Environmental Studies Department, University of California Santa Cruz, Santa Cruz, California, United States of America.
PLoS One. 2012;7(8):e38558. doi: 10.1371/journal.pone.0038558. Epub 2012 Aug 7.
Coastal salt marshes are among Earth's most productive ecosystems and provide a number of ecosystem services, including interception of watershed-derived nitrogen (N) before it reaches nearshore oceans. Nitrogen pollution and climate change are two dominant drivers of global-change impacts on ecosystems, yet their interacting effects at the land-sea interface are poorly understood. We addressed how sea-level rise and anthropogenic N additions affect the salt marsh ecosystem process of nitrogen uptake using a field-based, manipulative experiment. We crossed simulated sea-level change and ammonium-nitrate (NH(4)NO(3))-addition treatments in a fully factorial design to examine their potentially interacting effects on emergent marsh plants in a central California estuary. We measured above- and belowground biomass and tissue nutrient concentrations seasonally and found that N-addition had a significant, positive effect on a) aboveground biomass, b) plant tissue N concentrations, c) N stock sequestered in plants, and d) shoot:root ratios in summer. Relative sea-level rise did not significantly affect biomass, with the exception of the most extreme sea-level-rise simulation, in which all plants died by the summer of the second year. Although there was a strong response to N-addition treatments, salt marsh responses varied by season. Our results suggest that in our site at Coyote Marsh, Elkhorn Slough, coastal salt marsh plants serve as a robust N trap and coastal filter; this function is not saturated by high background annual N inputs from upstream agriculture. However, if the marsh is drowned by rising seas, as in our most extreme sea-level rise treatment, marsh plants will no longer provide the ecosystem service of buffering the coastal ocean from eutrophication.
滨海盐沼是地球上生产力最高的生态系统之一，提供了多种生态系统服务，包括在氮（N）到达近岸海洋之前拦截流域来源的氮。氮污染和气候变化是全球变化对生态系统影响的两个主要驱动因素，但它们在陆海界面的相互作用影响仍知之甚少。我们通过基于现场的操纵性实验，研究了海平面上升和人为添加氮如何影响盐沼生态系统的氮吸收过程。我们以加利福尼亚中部河口的一种盐沼植物为研究对象，采用完全析因设计，交叉模拟了海平面变化和铵-硝酸盐（NH 4 NO 3 ）添加处理，以检验它们对盐沼植物的潜在交互影响。我们季节性地测量地上和地下生物量以及组织养分浓度，发现氮添加对以下方面有显著的积极影响：a）地上生物量，b）植物组织 N 浓度，c）植物中固定的 N 储量，以及 d）夏季的茎叶比。相对海平面上升对生物量没有显著影响，除了最极端的海平面上升模拟，在这种情况下，所有植物在第二年的夏天都死亡。尽管对氮添加处理有强烈的响应，但盐沼的响应因季节而异。我们的研究结果表明，在我们位于 Coyote Marsh 的地点，Elkhorn Slough，滨海盐沼植物是一种强大的氮汇和海岸过滤器；这种功能不会因上游农业每年输入的高背景氮而饱和。然而，如果由于海平面上升而淹没了沼泽，就像我们最极端的海平面上升处理那样，沼泽植物将不再为缓冲沿海海洋富营养化提供生态系统服务。
