Linking seedling wood anatomical trade-offs with drought and seedling growth and survival in tropical dry forests

IF 8.3 1区 生物学 Q1 PLANT SCIENCES
New Phytologist Pub Date : 2024-10-29 DOI:10.1111/nph.20222
Andrés González-Melo, Beatriz Salgado-Negret, Natalia Norden, Roy González-M, Juan Pablo Benavides, Juan Manuel Cely, Julio Abad Ferrer, Álvaro Idárraga, Esteban Moreno, Camila Pizano, Juliana Puentes-Marín, Nancy Pulido, Katherine Rivera, Felipe Rojas-Bautista, Juan Felipe Solorzano, María Natalia Umaña
{"title":"Linking seedling wood anatomical trade-offs with drought and seedling growth and survival in tropical dry forests","authors":"Andrés González-Melo, Beatriz Salgado-Negret, Natalia Norden, Roy González-M, Juan Pablo Benavides, Juan Manuel Cely, Julio Abad Ferrer, Álvaro Idárraga, Esteban Moreno, Camila Pizano, Juliana Puentes-Marín, Nancy Pulido, Katherine Rivera, Felipe Rojas-Bautista, Juan Felipe Solorzano, María Natalia Umaña","doi":"10.1111/nph.20222","DOIUrl":null,"url":null,"abstract":"<h2> Introduction</h2>\n<p>Water availability is a main factor driving functional and demographic variations across plant species and communities (Poorter &amp; Markesteijn, <span>2008</span>; Phillips <i>et al</i>., <span>2010</span>; Comita &amp; Engelbrecht, <span>2014</span>) and is expected to become increasingly important as drought is predicted to intensify in many regions world-wide (Intergovernmental Panel on Climate Change, <span>2022</span>). In this sense, understanding how plants persist under drought conditions is an important step toward predicting their response to future drier climates (Poorter &amp; Markesteijn, <span>2008</span>; Comita &amp; Engelbrecht, <span>2014</span>). Wood plays a central role in water transport (Carlquist, <span>2001</span>; Baas <i>et al</i>., <span>2004</span>) and, thus, in species ability to persist under drought conditions (Anderegg &amp; Meinzer, <span>2015</span>). In angiosperm wood, the vascular system responsible for transporting water consists of a network of interconnected vessels, and occasionally tracheids, all embedded in a matrix of fibers and parenchyma cells. Fibers primarily provide mechanical support and participate in storage in the case of living fibers, while living parenchyma cells are mainly involved in the storage of water and nonstructural carbohydrates (NSC; Carlquist, <span>2001</span>). Although fibers and parenchyma cells may also participate in water transport, their roles in plant hydraulics are less recognized than that of vessels. Fibers, for example, can reinforce vessel walls and avoid vessel implosion under extreme negative pressures induced by drought (Jacobsen <i>et al</i>., <span>2005</span>). In turn, parenchyma cells can favor stem capacitance by storing water, which buffers fluctuations in xylem water potentials, or they can participate in vessel refilling when they are in direct contact with vessels (Sauter <i>et al</i>., <span>1973</span>; Morris <i>et al</i>., <span>2018a</span>,<span>b</span>; Aritsara <i>et al</i>., <span>2021</span>). However, the interplay among vessels, fibers and parenchyma cells under drought conditions remains elusive, as well as its effect in growth and survival.</p>\n<p>The allocation of wood volume to vessels, fibers and parenchyma cells may lead to anatomical and functional trade-offs (Baas <i>et al</i>., <span>2004</span>; Bittencourt <i>et al</i>., <span>2016</span>; Pratt &amp; Jacobsen, <span>2017</span>). Two of these trade-offs may be particularly relevant to species performance under drought conditions. The first is between the wood fraction (i.e. % of wood cross-sectional area) allocated to either fibers or parenchyma cells (e.g. Ziemińska <i>et al</i>., <span>2015</span>; Pratt &amp; Jacobsen, <span>2017</span>). Species with larger parenchyma fractions, and thus lower fiber fractions, generally store higher amounts of water or NSC (Plavcová &amp; Jansen, <span>2015</span>; Zhang <i>et al</i>., <span>2023</span>), at the expense of mechanical support or vessel reinforcement due to a lower investment in fibers (Ziemińska <i>et al</i>., <span>2015</span>). The second is between wood density and vessel lumen size (Ziemińska <i>et al</i>., <span>2015</span>; Hietz <i>et al</i>., <span>2017</span>). Plants with denser wood and narrower vessels tend to exhibit greater drought tolerance (e.g. Preston <i>et al</i>., <span>2006</span>; Chave <i>et al</i>., <span>2009</span>; Fajardo <i>et al</i>., <span>2022</span>), although this implies a decreased in water transport efficiency, as xylem hydraulic conductivity is proportional to vessel lumen size (e.g. Tyree &amp; Zimmermann, <span>2002</span>; Baas <i>et al</i>., <span>2004</span>; Hietz <i>et al</i>., <span>2017</span>).