土壤水分和覆土厚度对油松种子萌发和幼苗出土的影响

The responses of seed germination and seedling emergence of Pinus tabulaeformis Carr.to soil water content and covering depth

研究了子午岭林区内油松种子的萌发和幼苗出土对土壤水分和覆土深度的响应机理.结果表明：油松种子萌发适宜的土壤含水量范围是20%-30%,最适含水量为25%;在土壤含水量低于10%时,种子发芽率低于61.33%;当土壤含水量超过40%时,发芽率下降到59.33%.种子出苗适宜的土壤含水量是25%-35%,在土壤含水量达到30%时,出苗效果最好;土壤含水量高于40%或低于10%时,幼苗出苗率均降低到20%以下.油松幼苗出土与覆土厚度有密切关系,当土层厚度为0.5 cm时,出苗率最高,可达到94.67%.随着覆土厚度的增加,出苗率逐渐降低;当覆土厚度超过2.5 cm后,几乎不能出苗.在油松人工林中,油松种子的萌发在林分中优于林窗中,出苗在林窗中优于林分中.种子萌发和幼苗出土效果在覆土条件下优于覆盖枯落物.种子经过预处理（室温下蒸馏水浸泡24 h）后种子萌发和幼苗出土效果优于未处理条件下.

The responses of seed germination and seedling emergence of Pinus tabulaeformis Carr.in the Ziwu Mountains od Gansu Province to different soil water contents（15 %,20 %,25 %,30 %,35 %,40 % and 45 %,respectively） and covering depth were investigated by laboratory tests and field experiments.The results from the laboratory tests showed that the suitable soil water content for seed germination ranged from 20 % to 30 %,among which about 25 % of soil water content was corresponding to both the highest seeds germination index and higher germination rate.Once the soil water content was under 10 %,the germination rate of seeds was lower than 61.33 %.However,when the soil water content was above 40 %,the germination rate decreased to 59.33 %.The most suitable soil water content for seedling emergence was 25 %～35 %,among which about 30 % of soil water content was corresponding to both the highest seedling emergence rate and index.When soil water content was above 40 % or below 15 %,a few seedlings（below 20 %） emerged.The results from the field experiments showed that the seedling emergence rates were greater than 90 % when seeds were buried in 0.5～1 cm depth below the surface of soil,and the covering depth 0.5 cm was corresponding to the highest seedling emergence rate（94.67 %）.But seedling emergence rates would decrease with further increase of covering depth,and once the covering depth increased to above 2.5 cm,the seedlings almost couldn＇t emerged.In addition,seed germination rate of Pinus tabulaeformis of the artificial stands was greater under the forest canopy than in canopy gaps,whereas seed emergence in canopy gaps was better than that under the forest canopy.The performance of both seed germination and seed emergence under soil coverage were better than that under litter coverage.Those seeds pretreated by soaking in distilled water for 24 h at room temperature had higher germination and emergence rate than that of untreated seeds.