Young navel orange rootstock improves phosphorus absorption from poorly soluble pools through rhizosphere processes

Abstract

An increased plant capacity to efficiently use the poorly available pools will be very helpful in citrus production. Information on the various mechanisms evolved by citrus rootstocks to optimize soil phosphorus (P) access is limited. Thus, the objectives of this study were: To evaluate P acquisition efficiency (PAE) in Thomson Navel Orange (Citrus sinensis L. Osbeck.) plants grafted on three rootstocks and adaptive mechanisms developed by each to these rootstocks to increase P uptake in one calcareous soil. For this purpose, a pot experiment was conducted in a completely randomized design with three replications. Treatments consisted of three rootstocks of citrus, including Sour Orange (SO), Swingle Citrumelo (SC) and Troyer Citrange (TC). 18 months after planting seedlings in pots, plants were harvested and the rhizosphere soils were separated. Dissolved organic carbon (DOC), the population of fungi and bacteria, microbial biomass P (MBP), alkaline (AlP) and acid (AcP) phosphatases, available P (P-Olsen), and P fractionation according to the modified Hedley’ sequential fractionation procedure were determined in the rhizosphere soils. After the harvest, P acquisition efficiency of plants (PAE) was determined. The results of this study showed that SO promoted higher scion P uptake and increased PAE. The fungal and bacterial population, MBP, AcP in the SO rhizosphere soils was greater than the SC and TC rhizosphere soils (P < 0.05). P availability closes the root surface of SO rootstock was higher in comparison to the other rootstocks. Moreover, the effect of the rhizosphere on various fractions of P was under rootstock control. The highest amount of exchangeable P and Fe and Al soil P in the rhizosphere soils was found in SO grafting, while the lowest P associated with Ca compounds and residual P in the rhizosphere soils was found in SO-grafting. This necessarily implies the P mobilization of poorly available pools are vital mechanisms for P acquisition by plants on SO in this P-poor soil. In conclusion, the results of the present study showed that different PAE of rootstocks may be associated with the various mechanisms of action of each rootstock involved in P absorption.