</p>\n<p>Given that NSC stored in parenchyma cells play a key role in maintaining hydraulic balance (O'Brien <i>et al</i>., <span>2014</span>; Morris <i>et al</i>., <span>2016</span>), one may expect larger parenchyma fractions, and thus lower fiber fractions, in drier environments (e.g. Morris <i>et al</i>., <span>2016</span>). However, since parenchyma cells are alive and metabolically active (Spicer &amp; Holbrook, <span>2007</span>), having a higher proportion of parenchyma cells can result in increased maintenance costs, particularly in low-resource environments such as drier sites (Grime, <span>1977</span>; Reich, <span>2014</span>). Therefore, plants growing in drier sites may have stems with lower parenchyma and thus higher fiber fractions. Likewise, as narrow vessels are generally less vulnerable to drought-induced embolisms than wider ones (Hacke <i>et al</i>., <span>2017</span>; Lens <i>et al</i>., <span>2022</span>), it is likely that selection pressures favor the prevalence of plants with narrower vessels, and thus denser woods, in drier sites. Selection should also favor denser woods in drier sites because dense wood typically has more and thicker fibers (Ziemińska <i>et al</i>., <span>2015</span>), which can reduce the risk of vessel implosion during severe droughts (Jacobsen <i>et al</i>., <span>2005</span>). These expectations have been supported by a number of studies (e.g. Carlquist, <span>2001</span>; Swenson &amp; Enquist, <span>2007</span>; Wheeler <i>et al</i>., <span>2007</span>; Chave <i>et al</i>., <span>2009</span>; Hacke <i>et al</i>., <span>2017</span>), though are also exceptions (see ter Steege &amp; Hammond, <span>2001</span>; Muller-Landau, <span>2004</span>).</p>\n<p>As these two trade-offs can influence plant functioning, they are expected to affect growth and survival. A higher allocation to parenchyma cells might increase survival by enabling a higher storage of NSC (Plavcová &amp; Jansen, <span>2015</span>; Herrera-Ramírez <i>et al</i>., <span>2021</span>), favoring recovery after herbivory (Myers &amp; Kitajima, <span>2007</span>), or by providing an active response against pathogens (Morris <i>et al</i>., <span>2016</span>). It is less clear, however, how this trade-off might influence growth. One possibility is that species with higher parenchyma fractions, and lower fiber fractions, may incur in higher maintenance costs, which could ultimately limit growth (Chapin <i>et al</i>., <span>1990</span>; Myers &amp; Kitajima, <span>2007</span>; Spicer &amp; Holbrook, <span>2007</span>). Alternatively, species with larger parenchyma fractions might grow faster given that wood with fewer fibers is in principle cheaper to build, and because these species likely have a higher number of parenchyma cells in direct contact with vessels (Morris <i>et al</i>., <span>2018a</span>,<span>b</span>), which can favor growth by increasing hydraulic conductivity (Aritsara <i>et al</i>., <span>2021</span>). Regarding the wood density–vessel size trade-off, it is well-established that low wood density and wider vessels promote faster growth by reducing construction costs and increasing xylem hydraulic conductivity, respectively (Chave <i>et al</i>., <span>2009</span>; Hietz <i>et al</i>., <span>2017</span>). Similarly, evidence indicates that species with high wood density and narrow vessels typically have lower mortality rates, as high wood density favors decay resistance and strength, and narrow conduits make species less vulnerable to drought-induced embolisms that may eventually cause hydraulic failure and tissue or plant death (Muller-Landau, <span>2004</span>; King <i>et al</i>., <span>2006</span>; Chave <i>et al</i>., <span>2009</span>; Hietz <i>et al</i>., <span>2017</span>; González-M <i>et al</i>., <span>2021</span>; Hacke <i>et al</i>., <span>2022</span>; Lens <i>et al</i>., <span>2022</span>; Jacobsen &amp; Pratt, <span>2023</span>). However, the link between vessel lumen size and vulnerability to drought-induced embolisms can be weak (Zanne <i>et al</i>., <span>2010</span>; Lens <i>et al</i>., <span>2022</span>), and it ultimately depends on how vessel size is related to intervessel pit traits that are more mechanistically linked to embolism formation and spread (Choat <i>et al</i>., <span>2008</span>; Lens <i>et al</i>., <span>2022</span>).