Journal of Ecology ( IF 5.3 ) Pub Date : 2022-06-10 , DOI: 10.1111/1365-2745.13943 Shan Luo 1, 2 , Richard D. Bardgett 3 , Bernhard Schmid 4 , David Johnson 3 , Kenny Png 3 , Urs Schaffner 5 , Huakun Zhou 6 , Buqing Yao 6 , Xiangyang Hou 7 , Nicholas J. Ostle 1
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1 INTRODUCTION
Understanding how biodiversity (B) affects ecosystem functioning (EF) is essential for assessing the consequences of biodiversity changes under anthropogenic disturbances (Newbold et al., 2015; Tilman et al., 1994). Many studies demonstrate that plant diversity can promote community productivity (Duffy et al., 2017; Grace et al., 2016; Tilman et al., 2001), which has been attributed to a variety of mechanisms relating to plant resource competition and plant–soil interactions (Loreau & Hector, 2001; Schnitzer et al., 2011). However, evidence is also mounting that the magnitude and sign of biodiversity effects vary with ecological context (Baert et al., 2018; Fridley, 2001; Isbell et al., 2011). Moreover, biodiversity effects can increase over time due to the evolution of species interactions (Fiegna et al., 2014; Schöb et al., 2018; Zuppinger-Dingley et al., 2014). Despite increased efforts testing the influence of contemporary environmental context on BEF relationships, the importance of historical context for biodiversity effects via plant species interactions and plant–soil interactions remains unclear. This lack of understanding hampers our ability to predict possible long-term anthropogenic impacts on ecosystem functioning.
Biodiversity effects on ecosystem functions depend on how species function differently in the presence of other species, which is mediated by species interactions (Fox, 2005; Loreau & Hector, 2001). Two classes of biodiversity effects have been proposed: complementarity and sampling effects (Fox, 2005; Loreau & Hector, 2001). The complementarity effect refers to niche complementarity and facilitation among species that increase species' functioning by reducing the intensity of competition individuals experience in diverse communities compared to monocultures. In contrast, the sampling effect is caused by an increased probability of diverse plant communities to contain competitive species with high functional contributions (Fox, 2005; Loreau & Hector, 2001). In addition to plant species interactions, there is growing evidence that soil microbes contribute to positive plant diversity effects on community productivity (Liang et al., 2019; Luo et al., 2018; Schnitzer et al., 2011), for instance by promoting complementarity effects among plant species through soil nitrogen partitioning (Luo et al., 2018).
The realized effects of mechanisms relating to plant species interactions and plant–soil interactions on ecosystem functioning can be dependent upon ecological context. The nature and intensity of species interactions usually change with contemporary environmental context (Callaway et al., 2002; Maestre et al., 2009; Michalet et al., 2014; Wright et al., 2014). For instance, a theoretical study suggested that an intermediate level of environmental stress increases interspecific competition that reduces positive complementarity effects among species, but increases positive sampling effects (Baert et al., 2018). The context dependency of species interactions may thus drive varying BEF relationships under different environmental conditions, including positive (Fridley, 2002; Steudel et al., 2012), non-significant (Fridley, 2002; Steudel et al., 2012) and even negative biodiversity effects on ecosystem functioning (Wang et al., 2019). Plant–soil interactions also change with contemporary environmental context. For example, high soil fertility can increase the negative effects of soil pathogens (Walters & Bingham, 2007), but decrease the positive effects of mycorrhizal fungi on plants (Hoeksema et al., 2010). As a result, changes in plant–microbe interactions under different soil nutrient conditions can lead to different plant diversity–community productivity relationships (Luo et al., 2017). Therefore, context-dependent plant species interactions and plant–soil interactions may result in the context dependency of BEF relationships (Baert et al., 2018; Steudel et al., 2012; Wang et al., 2019).
