Dynamics of tissue nutrient content in relation to declining seedling growth in Malania oleifera

Abstract

The decline in seedling growth of Malania oleifera as the age increases is often observed in the absence of host plants. A better knowledge of nutrient dynamics in terms of concentration and distribution patterns in different parts of the declining seedlings, the concentrations of N, P, and K were comparatively analyzed in various organs of unattached M. oleifera seedlings grown for half a year, two years, and three years. Additionally, the starch content and distribution patterns in the roots and stems of seedlings with different vigor levels were qualitatively assessed by staining cross-sections. The results were as follows: (1) As the growth vigor of M. oleifera seedlings declined, the concentrations of N, P, and K in most organs decreased, except for a significant increase in K concentration in lateral roots. The leaf N/P ratios of the declining seedlings became increasingly imbalanced, indicating different nutrient deficiency types among the seedlings with varying decline degrees. Unattached M. oleifera seedlings grown for half a year were primarily limited by insufficient N supply (with an average N/P ratio of 11.33) and subsequently by P limitation after two years (average N/P ratio 17.81). The leaf N/P ratio of unattached M. oleifera seedlings grown for three years was remarkably imbalanced (with an average value of 52.46). As the growth vigor of unattached three-year seedlings was considerably low, they are deemed unsuitable for afforestation. (2) A decrease in starch content was observed in declining seedlings, as evidenced by the reduced staining intensity of cross-sections. After three years, the starch content of unattached M. oleifera seedlings was found to have decreased to an extremely low level. Significant differences in starch content were observed at various locations, including the connecting point of the stems and roots, the basal swelling top of the root, the main root, and lateral roots, among seedlings with different degrees of decline. These findings suggested that starch content levels could serve as crucial criteria for evaluating the growth vigor of seedlings. Specifically, lateral roots were identified as optimal sampling materials for assessing seedling growth vigor through a minimally invasive method. Given the gradual decline in vitality and decreased nutrient content observed in M. oleifera seedlings grown in the absence of a host plant, it is recommended, during the propagation phase, to ensure adequate mineral nutrient supplementation, select appropriate host plants for cultivation, and facilitate early-stage transplantation. This proactive approach serves to mitigate a potential decline in survival rates during afforestation, attributed to the reduced vitality of the seedlings. The results of this study provide valuable information for evaluating seedling growth vigor and offer scientific guidance for rational fertilization in M. oleifera nurseries.

Keywords

• root hemiparasitic plant
• macromineral elements
• starch
• staining of tissue sections
• growth vigor of seedlings
• study of rare and endemic plants