Assessment of the Type of Deficit Irrigation Applied during Berry Development in ‘Crimson Seedless’ Table Grapes

Round 1

Reviewer 1 Report

Why 110% of crop evapotranspiration (ET_c) rather than 100% ET_c（sufficient  irrigation）was used in the study? Will the excess water affect conclusion?

 In line 110-111. Is water stress occurring under PRD treatment(also other treatment as described in line 113)  if 75% field capacity is used as the threshold criteria in dry root-zone?

  How the water volume measured and applied was not clearly described in the 2.2 irrigation treatment and should be added in order to be well understood.

For example : Regarding goal of the paper in line 80, “RDI and PRD that received the same irrigation volume”, but they received different amount(as shown in Fig 1), such as 65% and 65% reduction for SDI and SPRD.  What caused the difference of water between SDI and SPRD as well as between RDI and PRD?

     Line 296-297 Intrinsic water use efficiency (Pn/gs) was not correctly calculated. It should be defined as the ratio of  Pn/T, T is the transpiration rate rather than Gs . The results and conclusion in Fig 5 should checked

Lin 468-489  the conclusion of  “The higher stomatal closure observed (Figure 4B) was sufficient to ensure the root water uptake and thus, the supply of the water and carbohydrates needed for berry development” seems unreasonable. As well as deficit can as increase cluster transpiration rates in line 465.

SDI and SPRD deceased Pn significantly as shown in Fig 5. while yield increased. Reasons for it should be discussed .

Author Response

#REVIEWER 1

Why 110% of crop evapotranspiration (ETc) rather than 100% ETc（sufficient  irrigation）was used in the study? Will the excess water affect conclusion?

The irrigation scheduling was based on crop evapotranspiration values ETc through the product of ET₀ (Allen et al., 1998) × k_c (Williams and Ayars, 2005).

The climatic data for calculating ET₀ were recorded by an automatic weather station of the Servicio de Información Agraria de Murcia, located 8.5 km from the experimental plot (CIA-42, www.siam.es).

Furthermore, for the irrigation scheduling of ETc, the climatic data used corresponded with the previous week. For this reason, the percentage of ETc was increased to 110% in order to satisfy the crop water needs during the summer hot and dry days that might be carried out and thus it would affect the CTL treatment.  

Anyway, this fact do not affect the conclusions, because the CTL treatment was irrigated as 110% ETc, and the irrigation deficit treatment (RDI, SDI, PRD, SPRD) were applied to respect with the CTL.   

For a better understating, the following text has been added accordingly.

Lines 119-125: Crop evapotranspiration (ETc = ET₀ x kc) was estimated using crop coefficients (kc) based on Williams and Ayars (2005) varying from 0.2 to 0.8 according to the phenological stage, whereas reference crop evapotranspiration (ET₀) was calculated with the Penman Montheith-FAO method (Allen et al., 1998), with daily climatic data recorded by an automatic weather station of the Servicio de Información Agraria de Murcia, located 8.5 km from the experimental plot (CIA-42, www.siam.es). Climatic data was computed as an average of the 7 previous days.

References:

• Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper No 56. Rome, Italy. pp. 15–27.
• Williams, L.E., Ayars, J.E., 2005. Grapevine water use and the crop coefficient are linear functions of the shaded area measured beneath the canopy. Agric. For. Meteorol. 132, 201–211.

In line 110-111. Is water stress occurring under PRD treatment (also other treatment as described in line 113)  if 75% field capacity is used as the threshold criteria in dry root-zone?

PRD involves the deliberate wetting and drying of alternate sites of the root zone so that the production of specific root-sourced chemical signals will be optimised inducing partial stomatal closure and thereby increasing water use efficiency/ABA. The management of the PRD (regulated) and SPRD (sustained) follows the protocol to alternate the irrigation of the dry side every 10-14 days as reported in others manuscripts of grapevines i.e: Stoll, 2000; Chaves et al. 2010. The part of the sentence ‘when the dry side of the root zone reaches 75% of field capacity’ is an informative data.

