Xiaoliang Research Station of Tropical Coastal Ecosystems, Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, and the CAS engineering Laboratory for Ecological Restoration of Island and Coastal Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China; University of Chinese Academy of Sciences, Beijing 100049, China; Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, PR China.
Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK; Smithsonian Tropical Research Institute, P.O. Box 0843-03092, Balboa, Ancon, Panama, Panama.
Sci Total Environ. 2021 Dec 1;798:149341. doi: 10.1016/j.scitotenv.2021.149341. Epub 2021 Jul 30.
The turnover of SOC in soils is strongly influenced by the availability of substrate and nutrients, especially nitrogen (N) and phosphorus (P). Here, we assessed how long-term fertilization modified SOM mineralization in response to added substrate in a tropical forest. We carried out a 90-day incubation study in which we added two structurally similar compounds which differed in microbial metabolic availability: corn cellulose or corn starch to soils collected from a long-term (11 years) factorial N and P fertilization experiment site in a tropical forest in south China. We measured total soil mineralization rate (CO efflux) to characterize SOM mineralization and using C isotope signatures to determine the source of the CO (original soil C or added substrate) and assessed changes in extracellular enzyme activities: acid phosphomonoesterase (AP), β-1,4-glucosidase (BG), β-1,4- N-acetaminophen glucosidase (NAG), phenol oxidase (PHO) and peroxidase (PER), and microbial biomarkers to determine whether nutrient stoichiometry and decomposer communities explain differences in SOM mineralization rates. Total C mineralization increased substantially with substrate addition, particularly cellulose (5.38, 7.13, 5.58 and 5.37 times for N, P, NP fertilization and CK, respectively) compared to no substrate addition, and original soil C mineralization was further enhanced in long-term N (3.40% and 5.18% for cellulose and starch addition, respectively) or NP (35.11% for cellulose addition) fertilized soils compared to control treatment. Enzyme activities were stimulated by the addition of both substrates but suppressed by P-fertilization. Addition of both substrates increased microbial investment in P-acquisition, but only starch addition promoted C investment in N-acquisition. Finally, fungal abundance increased with substrate addition to a greater extent than bacterial abundance, particularly in cellulose-amended soils, and the effect was amplified by long-term fertilization. Our findings indicate that SOM mineralization might be enhanced in N and P enrichment ecosystems, since the litter input can liberate microbes from C limitation and stimulate SOM mineralization if N and P are sufficient. Our study further demonstrates that structurally similar substrates can have distinct effects on SOM mineralization and the extent of SOM mineralization is strongly dependent on elemental stoichiometry, as well as the resource requirements of microbial decomposers.
土壤中 SOC 的周转率强烈受到基质和养分（尤其是氮（N）和磷（P））可利用性的影响。在这里，我们评估了长期施肥如何在热带森林中响应添加的基质来改变 SOM 矿化。我们进行了为期 90 天的培养研究，其中我们向从中国南方热带森林中长期（11 年）N 和 P 施肥实验中收集的土壤中添加了两种结构相似但微生物代谢可用性不同的化合物：玉米纤维素或玉米淀粉。我们测量了总土壤矿化率（CO 通量）以表征 SOM 矿化，并使用 C 同位素特征来确定 CO 的来源（原始土壤 C 或添加的基质），评估了细胞外酶活性的变化：酸性磷酸单酯酶（AP），β-1,4-葡萄糖苷酶（BG），β-1,4-N-乙酰氨基葡萄糖苷酶（NAG），多酚氧化酶（PHO）和过氧化物酶（PER）以及微生物生物标志物，以确定养分化学计量和分解者群落是否解释了 SOM 矿化率的差异。与不添加基质相比，添加基质后总 C 矿化量大大增加，尤其是纤维素（N、P、NP 施肥和 CK 分别为 5.38、7.13、5.58 和 5.37 倍），而在长期 N（纤维素添加分别为 3.40%和 5.18%）或 NP（纤维素添加为 35.11%）施肥土壤中，原始土壤 C 矿化进一步增强与对照处理相比。两种基质的添加均刺激了酶活性，但 P 施肥抑制了酶活性。两种基质的添加均增加了微生物对磷的获取投资，但只有淀粉添加促进了 C 在 N 上的获取投资。最后，与细菌丰度相比，基质添加更能促进真菌丰度的增加，特别是在纤维素添加的土壤中，并且长期施肥会放大这种效应。我们的研究结果表明，在 N 和 P 富集的生态系统中，SOM 矿化可能会增强，因为如果 N 和 P 充足，凋落物输入可以使微生物摆脱 C 限制并刺激 SOM 矿化。我们的研究进一步表明，结构相似的基质对 SOM 矿化可能具有不同的影响，SOM 矿化的程度强烈取决于元素化学计量以及微生物分解者的资源需求。
