Effects Of Slope Aspect And Gradient On Soil Organic Carbon In Afforestation Area On The Loess Plateau

Afforestation is widely regarded as an important strategy to increase soil carbon storage and reduce soil erosion.The Loess Plateau has become one of the important afforestation areas in China due to its serious soil erosion and fragile ecological environment.Soil organic carbon in afforestation areas of the Loess Plateau is mainly affected by topographic factors.A thorough understanding of the effects of topographic factors on soil organic carbon in afforestation areas is of great significance to the ecological restoration of arid and semi-arid areas.This article takes the apricot?Prunus armeniaca?plantation area in southern Huining as an example,selects three sampling sites,and analyzes the changes of soil organic carbon,physical and chemical properties,stand density and above-ground biomass under different slope aspects?sunny or semi-sunny vs.shady or semi-shady?,and different slopes?15o²0o?21o²5o?26o³0o?,and in different soil layers?0-10 cm,10-20 cm,20-40 cm,40-60 cm,60-80 cm,and 80-100 cm?to discuss the impact of topographic factors on soil organic carbon in afforestation.The results of the study are as follows:?1?Across a depth of 1 m,the mean soil organic carbon content and total organic carbon storage under the sunny slope are 6.36 g kg^-1 and 69.92 Mg ha^-1,respectively,which are significantly lower than those on the shady s lope(7.74 g kg^-1 and 82.44 Mg ha^-1,respectively).Both the soil organic carbon content and total organic carbon storage in the 1 m soil deepth increase with slope gradient,with soil organic carbon content increasing from 6.48 g kg^-1,to 6.98 g kg^-1,and to7.67 g kg^-1,and total organic carbon storage changing from 70.18 Mg ha^-1,to75.55 Mg ha^-1,and to 82.84 Mg ha^-1,respectively.Slope aspect and gradient interact in influencing soil organic carbon content but not organic carbon storage.?2?There is no difference in stand density between the sunny slope and the shady slope,while the above-ground biomass and soil temperature under the sunny slope(37.75 g m^-2 and 23.53?C,respectively)are significantly higher than under the shady slope.Across a depth of 1 m,the mean soil water content?9.04%?,total nitrogen content(0.86 g kg^-1),and total phosphorus content(0.28 g kg^-1)under the shady slope are 19.89%,24.64%and 154.55%higher than those of the sunny slope,respectively;while the soil bulk density(1.12 Mg m^-3)and pH?8.50?under the shady slopes are 0.02 Mg m^-3 and 0.06 lower than those under the sunny slope,respectively.With the increase of soil depth,soil water content decreases first and then increases,and reaches a minimum value in the 20-40 cm soil layer.The soil bulk density gradually decreases with the soil depth,and the soil pH showes the opposite trend.The total nitrogen under the sunny slope and 26o³0ogradually decreases with soil depth,but there is no change under other slope aspects and gradients.There is no difference in soil total phosphorus among different soil layers.?3?In the 0-100 cm soil layer,as soil depth increases,the soil organic carbon content and organic carbon storage gradually decreases.Soil organic carbon is mainly distributed in the surface layer,and the organic carbon storage in the 0-40cm soil layer is about 50%of the organic carbon storage in the 1 m soil layer.?4?Stepwise regression analysis shows that the main environmental factors affecting soil organic carbon storage are stand density,soil total nitrogen content,and total phosphorus content.These three factors together explain 63.0%of the change in soil organic carbon storage.Soil moisture,total nitrogen content,and total phosphorus content were the main factors affecting soil organic carbon content,and these three together explained 67.2%of the changes in soil organic carbon content.Overall a steep shady slope?vs.sunny gentle slope?is more favourable to the preservation of soil organic carbon,and will,accordingly,be of greater importance with respect to soil organic carbon protection,ecosystem restoration,carbon emission reduction,soil carbon sink and implementation of afforestation policy on the Loess Plateau and similar fragile environments worldwide.