Abstract
Due to both anthropogenic and natural causes, the number of Horsfieldia hainanensis has been decreasing each year in the Tongza Branch nursery (109.534 525°E, 18.763 516°N) of the Hainan Academy of Forestry, China. Consequently, the protection of H. hainanensis is urgent, as is that of most rare tree species. To develop a more comprehensive understanding of the H. hainanensis growth environment, we took 3-year-old H. hainanensis saplings as the research object. We controlled the light intensity by setting different shade amounts to explore the growth and photosynthetic characteristics of H. hainanensis under different light intensities. We found that shade can promote growth and increase the contents of certain substances. Light transmittance of 44.41% can increase plant height (by 29.545%) and biomass (by 66.676%). Light transmittance of 16.19% can increase the pigment content; Chl increased by 40.864%, Chl a increased by 38.031%, and Chl b increased by 48.412%. Light transmittance of 7.30% can increase the soil plant analysis development (SPAD) value of each part of the leaf; the leaf base increased by 41.000%, the leaf margin increased by 32.574%, the blade tip increased by 49.003%, and the leaf average increased by 40.466%. The specific leaf area can reduce the specific leaf weight. We also found that compared to full light, reducing the light transmittance can increase the total chlorophyll (Chl), chlorophyll A (Chl a), and chlorophyll B (Chl b) contents, and the Chl-SPAD-leaf base, leaf edge, leaf tip, average content, and light-saturated net photosynthetic rate. This can in turn reduce the apparent quantum efficiency (AQY), light compensation point (LCP), and dark respiration rate (Rd). In addition, we found a strong correlation between seven of the photosynthetic pigment indicators (Chl, Chla, Chl b, Chl-SPAD-leaf base, leaf margin, leaf tip, and mean) and the three photosynthesis physiological parameters (AQY, LCP, and Rd). The light transmittance of 44.41% (one layer of shading net) treatment group was conducive to the growth of H. hainanensis and photosynthetic characteristic improvement. Therefore, our light transmittance selection of approximately 44.4% is significant for the natural return of H. hainanensis.
Highlights
Horsfieldia hainanensis belongs to the Myristicaceae family and Horsfieldia Willd genus
For treatment group 1, the H is 1.90 times that of treatment group 3, D is 1.54 times that of treatment group 3, H/D is 1.27 times that of treatment group 3, and D2H is 4.06 times that of treatment group 3, with significance at the P < 0.01 level. This demonstrates that light shade is beneficial to the growth of the H, D, and H/D of H. hainanensis and in increasing its biomass
This study found that the soil plant analysis development (SPAD) value of H. hainanensis is significantly correlated with its chlorophyll content (Table 2)
Summary
Horsfieldia hainanensis belongs to the Myristicaceae family and Horsfieldia Willd genus. In China, they are primarily distributed in southern Yunnan, western Guangxi, and southwestern Hainan Because they are one of the most iconic humid tropical rainforest plants, they exhibit high reference value for studying the flora, geographical distribution, and ecological characteristics of tropical rainforests (Editorial Committee of Chinese Flora of Chinese Academy of Sciences, 1977; Xu et al, 2012). Due to their small distribution area and number, the excessive destruction of rainforests, the anthropogenic destruction and hacking of the plant, and their extremely poor natural regeneration capacity, Horsfieldia hainanensis are on the verge of extinction of China. Research is lacking on the effect of shading on the physiology and photosynthesis of H. hainanensis that provides a theoretical basis for the selection of an appropriate light intensity for seedling breeding and natural return planting of H. hainanensis
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