Department of Environmental Science-Botany, University of Basel, Basel, Switzerland.
PLoS One. 2020 Feb 13;15(2):e0228993. doi: 10.1371/journal.pone.0228993. eCollection 2020.
Bioirrigation has been defined as the transfer of hydraulically lifted water by a deep-rooted plant to a neighbouring shallow-rooted plant which cannot access deep soil moisture. In this study, we tested if facilitative effects of bioirrigation or the competition for water dominate the interaction of two intercropped plants-deep-rooted pigeon pea (PP) and shallow-rooted finger millet (FM) before and during a drought. Additionally, we tested how the presence of a common mycorrhizal network (CMN) affects the balance between facilitative (i.e. bioirrigation) and competitive interactions between two intercropping species. Our results show that PP can indeed promote the water relations of FM during a drought event. Specifically, stomatal conductance in FM controls dropped to low values of 27.1 to 33.6 mmol m-2s-1, while FM in intercropping treatments were able to maintain its stomatal conductance at 60 mmol m-2s-1. In addition, the presence of PP reduced the drought-induced foliar damage and mortality of FM. The observed facilitative effects of PP on FM were partially enhanced by the presence of a CMN. In contrast to the facilitative effects under drought, PP exerted strong competitive effects on FM before the onset of drought. This hindered growth and biomass production of FM when intercropped with PP, an effect that was even enhanced in the presence of a CMN. The results from our study thus indicate that in intercropping, deep-rooted plants may act as "bioirrigators" for shallow-rooted crops and that a CMN can promote these facilitative effects. However, the interspecific competition between the intercropped plants under conditions of abundant moisture supply can be strong and are enhanced by the presence of a CMN. In more general terms, our study shows that the extent by which the antagonistic effects of facilitation and competition are expressed in an intercropping system strongly depends on the availability of resources, which in the case of the present study was water and the presence of biotic interactions (i.e. the presence of a CMN).
生物灌溉被定义为一种由深根系植物将水力提升的水传递给不能接触深层土壤水分的相邻浅根系植物的过程。在这项研究中，我们测试了在干旱之前和期间，生物灌溉的促进作用或对水的竞争是否主导两种间作植物（深根系羽扇豆（PP）和浅根系珍珠粟（FM））之间的相互作用。此外，我们还测试了常见菌根网络（CMN）的存在如何影响两种间作物种之间促进（即生物灌溉）和竞争相互作用之间的平衡。我们的结果表明，PP 确实可以在干旱事件中促进 FM 的水分关系。具体来说，FM 的气孔导度下降到 27.1 到 33.6 mmol m-2s-1 的低值，而间作处理中的 FM 能够将其气孔导度维持在 60 mmol m-2s-1。此外，PP 的存在减少了 FM 因干旱引起的叶片损伤和死亡率。PP 对 FM 的观察到的促进作用部分受到 CMN 的存在增强。与干旱下的促进作用相反，PP 在干旱发生之前对 FM 表现出强烈的竞争作用。当与 PP 间作时，这会阻碍 FM 的生长和生物量产生，而在 CMN 的存在下，这种作用甚至会增强。因此，我们的研究结果表明，在间作中，深根系植物可能成为浅根系作物的“生物灌溉者”，并且 CMN 可以促进这些促进作用。然而，在水分供应充足的条件下，间作植物之间的种间竞争可能很强，并且 CMN 的存在会增强这种竞争。更一般地说，我们的研究表明，促进和竞争的拮抗作用在间作系统中表达的程度强烈取决于资源的可利用性，就本研究而言，资源是水和生物相互作用（即 CMN 的存在）。
