Negative Allelopathic Effects of Root Exudate of Alternanthera Philoxeroides on Growth and Phosphate Dissolution of Inorganic Phosphorus Bacteria

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the National Basic Research Program of China (973 Program) (No.2013CB127405)

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    【Objective】Alternanthera philoxeroides Griseb, a kind of ill weed hard to eliminate in the world, is able to grow in both soils and waters low in available phosphorus (P) and now widely distributed in over twenty provinces (regions or municipalities) in this country, causing enormous hazard to agriculture, forestry, animal husbandry and aquiculture. It is, therefore, essential to get to know how the weed affects microbes transforming inorganic P in soil. Hopefully, the knowledge will help understand its invasive mechanism, and serve as a scientific basis for effective control of the weed.【Method】 Plants of A. philoxeroides were gathered and cultured in deionized water (fresh root weight : deionized water volume = 1 : 1.5) for 48 hours formed of two cycles of day and night, 12 hours each shift, at 25℃2 ℃with light intensity being 15000 Lex in the day shift. Then the plants were removed, leaving the water as root exudate solution of the plant for the follow-on experiment, which was designed to have two types of culture media, liquid and solid, inoculated with three P-dissolving strains of Burkholderia Yabunchi (B05, B07 and B09) and then amended with the root exudate solution atexudates of A. philoxeroides roots(EAR )0.000 (CK), 0.013, 0.025, and 0.050 g ml-1, separately. Bacterial colonies on the solid media were measured for diameters and diameters of their P-dissolving rings and then P-dissolving indexes worked out. And the liquid media were analyzed for proton, organic acids, and dissolved phosphorus with a pH meter, a high performance liquid chromatography (HPLC), and the molybdenum blue colorimetric method, separately.【Result】Bacterial colonies, P-dissolving rings and P-dissolving indexes in the solid culture media decreased with increasing EAR concentration. The effect on was found the highest with Strain B09, which was followed by Strain B05 and B07. In the solid culture media amended with EAR 0.050 g ml-1 of the root exudate, bacterial colonies decreased by 40.32%~50.00% in diameter, by 49.09%~67.98%in diameter of P-dissolving rings, and by 9.86%~27.38% in P-dissolving index. Growth of the PSB in the liquid culture media was also inhibited by EAR in varying degrees, and hence their populations reduced by 48.13%~73.03%. In the liquid culture media amended with EAR 0.050 g ml-1, the amount of P dissolved by phosphate-solubilizing bacteria (PSB) decreased by 47.32% (B05), 11.43% (B07) and 36.00% (B09) as compared with the control. All the three tested strains of bacteria released protons, oxalate and citrate into culture solutions. Besides these, acetate was also found in the culture solution of B05, malate of B09, and acetate and succinate of B07. Oxalate and citrate together accounted for 66.02%~74.72% of total organic acids released from PSB. In addition, the content of inorganic P dissolved by the bacteria was positively related to the efflux of proton (r = 0.836, p< 0.05, n = 12) and total organic acids (r= 0.947, p< 0.05, n = 12). EAR inhibited significantly the release of protons and organic acids from PSB and hence the dissolution of P remarkably.【Conclusion】Obviously EAR has some negative allelopathic effects on PSB, which are reflected in inhibiting reproduction and growth of the bacteria, their release of protons and organic acids, and P-solubilization in varying degrees. In the invasive process of A. philoxeroides, EAR might inhibit PSB solubilizing inorganic P in the soil, thus hindering P mobilization in the soil and reducing P supply to other plants. In contrast, A. philoxeroides is able to absorb P efficiently through its root high in affinity with P to satisfy its own P requirement, which favors multiplication of its own population, competition for P with other plants and formation of pure A. philoxeroides communities.

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WANG Yushu, LIU Hai, YUAN Ling. Negative Allelopathic Effects of Root Exudate of Alternanthera Philoxeroides on Growth and Phosphate Dissolution of Inorganic Phosphorus Bacteria[J]. Acta Pedologica Sinica,2017,54(6):1486-1496.

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  • Received:March 09,2017
  • Revised:July 10,2017
  • Adopted:August 25,2017
  • Online: September 04,2017
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