Effect Of Biochar On Cucumber Growth And Soil Microbial And Nematode Community Structure In Sunlight Greenhouse

The development of greenhouse vegetable is rapid in China.The specified managementincluding higher input,higher cropping index,compare to the traditional cultivation,had led to the soil quality degradation and soil ecosystem instability,as well as crop disease aggravated and decrease the soil sustainability,which threaten the yield and quality of greenhouse vegetables.It becoming a challenge of how to control pests and diseases,enhance vegetable yield and improve the quality during the vegetable management.In the current years,the conversion of agricultural bio-waste to biocharthrough pyrolysis and used in agricultural production has been widely recommended as way for resource utilization of agricultural residues.As previous reports showed that:biochar soil amendment has a potential role in crop yield enhancement,soil quality improvement,as well as soil ecosystem stability and vegetable quality increasing.The previous papers mostly focus on the growth and yield of vegetables,while limit research was devoted to soil biological properties,especially to soil nematode community structure.In this study,we conducted an experiment in a sunlight greenhouse with long-term cucumber planting.Three treatments were conduted:C0(no biochar),C1(24t/hm2)),C2(48t/hm2).We aimed to investigate the effect of biochar on soil properties,cucumber growth and quality;the effect of biochar on soil microbial community structure;the effect of biochar on soil nematode community structure(including root-knot nematode).The main results were as follows:(1)Biochar addition significantly increased soil organic matter by 22.4%-37.2%,total N,NH4+ and available K was increased with C2 by 10.2%,53.3%and 43.7%,respectively.At the same time,soil pH was significantly increased with biochar amendment,and soil bulk density decreased by more than 11.0%,compare to C0.Additionally,C2 treatment enhanced cucumber root biomass by 56.9%,and increased cucumber soluble sugar and organic acid content by 25.0%and 17.6%,respectively,and Cl treatment decreased the nitrate content by 25.5%,compared to CO.(2)The effect of biochar amendment on soil microbial community structure:the microbial biomass carbon content was increased with the increase of biochar amendment rate,and C2 treatment significantly higher than CO by 14.7%.Using PLFA method,biochar amendment showed no effect on the the relative abundance of PLFA markers bacteria,fungal,actinomycetes,as well as the total PLFA.While difference was observed for fungi/bacteria ratio between C1 and C2,where C2 was 9.9%lower than C1.There were no significant differences in Gram-positive to Gram-negative bacteria,monounsaturated fatty acids/branched fatty acids,and normal saturated fatty acids/monounsaturated fatty acids.Principal component analysis showed that higher rate of biochar amendment(C2)lead to the instability of soil microbial community.(3)The effect of biochar amendment on soil nematode community structure:biochar amendment had no effect on soil nematode total number,while altered nematode community structure.C2 significantly decreased soil bacterivorous nematodes by 38.3%,compare to CO treatment,and no different between C1 and CO.At the same time,the abundance of soil fungivores with C1 was lower than CO by 61.9%,and no changing observed for plant-parasites and omnivores-predators.From the nematode ecological indices,the NCR index significantly increased by 27.1%with biochar amendment,on the contrary,the F/B ratio decreased by 50.7%with C1,it indicated the leading role of bacterivorous with lower biochar amendment level.Additionally,the other ecological indices(H',Margalef and MI)showed no difference between the treatments,it suggest that the application of biochar to the greenhouse soil did not significantly disturb soil nematode community diversity and stability.In addition,biochar amendment in greenhouse soil significantly influenced the root-knot nematode,and C2 significantly increased gall index by 89.7%.Egg masses per plant increased by 0.9 and 3.8 times with C2 treatment,respectively,compared to CO.Overall,biochar amended to greenhouse soil can significantly improve the soil property and enhance the cucumber quality,increased the root growth.The changing of soil microbial community structure mostly reasoned by the soil environmental improvement,and higher level of biochar amendment in greenhouse soil lead to the instability of soil microbial community.The effect of biochar on soil nematode mostly reflected on the total number and abundance of bacterivorous and fungivores nematode,and appropriate biochar level promote the bacterivorous dominant energy flow.The effect of biochar on soil ecosystem food web had not reached high trophic level,and can keep the stability of nematode stability.C2 treatment increased the gall index,while no effect on cucumber yield.