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Watershed Alnus cover alters N:P stoichiometry and intensifies P limitation in subarctic streams
Biogeochemistry ( IF 4 ) Pub Date : 2021-03-19 , DOI: 10.1007/s10533-021-00776-w
Denise A. Devotta , Jennifer M. Fraterrigo , Patrick B. Walsh , Stacey Lowe , Daniel K. Sewell , Daniel E. Schindler , Feng Sheng Hu

In many watersheds, nitrogen (N)-fixing alder (Alnus spp.) provides key nutrient subsidies to terrestrial and aquatic ecosystems. The importance of these subsidies may increase as alder cover expands under climate warming at high latitudes. We assessed how landscape features and meteorological conditions affect aquatic N and phosphorus (P) availability and stoichiometry in 26 streams across natural gradients of alder cover in southwestern Alaska over the spring and summer, covering 4 years. Analyses of resin lysimeter samples from select watersheds showed that annually, soils under alder leached almost three times more N, and two times more P than under non-alder vegetation. Stream NO3 concentrations displayed a non-linear relationship with alder cover; NO3 was low where alder cover was < 30%, but increased markedly where alder cover was > 30%. Watershed elevation was inversely related to alder cover, stream NO3 concentrations, and stream NO3 yields. Dissolved and particulate stream P were unrelated to alder cover, watershed elevation or discharge, highlighting decoupling of controls on P between terrestrial and aquatic ecosystems. Snowmelt-associated nutrient pulses and hydrology likely resulted in greater stream N and P in the spring, compared to the summer. However, weather parameters only impacted stream N via their interaction with alder. Stream DIN:TP increased with alder cover and decreased with elevation, suggesting that alder intensified P-limitation. Hence, aquatic P-limitation may become increasingly pronounced as climate-induced alder expansion continues. These results demonstrate that the elevational gradient in watershed alder cover determined spatial patterns in stream N availability and nutrient limitation.



中文翻译:

分水岭的nu木覆盖改变了N:P的化学计量并增强了北极弧流中的P限制

在许多流域中,固氮al木(Alnus spp。)为陆地和水生生态系统提供了关键的养分补贴。随着高纬度地区气候变暖,al木覆盖面积的扩大,这些补贴的重要性可能会增加。我们评估了春季和夏季长达4年的景观特征和气象条件如何影响阿拉斯加州西南部al木覆盖自然梯度的26条溪流中水氮和磷(P)的利用率和化学计量。对部分集水区的树脂溶渗仪样品进行的分析表明,al木下的土壤每年淋溶的氮几乎是非-木下的土壤的三倍,磷的两倍。流NO 3 -的浓度显示与桤木盖的非线性关系; NO 3 al木覆盖率<30%时较低,但al木覆盖率> 30%时显着增加。流域海拔呈负相关桤木盖,流NO 3 -浓度和流NO 3 -产量。溶解的和颗粒状的磷与al木的覆盖,分水岭的高低或流量无关,突显了陆地和水生生态系统对磷的控制的解耦。与夏季相比,与融雪有关的养分脉冲和水文状况可能导致春季的溪流N和P更大。然而,天气参数仅通过它们与al木的相互作用而影响了溪流N。DIN:TP流随al木的覆盖而增加,随elevation高而降低,表明suggest木增强了P限制。因此,随着气候引起的al木扩张的持续,水生P限制可能会变得越来越明显。这些结果表明,流域al木的海拔梯度覆盖了氮流有效性和养分限制中确定的空间格局。

更新日期:2021-03-21
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