Freeze or famine: do uncoupled temperature and light regimes drive unique seasonal production-demand relationships in arctic spring-stream ecosystems?

研究人员将研究季节性光照和温度之间的相互作用，以及这些相互作用如何通过利用春季觅食的栖息地在冬季保持在冰点以上的优势来影响生态系统过程，否则北极地区的季节性很强。阿拉斯加的溪流常年流动，温度相对稳定，为多莉·瓦尔登(Dolly Varden)等物种提供了冬季栖息地，否则这些物种可能无法生存。这些系统还提供了一个独特的机会来研究季节光和温度模式的解耦。这个项目将研究与冬季相对温暖的温度相关的能源成本，当没有高生产率支持时，高生产率通常伴随着温暖和光线充足的夏季，如何影响北极生物、种群和食物网。调查人员将专注于阿拉斯加的十个地点，这些地点的平均冬季气温在1到13摄氏度之间，并在所有季节对这些地点进行采样。研究结果将有助于评估重要水生物种的栖息地质量，调查人员将与联邦和州资源管理人员分享调查结果。此外，该项目将支持一名早期职业教师和两名研究生，四名本科生将参与暑期实地考察。这项研究将促进对北极科学和生态领域的基础理解。数据将在阿拉斯加的10个泉水溪流中收集，跨越温度梯度，覆盖所有季节。首要目标是评估光和温度对这些生境中的生态系统过程(总初级生产、生态系统呼吸、养分吸收、二次生产、食物网属性)以及生物生长速度、新陈代谢和组织化学计量的交互影响。在北极的阿拉斯加，泉水流入的溪流常年流动，温度稳定，年波动只有3-4摄氏度，在那里，其他类型的溪流在冬天可以冻结为固体。这些生态系统的特点是在季节性强烈的北极地貌中嵌入了相对温暖的热制度，具有很高的生产力，为关键物种(如Dolly Varden char、Salvelinus Malma)提供了关键的冬季栖息地。它们还提供了独特的研究背景，特别是关于年度光和温度制度的分离，以及随后对季节性生态系统过程的影响。阿拉斯加Ivishak Spring先前的研究表明，与大多数其他生态系统不同的是，在其他大多数生态系统中，光驱动的初级生产总值(GPP)和有机碳(C)需求的季节性周期与夏季的高产量和需求以及冬季的低产量和需求密切相关，而北极泉水的周期与季节无关。换句话说，在GPP光照有限的季节，温暖的冬季气温推动了消费者对C的高需求率。因此，尽管这些泉水提供了基本的冬季避难所(“不冻就是饥荒”的情况)，但却带来了巨大的生物能量成本。由于北极春季溪流的冬季平均温度从~1摄氏度到13摄氏度不等，冬季生物能量成本的严重程度可能会很大，最温暖的溪流中的代谢损失可能会导致一些分类群无法成功越冬。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The investigators will examine the interactions between seasonal light and temperature and how these affect ecosystem processes by taking advantage of spring-fed habitat that remains above freezing in winter during the otherwise intensely seasonal Arctic. Streams with year round water flow and relatively stable temperatures are widespread in Alaska and provide winter habitat for species such as Dolly Varden (an important subsistence fish) that might otherwise be unable to survive. These systems also provide a unique opportunity to study the uncoupling of seasonal light and temperature patterns. This project will examine how the energy costs associated with relatively warm temperatures in winter, when not supported by high productivity that would typically accompany warm and light-filled summer months, affect Arctic organisms, populations, and food webs. The investigators will focus on ten sites in Alaska with average winter temperatures ranging from 1 to 13 degrees C and sample these in all seasons. Results will help evaluate habitat quality for important aquatic species, and the investigators will share findings with federal and state resource managers. In addition, the project will support an early career faculty member and two graduate students, and four undergraduates will be involved with summer fieldwork.This research will advance fundamental understanding in both Arctic sciences and the field of ecology. Data will be collected at 10 spring-streams in Alaska across a thermal gradient and covering all seasons. The overarching goal is to assess the interactive effects of light and temperature on ecosystem processes (gross primary production, ecosystem respiration, nutrient uptake, secondary production, food-web attributes) and organismal growth rates, metabolism, and tissue stoichiometry in these habitats. Spring-fed streams with perennial flow and stable temperatures with annual fluctuations of only 3-4 degrees C are widespread in arctic Alaska, where other stream types can freeze solid during winter. These ecosystems, characterized by relatively warm thermal regimes embedded in an intensely seasonal arctic landscape, are highly productive and provide critical winter habitat for key species (e.g. Dolly Varden char, Salvelinus malma). They also provide a unique research context, particularly with regard to the uncoupling of annual light and temperature regimes, with subsequent effect on seasonal ecosystem processes. Prior research at Ivishak Spring, Alaska, has shown that unlike most other ecosystems where light-driven seasonal cycles of gross primary production (GPP) and organic carbon (C) demand are closely coupled with high production and demand during summer and low production and demand during winter, arctic spring-streams have cycles that are seasonally uncoupled. In other words, warm winter temperatures drive high rates of C demand by consumers during the season when GPP is light-limited. Consequently, these springs impose significant bioenergetic costs despite providing an essential winter refuge (a "freeze-or-famine" scenario). Since mean winter temperatures among arctic spring-streams range from ~1 to 13 degrees C, the range in severity of winter bioenergetic costs is likely to be wide, with metabolic penalties in the warmest streams to the point that some taxa may be unable to overwinter successfully.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.