土壤水分对单性木兰幼苗光合特性的影响

The Effects of Soil Water Content on Photosynthesis in Leaves of Kmeria septentrionalis Seedlings

摘要:

2001年夏季(7月15-19日)和秋季(10月20-25日)分别测定了在3组土壤水分条件下(高WH、中WM和低WL3种土壤水分处理)单性木兰(Kmeriaseptentrionalis)叶片净光合速率(Pn)、气孔导度(Gs)、潜在水分利用效率(IntrinsicWUE)和叶绿素含量等特性。夏季和秋季土壤水分的减少均引起单性木兰叶片单位面积干重和叶绿素含量的降低。夏季,单性木兰的Pn均在上午900达到峰值,其日进程为鞍型格式,WH、WM和WL处理组的Pn分别为4.41±1.10、4.28±1.23和1.89±0.94 μmol m^-2s^-1,土壤水分的降低限制了单性木兰叶片的Pn,它们的Gs和IntrinsicWUE的日进程与Pn相似。秋季,WH组的Pn在上午1200达到峰值,WM和WL组在900达到峰值,3组的Pn的日进程相似,都为单峰曲线格式。3组的Pn、Gs和IntrinsicWUE的日平均值都是秋季比夏季高。不管夏季和秋季,凡土壤水分低的,其Pn、Gs和IntrinsicWUE都低。因此,调节土壤水分将有助于促进单性木兰的生长和有效提高单性木兰的迁地保护。

Abstract:

Net photosynthetic rate (Pn), stomatal conductance (Gs), intrinsic water use efficiency (WUE) and chlorophyll content were measured in the leaves of Kmeria septentrionalis seedlings grown in pots withvarious soil water contents during July 15-19 and October 20-25, 2001. Decrease of soil water content in summer and autumn reduced the leaf dry weight per unit area and chlorophyll content in the seedlings. In July, highest photosynthetic rate was found at 9:00 pm in sunny day. The Pn of seedlings in treatments with soil water content at high(WH)，mediam(WM) ，and low levels were 4.41±1.1O μmol m^-2s^-1 ,4.28±1.23 μmol m^-2s^-1 and 1.89±0.94 μmol m^-2s^-1，respectively．WH，WM and WL represent the soil water contents are 60％-65％, 45％-50％ and35％-40％ of the field water holding capacity， respectively． Low Pn occurred in plants grown under soil water treatments of WL． A pattern with double peaks in daily photosynthetic course was observed in leaves of the seedlings under soil with all the three treatments．Gs an d intrinsic WUE daily courses also showed similar paUem ． In October，daily high Pn appeared at 12：00 in plants in WH group and those in WM and WL groups were found at 9：00．A pattern with single peak in daily photosyn thetic course was observed in 3 groups． Average values of Pn，Gs and intrinsic WUE were higher in autumn than those in summer in all the three groups．However,the Pn，Gs and intrinsic WUE were all low in soils with low water content, whatever in summer or autumn． The results suggest that the control of soil water content may help to promote the growth of septentrionalis and increase the effectiveness of ex situ conservation.