Stable Isotope Analysis of Plant Water Sources and Transpiration Efficiency in Three Vegetation Zones of the Lake Chad Basin, Borno State

Understanding plant water sourcing strategies and transpiration efficiency is critical for assessing plant responses to desiccation in the Lake Chad Basin, where declining water availability is fundamentally altering vegetation structure in Borno State. This study used stable isotope analysis (delta 18O, delta 2H, and delta 13C) to determine plant water sources, water use efficiency, and drought adaptation strategies of dominant plant species across three vegetation zones in the Lake Chad Basin: lake margin wetlands, seasonal floodplain, and dry sub-humid upland, in Borno State. Twenty plant species dominant in each zone were selected, and xylem water, leaf water, and source water (groundwater, rainwater, and surface water) were sampled for hydrogen and oxygen isotope analysis using a cavity ring-down spectroscopy analyser. Leaf carbon isotope discrimination (delta 13C) was measured as a proxy for long-term water use efficiency. Linear mixing models were used to estimate the proportional contribution of different water sources to plant xylem water. Results showed that lake margin species relied primarily on shallow groundwater (mean contribution: 74%), while upland dry sub-humid species showed greater reliance on deep groundwater (mean: 61%). Delta 13C values differed significantly among vegetation zones, with upland species showing less negative values (mean: -25.8 per mil) compared to lake margin species (mean: -28.4 per mil), indicating higher water use efficiency in drier habitats. C4 grasses dominated in both upland and floodplain zones. The study provides the first stable isotope plant ecohydrology dataset for the Nigerian Lake Chad Basin and recommends its use in vegetation vulnerability modelling for climate change adaptation planning.

Keywords: stable isotope analysis, plant water sources, water use efficiency, Lake Chad Basin, drought adaptation