子午岭林区山杨-辽东栎混交林的生理生态效应

研究了黄土高原子午岭次生林区山杨林、辽东栎林和山杨-辽东栎混交林3种林分的土壤物理特性和叶片光合特性.结果表明,山杨林地在0～300 cm土层的土壤含水量最大，而在200 cm土层以下，山杨 辽东栎混交林的土壤水分明显改善,并优于辽东栎林；在0～60 cm土层内，山杨林地土壤容重最大、土壤孔隙度最小，而山杨-辽东栎混交林的土壤容重最小、土壤孔隙度最大，且均优于纯林，说明混交林地有深层土壤水分可供利用，同时土壤理化特性得到改善.山杨林和辽东栎林的叶绿素含量较高，且均明显高于山杨-辽东栎混交林.辽东栎林的光合速率和气孔导度最大，其次为山杨林, 二者均明显高于山杨-辽东栎混交林.从叶片水分利用效率来看，辽东栎林>山杨-辽东栎混交林辽东栎>山杨-辽东栎混交林山杨>山杨林.山杨-辽东栎混交林中辽东栎的PSⅡ最大光化学转换效率(F_v/F_m)和PSⅡ潜在活性(F_v/F_o)值均较大，但与辽东栎林的F_v/F_m和F_v/F_o值差异不显著，而混交林中山杨的F_v/F_m和F_v/F_o值均相对小于山杨林，且与山杨林的F_v/F_m差异显著，山杨林和辽东栎林的荧光光化学猝灭系数和非光化学猝灭系数值均大于混交林地.因此，子午岭林区辽东栎林更趋于稳定且生长优于其混交林，而山杨林群落将逐步被替代，与纯林类型相比较，其混交林类型可能较不利于山杨的生长.

Physiological-ecological effects of Populus davidiana-Quercus liaotungensis mixed forest in Ziwuling forest area

This paper studied the soil physical-properties under Populus davidiana, Quercus liaotungensis, and Populus davidiana-Quercus liaotungensis mixed forest in the Ziwuling forest asea of Loess Plateau, and the leaf photosysthetic characteristics of these three types of forests. The results showed that soil moisture content in 0~300 cm layer was the highest under P. davidiana forest, and obviously increased below 200 cm in depth under P. davidiana-Q. liaotungensis mixed forest, which was 10.5%~19.76% higher than that under Q. liaotungensis forest. In 0~60 cm layer, P. davidiana forest showed the highest soil bulk density and the lowest soil porosity, while P. davidiana-Q. liaotungensis mixed forest presented the lowest soil bulk density and the highest soil porosity, and both of these indices surpassed their corresponding values under pure forests, which indicated that the mixed forest could make effective use of water in deep soil, and obviously improved soil physical and chemical properties. P. davidiana and Q. liaotungensis had a higher content of leaf chlorophyll than P. davidiana-Q.liaotungensis mixed forest, and Q. liaotungensis presented the highest leaf chlorophyll content. Q. liaotungensis had the highest photosynthetic rate and stomatal conductance, followed by P. davidiana, and by P. davidiana-Q. liaotungensis mixed forest. The water use efficiency of the forests ranked in the decreasing order of Q. liaotungensis in pure forest, Q. liaotungensis in mixed forest, P. davidiana in mixed forest, and P. davidiana in pure forest. Q. liaotungensis in mixed forest presented the highest F_v/F_m and F_v/F_o, and did not remarkably differ from those in pure forest, but in the mixed forest, the F_v/F_m and F_v/F_o of P. davidiana were markedly lower than those of P. davidiana in pure forest. Both the q_p and NPQ of P. davidiana and Q. liaotungensis in pure forests were higher than those in mixed forest, respectively. In Ziwuling forest area, Q. liaotungensis in Q. liaotungensis-dominant climax community tended to be more stable, and grew better than Q. liaotungensis in P. davidiana-Q. liaotungensis mixed forest, and P. davidiana would be gradually replaced. Compared with P. davidiana in pure forest, P. davidiana in its mixed forest was at a disadvantage in its growth.