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，它深刻地影响着全球生物地球化学和气候。与复杂的C和N的生物地球化学动力学及其多个无机库相比，它们的完整微生物预算不能通过实验精确确定，地表水中的磷酸盐(P)预算更容易量化，特别是在P枯竭的北大西洋环流中，因为无机P只有一种溶解形式，它被微生物吸收。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着两种优势的浮游细菌种群，即原绿球菌蓝藻和SAR11进化支，它们争夺枯竭的无机磷。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：(1)混合营养原生生物而不是异养原生生物在低营养水域主导细菌的吞噬；（ii）混合营养原生生物而非光养原生生物或蓝藻主导低营养水域的初级生产；（iii）原生生物的吞噬作用，而不是浮游细菌，衰老死亡/病毒裂解主导了贫营养水域的营养循环；（iv）由混合营养原生生物控制的低营养生态系统在磷循环和碳预算方面是可持续的。上述假设将通过采用和进一步发展的方法进行验证，该方法将微生物的多重标记与同位素示踪剂和流式细胞分选相结合，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.