Mixed culture enhances coral sand weathering more than monoculture

The success of vegetation establishment on barren lands, particularly those derived from poor-structured or nutrient-deficient parent materials like coral sand, hinges upon complex interactions between plants and their environment. To unravel these dynamics, we investigated how coral sand weathering responded to a factorial design combining four distinct culture modes (plant-free controls, monocultures of Casuarina equisetifolia and Scaevola taccada, and their mixed culture) with three particle compositions of coral sand, in a greenhouse. Results showed that the particle size of coral sand neither affected nor interacted with culture modes on coral sand weathering. All plant cultures significantly enhanced the weathering releases of Ca and Mg, compared to the plant-free control. The C. equisetifolia monoculture enhanced coral sand weathering (Ca: 3152 mg pot-1; Mg: 629 mg pot-1) more than the S. taccada monoculture (Ca: 2413 mg pot-1; Mg: 500 mg pot-1), preliminarily due to its higher root specific length and surface area. Nutrients released from coral sand in the C. equisetifolia monoculture was mainly leached out (Ca: 72%; Mg: 85%), while in the S. taccada monoculture it was mainly stored in the plant biomass (Ca: 71%; Mg: 59%), due to a larger aboveground biomass of S. taccada. These differences between species resulted in a 6% ∼ 32.4% enhancement of coral sand weathering in their mixed culture than in their monocultures. Overall, our study underscores the priority of selecting plant species with complementary functional traits for constructing vegetation on coral islands.