Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, PR China.
Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou, 511458, PR China.
BMC Plant Biol. 2022 Jun 16;22(1):296. doi: 10.1186/s12870-022-03647-0.
Sediment is crucial for the unique marine angiosperm seagrass growth and successful restoration. Sediment modification induced by eutrophication also exacerbates seagrass decline and reduces plantation and transplantation survival rates. However, we lack information regarding the influence of sediment on seagrass photosynthesis and the metabolics, especially regarding the key secondary metabolic flavone. Meanwhile, sulfation of flavonoids in seagrass may mitigate sulfide intrusion, but limited evidence is available.
We cultured the seagrass Thalassia hemprichii under controlled laboratory conditions in three sediment types by combining different ratios of in-situ eutrophic sediment and coarse beach sand. We examined the effects of beach sand mixed with natural eutrophic sediments on seagrass using photobiology, metabolomics and isotope labelling approaches. Seagrasses grown in eutrophic sediments mixed with beach sand exhibited significantly higher photosynthetic activity, with a larger relative maximum electron transport rate and minimum saturating irradiance. Simultaneously, considerably greater belowground amino acid and flavonoid concentrations were observed to counteract anoxic stress in eutrophic sediments without mixed beach sand. This led to more positive belowground stable sulfur isotope ratios in eutrophic sediments with a lower Eh.
These results indicated that coarse beach sand indirectly enhanced photosynthesis in T. hemprichii by reducing sulfide intrusion with lower amino acid and flavonoid concentrations. This could explain why T. hemprichii often grows better on coarse sand substrates. Therefore, it is imperative to consider adding beach sand to sediments to improve the environmental conditions for seagrass and restore seagrass in eutrophic ecosystems.
沉积物对于独特的海洋被子植物海草的生长和成功恢复至关重要。富营养化引起的沉积物改变也会加剧海草衰退，降低种植和移植的存活率。然而，我们缺乏关于沉积物对海草光合作用和代谢的影响的信息，特别是关于关键的次生代谢黄酮类化合物。同时，海草中黄酮类化合物的硫酸化可能减轻了硫化物的侵入，但可用的证据有限。
我们在三种沉积物类型下通过组合不同比例的原位富营养化沉积物和粗沙滩，在控制的实验室条件下培养了海草 Thalassia hemprichii。我们使用光生物学、代谢组学和同位素标记方法研究了沙滩沙与天然富营养化沉积物混合对海草的影响。与未混合沙滩沙的富营养化沉积物相比，在富营养化沉积物中混合沙滩沙的海草表现出更高的光合作用活性，相对最大电子传递率更大，最小饱和辐照度更小。同时，我们观察到，在没有混合沙滩沙的富营养化沉积物中，地下氨基酸和黄酮类化合物浓度显著增加，以抵抗缺氧应激。这导致富营养化沉积物中 Eh 值较低时，地下稳定硫同位素比值更为正值。
这些结果表明，粗沙滩沙通过降低硫化物侵入，减少低氨基酸和黄酮类化合物浓度，间接地增强了 T. hemprichii 的光合作用。这可以解释为什么 T. hemprichii 通常在粗砂基质上生长得更好。因此，考虑在沉积物中添加沙滩沙以改善海草的环境条件并在富营养化生态系统中恢复海草是至关重要的。
