扁穗牛鞭草地不同层面光合作用差异及贡献率的研究

通过对扁穗牛鞭草地不同层面光合作用差异及贡献率的研究,结果说明:外界光合有效辐射从上往下以19.84μmol/(m2.s.cm)速度递减;Ci起伏较大,最大值c(CO2)=943.11μmol/mol出现在最下层光合速率最低的8 cm处,最小值c(CO2)=147.81μmol/mol出现在光合速率最高的65 cm处;Gs的变化范围为0.033~0.220 mol/(m2.s),但从下往上递增,在顶层有所下降;Tr与Gs密切相关;不同层面叶片单位面积的Pn差异很大,8 cm处c(CO2)=2.42μmol/(m2.s),65 cm处c(CO2)=42.57μmol/(m2.s)达最大值。单叶光合效率变异范围为1.105~53.450 nmol/s,单叶光合效率是外界光合作用有效辐射与叶片面积和光合速率三者共同偶合作用的结果;不同株层贡献率差异很大,0~20 cm光合贡献率仅1.73%,0~40 cm的贡献率仅为12.19%,而55~75 cm占全部叶片数的40.89%,光合贡献率达56.88%;扁穗牛鞭草地应当在低于80 cm时利用,不仅可以保证牧草的产量与质量,也可以提高草地的年生产能力。

Photosynthesis and its Contribution Ratio of the Different Leaf Layers of Hemarthria compressa

The photosynthetic parameters including the photosynthesis available radiation(PARo),the guide stoma(Gs),the concentration of intercellular CO_2(Ci),the transpiration rate(Tr),the photosynthesis rate(Pn) of different leaf layers(8、 12、 15、 20、 25、35、 40、 45、 50、 55、 65、 75 and 80) for artificial grassland of Hemarthria compressa were measured,which was in vegetative growth phase with the density of 40 plant/m~2,nature height of 80?cm,CO_2 density of(372±8)?μmol/mol,temperature of(33±1)?℃ and relative humidity of(45±3)%.The leaf distribution and its photosynthetic characteristic in different layers,the photosynthetic characteristic and the contribution rate of different height were analysed and studied.The results showed that,from upper to low,the photosynthesis available radiation was gradually decreasing with the velocity of 19.84 μmol/m~2·s·cm.The larger wave was found in the Ci parameter,and the largest value CO_2 943.11 μmol/(m~2·s·cm)] was emerged in the leaf layer of 8 cm,which had the lowest photosynthesis rate,and the smallest valueCO_2 147.81 μmol/(m~2·s·cm)] was the leaf layer of 65 cm,with the highest photosynthesis rate.Gs had the change range of H_2O 0.033～0.220 mol/(m~2·s·cm),which was gradually increasing from low to upper,but at the top layer the value slightly dropped.Tr was obviously relative to Gs.There was a visible difference among the Pn value of unit area in different leaf layers,with the smallest value of CO_2 2.42 μmol/(m~2·s·cm) in 8 cm height and the largest value of CO_2 42.57 μmol/(m~2·s·cm) in 65 cm height.The simple leaf's photosynthetic efficiency was the result of collaborative action of available radiation,leaf area and photosynthesis rate,and its fluctuant range was CO_2(11.05～534.50)×10~(-4)μmol/(m~2·s·cm).The different heights of plant had different photosynthesis contribution rates,the rate of 0～20 cm and 0～40 cm was 1.73% and 12.19%,respectively,while the rate of 55～75 cm was 56.88% with 40.89% leaves of the whole plant.Consequently,Hemarthria compressa should be sliced off under 80 cm height,which not only guaranteed the quality and quantity of forage,but also the annual production capacity of grassland must be practically improved.