|Review of « Water movement through plant roots : Exact solutions of the water flow equation in roots with linear or exponential piecewise hydraulic properties » by Meunier et al., 2017, 2nd revision|
Submitted to HESS, N° hess-2016-633
I thank the authors for this revision of their initial manuscript where they accounted for most of my preceding comments. The incorporation of pressure probe derived root hydraulic conductance data is to me a very interesting added value to the paper, as is the simulation example coupling soil transfer – root uptake. Overall, this results in a very interesting, but “dense”, paper. To me, some minor revisions are required throughout the paper, but particularly in the new sections concerning pressure probe data inversion and root uptake in soil.
About root pressure probe data and inversion, it would be necessary to fix some scenarios (ie ~3) and explain them and their assumptions (ie why these conductance variations’ scenarios) to make the study easier to read. Presently, Figure 9 is not really understandable and is not coherent with text description (non-coherent lines colors..). What is a missing result from of this study is the fact that different solutions are possible for root radial conductance variations, even when axial conductance variation is known. This shows that more knowledge/measurement on local variations of root conductance is needed.
Concerning the root in soil water uptake simulations (sections 3.3 – 4.3), there is a need to present/recap how is calculated the soil root water potential, as well as the soil water transfer. Why you choosed this scenario (i.e including growth in your case) needs to be also better explained and shall be recalled in interpreting results of section 4.3, with regards to this scenario. Surprising results are found in Fig. 10, where water potential (at collar, but soil too) increases with time for the heterogeneous root case : this is unexpected, but may be false ? (check alos the inversion between psi_collar and psi_seq in Fig 10 – see annotated paper).
The new, added part, final part of the conclusion is unclear for me. It could be stated more simply. Finally the “root conductance” expression is not really precise, as we don’t know exactly which conductance it refers to (cf line 4, p22 for example). I would suggest that when author refer to Krs (and not kr or kx) they could call it “effective root conductance” because Krs is indeed an effective macroscopic property emerging from geometry and kx, kr variations.
See annotated pdf which recap both typos/grammar and questions.