Abstract
Phosphorus (P) deficiency affects plant yield and quality, yet at the same time, excessive phosphorus application does not necessarily promote the growth of plants. How to maintain a balance between biomass accumulation and phosphorus application is a problem. Therefore, the purpose of this research was to explore the relationship between yield and quality of Bupleurum and phosphorus fertilization, based on three phosphorus fertilization levels (20 kg∙ha−1; 10 kg∙ha−1; and 0 kg∙ha−1). We adopted gas chromatography-mass spectrometry to assess the response of primary metabolites of different plant tissues (flowers, main shoots, lateral shoots and roots) to phosphorus fertilization. At the same time, high-performance liquid chromatography was used to quantify saikosaponin A and saikosaponin D, the main active ingredients of Bupleurum. Our research showed that low phosphorus level application has a positive impact on the yield and quality of Bupleurum, especially the above-ground parts increasing the fresh weight of flowers and lateral shoots and the length of main shoots, and moreover, increasing the saikosaponins content in all above-ground parts while decreasing the content in roots which show no significance increase in fresh weight and length. However, high phosphorus level showed a negative impact as it decreases the saikosaponins content significantly in flowers and roots. Furthermore, phosphorus application changed the proportion of saikosaponins, promoting the content of saikosaponin A and inhibiting the content of saikosaponin D in most organs of Bupleurum. Therefore, we can say that high phosphorus application is not preferable to the yield and quality of Bupleurum. To identify the metabolic pathways and special key metabolites, a total of 73 metabolites were discovered, and four differential metabolites—ether, glycerol, chlorogenic and L-rhamnose—were considered to be the key metabolites of Bupleurum’s response to phosphorus fertilization. Furthermore, Bupleurum’s response to phosphorus fertilization was mainly related to metabolic pathways, such as starch and sucrose metabolism and galactose metabolism. Under the phosphorus level, the content of sugars, organic acids and their derivatives, polyols and their derivatives and alkyl were upregulated in flowers. Furthermore, the contents of compounds in the main shoot and lateral shoots showed the same upward trend, except glycosides and polyols and their derivatives.
Highlights
As it is known, the compositions and contents of the plant largely depend on genetics, growth stage, environment and cultivation, and so on [1]
The whole Bupleurum individuals growing under three levels of phosphorus fertilization—low-phosphorus (LP), control-phosphorus (CP) and highphosphorus (HP)—were divided into four parts (Figure 1), including flowers (F), main shoots (MS), lateral shoots (LS) and roots (R)
The fresh weight of Bupleurum’s lateral shoots and flowers significantly increased (p ≤ 0.01) under LP level compared with the CP level, and a further weight increase was observed under HP level (Figure 2A)
Summary
The compositions and contents of the plant largely depend on genetics, growth stage, environment and cultivation, and so on [1]. The availability of plant nutrients has received more attention. Phosphorus (P) is an imperative nutrition element for plant growth and development, which affects energy metabolism, nucleic acid synthesis, glycolysis in plants and vital physiological processes [2–4]. As the available soil phosphorus is low, crop yield and growth is limited [5]. In order to cope with phosphorus deficiency, plants have developed flexible strategies through complex biological processes, such as changing metabolic processes, regulating root system structure, accumulating and secreting organic acids, making plant roots and mycorrhizas fungal symbiosis [6–8]. Changes in root system structure in reaction to insufficient phosphorus are usually involved in phosphorus uptake, while changes of metabolic processes are related to phosphorus use efficiency [9]. Rational phosphorus fertilization and improved phosphorus use efficiency are effective methods to ensure sustainable development of agricultural production [10,11]
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