Data_Sheet_1_Response of a Pioneering Species (Leptospermum scoparium J.R.Forst. & G.Forst.) to Heterogeneity in a Low-Fertility Soil.PDF

Root foraging may increase plant nutrient acquisition at the cost of reducing the total volume of soil explored, thereby reducing the chance of the roots encountering additional patches. Patches in soil seldom contain just one nutrient: the patch may also have distinct textural, hydrological, and toxicological characteristics. We sought to determine the characteristics of root foraging by a pioneering species, Leptospermum scoparium, using pot trials and rhizobox experiments with patches of biosolids. The growth of L. scoparium was increased by <50 t/ha equiv. of biosolids but higher doses were inhibitory. Roots foraged patches of biosolids in a low-fertility soil. There was no evidence of chemotaxis, rather, the roots proliferated toward the patch of biosolids, following chemical gradients of nitrate. While the biosolids also contained high concentrations of other nutrients (P, K, and S), only significant chemical gradients of nitrate were found. Once the roots encountered a patch of biosolids, the growth of the plant increased to a level similar to plants growing in soil homogeneously mixed with biosolids or surface-applied biosolids. Our results indicate that roots forage nitrate, which is mobile in soil, and that gradients of nitrate may lead to patches containing other less mobile nutrients, such as phosphate or potassium.

根系觅食（root foraging）可在提升植物养分获取能力的同时，以缩减土壤总探查体积为代价，进而降低根系遇到额外养分斑块的概率。土壤中的养分斑块极少仅含单一养分：此类斑块往往还具备独特的质地、水文与毒理学特征。本研究旨在通过施加生物固体（biosolids）斑块的盆栽试验与根箱（rhizobox）试验，探究先锋物种细籽树（Leptospermum scoparium）的根系觅食特征。当生物固体施用量低于50吨/公顷当量时，细籽树的生长量得以提升，但更高剂量则会产生抑制作用。在低肥力土壤中，细籽树根系会主动觅食生物固体斑块。未发现根系存在趋化性（chemotaxis）现象，反而，根系会顺着硝酸盐的化学浓度梯度向生物固体斑块增殖生长。尽管生物固体中还含有高浓度的其他养分（P、K和S），但仅硝酸盐存在显著的化学浓度梯度。一旦根系接触到生物固体斑块，植株生长量便可提升至与土壤中均匀混施或地表施加生物固体的植株相当的水平。本研究结果表明，根系会主动探查在土壤中具有移动性的硝酸盐；而硝酸盐的浓度梯度，可能会引导根系接触到含有磷酸盐或钾素等移动性较弱养分的斑块。