Litter Decomposition Characteristics Of Main Species In Tarim Desert Highway Shelterbelt

The Tarim Desert Highway,which was the important transport highway across the Taklimakan Desert from north to south,it was the world's longest highway that through mobile desert.It is extreme arid climate,scarcity of surface water resource,highly salinity groundwater,intensive wind erosion activity and shifting dunes along the Tarim Desert Highway.To build biological sand control system along the highway on both sides of the Tarim Desert Highway,which was drip irrigation with local salinity groundwater,and have the high stress resistance genus of Calligonu,m L.,Haloxylon Bunge and Tamarix Linn,as the main forestation.Because of the special geographic environment of the Tarim Desert Highway Shelterbelt,the nutrients release by litter decomposition was the main source of plant nutrients and soil fertility.This study has selected the main litter components of Calligonum arborescens,Haloxylon ammodendron and Tamarix ramosissima in the Tarim Desert Highway Shelterbelt as object.From 2012 to 2014,through wild fixed point observation,in-situ decomposition experiment,control experiment,and laboratory analysis of litter,we have studied the dynamics of litterfall biomass and components changed with the planting year of shelterbelt.The litter mass remaining,litter decomposition rate,dynamic variation of elements(C,N,P,K,Ca,Mg,lignin,and cellulose)and element ratios on different litter types,planting year of shelterbelt,different stand ages and regulation treatments.To reveal the litterfall biomass dynamics,to discuss the effects of reguhtory treatments on litter decomposition;to preliminary understanding the decomposition and nutrients release and controlling factors to the main litter type for three species in the Tarim Desert Highway Shelterbelt.The main results as following:In the Tarim Desert Highway Shelterbe lt,the annual litterfall biomass of shelterbelt planting years for 1995a,1998a,2001a,2004a and 2006a were 7.93 t·hm-2;6.19 t·hm-2,10.54 t·hm-2,9.10 t·hm-2 and 8.31 t·hm-2 respectively.The total biomass of litterfall and components among species were decreased in the order of H.ammodendron,T.ramosissirma and C.arborescens with different planting years,and the highest litterfall biomass in autumn.The largest litterfall biomass components were assimilative branches of H.ammodendron,branches of T.ramosissima,and assimilative branches of C.arborescens,accounting for 70.58%?88.93%of the total amount.There was similar seasonal dynamic in different planting year's shelterbelt.Monthly changes in litterfall pattern showed three peaks in the total biomass and biomass for the assimilative branches of C.arborescens and H.ammodendron,and the branches of T.ramosissima,reaching the peaks in March to May,July,and September to November,and the highest amount in November.While no obvious litterfall pattern was found for leaves,seeds and others,they reaching the peaks in different times,branches of H.ammodendron and leaves of T.ramosissima in May to July,seeds of H.ammodendron in September to October,seeds of C.arborescens in June and July,flowers of C.arborescens and T.ramosissima only present from May to August.The genetic and ecological physiological processes and climatic conditions for the species in Tarim Desert Highway Shelterbelt have effect on the dynamics of litterfall biomass and components.The study on litter decomposition in shelterbelt of different planting years showed that litter decomposition rate were decrease as the order of branches of T.ramosissima(0.24?0.32g·g-1·a-1),assimilative branches of C.arborescens(0.17?0.23g·g-1·a-1),and branches of H.ammodendron(0.13?0.18g·g-1·a-1).The lowest decomposition rate was appeared at 1995a planting shelterbelt for three litters,the largest decomposition rate was appeared at 2004a planting shelterbelt for branches of T.ramosissima and assimilative branches of C.arborescens.at 2001a planting shelterbelt for branches of H.ammodendron.Shelterbelt planting years mainly through the micro environmental conditions have significant directly or indirectly effects on litter decomposition rates.The initial litter C,P,K and Mg content were the main controlling factors of early decomposition,initial lignin,cellulose and C/N,N/P ratio were the main limiting factors to later decomposition.During the litter decomposition for 720 days,C element for three litters showed net release pattern,N and P element showed enrichment-release pattern,K element present release-enrichment pattern.Ca and Mg element for assimilative branches of C.arborescens and branches of H.ammodendron were showed accumulation pattern,and for the branches of T.ramosissima was showed release-enrichment pattern.The concentration of lignin and cellulose was showed the rise to reduce trend,the lignin concentration was lower than initial concentration at the later decomposition stage,while the cellulose concentration was always higher than initial concentration.The dynamics of elements was mainly influenced by litter substrate,the properties of elements,decomposition stage and micro environment.The study on litter decomposition under different regulation treatments and litter of different stand ages showed that