Yuan Lester L, Mitchell Richard M, Pollard Amina I, Nietch Christopher T, Pilgrim Erik M, Smucker Nathan J
Office of Water, U. S. Environmental Protection Agency, Washington, District of Columbia, U.S.A.
Office of Research and Development, U. S. Environmental Protection Agency, Cincinnati, Ohio, U.S.A.
Freshw Biol. 2023 Mar 1;68(3):473-486. doi: 10.1111/fwb.14040.
Changes in phosphorus concentrations affect periphytic diatom composition in streams, yet we rarely observe strong relationships between diatom richness and phosphorus. In contrast, changes in conductivity are strongly associated with differences in both diatom composition and richness. We hypothesised that we could better understand the mechanisms that control the phosphorus-richness relationship by examining relationships between phosphorus and the occurrence of individual diatom taxa, comparing these with relationships between conductivity and taxon occurrence, and documenting how niche breadths of taxa affect richness patterns. We estimated relationships between phosphorus and taxon occurrence using DNA metabarcoding data of diatoms collected from 1,811 sites distributed across the conterminous U.S.A. and contrasted patterns in these relationships with those between conductivity and taxon occurrence. The distribution of taxon optima for phosphorus was bimodal, with most optima located at either the maximum or minimum observed phosphorus concentration. The distribution of taxon optima for conductivity was unimodal. Niche breadths of taxa for phosphorus and for conductivity both generally increased with optimum values. The distribution of conductivity optima gave rise to a prominent hump-shaped relationship between richness and conductivity. The relationship between richness and phosphorus was also slightly hump-shaped, but this relationship would not be expected from the bimodal distribution of optima. Instead, we determined that broad niche breadths caused the hump-shaped relationship between richness and phosphorus. Our results highlight the nuanced effects that increased P loadings exert on diatom assemblages in rivers and streams and identify reasons that weak relationships between taxon richness and increased phosphorus have been observed. These findings allow us to better describe how excess phosphorus and subsets of taxa and their niche breadths contribute to patterns of taxa richness in diatom assemblages, and to improve the tools used to manage phosphorus pollution.
磷浓度的变化会影响溪流中附生硅藻的组成，但我们很少观察到硅藻丰富度与磷之间有很强的关系。相比之下，电导率的变化与硅藻组成和丰富度的差异都密切相关。我们推测，通过研究磷与单个硅藻分类群出现情况之间的关系，将这些关系与电导率和分类群出现情况之间的关系进行比较，并记录分类群的生态位宽度如何影响丰富度模式，我们可以更好地理解控制磷-丰富度关系的机制。我们利用从美国本土分布的1811个地点收集的硅藻DNA宏条形码数据估计了磷与分类群出现情况之间的关系，并将这些关系模式与电导率和分类群出现情况之间的关系模式进行了对比。磷的分类群最适值分布是双峰的，大多数最适值位于观察到的磷浓度的最大值或最小值处。电导率的分类群最适值分布是单峰的。磷和电导率的分类群生态位宽度通常都随着最适值的增加而增加。电导率最适值的分布导致丰富度与电导率之间呈现出显著的驼峰状关系。丰富度与磷之间的关系也略呈驼峰状，但从最适值的双峰分布来看，这种关系是出乎意料的。相反，我们确定是宽泛的生态位宽度导致了丰富度与磷之间的驼峰状关系。我们的结果突出了磷负荷增加对河流和溪流中硅藻群落产生的细微影响，并确定了观察到分类群丰富度与磷增加之间关系较弱的原因。这些发现使我们能够更好地描述过量的磷以及分类群子集及其生态位宽度如何促成硅藻群落中的分类群丰富度模式，并改进用于管理磷污染的工具。
