Journal of Ecology ( IF 5.3 ) Pub Date : 2024-09-23 , DOI: 10.1111/1365-2745.14412
Alexandra L. Bijak, Laura K. Reynolds, Willm Martens-Habbena, Ashley R. Smyth
1 INTRODUCTION
Plant traits linked to species-specific life history or resource acquisition strategies often drive ecosystem functioning (Funk et al., 2017; Hillebrand & Matthiessen, 2009; Lavorel & Garnier, 2002). For example, in grassland assemblages, species-specific traits that increase nutrient use efficiency by maximizing photosynthetic capacity (e.g. plant height) enhance plant productivity (Dietrich et al., 2023; Marquard et al., 2009; Roscher et al., 2012) and accelerate soil nitrogen cycling (Henneron et al., 2020). While the effects of species-specific traits have been well studied, within-species trait variability from genotypic and/or environmental variation can also have strong effects on ecosystem functioning (Raffard et al., 2019). Overlooking within-species variability can obscure relationships between plant traits and functioning (Chacón-Labella et al., 2023). Assessing the relative role of within- and between-species variability in driving ecosystem functioning is therefore critical to scaling from the individual to ecosystem processes.
Identifying plant traits that drive aspects of the carbon cycle, including soil carbon storage and greenhouse gas emissions, can improve the accuracy of global carbon budgets and enhance efforts to manage ecosystems for climate change mitigation. For example, in managed grasslands, species with acquisitive growth strategies are associated with lower nitrous oxide (N2O) emissions than species with conservative strategies (Abalos et al., 2018). In tidal wetlands, differences in plant species' ability to oxygenate the rhizosphere or release plant-derived dissolved organic carbon into the rhizosphere control methane (CH4) emissions (Mueller et al., 2020; Noyce & Megonigal, 2021). While species-specific traits can clearly impact greenhouse gas emissions, the extent to which plant trait variability within species also affects emissions is less clear. The central aims of this study were to identify plant traits that drive greenhouse gas emissions and evaluate how within- and between-species trait variation across seasons affects emissions in a mixed-species seagrass meadow.
Seagrass meadows store globally significant amounts of carbon in underlying sediments (Fourqurean et al., 2012) though other aspects of meadow carbon cycling that can diminish net carbon storage capacity—for example, greenhouse gas production—are often unaccounted for (Oreska et al., 2020; Van Dam et al., 2021). Globally, CH4 and N2O emissions from seagrass meadows are generally low but are not measured nearly as often as carbon accumulation and storage (Al-Haj & Fulweiler, 2020; Rosentreter et al., 2021). Yet emissions may vary at small spatial scales, similar to sediment carbon storage (Oreska et al., 2017). Identifying localized drivers of seagrass meadow greenhouse gas emissions, including plant traits, enables better prediction and more accurate accounting of seagrass meadow carbon storage capacity.
Seagrass traits vary widely between species (de los Santos et al., 2016; Kilminster et al., 2015) and within species (Barry et al., 2017; Lee & Dunton, 1999; Short, 1983). Variability in seagrass traits has potential to influence several ecosystem functions related to carbon cycling (Gillis et al., 2023; Moreira-Saporiti et al., 2023). For example, seagrass rooting depth can differ by species (Williams, 1990) and root length can differ by genotype (Hughes et al., 2009). The ability to stabilize carbon-rich sediments may therefore differ between species and genotypes, too. Other traits related to structural complexity, like leaf area index and below-ground biomass, also affect the ability of seagrasses to trap and bury carbon (Kammann et al., 2022; Mazarrasa et al., 2018; Samper-Villarreal et al., 2016). The influence of seagrass trait variation on sediment carbon accumulation has not been explicitly measured, but past studies have found that meadows dominated by larger-bodied, persistent species are associated with higher surface sediment carbon densities (Bijak et al., 2023; Kennedy et al., 2022). If plant size and other traits that promote carbon burial over longer time scales also promote greenhouse gas emissions from sediments, the potential climate benefits of carbon storage would be diminished. However, traits are not fixed and can change across space and time, complicating efforts to link traits with ecosystem functions relevant to carbon cycling.
