Advancing Design and Functionality of Lysimeter/Ecotron Systems through Modeling 

Lysimeter systems play a crucial role in understanding the complex interactions within the soil-plant-atmosphere  continuum.  In  the  context  of  climate  change,  where  precise  insights  into  water  and nutrient fluxes, energy exchange, and greenhouse gas dynamics are essential, lysimeters equipped with advanced hydraulic and thermal controls are increasingly indispensable. A key innovation in this field is the integration of suction-controlled hydraulic boundary conditions and active temperature regulation, which significantly enhances the capability of lysimeters to mimic natural processes while maintaining  experimental  control.  These  functionalities  are  particularly  critical  in  ecotron experimental platforms, where controlled yet realistic environmental conditions are required for high-resolution and high-quality observations. Our  research  focuses  on  the  optimization  of  lysimeter  design  and  functionality  using  advanced computational tools. Specifically, we developed a 2D- and a comprehensive 3D-modeling approaches to  investigate  and  refine  the  technical  design  of  lysimeter  systems  equipped  with underpressure-controlled hydraulic boundary conditions and temperature regulation mechanisms. Two simulation models,  HYDRUS  and  FEFLOW,  were  systematically  tested  and  compared  for  their  suitability  in simulating these complex systems. We  present  the  results  of  scenario  analyses  conducted  to  evaluate  and  optimize  critical  design parameters, including (1) the number and spatial arrangement of suction cups required to achieve precise suction-controlled hydraulic boundary conditions, (2) the number, positioning, and dimensions of  heat  exchanger  pipes  for  effective  temperature  regulation  and  (3)  the  influence  of  insulation thickness at the bottom of the lysimeter on thermal efficiency and system stability. Our findings also demonstrate the strengths and limitations of both HYDRUS and FEFLOW in capturing the dynamics of water and energy transport in lysimeters. Our work not only contributes to the technical advancement of lysimeter and ecotron platforms but also supports their broader application in ecosystem research. By  integrating  robust  design  methodologies  with  cutting-edge  simulation  tools,  we  provide  a framework for enhancing the reliability and functionality of these experimental systems.  In  conclusion,  this  study  highlights  the  potential  of  modeling  and  scenario-based  optimization in improving the design and operational efficiency of lysimeters with advanced hydraulic and thermal controls.  The  insights  gained  from  our  research  are  expected  to  support  future  applications of lysimeter and ecotron systems in addressing critical questions related to climate change impacts on terrestrial ecosystems.