Integrated root phenotypes for improved rice performance under low nitrogen availability

Abstract

Greater nitrogen efficiency would substantially reduce the economic, energy and environmental costs of rice production. We hypothesized that synergistic balancing of the costs and benefits for soil exploration among root architectural phenes is beneficial under suboptimal nitrogen availability. An enhanced implementation of the functional-structural model OpenSimRoot for rice integrated with the ORYZA_v3 crop model was used to evaluate the utility of combinations of root architectural phenes, namely nodal root angle, the proportion of smaller diameter nodal roots, nodal root number; and L-type and S-type lateral branching densities, for plant growth under low nitrogen. Multiple integrated root phenotypes were identified with greater shoot biomass under low nitrogen than the reference cultivar IR64. The superiority of these phenotypes was due to synergism among root phenes rather than the expected additive effects of phene states. Representative optimal phenotypes were predicted to have up to 80% greater grain yield with low N supply in the rainfed dry direct-seeded agroecosystem over future weather conditions, compared to IR64. These phenotypes merit consideration as root ideotypes for breeding rice cultivars with improved yield under rainfed dry direct-seeded conditions with limited nitrogen availability. The importance of phene synergism for the performance of integrated phenotypes has implications for crop breeding.

Aus rice root architecture variation contributing to grain yield under drought suggests a key role of nodal root diameter class

“…More research is necessary to characterize rice nodal root types and their function. Although our study suggests a positive relationship between the proportion of the total number of nodal roots classified as 'large‐diameter' and grain yield (via RDW 15–30 cm in the phenotypic correlations and directly by GWAS colocations), this is in contrast to recent results from simulation modelling of rice roots which concluded that a larger proportion of 'small‐diameter' nodal roots was beneficial to plant growth and yield under low‐nitrogen, rainfed direct‐seeded conditions (Ajmera et al, In Press). Therefore, the function of various nodal root class distributions may differ depending on the soil conditions and should be further investigated.…”

Root phenotypes for the future

“…Root traits can help improve the efficient capture of nutrients like nitrate which is highly mobile in soils. In this issue, combining models for root architecture and for crop performance, Ajmera et al (2022) identified synergistic effect of several root phenes in rice that were linked to better performance under low nitrogen supply. Wacker et al (2022) report how deeper rooting winter wheat varieties exhibit reduced nitrate (N) leaching losses and increase N uptake.…”

RootSlice– a novel functional-structural model for root anatomical phenotypes

“…The actual response greater than, equal to, and less than the expected response respectively corresponds to the synergistic, additive, and antagonistic relationship between the number of cortical cell files and the proportion of aerenchyma formation. More details on this can be found (Ajmera et al, 2022; Ma et al ., 2001).…”

“…Exploring the impact of root anatomical phenotypes on soil resource capture is important for informing the development of resource-efficient crop varieties. However, the utility of a phene state depends on the environment as well as interactions with other phene states in integrated phenotypes (Ajmera et al ., 2022; Klein et al ., 2020; Rangarajan et al ., 2018). The number of potential combinations involving multiple phene states over multiple environments exceeds the capabilities of empirical research (Rangarajan et al ., 2022).…”