| “Soil-roots-microbes and enzyme” constitutes root-zone soil environment,which is a complex system.The material exchange and energy flow between soil and plant would be determined by the jointly interaction among soil,roots and microbes and enzyme,ultimately to affect crops growth and yield.Irrigation regime would play a decisive role on root-zone soil microenvironment development when in a relative stable condition of fertility,climate and soil matrix,especially in plastic greenhouse crops planting of arid and semiarid region.Therefore,it would be more necessary to compare influences of different mulched drip irrigation modes on root-zone soil microenvironment from “soil-roots-microbes and enzyme” interaction points,to provide stronger supports for rational allocating drip irrigation measures and improving soil and water resources utilization in plastic greenhouse cultivation.This study had taken “soil-roots-microbes and enzyme” in melon and tomato rootzone as the research object,adjusted root-zone soil water and thermal environment with drip irrigation layout measures(mulched modes,drip lines density and irrigation limits)and water supply modes in drip irrigation(surface,subsurface and alternate drip irrigation)commonly used in mulched drip irrigation technology;studied soil microorganisms and bacteria community structure and the response of interaction among soil microbes,soil enzyme and crop roots to the soil water and thermal environment change in root-zone,with the combination methods of high-throughput sequencing technology and traditional microbial cultures measure;analyzed the influence of dynamic change of “soil-roots-microbes and enzyme” on the activation and absorption of soil nitrogen,phosphorus and other nutrients,crop growth,photosynthesis product distribution,crop yield and quality,greenhouse gas emissions in soil,and so on;discussed the soil internal mechanism about the effects of mulched drip irrigation on crops yield and quality in greenhouse cultivation.Mainly conclusion is following:(1)Half covering mode could improve soil nutrients activity,promote crop growth and increase yields.And,it would enhance bacteria and actinomycetes quantities significantly in whole crop growth stages,maintain high root activity and improve soil enzyme activity greatly.Fresh and dry weight of ground plant increased by 12.45% and 7.57% respectively under half covering mode than under no covering mode.Root fresh weight increased by 22.77% and 10.83% respectively under half covering mode than under no and full covering modes,and root-top ratio increased by 14.36% and 16.92%.Therefor,half covering mode would be benefit for photosynthesis product distribution to the fruit.Compared with no and full covering modes,PMR(plant mass ratio)under half covering mode reduced 11.03% and 8.34% respectively,FMR(fruit mass ratio)increased by 4.79% and 3.31% respectively,NPFP(nitrogen partial factor productivity)increased by 22.64% and 7.4% respectively and melon production increased by 29.26% and 7.99% respectively.(2)Irrigation lower limits affect photosynthesis product distribution significantly.60% F(Field threshold capacity,F)soil was under certain drought stress,which would make more photosynthetic products to distribute to root and plant.Compared with 70% F and 80% F,RMR(root mass ratio)increased by13.74% and 9.5% with 60% F,however NPFP(nitrogen partial factor productivity)reduced by 18.42% and 16.45%.PMR(plant mass ratio)of 60% F increased 13.92% than 70% F,but FMR(fruit mass ratio)reduced 5.18% than 70% F.High soil moisture content of 80% F prompted more plant photosynthesis product distribution to crop plant,and PMR(plant mass ratio)of 80% F increased 13.12% than 70% F.Moderate soil moisture content in 70% F could promote soil nutrient activation,and consumption of soil total nitrogen and organic matter in 70% F increased significantly by 151.8% and 9.7% than 80% F.At the same time,more plant photosynthesis product was distributed to fruit,FMR(fruit mass ratio)of 70%F increased 4.96% than 80% F,and melon production increased by 22.58% and 2.42% respectively than 60% F and 80% F.(3)Over drip lines density would limit yield improvement.3 pipes for 4 lines could improve soil urease during full growth period of crop and root growth,enhance root-top ratio 17.75% and 48.72% than 1 pipe for 2 lines and 1 pipe for 1 line.Plant photosynthesis product of 3 pipes for 4 lines was distributed to fruit greatly,FMR(fruit mass ratio)increased 14.20% than 1 pipe for 1 line,melon yield increased 3.37% and 8.56% respectively than 1 pipe for 2 lines and 1 pipe for 1 line.1 pipe for 2 lines could increase flowering period soil urease activity by 17.14% than 3 pipes for 4 lines,increase fruit swelling period and mature period soil phosphatase activity by 31.99% and 15.06% than 3 pipes for 4 lines.And root-top ratio of 1pipe for 2 lines was next to 3 pipes for 4 lines.1 pipe for 2 lines would also make plant photosynthesis product distribute more to fruits.FMR of 1 pipe for 2 lines increased 12.29% than 1 pipe for 1 line,but melon yield and NPFP of 1 pipe for 2 were no significant difference with 3 pipes for 4 lines.The root area and root volume of 1 pipe for 1 line were significantly lower than 3 pipes for 4 lines,and root activity was inferior to 1pipe for 2 lines,therefor,melon yield and NPFP were lowest.