Do mixotrophic protists make oligotrophic oceanic gyres sustainable ecosystems?

该提案的目的是解释地球上最大的生态系统--少营养海洋环流的功能，它们深刻地影响着全球生物地球化学和气候。与C和N的复杂生物地球化学动力学及其多个无机库相比，无法通过实验准确确定其完整的微生物收支，而地表水中的磷(P)收支更容易量化，因为无机磷只有一种溶解形式被微生物吸收。该项目建议对最简单生态系统的新概念进行实验测试和数值模拟，即：混合营养原生生物控制两个主要浮游细菌种群，原氯球菌蓝藻和SAR11分支，竞争枯竭的无机磷。通过概述的实验室和海洋巡航实验的结合，将解决以下假设：(I)在少营养水域中，混合营养原生生物而不是异养原生生物主导细菌吞噬；(Ii)混合营养原生生物而不是光营养原生生物或蓝藻主导初级生产力；(Iii)在少营养水域中，原生生物吞噬而不是浮游生物死亡/病毒裂解；(4)在磷循环和碳收支方面，由混合营养原生生物控制的寡营养生态系统是可持续的。上述假设将通过采用和进一步开发的方法学来验证，该方法论将微生物的多重标记与同位素示踪剂和流式细胞仪分类相结合，并结合营养生物测定实验。

The aim of the proposal is to explain the functioning of the oligotrophic oceanic gyres, the Earth's largest ecosystems, which profoundly affect global biogeochemistry and climate. Compared to complex biogeochemical dynamics of C and N with their multiple inorganic pools that do not allow their complete microbial budgets to be accurately determined experimentally, a phosphate (P) budget in surface waters, particularly in the P depleted North Atlantic gyre, is easier to quantify because inorganic P has only one dissolved form in which it is taken up by microbes. The project proposes to experimentally test and to numerically model a new concept of a simplest ecosystem i.e. that: mixotrophic protists control the two dominant bacterioplankton populations, Prochlorococcus cyanobacteria and the SAR11 clade, competing for depleted inorganic P. Using a combination of outlined laboratory and oceanic cruise experiments the following hypotheses will be addressed (i) mixotrophic protists rather than heterotrophic protists dominate bacterial phagotrophy in oligotrophic waters; (ii) mixotrophic protists and not phototrophic protists or cyanobacteria dominate primary production in oligotrophic waters; (iii) protist phagotrophy rather than bacterioplankton senescent death / viral lysis dominate nutrient recycling in oligotrophic waters; (iv) an oligotrophic ecosystem controlled by mixotrophic protists is sustainable in terms of P recycling and C budget. The above hypotheses will be tested by employing and further developing methodology that combines multiple labelling of microorganisms with isotopic tracers and flow cytometric sorting, in combination with nutrient bioassay experiments.