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Acta Prataculturae Sinica ›› 2010, Vol. 19 ›› Issue (4): 243-250.

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A study on the variations of pivotal photosynthetic active radiation parameters of a Leymus chinensis meadow-steppe in Hulunber

LI Jin1,2, ZHANG De-gang1, ZHANG Hong-bin2,3,4, LI Gang4, YANG Gui-xia2,3,4, LI Lin-zhi1,2, XIN Xiao-ping2,3,4   

  1. 1.College of Pratacultural Science, Gansu Agricultural University, Lanzhou 730070, China;
    2.Hulunber
    State Station of Grassland Ecosystem Field Observation and Scientific Research, Beijing 100081,
    China;
    3.Key Laboratory of Resources Remote Sensing and Digital Agriculture, Ministry of
    Agriculture, Beijing 100081, China;
    4.Institute of Agricultural Resources and Regional
    Planning of Chinese Academy of Agricultural Sciences, Beijing 100081, China
  • Received:2009-08-21 Online:2010-08-20 Published:2010-08-20

Abstract: The diurnal and seasonal variations of photosynthetic active radiation (PAR) parameters, the calculation of reflectance of canopy and transmittance of soil in a Leymus chinensis meadow-steppe in Hulunber were studied. The seasonal variations of both PAR and absorbed photosynthesis active radiation (APAR) tended to decrease in the growth period from early June to late September. PAR fluctuated over a wider range (25 and 58 mol/m2) than APAR (17 and 34 mol/m2). However, the fraction of photosynthetic active radiation (FPAR) tended to increase during the season. It fluctuated between 0.46 and 0.77 with the highest FPAR value of 0.77 in the last ten days of August. Changes of incident PAR, reflectance PAR, and transmittance PAR of the canopy and the soil reflectance PAR during clear days were standard sine curves. The diurnal variation of canopy reflectance ratio was highest in the morning and evening but lowest around 12:00 noon. The diurnal change (0.4) of the reflectance ratio of soil varied over a wider range in June than in July and September (0.08). The diurnal variation of APAR was identical with the incident PAR. The diurnal FPAR variation was a curve of cosine on clear days in June, July, and the middle of August, with a variation of 0.60, compared with a variation of only 0.13 in September. The relative correct PAR data were obtained by measuring on the ground as well as FPAR and it provided a reference for the evaluation of precision and validation of FPAR in grassland.

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