Characteristics Of Community And Carbon Sequestration With Growth Ages Of Pinus Tabulaeformis Plantation In Ziwuling Area

By taking an abandoned land as control and the young(13~15 year-old), middle-age(25~27 year-old) and mature(41~43 year-old) plantation of Pinus tabuliformis in Ziwuling area of Loess Plateau as research objects, we study the species composition, the distribution characteristic root and soil organic carbon(SOC) and soil active organic carbon in 0~200 cm soil layer, seeking the law of characteristics of community and carbon sequestration and their impact factors, aimed to provide a scientific basis for evaluating the effect of ecological restoration of plantation and soil quality management. The primary results were as follows:(1) The composition of Pinus tabulaeformis plantation has a great change at different growth ages. In the shrub layer, the richness index increased with the growth ages of Pinus tabulaeformis plantation, the dominance index showed middle-age forest > young forest > mature forest, but the variational trend of diversity index was opposite to the dominance index, and the evenness index showed young forest > mature forest > middle-age forest. In the herb layer, the dominance index and evenness index increased with the ages of Pinus tabulaeformis plantation, but the richness index and diversity index decreased. The shrub layer and herb layer in the young forest were more stable than the middle-age forest, and the stability of the shrub layer increased in the mature forest, but decreased in the herb layer.(2) The root characteristics also changed at different growth ages. The root biomass increased significantly with the ages, and decreased with soil depth. In different growth ages, the root biomass with different diameters was the highest in the surface soil, accounted for 49.99%~79.51% in 0~60 cm soil layer. The root length density showed a similar variation law with the root biomass, which increased with the growth ages, and decreased with soil depth. There was no significant changes in specific root length in different growth ages, when the root diameter > 2 mm, 1~2 mm and 0.5~1 mm, the specific root length showed no significant difference, however, when the root diameter < 0.5 mm, the specific root length of increased significantly with the growth stages in 40 ~ 60 cm soil layer.(3) The average SOC content increased with the growth ages of Pinus tabulaeformis plantation, and decreased with soil depth, showing strong enrichment phenomenon in the surface soil. The SOC content and storage increased significantly in compared with abandoned cropland in 0~200cm soil profile. During 0~100 cm soil layers, SOC average content of mature forest, middle age forest and young forest were 2.03, 1.85 and 1.59 times superior to abandoned cropland, respectively. SOC storage in shallow and deep soil layers contributed 61.0%~69.8% and 30.2%~39.0% to total SOC storage in the whole profile(0~200cm) under all of the investigated ages. SOC storage in shallow soil layer was varied significantly in different growth ages, however no obvious difference was observed in deep soil layer in all of the growth ages.(4) The active organic carbon fractions of Pinus tabulaeformis varied significantly at different growth ages. The average content of readily oxidizable organic carbon(ROC), soil microbial biomass carbon(SMBC) and water-soluble organic carbon(WSOC) increased significantly with the growth age, and decreased with the soil depth. The variation ranges of ROC content were big at different growth ages in 0~60 soil layer, and the variation range was stable below 60 cm, which is mainly concentrated in shallow soil layer, accounting for 70.0%~72.9% in 0~200 cm soil layer. The ROC content in shallow soil layer increased significantly in different growth ages, the ROC content in middle-age forest and mature forest was significantly higher than that in young forest. The maximum of WSOC content was in 0~20 cm soil layer in different growth ages of Pinus tabulaeformis, which were 1.21, 1.42 and 1.70 times superior to abandoned cropland, respectively. The variation law of WSOC is similar to the rule of ROC. Compared with the abandoned land, SMBC content increased greatly with the growth ages, the increase amplitude reached 104.84%~373.41% in the 0~100 cm soil layer and 8.99%~289.36% in 100~200 cm soil layer. In addition, the SMBC content increased significantly with the age in shallow and deep soil layer.(5) The correlation analysis showed that the herb community structure had a more significant effect on soil organic carbon and active organic carbon in different growth ages compared with the shrub community. The root characteristics and litter biomass of Pinus tabulaeformis were the main factor affecting soil organic carbon and active organic carbon. In addition, soil particle composition also affected the soil carbon pool to a certain extent.