Plant phenotype response of Sarcandra glabra to light intensity and nitrogen nutrition supply

Objectives Sarcandra glabra, perennial herb or subshrub plant, is well known for its medicinal and ornamental value. Both nitrogen and light intensity play very important role in its growth and development. In this paper, the morphological characteristics, biomass accumulation and distribution of S. glabra under different light intensities and nitrogen supply rates were studied, and the suitable light-nitrogen combinations for artificial cultivation of S. glabra were preliminarily proposed.

Methods Taking annual S. glabra as the experiment material, a pot experiment was carried out in South China Agricultural University (N23°09'58.80", E113°21'46.00", at an altitude of about 60 m). Three intensity levels of natural light of 80% (L1), 60% (L2) and 40% (L3) were setup, and four nitrogen rates of 0 (N0), 83.3 mg/kg (N1), 167 mg/kg (N2) and 250 mg/kg (N3) were applied under each light treatment. The seedlings were transplanted in March 2016, and the seedling height, ground diameter, biomass, root characteristics and leaf characteristics of the seedlings were monitored in December.

Results The main root length, root tip number, seedling height, ground diameter and leaf area of S. glabra reached the highest under L2N2 treatment, and the specific leaf area reached the maximum under L2N1 treatment. At the same nitrogen level, both the fresh and dry weight of roots, stems and leaves reached the maximum under L2 treatment; under the same light intensity, they reached the maximum in the N2 treatment. Biomass allocation was significantly affected by N rate instead of light intensity, however, there was a certain interaction between light and nitrogen. The percentage of root biomass in total plant and the root to shoot ratios in treatments of N0 and N1 were significantly higher than those in N2 and N3 ones, while the percentages of stems and leaves biomass and the ratio of leaf to root were significantly higher in N2 and N3 treatments than in N0 and N1 treatments. Leaf biomass was significantly higher in N2 treatment than in other treatmen, and the leaf biomass and leaf to root ratio of L2 treatment were the highest under N2 treatment. The plasticity indexes of morphological parameters for changes in light intensity and nitrogen concentration were PI_light = 0.38 and PI_nitrogen = 0.37, respectively. The plasticity index of biomass accumulation to nitrogen concentration change was PI_nitrogen = 1.43, which was 1.65 times of that of light intensity. The phenotypic plasticity parameter of biomass allocation, PI_nitrogen = 0.19, which was 3.80 times of that light.

Conclusions Under the experimental conditions, S. glabra has better adaptability to nitrogen concentration change, that is, when the nitrogen concentration changes greatly within the experimental range, S. glabra can still grow better adaptively. The plasticity of the change of light intensity is low, that is, when the light intensity changes greatly within the experimental range, it is not conducive to the growth of S. glabra, and the adaptability to changes in light intensity is low. Under the combination of 60% natural light + nitrogen application 167 mg/kg, S. glabra grows best, which is beneficial to increase S. glabra production. The strategy of S. glabra to cope with different light-nitrogen environments is to adapt to the changes of light and nitrogen by adjusting the morphological characteristics of roots and stems, and to adapt to the changes of nitrogen by adjusting the accumulation and distribution of root and leaf biomass.