Seasonal and other environmental fluctuations in traits might lead to an under-estimation of the role the plants themselves play in carbon cycling (Chacón-Labella et al., 2023; Freschet et al., 2021). For example, seasonal differences in seagrass growth can affect leaf strength and related ecosystem functions including sediment stabilization (Hansen & Reidenbach, 2013; Soissons et al., 2018). Other traits respond to nutrient availability (leaf length; Barry et al., 2017) or to stressors such as elevated seawater temperatures and grazing (below-ground biomass; Roth et al., 2023). Hence, environmental variability, including seasonality, not only affects seagrass performance, but also indirectly drives ecosystem processes related to carbon cycling through trait modification (Gillis et al., 2023; Moreira-Saporiti et al., 2023). Applying a trait-based framework can therefore aid in assessing the relative importance of within- and between-species trait variation and teasing apart effects of seasonality and traits, and the interaction of both, in driving seagrass meadow greenhouse gas emissions.
Plant traits that modify sediment conditions can indirectly affect greenhouse gas emissions because these gases are produced mainly through sediment microbial metabolism. For example, leaf canopy structure and below-ground biomass are traits involved in concentrating organic matter and carbon through burial in underlying sediments over longer time scales (Gacia et al., 2002; Hendriks et al., 2008) and releasing root exudates to the rhizosphere over shorter time scales (Holmer et al., 2001). Both mechanisms enhance resource availability for the microbial community, and in this way, leaf and root traits may indirectly promote emissions. However, seagrass metabolism may alter rhizosphere oxygen conditions via radial root oxygen loss (Borum et al., 2006) in ways that stimulate or inhibit microbial oxidation of CH4 (Bahlmann et al., 2015) and affect nitrogen cycling related to the production and consumption of N2O (Caffrey & Kemp, 1990). It is therefore difficult to predict the net effect of seagrass trait variation on greenhouse gas emissions.
Our objective was to quantify fluxes of CH4 and N2O, two potent greenhouse gases, from seagrass meadow sediments and identify sources of variation in fluxes due to plant traits and seasonal variability. We conducted ex situ incubations in the dormant, early and peak growing seasons on mesocosm cores collected from a subtropical mixed-species meadow, where the presence of two seagrass species with contrasting life histories allowed us to examine variation in gas fluxes due to within- and between-species trait variability. We measured dissolved CH4 and N2O fluxes that captured sediment-water and water column processes, and we also measured oxygen (O2) fluxes to interpret greenhouse gas fluxes within the context of seagrass community metabolism.
中文翻译:
季节性变化和海草特性影响亚热带草甸的甲烷通量
1 引言
与物种特异性生活史或资源获取策略相关的植物性状通常驱动生态系统功能(Funk等人,2017 年;Hillebrand & Matthiessen, 2009;Lavorel & Garnier,2002 年)。例如,在草原组合中,通过最大化光合作用能力(例如植物高度)来提高养分利用效率的物种特异性状可以提高植物生产力(Dietrich等人,2023 年;Marquard et al., 2009;Roscher et al., 2012)并加速土壤氮循环(Henneron et al., 2020)。虽然物种特异性状的影响已经得到了很好的研究,但基因型和/或环境变异引起的物种内性状变异也会对生态系统功能产生重大影响(Raffard et al., 2019)。忽视物种内部的变异性会掩盖植物性状和功能之间的关系(Chacón-Labella et al., 2023)。因此,评估物种内和物种间变异在驱动生态系统功能中的相对作用对于从个体扩展到生态系统过程至关重要。
