Ecohydrology of epiphytes: Modelling water balance, CAM photosynthesis, and their climate impacts

Epiphytes are aerial plants, often characterized by CAM (crassulacean acid metabolism) photosynthesis, which make up a significant portion of the biomass in some rainforests. Their unique characteristics have not yet been included in ecohydrological models, and their potential impact on local hydrometeorology is largely unexplored. This work introduces a water balance model for epiphytes, which adapts the soil-plant-atmosphere continuum model to represent a plant system without soil and couples it to the Photo3 photosynthesis model, which includes CAM photosynthesis. The model, which is parameterized with field data of Guzmania monostachia, accurately captures the observed hydraulic and photosynthetic behaviour of the epiphytic species. The application of vertical profiles of environmental inputs within the rainforest canopy shows increasing transpiration rates and decreasing water use efficiency with increasing canopy height, which corresponds to observed distributions of epiphytes in rainforests. Given that vascular epiphytes constitute a maximum of 35-50% of the foliar biomass in rainforests and contribute up to 13% of forest net primary production, they may contribute up to 10-50% of total rainforest evapotranspiration, a significant portion of the water cycle on the local ecosystem scale. The results of this work provide a missing piece to current ecohydrological models and can be integrated into Earth system models to help improve the physical representation of transpiration and free-surface evaporation from canopy in current and future climates.

Automated summary

This study introduces a water balance model for epiphytes and reveals their potential impact on local hydrometeorology. The distribution of epiphytes in the rainforest canopy is correlated with vertical profiles of environmental inputs. Epiphytes play a significant role in the water cycle of rainforests.