Sun Yuhao, Kang Xiangli, Li Ruoxuan, Cui Yannong, Long Mingxiu, He Shubin
College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi, 712100, China.
College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi, 712100, China.
Plant Physiol Biochem. 2025 Aug 8;229(Pt A):110353. doi: 10.1016/j.plaphy.2025.110353.
Arbuscular mycorrhizal fungi (AMF) and rhizobia enhance the ability of crops to access nitrogen (N) and phosphorus (P) and are keystone microorganisms that engage in reciprocal interactions with plants. However, their contributions and impacts in alleviating plant nutrient dependency and mitigating N deposition and P limitation under various N and P additions remain unclear. We hypothesized that co-inoculation with AMF and rhizobia would synergistically enhance crop nutrient absorption and stabilize N:P stoichiometry for mitigating N deposition and P limitation and enhancing biomass. Here, two experimental systems were established: (1) constant low P with three increasing N levels, and (2) constant low N with three increasing P levels. Within each system, we examined the effects of inoculation with AMF alone, rhizobia alone, both AMF and rhizobia, and no inoculation on alfalfa biomass, photosynthesis, nutrient content, and N:P stoichiometry. Results revealed that co-inoculation with AMF and rhizobia significantly increased alfalfa aboveground biomass (AGB) and belowground biomass (BGB) by 88.54 % and 236.96 %, respectively, under low N and low P conditions. Additionally, co-inoculation significantly enhanced the content of photosynthetic pigments, N and P. However, co-inoculation did not significantly affect photosynthetic rate (Pn) or transpiration rate (Tr), while significantly reducing stomatal conductance (Gs). Furthermore, co-inoculation alleviated N limitation in alfalfa, shifting its limitation from N to P by increasing N:P stoichiometry. Notably, co-inoculation buffered leaf N:P stoichiometry against nutrient change, while maintaining the maximum leaf N:P stoichiometry. In contrast, as N or P levels rose, alfalfa BGB, photosynthetic pigments content, Pn, and N content, and P content were inhibited to varying degrees across all inoculation treatments, with increased N limitation. Moreover, partial least squares path modeling (PLS-PM) demonstrated a unique mechanism in the co-inoculation treatment whereby alfalfa AGB and BGB was enhanced through the root N:P stoichiometric regulation. Overall, our findings highlight multifaceted benefits of co-inoculation under low-input conditions, including increased alfalfa biomass, improved nutrient use efficiency, and reduced reliance on exogenous N. These results suggest the potential of co-inoculation with AMF and rhizobia to reduce fertilizer dependency and enhance alfalfa productivity in low-input agricultural ecosystems, promoting sustainable forage crop production.
丛枝菌根真菌（AMF）和根瘤菌可提高作物获取氮（N）和磷（P）的能力，是与植物进行相互作用的关键微生物。然而，在不同氮磷添加条件下，它们在缓解植物养分依赖、减轻氮沉降和磷限制方面的贡献和影响仍不明确。我们假设，联合接种AMF和根瘤菌能协同增强作物对养分的吸收，并稳定氮磷化学计量比，以减轻氮沉降和磷限制并增加生物量。在此，我们建立了两个实验系统：（1）低磷恒定，氮水平逐渐增加的三个梯度；（2）低氮恒定，磷水平逐渐增加的三个梯度。在每个系统中，我们研究了单独接种AMF、单独接种根瘤菌、同时接种AMF和根瘤菌以及不接种对苜蓿生物量、光合作用、养分含量和氮磷化学计量比的影响。结果表明，在低氮和低磷条件下，联合接种AMF和根瘤菌使苜蓿地上生物量（AGB）和地下生物量（BGB）分别显著增加了88.54%和236.96%。此外，联合接种显著提高了光合色素、氮和磷的含量。然而，联合接种对光合速率（Pn）或蒸腾速率（Tr）没有显著影响，但显著降低了气孔导度（Gs）。此外，联合接种缓解了苜蓿的氮限制，通过提高氮磷化学计量比将其限制从氮转变为磷。值得注意的是，联合接种缓冲了叶片氮磷化学计量比以应对养分变化，同时维持了叶片最大氮磷化学计量比。相比之下，随着氮或磷水平的升高，在所有接种处理中苜蓿的BGB、光合色素含量、Pn、氮含量和磷含量均受到不同程度的抑制，氮限制增加。此外，偏最小二乘路径模型（PLS-PM）证明了联合接种处理中的一种独特机制，即通过根氮磷化学计量调控增强苜蓿的AGB和BGB。总体而言，我们的研究结果突出了低投入条件下联合接种的多方面益处，包括增加苜蓿生物量、提高养分利用效率以及减少对外源氮的依赖。这些结果表明，联合接种AMF和根瘤菌在低投入农业生态系统中具有降低肥料依赖性和提高苜蓿生产力的潜力，可促进可持续饲料作物生产。