The findings obtained in the physiological behaviour showed in Fig. 5 indicate that the water uptake in PRD treatment was enough to compensate the water deficit suffered in the dry side.

More information can be found in Conesa et al. 2018 https://doi.org/10.1016/j.agwat.2018.06.019

References:

• Stoll, M., Loveys, B.R., and Dry, P. 2000. Hormonal changes induced by partial rootzone drying of irrigated grapevine. Journal of Experimental Botany, 51: 1627–1634.
• Chaves, M.M., Zarrouk, O., Francisco, R., Costa, J.M., Santos, T., Regalado, A.P., Rodrigues, M.L. and Lopes, C.M. (2010). Grapevine under deficit irrigation – hints from physiological and molecular data. Annals of Botany, 105: 661–676.

How the water volume measured and applied was not clearly described in the 2.2 irrigation treatment and should be added in order to be well understood.

Ok. The text has been changed accordingly.

Line117-119: The volume of water applied in each irrigation treatment was measured by in-line water meters with digital output pulses by installing one per replication (n = 4 per treatment).

For example : Regarding goal of the paper in line 80, “RDI and PRD that received the same irrigation volume”, but they received different amount(as shown in Fig 1), such as 65% and 65% reduction for SDI and SPRD.  What caused the difference of water between SDI and SPRD as well as between RDI and PRD?

L19-20. “RDI and PRD received 24% and 28% less water than CTL, respectively. These reductions were higher in SDI and SPRD (65% and 53%, respectively).”

L80. “the main goal of this work was to compare RDI and PRD that received the same irri-gation volume but with the difference of the period of deficit’s application”

We agree with the reviewer. The main objective of the manuscript is not only to compare the DI treatments by regulated and sustained applications, but also to assess the effects of these DI treatments in a short term, under a situation of low water supply (as occurred in the Mediterranean region) in order to give to the farmer a guidelines of how to proceed with similar experimental conditions. 

The slight difference for the total irrigation amount received in the SDI and SPRD treatments is associated to the management of SPRD during the whole berry growth – by alternating the dry side every 10-14 days when the dry side of the root zone reaches 75% of FC–.

For a better understanding of the text, the objective has been rewritten as follow:

Lines 80-88: In this sense, the main goal of this work was to compare the effects of the DI treatments that were applied: (i) regulated way: at post-veraison and, (ii) sustained way: during the whole berry growth, with a different field experimental design based on one single-line of emitters (RDI management) and two-line of emitters (PRD management). All DI treatments were compared with a Control treatment that received the full vine water needs throughout the irrigation season. Furthermore, the findings established guidelines for table grapes’ farmers of how proceeding with similar Mediterranean experimental conditions.

Line 296-297 Intrinsic water use efficiency (Pn/gs) was not correctly calculated. It should be defined as the ratio of Pn/T, T is the transpiration rate rather than Gs . The results and conclusion in Fig 5 should checked

In our manuscript, intrinsic water use efficiency as the ratio Pn/gs is right calculated (Medrano et al. 2015 for grapevines).

From gas exchange parameters, intrinsic and instantaneous water use efficiency can be obtained as follows:

• Instantaneous water use efficiency Pn/E (μmol CO2/mol H2O): CO₂ assimilation/transpiration
• Intrinsic water use efficiency (Pn/g, μmol CO₂/mol H₂O): CO₂ assimilation/stomatal conductance.

The fundamental difference between both is that the instantaneous water use efficiency (Pn/E) is more influenced by environmental conditions, since E depends on the degree of stomatal opening and the vapor pressure deficit (VPD) of the atmosphere surrounding the leaf (Bierhuizen et al. 1965, Medrano et al. 2002, 2015), whereas Pn/g_s excludes the effects of changing evaporative demand on water flux out of the leaf, and depends only on the stomatal opening being then, independent of the atmospheric conditions at the time of measurement (Jarvis et al. 1986).