(4)Alternate partial root-zone drip irrigation of suitable irrigation lower limits could promote root growth,optimize soil microbial communities structure of,promote soil nutrient absorption and improve production.Root length,root area and root forks under alternate drip irrigation with 60% F were 1.41,1.33 and 2.26 times respectively than surface drip irrigation,and root activity significantly increased by 45.81% than surface drip irrigation;Root length,root area and root forks under alternate drip irrigation with 70% F were 1.27,1.29 and 2.86 times respectively than surface drip irrigation,and root activity significantly increased by 48.60% than surface drip irrigation.Greater root activity and forks significantly increased the related bacteria abundance about nitrogen and phosphorus metabolism,optimized the soil bacterial community composition,and promote activation and absorption of soil nitrogen,phosphorus and other nutrients.Soil available nitrogen under alternate drip irrigation with 60% F and 70% F were 2.91 and 1.91 times respectively than surface drip irrigation,soil available phosphorus were 1.65 and 2.91 times respectively,total nitrogen in root were 1.07 and1.14 times respectively,total phosphorus in root were 1.94 and 1.59 times respectively,total nitrogen in stem were 1.21 and 1.12 times respectively,total phosphorus in stem were 1.75 and 2.84 times respectively,and tomato yield per plant increased 12.77% and 24.23% respectively.(5)Subsurface drip irrigation of moderate buried depth of drip pipes would improve soil porosity,promote root growth,and increase soil nitrogen and phosphorus metabolism,dry matter accumulation and yield.Soil porosity of 0 to 40 cm layer under subsurface drip irrigation with drip lines in 20 cm burial depth significantly increased,and soil porosity of 0 to 10 cm layer under subsurface drip irrigation with drip lines in 30 cm burial depth significantly increased.The improvement of soil structure promoted crop root growth greatly.Root length and area under subsurface drip irrigation with drip lines in 20 cm burial depth increased by 43.21% and 20.82% than surface drip irrigation,root forks were 2.26 times than surface drip irrigation.Root length under subsurface drip irrigation with drip lines in 30 cm burial depth increased by 46.101% than surface drip irrigation,root forks were 2.22 times than surface drip irrigation.Root growth had improved soil nutrient uptake.Soil available nitrogen,soil available phosphorus,total nitrogen in root,total phosphorus in root,total nitrogen in root and total phosphorus in stem under subsurface drip irrigation with drip lines in 20 cm burial depth were 2.28,1.49,1.18,1.47,1.11,1.66 times respectively than surface drip irrigation,and these value under subsurface drip irrigation with drip lines in 30 cm burial depth were 1.54,1.38,1.19,1.20,1.03,1.07 times respectively than surface drip irrigation.Soil nutrient absorption increase eventually influenced on dry matter accumulation of plant,photosynthesis production distribution and yield improving.Stem dry weight and tomato yield of 20 cm burial depth subsurface drip irrigation significantly increased by 11.13% and 22.35% higher than surface drip irrigation.Tomato plant dry matter,stem dry weight,leaf dry weight and tomato yield of 20 cm burial depth subsurface drip irrigation significantly increased by 50.73%,92.67%,57.54% and 19.53% higher than surface drip irrigation.(6)Suitable mulched drip irrigation modes could increase irrigation water use efficiency(IWUE)and improve fruit quality.Irrigation water use efficiency(IWUE)under half and full covering mode were 56.41% and 57.21% higher than no covering mode;3 pipes for 4 lines increased melon IWUE by 3.54% and 0.80% than 1 pipe for 2 lines and 1pipe for 1 line.Half covering mode had 1.72 and 1.74 times sugar acid ratio respectively than full and no covering mode;sugar acid ratio under 80% F was 1.61 and 2.08 times than 60% and 70% F;sugar acid ratio under 1 pipe for 2 lines was 1.57 and 1.5 times than under 1pipe for 1 line and 3 pipes for 4 lines.IWUE under alternate drip irrigation with 60% F and 70% F had improved 19.54% and 17.05% than surface irrigation.Fruit organic acid with 70% F alternate drip irrigation significantly reduced 43.75% than surface irrigation,but sugar acid ratio is 1.97 times than it.Soluble sugar,total soluble solid,soluble protein,lycopene and sugar-acid ratio under alternate drip irrigation with 60% F were 2.06,1.26,1.61,1.4 and 3.2 times than surface drip irrigation.IWUE,total soluble solid,soluble protein,Vc and lycopene under subsurface drip irrigation with 20 cm burial depth were improved 35.91%,10.86%,32.34%,35.66%,33.97% and 53.01% than surface drip irrigation.Different drip irrigation layout measures(mulched modes,drip lines density and irrigation low limits)and water supply modes in drip irrigation(surface,subsurface and alternate drip irrigation)would change “soil-roots-microbes and enzyme” significantly and significantly affect crops growth.Considering on soil water use efficiency,soil nutrient availability,crop plant growth and fruit yield and quality,half covering mode and 1pipe for 2 lines were appropriate layout mode,the irrigation low limits should be 70% F for seedling period,80% F for other period when under surface drip irritation in plastic greenhouse.Alternate partial drip irrigation could significantly promote root growth,and 60% F would be chosen for significantly increasing dry matter accumulation,production and fruit quality.Subsurface drip irrigation with 20 cm burial depth and 60% F also would be recommended to increase production,enhance fruits quality and improve water use efficiency. |
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