PriOrity Effect Mechanisms (POEM): mechanisms of priority effects and their persistence over time in dry acidic grasslands

历史很重要：生物多样性丧失是全球变化的一个关键组成部分，这要求我们提高生态知识对恢复自然系统生物多样性的预测能力。生物多样性-生态系统功能实验已经清楚地表明，植物多样性是温带草原生态系统功能的重要驱动因素，但现在一个有争议的讨论提出了这样一个问题：这种“人工”群落（在不允许自然组装的实验中）在“真实世界”的生态系统中有多大的相关性？最近的研究表明，植物功能群的聚集历史，特别是由不同到达顺序引起的优先效应，不仅影响群落结构，而且影响地下和地上生产力等生态系统功能。尽管优先效应对理解群落聚集具有重要意义，但由于方法上的挑战，优先效应受到的关注远远少于系统发育或性状方法。然而，我们知道历史是重要的，提高对优先效应的认识，特别是其机制，对于提高我们对植物群落集合的整体理解和提高对自然生物多样性的预测能力至关重要。我们的项目旨在通过(1)将优先效应（生态位抢占和修改）的产生和持续机制研究与更常见的植物物种共存理论联系起来，以及(2)研究植物建立期间的天气条件如何调节干旱酸性草地优先效应的产生和轨迹，来填补这一知识空白。我们的主要假设是，早到物种对植物-土壤-微生物组环境的影响将取决于首先到达一个地点的功能群，从而影响晚到的物种，导致群落在结构和功能上的差异，而这反过来又会受到植物建立期间天气条件的调节。在连续数年的时间里，将开展不同植物功能群到达顺序的田间试验（首先播种豆科植物、禾本科植物和牧草），并与温室试验相结合，测试植物-土壤反馈在解释植物到达顺序反应中的相对作用。根系研究的最新方法将使我们能够在物种（基于下一代测序的方法）和群落水平（minirhizotrons）上研究根生态位分配。实验处理对土壤和植物相关微生物组细菌和真菌多样性的影响也将使用分子条形码方法进行研究。本项目的附加价值在于将不同的生态知识进行链接和整合，从而更好地理解优先效应的产生、持续和轨迹。这样做，我们的目标是对植物物种如何随着时间的推移在群落中共存有一个更好的理解。

History matters:Biodiversity loss as a key component of global change requires us to increase the predictive power of ecological knowledge for restoring biodiversity in natural systems. Biodiversity-ecosystem functioning experiments have clearly demonstrated that plant diversity is an important driver of ecosystem functioning in temperate grasslands, but a controversial discussion now asks the question how relevant such “artificial” communities (in experiments that do not allow natural assembly) are in “real world” ecosystems. Recent work has shown that assembly history, in particular so-called priority effects caused by different order of arrival of plant functional groups not only affects community structure, but also influences ecosystem functions such as belowground and aboveground productivity. Despite their importance for understanding community assembly, priority effects have received much less attention than phylogenetic or trait approaches, probably due to methodological challenges. Yet we know that history matters, making improved knowledge on priority effects, in particular their mechanisms, essential to improve our overall understanding of plant community assembly and the improve predictive power for natural biodiversity.Our project aims to fill this gap in knowledge by (1) linking research on the mechanisms behind the creation and persistence of priority effects (niche preemption and modification) with more common theories of plant species coexistence (and (2) investigating how weather conditions during plant establishment modulate the creation and trajectory of priority effects in dry acidic grasslands. Our main hypothesis is that the effect of early-arriving species on the plant-soil-microbiome environment will differ depending on the functional group that arrives first at a site, thus affecting the species arriving later, leading to communities differing in structure and functioning, and this will in turn be modulated by weather conditions during plant establishment. A field experiment with different plant functional group order of arrival (legumes, grasses, forbs sown first) will be initiated over consecutive years and paired with a greenhouse experiment testing the relative role of plant-soil feedback in explaining responses to the plant order of arrival. State of the art methods in root research will allow us to study root niche partitioning at the species (next generation sequencing-based method) as well as the community level (minirhizotrons). The effect of experimental treatments on the bacterial and fungal diversity of the soil and plant-associated microbiomes will also be studied using a molecular barcoding approach.The added value of this project lies in the linking and integration of different ecological knowledge to better understand the creation, persistence, and trajectory of priority effects. Doing so, we aim at gaining a much-improved understanding of how plant species coexist in communities over time.