In our manuscript, considering that the measured conditions were the same for the all irrigated treatments it is good to work with the intrinsic water use efficiency (Pn/gs) in order to ascertain significant differences among the irrigation treatments.  

References:

• Bierhuizen, J. F.; Slatyer, R. O. Effect of atmospheric concentration of water vapour and CO₂ in determining transpiration - photosynthesis relationships of cotton leaves. Meterol. Elsevier BV. 1965, 2(4), 259–270.
• Jarvis, P. G.; McNaughton, K.G. Stomatal control of transpiration: Scaling up from leaf to region. Ecol. Res. 1986, 15, 1– 49. https://doi.org/10.1016/s0065-2504(08)60119-1 
• Medrano H.; Escalona J.; Bota J.; Gulias J.; Flexas J. Regulation of photosynthesis of C-3 plants in response to progressive drought: stomatal conductance as a reference parameter. Bot. 2002, 89, 895–905. https://doi.org/10.1093/aob/mcf079 
• Medrano H.; Tomás M.; Martorell S.; Escalona J.; Pou A.; Fuentes S. Improving water use efficiency of vineyards in semi-arid regions. A review. Sustain. Dev. 2015, 35, 499–517. https://doi.org/10.1007/s13593-014-0280-z 

Lin 468-489 the conclusion of “The higher stomatal control observed (Figure 4B) was sufficient to ensure the root water uptake and thus, the supply of the water and carbohydrates needed for berry development” seems unreasonable. As well as deficit can as increase cluster transpiration rates in line 465.

We agree with the reviewer. In the sentence, the term of -stomatal closure- was not ok. This has been changed by -stomatal control-, that promoted a higher leaf intrinsic water use efficiency Pn/gs. The sentence has been modified accordingly.

SDI and SPRD deceased Pn significantly as shown in Fig 5. while yield increased. Reasons for it should be discussed.

Ok. The discussion has been rewritten in this regard.

Lines 491-504: Generally, gs decreases with an increase in water deficit, beings more sensitive than Pn (Figure 5). As a result, intrinsic water use efficiency (Pn/gs) usually increases under moderate water stress conditions while ensure the crop productivity [35,36]. Nevertheless, our results showed that despite the fact the Pn and gs in the SDI and SPRD treatments significantly decreased, the total yield was not reduced compared with the CTL treatment. Indeed, the values of the yield parameters obtained in the vines from sustained irrigated practices were slightly higher than full-irrigated vines. This fact suggests that the water deficit registered before veraison could promote an accumula-tion of carbohydrates reserves that improved the berry development as well as en-couraged the crop yield. Anyway, we did not find significant differences in the yield components assessed among irrigation treatments (Table 1). Xue et al. [37] reported in wheat that when photosynthesis and biomass were reduced by water stress during grain filling, remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield.

Pazzagli et al. 2016. https://doi.org/10.1016/j.agwat.2016.02.015

Xue et al. 2006. https://doi.org/10.1016/j.jplph.2005.04.026.

Conesa et al. 2018. https://doi.org/10.1016/j.agwat.2018.06.019

Special thanks are due to the reviewer for constructive remarks.

Author Response File: Author Response.docx

Reviewer 2 Report

This work assessed the effects of the sustained and regulated practices of deficit irrigation on water relations, yield components and berry quality in a commercial vineyard of ‘Crimson Seedless’ table grapes. Generally，the structure of the paper is complete, the method is basic proper, and the process of experiment and data analysis is clear. However, the innovation of the paper is not enough. The practical significance of the paper is greater than the innovative significance. Some comments are as follows：

1. There are five irrigation treatments. Why?
2. The names or methods used in the results should be spelled out as clearly as possible in the research methodology part. forexample, 3.3 gas exchange parameteres.
3. line 205 the mean water reduction is suggested be added with +SD

Author Response

Thank you very much for your review. We have tried to respond to your interesting suggestions throughout the document.

Reviewer 3 Report

Dear Author ,

it was a pleasure to read your manuscript , well written and clear. I have no comment to do.

Author Response

Thank you very much for your very kind review.