Repetitive desiccation events weaken a salt marsh mutualism
Repetitive desiccation events weaken a salt marsh mutualism
复制标题
DOI：
10.1111/1365-2745.13178
复制
发表时间：
2019-09-01
影响因子：
5.5
通讯作者：
van der Heide, Tjisse
中科院分区：
文献类型：
--
作者：
Derksen-Hooijberg, Marlous;Angelini, Christine;van der Heide, Tjisse
1. 近几十年来，盐沼遭受了大规模的退化。极端事件，如炎热和干燥期，对这一现象起到了重要作用，预计在未来的气候情景下，这些事件不仅强度会增加，频率也会增加。这种重复的极端事件可能对生态系统的恢复能力产生累积效应。因此，阐明沼泽植被如何应对重复压力，以及关键物种相互作用的变化是否可以调节植被的恢复能力是很重要的。在这项研究中，我们研究了由干旱和高温共同作用引起的中度但重复的干燥事件如何影响美国东南部盐沼中主要的生境形成草（互花米草）。在为期4个月的田间试验中，我们通过周期性地排除潮汐洪水和降雨，同时提高温度，模拟了4个连续的干燥事件。我们将这种干燥处理与肋贻贝（Geukensia desmissa）的存在/缺失进行了对比，肋贻贝（Geukensia desmissa）是一种已知能增强其干燥恢复力的绳草共生动物，而沼泽长尾花（Littoraria irorata）的放牧压力则抑制了绳草的干燥恢复力。我们发现，随后的每次干燥事件都会使沉积物孔隙水条件恶化，导致高盐度（53 ppt）、低ph水平（3.7）和孔隙水中Al和Fe浓度增加（约800 μ mol/L和约1500 μ mol/L）。放牧蜗牛对孔隙水化学没有影响，而肋贻贝则能有效地缓解干燥效应，几乎达到控制水平，并使网草生物量增加了约128%。重要的是，尽管在实验结束时，地上的脐带草总体上看起来很健康，但我们发现，无论贻贝和/或蜗牛是否存在，重复干燥处理对脐带草地下生物量、芽中的脯氨酸（渗透物）水平和分蘖数（-40%）都有明显的负面影响。合成。尽管在整个实验过程中，与贻贝的共生关系强烈地减轻了沉积物孔隙水中的化学效应，但贻贝不能缓冲在脐草组织中观察到的不利生态生理效应。因此，我们的研究结果表明，尽管贻贝可以缓解干旱胁迫，但预测的干热期频率和强度的增加最终可能会通过使共生关系超出其缓冲能力而影响盐沼的恢复能力。
1. Salt marshes suffered large-scale degradation in recent decades. Extreme events such as hot and dry spells contributed significantly to this, and are predicted to increase not only in intensity, but also in frequency under future climate scenarios. Such repetitive extreme events may generate cumulative effects on ecosystem resilience. It is therefore important to elucidate how marsh vegetation responds to repetitive stress, and whether changes in key species interactions can modulate vegetation resilience.2. In this study, we investigated how moderate but repetitive desiccation events, caused by the combined effects of drought and high temperatures, affect cordgrass (Spartina alterniflora), the dominant habitat-forming grass in southeastern US salt marshes. In a 4-month field experiment, we simulated four consecutive desiccation events by periodically excluding tidal flooding and rainfall, while raising temperature. We crossed this desiccation treatment with the presence/absence of ribbed mussels (Geukensia demissa) - a mutualist of cordgrass known to enhance its desiccation resilience - and with grazing pressure by the marsh periwinkle (Littoraria irrorata) that is known to suppress cordgrass' desiccation resilience.3. We found that each subsequent desiccation event deteriorated sediment porewater conditions, resulting in high salinity (53 ppt), low pH-levels (3.7) and increased porewater Al and Fe concentrations (approximate to 800 mu mol/L and approximate to 1,500 mu mol/L) upon rewetting. No effects on porewater chemistry were found as a result of snail grazing, while ribbed mussels strongly mitigated desiccation effects almost to control levels and increased cordgrass biomass by approximately 128%. Importantly, although cordgrass generally appeared healthy above-ground at the end of the experiment, we found clear negative responses of the repetitive desiccation treatment on cordgrass below-ground biomass, on proline (osmolyte) levels in shoots and on the number of tillers (-40%), regardless of mussel and/or snail presence.4. Synthesis. Even though the mutualism with mussels strongly mitigated chemical effects in the sediment porewater throughout the experiment, mussels could not buffer the adverse ecophysiological effects observed in cordgrass tissue. Our results therefore suggest that although mussels may alleviate desiccation stress, the predicted increased frequency and intensity of hot dry spells may eventually affect saltmarsh resilience by stressing the mutualism beyond its buffering capacity.