Laboratory study of subtropical wetland plant Lepironia articulata’s water use and sensitivity to groundwater availability

Abstract

Few ecohydraulic studies have been conducted on groundwater dependent wetland ecosystems despite their ecological and environmental importance. In particular, there is a substantial gap in quantifying plant and groundwater interaction. Our study considered groundwater-vegetation-atmosphere interaction for a wetland reed species. It has improved our understanding of the dynamic feedback between the subtropical wetland emergent plant Lepironia articulata and groundwater, especially in the context of developing plant response models. More specifically, we have generated growth response functions for Lepironia under water stressed conditions (different depths to groundwater).Concurrently, we measured the response of groundwater discharge (i.e., via evapotranspiration) for different depths to groundwater . Laboratory experiments and new methodologies have been developed to control groundwater drawdown rates and amplitudes in order to study these interactions. The experiments use a column lysimeter setup where water levels are controlled at 0, 30 and 60 cm after a fast drawdown rate of 8 cm/day. The response of Lepironia to groundwater drawdown is investigated through population changes, rhizome horizontal development, green culm lengths, green culm areas with time and the distribution of biomass at the start and the end of the experiment; ET rates are measured using a Mariotte bottle -load cell system. An L-system based L-Lepironia model is created to simulate the growth and structural development of Lepironia from the experimental results.Our results show that groundwater drawdown to 60 cm causes significant water stress to, and can be regarded as a survival threshold for, Lepironia. Groundwater drawdown to 30 cm causes a reduction in the growth of Lepironia and resulting ET rates compared to the unstressed 0 cm drawdown groups.The physical growth responses of Lepironia also have an impact on the amount of water discharged from the system. It is found that the long-term trend of ET for Lepironia is mostly governed by leaf areas while the short-term changes in ET are controlled by local meteorological conditions. Based on these results, we have developed empirical equations to predict the change in total leaf areas with time and long-term daily ET for Lepironia at different water table depths taking seasonal differences into account. Furthermore, the L-Lepironia model is able to capture and predict the growth and development of Lepironia in response to changing groundwater and seasonal conditions; its extension shows a better ET prediction than using the empirical equations. Our study demonstrates a new methodology for quantifying plant-groundwater interactions and may have implications for future plant-groundwater feedback and coupled model studies.