确定驱动碳循环各个方面的植物性状,包括土壤碳储存和温室气体排放,可以提高全球碳预算的准确性,并加强管理生态系统以缓解气候变化的努力。例如,在受管理的草原中,与采用保守策略的物种相比,具有获取性生长策略的物种与较低的一氧化二氮 (N2O) 排放相关(Abalos et al., 2018)。在潮汐湿地中,植物物种为根际充氧或将植物来源的溶解有机碳释放到根际控制甲烷 (CH4) 排放的能力存在差异(Mueller 等人,2020 年;Noyce & Megonigal,2021 年)。虽然物种特异性状可以明显影响温室气体排放,但物种内植物性状变异性在多大程度上也会影响排放尚不清楚。本研究的核心目的是确定驱动温室气体排放的植物性状,并评估不同季节的物种内和物种间性状变化如何影响混合物种海草草甸的排放。
海草草甸在底层沉积物中储存了全球大量的碳(Fourqurean et al., 2012),尽管草甸碳循环的其他方面可能会减少净碳储存能力,例如,温室气体产生——往往没有得到解释(Oreska et al., 2020;Van Dam et al., 2021)。在全球范围内,海草草甸的CH4和N2O排放量通常较低,但测量的频率远不如碳积累和储存(Al-Haj & Fulweiler,2020年; Rosentreter等人,2021 年)。然而,排放量可能在较小的空间尺度上发生变化,类似于沉积物碳储存(Oreska et al., 2017)。确定海草草甸温室气体排放的局部驱动因素,包括植物性状,可以更好地预测和更准确地核算海草草甸碳储存能力。
海草性状因物种而异(de los Santos et al., 2016;Kilminster等人,2015 年)和物种内(Barry等人,2017 年;Lee & Dunton, 1999;Short,1983 年)。海草性状的变异性有可能影响与碳循环相关的多种生态系统功能(Gillis et al., 2023;Moreira-Saporiti等人,2023 年)。例如,海草的生根深度可能因物种而异(Williams, 1990),根长可能因基因型而异(Hughes et al., 2009)。因此,稳定富含碳的沉积物的能力也可能因物种和基因型而异。与结构复杂性相关的其他性状,如叶面积指数和地下生物量,也会影响海草捕获和埋藏碳的能力(Kammann et al., 2022;Mazarrasa等人,2018 年;Samper-Villarreal et al., 2016)。海草性状变化对沉积物碳积累的影响尚未得到明确测量,但过去的研究发现,以体型较大、持久性物种为主的草甸与较高的表面沉积物碳密度有关(Bijak 等人,2023 年;Kennedy et al., 2022)。如果植物大小和其他促进长期碳埋藏的性状也促进了沉积物的温室气体排放,那么碳储存的潜在气候效益就会减少。然而,性状不是固定的,可以随空间和时间变化,这使得将性状与碳循环相关的生态系统功能联系起来的努力变得复杂。
Seasonal and other environmental fluctuations in traits might lead to an under-estimation of the role the plants themselves play in carbon cycling (Chacón-Labella et al., 2023; Freschet et al., 2021). For example, seasonal differences in seagrass growth can affect leaf strength and related ecosystem functions including sediment stabilization (Hansen & Reidenbach, 2013; Soissons et al., 2018). Other traits respond to nutrient availability (leaf length; Barry et al., 2017) or to stressors such as elevated seawater temperatures and grazing (below-ground biomass; Roth et al., 2023). Hence, environmental variability, including seasonality, not only affects seagrass performance, but also indirectly drives ecosystem processes related to carbon cycling through trait modification (Gillis et al., 2023; Moreira-Saporiti et al., 2023). Applying a trait-based framework can therefore aid in assessing the relative importance of within- and between-species trait variation and teasing apart effects of seasonality and traits, and the interaction of both, in driving seagrass meadow greenhouse gas emissions.
改变沉积物条件的植物性状可以间接影响温室气体排放,因为这些气体主要通过沉积物微生物代谢产生。例如,叶冠结构和地下生物量是通过埋藏在较长时间尺度上底层沉积物中来浓缩有机物和碳的特征(Gacia et al., 2002;Hendriks等人,2008 年)并在较短的时间尺度上将根系分泌物释放到根际(Holmer 等人,2001 年)。这两种机制都提高了微生物群落的资源可用性,通过这种方式,叶和根性状可能会间接促进排放。然而,海草代谢可能通过径向根系的氧气流失(Borum等人,2006)改变根际氧气条件,从而刺激或抑制CH4的微生物氧化(Bahlmann等人,2015)并影响与N2O的产生和消耗相关的氮循环(Caffrey & Kemp,1990)。 因此,很难预测海草性状变化对温室气体排放的净影响。
我们的目标是量化海草草甸沉积物中两种强效温室气体 CH4 和 N2O 的通量,并确定由于植物性状和季节性变化而导致的通量变化来源。我们在休眠、早期和高峰生长季节对从亚热带混合物种草甸收集的中宇宙岩芯进行了异位孵化,其中两种生活史截然不同的海草物种的存在使我们能够检查由于物种内和物种间性状变异而导致的气体通量变化。我们测量了捕获沉积物-水和水柱过程的溶解 CH4 和 N2O 通量,我们还测量了氧 (O2) 通量,以解释海草群落新陈代谢背景下的温室气体通量。