Response Of Degraded Typical Steppe To Phosphorus Fertilization

Inner Mongolia grassland is an important component of the steppe,and it is also a typical temperate grassland in China.It is mainly distributed in arid and semi-arid regions.Due to severe natural conditions,typical steppe productivity is low.Long-term overgrazing,patterns of land use,and increased human production activities,90%of the grassland have undergone varying degrees of degradation.Resulting in serious deterioration of the physical,chemical,and biological properties of the soil.The available phosphorus in soil is easily adsorbed and fixed by active calcium,iron and aluminum,which can easily converte into insoluble phosphorus such as Ca-P,Fe-P and Al-P.Only1%of insoluble phosphate can be absorbed and utilized by plants,which result in soil.The"genetic deficiency"of phosphorus,that is to say the total phosphorus content in soil is high,but the available phosphorus content that can be absorbed and utilized by plants is very low.Stipa krylovii is a dominant plant species in the typical steppe of Inner Mongolia.It is a dominant specie that is resistant to cold,drought and soil infertility.Previous studies focused on the drought tolerance and nitrogen utilization of Stipa krylovii,and most of the studies focused on the yield and phenotype of forage grasses.However,few studies on the mechanism of phosphorus fertilizers.Therefore,the paper studied the response mechanism of degraded typical steppe to the phosphate fertilizer,the main research results are as follows:In the first experiment,degraded typical grassland?Xilinhot,Inner Mongolia?was selected and fenced in June 2014.Phosphorus fertilizer was applied in July 2014,2015 and June 2016.Three levels of phosphorus fertilizer were:0 kg P₂O₅/ha,30 kg P₂O₅/ha and 60 kg P₂O₅/ha,and three repetitions were set for each level.Through continuous 3 years of analysis,it was found that with the increase of phosphorus fertilizer levels,the above-ground biomass production has an increasing trend,and the root ratio shows a decreasing trend.But none of them has reached a significant level.In 2015?412mm?,with sufficient rainfall,the effect of increasing production was obvious.Under no fertilization conditions,the above-ground biomass in 2015 increased by 52.19%and 64.63%respectively compared with 2014?255 mm?and 2016?198 mm?.It shows that rainfall is the main factor that affects the primary productivity of typical steppe in Inner Mongolia.There wre little effect on plant richness,biodiversity and evenness after fertilization for three years.Overall,the proportion of Convolvulaceae has been decreasing,and the sedge,leguminous and legumes have shown an overall increasing.The change in the proportion of families shows that the community underwent succession under fertilization but did not reach a stable top-level community.The Convolvulus ammannii as a sign of grassland degradation,from 7.8%to 2.23%and 0.23%in 2014,2015 and 2016.Which indicates that fertilization promotes the restoration of degraded grassland.Phosphorus content,total phosphorus and available phosphorus content of plants showed an increasing trend.Under high phosphate fertilizer levels,soil available phosphorus in 2014,2015 and 2016 increased 42.85%,67.11%and 77.7 3%,respectively.The phosphorus content of Stipa krylovii increased by 7.84%,38.80%and 61.47%,which indicating that the increase of available phosphorus in soil promoted the absorption of phosphorus in Stipa krylovii.In the second experiment,on the basis of the first experiment.In April 2016,the soil of the typical steppe?Xilinhe reservoir?was collected.Nitrogen fertilizer and water were sufficient under potting conditions,and the response of Stipa krylovii to application of phosphorus fertilizer was studied.At the same time,the soils of temperate meadow steppe?Dali Lake?and desert steppe?Sunit Zuoqi?were collected to compare whether the performance of Stipa krylovii in the three soils was different.The results showed that the phosphorus fertilizer could increase the above-ground biomass of Stipa krylovii in different steppe,and reached a significant level only in typical steppe.Underground biomass and root-shoot ratio showed a decreasing trend,and the root-shoot ratio also decreased significantly.It shows that nitrogen fertilizer has a positive effect on the absorption of phosphorus fertilizer under adequate water in typical steppe.In the third experiment,there are different levels of phosphorus,in order to investigated the low phosphorus adaptation of Stipa krylovii under hydroponic conditions.The results showed that the above-ground biomass and underground biomass increased significantly.The root-shoot ratio decreased significantly.Root length,root surface area,and root volume also increased with the phosphorus fertilizer applied.The activity of intracellular phytase,extracellular phytase,intracellular acid phosphatase and extracellular acid phosphatase were not change significantly.In the fourth experiment,the application levels of different trace elements?B,Cu,Zn?under potting conditions.Under the conditions of nitrogen fertilizer,phosphorus fertilizer,and sufficient water,it was explored whether the trace elements limit the plant biomass.The results showed that the three kinds of trace elements could significantly increase the above-ground biomass,underground biomass and root-shoot ratio of Stipa krylovii,which can be order:Cu>Zn>B.It indicates that trace elements play an important role in the biomass in the typical steppe.Through in-situ control experiments,pot experiments with phosphorus fertilizer,hydroponic experiments and pot experiments with micro-fertilizers,comprehensive analysis concluded that precipitation,nitrogen-phosphorus fertilizer interactions,adaptability of plants,and trace elements in soil all affect Stipa krylovii growth in typical steppe.Rainfall is the main factor affecting the primary productivity of typical grasslands.Phosphorus fertilizer can not effectively increase above-ground biomass.