2种PBAT/PLA生物降解地膜碎片对土壤溶解性有机碳氮的影响及其植物毒性

Effects of Two PBAT/PLA Biodegradable Mulch Film Fragments on Soil Dissolved Organic Carbon and Nitrogen and Their Phytotoxicity

为了解生物降解地膜的生态毒性,科学评价其应用的环境安全性,采用盆栽试验,以单子叶植物小麦和双子叶植物小白菜为材料,研究了国内2家企业的聚己二酸-对苯二甲酸丁二酯(butyleneadipate-co-terephthalate,PBAT)/聚乳酸(polylactic acid,PLA)型生物降解地膜(分别用BDM1和BDM2表示)在不同添加量(0、0.5、0.8、3.2、8、16、32、40和80 g·kg^(-1))下对紫色土pH、溶解性有机碳(dissolved organic carbon,DOC)和有机氮(dissolved organic nitrogen,DON)、植物种子发芽及幼苗生长的影响。结果表明,随地膜添加量提高,土壤pH和DOC含量增高,DON含量降低,其中,土壤pH在2种地膜处理间差异不显著,DOC表现为BDM2>BDM1,DON为BDM1>BDM2。除BDM2添加量高于32 g·kg^(-1)时对小白菜种子发芽有抑制作用外,其余处理对2种作物种子发芽的影响不明显。2种地膜碎片对作物均无致死效应。随着地膜添加量提高,BDM1处理小白菜幼苗干质量呈先增高再降低的变化趋势,BDM2处理小白菜幼苗干质量降低,在添加量高于8 g·kg^(-1)时降幅达显著水平(P<0.05);BDM1处理可提高小麦根干质量,提高幅度呈先增高后降低的变化趋势,在添加量低于8 g·kg^(-1)时地上部干质量变化不明显,但高于此值时显著降低,而BDM2处理根和地上部干质量在地膜添加量低于3.2 g·kg^(-1)时显著提高,高于此值则显著降低;小麦根冠比(R/S)均随地膜碎片用量的提高而增大。生物降解地膜对小麦和小白菜幼苗生长的影响存在剂量-效应关系,基于拟合方程,求得小白菜幼苗、小麦根和地上部生长的半抑制添加浓度(EC 50)为BDM1>BDM2,小白菜幼苗>小麦幼苗。由此说明,生物降解地膜可导致土壤微生物对氮素的固定,BDM2对小麦和小白菜种子发芽和幼苗生长的抑制效应更强。2种作物中,小麦幼苗生长对生物降解地膜的响应较小白菜幼苗敏感。

The ecological toxicity and environmental safety of biodegradable mulch films(BDMs)are of prime concern along with their application in plant growth and nutrition.To investigate the effects on soil pH,dissolved organic carbon(DOC)and nitrogen(DON),seed germination,and seedling growth of plants grown in purple soil,a pot experiment was conducted employing two butyleneadipate-co-terephthalate(PBAT)/polylactic acid(PLA)biodegradable mulch film fragments(designated as BDM1 and BDM2).This experiment aimed to investigate the effects of BDMs on plants as well as evaluate their ecological toxicity and environmental safety.The tested plants included a monocotyledon and a dicotyledonous,i.e.,wheat(Triticum aestivum L.var.Ruomai No.1)and pakchoi(Brassica campestris L.var.Sijiqing),respectively.A total of 8 application rates of BDM fragments were used i.e.,0.5,0.8,3.2,8,16,32,40 and 80 g·kg^(-1).For control treatments,soil without fragment addition was used.The results revealed that soil pH and DOC content increases,whereas DON content decreases with increasing film addition.There was no significant difference found between the two films treated soil for pH values,but the contents of DOC in BDM2 treatment was much higher than those of BDM1 treated soils.In contrast,the content of DON in BDM2 treated soil was lower than those of BDM1 treated soils.Apart from the treatments of BDM2 with application rates higher than 32 g·kg^(-1) that inhibited the pakchoi seed germination,all other treatments didn’t affect the seed germination of both crops.Both the film fragments had no lethal effect on crops.Initially,the biomass of pakchoi seedlings in BDM1 treatment increased,followed by a reduction with the increasing rates of fragment addition.However,in the BDM2 treatment,when the addition rate was higher than 8 g·kg^(-1),the biomass of pakchoi seedlings showed a significant decrease.For wheat seedlings,BDM1 treatment improved the root biomass but significantly decreased the shoot biomass when applied higher than 8 g·kg^(-1).The biomass of wheat root and shoot in BDM2 treatments initially increased,followed by a significant reduction,and the highest biomass was found at the rate of 3.2 g·kg^(-1).In response to a higher rate of plastic fragments,the root to shoot ratio(R/S)of wheat seedlings also increased.There was a dose-dependent relationship between the growth of crop seedlings and rates of fully biodegradable plastic application.According to the fitted dose-response curves for both plants,the EC 50 values were BDM1>BDM2,and for the same plastic film,EC 50 values for pakchoi seedlings were higher than those of wheat seedlings.The obtained results demonstrated that biodegradable plastic application can lead to nitrogen immobilization and the BDM2 treatment had a greater inhibitory effect on seed germination and seedling growth than BDM1 treatment.Moreover,the wheat seedlings were more sensitive to biodegradable plastic film than pakchoi seedlings.