The Decomposition Characteristics Of Grass Litter And Its Effects On Soil Properties In Loess Hilly Region

Litter,as an important carrier connecting plant and soil in the grassland ecosystem,cannot be ignored in the vegetation restoration and soil improvement of grassland.With the accumulation and decomposition of litter and root,the changes in the nutrient cycle of grassland ecosystem has been significantly observed,and a series of changes in soil chemical and biological processes have been reported.It is of great theoretical and practical significance for the ecological restoration of degraded grassland to study the characteristics of litter decomposition and its effect on soil properties.In this study,aiming at the decomposition of grass leaves and plant roots?Stipa bungeana Trin/St.B,Artemisia sacrorum Ledeb/Ar.S,Thymus quinquecostatus Celak/Th.Q?in the grassland succession in the loess hilly region,the litter bag method was used to simulate the decomposition process of single leaf litter,mixed leaf litter and root.The variations of litter mass remaining and substrate quality?total carbon,total nitrogen,total phosphorus,lignin and cellulose?,and the release or enrichment characteristics of microelements?Ca,Mg,Fe,Mn,Cu,Zn?were researched.The effect of litter decomposition on soil chemical properties,microelements,soil enzyme activities and microbial community were studied.We simulated the process of litter decomposition using the Olson model and predict its turnover time,quantified the characteristics of nutrient release and lignin and cellulose degradation,explored the effects of litter decomposition on soil chemical and biological properties,and clarify the correlation mechanism between litter decomposition characteristics and soil properties,and revealed the ecological conservation function of leaves and plant roots in grassland,in order to provide theoretical basis for clarifying the earth element cycle in grassland ecosystem.The main conclusions are as following:?1?With litter decomposition,the decomposition processes of single leaf litter,mixed leaf litter and plant root were significantly different.Decomposition processes of single leaf litter were divided into four stages:fast decomposition,slow decomposition,secondary rapid decomposition and keeping stable.The decomposition rate of mixed leaf litter decreased with time.The decomposition processes of plant root showed as:fast decomposition,slow decomposition and secondary rapid decomposition.The decomposition rate of single leaf litter and root decreased as Ar.S>St.G>Th.Q.The mixture of St.G and Ar.S leaf litter and the mixture of St.G and Th.Q leaf litter were observed synergistic effect to promote the decomposition process.The determination coefficient R² and significance test showed that the Olson model could well represent the decomposition process of litter and plant roots in this region.Using the Olson model,the decomposition time of single leaf litter,mixed leaf litter,root would require 11.0¹8.0 a,9.2¹0.7 a,and 15.9²3.3 a,respectively.?2?After 1035 d-decomposition,the total carbon,total nitrogen,total phosphorus,cellulose and lignin of single leaf litter,mixed leaf litter and root were all released.Litter carbon presented wave release,with a release rate of 64.3⁸5.1%;litter nitrogen showed rapid release,enrichment,wave release,in turn,with a release rate of 45.7⁶7.7%;litter phosphorus presented wave release,rapid enrichment,gradually release,remaining stable,with a release rate of 30.8⁹0.7%;litter cellulose presented rapid release in the early stage and slow release in the later stage,with a release rate of 72.3⁹3.6%;litter lignin was observed enrichment and release alternately,with a release rate of 43.3⁶2.6%.The release rate of carbon and lignin between leaf litter and root were almost the same,the release rate of nitrogen,phosphorus,and cellulose of leaf litter were observed higher than that of root.The mixture of leaf litter showed different non-additive effect on litter nutrient release.The mixture of St.G and Ar.S leaf litter and the mixture of St.G and Th.Q leaf litter showed a synergistic effect on carbon release and cellulose degradation,and a synergistic effect in the early stage and a antagonism effect in the later stage on nitrogen release and phosphorus release;The mixture of St.G and Th.Q leaf litter showed a synergistic effect on litter lignin degradation,and The mixture of St.G and Th.Q leaf litter was observed a antagonism effect on litter lignin degradation.?3?Except the Cu and Zn of St.B litter,after 1035 d-decomposition,the amounts of Ca,Mg,Fe,Mn,Cu and Zn of single leaf litter,mixed leaf litter and plant root were observed release.The release rate of microelements of leaf litter decreased as Mg>Ca>Cu>Fe>Mn>Zn,and the release rate of microelements of roots decreased as Ca>Fe>Mg>Zn>Mn>Cu.As litter decomposition progresses,the variations of litter Ca,Mg and Cu showed a characteristic of leaching,enrichment,and release,the release rates of litter Ca,Mg and Cu were 62.0⁷9.1%,58.4⁷7.8%,0.4⁶4.9%,respectively.The changes of litter Fe,Mn,and Zn presents enrichment and wave release in turn,the release rates of litter Fe,Mn,and Zn were21.8⁷1.7%,10.4⁵0.8%and 12.3⁶0.0%.The changes characteristics and release rate of Ca and Mg of single leaf litter,mixed litter and root were similar.The release rate of Fe,Mn,and Zn were higher in leaf litter than plant root;the release rate of Cu was higher in Ar.S and Th.Q leaf