Effects Of Typical Plant Root Productivity And Its Decomposition On Soil Organic Carbon And Nutrients In Southern Ningxia

Since the end of the 20th century,the state has implemented the policy of returning farmland to forests and grasslands.The ecological environment and the vegetation coverage of the Loess Plateau has been improved.At the same time,the increase of roots biomass has played an important role in improving soil nutrients.Therefore,the influence of roots on soil organic carbon and nutrients has received more and more attention in the process of vegetation restoration.The mountainous area of Southern Ningxia which is a part to Loess Plateau has good vegetation restoration.This study was conducted in YunWu mountain which belongs to Southern Ningxia.We used the in-growth cores method for root productivity testing in five different plots which have different plant communities.The root decomposition test was carried out by using the decomposition bag method for three typical plants?Stipa bungeana?Artemisia sacrorum?Thymus mongolicus?.Study the effects of root productivity and root decomposition characteristics on soil organic carbon and nutrients can help us determine the contribution of root to soil nutrients during vegetation restoration.And we hope to provide a theoretical basis for nutrient cycling between plants and soils through this study.The main conclusions are congregated as the following:?1?The composition of plant community and root biomass changed significantly with the age of enclosure.In the 1 year of fencing,the plant community was mainly composed of Cleistogenes squarrosa?Potentilla acaulis;In the 5 years of fencing,the plant community was mainly composed of Thymus mongolicus;In the 10 years of fencing,the plant community was mainly composed of Stipa bungeana?Agropyron cristatum;In the 25 years of fencing,the plant community was mainly composed of Artemisia vestita?Stipa bungeana;In the 30 years of fencing,the plant community was mainly composed of Stipa bungeana?Stipa grandis.After 30 years of fencing,the plant community has basically reached a stable state.Root biomass was mainly distributed in the 0-15 cm soil layer,and it was increased with the.increase of fencing years.?2?As the increase of fencing years,Belowground Net Primary Production?BNPP?of plant communities increased gradually.The BNPP was 61.54 gC·m^-2·yr^-1 after 5years of fencing and it was increased to 140.23 gC·m^-2·yr^-11 after 25 years of fencing.Among the two components that make up BNPP,the proportion of root-derived C?57%⁸1%?was greater than the proportion of?C_root?fine??19%⁴3%?.As the increase of fencing years,the proportion of root-derived C was decreased.The longer of fencing time,the greater contribution of root biomass carbon to BNPP.?3?The loss of root mass had obvious stage.In 0⁴5 days,it belongs to the rapid decomposition stage,and it was the slow stage in 45³60 days.After 360 days of decomposition,the residual rate of roots was between 49%and 87%.Root decomposition rate was positively correlated with initial N content and negatively correlated with initial lignin content.And the decomposition rate was:Artemisia sacrorum>Stipa bungeana>Thymus mongolicus.The change of root mass was basically consistent between in-situ land and abandoned land.?4?During the root decomposition process,carbon was always released,while nitrogen and phosphorus were first released and then enriched.This ws because the carbon in the decomposition process was largely lost and the mass was concentrated,so the nitrogen and phosphorus were concentrated..Among the three roots,the NAL-C of Artemisia sacrorum decreased fastest.Changes of root nutrients was basically consistent between in-situ land and abandoned land.?5?Root decomposition can significantly increase soil organic carbon content,but has little effect on soil total nitrogen and total phosphorus.The improvement effect of root decomposition on the soil organic carbon in the in-situ plots was 0-45 days,and the improvement effect in the abandoned plots was 45-90 days,which was concentrated in the early stage of the decomposition test.The roots decomposition had greater influences on organic carbon in 0-5 cm soil layer than 5-10 cm soil layer.?6?Root decomposition can significantly increase soil microbial biomass carbon?MBC?,dissolved organic carbon?DOC?,but there were less effect on microbial biomass nitrogen?MBN??nitrate nitrogen?NO₃^—-N??ammonium nitrogen?NH₄⁺-N?.Soil active carbon and nitrogen components were sensitive to the change of environment,showing obvious seasonal changes.Overall,soil MBC was most sensitive to root decomposition0-5cm soil layer.