APAR of the areas more modified by humans (outside the park) showed a lower sensitivity to changes in precipitation than those under protection. The differences were higher if the accumulated precipitation of the previous three growing seasons was considered. The description of such differences in the response of absorbed PAR to water availability are proposed as the base of a monitoring system for semi-arid and arid areas. [source] A New HPLC-ELSD Method To Quantify Indican in Polygonum tinctorium L. and To Evaluate ,-Glucosidase Hydrolysis of Indican for Indigo ProductionBIOTECHNOLOGY PROGRESS, Issue 6 2003Luciana G. Angelini A method to quantify the indigo precursor indican (indoxyl-,- d -glucoside) in Polygonum tinctoriumL. has been developed. Plant material was extracted in deionized water, and indican was identified and quantified using high performance liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD). Results confirmed that with this method it is possible to measure indican content in a short time, obtaining reliable and reproducible data. Using this method, leaf indican content was quantified every 15 days during the growing season (from May to October) in P. tinctorium crops grown in a field experiment in Central Italy. Results showed that indican increased along the growing season until flowering and was positively affected by photosynthetic active radiation (PAR). Indican is naturally hydrolyzed by native ,-glucosidase to indoxyl and glucose, the indoxyl yielding indigo. The activity of two enzymes, sweet almond ,-glucosidase and Novarom G preparation, were compared with P. tinctorium native ,-glucosidase to evaluate indigo production. Results showed that the ability to promote indigo formation increased as follows: almond ,-glucosidase , Novarom G. [source] | |||||||||||||