辽东栎幼苗根系形态特征对环境梯度的响应

Response of root morphological characteristics of Quercus liaotungensis seedlings to environmental gradients

以辽东栎(Quercus liaotungensis)在陕西不同分布区:秦岭北坡(太白)、黄土高原南部(黄龙)和黄土高原中部(延安)为研究地点并设置样地,对1—5年生辽东栎幼苗的根系形态指标进行测定,分析辽东栎幼苗根系形态特征及其与环境因子的关系。结果表明:由秦岭北坡到黄土高原中部,黄龙地区辽东栎幼苗根系在发育前期(1—2年)低于太白和延安,总体上黄龙地区幼苗根系总长度、表面积、总体积、根尖数、平均直径、组织密度和单株生物量高于太白和延安地区。在太白地区,辽东栎幼苗根系表面积、总体积和平均直径较小,根系分岔数较大,幼苗根系主要通过提高分岔数来拓展自己的营养空间以适应环境;在黄龙和延安地区,幼苗根系表面积、总体积和平均直径较大,根系分岔数较小,幼苗根系主要是通过根系的伸长生长适应胁迫环境。3个地区辽东栎幼苗根系总长度、表面积、总体积、根尖数和分岔数随年龄的增长呈线性函数变化格局,均可用线性函数方程y=ax+b(a>0,P<0.05)进行描述。冗余分析表明幼苗根系分岔数、总长度、比根长和根尖数与土壤速效磷、硝态氮、速效钾、降雨量、石砾含量和速效氮呈正相关;与较高的土壤pH值、年均温和夏季气温呈负相关。未来辽东栎林抚育经营中,含石砾的湿润土壤生境更有利于辽东栎幼苗根系生长。

The objectives of this study were to explore the effects of different environmental conditions on seedling root growth and to provide important guidelines for forest regeneration and sustainable management. Thus, morphological characteristics of seedling roots of Quercus liaotungensis were investigated. The concentrated distribution zone of Q. liaotungensis in Shaanxi Province is located in the Loess Plateau and the north slope of the Qinling Moutains. The study was conducted in three distribution areas of Q. liaotungensis, which including the north slope of the Qinling Moutains （Taibai）, southern Loess Plateau （Huanglong）, and central Loess Plateau （Yan＇an）. Root morphological indices of 1-5-year-old Q. liaotungensis seedlings were investigated and the influences of environmental factors on root growth were analyzed. The results showed that root morphological indices were significantly different between trees grown in southern and northern areas. During the early growth stages of the seedlings （1-2 years）, root morphological indices were constrained. The total root length, surface area, volume, root tips, averaged diameter, tissue density, and biomass per seedling increased and then decreased from the north slope of the Qinling Moutains to the central Loess Plateau, while the largest indices were documented in Huanglong. As a result, the roots of Q. liaotungensis seedlings in Taibai by improving root forks and decreasing the total surface area, volume, and average diameter to adapted to the environment. The roots of Q. liaotungensis seedlings in Huanglong and Yan＇an by improving the elongation, specifically increasing the total surface area, volume, and average diameter, as well as by reducing root forks to adapted to the arid environment. Relationships between seedling root system indices （including the total root length, surface area, volume, root tips, and forks per seedling） and seedling age were best described by a linear function （y=ax ＋ b, a 〉 0, P 〈 0.05）. Redundancy discriminate analysis revealed that root forks, total root length, specific root length, and root tips of Q. liaotungensis seedlings were significantly positively correlated with available phosphorous, nitrate nitrogen, available potassium, annual precipitation, gravel content, and available nitrogen, whereas they were significantly negatively correlated with soil pH, mean annual temperature, and mean summer temperature. We conclude that appropriate gravel content and moisture are favorable for the growth of Q. liaotungensis seedling roots.