RAPID: Is Carbon Starvation a Proximal Cause of Tree Mortality from Defoliation?

2015年，新英格兰南部爆发了严重的吉普赛飞蛾疫情。到2018年，这场疫情已经导致数千英亩橡树林的树木戏剧性死亡。自从这种入侵昆虫在北美东部造成如此广泛的树木破坏和死亡以来，已经有30多年了。这一事件为解决生态学中的一个基本问题创造了一个转瞬即逝的机会：树木死亡的直接原因是什么？硬木树在春天利用储存的淀粉和糖来长出新叶。吉普赛蛾吃树叶，限制了树储存足够糖和淀粉的能力，如果这些降到临界水平以下，树可能会死亡。在去年的疫情爆发期间，研究人员在经历了不同程度和频率的吉普赛蛾活动的橡树林中建立了一个地块网络。如果他们迅速采取行动，在今年春天落叶之前，对经历了0到3年落叶的橡树进行淀粉和糖的采样，然后在下一个生长季对这些树进行跟踪，研究人员可以确定饥饿是否直接导致了树的死亡。更好地了解树木死亡的时间和原因将为森林和景观树木管理提供信息。这项研究还将为学生提供回答科学问题以及如何应用科学知识解决森林管理问题的培训。恒温落叶树在春季利用非结构性碳水化合物(NSC)的储存来产生新的木质部和树叶。碳饥饿假说认为，当NSC的储藏枯竭时，二次生长和冲洗就不可能或不充分，树木就会死亡。落叶，如在吉普赛飞蛾侵袭期间发生的，是检验碳饥饿假说的直接机制。这项研究将评估NSC水平与落叶频率和严重程度的关系，以确定是否存在临界NSC阈值，低于该阈值将发生树木死亡。研究人员将通过从具有已知落叶历史的橡树的茎和根收集小木材样本来采样神经干细胞。这项研究有可能提供对树木死亡事件的机械理解，并为科学家和政策制定者预测生态系统对全球变化的反应所依赖的模型提供信息。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A severe gypsy moth outbreak began in 2015 in southern New England. By 2018, this outbreak had caused dramatic death of trees across thousands of acres of oak forest. It has been more than thirty years since this invasive insect caused such extensive tree damage and death in eastern North America. This event has created a fleeting opportunity to address a fundamental question in ecology: what are the immediate causes of tree death? Hardwood trees draw on stored starches and sugars in the spring to produce new leaves. Gypsy moths eat leaves, limiting a tree's ability to store enough sugars and starches, and if these drop below a critical level, the tree can die. During last year's outbreak, the researchers established a network of plots in oak forests that had experienced differing severity and frequency of gypsy moth activity. If they act fast and sample starches and sugars from oak trees that have experienced defoliation for 0 to 3 years before they leaf-out this spring, then follow these trees through the next growing season, the researchers can determine if starvation directly causes tree death. Better understanding of the timing and causes of tree mortality will inform forest and landscape tree management. This research will also provide student training in answering science questions and how to apply scientific knowledge to solving forest management problems.Temperate deciduous trees draw on stores of non-structural carbohydrates (NSC) in the spring to produce new xylem and foliage. The carbon starvation hypothesis posits that when NSC stores become depleted, secondary growth and flushing is impossible or inadequate, and the tree dies. Defoliation, such as occurs during gypsy moth infestations, is a straightforward mechanism for testing the carbon starvation hypothesis. This study will evaluate NSC levels in relationship to defoliation frequency and severity to determine if there is a critical NSC threshold below which tree mortality occurs. The researchers will sample NSCs by collecting small wood samples from the stem and root of oak trees with known defoliation histories. This study has the potential to offer a mechanistic understanding of tree mortality events and inform the models scientists and policy-makers rely on to forecast ecosystem responses to global change.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.