Phosphorus concentrations in growth rings of trees as indicators of P availability and recycling efficiency in forest ecosystems

长期监测点叶片磷浓度的下降趋势表明，许多欧洲森林的磷树营养在过去2-30年里有所下降。造成这一现象的可能原因包括土壤酸化、高氮沉积和树木生长改善导致的养分失衡、土壤石灰化以及干旱和丰产年的增加。对生长轮中元素浓度的分析提供了机会，以发现磷和其他营养物质的长期趋势，这些营养物质可能与土壤酸化(树轮中的钙、铝、钙、铝)、富营养化(N)和其他环境波动有关。此外，树干横截面中P的树轮轮廓可以评估木本生物量中P的循环效率，从而有助于解决DFG优先方案生态系统营养的核心问题之一。在优先方案的第一阶段，我们已经确定激光烧蚀-电感耦合等离子体质谱(LA-ICP-MS)方法适合于测量生长轮中的磷和其他元素。然而，这种方法还需要进一步发展，以捕捉生长轮内营养物质的空间异质性。在1.3m高处采集冷杉树心的初步结果表明，P循环的P循环效率并不高于P获取系统，最贫穷地点硬木中P的含量与土壤正在发生的酸化无关。目前正在对更多的地点和西弗兰进行进一步的分析。在这里，我们建议将这一分析扩展到包括树高较高的树轮和树皮，从而包括具有较高生理活性的树干区域。我们假设，在树轮内，边材中的磷浓度随着高度的增加而增加，而心材中的磷浓度保持不变。这将产生更能代表整个树干的结果。此外，这种方法使我们能够跟踪同一生长年轮内磷浓度随高度的变化，从而提供了一种新的方法来计算和模拟磷储量和吸收到木本植物生物量中。此外，将在三个磷有效性不同的地点，利用优先方案新设立的施肥试验，评估小叶藻对化肥中磷的短期固定潜力。在这里，我们假设磷在边材和树皮中的固定作用在磷循环中比在磷获取系统中更强。因此，我们的分析对于优先方案中分析的生态系统的磷预算是至关重要的，并解决了它的一个主要假设，即P循环的P循环效率高于P获取系统的循环效率。

Negative trends in foliar P concentrations at long-term monitoring sites have indicated that P tree nutrition in many European forests has declined over the last 2-3 decades. Possible reasons for this phenomenon comprise soil acidification, nutrient imbalances as a consequence of high N deposition and improved tree growth, soil liming, and increasing frequencies of droughts and mast (high seed production) years. Analysis of element concentrations in growth rings offer the opportunity to detect long-term trends in nutrition of P as well as other nutrients which may be related to soil acidification (Ca, Al, in tree rings), eutrophication (N), and other environmental fluctuations. In addition, tree ring profiles of P in stem cross-sections permit assessment of the recycling efficiency of P within the woody biomass and thus help to address one of the core questions of the DFG Priority Programme Ecosystem Nutrition. In the first phase of the Priority Programme, we have established that the Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) approach is suited to measure P and other elements in growth rings. The method needs to be developed further, however, to capture the spatial heterogeneity of nutrients within growth rings. Preliminary results for tree cores from P. abies taken at 1.3 m height show that the P recycling efficiency is not higher in a P-recycling than a P-acquiring system, and that P content in hardwood at the poorest site is unrelated to ongoing soil acidification. Further analyses for more sites and F. sylvatica are currently underway. Here we propose to expand this analysis to include tree rings and bark from upper tree heights and thus stem regions with higher physiological activity. We hypothesize that within tree ring P concentrations in sapwood increase with height whereas those in heartwood remain constant. This will yield results that are more representative of entire tree stems. In addition, this approach allows us to track height-related changes in P concentrations within the same growth ring and thus offers a new method to calculate and model P stocks and uptake into woody tree biomass. In addition, the short-term immobilization potential for P from fertilizer will be assessed for F. sylvatica using the newly established fertilization trial of the Priority Programme at three sites differing in P availability. Here we hypothesize that immobilization of P into sapwood and bark is stronger in P-recycling than in P-acquiring systems. Our analyses are therefore essential for P budgets of the ecosystems analyzed in the priority program and to address one of its main hypotheses that recycling efficiency of P is higher in P-recycling than in P-acquiring systems.