减少降水和草本竞争对白桦幼苗细根形态和生理特征的影响

为了解黄土高原半干旱区草本竞争对于造林树种幼苗细根的影响，以1年生白桦幼苗为试验对象，设置正常和减少天然降水2个水分处理，并以草地早熟禾作为竞争处理模拟草本竞争，进行1个生长季大田盆栽试验。通过测量白桦幼苗细根形态和营养指标，以期揭示白桦幼苗细根对土壤水分胁迫和草本竞争的响应机制，为黄土高原森林营造中阔叶树种选择和栽植技术提供理论依据。结果表明:1）生长季内，减少降水处理显著减少了土壤水分含量33%，但未显著影响白桦幼苗的存活率以及细根生物量和养分含量，仅导致细根表面积和体积减小。2）在草本竞争下，白桦幼苗细根全N含量显著下降，存活率以及总碳、可溶性糖、淀粉和非结构性碳水化合物（NSC）等营养指标未受影响。3）降水和草本地下竞争的交互作用显著影响了白桦幼苗细根生物量、淀粉及NSC含量。有草本地下竞争时，降水减少显著降低了白桦幼苗细根生物量，细根淀粉和NSC含量则显著升高，反映了土壤水分含量下降时白桦幼苗细根竞争能力的下降，从而与草本地下竞争减弱。白桦幼苗细根在正常天然降水下受草本地下竞争影响增加生物量，但在减少降水时其形态和营养特征受到草本地下竞争影响较小。表明在迹地和退耕还林地等养分含量较高土壤上使用白桦幼苗造林时，无需考虑草本竞争的影响。

Effects of Reduced Precipitation and Herb Competition on the Morphological and Physiological Characteristics of the Fine Roots of Betula platyphylla Seedlings

In order to understand the influence of herb competition on the fine roots of afforestation tree seedlings in the semi-arid area of the Loess Plateau,1-year-old birch seedlings were taken as the test objects,two water treatments were set:normal and reduced natural precipitation.Poa pratensis was used as the competitive treatment to simulate the herb competition.By measuring the fine root morphology and nutritional indicators of birch seedlings,we hoped to reveal the response mechanism of the fine roots of birch seedlings to soil water stress and herb competition,and to provide a theoretical basis for the selection and planting techniques of broad-leaved tree species in forest construction in the Loess Plateau.The results showed that 1) during the growing season,the precipitation reduction treatment significantly reduced the soil moisture content by 33%,but did not significantly affect the survival rate of the birch seedlings,the biomass and nutrient content of the fine roots,and only reduced the surface area and volume of the fine roots.2) Under herb competition,the total nitrogen content of the fine roots of birch seedlings decreased significantly,and the survival rate and nutritional indicators such as total carbon,soluble sugar,starch and non-structural carbohydrates (NSC) were not affected.3) The interaction of precipitation and herb underground competition significantly affected the fine root biomass,starch and NSC content of birch seedlings.When there existed herb underground competition,the biomass of fine roots was significantly reduced under reduced precipitation,and the content of fine root starch and NSC significantly increased,reflecting the decline in the competitive ability of the birch seedlings fine roots when the soil moisture content decreased,thus weakening the underground competition with herbs.The fine roots of birch seedlings increased the biomass under normal natural rainfall,but the morphological and nutritional characteristics of birch seedlings were less affected by underground competition when rainfall was reduced.The results showed that using birch seedlings for afforestation on soils with high nutrient content such as cutting blanks and conversion of farmland to forests,there was no need to consider the influence of herb competition.