litter decomposition rates were decreased in the order of assimilative branches of H.ammodendron,the branches of T.ramosissima and assimilative branches of C.arborescens.The different regulation treatments have significantly effects on litter decomposition rate,the decomposition rate for assimilative branches of C.arborescens,assimilative branches of H.ammodendron and the branches of T.ramosissima in control group were 0.53g·g-1·a-1,0.94g·g-1·a-1,0.55g.g-1·a-1.The highest decomposition rate for three litters was under sand buried depth of 10cm treatment(0.92?1.69g·g-1·a-1),lowest under irrigation with 29.7g·L-1 saline water(0.31?0.54g·g-1·a-1).The regulation treatments that have increase the decomposition were the treatments of sand buried(0.69?1.69g·g-1·a-1),irrigation period of 7 days(0.69?1.34g·g-1·a-1),phosphorus and potassium compound fertilizer addition(0.57?1.25g·g-1·a-1),and irrigation with fresh water(0.59?1.12g·g-1·a-1).The regulation measure affected the litter composition rate by changing the micro environment of litter decomposition,while moisture is the main factors.Initial litter N content and ratio of C/N lignin/N were the main factors affecting litter decomposition rates under different regulation treatments.The initial nutrients contents can forecast the initial decomposition rate,and the recalcitrant compounds were the controlling factors for late decomposition rate.The main determining factors for litter decomposition will make changed with the decomposition stage and regulation treatments.During the litter decomposition for 420 days,the influences of regulation treatments on litter element dynamics difference with treatments.The irrigation with fresh water will change assimilative branches of C.arborescens and branches of T.ramosissima to P accumulation at the middle and late decomposition stages.The irrigation with high saline water will change assimilative branches of C.arborescens to Ca accumulation at the middle and late decomposition stages.The sand buried will change assimilative branches of C.arborescens and branches of T.ramosisszima to N accumulation at the initial decomposition stages,and will change assimilative branches of H.ammodendron to P accumulation.The nitrogen fertilizer addition will change three litters to N accumulation,and assimilative branches of H.ammodendron to Ca accumulation.The phosphorus and potassium compound fertilizer addition will change assimilative branches of C.arborescens to N accumulation at the initial and middle decomposition stages,three litters to P and K accumulation.The film will change branches of T.ramosissima to P release,assimilative branches of H.ammodendron to Ca accumulation.The regulation treatments have contributed to the accumulation of some elements,increasing the nutrient return of litter.During the decomposition,the concentration of lignin was showed the rise-reduce trend,because of the litter substrate quality and influence of regulation treatments,the point for declining was different,the lignin concentration for assimilative branches of C.arborescens and branches of T.ramosissima was lower than initial concentration at the later decomposition stage,while assimilative branches of H.ammodendron was always higher than initial concentration.The cellulose concentration was showed rising trend and always higher than initial concentration.The study on litter decomposition with litter of different stand ages showed that the decomposition rate for assimilative branches of H.ammodendron and C.arborescens were highest at stand ages of 7a,for branches of T.rarmosissima were highest at stand ages of 15a.The litter decomposition rate for different stand ages litters were significantly correlated with initial content.the initial C and N content were the main limiting factor in early decomposition,initial lignin and cellulose content were the leading factors for late decomposition.The C,P;K,and Mg element of three litters for different stand ages under surface and buried treatments was showed release pattern.The N element was mainly showed release pattern.The Ca element was mainly showed enrichment-release pattern.During the decomposition process,the lignin concentration was showed rise-downward trend,the lignin concentration was lower than the initial value after decomposition 120 days for assimilative branches of C.arborescens,and always higher than the initial value for assimilative branches of H.ammodendron and branches of T.ramosissima.The cellulose content was always higher than the initial concentration for three litters.In conclusion,the litter initial content was the determine factors on litter decomposition rate,and moisture and nutrient condition have effect on decompo,ition rate and nutrient return in extreme arid shelterbelt.The research on the litterfall biomass and litter decomposition characteristics of Tarim Desert Highway Shelterbelt,not only important in theory for understanding the litterfall biomass dynamics.litter decomposition rate and nutrient cycles under special habitats,but also provides data support and scientific basis for improving soil properties,enhancing soil fertility,and optimizing management treatments for the stability and sustainable development of Tarim Desert Highway Shelterbelt.