than root.The mixture of St.B and Ar.S leaf litter and the mixture of St.B and Th.Q leaf litter showed synergistic effect on Gu,Mg and Zn release,and antagonism effect on Ca release.The mixture was found antagonism effect on Fe and Mn release in the early stage,and synergistic effect in the later stage.?4?The decomposition of litter and root had significant effects on soil organic carbon?SOC?,chemical properties and microelements.As litter decomposition progresses,SOC showed the change characteristics of wave decline and rapid rise alternately,soil nitrogen showed the variation of rise,stable and decline alternately,soil nitrate nitrogen?NO₃-N?,soil ammonium nitrogen?NH₄-N?,and soil available phosphorus?AP?presented rise and decline alternately.The litter decomposition could significantly improve SOC,NO₃-N,NH₄-N,and AP,the decomposition of leaf litter can increase soil total nitrogen,while plant root had no significant effect on soil total nitrogen.At the end of decomposition,SOC,NO₃-N,NH₄-N,and AP of litter treatments were 0.50¹.15 g/kg,0.91⁶.85 mg/kg,0.47².87 mg/kg and 0.49².62 mg/kg higher than that that of control,respectively.The decomposition of leaf litter and root resulted in the increasing of soil Ca and Mg,the increasing levels showed as leaf litter>root.The effect of litter decomposition on soil Fe,Mn,Cu and Zn was found different.Litter decomposition could enhance soil Fe,Mn and Cu in the mid stage,and had little effect on soil Fe,Mn and Cu in the end.Except St.B leaf litter and mixed leaf litter,other litter decomposition resulted in the decrease of soil Zn.The mixture of leaf litter showed different non-additive effects on soil chemical nutrients and microelements.?5?The decomposition of single leaf litter,mixed leaf litter and root could improve the activities of soil invertase,urease,and alkaline phosphatase in the whole process.At the end of litter decomposition,soil invertase of single leaf litter,mixed leaf litter and root treatment was 3.38⁷.10 mg glucose/g/24h,0.95⁵.48 mg glucose/g/24h,1.04².82 mg glucose/g/24h higher than that of control,soil alkaline phosphatase of single leaf litter,mixed leaf litter and root treatment was 0.62¹.25 mg phonol/g/24h,0.49¹.01 mg phonol/g/24h,0.21⁰.51 mg phonol/g/24h higher than that of control.As litter decomposition progresses,soil invertase and alkaline phosphatase showed a wave characteristic of rise and decline alternately,soil urease increased first and decreased later.Soil invertase,urease,and alkaline phosphatase in the leaf litter treatment was obviously higher than those of root.Compared to single leaf litter,the mixture of leaf litter showed non-additive effects on the development of soil enzyme activity.The mixture of St.B and Th.Q leaf litter revealed synergistic effect on the increasing of soil invertase and alkaline phosphatase,while the mixture of St.B and Ar.S leaf litter showed antagonism effect.The mixture of St.B and Th.Q leaf litter and St.B and Ar.S leaf litter revealed synergistic effect on the increasing of soil urease,and antagonism effect on the increasing of soil urease.?6?The decomposition of leaf litter and root altered the structure of soil bacteria and fungi.The soil bacterial community is mainly composed of Actinobacteria?38⁴5%?,Proteobacteria?16²1%?,Chloroflexi?13¹7%?,Acidobacteria?9¹8%?and Cyanobacteria?1¹2%?.The fungal community mainly consisted of Ascomycota?46⁷0%?,Glomeromycota?11²4%?and Basidiomycota?13⁴0%?.The decomposition of leaf litter and plant roots altered the structure of soil microbial community.The litter decomposition increased the relative abundance of acidobacteria and chloroflexi,and the relative abundance of glomeromycota,decreased the relative abundance of basidiomycota.Additionally,the decomposition of St.B leaf litter and St.B-Th.Q leaf litter enhanced the relative abundance of Ascomycota.The litter decomposition enhanced the diversity and richness of soil bacteria and fungi.The diversity and richness of soil bacteria was found no significant differences in different litter type treatment.The richness of soil fungi in different litter type treatments decreased as root>single leaf litter>mixed leaf litter,the diversity of soil fungi of leaf litter treatment was higher than that of root.?7?The results of correlation analysis of litter decomposition characteristics and changes of soil properties showed that the transfer process of N,Ca,Mg,Fe,Cu between soil and leaf litter were observed,and the transfer process of N,P,Ca,Mg,Fe between soil and root were found in the study.The effect of litter decomposition on soil enzyme activity and soil available nutrients showed almost the same,which was controlled by the litter decomposition characteristics.During litter decomposition,soil organic carbon,chemical nutrients and so on are influenced by the changes of substrate quality,and then altered soil microbial community indirectly.The above results indicated that the decomposition characteristics of St.B,Ar.S and Th.Q leaf litter root were different,and controlled by litter substrate quality and microelements collectively.The ecological conservation of grassland soil was sustained by the decomposition of leaf litter and root.The decomposition of leaf litter and root had a significant impact on soil organic carbon,available nutrients,medium and microelements and enzyme activity,which changed the soil microbial community and increases the diversity and richness of soil bacteria and fungi indirectly.