Feigin-Odesskii brackets associated with Kodaira cycles and positroid varieties

We establish a link between open positroid varieties in the Grassmannians G (k, n) and certain moduli spaces of complexes of vector bundles over Kodaira cycle Cⁿ, using the shifted Poisson structure on the latter moduli spaces and relating them to the standard Poisson structure on G (k, n). This link allows us to solve a classification problem for extensions of vector bundles over Cⁿ. Based on this solution we further classify the symplectic leaves of all positroid varieties in G (k, n) with respect to the standard Poisson structure. Moreover, we get an explicit description of the moduli stack of symplectic leaves of G (k, n) with the standard Poisson structure as an open substack of the stack of vector bundles on Cⁿ.