Nutrient cycling in lakes

我的研究项目涉及微生物食物网和营养循环，在这个拨款周期中，我的实验室将针对四个领域。第一个领域涉及湖水中的溶解有机磷(DOP)。这是这种限制性营养物质中最大的溶解部分，但我们最近的工作表明，它主要是在样品制备的过滤步骤中提取的，可能是通过细胞破碎。我们的假设是，真正溶解的有机磷也来自细胞破坏，但由于病毒裂解和放牧等自然机制。为了完成这一系列研究，我们将检验这样的假设，即DOP的高分子量部分主要是核酸，这些核酸通过低分子DOP变成PO4，DOP主要是浮游生物通过细胞膜相关磷酸酶获得的核苷酸和其他底物。 第二条线的研究来自我们开发的一种放射性生物测定方法，可以估计PO4的浓度，PO4是限制湖水中藻类生长的最重要的营养物质。我们将在经验和实验方法中使用这种生物测定方法来检验关于光和食物网相互作用在确定磷限制湖泊中PO4浓度方面的作用的假设。 我们的第三个重点将是全湖P循环，在那里我们将检验一个假说，该假说源于我们最近对TP和层状湖泊中沉积作用的文献的回顾。其假设是，磷的沉积与总磷的异速同速增长，使得在中等(中营养)范围内，湖泊抵抗总磷浓度的增加，而在层结期间，沉积使总磷向贫营养范围内的值移动。 最后，我们将把我们的一些努力转移到研究磷有限的湖泊中的NH4。虽然实验证据表明，只有磷负荷可以增加这类湖泊的生物量，而N循环相对较少受到关注，但NH4也处于低浓度，难以测量，而且周转迅速。其浓度以及PO4的浓度也是浮游植物营养环境的重要决定因素，需要考虑才能了解浮游生物的物种组成。

My research program concerns microbial food webs and nutrient cycles, and in this grant cycle my lab will target four areas. The first area concerns dissolved organic phosphorus (DOP) in lake water. This is the largest dissolved fraction of this limiting nutrient, but our recent work demonstrates that it is mostly derived during the filtration step of sample preparation, probably by cell breakage. Our hypothesis is that truly dissolved organic P is also derived from cell breakage, but due to natural mechanisms such as viral lysis and grazing. To complete this line of research we will test the hypotheses that the high molecular weight fraction of DOP is mostly nucleic acids, and that these become PO4 via low molecular weight DOP that is mostly nucleotides and other substrates available to plankton via cell-membrane associated phosphatases. The second line of research follows from our development of a radiobioassay that can estimate the concentration of PO4, the most important nutrient limiting the growth of algae in lake water. We will use this bioassay in both empirical and experimental approaches to test hypotheses concerning the role of light and food web interactions in determining the concentration of PO4 in P-limited lakes. Our third focus will be the whole-lake P cycle, where we will test a hypothesis arising from our recent review of the literature on TP and sedimentation in stratified lakes. The hypothesis is that P sedimentation increases allometrically with TP such that within an intermediate (mesotrophic) range, lakes resist increases in TP concentration, and during stratification sedimentation moves TP towards a value in the oligotrophic range. Finally, we will shift some of our effort to looking at NH4 in P-limited lakes. While experimental evidence suggests that only P-loading can increase the biomass of such lakes, and N-cycling has received relatively little attention, NH4 is also in low concentration, difficult to measure, and turning over rapidly. Its concentration, along with that of PO4, is also an important determinant of the nutrient environment of phytoplankton and needs to be considered to understand species composition of plankton.