In a grassland ecosystem, the dynamics and coexistence mechanisms of two herbivores competing for one herbaceous plant have been widely studied, while the chemical heterogeneity of herbaceous plant's aboveground and belowground parts is usually ignored in dynamic modeling. Based on the traditional two herbivore-one herbaceous plant competition model, a new stoichiometric competition model, which incorporates the chemical heterogeneity of herbaceous plants, is formulated to investigate effects of the aboveground-belowground interactions and the chemical heterogeneity on the dynamics of the two herbivore-one herbaceous plant system. We perform theoretical analysis for the stability of boundary equilibria and show that a stable coexistent equilibrium is possible with two herbivores on one herbaceous plant. Moreover, numerical simulations reveal that various light intensity and nitrogen input can also allow all populations to coexist in periodic oscillations or irregularly cyclic oscillations. Our findings further indicate that when the nitrogen input is fixed, higher light intensity leads to a dominance of the lower N-demand herbivore, while the light intensity is fixed, higher nitrogen input leads to a dominance of the higher N-demand herbivore. Moderate levels of light and nutrient could promote the coexistence of two herbivores and herbaceous plant. This study also explains the functional mechanism for the decline of species diversity in response to nitrogen enrichment.

中文翻译：

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草本植物与两种食草动物地上-地下相互作用的化学计量模型

在草地生态系统中，两种草食动物争夺一种草本植物的动力学和共存机制已被广泛研究，而在动力学建模中通常忽略草本植物地上和地下部分的化学异质性。在传统的两草食动物一草本植物竞争模型的基础上，建立了一种新的化学计量竞争模型，结合草本植物的化学异质性，研究了地上-地下相互作用和化学异质性对两种草食动物动力学的影响。 -一种草本植物系统。我们对边界平衡的稳定性进行了理论分析，并表明一种草本植物上的两种食草动物可以实现稳定的共存平衡。而且，数值模拟表明，不同的光强度和氮输入也可以使所有种群以周期性振荡或不规则循环振荡共存。我们的研究结果进一步表明，当氮输入固定时，较高的光强度导致较低 N 需求的食草动物占优势，而光强度固定，较高的氮输入导致较高 N 需求的食草动物占优势。适度的光照和养分可以促进两种食草动物和草本植物的共存。该研究还解释了物种多样性因富氮而下降的功能机制。我们的研究结果进一步表明，当氮输入固定时，较高的光强度导致较低 N 需求的食草动物占优势，而光强度固定，较高的氮输入导致较高 N 需求的食草动物占优势。适度的光照和养分可以促进两种食草动物和草本植物的共存。该研究还解释了物种多样性因富氮而下降的功能机制。我们的研究结果进一步表明，当氮输入固定时，较高的光强度导致较低 N 需求的食草动物占优势，而光强度固定，较高的氮输入导致较高 N 需求的食草动物占优势。适度的光照和养分可以促进两种食草动物和草本植物的共存。该研究还解释了物种多样性因富氮而下降的功能机制。