| Biosolid is a solid organic matter produced in the process of sewage treatment,which contains rich nutrients such as nitrogen and phosphorus,and it can be used in agriculture and landscape greening to realize its resource utilization.In addition to basic nutrients,biosolid is rich in humus,amino acids,vitamins and other bioactive substances,which can improve the ability of turfgrass to resist environmental stresses such as drought,cold,high temperature and so on.In order to clarify the effects of biosolid on drought resistance physiology and gene expression of perennial ryegrass,split plot design was used in this experiment,the moisture was divided into well watering and drought stress(50%deficient irrigation).The auxiliary biosolid processing meant different nitrogen sources:control(75 mg·kg-1 of nitrogen fully provided by NH4NO3 solution),and biosolid measure(75 mg·kg-1 of nitrogen fully provided by biosolid solution).During the study,perennial ryegrass leaves and soil matrix were sampled and determined.The results were as follows:1)Under 50% deficient irrigation,the turf quality and relative water content of perennial ryegrass were significantly improved and the electrical conductivity was significantly decreased after biosolid treatment(P<0.05).On the 40th day of drought resistence,compared with the control group,the turf quality of perennial ryegrass leaves treated with biosolid increased by 12.0%,the relative water content of leaves increased by 13.3%,and the electrical conductivity of leaves decreased by 21.9%.This indicated that biosolid could help perennial ryegrass to improve turf quality,increase the relative water content of turfgrass leaves and maintain the leaves under drought stress.More water can grow normally,and biosolid application can alleviate the harm of water deficit to perennial ryegrass by slowing down the increase of electrolyte permeability to a certain extent,and improve its growth status.At the same time,the soluble sugar and proline content of perennial ryegrass increased by 62.3%and 57.4%respectively after adding biosolid under 50%deficient irrigation condition,which was much greater than that of control treatment(P<0.05).This indicated that the biosolid had better osmotic regulation effect on turfgrass under drought stress.It could increase the content of proline and soluble sugar in perennial ryegrass,enhance its osmotic regulation ability and improve the drought resistance of turfgrass.2)Under two water conditions,the application of biosolid could significantly slow down the decline rate of net photosynthetic rate in perennial ryegrass leaves,reaching 1.06 times and 1.17 times of the control group(P<0.05).This indicated that the biosolid could reduce the harmful effects of drought stress on plant photosynthesis as much as possible under the condition of plant water shortage,thus improving the drought tolerance of turfgrass.The stomatal conductance,transpiration rate and water use efficiency of perennial ryegrass leaves decreased in different degrees under two water conditions,and significant differences in transpiration rate and stomatal conductance of perennial ryegrass leaves were existed under different water conditions on the 30th and 40th days after the experiment.The transpiration rate and stomatal conductance of leaves under full irrigation were significantly better than those under drought stress(P<0.05).This indicated that drought conditions would damage the transpiration rate of perennial ryegrass leaves and cause the decrease of photosynthesis.Compared with the control group,the decrease of stomatal conductance,transpiration rate and water use efficiency of the treated leaves slowed down to a certain extent,but did not reach a significant level(P>0.05).This indicated that the application of biosolid as a source of nitrogen had a certain effect on improving the photosynthesis of turfgrass and further improving the photosynthetic capacity of plants3)Under normal watering conditions,the contents of IAA,GA3 and t-ZR in turfgrass leaves were significantly increased by adding biosolid(P<0.05),and the maximum values were 62.6 ng·g-1、8.9 ng·g-1 and 11.5 ng·g-1,respectively.This indicated that under normal water conservation conditions,adding biosolid into the substrate could increase the growth-promoting hormone content in turfgrass leaves,and improve the antioxidant and nitrogen metabolism regulation system of turfgrass.Under 50%deficit irrigation,the contents of IAA,GA3,t-ZR and ABA in perennial ryegrass leaves were 1.16,1.34,1.11 and 1.09 times of those in control group(P<0.05).This indicated that the application of biosolid in the substrate could increase the phytohormone content of turfgrass leaves under drought stress and alleviate the plant damage caused by drought stress.After the rise of IAA content in soil,the content of GA3 decreased clearly,and the content of ABA promoted gradually.The content of hormones in the soil treated with biosolid was significantly higher than that in the control group(P<0.05).This indicated that the application of biosolid as nitrogen source could increase the hormone content in soil to enhance the ability of turfgrass to resist or reduce drought stress.4)The expression level of drought tolerance related genes in perennial ryegrass leaves increased or decreased due to their different functions.The gene P5CS and INPS involved in osmotic regulation system were significantly up-regulated due to insufficient nitrogen sources and persistent drought stress(P<0.05),and the expression of P5CS and INPS was significantly increased by biosolid treatment(P<0.05).This indicated that adding biosolid to soil matrix could promote the expression of osmotic regulation-related synthetic genes in turf grass leaves and enhance their expression.Under 50%deficit irrigation,the highest expression of Russisco gene was 2.54 times that of the control group.That is to say,adding biosolid could improve the expression level of photosynthesis-related genes and alleviate the damage caused by water deficit.Compared with the control,biosolid treatment significantly increased YUCCA,GA20ox,CKX1 and NCED expression in perennial ryegrass leaves(P<0.05).On the 20th day of the experiment,the expression of YUCCA,GA20ox,CKX1 and NCED in normal irrigation group was 3.20,3.42,2.19 and 2.46 times higher than that in control group.On the 10th day of 50%deficient irrigation,the expression of YUCCA,GA20ox,CKX1 and NCED in normal irrigation group was 1.05,1.26,2.51 and 1.80 times higher than that in control group.This indicated that the application of biosolid could increase the expression of hormone gene in turfgrass leaves,affect the pathway of plant hormone synthesis and metabolism,and enhance drought resistance in a certain range.5)Compared with the control group,the soil microbial biomass carbon content decreased slowly under sufficient irrigation conditions,and the microbial carbon content in the biosolid treatment matrix was always higher than that in the control group,but without significant difference(P>0.05).This indicated that biosolid had no significant effect on soil microbial biomass carbon content under normal water conservation.Under 50%deficient irrigation,the soil microbial biomass carbon content of all treatments decreased gradually and was lower than that of the normal irrigated soil.On the 30th day of drought,the soil microbial biomass carbon content of biosolid application was 161 mg·kg-1,which was 10.3%higher than that of control treatment(P<0.05).This indicated that the addition of biosolid to soil under drought conditions could increase the microbial biomass carbon content in a certain range and increase the available active ingredients in soil.In conclusion,the application of biosolid can significantly improve the growth and osmotic adjustment ability of perennial ryegrass,increase its photosynthesis and water use efficiency,promote the increase of plant and soil hormones,control drought-tolerant genes expressions and increase soil microbial biomass carbon content,ultimately to enhance the drought resistance of turfgrass. |
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