Deep soil water ( θ _d ), defined here as past precipitation stored in deep unsaturated soils and not replenished by precipitation in a single growing season, plays a vital role in helping trees withstand prolonged droughts in deep‐vadose‐zone regions. However, its contribution to total water use across tree growth stages and the effects of limited θ _d access on tree transpiration and photosynthesis remain unclear. To address this, a process‐based model was parameterized using in situ root‐zone measurements (from the soil surface to the apparent maximum root depth) and then used to simulate root‐zone soil moisture, canopy transpiration and photosynthesis for two common species, apple ( Malus domestica fuji ) and black locust ( Robinia pseudoacacia ), in northern China. For trees aged 3–22 years, θ _d below 200 cm ( θ _d200 ) accounted for an average of 31.9% and 40.9% of total water use in apple and black locust trees, respectively. Restricted access to θ _d200 led to decreases in annual transpiration rates and daily photosynthetic rates by 19.7% and 17.4% in apple, and by 26.2% and 20.2% in black locust. On a monthly scale, precipitation and transpiration greatly influenced θ _d200 for both species, while tree age and diameter at breast height were key annual determinants. These findings highlight a trade‐off between physiological stability achieved via deeper rooting and the associated carbon costs of accessing θ _d . The findings here provide insights into sustainability of planted trees in deep vadose‐zone regions.

The instability of diafiltration is a widespread problem in the practical application of microporous ceramic filtration membranes. In this paper, a series of microporous ceramic filter membranes were prepared using inexpensive standard sand and river sand as matrix materials. Semi-empirical formula for the effective permeability radius of ceramic membranes with respect to time was established from analysis of the response mechanism between water flow and material properties. Finally, on the basis of theoretical analysis, some measures were proposed to improve permeate flux. The experimental results showed that during the initial stage of filtration, the microporous ceramic filter membrane had a large change in permeate flux, and during the late stage of filtration, permeate flux tended to be stable. Over time, open porosity and closed porosity changed the actual seepage area of the ceramic membrane, and this affected the stability of permeate flux and final stable permeate flux. The roughness of the inner wall of microporous ceramic pores affected the hydraulic loss coefficient, and this controlled the outflow process. Trace elements that were rich in sand produced a large amount of glass phase after sintering. The glass phase was rich in polar groups and formed a temporary hydrogen bond with the small flow of water molecules. It led to an increase in viscous resistance effect of the side wall along the water flow and the extent of the permeate flux of the ceramic membrane changed with time.