呼伦贝尔羊草草甸草原光合有效辐射分量变化规律分析

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

通过实测呼伦贝尔羊草草原冠层光合有效辐射(PAR)各分量并计算冠层反射率、土壤反射率,对其季节变化、日变化进行浅析。研究表明,在生长季6月初-9月下旬,PAR和APAR(吸收性光合有效辐射)季节变化均呈减小趋势。PAR波动较大,在25～58mol/m2;APAR则在17～34mol/m2波动。光合有效辐射吸收比例(FPAR)随季节推移呈增大趋势,波动范围在0.46～0.77,最大值出现在8月下旬,可达0.77。晴天冠层入射PAR、反射PAR、透射PAR和土壤反射PAR日变化均呈较标准正弦曲线。冠层反射率在中午12点前后最低而早晚值较高。土壤反射率日变化6月波动较大,在0.4之内,7-9月,仅在0.08内。APAR日变化趋势和入射PAR基本一致。6月、7月至8月中旬,晴天FPAR日变化呈较标准的余弦曲线,变动幅度为0.60,9月变动幅度仅为0.13,几乎趋于常数。本研究在获取较准确地面实测PAR数据的同时得到FPAR,可为本地区草地FPAR的精度评估和验证提供参考。

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. 4：6 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.