Variation of water uptake in degradation agroforestry shelterbelts on the North China Plain

Abstract Agroforestry shelterbelts are important ecological barriers providing protection against wind and sand-related disasters in the North China Plain. However, large proportions of these agroforestry shelterbelts are degenerating or have died in recent years and the causes of degeneration are extremely complex. In this study, stable hydrogen and oxygen isotope techniques were used to quantify water sources for P. simonii Carr vegetation in four degrees of degradation (undegraded, U.D; slightly degraded, L.D; moderately degraded, M.D and seriously degraded, S.D), and to investigate how the vegetation can adapt to degradation. Results show that P. simonii Carr exhibited considerable plasticity in depth of water uptake; it prefers to utilize deeper water sources which have higher soil moisture. This vegetation predominantly absorbs water from depths below 160 cm and treatments with a relatively stable and high water content source, are characterized by U.D and L.D. The utilization of deep soil water has gradually decreased, while the utilization rate of surface soil water has gradually increased with an increase in the degree of degradation. Water and nutrient availability in depths of 0–40, 40–80, 80–120 and 120–160 cm were relatively low in M.D and S.D treatments. Therefore, P. simonii Carr degeneration in this region was attributed lack of available water and nutrients. The low precipitation levels and continuous decline in the groundwater level will be accelerating degradation and death of P. simonii Carr shelterbelts.