| As products of agricultural and forestry wastes,biochar can not only improve the physicochemical properties,fertility and the productivity of soil but also promote plant growth,increase crop yield and reduce the bioavailability of heavy metal pollutants in soil,which is widely used in the fields of agriculture,forestry and environmental protection.Intercropping is helpful to improve the utilization efficiency for the use of light and heat in different levels of plants and the absorption of nutrients and moisture from soil,which is conducive to the promotion of crop growth and dry matter accumulation and may also affect the heavy metals bioavailability to neighboring plants.Arbuscular mycorrhizal fungi(AMF)can also change the soil heavy metal speciation and bioavailability through adsorption,directly releasing the toxicity of heavy metals to the host plant,and enhance plant mineral nutrition,growth and resistance to heavy metals and many other aspects of physiology.It will be worthwhile to study whether biochar can be used in combination with intercropping and AMF inoculation to improve the remediation efficiency of soil contaminated by heavy metals and to restore ecological restoration of contaminated areas efficiently.In view of this,in order to better promote the application of biochar in agriculture and forestry,this paper,taking biochar as the core and Machilus pauhoi and Cassia occidentalis as the research plant,adopting the test method of indoor pot experiment,under heavy metal pollution,studied the combined effects of different application amount(0%?1%?4%?8%)of biochar and intercropping as well as the combination effects of two types of biochar and arbuscular mycorrhizal fungi(AMF)on the soil improvement,plant growth and heavy metal pollution remediation.Using the field test of cement pool,under different application amount of biochar,growth dynamics and physiological characteristics of Machilus pauhoi seedlings in Machilus pauhoi/Ilex asprella intercropping system were studied,soil samples of 0-15 cm topsoil and 15-30 cm bottom-soil from year 2015 to year 2017 were selected to discuss the interannual dynamics change of soil pH and nutrient and the change of soil fungal diversity and community structure in soil.The main results of this paper are as follows:(1)Under the compound stress of Cd,Cr and Pb,applying different amount of biochar(0%,1%,4%,8%)could promote the plant growth,root morphological development and dry matter accumulation of Machilus pauhoi.1% and 4% dosage of biochar were more conducive to plant growth while high dosage of biochar(8%)had no significant effect on growth and even inhibited growth.There was no significant difference in plant height of Cassia occidentalis among different dosage of biochar,but all of them were significantly higher than that of control.The influence of intercropping on the growth indices of plants were relatively insignificant.The effect of combination treatment of biochar and intercropping was more significant than that of single treatment.The application of biochar could improve the photosynthetic electron transfer efficiency,increase the photosynthesis of plants to some extent under heavy metal stress,and alleviate the toxic effects of heavy metals to plants,while those indexs were not significant different between intercropping and monoculture.Biochar significantly increased soil carbon and nitrogen nutrient content,improved soil pH,reduced soil available components of Cd,Cr and Pb and the heavy metal absorption of Machilus paunoi.There was synergism between biochar and intercropping and,compared with the single effect,the combined effect was more effective in reducing the toxicity of heavy metals to plants,promoting plant growth and improving soil environment.(2)In the soil with compound pollution of Cd,Cr,Cu,Fe and Pb,a pot experiment was conducted to explore the effects of the biochar and iron modified biochar and their combination with AMF inoculation(Funneliformis mosseae)on Cassia occidentalis growth and soil characteristics.The experimental result indicated that there were no observed infection of AMF at Cassia occidentalis root of non-inoculation treatment groups while inoculation groups infected well.Besides,ordinary biochar significantly increased the rate of AMF infection at Cassia occidentalis root,while iron modified biochar had the opposite effect.AMF inoculation alone can significantly promote the growth and the morphology and structure construction of root as well as the growth of shoots,dry matter accumulation and phosphorus absorption.The promotion effect of single biochar treatment was not obvious or even exhibited negative effect,but the promotion effect of AMF and biochar was more obvious than the single treatment.Among them,the combination of AMF and ordinary biochar showed the best effect.Soil pH and soil nutrient content were not significantly effected by AMF inoculation,but they were significantly increased by both of two kinds of biochar,especially that soil pH,organic matter,total nitrogen,available phosphorus and available potassium contents were significantly increased.In addition,the application of 2 kinds of biochar alone could reduce the contents of all the other elements except the Cr in the stems of Cassia occidentalis and the contents of Cd,Cu and Fe in the leaves.The composite effect of the two kinds of biochar and AMF both significantly decreased the content of every heavy metal element in Cassia occidentalis shoots and reduced the heavy metal transfer to shoots.The Cu and Fe content in root of Cassia occidentalis was greatly increased by the combined treatment of iron modified biochar and AMF inoculation.Besides,the effect of the combination of AMF and ordinary biochar in promoting plant growth and reducing the risk of heavy metals on plant performed most remarkable.