Intra‐specific kin recognition contributes to inter‐specific allelopathy: A case study of allelopathic rice interference with paddy weeds

Abstract

Summary Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter‐specific and intra‐specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non‐kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non‐kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly.

Kin Recognition in Plants: Did We Learn Anything From Roots?

“…Production of allelopathic compounds has been well documented in many plant species, including rice. Xu et al (2021) recently investigated the influence of kin interactions on the allelopathic interactions between Oryza sativa and various species of paddy weeds. The study found that plants grown with close relatives shifted their resource allocation to increased growth of intrusive roots toward weeds and decreased their production of allelochemicals.…”

Kin discrimination in allelopathy and consequences for agriculture

“…However, this raises the question why the highest allelopathic activities were found in plants interacting with neighbours of the same cultivar (i.e., the treatment with the greatest degree of neighbour relatedness).Recent research has shown for wheat that plants may produce allelochemicals in response to exudates produced by neighbours, particularly loliolide and jasmonic acid (Kong et al, 2018). It is possible that such signalling also occurs in rice and that it differs between cultivars, independently of relatedness, and that the two focal cultivars in Xu et al (2021) may have happened to be active producers of such signalling compounds. Clearly, more research is needed to better understand the possible connection between kin recognition and allopathy.…”

“…This variation in definition makes it difficult to compare results across studies, and could explain some of the discrepancies between different studies. Moreover, most studies on kin discrimination simply compare trait values and performance between discrete kin-and non-kin groups, often without actually quantifying the level of genetic relatedness (but see Karban, Shiojiri, Ishizaki, Wetzel, &Evans, 2013 andXu et al, 2021 as notable exception). As kinship describes the extent of genetic similarity between individuals, it is rather arbitrary to categorise this relationship.…”

“…In crops allelopathy can also be beneficial in suppressing weeds (Macías, Mejías, & Molinillo, 2019). In the current issue, Xu, Cheng, Kong, and Meiners (2021) published the first study to show that kin discrimination can also affect the balance between direct competition for resources and allelopathy, and this together may lead to improved weed suppression in rice.Kin discrimination in allelopathy and consequences for agriculture.…”

Effects of indirect plant–plant interaction via root exudate on growth and leaf chemical contents in Rumex obtusifolius

“…Plant–plant interactions are an important part of terrestrial ecosystems because they affect not only the outcome of competition between plants, 1 , 2 but also functional leaf traits, 3–7 hervibory, 8 , 9 and herbivore distributions. 9 In a previous study, we experimented with Rumex obtusifolius (Polygonaceae) to examine the effects of intraspecific, interspecific, and no belowground direct interactions on leaf chemical content and herbivore distribution.…”