</p>\n<p>Given that the effects of traits on plant functioning can vary according to resource availability (Grime, <span>1977</span>; Reich, <span>2014</span>), the links between trait trade-offs and demographic rates may be better understood by considering the abiotic environment (Laughlin <i>et al</i>., <span>2018</span>; Yang <i>et al</i>., <span>2018</span>; Iida &amp; Swenson, <span>2020</span>; Li <i>et al</i>., <span>2022</span>). For example, as having light wood and wider vessels is a strategy that favors growth, it would represent a demographic advantage in sites with relatively higher water availability, but it can be disadvantageous in low-resource environments such as drier sites (Chave <i>et al</i>., <span>2009</span>; Reich, <span>2014</span>; Hietz <i>et al</i>., <span>2017</span>). Likewise, since investing in larger amounts of parenchyma cells, and hence lower amounts of fibers, is a strategy that can reduce the risk of drought-induced mortality (e.g. Morris <i>et al</i>., <span>2016</span>; Aritsara <i>et al</i>., <span>2021</span>), it would be particularly advantageous in more drier sites, but it could be too costly in less dry sites where the benefits may not offset the costs of this allocation strategy (Reich, <span>2014</span>).</p>\n<p>Although previous research has examined the links of wood anatomical structure with environmental factors (Martínez-Cabrera <i>et al</i>., <span>2009</span>; Fortunel <i>et al</i>., <span>2014</span>; Lourenço <i>et al</i>., <span>2022</span>; Zhang <i>et al</i>., <span>2023</span>), and with demographic rates (Russo <i>et al</i>., <span>2010</span>; Hietz <i>et al</i>., <span>2017</span>; Aritsara <i>et al</i>., <span>2021</span>), these studies have been mainly focused on adults. By contrast, our understanding of these links in the case of seedlings remains limited (but see Corcuera <i>et al</i>., <span>2006</span>; Durante <i>et al</i>., <span>2011</span>; Aref <i>et al</i>., <span>2013</span>), despite the key role that the seedling stage plays in shaping species diversity and abundance at later stages due to its high mortality rates (e.g. Muller-Landau <i>et al</i>., <span>2002</span>). As seedlings and adults experience contrasting local environments (e.g. Iida &amp; Swenson, <span>2020</span>), and given that wood anatomy and demographic rates can vary considerably during ontogeny (Osazuwa-Peters <i>et al</i>., <span>2017</span>; Rungwattana &amp; Hietz, <span>2018</span>; Iida &amp; Swenson, <span>2020</span>), the trait–environment and trait–demography links reported previously for adults may not always hold true for seedlings. For instance, wood density seems to be a better predictor of growth rates for adults than for seedlings (Visser <i>et al</i>., <span>2016</span>). Furthermore, recent studies have highlighted that vessel traits can explain mortality rates at the sapling, but not at the adult stage (Osazuwa-Peters <i>et al</i>., <span>2017</span>; González-Melo <i>et al</i>., <span>2023</span>). To our knowledge, our study is the first in evaluating seedling wood anatomical trade-offs and their relationships with drought conditions and demographic rates for species-rich communities in tropical regions.</p>\n<p>In this study, we examined how wood anatomical trade-offs are related to drought conditions and 1-yr growth and survival in 65 species from four tropical dry forests in Colombia representing a steep gradient in rainfall conditions. In particular, we wanted to address the following questions: (1) How do the fiber vs parenchyma and wood density vs vessel size trade-offs change in response to drought? We anticipated that seedlings will allocate more wood volume to parenchyma cells and less to fibers as drought increases and that seedlings will have denser woods with narrow vessels in drier sites. (2) How are the fiber vs parenchyma and the wood density vs vessel size trade-offs related to growth and mortality, and to what extent are these relationships mediated by drought? We predicted that higher fractions of parenchyma, together with lower fractions of fibers, will be positively related to survival, but negatively to growth. We anticipated that low-density wood and wider vessels will favor growth, but increase mortality. 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引用次数: 0

Abstract

Introduction