(3)Based on the planting experiment to explore the effects of biochar on the intercropping system of Machilus paunoi and Ilex latifolia in cement pond in 2015-2017,after appling biochar to soil in the first year,the early effect on Machilus paunoi growth,chlorophyll fluorescence characteristics and dry matter accumulation was not significant,but with the extension of their growing periods,in the second year for the later,the promotion effect was progressively significant.Besides,the suitable application amount(T2)performed the strongest effect.Biochar could increase soil pH and soil nutrient content,especially for soil pH,organic matter and available potassium content,the contents of them was proportional to the amount of biochar.The results shown that there was a significant effect of soil improvement and this effect was reflected in the initial stage of plant growth(year 2015),mid stage(year 2016)and late stage(year 2017),characterized by long-acting characteristics.Biochar was applied directly to the surface soil,so the response of soil pH and soil nutrient content to biochar in 0-15 cm soil layer was significantly higher than that in 15-30 cm.In addition,the soil nutrient contents gradually decreased with time,and the upper soil(0-15cm)nutrient content was significantly higher than that in the lower soil(15-30cm).Moreover,the heavy metal content in the soil was low,which had not reached the pollution levels.The heavy metal content increased with biochar application amount increasing and there was strong correlation between the content of each element,showing significant homology.The contents of soil nutrient also shown significant correlation.(4)After biochar application,in the third year,the soil in the intercropping system of Machilus paunoi and Ilex latifolia in field cement pond was sampled to study the fungal community structure.The experimental result indicated that biochar could increase soil OTU number,change the original set of fungal communities,improve soil fungal community richness and diversity.Besides,the response of fungal community in 0-15 cm soil layer to biochar was more significant than that in 15-30 cm soil layer.The effect of T2 treatment was the most obvious.Compared with CK,soil fungal dominance was also increased in low dosage of biochar treatment(T1),but no significant changes was reported in the high amount of biochar application(T2,T3).The result of fungal community structure analysis showed that 5 predominant fungi phyla(Mortierellomycotina,Chytridiomycota,Glomeromycota,Ascomycota and Basidiomycota)were detected among all treatents.After the application of biochar,in 0-15 cm soil layer,the relative abundance of Mortierellomycotina,Chytridiomycota,Glomeromycota and Ascomycota in the phyla level and that of Ostropa,Ochroconis,Capnobotryella,Muyocopron and Hydropisphaera in the the level of genus were increased,the relative abundance of Lulworthia and Thamnocephalis in the the level of genus were decreased and the relative abundance under the T2 treatment was highest,which was significantly different with other treatments.At the same time,with the application of biochar,in 15-30 cm soil layer,Basidiomycota,Glomeromycota in phyla level and Glomus,Myriangium,Capnobotryella,Zoophagus and Trichoderma in the the level of genus were decreased.RDA analysis showed that the abundance of Funneliformis,Ostropa,Piriformospora and Plectosphaerella in soil were positively related to soil nutrient content and negatively related to soil pH.There was a positive correlation between the abundance of Glomus,Mycotribulus and Gyroporus and soil pH.Among them,Plectosphaerella and Gyroporus were the most sensitive to the environment,the sensitivity of Piriformospora was the worst.To sum up,the biochar could be used as heavy metal contaminated soil amendment and soil fungi carrier.Combining biochar with intercropping and AMF could reduce the toxicity of heavy metals to the target plant,promote plant growth and improve soil environment,achieving the purpose of repair and production.Besides,the soil improvement effect of biochar showed a long-term characteristic,which could be used for forest ecological reconstruction.This paper provided technical reference for the utilization of agricultural waste,ecological restoration of pollution land and the promotion of fine tree species in lightly polluted areas. |
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