A broadleaf species enhances an autotoxic conifers growth through belowground chemical interactions

Abstract

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.

Interference of allelopathic rice with paddy weeds at the root level

“…The performance of plants in a mixed species system heavily depends on belowground ecological interactions, where allelochemicals can alter belowground ecological interactions, inhibit root growth of competing and shape the soil microbial community, and thus subsequently affect the performance of the plants themselves and of co‐occurring plants (Xia et al . ). Through the release of allelochemicals, allelopathic rice cultivars induce specific changes in soil microbial communities that provide an advantage for their own growth (Sun et al .…”

“…; Belter & Cahill ; Xia et al . ). In particular, plants are capable of recognising and responding to neighbouring roots, altering their growth and behaviour, resulting in three root placement patterns: spatial segregation of neighbouring root systems (avoidance pattern), over‐proliferation of roots in the area of root interactions (intrusive pattern) and no response (unresponsive pattern) as a consequence of different types of interaction between roots (Semchenko et al .…”

Interference of allelopathic rice with penoxsulam‐resistant barnyardgrass

“…The impact of root interactions on interspecific competition among plants is well‐known . A great deal of attention has recently been paid to the species‐specific effects of allelochemicals on root interactions in mixed‐species systems . In particular, the sensitivity of roots to other roots may be mediated by the roots' own allelochemicals .…”

“…A great deal of attention has recently been paid to the species‐specific effects of allelochemicals on root interactions in mixed‐species systems . In particular, the sensitivity of roots to other roots may be mediated by the roots' own allelochemicals . Furthermore, roots may be capable of detecting neighboring roots and responding them by root‐secreted allelochemicals and non‐toxic signals .…”

Soil nutrients dynamics in broadleaved forest and chinese fir plantations in subtropical forests

“…This difference was due to more biomass accumulating in the soil from the understorey vegetation and broadleaved litter, which was also suggested by Chen et al (2004) and Wan et al (2013). Cultivation of selected broadleaved species reduces alleo-chemicals levels (Xia et al 2016). Thus, the presence of broadleaved stands within Chinese fir monoculture could help improve soil properties and enhance wood production.…”