| At present,the research on the yield increment mechanism of soil-plastic mulching technology is mainly focused on the relationship between soil thermal-moisture process,dry matter accumulation,and yield composition.However,the water demands and water consumption characteristics of spring wheat,which mulched by plastic and soil,was lacked.Additionally,the study sbout the relationshop among soil stoichiometric,flag leaves stoichiometric,photosynthetic function,and yield composition,to understand the eco-physiological mechanism of wheat response to the plastic-soil muclching technology,were unsufficient.In order to solve the above problems,two field experiments were conducted,to study the water consumption characteristics of spring wheat and its effects on yield and water use efficiency.And analyze the relationships of C/N,C/P,N/P and other chemical metering characteristics,water use efficiency,physiological and photosynthetic characteristics and yield componement,to provide theoretical basis for exploring the method to increase resource efficient and crop yield.The main results are as follows:The total water consumption is 439.9 mm at the whole growth period of soil-plastic mulched spring wheat in semi-arid areas of Loess Plateau in Northwest China.The average water requirement were 159.5,115.0,47.7 and 117.7 mm from sowing to jointing,jointing to heading,heading to filling,and filling to maturity of PMSI,respectively.The water consumption intensity of PMS increased by 5.8%—20.0% from sowing to jointing,but it decreased by 14.1%—26.4% from filling to maturity,as compared with CK.The soil water storage in 0—100 cm profile of PMS and SM were higher than CK at harvesting stage,and it were lower than CK in 100—300 cm profile.The soil water storage in 100—300 cm profile of PMS at harvesting stage were decreased by 52.2—66.2 mm than the sowing stage.Consequently,PMS could promote the use of deep soil water,to meet the water requirement of wheat,as well as regulated the water consumption process in different precipitation year.Additionally,PMS improved the water consumption modulus coefficient and water consumption intensity in productive growth stage of spring wheat,it is benefited to ‘source’ development and resulted in the increased yield and WUE while the evapotranspiration decreased in filling stage.Under the joint effect of soil water and crop growth,the soil C,N and P concentration in PMS,SM and CK were alternated significantly in different soil profile and wheat growth stages.The organic carbon changed slightly among three treatments through spring wheat growth period.However,the available soil phosphorus concentration of PMS in 0—30 cm profile was lower than CK,the available nitrogen concentration of PMS in 0—30 cm profile was significantly higher than SM and CK after abundant rainfall,and lower than SM and CK in dry season.It indicated that the nitrogen mineralization promoted by plastic mulchingunder the wet condition,which benefited to improve water and nitrogen use efficiency.The soil stoichiometric parameters of C/N,C/P and N/P values in 0-30 cm changed more significntly than those below 50 cm soil profile.For example,the N/P value of PMS in 0—20 cm soil profile is higher than CK in picking period but lower at heading stage.The one main reason is that the wheat canopy of PMS is larger than CK,the wheat absorption of available nitrogen reached to the peak at the heading stage;the another reason is that the soil nitrogen mineralization increased and available nitrogen concentration is higher after 80 mm rainfall in picking period.Therefore,the soil stoichiometric characteristics were affected by environmental factors and crop development,and these effects not only has an important effect on the nutrient uptake and utilization of wheat,but also affect photosynthetic carbon assimilation and water use by changing the leaf stoichiometric characteristics.Under the co-influence of soil C,N,P stoichiometric and precipitation,the stoichiometric characteristics of flag leaves were significantly different among three treatments,and it significantly changed in different growth period.The average nitrogen concentration in flag leaves of PMS,SM and CK were 32.6 g/kg,30.3 g/kg and 33.5 g/kg respectively,the concentration of phosphorus were 2.73 g/kg,2.78 g/kg and 2.72 g/kg,and the concentration of carbon were 436.9 g/kg,451.8 g/kg and 432.1 g/kg.the leaf C/N value of SM was highest and CK was lowest.The leaf C/P of PMS was significantly higher than CK at picking period,and the N/P ratio of PMS was significantly higher than CK at heading stage.It was proved that the limiting elements for wheat growth changed with wheat growth and precipitation distribution,and the limiting effect differed in different treatments.Generally,the wheat growth was mainly limited by nitrogen under drought conditions,but there were no significant difference with CK.Especially,the limitation of N and P on wheat growth in PMS was relieved after sufficient precipitation.Therefore,the soil-plastic mulching relieved the N and P limitation for wheat growth,and these limitation also could be alleviated quickly after adequate precipitation.The leaf SPAD value of spring wheat in PMS was highest,and CK was lowest through growth period.It indicated that PMS enhanced the soil nitrogen uptake and utilization of spring wheat,and the more nitrogen distriuted to chlorophyll.The net photosynthetic rate and stomatal conductance of wheat flag leaves in PMS and SM were higher than CK at the spring wheat early growth stage.It’s mainlybecause the water condition of PMS and SM was better than CK.however,the photosynthetic rate and stomatal conductance of wheat flag leaves in PMS and SM were lower than CK in drought condition.The non-stomatal limitation of wheat flag leavesin PMS was lower than CK in wet condition,but it was stronger than CK under drought condition.Combined with the results of leaf stoichiometric,we regarded that the non-stomatal limitation of photosynthesis was mainly due to the limitation of P,it means the photosynthetic phosphorylation inhibit the increment of photosynthetic rate,it caused by the combined effect of soil N/P and soil water storage.Under the interactive effects by stomatal limitation,the leaf stoichiometry and soil moisture,the leaf instantaneous water use efficiency in PMS were significantly lower than CK at flowing stage in normal rainny years but significantly higher than CK at the other growth stages;and it was significantly higher than CK at picking period in poor year,but significantly lower than CK at the other growth stages.In PMS,the soil stoichiometry was changed by the improvement of soil water content and the increase of soil available N concentration.Under the combined effects of soil stoichiometric and water content,the stoichiometric characteristics of wheat flag leaves relieed the elements limitation for wheat growth and promoted nitrogen distributed to chlorophyll,resulted in the improved ability of light utilization in flag leaf.So that the non-stomatal limitation of photosynthesis is decreased,caused the photosynthetic rate increment,the leaf water use efficiency also increased,as well as the leaf area index increased and the canopy temperature decreased significantly.Under the synergistic effect of above factors,the number of grains per spike and the grain weight per spike of PMS were significantly higher than those of SM and CK,it increased by 6.9% and 13.8% than SM in normal rainny years,and by 11.1% and 24.7% than SM in drought year.Therefore,based on the optimization of soil hydrothermal conditions and the use of deep water,PMS optimized the soil stoichiometry,reduced the elemental limitation of flag leaves under drought conditions and enhanced photosynthesis,which resulted in a significant increase in wheat yield and water use efficiency,Especially,it better than SM in arid years for yield and WUE increment. |
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