Data_Sheet_1_Oyster Biodeposition Alleviates Sediment Nutrient Overload: A Case Study at Shenzhen Bay, China.docx

Oysters are ecological engineers, and previous studies have examined their role as competent facilitators of ecological restoration. However, the decisive role of oysters in the aquatic environment is still debatable because oyster biodeposition (OBD) may also increase the nutrients enriched in sediments. In order to better interpret this problem, we sampled sediment cores from representative oyster culture areas and uncultured areas in Shenzhen Bay. The results have shown that the TOC (total organic carbon) and TN (total nitrogen) decreased significantly (p < 0.05) at the surface sediment layer (0–20-cm deep) and the sediment layer (20–40-cm deep) of the oyster site compared with the reference site. The decreased TOC and TN were also observed at 60- to 100-cm sediment depth in the oyster site. This indicated that the OBD significantly impacted the concentration of TOC and TN in the sediment. To confirm the alleviative role of OBD, we conducted stable isotope (δ13C and δ15N) analyses, which further demonstrated the presence of heavier and less lighter forms of organic carbon and nitrogen sediment. The surface sediment layer (0–20 cm) at the oyster site showed 8% more δ13C‰ compared with the control site (p < 0.05), reflecting the reduction in the TOC. In order to reveal the potential microbial mechanisms involved in OBD, we performed a functional analysis using the Geochip5 advanced microarray technology. Regarding carbon metabolism, we observed that genes (encoding pullulanase, glucoamylase, exoglucanase, cellobiase, and xylanase) involved in the degradation of relatively labile C-based molecules (e.g., starch, cellulose, and hemicellulose) were highly represented in an experimental area (p < 0.05). In addition, microbes in the experimental area exhibited a greater capacity for degrading recalcitrant C (e.g., lignin), which involves glyoxal oxidase (glx), manganese peroxidase (mnp), and phenol oxidase. Among the genes controlling nitrogen metabolism, the genes involved in denitrification, assimilation, ammonification, and nitrification were differentially expressed compared with the control area. These results indicated that microbial metabolic roles might have enhanced the C/N-flux speed and reduced the overall nutrient status. We concluded that OBD alleviates sediment nutrient overload under oyster farming from a microbial ecological perspective in a rapidly urbanized coastal area.

牡蛎作为生态系统工程师，既往研究已证实其可有效助力生态修复。然而，牡蛎生物沉积（Oyster Biodeposition，简称OBD）可能会提升沉积物中的营养盐富集水平，因此其在水生环境中的决定性作用仍存在争议。为厘清这一科学问题，本研究于深圳湾选取典型牡蛎养殖区与非养殖区，采集沉积物岩芯样品。研究结果显示，相较于对照样区，牡蛎养殖样区的表层沉积物（0~20 cm深度）与20~40 cm深度沉积物中的总有机碳（Total Organic Carbon，简称TOC）和总氮（Total Nitrogen，简称TN）含量均显著降低（p < 0.05）；牡蛎养殖样区60~100 cm深度沉积物中同样检测到TOC与TN含量降低的现象。这表明OBD对沉积物中TOC与TN的含量具有显著影响。为验证OBD的营养盐缓解效应，本研究开展了稳定同位素（δ13C与δ15N）分析，结果进一步证实沉积物中存在更重、轻量级占比更低的有机碳与氮形态。牡蛎养殖样区0~20 cm表层沉积物的δ13C‰值较对照样区高出8%（p < 0.05），这反映了TOC含量的降低。为揭示OBD相关的潜在微生物调控机制，本研究采用Geochip5高级微阵列技术开展功能基因分析。针对碳代谢过程，本研究发现实验样区中参与易降解碳基分子（如淀粉、纤维素与半纤维素）降解的编码基因（普鲁兰酶、葡糖淀粉酶、外切葡聚糖酶、纤维二糖酶与木聚糖酶）显著富集（p < 0.05）。此外，实验样区的微生物对难降解碳（如木质素）的降解能力更强，相关酶包括乙醛酸氧化酶（glx）、锰过氧化物酶（mnp）与酚氧化酶。在氮代谢相关基因中，与反硝化、同化作用、氨化作用与硝化作用相关的基因在实验样区与对照样区间存在显著表达差异。上述结果表明，微生物代谢作用可能提升了碳氮循环速率，进而降低了沉积物整体营养盐水平。本研究从微生物生态学视角得出结论：在快速城市化的沿海区域，牡蛎养殖产生的OBD可缓解沉积物营养盐过载问题。