| Ageratina adenophora Spreng（Crofton Weed）,a malignant weed in Compositae,is native to Mexico and Costa Rica in Central America.In the 1940s,this weed intruded into China from the Sino-Myanmar border and is currently widespread in agricultural lands,forests and pastures in Southwest China,resulting in huge economic loss and ecological disaster.A.adenophora has been considered as the most noxious invasive plant in China.Large amounts of A.adenophora’s residues have been remained after its manual and mechanical elimination in the field.It is necessary to develop an effective and rational way to utilize these plant biomass resources.Previous research shows that A.adenophora is toxic to animals,plants,and microbes,and its tissue is soft with short fiber and low combustion value.The attempts have failed to use plant biomass of A.adenophora as animal food,fuel wood,pulp,furniture,and building material.In contrast,A.adenophora plants grow rapidly,have a huge biomass and contain high level of mineral nutrients,including nitrogen,phosphorus and potassium.The plant residues may thus be potentially used as an organic fertilizer.However,A.adenophora plants contain more than 100 phytotoxic allelochemicals and reproduce asexually via roots,shoots and stems.The direct use of these residual materials in the field has a great risk for inhibiting crop growth and accelerating its spread unless being effectively treated.In the present experiments,Clostridium thermocellum inoculum and an additive agent were aerobically used to make A.adenophora plants into compost.The main objects were to（i）realize the composting process and the mechanisms relevant to the allelopathical decomposition;（ii）compare the biologicl toxicities of the composted and uncomposted A.adenophora to other plants,animals and microbes in soils;and（iii）understand the efficiency of the organic fertilizer made from A.adenophora under both greenhouse pot and field conditions.Our results could provided theoritic bases and an easy,economic and operative way for the harmless treatment and fertilizer utilization of A.adenophora plants.The main results are as follows:（1）According to the temperature change,the aerobically composting process of A.adenophora was divided into four periods,namely,（1）heating-up period（0-3 d）,（2）high temperature period（4-19 d,>50°C）,（3）cooling period（10-25 d）and（4）normal period（26-50 d）.With the increase of composting duration,the moisture and total organic carbon content of the composted material were decreased,its nitrogen,phosphorus,potassium,humic acid content and p H value were continuously increased.Compared with uncomposted A.adenophora,the contents of main allelochemicals（6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2（1H）-one and 4,7-dimethyl-1-（propan-2-ylidene）-1,4,4a,8a-tetrahydronaphthalene-2,6（1H,7H）-dione）（HHO and DTD,respectivately）were decreased by more than 94%in composted A.adenophora.In addition to moisture content,the p H and nutrients content of the compost fitted the national standard of organic fertilizer（NY525-2011）.Degradation of HHO and DTD is the result of chemical and microbial interactions under high temperatures.（2）With the increase of texted concentration,uncomposted A.adenophora extracts significantly inhibited the seed germination rate and seedling growth of three vegetable crops of pepper,tomato and eggplant,decreased the degradation of protein and starch in seeds,and free amino acids,soluble sugar and soluble phosphorus content,hindered the root activity,chlorophyll content and nitrate reductase activity in leaves of three 2-weeks seedlings.Therefore,uncomposted A.adenophora extracts inhibited the material transformation in seed endosperm,resulting in a decrease in germination rate.It could also be unbeneficial to photosynthesis,nutrient uptake and nitrogen assimilation,which might lead to an inhibition of seedling growth.On the contrary,composted A.adenophora extracts significantly increased seed germination rate and seedling growth of the young seedlings of these three crops.These results indicated that composted A.adenophora extracts promoted the hydrolysis of high molecular metabolites in endosperm,in turn increased soluble compounds in seeds,and also enhanced chlorophyll concentration,root activity and nitrate reductase activity in young seedlings.