Forest ecosystem functioning in response to wetter winters along a large climatic gradient (WetWin)

气候模式一贯预测，下个世纪大多数温带生态系统的气温将出现中度至大幅上升，中欧和北欧冬季的变暖将超过其他所有季节的变暖。此外，冬季降水预计将增加，并由雪转向雨。简而言之，欧洲的冬天将变得更加温暖和潮湿。然而，这些温暖潮湿的冬季对生态系统功能的净影响尚不清楚。一般认为，温暖的土壤会增强土壤生物活性和植物的养分有效性。在天然积雪少、冬季温暖的地区，可利用营养物质的增加要么导致植物生长加快，要么导致营养物质淋失增加，特别是在冬季降水增加的情况下。在积雪较深、覆盖时间较长的较冷地区，积雪的减少可能导致土壤温度较低，因为积雪失去了隔热作用、矿化减少和植物生长减少。在这里，由于氮淋失增加，额外的降雨可能加剧氮的限制。该项目的总体目标是调查冬季降水对温带阔叶林生态和生物地球化学的重要性。更具体地说，我们将测试冬季降水增加的影响及其与积雪减少的相互作用。假设氮淋溶的影响在温暖的地点更强，而积雪变化在寒冷的地点引起更强的响应。因此，操作实验将沿着一个较强的气候梯度进行，该梯度体现了气候变暖效应从以前梯度东部的寒冷和降雪条件到未来梯度西部的温暖和少雪条件。净生态系统对冬季降水、树木生长和氮淋失变化的影响将被量化，这些代用物的潜在影响将由以下一系列参数来解释：(1)土壤生物活性、分解和矿化；(2)中欧自然优势林木林木（Fagus sylvatica）和林下植被成虫和幼虫的地上、地下生长和资源分配。我们将确定这些生态和生物地球化学响应参数对冬季降水变化的相对敏感性，这些参数沿德国东北部和波兰北部的冬季温度梯度变化，以便更好地理解对生态系统功能的潜在影响，并将其扩展到未来气候条件。

Climate models consistently project moderate to large increases in air temperatures for most temperate ecosystems over the next century, with warming in winter exceeding warming in all other seasons for central and northern Europe. Furthermore, winter precipitation is expected to increase and to shift from snow towards rain. In short, European winters will become warmer and wetter. The net effect of these warmer and wetter winters for ecosystem functioning, however, is unclear.Warmer soils are generally expected to enhance soil biotic activity and nutrient availability for plants. In regions with little natural snow pack and warm winters, this increase in available nutrients will either result in increased plant growth or, in particular if winter precipitation increases, in increased nutrient leaching. Towards colder regions with deeper and longer snow cover, loss of snow may result in colder soil temperatures due to missing insulation by the snow pack, reduced mineralization and decreased plant growth. Here, additional rainfall may exacerbate N limitation due to increased N leaching. The broad objective for this project is the investigation of the importance of winter precipitation for the ecology and biogeochemistry of temperate broad-leaved forests. More specifically, we will test for the effects of increased winter precipitation and its interactions with reduced snow cover. It is hypothesized that effects of nitrogen leaching are stronger at warmer sites, while snow cover change causes stronger responses at colder sites. Therefore, the manipulation experiments will be carried out along a strong climatic gradient which exemplifies climate warming effects from formerly colder and snowier conditions in the east of the gradient to future warmer and less snowy conditions in the west of the gradient. Net ecosystem effects to changes in winter precipitation in tree growth and nitrogen leaching will be quantified and potential effects in these proxies will be explained by the following suite of parameters: (1) soil biotic activity, decomposition, and mineralization; (2) nutrient availability and leaching (3) above and below-ground growth and resource allocation of adult and juvenile individuals of the naturally dominating forest tree of central Europe, i.e. Fagus sylvatica, and understory vegetation. We will identify the relative sensitivities of these ecological and biogeochemical response parameters to winter precipitation change along a large gradient of winter temperature from across Northeastern Germany and northern Poland in order to develop a better understanding of the potential effects on ecosystem functioning and sound up-scaling to future climatic conditions.