Trait-Based Root Phenotyping as a Necessary Tool for Crop Selection and Improvement

Round 1

Reviewer 1 Report

You need to correct your references most of them are incorrectly numbered within the text, so this made it hard to follow the paper.

What is meant by this sentence, can you reword to make your point clearer: “The pairing of a larger leaf area and decreased root length as a result of nutrient stress does not bode well for plants without stress. Plants not under nutrient stress may have increased leaf area and a longer root system.”

There is a mix up with the Lynch (2) reference in the bibliography, it doesn’t have its own line.

Line254-255: cores are 3D, I am not sure how you can call them a 2D method?

Line274 – I would argue there are not “several” methods for non-destructive root imaging. I would also argue that they make even take more “time and resources” compared to field excavation. 

Rhizotrons should not be classed as non-destructive imaging. Line278 – what you have written about here are typically known as “minirhizotrons”

L284 – “offers the best assessment of roots in situ” what is your opinion based on? I find them very destructive, you only really get a 2D view, the roots have been forced to grow up against an artificial surface, there can be a fake pore space around the tube, soil can smear the tube and cause difficulties in growing. I am not aware of an automated software that can easily track and quantify the roots from the images....

L300 X in X-ray should be capitalised. X-ray CT is not only used for plants grown in the lab or glasshouse there have been several papers published that show scans of field structured soils. It is also computed and not computer tomography.

L339 reference 72 relates to EC and not X-ray, why is it cited here?

L340 reference 79 is from 2015 and not related to X-ray CT

Reference 69 is not related to X-ray CT but EC

L346 “Containers may have to be placed horizontally for large plants to be imaged” this is simply not true. Nikon and GE machines can accommodate very large samples vertically. You may be thinking of medical CT where the body would lie flat.

L365 – Roots do not typically penetrate agar, but grow on the surface of agar. Agar again does not really have pore space, if petri dishes are filled. Again these statements are not necessary as they are not relevant to the majority of agar root experiments.

L374: “ a superior method for measurements of RSA” ?? but it is a 2D method without the use of soil? If we want to discover how plant roots grow in the field, I am not sure agar can be classed as superior? What benefit anyway is there to rank RSA methods? As each experimental objective would be different. 

L398 Reference 81 is not the Wells paper.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Great review! I think it would be stronger if you thought about phenotypic plasticity as a response to nutrient stress. It is well documented that abiotic stress changes RSA, anatomy, and physiological responses of the plant in many genotypes. Genotypes vary in their capacity to express phenotypic responses to the environment and therefore could be an important trait in itself.

Line 138: It is not clear to me why roots with smaller diameters are indicative of topsoil foraging or beneficial for nutrient capture in the top soil. The phrase “smaller angles” is also confusing here. People measure root angle in many different ways, it would be better to say more shallow angles.

Line 141: Here you are describing a scenario of terminal drought where the water is located deeper in the soil profile as the season progresses. However, there are many different drought scenarios, perhaps in a drought scenario with intermittent rainfall, plants with enhanced topsoil foraging would be beneficial. Be clear on the drought scenario.

Line 147: “few laterals with abundant lateral branching”. It is unclear what you are trying to say here. Do you mean lateral root length and lateral branching density?

Line 163: Be careful here. I think many of the studies cited for root traits were from seedlings in controlled environments and yield was from mature plants in the field-it is hard to make that comparison. There are many studies demonstrating mature plants grown in the field have relatively low root architectural and anatomical trait heritabilities (e.g. Schneider et al 2020). I now see that this was briefly mentioned later in the paragraph, but it would be good to mention these ideas together

Figure 1. Are all of these your original images? If not, please cite where they are used or modified from.

Author Response

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Author Response File: Author Response.docx