Abstract: Coexisting plants in drylands with different rooting depths can exploit different spatial water sources to maintain productivity. The sequence of water potential thresholds for key physiological events during dehydration strongly influences overall plant function. However, how rooting depth coordinates with this water potential sequence remains poorly understood. Here, we measured leaf structural, hydraulic, and stomatal traits of eight coexisting desert woody species with rooting depths ranging from 69 to 337 cm. Rooting depth was positively related to hydraulic efficiency, turgor loss point, leaf embolism resistance and stomatal closure point, but negatively related to non-structural carbohydrates and water use efficiency. Positive correlations between rooting depth and hydraulic/stomatal safety margins suggested that deep-rooted species had a conservative water potential sequence, i.e. preemptively closing stomata to prevent substantial embolism occurrence. Conversely, shallow-rooted species displayed a risky water potential sequence but adopted compensatory strategies, including low water demand, strong embolism repair capacity and high carbon allocation to sapwood area relative to leaf area. Together, our results suggest that severe water limitation imposes strong selective pressure, resulting in tight coordination among rooting depth, stomatal regulation, water use, embolism resistance and repair and structural construction, which is critical for species coexistence in desert ecosystems.

Key words: drought resistance, embolism resistance, non-structural carbohydrates, rooting depth, stomatal regulation, stomatal safety margin