Stem-leaf tradeoff of Kobresia tibetica in alpine peat swamp study on the relationship of water use efficiency

Water use efficiency (WUE) is a key index to predict the impact of climate change on ecosystem carbon and water cycles; the tradeoff of stem and leaf traits determine the WUE and resource competitiveness of individual plants. Four altitudinal gradients of 3400 m, 3500 m, 3600 m, and 3700 m were selected as experimental sites in Gahai Wetland on the Ruoerge Plateau. The Mantel Test method and the standardized major axis estimation (SMA) method were employed to examine the relationship between stem-leaf tradeoff and WUE of Kobresia tibetica in alpine peat swamps at different elevations. The results showed that with the increase of altitude, the surface water area decreased gradually, and the height and fractional vegetation cover of wetland community, stomatal conductance (Gs), and transpiration rate (Tr) of Kobresia tibetica showed a decreasing trend (P < 0.05).WUE, photosynthetically active radiation (PAR), vapor pressure deficit (VPD), and the height, fractional vegetation cover, and root-shoot ratio of Kobresia tibetica showed an increasing trend (P < 0.05). The leaf area (LA), leaf thickness (LT), specific leaf area (SLA), stem length (SL), and WUE of Kobresia Tibetica showed different correlations at different elevations. With the increase of altitude, the tradeoff between stems and leaves of Kobresia tibetica changed from stems to leaves, the tradeoff between LA and LT changed from favoring LA to LT, stem and leaf configuration changed from long stem-large LA to short stem-small LA, the net photosynthetic rate (Pn) and WUE increased, and the structural cost and photosynthetic efficiency return of Kobresia tibetica leaves changed from 'high-input-slow return' to 'low-input-fast return'. It reflects the ecological strategy of synergistic adaptation between stem and leaf morphology and photosynthetic characteristics of plants in alpine peat swamp in a heterogeneous habitat.