Water availability is a main factor driving functional and demographic variations across plant species and communities (Poorter & Markesteijn, 2008; Phillips et al., 2010; Comita & Engelbrecht, 2014) and is expected to become increasingly important as drought is predicted to intensify in many regions world-wide (Intergovernmental Panel on Climate Change, 2022). In this sense, understanding how plants persist under drought conditions is an important step toward predicting their response to future drier climates (Poorter & Markesteijn, 2008; Comita & Engelbrecht, 2014). Wood plays a central role in water transport (Carlquist, 2001; Baas et al., 2004) and, thus, in species ability to persist under drought conditions (Anderegg & Meinzer, 2015). In angiosperm wood, the vascular system responsible for transporting water consists of a network of interconnected vessels, and occasionally tracheids, all embedded in a matrix of fibers and parenchyma cells. Fibers primarily provide mechanical support and participate in storage in the case of living fibers, while living parenchyma cells are mainly involved in the storage of water and nonstructural carbohydrates (NSC; Carlquist, 2001). Although fibers and parenchyma cells may also participate in water transport, their roles in plant hydraulics are less recognized than that of vessels. Fibers, for example, can reinforce vessel walls and avoid vessel implosion under extreme negative pressures induced by drought (Jacobsen et al., 2005). In turn, parenchyma cells can favor stem capacitance by storing water, which buffers fluctuations in xylem water potentials, or they can participate in vessel refilling when they are in direct contact with vessels (Sauter et al., 1973; Morris et al., 2018a,b; Aritsara et al., 2021). However, the interplay among vessels, fibers and parenchyma cells under drought conditions remains elusive, as well as its effect in growth and survival.

The allocation of wood volume to vessels, fibers and parenchyma cells may lead to anatomical and functional trade-offs (Baas et al., 2004; Bittencourt et al., 2016; Pratt & Jacobsen, 2017). Two of these trade-offs may be particularly relevant to species performance under drought conditions. The first is between the wood fraction (i.e. % of wood cross-sectional area) allocated to either fibers or parenchyma cells (e.g. Ziemińska et al., 2015; Pratt & Jacobsen, 2017). Species with larger parenchyma fractions, and thus lower fiber fractions, generally store higher amounts of water or NSC (Plavcová & Jansen, 2015; Zhang et al., 2023), at the expense of mechanical support or vessel reinforcement due to a lower investment in fibers (Ziemińska et al., 2015). The second is between wood density and vessel lumen size (Ziemińska et al., 2015; Hietz et al., 2017). Plants with denser wood and narrower vessels tend to exhibit greater drought tolerance (e.g. Preston et al., 2006; Chave et al., 2009; Fajardo et al., 2022), although this implies a decreased in water transport efficiency, as xylem hydraulic conductivity is proportional to vessel lumen size (e.g. Tyree & Zimmermann, 2002; Baas et al., 2004; Hietz et al., 2017).

Given that NSC stored in parenchyma cells play a key role in maintaining hydraulic balance (O'Brien et al., 2014; Morris et al., 2016), one may expect larger parenchyma fractions, and thus lower fiber fractions, in drier environments (e.g. Morris et al., 2016). However, since parenchyma cells are alive and metabolically active (Spicer & Holbrook, 2007), having a higher proportion of parenchyma cells can result in increased maintenance costs, particularly in low-resource environments such as drier sites (Grime, 1977; Reich, 2014). Therefore, plants growing in drier sites may have stems with lower parenchyma and thus higher fiber fractions. Likewise, as narrow vessels are generally less vulnerable to drought-induced embolisms than wider ones (Hacke et al., 2017; Lens et al., 2022), it is likely that selection pressures favor the prevalence of plants with narrower vessels, and thus denser woods, in drier sites. Selection should also favor denser woods in drier sites because dense wood typically has more and thicker fibers (Ziemińska et al., 2015), which can reduce the risk of vessel implosion during severe droughts (Jacobsen et al., 2005). These expectations have been supported by a number of studies (e.g. Carlquist, 2001; Swenson & Enquist, 2007; Wheeler et al., 2007; Chave et al., 2009; Hacke et al., 2017), though are also exceptions (see ter Steege & Hammond, 2001; Muller-Landau, 2004).

