Effects Of Land Uses On Soil PhytOC And Organic Carbon Of Soil Aggregates

In recent years,the development of social and economic led to the rapid change of land use,such as agricultural land occupied,forest destruction,the abandonment of arable land,the succession of bare land to secondary forest.On the one hand,the change of land use affects the photosynthesis and transpiration of the aboveground vegetation,and then affects the global climate and water cycle.On the other hand,the change of land use also destroys the physical structure of underground soil,resulting in soil erosion and soil carbon storage damage.Small changes in soil carbon pool are likely to disrupt global carbon balance or cause global climate change.And estimating the reserves of soil carbon storage and exploring the spatial distribution of soil carbon pool are the core contents of the carbon cycle of the terrestrial ecosystem.It is an effective way to increase the carbon fixation of soil by improving the stability of carbon accumulation in soil organic carbon pool.Phytolith-occluded organic carbon(Phyt OC)is an important kind of stable organic carbon in soil.Soil aggregates also have a great impact on soil organic carbon fixation,which have many pores.Phyt OC and organic carbon of soil aggregates as stable forms of organic carbon play an important role in regulating the global carbon cycle and mitigate the greenhouse effect.The scholars begin to pay attention to the stability of carbon,but most are still concentrated in different forest types and vegetation and litter layer.It is still lacking that quantitative comparison of soil phyt OC and organic carbon of soil aggregates for different land use.Therefore,this research chooses coniferous and broad-leaved mixed forest,bamboo forest,dry land,paddy field,orchard,weeds land as study object,to investigate the effects of land use change on Eco geographical process,aimed at comparing differences between soil phyt OC and organic carbon of soil aggregates for different land use,and provide scientific guidance for land use management.The main results showed as follows:1.The effects of land use on soil phytolith and phyt OC.In 0-100 cm soil depth,soil organic carbon were bamboo forest(16.75 g·kg-1)> paddy field(16.54 g·kg-1)> dry land(11.90 g·kg-1)> orchard(11.34 g·kg-1)> weeds land(11.19 g·kg-1 > coniferous broad leaf mixed forest(8.16 g·kg-1).In general,the contents of soil phytolith and phyt OC in bamboo forest were significantly higher than those in other types of land use(P<0.05).The order of carbon content of soil phyt OC is bamboo forest(1.96 g·kg-1)> dry land(1.12 g·kg-1)> paddy field(0.90 g·kg-1)> orchard(0.89 g·kg-1)> weeds land(0.81 g·kg-1)> coniferous and broad-leaved mixed forest(0.55 g·kg-1).In the six types of land use,the content of organic carbon in soil phytolith were 24.21~78.27 g·kg-1,the highest in dry land and lowest in bamboo forest.In this experiment,the soil organic carbon,soil phytolith and soil Phyt OC showed a trend of decreasing along with the increase of soil depth,and the soil organic carbon of the topsoil of the coniferous and broadleaf mixed forest,the bamboo forest and the paddy field was significantly higher than that of the other soil layers(P<0.05),but there was no significant surface enrichment phenomenon in soil phytolith and soil Phyt OC,and organic carbon in soil phytolith was mainly distributed in the topsoil and subsoil.2.The effects of land use on soil aggregates and organic carbon in soil aggregatesThe main fraction in six types of land use was macroaggregates,accounting for more than 61.67% of the total fractions.In the soil depth of 0-100 cm,the coniferous and broad-leaved mixed forests,orchard,dry land and paddy field are dominated by small macroaggregates,which account for 49.61%,39.43%,46.01% and 39.02%,respectively.While the bamboo and weeds land are dominated by large macroaggregates,which account for 48.76% and 48.71%,respectively.The mass fraction of silt+clay in the six types of land use was the smallest.In the soil depth of 0-100 cm,the order of mean weight diameter(MWD)in six types of land use was bamboo forest(2.05 mm)> weeds land(2.03 mm)> paddy field(1.65 mm)>orchard(1.26 mm)> dry land(1.17 mm)> coniferous and broad-leaved mixed forest(1.10 mm),and the order of geometric mean diameter(GMD)was bamboo forest(1.09 mm)> weeds land(1.01 mm)> paddy field(0.71 mm)>coniferous and broad-leaved mixed forest(0.59 mm)> orchard(0.53 mm)> dry land(0.47 mm).With the increase of particle size,the contents of organic carbon in soil aggregates increased first,then decreased and then increased,and it showed a trend of "V" shape.Compared with the coniferous broad-leaved mixed forest,the organic carbon in large macroaggregates of bamboo forest and paddy field increased by 7.32 g·kg-1 and 8.48 g·kg-1,respectively,the organic carbon in small macroaggregates increased by 11.15 g·kg-1 and 10.25 g·kg-1,respectively,the organic carbon in microaggregates increased by 6.93 g·kg-1 and 2.65 g·kg-1,respectively,the organic carbon in microaggregates increased by 6.93 g·kg-1 and 2.65 g·kg-1,respectively,the organic carbon in silt+clay increased by 11.01 g·kg-1 and 10.98 g·kg-1,respectively.Except for the dry land,the contents of organic carbon in soil aggregates decreased with the increase of soil depth under the other five types of land use,and showed a significant surface enrichment phenomenon(P<0.05).3.The fixation of soil organic carbon,Phyt OC and organic carbon in soil aggregates for different land useThe soil organic carbon fixation for different land use were significantly different in the soil depth of 0-100 cm,and the variation range was 95.51~202.07 t·hm-2,which the paddy field is the highest,while the coniferous broad-leaved mixed forest is the lowest.The soil Phyt OC fixation for different land use was bamboo forest(23.45 t·hm-2)> weeds land(12.75 t·hm-2)? paddy field(12.75 t·hm-2)> dry land(12.59 t·hm-2)> orchard(12.00 t·hm-2)> coniferous and broad-leaved mixed forest(8.19 t·hm-2).The total organic carbon fixation of soil aggregates in different land use was paddy field > bamboo forest > weeds land > orchard > dry land > coniferous and broad-leaved mixed forest.The organic carbon fixation in large macroaggregate were the highest in bamboo forest and weeds land,and the organic carbon fixation in small macroaggregate were the highest in other four types of land use.To sum up,the contents of soil organic carbon,soil phytolith,phyt OC and organic carbon of each size soil aggregates decreased with the soil profile.Bamboo forest and paddy field were the types of land use of rich silicon and organic carbon,and enlarging the planting of bamboo and rice could help to improve the carbon fixation of soil,so as to adjust the global carbon balance and alleviate the greenhouse effect.