Using isotopic labeling to investigate root water uptake in an alley cropping system within Taklimakan Desert Oasis, China

Abstract

Intercropped trees are becoming popular as an ecological protection screen for a desert oasis from wind-blown sand and sand erosion. However, trees also consume a large amount of water and thus could compete for water resources with other crops. Here, we evaluated the water uptake in a typical alley cropping system within an oasis of the South Taklimakan desert. The system consisted of a poplar tree (Populus L.) used for sand protection and a walnut (Juglans regia L.)-corn (Zea mays Linn.) intercropping system. We evaluated root distribution by isotopically-labeled water (δD) and water uptake (δ18O) via SIAR models as well as the direct inference approach for different periods after tracer injection. We found that the different plants used water from different soil layers. While corn used water mostly from the 0–40 cm soil layer during the jointing (61%) and silking–filling periods (58%), respectively, walnut used water mostly from deeper than 40-cm depth (65%), and poplar used water from both shallow (about 30%, 0–40 cm) and deep soil layers (about 40%, 140–200 cm). Furthermore, while walnut roots can reach 200-cm depth, poplar roots can reach down to 400-cm depth. Due to those root differences, we infer that poplar trees do not necessarily compete for water resources with walnut and corn, and, therefore, can provide a valuable ‘safety-net’ service in this alley cropping system.