Abstract:

Sediment is a vital nutrient source sustaining harmful algal blooms, and phosphate-solubilizing bacteria (PSB) are essential for promoting the cycle of phosphorus (P) in water. Therefore, it is of great significance to study the relationships between PSB and sediment P release during outbreak of an algal bloom. Two strains of organic phosphate-solubilizing bacteria (OPB) (Geobacillus stearothermophilus and Bacillus pumilus) isolated from Swan Lagoon and sediments collected from the algal-bloom area were employed as an indoor simulation to examine the effects of PSB on P release from lagoon sediments and growth of Chaetomorpha sp. In this work, we examined the influence of OPB inoculation on the concentration of water total P (TP), soluble reactive P (SRP), algal biomass, and tissue P in algae. Furthermore, the variations in P fractions and alkaline phosphatase activity (APA) in sediments pre- and post-experiment were examined. The concentration of TP and SRP in water during the experiment ranged between 0.018-0.621 mg·L^-1 and 0.004-0.376 mg·L^-1, respectively. The inoculation of OPB significantly promoted P release from lagoon sediments. The amount of OPB inoculation had a significant effect on the TP and SRP concentration in the absence of Chaetomorpha sp. The TP concentration in the high inoculation groups was all higher than that in the low inoculation treatment groups, whereas the SRP showed a significant difference between high and low OPB amount in coexistence with G. stearothermophilus. The APA in sediments of the inoculation group was higher than that of the control group, with a difference value of 0.01-0.81 μmol·g^-1·h^-1, indicating that OPB could promote P release from sediments by secreting alkaline phosphatase. The concentration of NH₄Cl-P and NaOH-P in sediments was lower than the initial value under most treatments. Chaetomorpha sp. grew well with low inoculation of G. stearothermophilus, along with higher tissue P concentration and P enrichment amount than that of other treatments. The inoculation of OPB significantly stimulated P release from sediments and the growth of Chaetomorpha sp. in Swan Lagoon. G. stearothermophilus has a strong ability to secrete APA, which could solubilize P in the sediments of algal-bloom area. Therefore, in terms of the interactions between sediments, PSB and macroalgal blooms, the influence of PSB on the blooms of Chaetomorpha sp. should not be ignored in coastal waters.

Key words: organic phosphate-solubilizing bacteria, sediments, phosphorus release, alkaline phosphatase, Chaetomorpha sp., Swan Lagoon

摘要：

沉积物是维持有害藻华的重要营养来源，其中解磷菌对水体磷的循环起着关键的驱动作用，研究藻华暴发过程中解磷菌与沉积物磷释放的关系具有重要意义。为探讨解磷菌对瀉湖沉积物磷释放以及绿潮硬毛藻（Chaetomorpha sp.）生长的影响，以前期从天鹅湖分离的2株解有机磷细菌（OPB）（Geobacillus stearothermophilus，Bacillus pumilus）和藻华区沉积物为试材进行室内模拟试验，分析了不同OPB接种条件下上覆水总磷（TP）、可溶性磷（SRP）、硬毛藻生物量以及藻体磷含量等参数的差异，比较了试验前后沉积物碱性磷酸酶活性（APA）及磷赋存形态的变化。结果表明：试验期间不同处理水体TP和SRP含量的变幅分别为0.018－0.621 mg·L^-1和0.004－0.376 mg·L^-1，解磷菌接种明显促进了沉积物磷的释放。无藻条件下，菌液量对水体TP和SRP含量具有极显著影响；各接种组TP含量均表现为高菌量大于低菌量处理，SRP含量在G. stearothermophilus接种处理的高低菌量间差异较大。试验结束时，接种组沉积物中APA均高于未接种组（差值为0.01－0.81 μmol·g^-1·h^-1），表明OPB可通过分泌碱性磷酸酶等来促进沉积物磷的释放。在大多数处理中，沉积物NH₄Cl-P和NaOH-P含量均较初始值有所降低。在G. stearothermophilus低菌量接种处理中，硬毛藻生长较好，藻体磷含量和磷富集量显著高于其余处理。研究表明，OPB接种能明显促进天鹅湖沉积物磷的释放以及硬毛藻生长，其中G. stearothermophilus具有较强的碱性磷酸酶分泌能力，且对藻华区沉积物具有较强的解磷能力。从沉积物、解磷菌和大型藻华之间的相互作用关系来看，解磷菌对于近海水体绿潮硬毛藻暴发的影响不容忽视。

关键词: 有机解磷菌, 沉积物, 磷释放, 碱性磷酸酶, 硬毛藻, 天鹅湖