Plant neighbor detection and response strategies are important mediators of interactions among species. Despite increasing knowledge of neighbor detection and response involving plant volatiles, less is known about how soil-borne signaling chemicals may act belowground in plant–plant interactions. Here, we experimentally demonstrate neighbor detection and allelopathic responses between wheat and 100 other plant species via belowground signaling. Wheat can detect both conspecific and heterospecific neighbors and responds by increasing allelochemical production. Furthermore, we show that (-)-loliolide and jasmonic acid are present in root exudates from a diverse range of species and are able to trigger allelochemical production in wheat. These findings suggest that root-secreted (-)-loliolide and jasmonic acid are involved in plant neighbor detection and allelochemical response and may be widespread mediators of belowground plant-plant interactions.

Highlights 15 • Sexual differences in P acquisition are affected by soil P level and distribution. 16 • P. cathayana females benefit more from high P level and heterogeneous distribution. 17• Males are favored more by low P availability due to their compensatory strategies.Abstract Soil phosphorus (P) availability and its distribution influence plant growth 23 and productivity, but how they affect the growth dynamics and sex-specific P 24 acquisition strategies of dioecious plant species is poorly understood. In this study, the 25 effects of soil P availability and its distribution on dioecious Populus cathayana Rehd. 26 were characterized. P. cathayana males and females were grown under three levels of 27 phosphorus (P) supply, and with homogeneous or heterogeneous P distribution. 28Females had a greater total root length, specific root length (SPL), biomass and foliar 29 P concentration. Under P deficiency, males had a smaller root system than females but 30 a greater exudation of soil acid phosphatase, and a higher colonization rate and 31 arbuscular mycorrhizal hyphal biomass, suggesting a better capacity to mine P and a 32 stronger association with arbuscular mycorrhizal fungi to forage P. Heterogeneous P 33 availability enhanced growth and root length density in females. Female root 34 proliferation in P-rich patches was associated with increased foliar P assimilation. 35Increased P availability by localized P application did not enhance the biomass 36 accumulation and the morphological plasticity of roots in males, but increased hyphal 37 biomass. Our results suggest that P. cathayana displays sexually different P acquisition 38 strategies, which explain the performance of females and males under variable soil P 39 environments. 40

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.

Through root-secreted chemical signals, allelopathic wheat can detect competing weeds and respond by increased allelochemical levels to inhibit them, providing an advantage for its own growth. Allelopathy and allelobiosis are two probably inseparable processes that occur together in wheat-weed chemical interactions. © 2016 Society of Chemical Industry.

The action of allelochemicals in soil needs their presence in the vicinity of the target plants. Using a soil TLC combined with bioassay approach, the mobility of 10 typical allelochemicals was evaluated. Ferulic, p-hydroxymandelic, p-hydroxybenzoic, and vanillic acids always had the lowest mobility (Rf < 0.1), whereas phenolic aldehyde and lactone (vanillin and coumarin) showed the highest mobility (Rf > 0.5). The Rf values of daidzein, 1α-angeloyloxycarotol, DIMBOA, and m-tyrosine ranged from 0.24 to 0.32. Binary mixtures of these allelochemicals led to an increase in mobility factors for selected combinations. Phospholipid fatty acid profiling indicated that there were different soil microbial communities in the segments containing allelochemicals residues in the developed TLC soil layer. A difference in microbial community structure occurred between two nitrogenous DIMBOA and m-tyrosine and another eight allelochemicals. The results suggest that the soil activity of allelochemicals on bioassay species and microbial communities depends on their mobility in soil.