Sapling Census:FAB 1: Forests and Biodiversity Experiment - High density diversity experiment

A forest biodiversity experiment (FAB) focused on trees of our region investigates the consequences of multiple dimensions of tree diversity for soil, food webs, plant communities and ecosystems. FAB is designed to unravel effects of three forms of biological diversity: species richness (SR), functional diversity (FD), and phylogenetic diversity (PD). We define FD as the representation of multiple traits of leaves, roots, seeds, and the whole organism that are correlated with species positions along gradients of resource supply, growth, and decomposition. PD is the representation of evolutionary lineages measured as the genetic distances between species. While PD and FD are often correlated, convergent evolution and adaptive differentiation can decouple them. When functional traits that drive specific ecosystem functions are not phylogenetically conserved, PD and FD may give contrasting predictions. SR, PD, and FD are not independent, and we posit that PD may help explain SR effects, and FD may help explain both PD and SR effects. Thus FAB is designed to examine the separate and combined effects of all three components of diversity for multiple ecosystem functions and to distinguish between ???sampling??? and ???complementarity??? effects of biodiversity. Due to the long lag between planting tree seedlings and determining effects of tree composition and diversity on ecosystem functioning, fewer experiments have been established to elucidate the role of biodiversity in the functioning of forest ecosystems than grassland experiments. FAB will contribute to this gap and is becoming a member of the IDENT and TreeDiv network of forest biodiversity experiments (www.treedivnet.ugent.be).

Hypotheses:
1. PD, FD, and SR will all contribute to increased productivity, stability, and diversity of other trophic levels (herbivores, predators, parasitoids, soil microbes, soil flora and fauna) as well as to greater soil C sequestration.
2. Because PD incorporates both the number of species and measurement of their evolutionary divergence, PD will explain more of the variation in ecosystem productivity and stability than SR. Similarly, among-species FD will explain more variation in these ecosystem functions than SR or PD.
3. Plant assemblages of similar SR but comprised of increasingly divergent PD or FD will show increasing divergence in ecosystem functions.
4. Species with functional traits not yet present in a plot will more easily invade than species with traits similar to the established species.

The FAB single species plots will allow us to test hypotheses about the importance of plant functional traits in influencing ecosystem properties (e.g., NPP, soil C, N mineralization) and plant-associated microbial communities. For example, we expect that plant species that increase concentrations of polyvalent soil cations (e.g., because of unique base cation chemistry or because of effects on soil acidity that influence Al and Fe solubility) will promote soil C stabilization through mineral-organic matter interactions and the formation of microaggregates that protect soil C from decomposition.

森林生物多样性实验（Forest Biodiversity Experiment，缩写FAB）聚焦于本地区林木，旨在探究林木多样性的多维度特征对土壤、食物网、植物群落及生态系统的影响。FAB旨在解析三类生物多样性的效应：物种丰富度（Species Richness，缩写SR）、功能多样性（Functional Diversity，缩写FD）以及系统发育多样性（Phylogenetic Diversity，缩写PD）。我们将功能多样性（FD）定义为叶片、根系、种子及全株的多重功能性状的表征，这些性状与物种在资源供给、生长及分解梯度上的分布位置密切相关。系统发育多样性（PD）则是以物种间遗传距离为度量标准的进化谱系表征。尽管二者通常存在关联，但趋同演化与适应性分化可使系统发育多样性与功能多样性脱耦。当驱动特定生态系统功能的功能性状不具有系统发育保守性时，二者可能会给出相悖的预测结果。物种丰富度、系统发育多样性及功能多样性三者并非相互独立，我们推测系统发育多样性可辅助解释物种丰富度的效应，而功能多样性则可辅助解析系统发育多样性与物种丰富度的效应。因此，FAB旨在探究这三类多样性组分对多种生态系统功能的单独及联合效应，并区分生物多样性的取样效应（sampling effect）与互补效应（complementarity effect）。由于林木幼苗定植与明确林木组成及多样性对生态系统功能的效应之间存在较长的时间滞后，相较于草地生态系统实验，针对森林生态系统中生物多样性作用的相关实验数量相对较少。FAB将填补这一研究空白，目前已加入森林生物多样性实验网络IDENT与TreeDiv（www.treedivnet.ugent.be）。

研究假说：
1. 系统发育多样性、功能多样性与物种丰富度均可提升生态系统生产力、稳定性及其他营养级（植食动物、捕食者、寄生性昆虫、土壤微生物、土壤动植物）的多样性，同时促进土壤碳固存。
2. 由于系统发育多样性同时涵盖物种数量与物种进化分化程度的度量，其对生态系统生产力与稳定性变异的解释力将强于物种丰富度。同理，种间功能多样性对上述生态系统功能变异的解释力也将优于物种丰富度或系统发育多样性。
3. 物种丰富度相似但系统发育多样性或功能多样性梯度递增的植物群落，其生态系统功能的差异程度将随之增大。
4. 相较于功能性状与定居物种相似的物种，具备样地中未出现的功能性状的物种更易成功入侵。

FAB的单物种样地可用于验证关于植物功能性状对生态系统属性（如净初级生产力（Net Primary Productivity，缩写NPP）、土壤碳、氮矿化）及植物关联微生物群落影响重要性的假说。例如，我们推测可提升土壤多价阳离子浓度的植物物种（例如因独特的碱基阳离子化学特性，或通过改变土壤酸度影响铝与铁的溶解性），将通过矿物-有机质相互作用及形成保护土壤碳免于分解的微团聚体，促进土壤碳固存稳定。