Merge branch 'jinyuntang/lnd/c_inbal_fix' into next (PR #3257)

For ELM, when use_pheno_flux_limiter=.true., the components
of maintance respiration are updated to avoid negative carbon
state variables. However, the total maintenance respiration
is not updated accordingly, causing an overesimation of total
maintenance respiration mr. Now this bug is fixed by ensuring
maintenance respiration is always recalculated by summing up
its components.

[non-BFB] due to very tiny value changes.

Fixes #3256

components/clm/src/data_types/VegetationDataType.F90

@@ -8070,12 +8070,10 @@ subroutine veg_cf_summary(this, bounds, num_soilp, filter_soilp, num_soilc, filt
             this%psnshade_to_cpool(p)
 
        ! maintenance respiration (MR)
-       if ( trim(isotope) == 'c13' .or. trim(isotope) == 'c14') then
-          this%leaf_mr(p)      = this%leaf_curmr(p)      + this%leaf_xsmr(p)
-          this%froot_mr(p)     = this%froot_curmr(p)     + this%froot_xsmr(p)
-          this%livestem_mr(p)  = this%livestem_curmr(p)  + this%livestem_xsmr(p)
-          this%livecroot_mr(p) = this%livecroot_curmr(p) + this%livecroot_xsmr(p)
-       endif
+       this%leaf_mr(p)      = this%leaf_curmr(p)      + this%leaf_xsmr(p)
+       this%froot_mr(p)     = this%froot_curmr(p)     + this%froot_xsmr(p)
+       this%livestem_mr(p)  = this%livestem_curmr(p)  + this%livestem_xsmr(p)
+       this%livecroot_mr(p) = this%livecroot_curmr(p) + this%livecroot_xsmr(p)
 
        this%mr(p)  = &
             this%leaf_mr(p)     + &