As these two trade-offs can influence plant functioning, they are expected to affect growth and survival. A higher allocation to parenchyma cells might increase survival by enabling a higher storage of NSC (Plavcová & Jansen, 2015; Herrera-Ramírez et al., 2021), favoring recovery after herbivory (Myers & Kitajima, 2007), or by providing an active response against pathogens (Morris et al., 2016). It is less clear, however, how this trade-off might influence growth. One possibility is that species with higher parenchyma fractions, and lower fiber fractions, may incur in higher maintenance costs, which could ultimately limit growth (Chapin et al., 1990; Myers & Kitajima, 2007; Spicer & Holbrook, 2007). Alternatively, species with larger parenchyma fractions might grow faster given that wood with fewer fibers is in principle cheaper to build, and because these species likely have a higher number of parenchyma cells in direct contact with vessels (Morris et al., 2018a,b), which can favor growth by increasing hydraulic conductivity (Aritsara et al., 2021). Regarding the wood density–vessel size trade-off, it is well-established that low wood density and wider vessels promote faster growth by reducing construction costs and increasing xylem hydraulic conductivity, respectively (Chave et al., 2009; Hietz et al., 2017). Similarly, evidence indicates that species with high wood density and narrow vessels typically have lower mortality rates, as high wood density favors decay resistance and strength, and narrow conduits make species less vulnerable to drought-induced embolisms that may eventually cause hydraulic failure and tissue or plant death (Muller-Landau, 2004; King et al., 2006; Chave et al., 2009; Hietz et al., 2017; González-M et al., 2021; Hacke et al., 2022; Lens et al., 2022; Jacobsen & Pratt, 2023). However, the link between vessel lumen size and vulnerability to drought-induced embolisms can be weak (Zanne et al., 2010; Lens et al., 2022), and it ultimately depends on how vessel size is related to intervessel pit traits that are more mechanistically linked to embolism formation and spread (Choat et al., 2008; Lens et al., 2022).

Given that the effects of traits on plant functioning can vary according to resource availability (Grime, 1977; Reich, 2014), the links between trait trade-offs and demographic rates may be better understood by considering the abiotic environment (Laughlin et al., 2018; Yang et al., 2018; Iida & Swenson, 2020; Li et al., 2022). For example, as having light wood and wider vessels is a strategy that favors growth, it would represent a demographic advantage in sites with relatively higher water availability, but it can be disadvantageous in low-resource environments such as drier sites (Chave et al., 2009; Reich, 2014; Hietz et al., 2017). Likewise, since investing in larger amounts of parenchyma cells, and hence lower amounts of fibers, is a strategy that can reduce the risk of drought-induced mortality (e.g. Morris et al., 2016; Aritsara et al., 2021), it would be particularly advantageous in more drier sites, but it could be too costly in less dry sites where the benefits may not offset the costs of this allocation strategy (Reich, 2014).

Although previous research has examined the links of wood anatomical structure with environmental factors (Martínez-Cabrera et al., 2009; Fortunel et al., 2014; Lourenço et al., 2022; Zhang et al., 2023), and with demographic rates (Russo et al., 2010; Hietz et al., 2017; Aritsara et al., 2021), these studies have been mainly focused on adults. By contrast, our understanding of these links in the case of seedlings remains limited (but see Corcuera et al., 2006; Durante et al., 2011; Aref et al., 2013), despite the key role that the seedling stage plays in shaping species diversity and abundance at later stages due to its high mortality rates (e.g. Muller-Landau et al., 2002). As seedlings and adults experience contrasting local environments (e.g. Iida & Swenson, 2020), and given that wood anatomy and demographic rates can vary considerably during ontogeny (Osazuwa-Peters et al., 2017; Rungwattana & Hietz, 2018; Iida & Swenson, 2020), the trait–environment and trait–demography links reported previously for adults may not always hold true for seedlings. For instance, wood density seems to be a better predictor of growth rates for adults than for seedlings (Visser et al., 2016). Furthermore, recent studies have highlighted that vessel traits can explain mortality rates at the sapling, but not at the adult stage (Osazuwa-Peters et al., 2017; González-Melo et al., 2023). To our knowledge, our study is the first in evaluating seedling wood anatomical trade-offs and their relationships with drought conditions and demographic rates for species-rich communities in tropical regions.

