Soil Aggregates Stability And Its Carbon, Nitrogen, Phosphorus Ecological Stoichiometry Characteristics Under Vegetation Restoration In Loess Hilly Region

Soil aggregates is the basic unit to sustain soil stable constitution, is also the determining factor of soil fertility. In different aggregate size, the existing form and stability of soil organic carbon(SOC), total nitrogen(TN), total phosphorus(TP) and their stoichiometry characteristics are different, this changing the process of the soil fertility evolution. Thus, the size distribution of SOC, TN and TP contents and their stoichiometry characteristics in aggregates plays a key roll in improving soil fertility. This article chooses Ansai County in Shaanxi Province of China as study area, in view of the soil aggregate among different vegetation types, including 20, 25, 40 and 50 year-old Robinia pseudoacacia plantations and 30 year-old Robinia pseudoacacia plantation, Platycladus orientalis plantation, Caragana microphylla plantation, Bothriochloa ischaemum plantation, Prunus davidiana plantation, Yoder method is used to analyze the soil classification in this study. SOC, TN and TP concentrations and their stoichiometry characteristics in soil aggregates were measured. The relationships among the measured soil attributes were determined using stepwise multiple regression analysis. This research not only provides new evidence that how to improve soil aggregate structure and facility during vegetation restoration process, but also provides a scientific basis for vegetation rehabilitation and reconstruction on the loess hilly region; evaluation of ecological benefits and soil quality evaluation. 1、Stability and distribution of soil aggregates under vegetation restorationThe aggregate particle size distribution in 0-20 cm and 20-40 cm layers appears both sides high and middle low trend under different vegetation types. the particle at the size >5 mm and <0.25 mm aggregate content are higher than others, the soil aggregate content at size 0.25-5 mm were significantly lower than other size fractions. Diffirent vegetation types through affecting the >5 mm size soil aggregates improved the content of soil micro-aggregates. The soil aggregate stability increased along with soil micro-aggregates.The soil aggregate stability under different vegetation types decreased in the following order: Platycladus orientalis plantation>Caragana microphylla plantation >Prunus davidiana plantation> Robinia pseudoacacia plantation>Bothriochloa ischaemum plantation> Solanum tuberosum cropland. The stability of soil aggregates improved through affecting >0.25 mm size soil aggregates under vegetation restoration. MWD value and GMD value under vegetation restoration are significantly increased, but D value law to the contrary. With age rising, the soil aggregate stability at Robinia pseudoacacia plantations presented the trend of increasing firstly, then decreasing. The highest value was observed in 25 a. 2、Accumulative effect of organic carbon and nitrogen in soil aggregates under vegetation restorationThe SOC, TN and TP concentrations in soil aggregates at 0-20 cm and 20-40 cm layers under different vegetation types appears both sides low and middle high trend. the particle at the size >5 mm and <0.25 mm aggregate are lower than other size fractions, the soil aggregate content at size 0.25-5 mm were significantly higher.The soil SOC and TN contents for the 0-20 cm and 20-40 cm soil layers of Platycladus orientalis plantation and Caragana microphylla plantation are significantly higher than other vegetation types. Conpare to cropland, the soil SOC and TN contents for the 0-20 cm and 20-40 cm soil layers were signifigantly increased under vegetation restoration. SOC, TN and TP concentrations in soil aggregates were increased with increasing of forest age, and decreased with decreasing of soil layer. However, the concentrations of TP had smaller variability. Stepwise regression analysis showed that SOC in 0.25-0.5 mm sizes soil aggregates, TN in <0.25 mm and 1-2 mm and TP in 2-5 mm sizes soil aggregates were dominant independent variables affecting SOC, TN and TP concentrations in bulk soils, respectively. However, the highest contribution rates in aggregate to soil SOC, TN and TP concentrations were in <0.25 mm fractions. Altogether, vegetation restoration significantly increased SOC and TN accumulation in all aggregate sizes, especially in the Platycladus orientalis plantation and Caragana microphylla plantation. 3、Soil aggregates ecological stoichiometry characteristics and relationship with soil nutrients under vegetation restorationThe C/N, C/P, N/P in soil aggregates at 0-20 cm and 20-40 cm layers under different vegetation types appears both sides low and middle high trend. the particle at the size >5 mm and <0.25 mm aggregate are lower than other size fractions, the soil aggregate content at size 0.25-5 mm were significantly higher.The soil C/P, N/P for the 0-20 cm and 20-40 cm soil layers of Platycladus orientalis plantation and Caragana microphylla plantation are significantly higher than other vegetation types. Soil aggregates C/N, C/P, N/P were increased with increasing of forest age, and decreased with decreasing of soil layer. The spatial variation of TP was lower than that of SOC and TN but there were significant positive correlations among them. And 0.25 to 2 mm size and <0.25 mm size soil aggregates had a significant effect on soil TOC, TN and TP contents and their ratios. In summary, Robinia pseudoacacia forest’s soil aggregates total nutrient balances were significantly affected under vegetation restoration. The affection mainly reflected in the aggregate particles with sizes raging from 0.25 to 2 mm and <0.25 mm size. Through affecting the 0.25 to 2 mm size soil aggregates improved the capacity of soil nutrient conservation and supply.