effective gauge couplings that are sensitive to the physics at the high- energy threshold. Such terms can always be interpreted as threshold corrections to the Wilsonian gauge couplings $f_{a}(\Phi)$,...”.

The intuition behind this statement is that once the string coupling is identified in terms of low energy fields the non-universal terms in gauge couplings coming from integrating out high energy fields should preserve the structure of SUGRA. Kaplunovsky and Louis go on to check this in explicit heterotic string theory examples. If this is violated in typeI/IIB theories then one would need to understand why this intuition is violated.

Heterotic case\[sub:Heterotic-case:-KL\] 
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The expression is expected to be valid to all orders in perturbation theory (at least in some renormalization scheme) but we will focus only on the one loop result. The holomorphic gauge coupling is $$f_{a}(S,M)=k_{a}S+\frac{1}{16\pi^{2}}f_{a}^{(1)}(M).\label{eq:f1loop}$$ The first term is the classical (universal) gauge coupling and the second is the holomorphic one-loop correction. Of course $f$ receives no further corrections. The other terms are already explicitly of at least one-loop order so that $K,g_{a}^{2},Z$ can be replaced by their classical values. Thus we put $$\begin{aligned}
K(\Phi,\bar{\Phi}) & = & -\ln(S+\bar{S})+\hat{K}(M,\bar{M})+O(\frac{1}{16\pi^{2}\Re S}),\\
Z_{\bar{I}J}(\Phi,\bar{\Phi}) & = & Z_{\bar{I}J}^{(0)}(M,\bar{M})+O(\frac{1}{16\pi^{2}\Re S}),\\
\frac{1}{g^{2}(\mu^{2})} & 