Nie Yunpeng, Chen Hongsong, Ding Yali, Yang Jing, Wang Kelin
Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of SciencesChangsha, China.
Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of SciencesHuanjiang, China.
Front Plant Sci. 2017 Sep 22;8:1651. doi: 10.3389/fpls.2017.01651. eCollection 2017.
For tree species adapted to shallow soil environments, rooting strategies that efficiently explore rock fractures are important because soil water depletion occurs frequently. However, two questions: (a) to what extent shallow soil-adapted species rely on exploring rock fractures and (b) what outcomes result from drought stress, have rarely been tested. Therefore, based on the expectation that early development of roots into deep soil layers is at the cost of aboveground growth, seedlings of three tree species (, and ) with distinct aboveground growth rates were selected from a typical shallow soil region. In a greenhouse experiment that mimics the basic features of shallow soil environments, 1-year-old seedlings were transplanted into simulated microcosms of shallow soil overlaying fractured bedrock. Root biomass allocation and leaf physiological activities, as well as leaf δC values were investigated and compared for two treatments: regular irrigation and repeated cycles of drought stress. Our results show that the three species differed in their rooting strategies in the context of encountering rock fractures, however, these strategies were not closely related to the aboveground growth rate. For the slowest-growing seedling, , percentages of root mass in the fractures, as well as in the soil layer between soil and bedrock increased significantly under both treatments, indicating a specialized rooting strategy that facilitated the exploration of rock fractures. Early investment in deep root growth was likely critical to the establishment of this drought-vulnerable species. For the intermediate-growing, , percentages of root mass in the bedrock and interface soil layers were relatively low and exhibited no obvious change under either treatment. This limited need to explore rock fractures was compensated by a conservative water use strategy. For the fast-growing, , percentages of root mass in the bedrock and interface layers increased simultaneously under drought conditions, but not under irrigated conditions. This drought-induced rooting plasticity was associated with drought avoidance by this species. Although, root development might have been affected by the simulated microcosm, contrasting results among the three species indicated that efficient use of rock fractures is not a necessary or specialized strategy of shallow-soil adapted species. The establishment and persistence of these species relied on the mutual complementation between their species-specific rooting strategies and drought adaptations.
对于适应浅层土壤环境的树种而言，能有效探索岩石裂隙的生根策略很重要，因为土壤水分经常耗尽。然而，两个问题：（a）适应浅层土壤的物种在多大程度上依赖于探索岩石裂隙，以及（b）干旱胁迫会产生什么结果，很少得到验证。因此，基于根系早期向深层土壤层生长是以地上部分生长为代价的预期，从一个典型的浅层土壤区域选取了三种地上生长速率不同的树种（、和）的幼苗。在一个模拟浅层土壤环境基本特征的温室实验中，将1年生幼苗移植到覆盖有裂隙基岩的模拟浅层土壤微观环境中。针对两种处理方式：定期灌溉和反复干旱胁迫循环，研究并比较了根系生物量分配、叶片生理活动以及叶片δC值。我们的结果表明，这三个物种在遇到岩石裂隙时的生根策略有所不同，然而，这些策略与地上生长速率并无紧密关联。对于生长最慢的幼苗，，在两种处理方式下，裂隙以及土壤与基岩之间土层中的根质量百分比均显著增加，表明其具有一种有助于探索岩石裂隙的特殊生根策略。早期对深根生长的投入可能对这种干旱敏感物种的定植至关重要。对于生长中等的，，基岩和界面土壤层中的根质量百分比相对较低，并且在任何一种处理方式下均未表现出明显变化。这种对探索岩石裂隙的有限需求通过保守的水分利用策略得到了补偿。对于生长快速的，，在干旱条件下，基岩和界面层中的根质量百分比同时增加，但在灌溉条件下则不然。这种干旱诱导的生根可塑性与该物种的避旱性相关。尽管根系发育可能受到模拟微观环境的影响，但这三个物种之间的对比结果表明，有效利用岩石裂隙并非适应浅层土壤物种的必要或特殊策略。这些物种的定植和存续依赖于其物种特异性生根策略与干旱适应性之间的相互补充。
