Applying vegetation science concepts to crops: how more diverse rice can lead to better productivity

“Trait diversity across rice varieties increases complementarity effects and productivity”

This research originally stems from the ideas of kin recognition, niche theory, and allelopathy. Kin recognition and niche theory are antagonistic in their premises, but both could have an agriculturally relevant effect. In the case of cooperation with the relatives, the monocultures of the same variety would give higher seed yield, as the kin recognition theory predicts fitness gains from interactions with relatives. On the other hand, the ecological niche theory predicts that mixtures would have a higher yield than monocultures because the individuals are more genetically different and their niche requirements are different as well. In total this would allow them to use a wider range of available resources.
How would this complementary resource use interact with weeds? Do different plants fill niche space more evenly, resulting in stronger weed suppression? Or could similar individuals recognizing each other as kin better resist invasion when cooperating with each other? Could mixing allelopathic varieties with non-allelopathic indirectly still benefit the rice variety that doesn’t have the ability to chemically suppress weeds?
To jump ahead – none of our chosen six varieties proved allelopathic, and the common weed of the rice fields Echinochloa crus-galli proved to be the most competitively effective plant species I have ever grown in an experiment, reaching nearly double the height and ten times the biomass of the neighboring rice plant – so, in the end, we couldn’t say much about which kinds of rice combinations suppress weeds better.

But not all the rice varieties and combinations were equally the same in their response to growing together with competitors. Functional diversification could still be a sustainable approach to managing modern cultivars, even if they are competitively inferior to weeds. Our research shows that mixing varieties resulted in higher aboveground biomass for most varieties compared to monocultures, although in seed production the effect didn’t differ from 0. Varieties differ from each other in their functional traits, and although the main focus is always on yield maximization, they have different strategies with leaves and roots for resource uptake and on how to convert these resources to grains. We found that the complementarity was the driver of the positive net diversity effect in mixtures and this was caused by dissimilarity in the leaves (root traits not yet analyzed). Weed suppression didn’t depend on any trait that we measured, but there is still a future prospective for allelopathic rice.

Echinochloa crus-galli is overgrowing the rice on a field in Italy (this is the first rice field I ever visited)

My own rice story started in the year 2019 when I was in Italy doing postdoctoral research on a completely unrelated topic of plant-inspired biorobotics. The project to study plant-plant interactions and niche partitioning was already accepted, but I hadn’t chosen the proper study species yet. As rice seeds are easier to count than the seeds of Arabidopsis and it has clear agricultural value I eventually switched to using rice as model species in 2020. And I endure the paella jokes from my Spanish colleagues ever since 😊

Here’s the list of my publications so far: Google Scholar

Modern short rice variety (left) and pre-Green Revolution old tall variety (right)

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