Plant traits and species interactions along gradients of N:P:K stoichiometry

由于施肥、大气沉积和地貌的改变，养分的增加改变了营养元素在限制生产力方面的相对重要性，许多以前磷(P)限制的水生系统现在是氮(N)限制的，许多陆地系统表现出磷限制的模式。更高的养分投入率的生态后果是养分比例的变化和更高的生产率，物种的丧失和濒危物种数量的增加。研究表明，不同的物种适应不同类型的营养限制。作为对营养限制的响应，植物表现出明显的特征，如N限制与较长的根长相关，而P限制则诱导较高的根磷酸酶活性。在这一背景下的一个重要研究领域是生态化学计量学(ES)理论，它描述了生物功能和过程中元素和能量的平衡。ES研究主要集中在N和P上，但另一种同样重要的常量营养素--钾(K)--却较少受到关注。钾是叶片中仅次于氮的第二丰富的营养物质，比磷更丰富。尽管土壤总钾库一般高于N、P库，但土壤-植物有效K含量往往较低，土壤中有机质几乎不含K。目前的研究表明，土壤K有效性的降低与N沉积有关，这使得K对土地利用和施肥的变化比N或P更敏感。关于植物对不同N、P和K供应水平的响应的研究很少，尽管有证据支持K已经是陆地生态系统中的一种限制性养分。然而，关于K在与N和P的直接比较中的作用的研究仍然缺乏。有了这个奖学金，我的目标是研究元素营养素对植物物种生长模式的作用。我将进行一项温室实验，重点是适应不同类型养分限制的物种之间沿N、P和K有效性梯度的竞争相互作用。其次，我将对大学景观生态小组收集的现有数据集进行研究。在Oldenburg，有关于110个物种(来自盐沼生态系统、芦苇、草地、半干旱草原、石南地和荒野生境)、所有组织类型(叶、茎、根)的元素浓度(N、P、K)以及生物量分配特性、比叶面积、树冠高度和生态系统特性(例如生产力、分解)的数据。土壤中的植物有效氮、磷和钾浓度是有效的，这使得在不同生态系统内以及从潮湿生境到干燥生境的梯度上，元素组织浓度与元素资源浓度直接相关。

Nutrient enrichment, as a consequence of fertilization, atmospheric deposition and modification of landscape has changed the relative importance of nutrient elements in limiting productivity, with many formerly phosphorus (P) limited aquatic systems being today nitrogen (N) limited and many terrestrial systems showing patterns of P limitation. Ecological consequences of higher nutrient input rates are shifts in ratios of nutrients and higher productivity rates, loss of species and increase in number of endangered species. It has been shown that different species are adapted to different types of nutrient limitation. As a response to nutrient limitation, plants show distinct traits, e.g. N limitation is associated with a higher root length, whereas P limitation induces higher root phosphatase activity. An important field of research in this context is ecological stoichiometry (ES) theory, which describes the balance of elements and energy in biological functions and processes. ES studies have mainly focused on N and P, but another macronutrient of similar importance, potassium (K), has received less attention. K is the second most abundant nutrient in leaves after nitrogen, and by that more abundant than phosphorus. Even though the total soil K pools are generally higher than those of N and P, soil-plant available K concentrations are often lower, also, organic matter in soils contains almost no K. Current studies indicate that reduction in soil K availability is related to N deposition, which makes K more sensitive to changes in land use and fertilization than either N or P. There are only few studies on the response of plants to different supply rates of N, P and K, although evidence supports that K is already a limiting nutrient in terrestrial ecosystems.A lot of research has been done on the effects of N and P on plant growth and competition. However, studies on the role of K in direct comparison to N and P are still missing. With this fellowship I aim at conducting research on the role of elemental nutrients on the growth patterns of plant species. I will conduct a greenhouse experiment with the focus on competitive interactions between species adapted to different types of nutrient limitation along gradients of N, P and K availability. Secondly, I will work on existing data sets collected by the Landscape Ecology Group of the Univ. of Oldenburg, with data on 110 species (from salt marsh ecosystems, reeds, grasslands, semi-dry grassland, heathlands and ruderal habitats), element concentrations (N, P, K) of all tissue types (leaves, stems, roots), as well as biomass allocation traits, Specific Leaf Area, canopy height and ecosystem properties (e.g. productivity, decomposition). Plant available N, P and K concentrations of the soil are available, which allows the direct relation of elemental tissue concentration with elemental resource concentration within the various ecosystems and along gradients from wet habitats to dry habitats.