Ratio of photosynthetically active to total incoming radiation above a Mediterranean deciduous oak forest
- 19 Downloads
Photosynthetically active radiation (PAR) is an important parameter in ecological research. However, it is not routinely measured and often is estimated as a constant ratio of the incoming solar shortwave radiation (Rs). There are only few reported PAR/Rs values worldwide concerning the Mediterranean climate and even fewer from rural or forest areas, especially at higher altitudes. Hourly PAR and Rs flux densities were measured above a deciduous oak forest in Greece from 1999 to 2005, and their relationship was investigated under various conditions. Results show that the annual mean hourly PAR/Rs is 0.454, ranging from 0.443 in spring to 0.478 in autumn, with intermediate values in summer (0.454) and winter (0.459). The ratio increases with dew point temperature but decreases as solar elevation angle or Rs increases. Atmospheric clearness index, Kt, and actual water vapor pressure, ea, are the key factors determining the ratio; however, relative humidity (RH) also seems to have an indirect effect by affecting Kt and ea values. PAR/Rs changes from 0.468 to 0.455 as sky conditions change from clear to overcast and appears to increase with ea. However, Kt affects the ratio when RH is lower than 60%, while ea has a more obvious effect at more saturated atmospheric conditions.
The important contributions of the reviewers are highly acknowledged by the authors. Also, the authors, would like to thank the SCIENTACT S.A. company for providing the equipment for the radiometers calibration.
This study was funded by the EC Project MEDEFLU-EUROFLUX “Carbon and water fluxes of Mediterranean forests and impacts of land use/cover changes” (ENV4-CT97-0455 DGXII-Environment and Climate) carried out by the Agricultural University of Athens and the Göttingen Institute of Bioclimatology.
- Alados I, Alados-Arboledas L (1999) Validation of an empirical model for photosynthetically active radiation. Int J Climatol 19:1145–1152. https://doi.org/10.1002/(SICI)1097-0088(199908)19:10<1145::AID-JOC428>3.0.CO;2-3 CrossRefGoogle Scholar
- Duffie JA, Beckman WA (1980) Solar engineering of thermal processes. Wiley, New York, pp 1–109Google Scholar
- Iqbal M (1983) An introduction to solar radiation. Academic Press, New York, p 390Google Scholar
- Jacovides CP, Tymvios FS, Asimakopoulos DN, Theofilou KM, Pashiardes S (2003) Global photosynthetically active radiation and its relationship with global solar radiation in the Eastern Mediterranean basin. Theor Appl Climatol 74:227–233. https://doi.org/10.1007/s00704-002-0685-5 CrossRefGoogle Scholar
- Meek DW, Hatfield JL, Howell TA, Idso SB, Reginato RJ (1984) A generalized relationship between photosynthetically active radiation and solar radiation. Agron J 76:939–945. https://doi.org/10.2134/agronj1984.00021962007600060018x CrossRefGoogle Scholar
- Mizoguchi Y, Ohtani Y, Aoshima T, Hirakata A, Yuta S, Takanashi S, Iwata H, Nakai Y (2010) Comparison of the characteristics of five quantum sensors. Bull FFPRI 9(3):113–120Google Scholar
- Mizoguchi Y, Yasuda Y, Ohtani Y, Watanabe T, Kominami Y, Yamanoi K (2014) A practical model to estimate photosynthetically active radiation using general meteorological elements in a temperate humid area and comparison among models. Theor Appl Climatol 115:583–589. https://doi.org/10.1007/s00704-013-0912-2 CrossRefGoogle Scholar
- Murray FW (1967) On the computation of saturation vapor pressure. J Appl Meteorol 6:203–204. https://doi.org/10.1175/1520-0450(1967)006<0203:OTCOSV>2.0.CO;2 CrossRefGoogle Scholar
- Tetens O (1930) Über einige meteorologische Begriffe. Z Geophys 6:297–309Google Scholar
- Udo SO, Aro TO (2000) New empirical relationships for determining global PAR from measurements of global solar radiation, infrared radiation or sunshine duration. Int J Climatol 20:1265–1274. https://doi.org/10.1002/1097-0088(200008)20:10<1265::AID-JOC530>3.0.CO;2-C CrossRefGoogle Scholar
- Wang Q, Tenhunen J, Schmidt M, Kolcun O, Droesler M, Reichstein M (2006) Estimation of total, direct and diffuse PAR under clear skies in complex alpine terrain of the National Park Berchtesgaden, Germany. Ecol Model 196:149–162. https://doi.org/10.1016/j.ecolmodel.2006.02.005 CrossRefGoogle Scholar
- Wortman E, Tomaszewski T, Waldner P, Schleppi P, Thimonier A, Eugster W, Buchmann N, Sievering H (2012) Atmospheric nitrogen deposition and canopy retention influences on photosynthetic performance at two high nitrogen deposition Swiss forests. Tellus Ser B Chem Phys Meteorol 64:17216. https://doi.org/10.3402/tellusb.v64i0.17216 CrossRefGoogle Scholar
- Zempila M-M, Taylor M, Bais A, Kazadzis S (2016) Modeling the relationship between photosynthetically active radiation and global horizontal irradiance using singular spectrum analysis. J Quant Spectrosc Radiat Transf 182:240–263Google Scholar