Abstract
The southwestern mountains of Hainan Island are the southernmost region with tropical karst landform in China. The frequent alternation of dry and wet seasons leads to the loss of the mineral nutrients of limestone, creating karst fissure habitats. Plants living in karst fissure habitats for long periods of time have developed local adaptation mechanisms correspondingly. In the paper, hydrogen–oxygen stable isotope technology was applied to determine the water-use sources of Impatiens hainanensis in the dry and wet seasons, hoping to expound the adaptation mechanism of I. hainanensis in karst fissure habitats to the moisture dynamics in the wet and dry seasons. In the wet season (May to October, 2018), the air humidity is relatively high in the I. hainanensis habitat; in the dry season (November 2018 to April 2019), there is a degree of evaporation. In the wet season, fine-root biomass increases with soil depths, while coarse-root biomass decreases with soil depths; in the dry season, fine-root biomass is lower and coarse-root biomass is higher compared with the wet season. It was found that the average rainfall reached 1523 mm and the main water-use sources were shallow (0–5 cm) and middle (5–10 cm) soil water, epikarst water, and shallow karst fissure water during the wet season; the average rainfall reached 528 mm, and the deep (10–15 cm) soil water and shallow karst fissure water were the main water-use sources during the dry season. Fog water has a partial complementary effect in the dry season. The differences in the distribution of root biomass and each source of water in the wet and dry seasons of I. hainanensis also reflect the different water-use strategies of I. hainanensis in the wet and dry seasons. In both dry and wet seasons, I. hainanensis formed a water-use pattern dominated by soil water and shallow fissure water (0–15 cm) under the influence of the “fissure-soil-plant” system in the karst region.
Highlights
We investigate the water use of I. hainanensis in shallow rift habitats during the dry and wet seasons based on hydrogen and oxygen stable isotope techniques and ask the following questions: (1) What are the differences in water δD (δ18 O) of I. hainanensis during the dry and wet seasons? (2) What is the impact of karst geological drought on water use in I. hainanensis? (3) What are the water-use strategies of I. hainanensis in a
The results from this study show that the isotopic composition of atmospheric precipitation in the I. hainanensis sample plots was correlated with precipitation, which may be caused by differences in the main water vapor sources between the wet and dry seasons in the I. hainanensis sample plot
The δD values of I. hainanensis plant water were between the δD values of atmospheric precipitation and deep soil water, indicating that I. hainanensis plant water mainly came from precipitation and deep soil water
Summary
The environment governs the geographical distribution, growth, and developmental status of plants, but the environment is influenced by plants at all times [1]. Plant–atmosphere continuum, plant water is influenced by environmental physical factors such as soil, air moisture limitation, and the regulation of organisms themselves [2]. Water is the most important limiting factor for ecosystem processes and functions in deserts and ecologically fragile areas [3], and it plays a critical role in plant growth and development, survival, and distribution [4]. The intensity and frequency of precipitation determine the survival, composition, structure, and functional assemblage of plant species in ecosystems [5]. In the context of global climate change, changes in precipitation patterns, in
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