Data from: Traits underlying community consequences of plant intra-specific diversity

A plant’s performance and interactions with other trophic levels are recorgnized to be contingent upon plant diversity and underlying associational dynamics, but far less is known about the plant traits driving such phenomena. We manipulated diversity in plant traits using pairs of plant and a substitutive design to elucidate the mechanisms underlying diversity effects operating at a fine spatial scale. Specifically, we measured the effects of diversity in sex (sexual monocultures vs. male and female genotypes together) and growth rate (growth rate monocultures vs. fast- and slow-growing genotypes together) on growth of the shrub Baccharis salicifolia and on above- and belowground consumers associated with this plant. We compared effects on associate abundance (# associates per plant) vs. density (# associates per kg plant biomass) to elucidate the mechanisms underlying diversity effects; effects on abundance but not density suggest diversity effects are mediated by resource abundance (i.e. plant biomass) alone, whereas effects on density suggest diversity effects are mediated by plant-based heterogeneity or quality. Sexual diversity increased root growth but reduced the density (but not abundance) of the dietary generalist aphid Aphis gossypii and its associated aphid-tending ants, suggesting sex mixtures were of lower quality to this herbivore (e.g. via reduced plant quality), and that this effect indirectly influenced ants. Sexual diversity had no effect on the abundance or density of parasitoids attacking A. gossypii, the dietary specialist aphid Uroleucon macolai, or mycorrhizae. In contrast, growth rate diversity did not influence plant growth or any associates except for the dietary specialist aphid U. macolai, which increased in both abundance and density at high diversity, suggesting growth rate mixtures were of higher quality to this herbivore. These results highlight that plant associational and diversity effects on consumers are contingent upon the source of plant trait variation, and that the nature of such dynamics may vary both within and among trophic levels.人们已认识到，植物的生长表现及其与其他营养级（trophic levels）的互作依赖于植物多样性及其内在的关联动态，但对于驱动这类现象的植物性状（plant traits）却知之甚少。本研究采用植物配对替换设计（substitutive design）操控植物性状多样性，以阐明精细空间尺度下多样性效应的内在机制。具体而言，我们分别检测了性型多样性（单性栽培组：仅单一性别基因型；混性栽培组：雌雄基因型共存）与生长速率多样性（单生长型组：仅单一生长速率基因型；混生长型组：快慢生长速率基因型共存）对灌木Baccharis salicifolia生长，以及该植物相关的地上、地下消费者的影响。我们通过对比伴生生物丰度（每株植物的伴生生物数量）与密度（每千克植物生物量的伴生生物数量）的效应差异，以解析多样性效应的内在机制：若仅对丰度产生影响而未影响密度，则表明多样性效应仅由资源丰度（即植物生物量）介导；若对密度产生影响，则表明多样性效应由植物介导的异质性或品质所介导。性型多样性提升了Baccharis salicifolia的根系生长，但降低了广食性蚜虫棉蚜（Aphis gossypii）及其相伴的照料蚜虫蚂蚁的密度（而非丰度），这表明混性栽培对该植食性动物的品质更低（例如通过降低植物品质），且该效应间接影响了蚂蚁种群。性型多样性对攻击棉蚜的寄生蜂、专食性蚜虫Uroleucon macolai以及菌根（mycorrhizae）的丰度与密度均无显著影响。与之相反，生长速率多样性未对植物生长或其他伴生生物产生影响，仅对专食性蚜虫U. macolai产生作用：在高多样性处理下，该蚜虫的丰度与密度均有所提升，这表明混生长型栽培对该植食性动物的品质更高。本研究结果表明，植物的关联效应与多样性效应对消费者的影响依赖于植物性状变异的来源，且这类动态的性质在营养级内部与营养级之间均可能存在差异。