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.