Rapid transgenerational effects in Knautia arvensis in response to plant-community diversity

1. Plant-species persistence in natural communities requires coping with biotic and abiotic challenges. These challenges also depend on plant-community composition and diversity. Over time, biodiversity effects have been shown to be strengthened via increasing species complementarity in mixtures. Little is known, however, whether differences in community diversity and composition induce rapid transgenerational phenotypic adaptive differentiation during community assembly. We expect, altered plant-plant and other biotic interactions (mutualists or antagonists) in high vs. low diverse communities to affect immediate within- and between species-trait differentiations due to competition for light and nutrients. 2. Three years after the initiation of a large-scale, long-term biodiversity experiment in Jena, Germany, we tested for effects of varying experimental plant-community diversity (1–60 plant species; 1–4 plant functional groups) and composition (with or without legumes and/or grasses) on phenotypic differentiation and variation of the tall herb Knautia arvensis. We measured reproduction at different diversity levels in the Jena experiment (residents hereafter) and, in an additional common garden experiment without competition, recorded subsequent offspring performance (i.e., growth, reproductive success and susceptibility to powdery mildew) to test for differentiation in phenotypic expression and variability. 3. We observed phenotypic differences among diversity levels with reduced fecundity of K. arvensis residents in more diverse communities. In the next generation grown under common garden conditions, offspring from high diversity plots showed reduced growth (i.e., height) and lower reproduction (i.e., fewer infructescences), but increased phenotypic trait variability (e.g., in leaf width and powdery mildew presence) and also tended to be less susceptible to powdery mildew infection. 4. Community composition also affected Knautia parents and offspring. In the presence of legumes resident plants produced more seeds (increased fecundity), however germination rate of those seeds was reduced at an early seedling stage (reduced fertility). 5. Synthesis: We conclude that rapid transgenerational effects of community diversity and composition on both mean and variation of phenotypic traits among offspring exist. Additional to heritable variation, environmentally induced epigenetic and/ or maternal processes matter for early plant community assembly and may also determine future species co-existence and community stability.

1. 自然群落中的植物物种存续，需应对生物（biotic）与非生物（abiotic）胁迫。此类胁迫同时取决于植物群落的组成与多样性。长期以来，已有研究表明，混播群落中物种生态位互补性的提升会强化生物多样性效应。然而，目前学界尚不清楚，群落多样性与组成的差异是否会在群落组装过程中引发快速的跨代表型适应性分化。我们推测，相较于低多样性群落，高多样性群落中改变的种间互作及其他生物互作（共生体或拮抗物），会因光与养分的竞争，直接影响物种内与物种间的性状分化。
2. 在德国耶拿启动一项大型长期生物多样性实验三年后，我们针对不同梯度的实验植物群落多样性（1~60种植物；1~4个植物功能群）与组成（是否包含豆科植物和/或禾本科植物），检验其对高大草本野山萝卜（Knautia arvensis）的表型分化与变异的影响。本研究在耶拿实验中测定了不同多样性梯度下的本地植株（下文简称“本地株”）的繁殖情况，并在另一项无竞争的同质园实验中记录后续子代的表现（即生长状况、繁殖成功率以及白粉病（powdery mildew）易感性），以此检验表型表达与变异的分化情况。
3. 我们观察到不同多样性梯度间存在表型差异：在更高多样性的群落中，野山萝卜本地株的繁殖力下降。在同质园条件下培育的子代中，源自高多样性样地的子代生长状况（如株高）与繁殖能力（如果序数量）均有所降低，但表型性状变异度（如叶宽、白粉病感染情况）有所提升，且对白粉病感染的易感性也趋于降低。
4. 群落组成同样对野山萝卜的亲本与子代产生影响。当群落中存在豆科植物时，本地株的结籽量更高（繁殖力提升），但此类种子在幼苗早期的萌发率有所下降，育性随之降低。
5. 综合分析：本研究证实，群落多样性与组成对子代表型性状的均值与变异度均存在快速跨代效应。除遗传变异外，环境诱导的表观遗传（epigenetic）及/或母源效应过程，在植物早期群落组装中发挥重要作用，同时也可能决定未来的物种共存与群落稳定性。