Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
South China National Botanical Garden, Guangzhou, China.
mSystems. 2024 Oct 22;9(10):e0054724. doi: 10.1128/msystems.00547-24. Epub 2024 Sep 10.
Biological nitrogen (N) fixation, an important pathway of N, inputs from the atmosphere to Earth's ecosystems, is well demonstrated to decline under N input. However, it remains unclear why N fixers sustain N fixation in many forests under high atmospheric N deposition. To address this knowledge gap, we analyzed the response of the diazotroph community to low N loads (short-term and low N addition; 3-year N addition at the rates of 25-50 kg N ha year) vs high loads (chronic and high N addition; 9-year N addition at the rate of 150 kg N ha year) in forest soils using high-throughput sequencing. Rates of N fixation decreased under low and high N loads (by 13%-27% and 10%-12%, respectively). Richness and alpha diversity (ACE and Chao1) of the soil diazotroph community decreased under low but not high N loads. Approximately 67.1%-74.4% of the gene sequences at the OTU level overlapped between the control and low N loads, but only 52.0%-53.6% of those overlapped between the control and high N loads, indicating a larger shift of diazotroph community composition under high N loads. Low N loads increased soil NH concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH concentrations under high N loads did not have negative impacts on the structure and function of the diazotroph community. These findings indicate that diazotrophs sustain N fixation under high N deposition adjustment of their community composition in forest soils.
This study examined the changes in soil diazotroph community under different loads of simulated N deposition and analyzed its relationship with N fixation rates in in five forests using high-throughput sequencing. The magnitudes of N fixation rates reduced by low N loads were higher than those by high N loads. Low N loads decreased richness and diversity of diazotroph community, whereas diazotroph community structure remained stable under high N loads. Compared with low N loads, high N loads resulted in a less similarity and overlap of gene sequences among the treatments and a larger adjustment of diazotroph community. Low N loads increased soil NH4+ concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH4+ under high N loads did not have negative impacts on diazotroph community structure and N fixation. Based on these findings, it is urgently needed to incorporate the loads of N deposition and the composition of diazotroph community into terrestrial N-cycling models for accurate understanding of N inputs in forest ecosystems.
生物固氮（N）是大气 N 输入到地球生态系统的重要途径，已有研究表明其在 N 输入增加的情况下会下降。然而，目前尚不清楚为什么在大气 N 沉降较高的情况下，许多森林中的固氮生物仍能维持固氮作用。为了填补这一知识空白，我们使用高通量测序分析了短期低氮添加（3 年 N 添加速率为 25-50kg Nha-1 年-1）和长期高氮添加（9 年 N 添加速率为 150kg Nha-1 年-1）对森林土壤中固氮菌群落的响应。固氮速率在低氮和高氮负荷下均降低（分别降低 13%-27%和 10%-12%）。低氮负荷下土壤固氮菌群落的丰富度和多样性（ACE 和 Chao1）降低，但高氮负荷下没有降低。OTU 水平的基因序列约有 67.1%-74.4%在对照和低氮负荷之间重叠，但只有 52.0%-53.6%在对照和高氮负荷之间重叠，表明高氮负荷下固氮菌群落组成的变化更大。低氮负荷增加了土壤 NH4+浓度，降低了固氮菌群落的丰富度、多样性和固氮速率，而高氮负荷下土壤 NH4+浓度的增加对固氮菌群落的结构和功能没有产生负面影响。这些发现表明，在高氮沉降下，固氮生物通过调整其群落组成来维持固氮作用。
