Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China.
CSIC, Global Ecology Unit CREAF-CSIC-UAB, 08913, Bellaterra, Catalonia, Spain.
Ecology. 2021 Jun;102(6):e03348. doi: 10.1002/ecy.3348. Epub 2021 Apr 18.
Natural abundance of carbon (C) and nitrogen (N) stable isotope ratios (δ C and δ N) has been used to indicate ecosystem C and N status and cycling; however, use of this approach to infer plant and microbial N preference under projected ecosystem N enrichment is limited. Here, we investigated natural abundance δ C and δ N of five dominant plant species, and soil δ N of microbial biomass and available N forms under N addition in a meadow steppe. Additional N, applied as urea, led to decreases in δ N of soil NO (δ N , from 3.0 to 0.4‰) and increases in δ N of soil (δ N , from -1.3 to 11‰) and dissolved organic N (δ N , from 8.5 to 15‰) that reflected increased net nitrification rates, a possible increase in NH volatilization, and greater availability of the three N forms. An overall increase in δ N of soil total N (δ N ) from 7.1 to 7.9‰ indicated accelerated and greater openness of soil N cycling that was also partially revealed by enhanced net N mineralization rates. Plant δ N, which ranged from -1.8 to 2.1‰, generally decreased with N addition, indicating a greater reliance on soil NO under N-enrichment conditions. Nitrogen addition decreased δ N of microbial biomass N (from 14 to 2.8‰), possibly because of a shift in preferential N form (DON to ), that indicated a convergence of plant and microbial preferential N forms and an increase in plant-microbial N competition. Microbes were thus more flexible than plants in the use of different forms of N. Addition of N decreased plant litter δ C, whereas plant species δ C remained unaffected, likely because of a shift in the abundance of dominant species with a greater proportion of biomass coming from δ C-depleted species. Enrichment factor (the difference in plant δ N relative to δ N ) of four nonlegume species was negatively related to soil inorganic N availability, net nitrification rate, and net N mineralization rate, and was proven to be a good indicator of ecosystem N status. Our study highlights the importance of natural abundance of N as an indicator of plant-microbial N competition and ecosystem N cycling in meadow steppe grasslands under projected ecosystem N enrichment.
自然存在的碳 (C) 和氮 (N) 稳定同位素比值 (δ C 和 δ N) 被用来指示生态系统的 C 和 N 状况和循环；然而，在预测的生态系统 N 富集下，利用这种方法推断植物和微生物对 N 的偏好是有限的。在这里，我们研究了在草原草甸中添加 N 时，五种主要植物物种的自然丰度 δ C 和 δ N，以及微生物生物量和可利用 N 形式的土壤 δ N。额外的 N，以尿素的形式添加，导致土壤中 δ N 的减少（δ N 从 3.0 到 0.4‰）和土壤中 δ N 的增加（δ N 从-1.3 到 11‰）和溶解有机 N（δ N 从 8.5 到 15‰），这反映了净硝化速率的增加，可能增加了 NH 挥发，以及三种 N 形式的可用性增加。土壤总 N 的自然丰度 δ N （δ N ）从 7.1 增加到 7.9‰，表明土壤 N 循环的加速和开放性增加，这也部分反映在净 N 矿化率的增加上。植物 δ N 范围为-1.8 到 2.1‰，一般随着 N 的添加而减少，表明在 N 富集条件下对土壤 NO 的依赖程度更大。添加 N 降低了微生物生物量 N 的 δ N（从 14 到 2.8‰），这可能是因为优先 N 形式（从 DON 到 ）的转变，这表明植物和微生物优先 N 形式的趋同，以及植物-微生物 N 竞争的增加。因此，与植物相比，微生物在利用不同形式的 N 方面更加灵活。添加 N 降低了植物凋落物的 δ C，而植物物种的 δ C 不受影响，这可能是由于优势物种的丰度发生了变化，来自 δ C 枯竭物种的生物量比例增加。四种非豆科物种的富集因子（植物 δ N 相对于 δ N 的差异）与土壤无机 N 有效性、净硝化率和净 N 矿化率呈负相关，被证明是生态系统 N 状况的良好指标。我们的研究强调了在预测的生态系统 N 富集下，自然丰度 δ N 作为植物-微生物 N 竞争和草原草甸生态系统 N 循环的指示物的重要性。
