Hope everything goes well.

I'm writing to ask about the function of soil-to-root conductance in the plant hydraulic pathway.

In Chapter 11 of CLM5 tech note (page 120), the calculation of soil-to-root conductance is calculated by the eq. 11.16-11.18 and the water flux from soil to root is calculated by eq.11.14 (attached f1.jpg)

However, when I checked the code about the calculation of soil-to-root conductance in CLM5, lines 3048-3090 in PhotosynthesisMod.F90, RAI is multiplied to the root conductance rather than soil-to-root conductance (I attached the code here)

Markdown (GitHub flavored):

```
! Lines 3048 - 3090
! calculate conversion from conductivity to conductance
root_biomass_density = c_to_b * froot_carbon(p) * rootfr(p,j) / dz(c,j)
! ensure minimum root biomass (using 1gC/m2)
root_biomass_density = max(c_to_b*1._r8,root_biomass_density)
! Root length density: m root per m3 soil
root_cross_sec_area = rpi*root_radius(ivt(p))**2
root_length_density = root_biomass_density / (root_density(ivt(p)) * root_cross_sec_area)
! Root-area index (RAI)
rai(j) = (tsai(p)+tlai(p)) * froot_leaf(ivt(p)) * rootfr(p,j)
! fix coarse root_average_length to specified length
croot_average_length = croot_lateral_length
! calculate r_soil using Gardner/spa equation (Bonan, GMD, 2014)
r_soil = sqrt(1./(rpi*root_length_density))
! length scale approach
soil_conductance = min(hksat(c,j),hk_l(c,j))/(1.e3_r8*r_soil)
! use vegetation plc function to adjust root conductance
fs(j)= plc(smp(c,j),p,root,veg)
! krmax is root conductance per area per length
root_conductance = (fs(j)*rai(j)*params_inst%krmax(ivt(p)))/(croot_average_length + z(c,j))
soil_conductance = max(soil_conductance, 1.e-16_r8)
root_conductance = max(root_conductance, 1.e-16_r8)
root_conductance_patch(p,j) = root_conductance
soil_conductance_patch(p,j) = soil_conductance
! sum resistances in soil and root
rs_resis = 1._r8/soil_conductance + 1._r8/root_conductance
! conductance is inverse resistance
! explicitly set conductance to zero for top soil layer
if(rai(j)*rootfr(p,j) > 0._r8 .and. j > 1) then
k_soil_root(p,j) = 1._r8/rs_resis
else
k_soil_root(p,j) = 0._r8
endif
```

Markdown (GitHub flavored):

```
! Lines 5005 - 5011
! calculate root water potential
if ( abs(sum(k_soil_root(p,1:nlevsoi))) == 0._r8 ) then
x(root) = sum(smp(c,1:nlevsoi) - grav2)/nlevsoi
else
x(root) = (sum(k_soil_root(p,1:nlevsoi)*(smp(c,1:nlevsoi)-grav2))-qflx_sun-qflx_sha) &
/sum(k_soil_root(p,1:nlevsoi))
endif
```