INTRODUCTION

Biological adaptations invariably rely on the assimilation of environmental information. At the population level, relevant information is genetically integrated via evolutionary processes, regardless of the involvement or awareness of the involved organisms. In contrast, adaptive behaviour and phenotypic plasticity directly rely on the perception of relevant information by responding individuals (Taborsky 2017). Selected for by their limited motility and fostered by their morphological modularity and continuous juvenility, plants present some of the most extreme and diverse examples of phenotypic plasticity (Schlichting 1986; Sultan 2000; Novoplansky 2009; Chevin & Hoffmann 2017). While most studies on plant phenotypic plasticity deal with responsiveness to resource availability, edaphic conditions, and biotic stresses (e.g., Arnold et al. 2019), evidence shows that adaptive plastic responses in plants often rely on the perception of signals and cues from other plants, also termed ‘plant communication’ (Karban 2021). For example, following local stress or herbivore damage, plants not only increase local defences but also emit various signals and cues that induce preemptive defensive responses in other organs of the same plant and in yet unaffected neighbours (for reviews, see Karban 2021; Endara et al. 2023).

An increasing number of studies demonstrate important adaptive implications of belowground interplant cueing by root exudates (Wang et al. 2021). Besides their crucial role in allelopathy (Weidenhamer et al. 2023) and facilitation (Li et al. 2016), root exudates have been shown to mediate communication with various soil microbes, neighbour detection (Karban 2021), competitive self/nonself (Mahall & Callaway 1991; Falik et al. 2003; Gruntman & Novoplansky 2004) and kin/non-kin responses (File & Dudley 2007; Biedrzycki et al. 2010; Murphy et al. 2017; Wang et al. 2021).

Although endogenous flowering signalling is one of the core topics of plant biology (Bao et al. 2020; Zhang et al. 2020), there is only a handful of studies dealing with interplant reproductive cueing. A study on Moricandia moricandioides demonstrated that plants increased flower production when growing near kin, compared to non-kin neighbours (Torices et al. 2018). In the parasitic plant Cuscuta australis, flowering induction has been demonstrated to depend on the transfer of FLOWERING LOCUS T (FT) protein from the host plant (Shen et al. 2020). We previously demonstrated that root leachates from Brassica rapa grown under flowering-inductive long-day conditions accelerated flowering and decreased allocation to vegetative organs in target plants growing under non-inductive short-day conditions (Falik et al. 2014).

Some plant taxa exhibit dimorphic cleistogamy, a mixed mating system whereby both closed self-pollinated cleistogamous (CL) and potentially outcrossing open chasmogamous (CH) flowers are produced on the same individual plant (Lord 1981). In many of these, the ratio of CH to CL flowers (CH/CL) is plastically responsive to various environmental conditions and cues, such as light intensity and spectral composition, photoperiod, temperature, resource availability, ontogeny, and competition (Lord 1981; Cortés-Palomec & Ballard 2006). Plasticity in CH/CL may have significant fitness implications for the progeny of individual mother plants (Stojanova et al. 2016; Cheplick 2023). Greater production of CH flowers could provide fitness advantages in heterogeneous habitats if outcrossing is sufficiently effective, where the progeny of CH flowers exhibit heterosis (Schmitt & Gamble 1990), or where seeds from CH flowers disperse further from the mother plant and thus reduce sibling competition (Cheplick 1993). Increased production of CL flowers could exacerbate inbreeding depression and decrease genetic diversity, although under certain circumstances consistent production of CL flowers could eventually reduce inbreeding depression via purging of deleterious recessive alleles (Glémin 2003; Grossen et al. 2020; but see Charlesworth, 1992; Zeitler et al. 2023). CL can provide reproductive assurance when pollinators are absent or scarce (Cheplick 2007). As insect-pollinated CH flowers are typically significantly larger and comprise costly display and reward elements, the production of inexpensive CL flowers may allow increased resource allocation to more or larger seeds, which in turn could have significant fitness implications related to competition and seed dispersal (Waller 1984; Cheplick 2023).

Here we tested the hypothesis that plants can adaptively modulate the production of cleistogamous and chasmogamous flowers based on the perception of conspecific neighbours. Specifically, we studied the possible effects of interplant root cueing on the production of CL and CH flowering in Lamium amplexicaule L. (Lamiaceae). The production and proportion of CH and CL flowers were examined in individual plants grown at variable densities and when treated with leachates from plants grown at variable densities. We predicted that plants would increase production of more expensive and showy CH flowers when they perceive the presence of potential conspecific reproductive partners.

