MCA: Ontogenetic constraints to climate change resilience – Investigating consequences of heteroblasty under increasing aridity in New Zealand forests

由于气温上升，降雨量不可预测，以及极端热浪，风暴和洪水等极端事件，森林树木正在经历越来越多的生理压力。由于植物在从幼苗到幼年再到成年的生长过程中，其形态和功能会发生很大变化，因此气候变化对植物生存和生长的影响预计会随着植物年龄的变化而变化。这可能对景观中物种的持久性产生重大影响。例如，在造成成年树木死亡的干扰（如飓风或森林火灾）之后，气候异常炎热或干旱，可能导致再生树苗的高死亡率，从而限制森林恢复。此外，不寻常的气候压力因素，如长期干旱，可能导致成年树木枯死，对流域功能，碳储存和野生动物栖息地产生影响。在单个植物物种的尺度上，我们不了解植物如何在从幼年到成年的过程中耐受气候变化，特别是对于在其生命周期内经历气候变化的长寿植物。该项目调查气候变化对几个森林树种的影响，通过比较新西兰森林中几个物种的不同少年形式与成年阶段树木的表现，以应对两种不同类型的模拟干旱。这些森林的面积因土地使用的变化和引进的动物而减少，其独特的生物多样性现在正受到气候变化的威胁。岛屿植物可能特别容易受到气候变化的影响，因为它们的分布有限，与大陆森林树种相比，它们的生长性状可能总体上的灵活性有限。这项工作将评估每个物种在自然气候梯度上的现有变异性，并评估不同种群在受控温室环境中对干旱的反应。这项研究将提高我们对这些森林树木不同生命阶段耐旱性的理解，有助于确定可能是避难所的气候条件，这些物种可以继续作为幼苗和成年人存在，因为气候变暖和干燥，以及景观上的地区，人口很可能因为青少年对气候变化或成年树死亡的敏感性而极易死亡。这些信息将有助于保护本土岛屿物种，同时吸引本土太平洋岛屿学生和土著森林管理人员参与研究过程。植物在生长过程中在形式和功能上发生很大变化，因此幼苗和幼龄树通常在叶子形状，光合作用速率和水分利用方面与成年树不同，并且在生产刺和毒素以防御食草动物方面也不同。这种个体发生的变化被认为有助于植物在随着植物成熟而变化的环境中生存和生长。例如，幼苗生长在地面附近，那里比成年植物经历的环境更冷，更干燥，更阴暗，风更少，并且它们可能经历不同类型和强度的食草动物。对于许多植物物种来说，随着植物经历发育阶段，环境条件的变化是可预测的，从而导致植物形态和功能的固定发育变化的进化，称为异胚性的生活史。 气候变化正在短时间尺度内引入新的变异性，包括更多的连续无雨日，更多的极端降雨事件，以及年平均降雨量的方向变化。这些气候变化将如何影响植物的整个生命周期，特别是那些在形式和功能上有固定个体发育转变的植物，目前还不清楚。该项目调查了具有固定（同源）与灵活（异源）个体发育变化的物种在形式和功能上如何在气候变化下使用多种方法进行，包括实地研究，以测量不同气候条件下幼苗和成年人的形态和生理特征，以及温室实验，以测试植物特征在模拟气候变化条件下的可塑性。许多具有固定发展模式的物种出现在岛屿上，这些岛屿上的物种特别容易受到环境变化的影响，因为它们的活动范围有限，而且由于历史上土地使用的变化而减少。因此，该项目将在新西兰进行，那里异胚性很常见。这项工作将提高我们对气候变化对植物生长影响的理解，并有助于在全球变化的威胁下保护本土岛屿物种。 它将使太平洋岛屿的本土学生参与研究，并将与土著森林知识持有者合作，交流有关重要岛屿树种及其对气候变化的潜在反应的信息。该项目由人口与社区生态计划和刺激竞争研究既定计划（EPSCoR）共同资助该奖项反映了NSF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。

Forest trees are experiencing increased physiological stress due to rising temperatures, less predictable rainfall, and more extreme events such as extreme heatwaves, storms, and floods. Because plants change considerably in form and function as they grow from seedlings to juveniles to adults, the effects of climate change on plant survival and growth are expected to change with plant age. This could have large consequences for the persistence of species on the landscape. For example, an unusually hot or arid climate period after a disturbance that kills adult trees (like a hurricane or a forest fire), could cause high mortality of regenerating tree seedlings thereby limiting forest recovery. Additionally, unusual climate stressors such as prolonged drought, could lead to dieback of adult trees with consequences for watershed functioning, carbon storage and wildlife habitat. At the individual plant species scale, we do not understand how plants will tolerate climate change as they grow from juveniles to adults, particularly for long-lived plants that experience changing climates within their lifetimes. This project investigates climate change effects on several forest tree species by comparing the performance of distinct juvenile forms versus adult stage trees of several species in New Zealand forests in response to simulated droughts of two different kinds. These forests have been reduced in area by land use change and introduced animals, and their unique biodiversity is now being threatened by climate change. Island plants may be particularly vulnerable to climate change due to their limited distributions and potentially limited overall flexibility in growth traits compared to mainland forest tree species. This work will evaluate existing variability within each species across a natural climate gradient and evaluate how different populations respond to drought in a controlled greenhouse setting. The study will improve our understanding of drought tolerance in different life stages of these forest trees, help to identify the climate conditions that might be refugia where these species can continue to exist as both seedlings and adults as climate warms and dries, and also areas on the landscape where populations are likely to be highly susceptible to mortality because of juvenile sensitivity to climate change or adult tree death. This information will contribute to the conservation of native island species while engaging native Pacific Island students, and Indigenous forest managers in the research process.Plants change considerably in form and function as they grow, with the result that seedlings and juvenile trees usually differ from adult trees in leaf shape, rates of photosynthesis and water use, and in the production of spines and toxins as defense against herbivores. Such ontogenetic changes are thought to help plants survive and grow through environments that also shift as plants mature. For example, seedlings grow near the ground where it is colder, drier, shadier, and less windy than the environment adult plants experience, and they may experience different types and intensities of herbivory. For many plant species, the shifts in environmental conditions as plants pass through developmental phases are predictable, leading to the evolution of fixed developmental changes in plant form and function, a life history known as heteroblasty. Climate change is introducing new variability within short time scales, including more consecutive days without rain, more extreme rainfall events, and directional changes in mean annual rainfall. How these climatic changes will affect plants throughout their lifetimes, especially those with fixed ontogenetic shifts in form and function, is unclear. This project investigates how species with fixed (homoblastic) versus flexible (heteroblastic) ontogenetic shifts in form and function perform under climate change using a combination of approaches, including field studies to measure morphological and physiological traits in seedlings and adults across different climates, and greenhouse experiments to test the degree to which plant traits are plastic under simulated climate change conditions. Many species with fixed developmental patterns occur on islands where species are particularly vulnerable to environmental change because they have limited ranges that have been reduced by historic land use change. Hence, this project will be carried out in New Zealand where heteroblasty is common. This work will improve our understanding of climate change effects on plants as they grow up, and contribute to the conservation of native island species under the threat of global change. It will engage native Pacific Island students in research, and will work with Indigenous forest knowledge holders to exchange information on important island tree species and their potential responses to climate change.This project is jointly funded by the Population and Community Ecology program and the Established Program to Stimulate Competitive Research (EPSCoR).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.