Duan Songlan, Guo Jinping, Zhang Yunxiang, Liu Libao, Wang Rui, Zheng Rongrong
College of Forestry, Shanxi Agricultural University, Jinzhong, China.
Front Plant Sci. 2024 Jul 30;15:1392934. doi: 10.3389/fpls.2024.1392934. eCollection 2024.
Rhizosphere effects (REs) have recently been identified as important regulators of root and microbial nutrient acquisition and are positively involved in nutrient cycling of belowground carbon (C), nitrogen (N), and phosphorus (P). Nutrient conditions of the fine roots and soil N are likely to influence REs. Still, it is unclear how REs of soil nutrients themselves variably impact the supply of nutrients to plants in terms of the responses to soil N due to succession.
In this study, we applied both fine roots and extracellular enzymes for vector analysis and stoichiometry of N:P to explore the metabolic limitations of roots and rhizospheric soil microbes and their relationships with REs across five levels of soil N (0, 5, 10, 15, and 20 kg N m year) along successional age classes of 42, 55, and 65 years in a forest.
Overall, the metabolism of root and rhizospheric soil microbes was mediated by soil N. N limitation of roots initially decreased before increasing, whereas that of microbes demonstrated opposite trends to the N levels owing to competition for inorganic N between them by REs of NO -N. However, N limitations of both roots and microbes were alleviated in young stands and increased with succession after the application of N. In addition, root N limitations were manipulated by REs of three different soil N-related indicators, i.e., total N, NH -N, and NO -N. Rhizospheric soil microbial N limitation was almost unaffected by REs due to their strong homeostasis but was an important driver in the regulation of root N limitation.
Our results indicated that successional age was the most critical driver that directly and indirectly affected root N metabolism. However, the level of N application had a slight effect on root N limitation. Microbial N limitation and variations in the REs of N indicators regulated root N limitation in the rhizosphere. As a result, roots utilized REs to sequester N to alleviate N limitations. These findings contribute to novel mechanistic perspectives on the sustainability of N nutrition by regulating N cycling in a system of plant-soil-microbes in the rhizosphere to adapt to global N deposition or the heterogeneous distribution of bioavailable soil N with succession.
根际效应（REs）最近被确定为根系和微生物养分获取的重要调节因子，并积极参与地下碳（C）、氮（N）和磷（P）的养分循环。细根的养分状况和土壤氮可能会影响根际效应。然而，由于演替，土壤养分自身的根际效应如何以对土壤氮的响应方式不同程度地影响植物的养分供应仍不清楚。
在本研究中，我们应用细根和细胞外酶进行矢量分析以及氮磷化学计量，以探究根和根际土壤微生物的代谢限制及其与森林中沿42、55和65年演替年龄类别的五个土壤氮水平（0、5、10、15和20 kg N m²年）下根际效应的关系。
总体而言，根和根际土壤微生物的代谢受土壤氮介导。根的氮限制最初下降后上升，而微生物的氮限制由于根际效应中硝酸根 - 氮对无机氮的竞争而呈现与氮水平相反的趋势。然而，在幼龄林分中，根和微生物的氮限制均得到缓解，施氮后随演替增加。此外，根的氮限制受三种不同土壤氮相关指标（即全氮、铵态氮和硝态氮）的根际效应调控。根际土壤微生物的氮限制因其强大的内稳态几乎不受根际效应影响，但却是调节根氮限制的重要驱动因素。
我们的结果表明，演替年龄是直接和间接影响根氮代谢的最关键驱动因素。然而，施氮水平对根氮限制影响较小。微生物氮限制和氮指标根际效应的变化调节了根际根的氮限制。因此，根利用根际效应来螯合氮以缓解氮限制。这些发现有助于从新的机制角度理解通过调节根际植物 - 土壤 - 微生物系统中的氮循环来适应全球氮沉降或生物可利用土壤氮随演替的异质分布，从而实现氮营养的可持续性。