Plant species interactions and plant–soil interactions may not only respond to contemporary environmental context, but also to historical context. For example, plant species with 8 years of co-occurrence history in diverse community showed greater niche complementarity and facilitative interactions than did plant species with a history of growing in monoculture (Schöb et al., 2018; Zuppinger-Dingley et al., 2014). In contrast, plants with history in monoculture have been shown to benefit more from positive plant–soil interactions (Zuppinger-Dingley et al., 2016). Thus, plant responses to historical context may be contingent upon interactions with soil microbes. Because these plant interactions and plant–soil interactions underlie the functional response of ecosystems to varied levels of plant diversity, it is reasonable to expect that biodiversity effects on ecosystem functioning are also sensitive to historical context. However, it remains unclear how BEF relationships respond to historical context and how the ecological mechanisms underlying this response may vary depending on how historical context affects plant species interactions and plant–soil interactions.
Here, we investigated how historical context influences biodiversity effects on plant community productivity via plant species interactions. Arbuscular mycorrhizal (AM) fungi represent a major group of soil microbes known to influence the relationship between plant diversity and ecosystem functioning (Klironomos et al., 2000; van der Heijden et al., 1998), so we also tested how historical context modifies interactions between plants and AM fungal communities to provide insights into potential below-ground mechanisms underlying how historical context influences plant diversity–community productivity relationships. We tested the effects of historical context in alpine grasslands on the Qinghai-Tibetan Plateau, using two sites with different disturbance histories related to grazing intensity—heavy versus light livestock grazing—but similar current management. We carried out an experiment of varying levels of diversity using the same six dominant species, but originating from the two sites with or without heavy-grazing histories, hereafter called ‘disturbed-’ and ‘undisturbed-plant types’. We compared plant–plant interaction intensity and plant diversity–community productivity relationships of the two plant types. Additionally, we carried out a mycorrhizal hyphae-exclusion experiment (Johnson et al., 2001; Liang et al., 2020) to address the roles of AM fungal communities in mediating plant responses to historical context. Combined, the two experiments enabled us to test whether historical context modified diversity–productivity relationships via plant species interactions and further plant–mycorrhiza interactions.
