Collaborative Research: Mechanisms driving positive and negative tree-fungal feedbacks across an abiotic-stress gradient

了解物种相互作用如何影响生物多样性一直是生态学家的兴趣所在。生态学理论和观察表明，同一物种的成树和幼苗之间的负相互作用稳定了种群，防止了局部灭绝，并维持了生物多样性。另外，成年树可以促进同一物种的年轻幼苗的生长和存活，特别是在压力大的环境中，这反过来又会导致生物多样性水平降低。然而，病原体和共生菌在介导这些相互作用和引起植物多样性在不同环境梯度中的作用仍然未知。本研究资助了植物和真菌种群与群落生态学家之间的合作，以揭示地上和地下植物-微生物相互作用在维持物种多样性中的积极和消极作用。它将进一步探讨环境压力的变化如何影响森林生态系统中树木的多样性。这项研究将使当地和区域土地管理者和利益相关者了解地上和地下互惠主义者在太平洋西北地区主要树种的生长和生存中所起的作用。随着全球气候的变化，对人口和社区如何适应环境变化的研究变得越来越重要。微生物及其与植物的相互作用，无论是积极的还是消极的，在决定物种分布、丰度以及它们对气候胁迫的预期反应方面发挥着未被充分研究的作用。因此，我们缺乏对微生物介导的相互作用，特别是植物物种内部和物种之间的地上和地下同种反馈，如何在环境胁迫梯度中改变其强度和方向的全面理解。由该奖项资助的研究将调查真菌共生体如何通过影响成树和幼树之间的密度依赖相互作用和反馈，直接或间接地沿着应力梯度对树种丰度、分布和多样性做出贡献。研究人员将验证真菌共生体对植物性能的净影响与环境中非生物干旱和营养胁迫水平相关的假设，并且随着非生物胁迫的增加，同种反馈从负向正转变。首先，在HJ Andrews长期生态研究（LTER）基地的野外实验中，研究人员将沿着自然水分和土壤养分胁迫梯度，在同种或异种成年树的树冠下交替移植三种焦点树种，操纵真菌共生体，评估它们对同种密度依赖反馈的影响。在温室试验中，树木、微生物、土壤养分和干旱胁迫将被控制。最后，本项目将把寄主-共生体动态整合到森林群落动态的区域模型中，以评估在非生物胁迫条件下树木种群/群落动态可能发生的变化。总的来说，提出的工作将测试关于真菌共生体如何对太平洋西北地区森林中优势树种的反馈方向和强度做出贡献的多种假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding how species interactions affect biological diversity has long been of interest to ecologists. Ecological theory and observations have shown that negative interactions between adult trees and seedlings of the same species stabilize populations, prevent local extinction, and maintain biological diversity. Alternatively, adult trees can increase the growth and survival of younger seedlings of the same species, particularly in stressful environments, which in turn can lead to lower levels of biological diversity. However, the role of pathogens and mutualists in mediating these interactions and giving rise to variation in plant diversity across environmental gradients remains unknown. This research funds a collaboration between plant and fungal population and community ecologists to uncover the role of positive and negative above and below ground plant-microbial interactions in the maintenance of species diversity. It will further explore how changes in environmental stress might impact tree diversity in forest ecosystems. This research will inform and engage local and regional land managers and stakeholders of the role of above and below ground mutualists in the growth and survival of key tree species in the Pacific Northwest.As the global climate shifts, research into how populations and communities adapt to environmental changes has become increasingly critical. Microbes and their interactions with plants, both positive and negative, play a underexamined role in determining species distributions, abundances, and their expected responses to climate-induced stress. As a result, we lack a comprehensive understanding of how microbially mediated interactions, and in particular above and below ground conspecific feedbacks within and among plant species, change in their strength and direction across environmental stress gradients. The research funded by this award will investigate how fungal symbionts contribute to tree species abundance, distribution, and diversity along stress gradients, both directly and indirectly, by influencing density-dependent interactions and feedbacks among adult and juvenile trees. Researchers will test the hypothesis that the net effect of fungal symbionts on plant performance is correlated with the level of abiotic drought and nutrient stress in the environment, with conspecific feedback shifting from negative to positive as abiotic stress increases. First, in a field experiment at the HJ Andrews Long Term Ecological Research (LTER) site, investigators will reciprocally transplant three focal tree species beneath the canopies of adult conspecific or heterospecific trees along natural moisture and soil-nutrient stress gradients, manipulating fungal mutualists to evaluate their effect on conspecific density-dependent feedback. In greenhouse experiments, trees, microbes, and soil nutrient and drought stress will be manipulated. Finally, this project will integrate host-symbiont dynamics into regional models of forest community dynamics to assess how tree population/community dynamics might be altered under conditions of abiotic stress. Overall, the proposed work will test multiple hypotheses regarding how fungal symbionts contribute to the direction and strength of feedback for dominant tree species in forests of the Pacific Northwest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.