In this study, we examined how wood anatomical trade-offs are related to drought conditions and 1-yr growth and survival in 65 species from four tropical dry forests in Colombia representing a steep gradient in rainfall conditions. In particular, we wanted to address the following questions: (1) How do the fiber vs parenchyma and wood density vs vessel size trade-offs change in response to drought? We anticipated that seedlings will allocate more wood volume to parenchyma cells and less to fibers as drought increases and that seedlings will have denser woods with narrow vessels in drier sites. (2) How are the fiber vs parenchyma and the wood density vs vessel size trade-offs related to growth and mortality, and to what extent are these relationships mediated by drought? We predicted that higher fractions of parenchyma, together with lower fractions of fibers, will be positively related to survival, but negatively to growth. We anticipated that low-density wood and wider vessels will favor growth, but increase mortality. We also predicted that the links between trait trade-off and demographic rates will be mediated by drought.

将热带干旱森林的幼苗木质解剖取舍与干旱、幼苗生长和存活联系起来
引言水的可获得性是驱动植物物种和群落之间功能和人口变化的主要因素(Poorter &amp; Markesteijn, 2008; Phillips 等人,2010; Comita &amp; Engelbrecht, 2014),而且由于预计干旱将在全球许多地区加剧(政府间气候变化专门委员会,2022 年),水的可获得性预计将变得越来越重要。从这个意义上讲,了解植物如何在干旱条件下存活是预测它们对未来更干旱气候的反应的重要一步(Poorter &amp; Markesteijn, 2008; Comita &amp; Engelbrecht, 2014)。木材在水分运输中起着核心作用(Carlquist,2001;Baas 等人,2004),因此也影响着物种在干旱条件下的生存能力(Anderegg &amp; Meinzer,2015)。在被子植物的木材中,负责运输水分的维管系统由相互连接的血管网络组成,有时还包括气管,所有这些都嵌入纤维和实质细胞的基质中。纤维主要提供机械支持,并参与活纤维的储存,而活的实质细胞主要参与水分和非结构碳水化合物(NSC;Carlquist,2001 年)的储存。虽然纤维和实质细胞也可能参与水分运输,但它们在植物水力学中的作用却不如血管那样得到认可。例如,纤维可以加固血管壁,避免血管在干旱引起的极端负压下内陷(Jacobsen 等人,2005 年)。反过来,实质细胞可以通过储存水分来缓冲木质部水势的波动,从而有利于茎的容积,或者当实质细胞与血管直接接触时,可以参与血管再充盈(Sauter等人,1973;Morris等人,2018a,b;Aritsara等人,2021)。然而,干旱条件下血管、纤维和实质细胞之间的相互作用及其对生长和存活的影响仍然难以捉摸。将木材体积分配给血管、纤维和实质细胞可能会导致解剖学和功能上的权衡(Baas 等人,2004 年;Bittencourt 等人,2016 年;Pratt &amp; Jacobsen, 2017 年)。其中两种权衡可能与物种在干旱条件下的表现特别相关。第一种是分配给纤维或实质细胞的木材比例(即木材横截面积的百分比)(例如 Ziemińska 等人,2015 年;Pratt &amp; Jacobsen,2017 年)。实质细胞比例较大、纤维比例较低的树种通常会储存较多的水分或NSC(Plavcová &amp; Jansen, 2015; Zhang等人,2023年),但由于对纤维的投资较少,因此以牺牲机械支撑或血管加固为代价(Ziemińska等人,2015年)。其次是木材密度与血管腔大小之间的关系(Ziemińska 等人,2015;Hietz 等人,2017)。