| Pennisetum sp.is a kind of typical C4 plant.It showes the features of large plant,strong root and resistance,high CP content and its fresh yield can reach 200t/hm2 every year.It is used to cultivate edible and medical mushrooms,burn the biomass for electricity,extract alcoholic,and produce fiberous materials,etc,which offers broad application prospect.At present,it has been planted in many provinces of China and in Papua New Guinea,Lesotho,Rwanda and other countries.Nitrogen(N)is one of the most important nutrients,known as the life element,and fts function is next only to water.Therefore,the adaptive characteristics of Pennisetum sp.for N were studied by water culturing and poting in order to explore the relationships between N fertilizer and growth,physiology,quality and nutrient utilization,providing theory for Pennisetum sp.in reasonable fertilization.The key results were as follbws:1.Effects of N on Pennisetum sp.seeding stage growth and photosynthetic physiological characteristicsHydroponic experiment was carried out to study the response of different concentrations of N on growth and photosynthetic physiological characteristics of Pennisetum sp.seeding stage to supply the evidence for optimum fertilizer of Pennisetum sp.The results showed that with the improvement of N concentration,plant height,total root length,root surace area,root volume,number of root forks,and number of root tips increased first and then decreased,leaf number,leaf area and stem diameter decreased;Pn,Tr and Gs rose and then dropped,Ci continuously dropped;the contents of photosynthetic pigment,soluble protein,soluble sugar,proline,and the activities of POD and SOD enzyme all showed a trend of first increasing and then decreasing,the content of NO3--N and the activity of CAT-enzyme increased,while the content of MDA decreased.The study indicated that optimal N supply(5.00?10.OOmmol/L)could promote plant shoot and root growth,enhance photosynthesis,raise the contents of osmotic adjustable substances,reduce the content of MDA,and promote the activities of antioxidant enzymes,which was in favor of the growth of plant and strengthened their adaptability to the adverse environments.The growth and physiological metabolism activity was limited in different extent when the N supply was in short(0.00?0.50mmol/L)or excessive(15.00mmol/L)conditions.2.Effects of N application rate on agronomic characters,quality and nutrient utilization of Pennisetum sp.(1)N fertilizer promoted the growth of aboveground part of Pennisetum sp.The plant height and leaf area were higher than CK,19.92%?36.96%,52.58%?129.21%respectively at harvest,but the amplification decreased with the increasing of the N application rate.A small amount of N fertilizer could increase the root volume.Plant height,leaf area,stem diameter were positively correlated with N application rate,while root volume was negatively correlated with N application rate.(2)N fertilizer to certain extent could significantly enhance the increasing of yield,but the anplification of yield decreased with the increasing of N application rate.Fresh weight of aboveground part raised,and dry weight of aboveground part increased firstly and then decreased along with the increasing of N application rate.Quadratic curve were consistent with change law of N application rate and aboveground biomass.Equation were as fbllows:y=-0.000446x2+0.349121x+107.9040(R2=0.9926**);y=-0.000185x2+0.116085x+31.8299(R2=0.9774**).Fresh and dry weight of the root were higbest when the N application rate was 75 kg/hm2.The ratio of stem-leaf and root-shoot gradually dropped,while fresh-dry ratio rose as N application rate increased.Aboveground biomass and fresh-dry ratio were positively correlated with N application rate,whereas root biomass,the ratio of stem-leaf and root-shoot were negatively correlated with N application rate.(3)Suitable N fertilizer rate could add the photosynthetic pigment contents,strengthen the efficiency of plant photosynthesis,and improve the accumulation of dry matter,but both inadequate and excessive N fertilizer were unfavourable to the photosynthesis.SPAD values continuously increased,while Ci decreased.Other photosynthetic indexes showed a trend of rising at first and then falling or raising(except WUE at T2 stage)at every stage with the increasing of N fertilizer rate.N fertilizer was significantly or high significantly positively correlated with SPAD values,positively or markedly positively correlated with Pn,but negatively correlated with CL(4)the development of plant growth period,CP content reduced,while CP accumulation added among N150-N450 treatments,the content and accumulation of CF rosed,the contents of EE and CA fell,whereas their accumulation raised,the content and accumulation of NFE increased.Proper quantity of N fertilizer could remarkably increase the contents of CP,EE,CA and NFE,decrease CF content,promote the accumulation of nutrients in some degree to improve the nutritional value of plant.However,both insufficient and more than enough amount of N supplying would bring about bad effects on quality.Positive or extremely positive correlation were found between the content and accumulation of CP and N fertilizer.CF content was obviously negatively correlated with N application rate at T2 and T3 stage,and AS content was negatively correlated with N application rate.(5)The content and accumulation of N significantly increased because of N fertilizer,but their amplification slowly weakened with the increasing of N application rate.The absorption of phosphorus and potassium improved by N fertilizer.Quadratic curve were consistent with change rule of N application rate and the N contents in aboveground and underground parts,the total N accumulation.Equation were as follows:y=-0.0133x2+0.1803x+0.3431(R2=0.9901**):y=-8.4656E-08x2+0.0019x+0.5065(R2=0.9984**);y=-11.7799x2+146.8935x+55.9574(R2=0.9907**).Inthe aboveground part,the distribution ratio of nitrogen and phosphorus(P)showed a trend of first rising and then falling,and the distribution ratio of potassium(K)consistently raised.There were significantly or extremely significantly positive correlation between N application rate and the total accumulation of N,P,K.The comprehensive analysis indicated the growth and photosynthesis enhanced and the quality improved at every stage,supplying N 225kg/hm2.The fresh and dry weight were 165.28 and 49.41g/plant at the harvest,and the amplification were 54.94%and 56.91%.Therefore,225kg/hm2 was proper N application rate under the condition of this experiment. |
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