ISOLATION AND IDENTIFICATION OF SPECIFIC ROOT EXUDATES IN ELEPHANTGRASS IN RESPONSE TO MOBILIZATION OF IRON- AND ALUMINUM-PHOSPHATES

Abstract

Elephantgrass (Pennise L., cv. Napier 62.) is forage of tropical origin, which grows well in the acid soils. In the previous experiments, we found that elephantgrass could utilize phosphorus (P) efficiently in acid soils, and rhizosphere acidification and the release of phosphatase could not explain this property. It was assumed that root exudate, especially specific root exudate would play an important role in mobilizing sparingly soluble phosphates and thereby increased P uptake. The main objective of the present work was to test this hypothesis. The root exudates of elephantgrass were collected to investigate their mobilization to iron-phosphate (FePO₄) and aluminum-phosphate (AlPO₄). It was observed that P-deficient root exudates had a strong ability to mobilize FePO₄ and AlPO₄ in comparison to P-adequate root exudates. Results from fractionation of root exudates with cation and anion exchange resins and molecular membrane of different molecular weight indicated that the anionic + below 1K fraction contained the dominant P-mobilizing activity in both P-deficient and P-adequate root exudates. Phosphorus deficiency rather than P adequacy induced the exudation of pentanedioic acid. High P-mobilizing activity in P-deficient root exudates was consistent with large exudation of pentanedioic acid, it suggested that pentanedioic acid represented higher P-mobilizing activity in P-deficient root exudates and thereby increased P mobilization. Specific analysis indicated that a specific transport was involved in the exudation of pentanedioic acid from roots of elelphantgrass. The results above indicate that the exudation of pentanedioic acid is a response specific to P deficiency in elephantgrass and constitutes a mechanism of tolerance to low P stress.

ACKNOWLEDGMENTS

Thanks are due to Dr.Wang Zhiming at the Jiangsu Institute of Soil Science and Fertilizers for providing seedlings of elephantgrass and Dr. Yongming Luo at Institute of Soil Science, Chinese Academy of Sciences for advisable suggestions. This study was supported by National Natural Scientific Foundation of China.