Collaborative Research: Nutrient co-limitation in young and mature northern hardwood forests

长期以来，人们一直认为温带森林是氮(N)有限的，但随着时间的推移，空气污染的慢性氮沉降应该会减少氮的限制，理论表明生态系统的生产力应该是由多种营养物质共同限制的。缺乏对温带森林系统氮磷限制的实验测试。本研究将结合模拟和实地研究，探索管理阔叶林生态系统演替变化中营养共生的调节过程。提高对资源利用生态系统优化的认识，包括维持共同限制，对森林管理、环境保护和基础科学知识具有重要意义。平衡的养分循环对维持森林的可持续性至关重要，白山国家森林的科学家和管理人员将根据拟议的研究结果评估造林实践。例如，它们的森林管理计划要求从森林获取养分以供再生长的能力来证明密集采伐的合理性。当营养物质有限时，矿物风化的生物增强等反馈显然与这一评价有关。多元素限制（MEL）模型从资源优化理论和生态系统生物地球化学的角度代表了共同限制。我们将模型扩展到包括磷、氮、碳、光和水，并将其应用于模拟北方阔叶林的初级和次级演替。单独使用营养添加N在一些森林,P仅在一些森林,N + P在一些森林,在复制三个年龄段的(~ 20、30和100年)在新罕布什尔州Bartlett实验森林,我们将测试资源限制的模式预测的模型和多个分配机制的努力获得N和P .具体来说,地上生产力的模型预测更大的反应单独N + P比N和P。在较老的林分中，该模型预测对N的响应大于对P添加的响应，但在较年轻的林分中，该模型表明来自腐质的N供应应该足以产生P限制。

Nutrient Co-limitation in Young and Mature Northern Hardwood ForestsTemperate forests have long been thought to be nitrogen (N) limited, but chronic N deposition from air pollution should reduce N limitation over time, and theory suggests that ecosystem productivity should be co-limited by multiple nutrients. Experimental tests of N vs. phosphorus (P) limitation in temperate forest systems are lacking. This study will combine modeling and field studies to explore processes mediating nutrient colimitation in relation to successional change in managed hardwood forest ecosystems. An improved understanding of ecosystem optimization of resource use, including the maintenance of co-limitation, is important to forest management, environmental protection, and basic scientific knowledge. Balanced nutrient cycling is essential to maintaining forest sustainability, and scientists and managers at the White Mountain National Forest will evaluate silvicultural practices in light of results from the proposed research. For example, their forest management plans require justifying intensive harvest removals in terms of the ability of forests to acquire nutrients for regrowth. Feedbacks such as the biological enhancement of mineral weathering when nutrients are limiting are clearly relevant to this appraisal.The Multi-Element Limitation (MEL) model represents co-limitation from the perspective of resource optimization theory and ecosystem biogeochemistry. We have extended the model to include P as well as N, carbon, light, and water, and applied it to simulate primary and secondary succession in northern hardwood forests. Using nutrient additions of N alone in some forest stands, P alone in some forest stands, N+P in some forest stands, in replicated stands of three ages (~20, 30, and 100 years) at the Bartlett Experimental Forest in New Hampshire, we will test the patterns of resource limitation predicted by the model and multiple mechanisms of allocation of effort to acquire N and P. Specifically, the model predicts a greater response of aboveground productivity to N+P than N or P alone. In older stands, it predicts a greater response to N than to P addition, but in younger stands, the model suggests that the supply of N from detritus should be sufficient to create P limitation.