中文翻译：
历史背景改变了高寒草原的植物多样性-社区生产力关系
1 简介
了解生物多样性 (B) 如何影响生态系统功能 (EF) 对于评估人为干扰下生物多样性变化的后果至关重要（Newbold 等人， 2015 年；Tilman 等人， 1994 年）。许多研究表明，植物多样性可以促进群落生产力（Duffy et al., 2017 ; Grace et al., 2016 ; Tilman et al., 2001），这归因于与植物资源竞争和植物-土壤相互作用（Loreau 和 Hector， 2001 年；Schnitzer 等人， 2011 年）。然而，越来越多的证据表明，生物多样性影响的大小和迹象随生态环境而变化（Baert et al., 2018 年；弗里德利， 2001；伊斯贝尔等人， 2011 年）。此外，由于物种相互作用的演变，生物多样性的影响会随着时间的推移而增加（Fiegna 等人， 2014 年；Schöb 等人， 2018 年；Zuppinger-Dingley 等人， 2014 年）。尽管增加了测试当代环境背景对 BEF 关系影响的努力，但历史背景通过植物物种相互作用和植物 - 土壤相互作用对生物多样性影响的重要性仍不清楚。这种缺乏理解阻碍了我们预测可能对生态系统功能产生的长期人为影响的能力。
生物多样性对生态系统功能的影响取决于物种在存在其他物种的情况下的不同功能，这是由物种相互作用介导的（Fox, 2005 ; Loreau & Hector, 2001）。已提出两类生物多样性效应：互补效应和抽样效应（Fox， 2005 年；Loreau & Hector， 2001 年）。互补效应是指物种之间的生态位互补性和促进作用，与单一栽培相比，通过降低个体在不同社区中的竞争强度来增加物种的功能。相比之下，抽样效应是由于不同植物群落包含具有高功能贡献的竞争物种的可能性增加（Fox， 2005；洛罗和赫克托， 2001 年）。除了植物物种的相互作用，越来越多的证据表明土壤微生物有助于植物多样性对群落生产力的积极影响（Liang 等人， 2019 年；Luo 等人， 2018 年；Schnitzer 等人， 2011 年），例如通过促进植物物种间通过土壤氮分配的互补效应（Luo et al., 2018）。
与植物物种相互作用和植物-土壤相互作用相关的机制对生态系统功能的实际影响可能取决于生态环境。物种相互作用的性质和强度通常会随着当代环境背景而变化（Callaway 等人， 2002 年；Maestre 等人， 2009 年；Michalet 等人， 2014 年；Wright 等人， 2014 年）。例如，一项理论研究表明，中等水平的环境压力会增加种间竞争，从而降低物种间的正互补效应，但会增加正抽样效应（Baert et al., 2018）。因此，物种相互作用的上下文相关性可能会在不同的环境条件下驱动不同的 BEF 关系，包括积极的 (Fridley, 2002 ; Steudel et al., 2012 )、不显着的 (Fridley, 2002 ; Steudel et al., 2012 ) 甚至消极的生物多样性对生态系统功能的影响（Wang 等人， 2019 年）。植物与土壤的相互作用也随着当代环境背景而变化。例如，高土壤肥力会增加土壤病原体的负面影响（Walters & Bingham, 2007），但会降低菌根真菌对植物的正面影响（Hoeksema et al., 2010）。因此，不同土壤养分条件下植物-微生物相互作用的变化会导致不同的植物多样性-群落生产力关系（Luo et al., 2017）。因此，依赖于背景的植物物种相互作用和植物-土壤相互作用可能导致 BEF 关系的背景依赖性（Baert 等人， 2018；Steudel 等人， 2012；Wang 等人， 2019）。
植物物种相互作用和植物-土壤相互作用可能不仅对当代环境背景作出反应，而且对历史背景也作出反应。例如，与具有单一栽培历史的植物物种相比，在不同群落中具有 8 年共生历史的植物物种表现出更大的生态位互补性和促进相互作用（Schöb 等人， 2018 年；Zuppinger-Dingley 等人， 2014 年） ）。相比之下，具有单一栽培历史的植物已被证明从植物与土壤的积极相互作用中受益更多（Zuppinger-Dingley 等， 2016）。因此，植物对历史背景的反应可能取决于与土壤微生物的相互作用。由于这些植物相互作用和植物-土壤相互作用是生态系统对不同水平植物多样性的功能响应的基础，因此可以合理地预期生物多样性对生态系统功能的影响也对历史背景敏感。然而，尚不清楚 BEF 关系如何响应历史背景，以及这种响应背后的生态机制如何根据历史背景如何影响植物物种相互作用和植物-土壤相互作用而变化。
在这里，我们研究了历史背景如何通过植物物种相互作用影响生物多样性对植物群落生产力的影响。丛枝菌根 (AM) 真菌是已知影响植物多样性和生态系统功能之间关系的主要土壤微生物群（Klironomos 等人， 2000 年；van der Heijden 等人， 1998 年）)，因此我们还测试了历史背景如何改变植物和 AM 真菌群落之间的相互作用，以深入了解历史背景如何影响植物多样性-社区生产力关系的潜在地下机制。我们测试了青藏高原高寒草原历史背景的影响，使用了两个具有与放牧强度相关的不同干扰历史的地点——重度放牧与轻度放牧——但目前的管理相似。我们使用相同的六种优势物种进行了不同水平的多样性实验，但起源于有或没有重度放牧历史的两个地点，以下称为“受干扰植物类型”和“未受干扰植物类型”。我们比较了两种植物类型的植物-植物相互作用强度和植物多样性-群落生产力关系。此外，我们进行了菌根菌丝排除实验（Johnson 等人， 2001；Liang 等人， 2020 年）探讨 AM 真菌群落在调节植物对历史背景的反应中的作用。结合起来，这两个实验使我们能够测试历史背景是否通过植物物种相互作用和进一步的植物 - 菌根相互作用来改变多样性 - 生产力关系。
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