白羊草根系形态特征对土壤水分阶段变化的响应

摘要

根系形态特征是评价植物适应胁迫环境的重要指标。以黄土丘陵半干旱区天然草地群落优势种白羊草为材料，研究了其根系生长和形态特征与水分供应条件的关系。采用盆栽控制试验，设置3个水分处理：高水（HW，80％田间持水量）、中水（MW，60％田间持水量）和低水（LW，40％田间持水量），分别在拔节期、开花期、结实期改善水分供应水平，在生育期末测定了白羊草根系生物量和各项形态指标。结果表明：白羊草根系生长与水分供应条件密切相关，持续高水处理有利于白羊草根系生长，其根系生物量、总根长和根表面积均显著提高（P ＜0．05）；水分胁迫抑制了白羊草根系生长，但对白羊草根系平均直径影响不显著；根系生物量、总根长和根表面积间存在显著的正相关关系（P ＜0．01）；不同生育期阶段胁迫后复水，白羊草根系表现出较强的可塑性，在拔节期复水且高的复水幅度能够显著提高白羊草根系生物量、总根长和根表面积（P ＜0．05）。这些说明白羊草根系对干旱胁迫有较强的耐受能力，其对阶段干旱胁迫后复水的响应与生育期及复水前干旱胁迫程度密切相关。%Root morphological characteristics are important parameters for evaluating plant adaptability to envi-ronmental stress.To clarify the relationship between the root morphological characteristics of old world bluestem (Bothroichloa ischaemum )and soil water conditions,pot experiments were conducted to investigate root biomass,total root length,root surface area,average root diameter,specific root length and specific root area under three soil water regimes:(1)sufficient water supply (HW,80% field capacity),(2)moderate wa-ter stress (MW,60% field capacity),and (3)severe water stress (LW,40% field capacity).Moreover,soil water contents were improved from MW to HW,LW to HW and LW to MW at the three main growth periods (jointing,flowering and maturing).At the end of the growth period,root biomass and morphological charac-teristics under the different water treatments were measured and analyzed.The results showed that old world bluestem root growth was closely related to soil water conditions.Root biomass,total root length and root sur-face area were also significantly higher with continuous sufficient water supply than under the other treatments (P <0.05).Water stress inhibited the root growth of old world bluestem but there were no significant differ-ences in average root diameter between the different water treatments.Positive linear relationships were found between root biomass and total root length as well as with root surface area.The roots exhibited strong mor-phological plasticity in response to changes in soil water conditions.Higher levels of water content improve-ment significantly improved root biomass,total root length and root surface area,especially during the jointing period.These results suggest that old world bluestem has strong water stress tolerance and that the growth re-sponse of its roots to soil water change is related to the plant growth period as well as to the degree of water stress prior to improvements in soil water content.