Variations of root traits in three Xizang grassland communities along a precipitation gradient

ZHOU Wei, LI Hong-Bo, ZENG Hui

Chin J Plant Ecol 2018, 42 (11): 1094-1102. DOI: 10.17521/cjpe.2018.0140

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Aims Root functional traits and their variations mediate coexistence and adaptive strategy of plant species. Yet, strong environmental constraints may induce convergence of root traits among different plant species. To study the variations of root traits and clarify the diverse adaptive strategies across plant species, we sampled three alpine grasslands along a precipitation gradient in the Xizang Plateau.
Methods In three grassland communities along a precipitation gradient: Nagqu, Baingoin and Nyima from east to west of Xizang Plateau, we collected 22 coexisting plant species and measured three key root traits: 1st-order root diameter, 1st-order lateral root length and root branch intensity.
Important findings The main results showed that: (1) the root of plants in the alpine grassland was generally thin, and the interspecific variation was also small (22.76%); (2) the root diameter of 86% plant species was in the range from 0.073 mm to 0.094 mm. Compared with the thick-root species, thin-root species had a higher root branching intensity, but shorter lateral root length. In addition, at community-level, plants mainly increased root diameter and lateral root length, but reduced root branching intensity to adapt to the decreasing precipitation; while at species-level, the plant species exhibited diverse adaptive strategies along the precipitation gradient.

22个不同植物种间, 一级根直径与一级侧根长度呈显著正相关关系, 而分支强度与一级根直径呈显著负相关关系, 与一级侧根长度也呈显著负相关(表3), 即粗根植物物种具有较大的一级侧根长度, 较低的分支强度, 而细根植物物种则具有高分支强度和低一级侧根长度。但去除种系发生信号后, 仅直径与一级侧根长度仍具有显著正相关关系, 其他根系属性间的这种相关关系不再显著(表3)。

本研究表明在青藏高原草原群落区域尺度上, 不同物种间根直径变异较小, 而一级侧根长度和根系分支强度变异较大(表2); 并且根系直径较细的物种比直径较粗的物种具有更高的根系分支强度, 以及更短的侧根长度(图1), 而这种属性间的权衡可能是不同物种共存的重要机制之一(Kraft et al., 2015)。Li等(2017)在内蒙古温带草原的研究发现, 细根物种的根系往往能够入侵到粗根物种的根系空间中, 从而使得共存物种可以充分地占据土壤空间及利用有限的土壤资源。同样, 在温带森林及亚热带森林中也发现了木本细根物种与粗根物种间根系分支强度与侧根长度的权衡, 同时结合菌根的侵染, 发现了植物多样性的地下资源获取策略(Eissenstat et al., 2015; Liu et al., 2015)。这些研究与我们的结果说明, 根直径、侧根长度及根系分支强度间的相关关系是普遍存在于高寒草原、温带草原及温带和亚热带森林中的。另外, 我们发现, 在去除了谱系信号影响之后,根系直径和侧根长度的相关性依然紧密(表3), 这说明二者的关系受谱系信号的约束较小。这也可能与植物本身发育的共性有关, 如根系直径和侧根分生组织的比例在不同功能群的植物之间差异很小(Bystrova et al., 2018)。