木质部更致密、血管更狭窄的植物往往表现出更强的耐旱性(例如 Preston 等人,2006 年;Chave 等人,2009 年;Fajardo 等人,2022 年),尽管这意味着水分运输效率会降低,因为木质部的水导率与血管腔的大小成正比(例如 Tyree &amp; Zimmermann, 2002; Baas et al、鉴于储存在实质细胞中的 NSC 在维持水力平衡方面起着关键作用(O'Brien 等人,2014 年;Morris 等人,2016 年),人们可能会期望在更干燥的环境中,实质细胞的比例会更大,从而纤维的比例会更低(例如 Morris 等人,2016 年)。然而,由于实质细胞有生命且代谢活跃(Spicer &amp; Holbrook, 2007),实质细胞比例较高会导致维护成本增加,尤其是在干旱等低资源环境中(Grime, 1977; Reich, 2014)。因此,在较干旱地区生长的植物,其茎的实质细胞比例可能较低,从而纤维比例较高。同样,由于狭窄的血管通常比宽大的血管更不容易受到干旱引起的栓塞的影响(Hacke 等人,2017 年;Lens 等人,2022 年),因此选择压力很可能有利于在较干旱的地点普遍生长血管较窄的植物,从而使林木更茂密。在较干旱的地点,选择也应倾向于较稠密的木材,因为稠密的木材通常具有更多更粗的纤维(Ziemińska 等人,2015 年),这可以降低严重干旱时血管内爆的风险(Jacobsen 等人,2005 年)。这些预期得到了许多研究的支持(如 Carlquist, 2001; Swenson &amp; Enquist, 2007; Wheeler 等人, 2007; Chave 等人, 2009; Hacke 等人, 2017),但也有例外(见 ter Steege &amp; Hammond, 2001; Muller-Landau, 2004)。向实质细胞分配更多的营养物质可能会增加 NSC 的储存量,从而提高存活率(Plavcová &amp; Jansen, 2015; Herrera-Ramírez et al. 2021 年),有利于草食后的恢复(Myers &amp; Kitajima, 2007 年),或通过提供积极的应对措施来抵御病原体(Morris 等人,2016 年)。不过,这种权衡如何影响生长还不太清楚。一种可能是,实质部分较高而纤维部分较低的物种可能会产生较高的维护成本,从而最终限制生长(Chapin 等人,1990 年;Myers &amp; Kitajima, 2007 年;Spicer &amp; Holbrook, 2007 年)。另外,由于纤维较少的木材原则上造价较低,而且这些树种可能有较多的实质细胞与血管直接接触(Morris等人,2018a,b),这可以通过增加水力传导性来促进生长,因此实质细胞比例较大的树种可能生长得更快(Aritsara等人,2021年)。关于木材密度--血管大小的权衡问题,已经得到公认的是,低木材密度和更宽的血管可分别通过降低建造成本和提高木质部的水传导性来促进更快的生长(Chave 等人,2009 年;Hietz 等人,2017 年)。同样,有证据表明,木质密度高、血管窄的物种死亡率通常较低,因为木质密度高有利于抗腐烂和增强强度,而血管窄则使物种不易受到干旱引起的栓塞的影响,这种栓塞最终可能导致水力衰竭和组织或植物死亡(Muller-Landau,2004 年;King 等,2006 年;Chave 等,2017 年)、2006;Chave 等人,2009;Hietz 等人,2017;González-M 等人,2021;Hacke 等人,2022;Lens 等人,2022;Jacobsen &amp;Pratt,2023)。然而,血管腔大小与易受干旱诱发的栓塞影响之间的联系可能很弱(Zanne 等人,2010 年;Lens 等人,2022 年),最终取决于血管大小与血管间凹坑特征之间的关系,而血管间凹坑特征与栓塞的形成和扩散有更多的机理联系(Choat 等人,2008 年;Lens 等人,2022 年)、鉴于性状对植物功能的影响可能因资源可用性而异(Grime,1977 年;Reich,2014 年),考虑非生物环境可能会更好地理解性状权衡与繁殖率之间的联系(Laughlin 等人,2018 年;Yang 等人,2018 年;Iida &amp; Swenson,2020 年;Li 等人,2022 年)。例如,由于拥有轻质木材和更宽的容器是一种有利于生长的策略,因此在水供应相对较多的地点,这将代表一种人口优势,但在干旱地点等低资源环境中,这可能是不利的(Chave 等,2009 年;Reich,2014 年;Hietz 等,2017 年)。同样,由于投资于更多的实质细胞,从而减少纤维数量,是一种可以降低干旱引起的死亡风险的策略(例如,Morris 等人,2016 年;Aritsara 等人,2021 年),因此投资于更多的实质细胞,从而减少纤维数量,是一种可以降低干旱引起的死亡风险的策略(例如,Morris 等人,2016 年;Aritsara 等人,2021 年)、2021 年),这在较干旱的地方特别有利,但在不太干旱的地方可能成本太高,因为在这些地方的收益可能无法抵消这种分配策略的成本(Reich,2014 年)、尽管之前的研究已经考察了木材解剖结构与环境因素(Martínez-Cabrera 等人,2009 年;Fortunel 等人,2014 年;Lourenço 等人,2022 年;Zhang 等人,2023 年)和人口比率(Russo 等人,2010 年;Hietz 等人,2017 年;Aritsara 等人,2021 年)之间的联系,但这些研究主要集中在成体上。