Chen Yuanqi, Zhang Yu, Zhang Xu, Stevens Carly, Fu Shenglei, Feng Teng, Li Xiaowei, Chen Quan, Liu Shirong, Hu Shuijin
Institute of Geographical Environment and Carbon Peak and Neutrality, School of Earth Sciences and Spatial Information Engineering, Hunan University of Science and Technology, Xiangtan, China.
Key Laboratory of Forest Ecology and Environment of Forestry and Grassland Administration, Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Beijing, China.
Glob Chang Biol. 2024 Jul;30(7):e17427. doi: 10.1111/gcb.17427.
Atmospheric nitrogen (N) deposition in forests can affect soil microbial growth and turnover directly through increasing N availability and indirectly through altering plant-derived carbon (C) availability for microbes. This impacts microbial residues (i.e., amino sugars), a major component of soil organic carbon (SOC). Previous studies in forests have so far focused on the impact of understory N addition on microbes and microbial residues, but the effect of N deposition through plant canopy, the major pathway of N deposition in nature, has not been explicitly explored. In this study, we investigated whether and how the quantities (25 and 50 kg N ha year) and modes (canopy and understory) of N addition affect soil microbial residues in a temperate broadleaf forest under 10-year N additions. Our results showed that N addition enhanced the concentrations of soil amino sugars and microbial residual C (MRC) but not their relative contributions to SOC, and this effect on amino sugars and MRC was closely related to the quantities and modes of N addition. In the topsoil, high-N addition significantly increased the concentrations of amino sugars and MRC, regardless of the N addition mode. In the subsoil, only canopy N addition positively affected amino sugars and MRC, implying that the indirect pathway via plants plays a more important role. Neither canopy nor understory N addition significantly affected soil microbial biomass (as represented by phospholipid fatty acids), community composition and activity, suggesting that enhanced microbial residues under N deposition likely stem from increased microbial turnover. These findings indicate that understory N addition may underestimate the impact of N deposition on microbial residues and SOC, highlighting that the processes of canopy N uptake and plant-derived C availability to microbes should be taken into consideration when predicting the impact of N deposition on the C sequestration in temperate forests.
森林中的大气氮（N）沉降可通过增加氮的有效性直接影响土壤微生物的生长和周转，也可通过改变植物源碳（C）对微生物的有效性间接影响土壤微生物的生长和周转。这会影响微生物残体（即氨基糖），而微生物残体是土壤有机碳（SOC）的主要组成部分。此前在森林中的研究主要聚焦于林下添加氮对微生物和微生物残体的影响，但通过植物冠层（自然界中氮沉降的主要途径）进行氮沉降的影响尚未得到明确探究。在本研究中，我们调查了在为期10年的氮添加条件下，添加氮的量（25和50 kg N ha⁻¹ 年⁻¹）和方式（冠层和林下）如何影响温带阔叶林土壤中的微生物残体。我们的结果表明，添加氮提高了土壤氨基糖和微生物残体碳（MRC）的浓度，但未改变它们对土壤有机碳的相对贡献，并且这种对氨基糖和MRC的影响与添加氮的量和方式密切相关。在表层土壤中，高氮添加显著增加了氨基糖和MRC的浓度，与添加氮的方式无关。在亚表层土壤中，只有冠层添加氮对氨基糖和MRC有正向影响，这意味着通过植物的间接途径发挥了更重要的作用。冠层和林下添加氮均未显著影响土壤微生物生物量（以磷脂脂肪酸表示）、群落组成和活性，这表明氮沉降下微生物残体的增加可能源于微生物周转的加快。这些发现表明，林下添加氮可能低估了氮沉降对微生物残体和土壤有机碳的影响，突出了在预测氮沉降对温带森林碳固存的影响时，应考虑冠层氮吸收过程以及植物源碳对微生物的有效性。
