Influence of nitrogen and phosphorous on the growth and root morphology of Acer mono

Influence of nitrogen and phosphorous on the growth and root morphology of Acer mono

Abstract

Nitrogen and phosphorous are critical determinants of plant growth and productivity, and both plant growth and root morphology are important parameters for evaluating the effects of supplied nutrients. Previous work has shown that the growth of Acer mono seedlings is retarded under nursery conditions; we applied different levels of nitrogen (zero, five, ten, and fifteen grams per plant) and phosphorous (zero, four, six, and eight grams per plant) fertilizer to investigate the effects of fertilization on the growth and root morphology of four-year-old seedlings in the field. Our results indicated that both nitrogen and phosphorous application significantly affected plant height, root collar diameter, chlorophyll content, and root morphology. Among the nutrient levels, ten grams of nitrogen and eight grams of phosphorous were found to yield maximum growth, and the maximum values of plant height, root collar diameter, chlorophyll content, and root morphology were obtained when ten grams of nitrogen and eight grams of phosphorous were used together. Therefore, the present study demonstrates that optimum levels of nitrogen and phosphorous can be used to improve seedling health and growth during the nursery period.

Introduction

The aesthetic and economic values of Acer mono Maxim L. (Aceraceae) make it an important species for afforestation, gardening, and road plantings. The species is widely distributed in the Yangtze River basin of north and northeast China. Nursery practices, such as sowing, seedbed density, pruning, and fertilization, are usually standardized for individual plant species, in order to produce high-quality seedlings. Fertilizer application is widely used in nurseries to improve plant vigor and productivity; however, fertilization can improve plant growth by either increasing soil resources or by enhancing the ability of seedlings to garner resources by modifying soil pH. As a result, plants increase their rate of photosynthesis, stem diameter, height, basal area, and volume. Deciduous and evergreen hardwood species have different nutrient requirements, and deciduous species have been reported to require fifty percent more nitrogen than conifers, such as pines. Therefore, the production of deciduous and pine seedlings have different nutrition and management requirements.

Of the necessary nutritional elements, nitrogen is required in the largest quantities, and its availability and internal concentration affect the partitioning of biomass between roots and shoots. The amount and timing of nitrogen application can also alter plant morphology, nutrient availability, and net photosynthesis. For example, Harper reported that nitrogen supplementation is required to maximize seedling biomass during initial nursery stages of growth, even for some legume species, and Costa et al. reported that root length and root surface area were increased under intermediate nitrogen levels and that root growth was reduced under both higher and lower fertilization levels. However, high nitrogen availability and its concomitant affect root and shoot biomass production. Phosphorus is considered a primary nutrient for plant growth and is needed to sustain optimum plant production and quality. The element is essential for cell division, reproduction, and plant metabolism; moreover, its role is related to the acquisition, storage, and use of energy. In addition, phosphorus plays an important role in lateral root morphology and root branching and influences not only root development, but also the availability of nutrients. Therefore, plants have developed various strategies for obtaining optimum phosphorus from soils, including increases in root surface area, specific root length, and root-shoot ratio.

Both nitrogen and phosphorus are important nutrients for ecosystem structure, processes, and function, since their availability limits the production of plant biomass and growth. For example, the combined application of nitrogen and phosphorus increases root surface area, root length, and root-shoot mass, and in Arabidopsis plant species, different nutrient levels have been shown to influence both root length and branching plasticity.

In the last few decades, the application of fertilizer in forest nurseries has attracted increasing attention throughout the world, as a result of increased demand for fiber, wood, and carbon dioxide offsets. These demands can be satisfied through the production of healthy seedlings, which would ultimately increase plant biomass production; however, this requires the proper diagnosis of specific limiting factors. In fact, the amounts of fertilizers used in forest seedling production are relatively lower than the amounts used in agriculture plant nurseries. Many factors influence the effectiveness of nutrient application on seedling growth. In particular, fertilizer type and amount affect the growth of plant seedlings.

Since growth of Acer mono seedlings is reportedly retarded under nursery conditions, species-specific combinations of nitrogen and phosphorus may be needed to ensure healthy seedling growth. Therefore, the present study was designed to determine the effects of nitrogen and phosphorus on Acer mono seedling growth, with a specific focus on root morphology (i.e., root length, root diameter, specific root length), and to establish a standard for nitrogen and phosphorus application in the production of Acer mono seedlings.