Emerging scientific evidence has shown that root exudates may trigger the mobilization of soil organic matter (SOM), particularly under nutrient limitation. However, the role of changes in root morphology, metabolism, exudation, and their impact on rhizospheric properties and SOM remain poorly known. To address this issue, we conducted a rhizobox experiment for 50 days in which pre-grown eucalypt plants (120 days-old) were supplied with nutrient solutions providing either limited (0.0 mg L^− 1) or normal N supply (196.0 mg L^− 1). After 48 days, we used a ¹³CO₂ pulse labeling to track the impact of N limitation on C translocation to roots and soil respiration. After the 50th day, we assessed root morphology and metabolism, rhizospheric pH, mineral crystallinity, C and N contents, and the molecular composition of SOM. Under N limitation, eucalypt plants showed reduced photosynthesis, increased their root-to-shoot ratio and root branching, with organic acids prevailing among root metabolites. Overall, N-limited eucalypt plants led to a cascading of changes in the rhizosphere: increased concentrations of recently fixed ¹³C-CO₂, citrate, and N-bearing compounds, whereas soil pH and Fe-bound SOM decreased. These results were not followed by significant changes in microbial biomass, neither fungi: bacteria nor Gram-positive: Gram-negative ratios. Our results show that under N limitation, eucalypt roots exhibited a cascade of morpho-physiological adjustments that ultimately increased the mobilization of some SOM pools. Therefore, the combined impacts of those root morpho-physiological traits on the mobilization of SOM may reduce the overall soil C sink of eucalypt forests under N limitation.

新的科学证据表明，根系分泌物可能会引发土壤有机质（SOM）的动员，特别是在养分限制的情况下。然而，根系形态、代谢、渗出物变化的作用及其对根际特性和 SOM 的影响仍然知之甚少。为了解决这个问题，我们进行了为期 50 天的根箱实验，其中向预生长的桉树植物（120 天龄）提供营养液，提供有限（0.0 mg L ^− 1 ）或正常的氮供应（196.0 mg L ^− 1 ）。 48 天后，我们使用 ¹³ CO ₂ 脉冲标记来追踪 N 限制对 C 易位到根部和土壤呼吸的影响。第 50 天后，我们评估了根的形态和代谢、根际 pH 值、矿物质结晶度、C 和 N 含量以及 SOM 的分子组成。在氮限制下，桉树植物的光合作用减少，根冠比和根分枝增加，根代谢产物中以有机酸为主。总体而言，氮限制的桉树植物导致了根际的一系列变化：最近固定的 ¹³ C-CO ₂ 、柠檬酸盐和含氮化合物的浓度增加，而土壤pH 值和 Fe 结合的 SOM 降低。这些结果之后，微生物生物量、真菌：细菌和革兰氏阳性：革兰氏阴性比率都没有发生显着变化。我们的结果表明，在氮限制下，桉树根表现出一系列的形态生理调整，最终增加了一些 SOM 库的动员。因此，这些根形态生理特征对 SOM 动员的综合影响可能会减少氮限制下桉树林的总体土壤碳汇。