Nutrient cycling in lakes

我的研究计划涉及微生物食物网和营养循环，在本次资助周期中，我的实验室将瞄准四个领域。 第一个领域涉及湖水中溶解的有机磷（DOP）。 这是这种限制性营养素的最大溶解部分，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产生的，可能是通过细胞破碎产生的。 我们的假设是，真正溶解的有机磷也源自细胞破损，但归因于病毒裂解和放牧等自然机制。 为了完成这一系列研究，我们将测试这样的假设：DOP 的高分子量部分主要是核酸，并且它们通过低分子量 DOP 变成 PO4，而低分子量 DOP 主要是核苷酸和其他底物，通过细胞膜相关磷酸酶为浮游生物提供。 第二项研究源于我们开发的放射生物测定法，该测定法可以估计 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法来检验有关光和食物网相互作用在确定磷限制湖泊中 PO4 浓度中的作用的假设。 我们的第三个重点是全湖磷循环，我们将检验我们最近回顾的关于总磷和分层湖泊沉积的文献中提出的假设。 假设是，P 沉降随着 TP 异速增加，因此在中间（中营养）范围内，湖泊抵抗 TP 浓度的增加，并且在分层沉降过程中，TP 向寡营养范围内的值移动。 最后，我们将把部分精力转向研究磷有限湖泊中的 NH4。 虽然实验证据表明，只有磷负荷才能增加此类湖泊的生物量，而氮循环受到的关注相对较少，但氨浓度也较低，难以测量，且周转较快。 它的浓度与 PO4 一样，也是浮游植物营养环境的重要决定因素，需要考虑到浮游植物的物种组成。

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.