地球表面的瞬时光合有效辐射(Photosynthetically Active Radiation,PAR)和植被吸收的光合有效辐射(Absorbed Photosynthetically Active Radiation,APAR)是许多集中于生物圈和大气之间交换过程研究的关键参量。光合有效辐射吸收比例(Fraction of Photosynthetically Active Radiation,FPAR)是APAR和PAR的比值,是许多气候模型及生产力模型的基本特征参量。因此,研究PAR/APAR/FPAR的时空变化规律,对准确估算草地NPP具有十分重要的作用。本文利用MODIS遥感影像和TOMS紫外波段反射率数据,在GIS和RS软件支持下,计算分析了内蒙古草地生长季的PAR/FPAR/APAR及其时空变化,并分析了气候因子对FPAR/APAR的影响。结果表明:内蒙古草地生长季平均PAR为1973.8MJ/m2,FPAR为0.275,APAR为516.64MJ/m2。内蒙古草地生长季的PAR/FPAR/PAR时空变化明显:FPAR及APAR空间上呈东北向西南地区递减的趋势,PAR与之相反。自生长季初期(4月份),随着时间的推移PAR/FPAR/APAR都开始增加,只是出现峰值的时间不同。内蒙古草地生长季不同草地类型的FPAR及APAR差异明显,在草地NPP估算及建模时应引起重视。
We studied a soil seed bank in the Stipa breviflora desert steppe under three grassland management systems,namely continuous grazing,rotational grazing,and no grazing,from 1999 until 2007.The germinable seed bank species in rotational,continuous and no grazing were 11,9 and 8 species,respectively.Rotational grazing increased the number of seed bank plant species and perennial grasses.The density of germinal soil seed bank was significantly higher in the enclosed area(19,533.33 seeds/m 2) than those in rotational(3,233.33 seeds/m 2) and continuous grazing areas(2,553.60 seeds/m 2).The vertical distribution of the soil seed bank had a similar trend:75.06%-83.19% of the seeds are distributed in the top 0-5 cm soil layer,14.16%-21.68% in the 5-10 cm layer,and 2.65%-4.95% in the 10-15 cm layer,which varied between the grazing treatments.Density of the soil seed bank was significantly higher in the enclosed area,and there was no significant difference between rotational and continuous grazing.The Margalef and Shannon-Wiener indices for the soil seed bank were higher for rotational grazing treatment than for continuous grazing.The Sorensen's similarity index for the soil seed bank between the enclosed and rotational grazing areas reached 0.857.
