Comments on abstract, title, references

This article brings a significant contribution to the understanding of the mechanisms governing P transfer into the grain in rice plants. The title and abstract are informative and relevant to the content of the article with a good description of the method used. The objectives are well defined and much of the references are recent including key studies.

Comments on introduction/background

The article is presenting sufficient introduction and background regarding the broad field of knowledge related to rice phosphorus nutrition particularly during the post-anthesis period. However, the introduction could be improved by providing more specific information on the physiological processes (eg: P availability, senescence etc.) driving P loading into grain.

Comments on methodology

The methodology used in Julia et al. 2016 are well explained. The data collected are tested in both field and in the laboratory. The P-tracer study provided interesting insight into P fluxes throughout rice grain filling. However, the statistics and calculation related to P-tracer needs to be described better in the materials and methods and included in all figures.

Comments on data and results

In general the reported data are complete and easy to read and comprehend. All the results are briefly mentioned in the article

Comments on discussion and conclusions

The discussion is well written and the conclusions are supported by the presented data. The authors present a model to describe P loading into grains which serve as a nice conclusion.