Abstract
This study examined the effects of light intensity on the plasticity of the leaves of Juglans regia f. luodianense seedlings in karst habitat and how they respond to changes in light intensity. The light intensity of 1-year-old seedlings of J. regia f. luodianense in different niches in a karst area was set as 100% (bare land), 75% (forest margin), 50% (forest gap), and 25% (under forest) of natural light. The material harvested after four months was compared to analyze the differences in various morphological characteristics, biomass allocation, and physiological characteristics of the leaves of seedlings of J. regia f. luodianense, and a comprehensive evaluation of the plasticity indexes was conducted. The results showed that under moderate (50%) full light intensity, the leaf area, specific leaf area, leaf biomass, and chlorophyll content increased, and improved photosynthesis and promoted the accumulation of free proline content and peroxidase (POD) activity. The accumulation of malondialdehyde was also the lowest in this treatment, indicating that the plants had the strongest adaptability under this light intensity. Moreover, under high (75%) full light intensity, the above functional characteristics of plants showed good performance. Under low (25%) full light intensity, plants also had higher specific leaf area, leaf biomass, and photosynthetic parameters. However, under full light, the cell membrane permeability decreased, the chlorophyll accumulation was the lowest, and the photosynthetic index was seriously inhibited. Our results showed that the plasticity of morphological characters was greater than that of biomass allocation and physiological characters; POD activity and stomatal conductance were the highest, followed by leaf area and chlorophyll b, whereas the plasticity of palisade tissue/sponge tissue thickness and lower-epidermis thickness were the lowest. In summary, there are evident differences in the sensitivity and regulation mechanisms of morphological characteristics, biomass allocation, and physiological indices of the seedling leaves of J. regia f. luodianense in response to light intensity. During the stage of seedling establishment, only the plants in the bare ground under full light can be induced to show obvious inhibition of phenotypic traits. In contrast, the plants in the forest margins and gaps and under the forest habitats under light intensity can regulate their own characteristics to maintain their growth and development. The wide light range and strong plasticity of the species might be two of the important reasons for its existence in a highly heterogeneous karst habitat.
Highlights
Seedling growth and development are critical to population dynamics, and they include complex processes of detecting, acceptance, and interpreting endogenous and environmental signals [1]
Under 50% full light intensity, the photosynthetic parameters of J. regia f. luodianense seedlings reached the highest, and there was no significant difference with 75% full light intensity
The results showed that the leaf area and specific leaf area of J. regia f. luodianense seedlings increased significantly with the decrease of light intensity
Summary
Seedling growth and development are critical to population dynamics, and they include complex processes of detecting, acceptance, and interpreting endogenous and environmental signals [1]. Plants respond to endogenous and environmental signals in many different ways [2]. Many of their responses stem from phenotypic plasticity, which is the ability of specific genotypes to respond to environmental changes [3]. Among the many environmental conditions that plants experience, light plays an important role in the growth and development of species [5]. Changes in available light can lead to the differentiation of the morphological, anatomical, and physiological characteristics of plants [6]
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