| Vegetation restoration and re-vegetation has produced great changes on the land use/cover in the hilly Loess Plateau, especially in the grain for green project. This research is focus on the influence of re-vegetation on temporal and spatial variation of soil organic carbon (SOC) sequestration in the hilly Loess Plateau,and investigate the seasonal variation trend of the components of SOC and soil respiration with the effects of environment factors in the planted woodland during re-vegetation in this region. Aim to contribute for the evaluation of the effects of re-vegetation on soil carbon stock in this region.1) Vegetation restoration and re-vegetation in the hilly Loess Plateau formed a gradually increased soil carbon sink, but it had great temporal and spatial varaitons. SOC density (SOCD) increased along conversion chronosequence were also much fitted to the Polynomial curve and the correlation between observed data and the simulated curves were all significantly in planted woodland, shrubland and abandoned cropland. The SOCD changed slightly in the first 10/15yrs when revegetation on cropland, but during the nest 20/25yrs the accumulation rates of SOCD dramatically increased to 0.66-0.23 t·hm-2·yr-1. This demonstrated that SOC could accumulate more efficiently when re-vegetation lands were preserved for long time. SOCD in restored wild grassland were 8.38 t·hm-2 and 14.11 t·hm-2 for conversion 9 yr and 35 yr, which were pretty similar to those of abandoned cropland. But SOCD in restored wild shrubland was significantly higher than that of revegetated croplands and increased rapidly with accumulation rate of 0.93 t·hm-2·yr-1 in the first 9yrs, and 0.56 t·hm-2·yr-1 in the future 25 yrs. Re-vegetation dominated the SOCD distribution in this region, SOCD spatial distribution of a watershed was coincided with land use distribution. SOC concentration decreased along soil profile, and the surface soil (0-5cm) was the most sensitive soil layer of SOC dynamics under land use change. SOCD in semi-shady to shady slope was mostly significant higher than semi-sunny to sunny slope since conversion 9yr to 35yr. And valley slope was significant higher than gulley slope in conversion 9 yr. Generally SOCD in gentle slope was higher than steep slope, and top of replat was higher than valley slope in conversion lands.SOC stratification ratio (SR) had a consistent significant linear growth trend along re-vegetation chronosequence, and annual increase rates of SR (0-5:5-10cm) and SR (0-5:20-30cm) to that of SOCD were about 1:5 and 1:15, which meant that SR of shallow soil layer (0-10cm) could estimate SOC accumulation of 0-30cm depth. Soil quality parameters (i.e., soil organic matter (SOM), total N (TN) and available N) improved significantly during rehabilitation and had the same variation as SR with re-vegetation years. SR also indicated the differences of SOC sequestration and soil quality (i.e., SOM, TN and available N) among different re-vegetation types. But SR could not precisely indicate the variation of SOC sequestration and soil quality of different agricultural managements in our study, because all these managements contented soil disturbance or surface organic matter loss. SR (0-5:5-10cm, 0-5:20-30cm) strongly correlated with SOCD of all sites in this study (R2=0.5214, 0.7915), as well as main soil quality parameters (i.e., SOM, TN and available N). The results showed that SR was an efficient indicator of SOC sequestration and soil quality, and SR (0-5:20-30cm)>2 could indicate a distinct improvement of SOC sequestration and soil quality as ecosystem rehabilitated in the hilly Loess Plateau.The deep soil layer of the hilly Loess Plateau conserved a large amount of soil organic carbon. The results demonstrated that total SOC storage will be underestimated by approximately 1/3 in this region if SOC was only measured to a depth of 1m. For the entire revegetation chronosequence (9yr—34yr) the increase in SOC storage down to a depth of 2m (43.02 t·hm-2) was distinctly higher than that in 1m (34.65 t·hm-2).The average daily soil respiration rate in growing season were 2.15, 2.14 and 2.75μmol·m-2·s-1 for 3 kinds of planted woodland ch9h (revegetation 9yr planted woodland in semi-sunny slope), ch9y (revegetation 9yr planted woodland in semi-shady slope) and ch25 (revegetation 25yr planted woodland in semi-sunny slope), which were significantly higher than 0.20, 0.37 and 0.49μmol·m-2·s-1 in non-growing season. But the soil respiration in non-growing season also accounted for 10-18% of that in growing season. The minimum soil respiration rate occurred in January in all of the 3 planted woodlands, and the maximum soil respiration rates occurred in July or September. The annual soil respiration in ch25 was significantly higher than those in ch9h and ch9y, and soil respiration rate of ch9y were higher than those of ch9h in non-growing season. The relationship between soil respiration and variation of temperature and soil water content indicated that in normal range of temperature and soil water content, higher temperature and soil water content would lead to much higher soil respiration in this region. Seasonal variation of soil respiration was mainly controlled by temperature, but soil water content, easily oxidized SOC and soil microbial biomass carbon could modified the variation of soil respiration. However, the difference of total soil respiration among different planted woodlands was determined by the concentrations of easily oxidized SOC and soil microbial biomass carbon.SOC concentration decreased in growing season in all of the 3 kinds of planted woodlands, which was just opposite to the seasonal variation of soil respiration. And the variation of SOC concentration had a strong correlation with these concentration variations of SOC active components. In spring and autumn, there were the moderate temperature and soil water content conditions, and easily oxidized SOC and soil microbial biomass carbon reached high concentrations. |
PDF Full Text Request