CAREER: Functional Bases for the Trade-Off Between Growth and Survival of Tree Seedlings

如何将有限的资源分配到不同的功能上，对生物在个体和种群水平上的生长速度和生存都有重大影响。快速生长与高生存潜力本质上是不相容的，最近对热带和温带森林树木再生的研究强烈表明，这是一种权衡。耐阴物种通过维持生长缓慢的幼苗来招募树苗，这些幼苗可以忍受林下各种生物和非生物胁迫。相比之下，依赖于光隙的物种具有丰富且分散良好的种子和快速生长的幼苗，对生物和非生物胁迫的耐受性较低。对于这种权衡关系，最简单但最普遍的假设是，将更多资源分配给储存和防御的物种生存得更好，但表现出较慢的生长（至少在短期内）。在植物中，更高的碳分配（即光合作用捕获的能量）用于新叶的构建，导致碳收入的复合回报和快速的生长率。然而，这种分配模式必须以相对较少的碳分配给储存（即，作为非结构性碳水化合物的能源节约）和防御（例如，坚韧的支持组织和抵抗草食和疾病的化学毒素）为代价。因此，采用快速生长分配策略的物种应该遭受高死亡率，因为这些物种更容易受到草食，病原体攻击和物理干扰。Kitajima将通过对巴拿马热带树种幼苗的碳储存和碳基防御的一系列比较研究来验证这一总体假设。将在温室的标准化条件下培养7个表现出不同生长速度和存活率的科对物种，以比较茎和根的能量储存分配以及碳基防御（木质素和其他酚类化合物）。在第二个实验中，该研究人员将通过检查不同物种幼苗的生长和存活来测试储存分配在野外的生态作用，这些物种幼苗在对遮荫和模拟草食处理的反应中表现出不同程度的储存分配。在第三项研究中，我们将研究储存和防御的分配模式，以阐明它们与森林林下自然招募幼苗的长期生长和生存的关系。在最后的研究中，将对野生咖啡属（Psychotria）的两种植物进行全植物碳收支（总碳增益和净碳增益、碳增益与呼吸、组织构建、储存和根分泌物的比例）的量化。这项研究将与教育活动相结合。生态相互作用中生理约束的哲学含义超越了纯粹的生物相互作用。基于分配权衡的生态模型不仅对那些期望以生态学家为职业的学生很重要，而且对那些从事影响社会对生态和环境问题反应的非科学学科的学生也很重要。因此，北岛大学在本科和研究生课程的教学中将强调分配的权衡。她的研究和教学将最直接地整合到“热带生态学的夏季研究经验”课程中，在这门课程中，本科生将作为在巴拿马进行的这项研究的实际参与者，获得出色的教育经验。

How limited resources are allocated to different functions has strong consequences to growth rates and survival of organisms at both individual and population levels. Fast growth is inherently incompatible with high survival potential, a trade-off strongly suggested in recent studies of regeneration of trees in tropical and temperate forests. Shade tolerant species recruit saplings through maintenance of slow-growing seedlings that tolerate various biotic and abiotic stresses in the understory. In contrast, light-gap dependent species colonize with abundant and well-dispersed seeds and fast-growing seedlings having low tolerance of biotic and abiotic stress. The simplest yet most general hypothesis for such a trade-off relationship is that species allocating more resources to storage and defense survive better, but exhibit slower growth (at least in a short term). In plants, higher allocation of carbon (i.e., photosynthetically captured energy) to construction of new leaves leads to a compound return of carbon income and fast growth rates. However, this allocation pattern must come at the cost of relatively less carbon allocated to storage (i.e., energy savings as non-structural carbohydrates) and defense (e.g., tough support tissue, and chemical toxins that resist against herbivory and disease). Consequently, species that employ allocation strategies for fast growth should suffer from high mortality rates because these species are more vulnerable to herbivory, pathogen attack and physical disturbance. Kitajima will test this overall hypothesis through a series of comparative studies of carbon storage and carbon-based defenses in seedlings of tropical tree species in Panama. Seven family pairs of species exhibiting contrasting growth rates and survival will be raised under standardized conditions in a greenhouse for comparison of allocation to energy storage in stems and roots, and carbon-based defenses (lignin and other phenolic compounds). In a second experiment, this researcher will test the ecological role of storage allocation in the field by examining growth and survival of seedlings of species displaying contrasting degrees of storage allocation as they respond to shading and simulated herbivory treatments. In the third study, patterns of allocation to storage and defense will be examined to elucidate their relationship to longer-term growth and survival in naturally recruited seedlings in the forest understory. Whole-plant carbon budgets (total gross and net carbon gain, proportion of carbon gain to respiration, tissue construction, storage, and root exudate) will be quantified for two species of plants in the wild-coffee genus (Psychotria) in the final study. This research will be integrated with educational activities. The philosophical implications of the physiological constraints in ecological interactions go beyond purely biological interactions. Ecological models based on allocation-based trade-offs are important in training not only those students anticipating professional careers as ecologists, but also for those students pursuing studies in non-scientific disciplines that affect the societal responses to ecological and environmental issues. Allocation trade-offs, thus, will be emphasized in Kitajima's teaching in both undergraduate- and graduate-level courses. Her research and teaching will be most directly integrated in the course "Summer Research Experience in Tropical Ecology," in which undergraduate students will have an outstanding educational experience as hands-on participants in this research in Panama.