Effects Of Different Phosphorous Fertilizer And Phosphorus Fractions On Leaf Micromorphology,N/P Acquisition And Yield Of Sickle Lucerne(Medicago Falcata L.)

Medicago falcata L.was a main construction species of artificial grassland in North China because of its characteristics of drought resistance and cold resistance.It was also the forage cash crop in China.Phosphorus was necessary for plant growth.However,the availability of phosphorus in the Mongolian Plateau soils was weak and the yield of alfalfa was generally low.Therefore,it was very important to explore the relationship between the growth of alfalfa and soil phosphorus under phosphorus addition.To solve this problem,this study studied the following scientific problems from the perspectives of phosphorus fertilizer,soil and alfalfa:(1)The effects of different P fertilizers and P levels on the contents of various P forms,total P contents and available P contents in soil,and the relationship between total P content and various P forms in soil;(2)The effects of different P fertilizers and P levels on nitrogen and phosphorus content in alfalfa,and whether the changes of soil P and P form content affect the absorption of nitrogen and phosphorus in soil by alfalfa;(3)As one of the important vegetative organs of plants,the effects of different phosphorus fertilizer and phosphorus levels on the growth of alfalfa were studied from the perspective of leaf microstructure;(4)The main factors affecting the growth of alfalfa under applying phosphorus fertilizer.In this study,Medicago falcata L.was taken as a research object.In fertilization experiments were carried out in the former life science experimental base of Inner Mongolia University in Hohhot(2011-2013)and the grassland ecology research base of Inner Mongolia University in Maoteng pasture in Xilinhot(2012-2014)respectively.A random block design was adopted in the test sample plots,and seven fertilization treatments were set.They were treated with no fertilizer(CK),9.6kg P·ha^-1 superphosphate(P?-1),14.4kg P·ha^-1 superphosphate(P?-2),19.6kg P·ha^-1superphosphate(P?-3),9.6kg P·ha^-1 triple superphosphate(P?-1),and 14.4kg P·ha^-1 triple superphosphate(P?-2)and 19.6kg P·ha^-1 triple superphosphate(P?-3)were used in 35 plots with five replicates per treatment.During the experiment,aboveground biomass,plant height,stem biomass,leaf biomass,stem-leaf ratio,leaf thickness,leaf palisade tissue thickness,leaf spongy tissue thickness,nitrogen content,phosphorus content,soil nitrogen content,phosphorus content,organic phosphorus form,inorganic phosphorus form of alfalfa were measured.The preliminary conclusions were as follows:Soil P forms were positively correlated with alfalfa P,and negatively correlated with alfalfa N/P ratio,indicating a close relationship between plant P and soil P forms.Soil total phosphorus,soil available phosphorus and the contents of all forms of phosphorus were significantly positively correlated,the change of soil phosphorus form can provide a basis for the change of soil phosphorus content.In this experiment,with the growth of plants,the proportion of Ca₈-P inorganic phosphorus and Ca₁₀-P inorganic phosphorus in the soil changed greatly;At the same time,in the organic phosphorus state,the proportion of medium active organic phosphorus content changed greatly,indicating that these inorganic phosphorus and plant growth were more closely related.The results of experiments showed that P application could increase alfalfa P content and decrease alfalfa N/P ratio.To analyse relationship between soil phosphorus,soil nitrogen,soil N/P ratio and plant growth indexes:P could improve soil phosphorus content,soil nitrogen and phosphorus,but results in excessive amounts of phosphorus in the soil after applying too much phosphorus,nitrogen and phosphorus was lower,will directly affect the absorption of plants on soil nitrogen utilization,which was the main cause of high phosphorus decrease plant growth.According to the analysis of soil N and P content and plant growth,aboveground biomass and plant height were significantly negatively correlated with soil total N content,positively correlated with soil total P content,and negatively correlated with available N content.Therefore,the application of phosphorus fertilizer to promote the growth of alfalfa was mainly accomplished by increasing the soil phosphorus content.Leaf thickness and leaf palisade tissue thickness increased first and then decreased with the increase of P fertilizer,and the leaf thickness and leaf palisade tissue thickness were the largest under medium P concentration.From 2012 to 2014,leaf thickness decreased significantly after applying heavy superphosphate fertilizer,but there was no difference between the second year of sowing and 2014.The spongy tissue decreased with the increase of P,but was slightly higher than that of CK without P fertilizer.The difference of sponge tissue thickness between two kinds of phosphate fertilizers was small.The ratio of leaf gate to sea level increased first and then decreased with the increase of superphosphate level,while the ratio of leaf gate to sea level increased slightly with time under the condition of no fertilization.CTR(leaf compactness)decreased with the increase of P level.The effects of phosphorus fertilizer on CTR(leaf compactness)and SR(leaf porosity)were not obvious.In conclusion,the growth changes of alfalfa were closely related to leaf thickness and palisade tissue thickness.In the nitrogen and phosphorus content of yellow alfalfa,the phosphorus content of alfalfa plays a decisive role.In the soil phosphorus form,the phosphorus content of alfalfa was Ca₈-P type inorganic phosphorus,Fe-P type inorganic phosphorus,Ca₁₀-P type inorganic phosphorus,active organic phosphorus and medium stable organic phosphorus.The Ca₂-P type inorganic phosphorus,Fe-P type inorganic phosphorus and active organophosphorus in organic phosphorus of soil inorganic phosphorus had most significant effect on alfalfa growth.After applying inorganic phosphorus fertilizer to the soil,Ca₂-P type inorganic phosphorus,Fe-P type inorganic phosphorus and active organic phosphorus of organic phosphorus in the soil inorganic phosphorus were firstly increased,and then soil phosphorus content was increased.Alfalfa absorbed and utilized phosphorus of soil,and the thickness of alfalfa leaves was increased in the microstructure.The macroscopic growth showed that the aboveground biomass of alfalfa increased.This was the main reason that inorganic phosphate fertilizer can increase the growth of alfalfa.