Strategies Of Phosphorus Uptake And Utilization And Transcriptome Analysis Of Leymus Chinensis And Artemisia Frigida In Typical Steppe Of Inner Mongolia

Long-term over-grazing leads to severe degradation of grasslands in Inner Mongolia.The damage to grassland ecology and production functions has severely restricted the sustainable development of the animal husbandry economy in pastoral areas.The process of grassland degradation involves continous change in the interspecific status of dominant species under the influence of disturbance and stress.The ability of a pasture plant to persist in a grassland community is dependent on its adaptive strategies to stress and disturbance.Phosphorus is an important element for plant growth.Due to its easy fixation and low diffusivity,it is likely to exert more stress on plant growth during the degradation process.Thus,this study selects Leymus chinensis,a dominant plant species in Inner Mongolian steppe,and Artemisia frigida,a dominant plant in the late stage of degradation.To investigate the relationship between the two species and their adaptation strategy under different phosphorus environment(P1=2.5 mg kg-1,P2=25 mg kg-1),the planting patterns of L.chinensis,A.frigida,and mixed plantings of the two species were set.In order to investigate changes in nutrient uptake,and the intrinsic regulatory mechanisms of nutrient utilization by L.chinensis and A.frigida under different phosphorus levels and different pattern treatments,the root system of the plants were analyzed at transcriptomic level.The main conclusions are as follows:1.Through the determination of biomass and nitrogen and phosphorus content and the calculation of nitrogen and phosphorus absorption and utilization efficiency under different treatments of two plants.In the low-phosphorus environment,the biomass of the two plants increased when they were mixed,showing a positive interaction.A.frigida had a greater increase in its biomass due to its large increase in nitrogen and phosphorus uptake efficiency.Therefore,A.frigida showed a stronger ability to survive in a low-phosphorus environment,and eventually became a dominant species of grassland degraded communities.In the high-phosphorus environment,the interspecific relationship between L.chinensis and A.frigida becomes negative interaction,that is,competition.The mixed species reduced the nitrogen and phosphorus uptake efficiency of A.frigida,improved the nitrogen and phosphorus uptake and utilization efficiency of L.chinensis,and coupled with the high phosphorus production efficiency of L.chinensis,effectively changed the accumulation of biomass in A.frigida.The competitive environment shows strong competitiveness,so this may be one of the reasons why L.chinensis becomes a dominant species on the typical grassland.2.By studying the acid phosphatase activity,organic acid content and soluble protein content of L.chinensis and A.frigida under different environmental conditions,it can be found that the two plants have different internal response mechanisms of improving phosphorus efficiency in different environments.L.chinensis and A.frigida differ significantly in the content of their root exudates in response to phosphorus deficiency.At low phosphorus levels,mixed cultivar of L.chinensis increased the absorption of phosphorus by increasing the activity of acid phosphatase,and the mixed species of A.frigida increased the absorption of phosphorus mainly through the increase of acetic acid content.In the case of highphosphorus,mixed L.chinensis reduced the content of acid phosphatase,malic acid,and acetic acid.The mixed species of A.frigida reduced the acid phosphatase and increased the content of acetic acid.3.According to the Illumina HiSeq2000 platform's,sequencing of the roots of L.chinensis get 140.30 G data.On the other hand,sequencing of the roots of A.frigida get 140.30 G data.After comparing the differentially expressed genes and enrichment conditions in each of the comparison groups of L.chinensis and A.frigida,the related plant hormone signaling pathways were analyzed.The phytohormone signaling pathways were analyzed,and phosphorus efficiency-related regulatory genes(genes related to phosphorus transporters,acid phosphatase,organic acid secretion,and transcription factors)were analyzed.The results showed that the induction of L.chinensis in the high-phosphorus environment enhanced the hormone signaling pathway and increased the expression of these genes,while A.frigida expressed less of the genes.This showed that in the high-phosphorus environment,where competition exist between the two plants,the molecular mechanism of regulating phosphorus use efficiency differs,thus affecting plant growth.When mixed-plant in a high-phosphorus environment,L.chinensis could be more competitive owing to its numerous regulation pathways compared to A.frigida.