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Abstract
The southwestern mountains of Hainan Island are distributed in the southernmost tropical karst landscape of China, and the unique hydrological structure and frequent solifluction droughts lead to double water stress for local plants. Highly heterogeneous water environments affect the water–use characteristics of plants. Plants develop local adaptative mechanisms in response to changes in the external environment. In this paper, hydrogen–oxygen and carbon stable isotope technology, and physiological index measurements were applied to determine the leaf traits, water–use efficiency, and photosynthetic characteristics of Impatiens hainanensis leaves in dry and foggy seasons, hoping to expound the adaptation mechanism of I. hainanensis leaves to the water dynamics in dry and foggy seasons. In dry and foggy seasons (November 2018 to April 2019), the leaves of I. hainanensis at low and medium altitudes have the following combination of traits: larger leaf dry weights, leaf areas, and specific leaf areas; smaller leaf thicknesses and leaf dry matter contents; and higher chlorophyll contents. In comparison, the leaves of I. hainanensis at high altitudes have the following combination of traits: smaller leaf dry weights, leaf areas, and specific leaf areas; larger leaf thicknesses and leaf dry matter contents; and lower chlorophyll contents. The leaves of I. hainanensis can absorb fog water through their leaves. When the leaves are sprayed with distilled water, the water potential is low, the water potential value gradually increases, and the leaves have a higher rate of water absorption. The leaves of I. hainanensis at low and medium altitudes have the following water–use characteristics: high photosynthesis, high transpiration, and low water–use efficiency. At high altitudes, the Pn of I. hainanensis decreases by 8.43% relative to at low altitudes and by 7.84% relative to at middle altitudes; the Tr decreased by 4.21% relative to at low altitudes and by 3.38% relative to at middle altitude; the WUE increased by 16.61% relative to at low altitudes and increased by 40.79% relative to at middle altitudes. The leaves of I. hainanensis at high altitudes have the following water–use characteristics: low photosynthesis, low transpiration, and high water–use efficiency. I. hainanensis develop different physiological mechanisms of water adaptation by weighing the traits of the leaves and their use of light and water to obtain resources during dry and foggy seasons.
Highlights
Changes in climate extremes and precipitation patterns resulting from global climate change have important implications for the growth, development, and distribution of plants [1]
Leaf dry weight was highly significantly negatively correlated with specific leaf area (p < 0.01), and leaf fresh weight was significantly negatively correlated with specific leaf area (p < 0.05); both leaf dry weight and leaf fresh weight were significantly positively correlated with leaf thickness (p < 0.05), and leaf dry matter content was significantly positively correlated with leaf thickness (p < 0.05), leaf dry weight, and leaf fresh; and the leaf dry matter content increased with increasing leaf thickness
Studies have shown that some lianas in karst areas have smaller leaf thickness, and larger leaf area and leaf dry matter content, which are similar to the leaf traits of I. hainanensis at low and medium altitudes but differs from those of I. hainanensis at higher altitudes because, compared with karst trees and herbs, some lianas tend to increase their leaf area and because some lianas tend to increase their leaf area and chlorophyll content compared with karst trees and herbs, expanding the range of light absorption and maintaining better photosynthetic capacity [53]
Summary
Changes in climate extremes and precipitation patterns resulting from global climate change have important implications for the growth, development, and distribution of plants [1]. The ability of plants to coordinate carbon assimilation and water dissipation governs their adaptation to drought conditions [2]. The ability of plants to synergize carbon assimilation and water dissipation, i.e., water–use efficiency (WUE), is an essential physiological indicator of plant adaptation to habitats [5,6]. WUE is a key factor for plant growth in arid rocky deserts, and an essential link in the carbon and water cycle of terrestrial ecosystems [7,8,9]. The δ13C of leaves can indicate plants’ long–term WUE and water use [12], revealing the coupling between carbon and water changes in plant leaves and habitat [13]
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