3.3 Impact of kin recognition on weed-induced rice allelochemical production
Weed inhibition of allelopathic rice cultivars mainly results from rice allelochemicals. Furthermore, the presence of paddy weeds can induce the production of rice allelochemicals (Kato-Noguchi, 2011; Kong, Li, Hu, Xu, & Wang, 2006; Li, Zhao, & Kong, 2020). In experiment 2, when allelopathic rice cultivars were grown in the presence of paddy weeds, the weed-induced rice allelochemical (tricin and momilactone B) production was lowered in cultivar mixtures. In particular, the mixture with closely related cultivars always led to a greater reduction in the production of allelochemicals regardless of the presence of the dominant weed barnyardgrass (Echinochloa crusgalli ) or its mixtures with other paddy weeds (Figure 5). Though mixtures with closely related cultivars significantly reduced the production of rice allelochemicals, weed inhibition were increased (Supplementary Figure 5) and rice grain biomass were not significantly altered (Supplementary Figure 6). These results revealed that kin recognition within the rice cultivar mixtures could lower allelochemical defense cost but increase or maintain weed inhibition and rice grain biomass.
3.4 Soil microbialcharacteristics of rice cultivar mixture with barnyardgrass
The alteration of root placement patterns and allelochemical production by rice cultivars impacted soil microbial characteristics. In experiment 3, when allelopathic rice cultivars and their mixtures with kin and non-kin cultivars were grown in the presence of barnyardgrass, there were changes in soil microbial characteristics. PLFA profiling showed that the signature of lipid biomarkers of bacteria, fungi and actinomycetes were affected by the genetic relatedness of rice cultivar mixtures (Supplementary Figure 7). The relative abundances of bacterial PLFA (16:0) were significantly greater in the soil of allelopathic cultivars grown with closely related cultivars than distantly related cultivars. By contrast, PLFA (18:1ω7c) and PLFAs (10Me17:0, 10Me18:0) respectively belonging to fungi and actinomycetes, were reduced in the soil of allelopathic cultivars grown with closely related cultivars than distantly related cultivars (Supplementary Figure 7). PCA scores for the PLFA extracted from samples were clearly distinguished by the genetic relatedness of rice cultivar mixtures. The composition of soil microbial groups of allelopathic cultivars grown alone was similar when mixed with closely related cultivars and differed greatly from those mixed with distantly related cultivars. The first two principal components of PFLA composition together accounted for 77.12% (Huagan-3) and 68.97% (Lingyou-6173) of the variation in the sets of indica-inbred and indica-hybrid genotypes, respectively (Figure 6). The results indicated that the genetic relatedness of rice cultivar mixtures also determined soil microbial characteristics.
3.5 Role of allantoin in inhibition andresourcepartitioning of barnyardgrass with rice cultivar mixtures
In experiment 4, with or without application of a N-fertilizer NH4NO3, allelopathic rice cultivars and their mixtures with closely related cultivars inhibited the growth of barnyardgrass to a greater extent than the mixtures with distantly related cultivars. However, the inhibition was not observed when the nitrogen-rich compound allantoin was applied (Figure 7). Furthermore, there were different changes in carbon and nitrogen partitioning in barnyardgrass under application of NH4NO3 and allantoin. Relative to monocultures, barnyardgrass grown with rice had increased root carbon and nitrogen. In particular, kin cultivar mixtures had a higher root/shoot carbon and nitrogen ratios of barnyardgrass than non-kin cultivar mixtures. Compared with control (without N), NH4NO3 induced carbon and nitrogen partitioning of barnyardgrass from shoot into roots. However, the carbon and nitrogen partitioning were not altered by allantoin (Figure 8). The results indicated that allantoin did not served as a N-fertilizer for the inhibition and resource partitioning of barnyardgrass by rice cultivar mixtures.