<正>采用3种遮荫（全光照、60%遮荫、80%遮荫）和3种土壤水分（高、中和低）处理，研究了毛红椿幼苗叶片净光合速率（Pn）、气孔导度（（Co）、胞间CO2：浓度（Ci）和叶绿素含量及叶面积等特性。结果表明：毛红椿净七合速率日进程曲线呈”双峰”型，高峰值出现在10：OO和16：00，全光照和中度遮荫（60%）情况下有较明显的光台“午休”现象。而强度遮荫（80%）光合“午休”现象不明显。全光照下胞间C（）!浓度日进程基本与净光台遣率相反。当土壤含水量高时光合作用能力最强。气孔导度日变化呈下降趋势，胞间C（）。浓度变化平缓。表明上午10：00以后净光合速率降低主要受非气孔限制因素的影响。在遮荫条件下，毛红椿苗木通过增大叶面积、提高叶绿素含量有效地利用较弱的光辐射。形成适应遮荫条件的生态生存对策。

In this paper, researches were made on soil water conditions in arid river valley, Lixian, Sichuan from August 2002 to July 2003. The results.showed that average soil water content at 0~50cm depth at northern slope for different altitudes was higher than that at southern slope, while the reverse was for spatial heterogeneity of soil water. For the same slope aspect, the order of soil water contents in terms of altitudes was 2050m>1850m>1450m> 1650m. For the same altitude, soil water contents at different slope aspects all increased with increasing soil depth and the highest soil water content occurred at the depth of 30~50cm.