Foliar P-Fractions Allocation of Karelinia caspia and Tamarix ramosissima Are Driven by Soil and Groundwater Properties in a Hyper-Arid Desert Ecosystem

The allocation patterns of foliar phosphorus (P) fractions across various vegetation types generally reflect the adaptability to P-impoverished environments. However, the allocation of foliar-P fractions within the desert herb Karelinia caspia (K. caspica) and shrub Tamarix ramosissima (T. ramosissima) in soils with different environment-P availability and the impact of soil and groundwater properties on foliar-P fractions allocation remain unclear. The foliar-P fractions (metabolites-P, nucleic acid-P, structural-P, and residual-P) of K. caspica and T. ramosissima and the properties of 0–60 cm deep soil under their canopy and groundwater were determined at four different environment-P sites. Results found that as environment-P availability decreased, both plants allocated the higher proportions of foliar-P to nucleic acid-P than to metabolites-P and structural-P. With the exception of residual-P, foliar-P fractions were markedly higher for K. caspica than T. ramosissima. Soil Olsen-P, NO(3)(–)-N, soil water content, electrical conductivity (EC), groundwater EC, and total dissolved solids (TDSs) played an important role in allocating foliar P-fractions for both K. caspica and T. ramosissima. Compared with K. caspica, the foliar-P fractions of T. ramosissima were more tightly bounded to groundwater than soil properties. Overall, these findings show how desert plants flexibility take advantage of the foliar-P in low environment-P availability and illustrate the foliar-P fractions allocation of desert plants is driven by soil and groundwater properties.