Effect Of Forest Types On Soil Carbon In The Loess Plateau

With the implementation of the project of returning farmland to forests,different forest types coexisted in the loess plateau.Studying on the effects of different forest types on soil bulk density???,soil pH,conductivity,soil total nitrogen?STN?and soil total phosphorus?STP?,especially soil organic carbon?SOC?is of great importance for improving local afforestation management policies and evaluating soil quality.The southern area of Huining County in Gansu province was researched.In the study area,the soil physical and chemical properties in the three forest types?16-year-old of Prunus armeniaca L.and two shurbs?16-year-old of Caragana Korshinskii K.,16-year-old of Hippophae rhamnoides L.??and 15-20 years abandoned lands were compared.The results of the study are as follows:?1?From the perspective of vertical distribution,soil bulk density???decreased with the increase of soil depth in Prunus armeniaca L.,Caragana Korshinskii K.,Hippophae rhamnoides L.and abandoned lands,however,the soil pH and the soil electric conductivity showed opposite trends.There is significant difference between its surface soil and the deep soil in?,pH,and conductivity.The content of SOC,STN decreased with the increase of soil depths in Prunus armeniaca L.,Caragana Korshinskii K.,Hippophae rhamnoides L.and abandoned lands.However,STP content varied with soil depth.The content of STP decreased with the increase of soil depth in Prunus armeniaca L.and abandoned lands.But,the STP of Caragana Korshinskii K.decreased with the increase of soil depth in the top three soil layers,and the max value of STP of Caragana Korshinskii K.appeared in 0.40-0.60m soil layer,and then STP decreased with the soil depth in the rest of three soil layers.The STP of Hippophae rhamnoides L.decreased with the soil depth in the top two soil layers,and then decreased with the further deepening of soil after the maximum value of 0.20-0.40 m soil layer.?2?From the perspective of horizontal distribution,from largest to smallest of the?is Hippophae rhamnoides L.(1.28 Mg·m^-3)>abandoned lands(1.27 Mg·m^-3)>Caragana Korshinskii K.(1.20 Mg·m^-3)>Prunus armeniaca L.(1.16 Mg·m^-3).The mean value of?in Hippophae rhamnoides L.and abandoned lands is significantly higher than the mean value of?in the Prunus armeniaca L.,Caragana Korshinskii K.From largest to smallest of the soil pH is Prunus armeniaca L.?8.51?<abandoned lands?8.57?<Caragana Korshinskii K.?8.65?<Hippophae rhamnoides L.?8.83?.The mean value of soil pH in Prunus armeniaca L.and abandoned lands is significantly lower than the mean value of soil pH in Caragana Korshinskii K.and Hippophae rhamnoides L..From largest to smallest of the soil electric conductivity is Prunus armeniaca L.?80.55?s/cm?<Caragana Korshinskii K.?81.12?s/cm?<abandoned lands?91.49?s/cm?<Hippophae rhamnoides L.?117.36?s/cm?.The mean value of soil electric conductivity in Prunus armeniaca L.and Caragana Korshinskii K.is significantly lower than the mean value of soil electric conductivity in abandoned lands and Hippophae rhamnoides L..From largest to smallest of the SOC is abandoned lands(6.61 g·kg^-1)>Prunus armeniaca L.(5.22 g·kg^-1)>Caragana Korshinskii K.(4.98 g·kg^-1)>Hippophae rhamnoides L.(3.82 g·kg^-1).There were significant differences between three forests and the abandoned lands in average SOC contents.From largest to smallest of the STN is Prunus armeniaca L.=abandoned lands(0.67 g·kg^-1)>Caragana Korshinskii K.(0.56 g·kg^-1)>Hippophae rhamnoides L.(0.37 g·kg^-1).The mean value of STN in Prunus armeniaca L.and abandoned lands is significantly higher than the mean value of STN in Caragana Korshinskii K.and Hippophae rhamnoides L..From largest to smallest of the STP is Prunus armeniaca L.(1.03 g·kg^-1)>Abandoned lands(0.98 g·kg^-1)>Hippophae rhamnoides L.(0.90 g·kg^-1)>Caragana Korshinskii K.(0.82 g·kg^-1).The average STP contents of the three plantations and abandoned lands were significantly different.?3?The results of Pearson correlation analysis and regression analysis showed that the soil pH had a significantly negative correlation with SOC?r=-0.24,P<0.01?,however,?and SOC showed no significant correlation.The conductivity was negatively correlated with SOC?r=-0.24,P<0.01?.SOC,STN,and STP showed extremely significantly positively correlations.The correlation coefficient between SOC and STN was the highest,0.58.The results showed that the SOC of Prunus armeniaca L.was higher than that in shrub forests?Hippophae rhamnoides L.,Caragana Korshinskii K.?.Therefore,the cultivation of Prunus armeniaca L.can accumulate soil C in Huining County.However,compared to abandoned lands,the SOC of forests was significantly lower than that in abandoned lands,which indicated that the abandoned lands was more conducive to the accumulation of soil C in the same period of 15 to 20 years in the region of“Grain for Green Project”.