• Soil with 70 % weathered mudstone best supports plant drought resistance. • Photosynthetic water threshold signals the start of plant water stress. • Wilting water threshold marks the end of plant photosynthetic activity. • Weathered mudstone content changes how plants respond to water stress. • Mixed soil textures expand the range of water available for plant growth. Soil physical properties and water dynamics critically regulate plant growth. Understanding how plants respond to water deficit under mixed-medium soil conditions is essential. In this study, the drought resistance of mulberry in soils with varying weathered mudstone contents (0 % to 100 %) was investigated. Key physiological parameters, including the net photosynthetic rate ( P n ), stomatal conductance ( G s ), transpiration rate ( T r ), intercellular CO₂ concentration ( C i ), and water use efficiency ( WUE ), were monitored during soil water depletion controlled watering experiments. The key findings included the following: (1) As the water deficit intensified, P n , T r , G s , and WUE initially increased but subsequently decreased in soils with high (70 % and 100 %) weathered mudstone contents, whereas they decreased steadily in soils with lower contents (0 % to 30 %); however, C i initially decreased but then increased, independent of mudstone content. (2) Under progressive water deficit, distinct threshold responses were observed for P n , C i , and WUE . The photosynthetic water threshold (PWT) indicated the onset of water stress, marked by significant decreases in P n and WUE and an increase in C i . As the moisture further decreased to the wilting water threshold (WWT), all the three parameters stabilized at minimal levels. The PWT calculated from P n was slightly greater than the PWTs calculated from C i and WUE . (3) The soil with 70 % weathered mudstone content was optimal, combining a high total available water content (54.60 %) with the most extensive range of high-productivity high-efficiency water (soil relative water content: 57.27 % ∼ 91.39 %), thereby maintaining efficient water use from field capacity to severe water deficit. These findings reveal the adaptability of plants to different soil environments and moisture conditions, providing insights for developing agricultural irrigation strategies and evaluating soil water productivity.
Zhang et al. (Sun,) studied this question.