Response and mechanism of potassium content in leaves of alpine meadow plants to multiple nutrient additions

  Objective  Potassium (K) is the second most abundant element in plants, which is important to sustain plant growth and adapt to cold environment. Recent meta-analysis studies showed that grassland plant product was universally co-limited by multiple nutrients, while this study aimed to reveal the responses and mechanisms of leaf K concentration to main and interaction effects of the addition of K, nitrogen (N) and phosphorus (P).

  Method  Taking the alpine meadow in northwestern Sichuan as the research object, potassium, nitrogen and phosphorus addition and interactive control experiments were carried out to reveal the response and mechanism of potassium in the leaves of dominant plants in alpine meadow to a variety of nutrients and their interactions.

  Result  We found no significant interaction effect for the combined addition of K, N and P fertilizers on the leaf K concentration of Elymus nutans, Deschampsia cespitosa, Carex enervis and Anemone rivularis. P addition alone did not affect species’ leaf K, while K addition increased leaf K concentration in Carex enervis and Anemone rivularis significantly. In contrast, N addition consistently enhanced leaf K concentration across all species. The direct effect of increasing soil N availability by N addition only affected two species’ leaf K concentration. However, we found that the consistent increase in leaf K concentration among species was mainly driven by the indirect effect caused by N addition. To be specific, N addition firstly increased community biomass, further indirectly reducing soil temperature due to increasing shading effect. Moreover, we found a consistent increase in leaf K concentration with lower soil temperature among different species.

  Conclusion  Different from the traditional view that soil nutrient is the main factor affecting plant leaf potassium, this study finds that the indirect effect caused by nitrogen addition (decrease of soil temperature) is the main mechanism driving the change of leaf K content under the background of nutrient enrichment. The results indicate that the K utilization strategy of alpine meadow plants may be closely related to low temperature adaptability due to long-term low temperature stress.