（3）Uncomposted A.adenophora extracts at 10 mg L-1（oven-dried plant biomass base）almost stop the growth of Lactarius deliciosus and Ceriporia lacerate,and significantly reduced growth of Fomitopsis palustris on the soil surface and in the soils;remarkably decreased available nitrogen and phosphorus,and activities of protease and phosphatase in the fungus-inoculated soils.However,composted A.adenophora extracts promoted the activities of protease and phosphatase,and increased the bioavailability of soil nitrogen and phosphorus.Therefore,uncomposted A.adenophora extracts had negative effects on the fungal growth and decreased the mobilization of soil nitrogen and phosphorus,which might led to poor growth via lacking of nutrient supplies.（4）The LD50 of uncomposted A.adenophora extracts to earthworms was 16.15 g L-1（exposed to filter paper contact for 48 h）,while the LD50 of uncomposted A.adenophora to earthworms was 5.38 g kg-1（exposed to artificial soil for 28 d）.During the soil exposure test period,uncomposted A.adenophora obviously increased the contents of peroxidase,glutathione-S-transferase and malondialdehyde in earthworms,and significantly inhibited the activities of acetylcholinesterase and Ca2+-ATPase.Under the low concentration uncomposted A.adenophora treatment(0.01 g kg-1),the avoidance rate of earthworms was negative,and the maximum value exceeded 80%in the 1.00 g kg-1uncomposted A.adenophora（high concertration）.At the same time,the weight,cocoon production rate and hatching rate of tested earthworms were decreased with the increase of uncomposted A.adenophora’s exposure time and concentration.On the contrary,composted A.adenophora increased the Ca2+-ATPase activity of earthworms,and adversely affected the avoidance rate.There was no significant change or increase in earthworm weight,cocoon production rate and the number of young earthworms.Instead,uncomposted A.adenophora was toxic to earthworms,which might be due to the stimulation of reactive oxygen species,resulting in oxidative damage or even death of the whole body,and inhibition of the normal growth and reproduction of earthworms.No significant effects of composted A.adenophora on metabolism,behavior,growth and reproduction of earthworms were observed.（5）Uncomposted A.adenophora significantly inhibited ryegrass and maize growth,compared to the composted A.adenophora（CA）.Compared with chemical fertilizer（CF）,CF+CA promoted plant growth,increased plant nutrient absorption,and soil available nutrients,enzyme activity and microbial diversitities.Therefore,in situ aerobically composted A.adenophora eliminated the phytotoxicity of CA and provided a new,simple and economical approach for the potential use of A.adenophora biomass as an organic fertilizer.There were higher nutrient concentrations in the soil supplied with CF in the early fruit stage,while these with CF+CA contained higher available phosphorus and available potassium than CF,but Na OH hydrolyzed-N was similar in late fruit period.The pepper plants grown under CF+CA absorbed more nitrogen,phosphorus,and potassium,produced 14.42%more fruits improved fruit quality than under CF.（6）In a field experiment,soil applied with CA resulted in higher microbial biomass,soil enzyme activities and bacterial community diversity than soil with CF.Results showed that soil CA application improved the ecological environment,promoted the growth and reproduction of bacteria,and enriched the structure of bacterial community.Actinobacteria and Proteobacteria accounted for more than 50%of the total bacteria in each soil examined.Among top 20 predominant bacteria,seven were ubiquitous in all studied soils and six to eight were unique in each soil.It showed that soil was the main factor to determine the bacterial community and also varied with fertilizer.The amount of Ascomycota and unclassified fungi accounted for 78.90%-82.53%and predominant fungi with high abundance were Zygomycot,Fusarium graminearum,and uncultured Ascomycete in all soil tested.These results also suggested that soil was a main factor that governed the fungal communities.The CF soil contained largest number of 18S r DNA sequences,and fungal OTUs were also higher than these in CA soil.The diversity and dominant indexes of fungal communities in the soil supplied with CF was higher than CK,CA and CK+CF treatments.Therefore,CF promoted fungal growth and reproduction,and increased fungal numbers,species,and predominant strains,which could take the risk for crops to be infected by fungal pathogens.In contrast,CA could avoid fungal expansion,and decreased the possibility of over-production of these pathogens.In conclusion,in situ aerobically composting can degrade allelochemicals and decompose organic matter of A.adenophora residues,realize their harmless treatment in the field,and produce a plant-and soil-friendly organic fertilizer,which provides a theoretical basis and practical way for the effective control and resource utilization of A.adenophora. |
