Concentrations of dissolved organic carbon (DOC) have increased recently in many lakes at high latitudes in North America and Europe, but it is unclear what effect this will have on the identity of the limiting nutrient for phytoplankton [nitrogen (N) vs. phosphorus (P)]. Identifying the effect of changing DOC on phytoplankton nutrient limitation is complicated by spatial covariation between atmospheric N deposition and increasing DOC in areas where lake browning occurs. We conducted nutrient-limitation assays in 27 lakes from three sites along gradients of climate and atmospheric N deposition in Sweden. Within each site, lakes were selected to represent the range of DOC concentrations. We also conducted statistical analyses of large-scale lake survey data (n = 4768 lakes divided into 47 regions) to investigate relationships between DOC and nutrient stoichiometry while controlling for differences in N deposition. Our findings confirmed that most lakes were dual-limited by both N and P in the south, whereas northern lakes were primarily N-limited. Throughout Sweden the ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) declined with increasing DOC in most regions, suggesting that browner lakes are more likely to be N limited. These results were not supported by our nutrient limitation assays, which identified no relationship between DOC and relative strength of limitation by N or P. Increased DOC also resulted in significant increases in both total and inorganic N and P fractions, suggesting that other factors such as light limitation or increased top-down control become more important as DOC increases.

中文翻译：

---

褐变是否会影响湖泊中限制养分的特性？

最近，北美和欧洲高纬度地区的许多湖泊中溶解有机碳 (DOC) 的浓度有所增加，但尚不清楚这将对浮游植物的限制性营养物质 [氮 (N) 与磷 ( P)]。由于大气氮沉积与发生湖泊褐变的地区的 DOC 增加之间的空间协变，确定 DOC 变化对浮游植物营养限制的影响变得复杂。我们在瑞典气候和大气氮沉降梯度的三个地点的 27 个湖泊中进行了营养限制分析。在每个站点内，选择湖泊来代表 DOC 浓度的范围。我们还对大规模湖泊调查数据（n = 4768 个湖泊，分为 47 个区域）进行了统计分析，以研究 DOC 与养分化学计量之间的关系，同时控制 N 沉积的差异。我们的研究结果证实，大多数湖泊在南部受 N 和 P 双重限制，而北部湖泊主要受 N 限制。在整个瑞典，溶解无机氮 (DIN) 与总磷 (TP) 的比率随着大多数地区 DOC 的增加而下降，这表明棕色湖泊更有可能受到 N 限制。我们的营养限制试验不支持这些结果，该试验确定 DOC 与 N 或 P 限制的相对强度之间没有关系。 DOC 的增加也导致总和无机 N 和 P 分数的显着增加，