Wild Rice Population Dynamics and Nutrient Cycles

自然界中的动植物种群通常会经历规律的振荡或盛衰周期。生态学家长期以来一直对这些振荡的原因感兴趣。生态学理论预测，种群的任何延迟都会导致其振荡。大多数被认为是延迟原因的过程纯粹是人口过程，例如出生率的延迟。但是，如果在腐烂的植物材料(凋落物)和活的植物之间限制养分的循环被推迟，这也可能导致种群振荡。野生水稻是一种有趣的湿地植物物种，其种群长期以来一直被认为是振荡的。野生稻是一年生植物，因此种群必须通过前几年腐烂的凋落物中释放的营养物质来满足其生长所需的所有营养物质。野生水稻生长所需的几乎所有营养物质都在春季-初夏的短暂窗口中被吸收。但前一年的垃圾分解得如此之慢，以至于它甚至要到夏末才开始释放营养物质，甚至直到腐烂的第二年才开始释放养分。我们推测，这种通过腐烂的落叶循环营养物质的延迟导致了野生稻种群的振荡。除了具有生态意义外，野生稻也是明尼苏达州奥吉布韦(奇佩瓦)部落成员的重要主食。收割野生水稻是奥吉布韦社会的一个重要特征。奥吉布韦文化包括在收获季节举行的野稻精神仪式的传说。野生大米接近神圣的食物地位，乐队成员将野生大米视为奥吉布韦意味着什么的象征。奥吉布韦部落管理着明尼苏达州东北部的十几个野生稻米湖，以尽可能自然的方式生产野生稻米。因此，在文化和科学上，部落成员以及更广泛的科学界都感兴趣的是造成野生水稻产量波动的原因。这项研究将与Ojibway的Fond Du Lac乐队成员密切合作。养分释放延迟对野生稻种群动态的影响将通过以下三管齐下的方法进行测试：(1)在一系列野生稻湖中对野生稻生产力、种子产量和沉积物中养分的可获得性进行长期观察；(2)在大型中栖动物(贮藏箱)中操纵凋落物、养分输入和种子与幼苗的建立，并测量总生产力和养分吸收、平均植株重量和养分吸收、出苗和养分可获得性；以及(3)建立和测试一个关于野生水稻养分吸收、生产力、凋落物腐烂以及种子生产和出苗的计算机模型。将从部落社区学院招募学生来协助这项工作。该项目将帮助部落生物学家解决对奥吉布韦价值观具有重要意义的自然资源管理问题，并向部落学生展示在环境科学领域工作的潜力。该部落预计，这项研究的结果将为其制定专门针对野生水稻水域的营养标准提供关键信息，并通过更好地了解野生水稻生态系统中的营养循环来改进管理决策。

Populations of plants and animals typically undergo regular oscillations or boom-and-bust cycles in nature. Ecologists have long been interested in the causes of these oscillations. Ecological theory predicts that any delay in a population will cause it to oscillate. Most of the processes that have been proposed as causes of delays are purely population processes, such as delays in birth rate. But if the recycling of limiting nutrients between decaying plant material (litter) and live plants is delayed, this could also cause a population to oscillate.Wild rice is an interesting wetland plant species whose populations have long been known to oscillate. Wild rice is an annual plant and so the population must meet all its nutrients requirements for growth from the release of nutrients in decaying litter from previous years. Almost all the nutrients wild rice needs for growth are taken up in a brief window in spring-early summer of the year. But litter from the previous year decomposes so slowly that it does not even begin to release nutrients until at least the end of summer or not even until the second year of decay. We hypothesize that this delay in the recycling of nutrients through decaying litter causes wild rice populations to oscillate.Besides being ecologically interesting, wild rice is an important staple food for members of Minnesota's Ojibway (Chippewa) tribe. Wild rice harvesting is a defining feature of Ojibway society. Ojibway culture includes legends of wild rice spiritual ceremonies conducted during harvest time. Wild rice approaches sacred food status and band members identify wild rice as a symbol of what it means to be Ojibway. The Ojibway tribe manages over a dozen wild rice lakes in northeastern Minnesota for wild rice production in as natural a manner as possible. Therefore, what causes oscillations in wild rice production is of interest, culturally and scientifically, to tribal members as well as to a wider scientific community. This research will involve close collaboration with members of the Fond du Lac band of Ojibway.The effect of delays in nutrient release on wild rice population dynamics will be tested by the following three-pronged approach: (1) making long-term observations of wild rice productivity, seed production, and nutrient availability in sediments in a series of wild rice lakes; (2) manipulating litter, nutrient inputs, and seed vs. seedling establishment in large mesocosms (stock tanks) and measuring total productivity and nutrient uptake, mean plant weight and nutrient uptake, seedling emergence, and nutrient availability; and (3) constructing and testing a computer model of wild rice nutrient uptake, productivity, litter decay, and seed production and emergence.Students will be recruited from the tribal community college to assist in this work. This project will assist tribal biologists in addressing problems of natural resource management of significance to Ojibway values and show tribal students the potentials of a career in the environmental sciences. The tribe is anticipating that the results of this study will provide critical information for its development of nutrient criteria specifically for wild rice waters, and for improving management decisions from a better understanding of nutrient cycling in wild rice ecosystems.