【摘要】 针对科尔沁沙地南缘樟子松人工林不能天然更新的特征,从森林天然更新的必要条件出发,通过种子萌发、幼苗存活与生长所需条件的系列试验,探讨了科尔沁沙地南缘樟子松人工林不能天然更新的障碍特征。结果表明,沙地樟子松人工林不能天然更新的主要原因有:(1)由于土壤的干旱胁迫使沙地樟子松人工林中天然下种的种子很少有萌发的机会,尤其是在春季;(2)在水分条件相对充足的季节(秋季),樟子松种子能够萌发,但萌发产生的更新幼苗数量极少,即便这些更新幼苗得以存活,但由于沙地表层(0~5cm)与樟子松共生的外生菌根菌几乎不能存活而导致幼苗根系无法形成菌根,从而致使存活的樟子松幼苗抗旱、抗病能力非常弱,不能越冬,即不能更新。更多还原

【Abstract】 As a valuable conifer tree species (cold-resistant, drought-resistant and fast-grwoing tree), Pinus sylvestris var. mongolica has become a major tree species on sandy land in aird and semi-arid areas in "Three north" regions (north, northwest and northeast of China). However, the plantations of P. sylvestris var. mongolica have declined at different degrees in the earliest introduction areas (Keerqin sandy land, which located at Zhangwu county, Liaoning province, northeastern China) since early 1990s. The decline of P. sylvestris var. mongolica plantations on sandy land was characterized by two major features, i.e., one is top, needle and twig withered, low growth rate and tree death, the other is no natural regeneration. In order to examine the causes that led to the no natural regeneration in the plantations on sandy land, the conditions for seed germination, seedling survival and growth were tested in both lab and field. In addition, the influences of drought stresses and temperature on the growth of ectomycorrhizal fungi (ECM) strains, which are symbionts with P. sylvestris var. mongolica, were also examined because P. sylvestris var. mongolica is an ectomycorrhizal fungi depending species. The results indicated that the germination time of drought stressed seeds was longer than that of the control treatment; the germination percentage and germination rate were lower than those of the control treatment. The heavy drought stress and the extreme temperatures, especially the high temperature (over 37℃ or 40℃), made the ECM fatal. Combined the observations of soil water content (soil water potential) and surface temperature in the P. sylvestris var. mongolica plantation sites, we found that the extremely experimental conditions matched the soil water conditions and extreme temperatures within 5 cm soil in the P. sylvestris var. mongolica plantation sites. These suggested that no natural regeneration in the plantations on sandy land were caused by: (1) impact of drought stresses on seed germination; (2) the lack of ectomycorrhizal fungi within surface sand soil (0-5 cm), which led to the root systems of seedlings death without the symbiosis of ectomycorrhizal fungi, and the extreme environmental conditions on the sandy land, which caused the death of new shoots or seedlings.更多还原