Effects of Limited Phosphorus Supply on Growth, Root Morphology and Phosphorus Uptake in Citrus Rootstocks Seedlings

摘要

Phosphorus (P) deficiency in citrus plants is an important limiting factor in the agricultural production. The knowledge on the growth of citrus rootstocks under phosphorus (P) deficiency conditions, especially on the root morphology and genotype differences is limited. Therefore, it is very important to study the highly efficient citrus rootstock for enhancing the P efficiency under limited P supply. In this study, five citrus rootstocks were grown in Hoagland nutrient solution containing 1 mM P/L (moderate P-level control) and 0.1 mM P/L (P-deficiency) for 90 days. The results showed that there was a significant genotypic variation in plant-growth parameters (biomass, seedling height, root-shoot ratio), root-morphological traits (total surface area and total length of absorption root, first and second lateral roots biomass) and P-concentrations. Under P deficiency condition, the dry weight of plant and the expansion of leaf surface area were restricted. The growth and development of C. ichangensis underwent the least inhibitory effect, followed by Fragrant citrus, Sour orange, Red tangerine and Trifoliate orange with the strongest inhibitory effect. These results showed that C. ichangensis is P-efficient, whereas Trifoliate orange is P-inefficient rootstocks. By changing the structure of root system and morphological of C. ichangensis, it performed better under P deficiency than that of other rootstocks. C. ichangensis possessed the best physiological adaptation mechanism to P deficiency. Under the condition of low P stress, the activity of acid phosphatase (SAPase) in root system was stronger. Moreover, the ability and affinity of the roots to H2PO4 - were stronger than those of Fragrant citrus, Sour orange, Red tangerine and Trifoliate orange. Root surface area length absorption and lateral root number had extremely significant positive correlations to P acquisition efficiency. C. ichangensis exhibited a strong ability to withstand P deficiency, which showed a strong P absorption kinetics characteristics. In conclusion, maintaining numerous longer lateral root, higher R/S, larger root absorption area and higher activity of SAPase is very crucial to improve the P-efficiency and thus contribute much to the resistance of seedlings to P-deficiency in the C. ichangensis genotypes.