中文翻译：

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一种新型的邻居感知在具有混合交配系统的一年生植物中引发生殖可塑性

介绍

生物适应总是依赖于环境信息的同化。在种群水平上，相关信息通过进化过程在基因上整合，无论相关生物体的参与或意识如何。相反，适应性行为和表型可塑性直接依赖于做出反应的个体对相关信息的感知（Taborsky  2017）。植物因其有限的运动能力而被选择，并因其形态模块性和持续的幼年性而被培育，呈现出一些最极端和多样化的表型可塑性例子（Schlichting  1986；Sultan  2000；Novoplansky  2009；Chevin & Hoffmann  2017）。虽然大多数关于植物表型可塑性的研究涉及对资源可用性、土壤条件和生物胁迫的响应（例如，Arnold 等人， 2019  ），但有证据表明，植物的适应性可塑性反应通常依赖于对来自其他植物的信号和线索的感知，也称为“工厂通信”（Karban  2021）。例如，在局部应激或食草动物损伤后，植物不仅增强局部防御，而且会发出各种信号和线索，诱导同一植物的其他器官和尚未受影响的邻居发生先发性防御反应（有关评论，请参阅 Karban 2021  ； En​​dara等等2023  ）。

越来越多的研究表明，根系分泌物对地下间种植物的适应性具有重要意义（Wang等人，  2021）。除了在化感作用（Weidenhamer et al .  2023）和促进（Li et al . 2016 ）中的关键作用外，根系分泌物还被证明可以介导与各种土壤微生物的通讯、邻居检测（Karban  2021）、竞争性自我/非自我（Mahall & Callaway  1991；Falik等人2003  ； Gruntman 和 Novoplansky  2004）和亲属/非亲属反应（File 和 Dudley  2007 ； Biedrzycki等人2010  ；Murphy等人2017  ； Wang等人2021  ）。

尽管内源开花信号是植物生物学的核心主题之一（Bao et al .  2020；Zhang et al .  2020），但涉及株间生殖信号的研究却很少。对Moricandia moricandioides的一项研究表明，与非亲缘邻居相比，在近缘植物生长时，植物的花朵产量会增加 (Torices et al . 2018 )。在寄生植物菟丝子中，开花诱导已被证明取决于来自宿主植物的 FLOWERING LOCUS T (FT) 蛋白的转移（Shen等人，  2020）。我们之前证明，在开花诱导长日照条件下生长的白菜的根浸出液加速了开花，并减少了在非诱导短日照条件下生长的目标植物营养器官的分配（Falik等人，  2014）。

一些植物类群表现出二态性闭锁受精，这是一种混合交配系统，在同一株植物上产生封闭自花授粉闭锁受精（CL）和潜在异交开放裂受受精（CH）花（Lord  1981）。在许多这些花中，CH与CL花的比例（CH/CL）对各种环境条件和线索有塑性响应，例如光强度和光谱组成、光周期、温度、资源可用性、个体发育和竞争（Lord  1981；科尔特斯-帕洛梅克和巴拉德2006）。 CH/CL 的可塑性可能对单个母本植物的后代具有显着的适应性影响（Stojanova等人，  2016 年；Cheplick  ，2023 年）。如果异交足够有效，CH 花的后代表现出杂种优势（Schmitt & Gamble  1990），或者 CH 花的种子远离母体植物，从而减少兄弟姐妹竞争，那么更多的 CH 花产量可以在异质生境中提供适应性优势。 （切普利克 1993）。 CL 花产量的增加可能会加剧近交衰退并降低遗传多样性，尽管在某些情况下，持续生产 CL 花最终可以通过清除有害的隐性等位基因来减少近交衰退（Glémin  2003；Grossen等人2020  ；但参见 Charlesworth，1992； Zeitler等人，  2023）。当授粉媒介不存在或稀缺时，CL 可以提供繁殖保证（Cheplick  2007）。由于昆虫授粉的 CH 花通常要大得多，并且包含昂贵的展示和奖励元素，因此廉价的 CL 花的生产可能会增加对更多或更大种子的资源分配，这反过来可能会对竞争和种子传播产生重大的适应性影响。沃勒 1984 年；切普利克2023 年）。

在这里，我们测试了这样的假设：植物可以根据同种邻居的感知适应性地调节闭锁花和开放花的产生。具体来说，我们研究了间生根提示对唇形花（唇形科） CL 和 CH 开花产生的可能影响。在以不同密度生长的单个植物中以及用来自以不同密度生长的植物的渗滤液处理时，检查了 CH 和 CL 花的产量和比例。我们预测，当植物感知到潜在同种生殖伙伴的存在时，它们会增加更昂贵、更艳丽的 CH 花的产量。