Abstract: This paper studied the effects of different root zone irrigation modes (alternate partial drip irrigation, ADI; fixed partial drip irrigation, FDI; and conventional drip irrigation, CDI) and their watering amount on the whole-plant and its components hydraulic resistance and the stomata conductance and leaf area of apple seedlings. The results showed that both the irrigation mode and the watering amount had significant effects on the apple seedlings hydraulic resistance (R). Under the same irrigation modes, the root resistance (Rr) of apple seedlings was increased, but the shoot resistance (Rs) was decreased with decreasing watering amount; and under the same watering amounts, ADI and FDI increased the leaf and petiole resistance (Rl+p), but decreased the whole-plant resistance (Rt), Rr, Rs, and lateral branch and master rod resistance (Rlb+mr), compared with CDI. Under the irrigation quota of 20 mm and 30 mm, the Rl+p of ADI was 106% and 063% higher than that of CDI, respectively; and with the prerequisite of saving 33% of irrigation water, the average Rl+p of ADI and FDI was increased by 1965% and 2434%, while the average Rlb+mr was decreased by 483% and 1497%, respectively, compared with those of CDI. ADI and FDI effectively decreased stomata conductance and leaf area and increased Rl+p, and thus, decreased leaf blade luxurious transpiration dehydration while increased plant water use efficiency. By decreasing Rr and Rlb+mr, the ADI and FDI improved apple seedlings water regulation function and drought-resistant capability.

Key words: MixSIAR model, water source, riparian plant, PS index., stable hydrogen and oxygen isotopes