Department of Ecology, College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193, China.
State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China.
Ecology. 2016 Sep;97(9):2283-2292. doi: 10.1002/ecy.1465.
Plants may affect the performance of neighboring plants either positively or negatively through interspecific and intraspecific interactions. Productivity of mixed-species systems is ultimately the net result of positive and negative interactions among the component species. Despite increasing knowledge of positive interactions occurring in mixed-species tree systems, relatively little is known about the mechanisms underlying such interactions. Based on data from 25-year-old experimental stands in situ and a series of controlled experiments, we test the hypothesis that a broadleaf, non-N fixing species, Michelia macclurei, facilitates the performance of an autotoxic conifer Chinese fir (Cunninghamia lanceolata) through belowground chemical interactions. Chinese fir roots released the allelochemical cyclic dipeptide (6-hydroxy-1,3-dimethyl-8-nonadecyl-[1,4]-diazocane- 2,5-diketone) into the soil environment, resulting in self-growth inhibition, and deterioration of soil microorganisms that improve P availability. However, when grown with M. macclurei the growth of Chinese fir was consistently enhanced. In particular, Chinese fir enhanced root growth and distribution in deep soil layers. When compared with monocultures of Chinese fir, the presence of M. macclurei reduced release and increased degradation of cyclic dipeptide in the soil, resulting in a shift from self-inhibition to chemical facilitation. This association also improved the soil microbial community by increasing arbuscular mycorrhizal fungi, and induced the production of Chinese fir roots. We conclude that interspecific interactions are less negative than intraspecific ones between non-N fixing broadleaf and autotoxic conifer species. The impacts are generated by reducing allelochemical levels, enhancing belowground mutualisms, improving soil properties, and changing root distributions as well as the net effects of all the processes within the soil. In particular, allelochemical context alters the consequences of the belowground ecological interactions with a novel mechanism: reduction of self-inhibition through reduced release and increased degradation of an autotoxic compound in the mixed-species plantations. Such a mechanism would be useful in reforestation programs undertaken to rehabilitate forest plantations that suffer from problems associated with autotoxicity.
植物可以通过种间和种内相互作用对邻近植物的表现产生积极或消极的影响。混种系统的生产力最终是组成物种之间正、负相互作用的净结果。尽管人们对混种树木系统中发生的正相互作用有了越来越多的了解，但对这些相互作用背后的机制却知之甚少。基于 25 年野外实验林和一系列控制实验的数据，我们检验了这样一个假设，即一种阔叶、非固氮物种 Michelia macclurei 通过地下化学相互作用促进了自毒针叶树杉木（Cunninghamia lanceolata）的生长。杉木根系将化感环状二肽（6-羟基-1,3-二甲基-8-正十九烷基-[1,4]-二氮杂环辛烷-2,5-二酮）释放到土壤环境中，导致自身生长抑制和改善磷有效性的土壤微生物恶化。然而，当与 M. macclurei 一起生长时，杉木的生长始终得到增强。特别是，杉木增强了深层土壤层的根系生长和分布。与杉木的单一种植相比，M. macclurei 的存在减少了环状二肽在土壤中的释放和增加了其降解，从而从自我抑制转变为化学促进。这种关联还通过增加丛枝菌根真菌来改善土壤微生物群落，并诱导杉木根系的产生。我们得出的结论是，非固氮阔叶树种和自毒针叶树种之间的种间相互作用比种内相互作用的负面影响更小。这些影响是通过降低化感物质水平、增强地下共生关系、改善土壤特性以及改变根系分布来产生的，同时还改变了土壤中所有过程的净效应。特别是，化感物质的作用改变了地下生态相互作用的后果，这是一种通过减少自毒化合物在混种植物中的释放和增加其降解来减少自我抑制的新机制。这种机制对于实施造林计划以恢复因自毒性而遭受问题的森林种植园可能会很有用。
