Abstract
BackgroundNitrogen, as a limiting factor for net primary productivity in grassland ecosystems, is an important link in material cycles in grassland ecosystems. However, the nitrogen assimilation efficiency and mechanisms of grassland plants under grazing disturbance are still unclear. This study investigated Stipa breviflora desert steppe which had been grazed for 17 years and sampled the root system and leaf of the constructive species Stipa breviflora during the peak growing season under no grazing, light grazing, moderate grazing and heavy grazing treatments. The activities of enzymes related to nitrogen assimilation in roots and leaves were measured.ResultsCompared with no grazing, light grazing and moderate grazing significantly increased the activities of nitrate reductase (NR), glutamine synthetase (GS), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvate transaminase (GPT) in leaves, and GS, GOT and GPT in roots of Stipa breviflora, while heavy grazing significantly decreased the activities of GS in leaves and NR in roots of Stipa breviflora. NR, GOT and GPT activities in leaves and roots of Stipa breviflora were positively correlated with nitrogen content, soluble protein, free amino acid and nitrate content.ConclusionsGrazing disturbance changed the activities of nitrogen assimilation related enzymes of grassland plants, and emphasized that light grazing and moderate grazing were beneficial for nitrogen assimilation by grassland plants. Therefore, establishing appropriate stocking rates is of great significance for material flows in this grassland ecosystem and for the stability and sustainable utilization of grassland resources.
Highlights
Grazing is considered to be an important measure in grassland management
The results showed that heavy grazing increased the total nitrogen content in the roots and decreased the total nitrogen content in the leaves of S. breviflora to a certain extent, especially under heavy grazing
Our results showed that heavy grazing significantly reduced the content of soluble protein and amino acids in roots, and significantly increased the content of amino acids in leaves, and correlation analysis showed that this was related to the changes in Glutamine synthetase (GS), glutamic oxaloacetic transaminase (GOT), glutamic pyruvate transaminase (GPT) and Nitrate reductase (NR) activities in roots and leaves
Summary
Grazing is considered to be an important measure in grassland management. with the intensification of human activities, grazing disturbance in grasslands has become a concern [1, 2], and livestock grazing management remains very important for futureZhu et al BMC Plant Biology (2021) 21:436 effects of grazing on nitrogen uptake and utilization of plants [10,11,12], but these studies have mainly focused on the level of nitrogen stoichiometry, and relatively few studies have focused on the mechanisms through which grazing affects nitrogen assimilation by plants.Nitrogen is one of the essential elements for plant growth. Grazing is considered to be an important measure in grassland management. Nitrogen assimilation refers to the process by which plants absorb nitrogen from the environment and synthesize nitrogen-containing organic compounds such as amino acids and proteins, a process in which many enzymes participate (Fig. 1). The plants mainly rely on the cortex cells of the root to absorb nitrate from the rhizosphere soil. Glutamine synthetase (GS) and glutamic acid synthetase (GOGAT) are two important enzymes involved in catalysis during the glutamic acid synthetase cycle. There are few studies on the mechanism of plant nitrogen assimilation in grazing grassland. The nitrogen assimilation efficiency and mechanisms of grassland plants under grazing disturbance are still unclear. The activities of enzymes related to nitrogen assimilation in roots and leaves were measured
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