相比之下,我们对幼苗与这些联系的了解仍然有限(参见 Corcuera 等人,2006 年;Durante 等人,2011 年;Aref 等人,2013 年),尽管幼苗阶段因其高死亡率而在后期物种多样性和丰度的形成中扮演着关键角色(例如 Muller-Landau 等人,2002 年)。由于幼苗和成体所处的当地环境截然不同(例如,Iida &amp; Swenson, 2020),并考虑到木材解剖结构和繁殖率在本体发育过程中会有很大变化(Osazuwa-Peters 等人,2017;Rungwattana &amp; Hietz, 2018;Iida &amp; Swenson, 2020),之前报道的成体的性状-环境和性状-分布之间的联系可能并不总是适用于幼苗。例如,木材密度似乎比幼苗更能预测成株的生长率(Visser 等人,2016 年)。此外,最近的研究强调,容器特征可以解释树苗阶段的死亡率,但不能解释成苗阶段的死亡率(Osazuwa-Peters 等人,2017 年;González-Melo 等人,2023 年)。据我们所知,我们的研究是首次评估热带地区物种丰富的群落的幼苗木材解剖学权衡及其与干旱条件和人口统计率的关系。在这项研究中,我们考察了木材解剖学权衡与干旱条件以及哥伦比亚四种热带干旱森林中 65 个物种的 1 年生长和存活率之间的关系,这些物种代表了降雨条件的陡峭梯度。 我们尤其希望解决以下问题:(1)纤维与实质细胞、木材密度与血管大小之间的权衡如何随干旱而变化?我们预计,随着干旱的加剧,幼苗会将更多的木材体积分配给实质细胞,而将较少的木材体积分配给纤维;在较干旱的地方,幼苗的木材密度会更高,血管更窄。(2) 纤维与实质细胞以及木材密度与血管大小的权衡与生长和死亡率的关系如何?我们预测,较高的实质部分和较低的纤维部分与存活率呈正相关,但与生长呈负相关。我们预计,低密度木材和较宽的血管将有利于生长,但会增加死亡率。我们还预测,性状权衡与繁殖率之间的联系将受干旱影响。
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来源期刊
New Phytologist
New Phytologist 生物-植物科学
自引率
5.30%
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728
期刊介绍: New Phytologist is an international electronic journal published 24 times a year. It is owned by the New Phytologist Foundation, a non-profit-making charitable organization dedicated to promoting plant science. The journal publishes excellent, novel, rigorous, and timely research and scholarship in plant science and its applications. The articles cover topics in five sections: Physiology & Development, Environment, Interaction, Evolution, and Transformative Plant Biotechnology. These sections encompass intracellular processes, global environmental change, and encourage cross-disciplinary approaches. The journal recognizes the use of techniques from molecular and cell biology, functional genomics, modeling, and system-based approaches in plant science. Abstracting and Indexing Information for New Phytologist includes Academic Search, AgBiotech News & Information, Agroforestry Abstracts, Biochemistry & Biophysics Citation Index, Botanical Pesticides, CAB Abstracts®, Environment Index, Global Health, and Plant Breeding Abstracts, and others.
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