Small-scale processes, large effect: rhizosphere traits as key for P efficiency in upland rice

• Applicant: Dr. Maire Holz, Ph.D.
• Subject Area: Soil Sciences
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430055652

Rice is staple food for more than half of the earth’s population. Particularly in upland systems its growth is frequently challenged by low P availability due to high P-fixing soils and the lack of P fertilizers. Consequently, understanding which processes confer high P acquisition efficiency (PAE) is crucial to sustain crop yields in low-input systems. Previous work showed that contrasting PAE in upland rice lines can neither be explained by root morphological parameters (root system size, root hairs) nor by root physiology (P depletion efficiency). We therefore suggest that biogeochemical processes induced at the root-soil interface, i.e. the rhizosphere, play an important role in rice PAE. In this project, we aim to elucidate the role and interplay of biogeochemical processes in the rhizosphere of four rice genotypes with contrasting PAE and root hair properties (Oryza sativa DJ123 - high PAE, high root hair length and density (RLD); Nerica4 - low PAE, low RLD, Santhi Sufaid - high PAE, low RLD, Sadri Tor Misri - low PAE, high RLD). We hypothesize that high PAE is driven either by (i) high root exudation rates per root surface, (ii) high release of compounds such as phenolics, phosphatases and mucilage which are suggested to play a role in P mobilization (iii) a rhizosphere microbiome composition favoring high abundances of P solubilizing and plant growth promoting microorganisms or by (iv) a high degree of mycorrhization. In collaboration with plant geneticist Matthias Wissuwa (JIRCAS), we will investigate root exudation, the degree of genotype-specific mycorrhization as well as the rhizosphere microbial community composition of the selected rice lines under low and high P conditions in a field trial typical for upland growth conditions in Tsukuba, Japan. In a second step, we will thoroughly investigate the P solubilization capacity of genotype specific root exudates collected from the field trial in batch experiments to conclude whether differences in root exudate composition between the genotypes can explain differences in P acquisition efficiency. Focusing on the spatio-temporal interplay of P acquisition and related biogeochemical processes we will also apply various rhizosphere imaging approaches (phosphor imaging, zymography, planar optode measurements) as well as 33P labelling in laboratory trials under controlled conditions. Combining imaging and isotopic labelling techniques will allow us not only to correlate root types and regions showing increased root exudation and enzyme activity with those regions where P is taken up but also to quantify the contribution of mycorrhiza to P uptake. Taken together our results will elucidate which rhizosphere processes confer high P acquisition efficiency in upland rice. This will enable the transfer of rhizosphere traits to breeding programs of upland rice lines and improve selection of crops with highly efficient P acquisition to sustain yields in low-input agricultural systems.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partner: Dr. Eva Oburger