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. Stomatal regulation and whole plant hydraulic signaling affect water fluxes and stress in plants. Land surface models and crop models use a coupled photosynthesis–stomatal conductance modeling approach. Those modelsestimate the effect of soil water stress on stomatal conductance directlyfrom soil water content or soil hydraulic potential without explicitrepresentation of hydraulic signals between the soil and stomata. In orderto explicitly represent stomatal regulation by soil water status as afunction of the hydraulic signal and its relation to the whole planthydraulic conductance, we coupled the crop model LINTULCC2 and the rootgrowth model SLIMROOT with Couvreur's root water uptake model (RWU) and the HILLFLOW soil water balance model. Since plant hydraulic conductance depends on the plant development, this model coupling represents a two-way coupling between growth and plant hydraulics. To evaluate the advantage ofconsidering plant hydraulic conductance and hydraulic signaling, we compared the performance of this newly coupled model with another commonly used approach that relates root water uptake and plant stress directly to the root zone water hydraulic potential (HILLFLOW with Feddes' RWU model).Simulations were compared with gas flux measurements and crop growth datafrom a wheat crop grown under three water supply regimes (sheltered,rainfed, and irrigated) and two soil types (stony and silty) in westernGermany in 2016. The two models showed a relatively similar performance inthe simulation of dry matter, leaf area index (LAI), root growth, RWU, gross assimilation rate,and soil water content. The Feddes model predicts more stress and lessgrowth in the silty soil than in the stony soil, which is opposite to theobserved growth. The Couvreur model better represents the difference ingrowth between the two soils and the different treatments. The newly coupled model (HILLFLOW–Couvreur's RWU–SLIMROOT–LINTULCC2) was also able to simulate the dynamics and magnitude of whole plant hydraulic conductanceover the growing season. This demonstrates the importance of two-wayfeedbacks between growth and root water uptake for predicting the cropresponse to different soil water conditions in different soils. Our resultssuggest that a better representation of the effects of soil characteristicson root growth is needed for reliable estimations of root hydraulicconductance and gas fluxes, particularly in heterogeneous fields. The newlycoupled soil–plant model marks a promising approach but requires furthertesting for other scenarios regarding crops, soil, and climate.

hydrology and earth system sciences

Comparison of root water uptake models in simulating CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes and growth of wheat