Direct response of dissolved organic nitrogen to nitrate availability in headwater streams
Direct response of dissolved organic nitrogen to nitrate availability in headwater streams
复制标题
溶解有机氮对源头水流中硝酸盐有效性的直接响应
DOI：
10.1007/s10533-015-0153-9
复制
发表时间：
2015
期刊：
影响因子：
4
通讯作者：
W. McDowell
中科院分区：
文献类型：
--
作者：
A. Wymore;B. Rodríguez‐Cardona;W. McDowell
尽管几十年来的研究记录了生态系统中溶解有机氮（DON）的定量意义，但控制其生产和消耗的驱动因素尚未得到很好的理解。作为一种有机营养物，DON既可以作为能量源，也可以作为氮源。溪流中DON浓度的一个假设控制因素是硝酸盐（NO3−）的有效性。然而，DON和NO3−的天气性调查却产生了不一致的时空格局。利用营养脉冲法，我们对新罕布什尔州的三条源头溪流进行了NO3 -控制实验，并测量了控制后的溶质浓度和环境DON浓度的响应。这种直接实验添加NO3−经常改变原位环境DON浓度，观察到增加和减少。NO3 -和DON之间的总体关系表明，在这些河流中，DON主要被用作营养源，这一点可以通过添加NO3 -的净DON积累来证明。然而，在对NO3−添加的响应中，强烈的潜在季节模式也可以辨别出来，这表明DON的作用可以在作为营养来源和能量来源之间转换（正如添加NO3−时DON的净减少所证明的那样）。在同一个月内进行的实验中，我们还观察到在相距不到5英里的两条河流中NO3−-DON关系（净DON积累与净DON减少）的差异。基于这些结果，我们预计DON在生态系统中的作用会因流域和整个生长季节而异，根据环境条件在营养和能量来源之间交替。结合一种新的基于场的方法，我们证明了环境DON池可以在原位进行操纵。这种方法有可能进一步加深我们对跨生态系统DON的理解。
Despite decades of research documenting the quantitative significance of dissolved organic nitrogen (DON) across ecosystems, the drivers controlling its production and consumption are not well understood. As an organic nutrient DON may serve as either an energy or nitrogen source. One hypothesized control on DON concentration in streams is nitrate (NO3−) availability. Synoptic surveys of DON and NO3−, however, have yielded inconsistent spatial and temporal patterns. Using a nutrient pulse method we experimentally manipulated stream NO3− and measured the response of both the manipulated solute and ambient concentrations of DON in three New Hampshire headwater streams. This direct experimental addition of NO3− often altered ambient DON concentrations in situ, with both increases and decreases observed. The overall relationship between NO3− and DON suggests that DON is primarily used as a nutrient source in these streams, as evidenced by net DON accumulation with added NO3−. However, strong underlying seasonal patterns in the response to NO3− addition are also discernable, indicating that the role of DON can switch between serving as a nutrient source to an energy source (as evidenced by net DON reduction with added NO3−). We also observed differences in the NO3−—DON relationship (net DON accumulation vs. net DON reduction) in two streams less than five miles apart when experiments were conducted within the same month. Based on these results, we expect the role of DON within ecosystems to vary among watersheds and throughout the growing season, alternating between serving as a nutrient and energy source depending on environmental conditions. With the incorporation of a new field-based method we demonstrate that the ambient DON pool can be manipulated in situ. This approach has the potential for furthering our understanding of DON across ecosystems.