Carbon Sequestration By Fine Roots Of Typical Shrub Plantations In Alpine Sandy Land And Its Effect On Soil Carbon Pool

It is generally believed that the change of soil carbon pool mainly depends on the two processes of vegetation carbon return and soil organic carbon decomposition.The effect of fine roots on soil carbon sequestration may be greatly underestimated if we ignore the fine roots litter residue as the stage of soil carbon stabilization and its accumulation effect.The alpine sandy land is a relatively serious area because that fragile and sensitive ecological environment.A lot of practice has proved that vegetation restoration is an important approach to ecological restoration of degraded land,and the degraded and sandy soil in the process of restoration usually has a great potential of carbon sequestration.However,the carbon sequestration capacity of plantations after vegetation restoration has not been systematically studied,especially the role of fine roots in soil carbon sequestration in vegetation restoration areas is still unclear.The research object of this paper is the typical shrub plantations of different growth stages(Caragana intermedia: 5a young stage,12 a early middle stage,18 a late middle stage,32 a mature stage)and different planting patterns(5a pure forest of Caragana intermedia,5a pure forest of Salix cheilophila and 5a mixed forest of Caragana intermedia and Salix cheilophila)in Gonghe basin.In this paper,biomass density,turnover rate and decomposition process of fine roots in different plantations is measured using root drilling method,micro root canal method and burying bag method.We estimate the accumulation effect of fine root litter in different plantations,and analyze the carbon sequestration effect of plant fine root and its influence on soil carbon pool by combining the soil carbon storage and heterotrophic respiration rate of plantation land.The results are as follows:(1)The density of fine root biomass in the middle caragana plantation increased with the growth of the age of the plantation,and the phenomenon of "self-thinning" occurred in the mature stage.The distribution of fine roots is shallow,that is,more than 50% of them are concentrated in the 0-45 cm soil layer,and the adaptability of fine root distribution to soil moisture pattern in sandy area increased with the growth of forest age and reached the same level at maturity.With the increase of forest age,the turnover rate of plantations in deep soil gradually increased,among which the turnover rate of young and early middle age was higher in surface soil(0-30cm),while that of late middle age and mature stage was higher in deep soil(60-120cm).The utilization strategy of vegetation on soil water was influenced by the distribution and turnover characteristics of fine roots,which showed that the soil moisture with high turnover of fine roots was mainly used when there was no replenishment of natural precipitation,and the surface soil water was mainly used after precipitation.(2)The fine root litters in the middle jinjia plantation had significant accumulation effect,which was mainly affected by the density of fine root biomass and the amount of annual litters.The early stage of fine root decomposition is faster but the later stage is slower(it takes about5.74a-11.85 a to decompose 95%),and there are different degrees of carbon enrichment during decomposition.At the same time,the carbon sequestration of fine roots increased with the growth of recovery period,and it could affect the spatial and temporal pattern of soil carbon storage of plantation land,and improve the carbon sequestration potential of deep soil.It is shown that the longer the recovery period is,the larger the soil carbon reserves are,and the higher the carbon reserves are in the surface soil,while the carbon sequestration potential is greater in the deep soil.(3)The soil moisture content of each plantation is at a low level(Q10 < 2).The soil carbon release rate of intermediate caragana decreased gradually in the order of young stage,early middle stage,mature stage and late middle stage.It is also affected by soil carbon pool and environmental factors.In terms of soil carbon pool,it is mainly related to plantation soil carbon storage(negative correlation)and deep fine root litter decomposition(positive correlation).In terms of environmental factors,it is mainly affected by soil hydrothermal conditions and natural rainfall,as shown in the following aspects: when there is no interference from natural rainfall,it is mainly affected by the upper layer(0-60cm)soil temperature.The influence of soil moisture content on rainfall is greater,temperature sensitivity increases significantly,and the sensitivity to deep soil temperature is stronger.Natural rainfall has an inhibitory effect on soil carbon release,but the next day after rainfall will significantly increase the carbon release rate(lasting about 2-5d),which is not conducive to the carbon sequestration of fine root and soil.(4)Mixed forest soil carbon sequestration ability and the adaptability of soil moisture in sandy pattern is better than that of pure forest,and both plant fine roots are showing the growth of convergence strategy(biomass density,spatial distribution,turnover,etc.),and it formed the different layers of soil resources utilization,the characteristics of fine root distribution in the adolescent period is exactly the same as that of woodland soil moisture pattern.The fine root litters in all plantation modes have obvious accumulation effect,and their contribution rate to soil carbon reserves increases with the growth of recovery period,and they all show a large amount of carbon sequestration in surface soil(0-30cm).The release rate of soil carbon in different planting patterns of plantation decreased gradually according to the sequence of Caragana intermedia pure forest,mixed forest and Salix cheilophila pure forest.The soil carbon release rate of each plantation is mainly related to the carbon storage(negative correlation)and fine root decomposition(positive correlation)of the plantation land surface soil.However,natural rainfall can promote the soil carbon release rate of woodland,which is not conducive to the carbon sequestration of fine roots and soil.This paper researches the influence of the fine root characteristics(spatial distribution,turnover rate and decomposition)on the carbon sequestration of the fine root of the shrub plantation in different growth stages and planting modes of Gonghe basin systematically and comprehensively,and analyses the relationship between carbon sequestration of fine roots and soil carbon pool of plantation land deeply,and the contribution of plant fine root carbon sequestration to soil carbon sequestration in alpine sandy land is clarified in this paper.The results show that the fine root litter of plantation has a significant accumulation effect,and its carbon sequestration can affect the spatial-temporal pattern and carbon sequestration potential of plantation soil carbon pool,while natural rainfall promote the decomposition of fine root litter and soil carbon pool,which is not conducive to carbon storage.At the same time,mixed mode and long-term restoration are beneficial to improve the environmental adaptability and carbon sequestration ability of shrub plantation.