EFFECTS OF ROOT DEFORMATION AND LIGHT AVAILABILITY ON GROWTH AND BIOMASS ALLOCATION OF Senna multijuga SEEDLINGS (Rich) H. S. Irwin & Barneby

ABSTRACT The effects of root deformation caused by errors in the pricking-out process in forest nurseries are still unknown for tropical tree seedlings. We analyzed the effects of light availability and root deformation on growth and biomass allocation in seedlings of Senna multijuga, a pioneer tropical tree commonly used in forest restoration programs. Our hypotheses were: (a) as a typical light-demanding species, the seedlings of S. multijuga may have their growth compromised by low light availability; (b) root deformation impairs growth rates and induces changes in biomass allocation; and (c) the effects of low light availability on growth and biomass allocation are increased by root deformation. Seedlings with and without root deformation were cultivated for 43 days under three levels of total daily photosynthetically active radiation (PAR) (28, 12, and 1 mol photons m-2 day-1). Seedlings of S. multijuga had their growth rates severely affected by values of PAR at about 1 mol photons m-2 day-1, but root deformation did not affect the relative growth rates of the whole plant. Instead, root deformation caused a decrease in the relative growth rate of roots in all light availabilities. The changes in root growth affected biomass allocation to the roots. The interactive effects of light availability and root deformation on the allocation of biomass to leaves are more pronounced at low light availability. Root deformations may lead to the production of seedlings with a low competitiveness capacity regardless of light conditions.

摘要 目前针对热带树木幼苗，森林苗圃分苗移栽工序中的操作误差所引发的根系畸形对其产生的影响仍不明确。本研究以常用于森林恢复工程的先锋热带树种多花决明（Senna multijuga）为研究对象，分析了光照可获得性与根系畸形对其幼苗生长及生物量分配的影响。我们提出如下研究假说：（a）作为典型的喜光物种，多花决明幼苗的生长可能因光照不足而受到抑制；（b）根系畸形会削弱植株生长速率并改变生物量分配模式；（c）根系畸形会加剧低光照对植株生长及生物量分配的负面影响。本研究将带有根系畸形与不带根系畸形的多花决明幼苗分别置于三个每日总光合有效辐射（Photosynthetically Active Radiation，PAR）水平（28、12和1 mol photons m⁻² day⁻¹）下培养43天。结果显示，多花决明幼苗的生长速率在每日PAR约为1 mol photons m⁻² day⁻¹时受到显著抑制，但根系畸形并未影响整株植物的相对生长速率。与之相反，在所有光照水平下，根系畸形均降低了幼苗根系的相对生长速率，进而改变了植株的生物量分配格局。光照可获得性与根系畸形对叶片生物量分配的交互效应在低光照条件下更为显著。本研究表明，无论光照条件如何，根系畸形均可能导致幼苗的竞争能力下降。