黄土丘陵区刺槐、辽东栎林地土壤碳、氮、磷生态化学计量特征

黄土高原中部的丘陵沟壑区位于半湿润、半干旱气候带,生态环境脆弱,水土流失严重,植被恢复是该地区水土保持与生态重建的重要措施。辽东栎天然次生林和刺槐人工林是该地区典型的森林植被类型。以黄土丘陵森林分布区边缘的两种主要森林类型为对象,通过采集林地不同深度土壤样品,对比分析两种林地土壤中碳、氮、磷含量的计量关系及垂直分布特征,旨在探明该区域土壤化学计量特征及主要影响因素。结果表明:(1)在两种林地类型中,土壤有机碳与全碳含量呈正相关关系,两种林地可用同一曲线进行拟合,说明特定土壤类型在同一区域其有机碳和无机碳相对含量基本稳定。(2)土壤有机碳与全氮比值在10左右,在不同土层深度无明显变化;而土壤全碳与全氮比值则随土壤深度的增加而增加,超过1 m以后呈现饱和曲线的变化趋势。(3)土壤氮磷比随土壤深度的增加呈幂次型降低。

Ecological stoichiometry characteristics of soil carbon, nitrogen, and phosphorus in an oak forest and a black locust plantation in the Loess hilly region

Carbon, nitrogen, and phosphorus are the major plant growth elements, and are mainly absorbed by the plant from the soil. Research on the relationships among these elements is critical for understanding the mechanisms driving the status and balance of these elements in various soils of different land use types. However, to date, there have been relatively few studies on the ecological stoichiometry characteristics of soil carbon, nitrogen, and phosphorus in the sub-humid and semiarid Loess hilly region, which is characterized by severe soil erosion and a fragile ecological environment. Vegetation restoration is one of the most important management approaches for controlling soil and water loss, and for improving soil quality. In the sub-humid and semiarid Loess hilly region, Quercus liaotungensis (oak), which dominates the secondary forests, and Robinia pseudoacacia (black locust) plantations are the major natural and planted vegetation types, respectively. In this study, we investigated the soil organic carbon (SOC), soil total carbon (STC), soil inorganic carbon (SIC), total nitrogen (N), and total phosphorus (P) contents throughout the soil profiles of the two forest types. In addition, the relationships among the aforementioned fractions were analyzed to reveal the ecological stoichiometry of forests in the region. Three stands were selected for each forest type, and a 20 m × 40 m representative plot was surveyed in each stand. Soil samples were collected (using a soil auger with a 6 cm internal diameter) at three points diagonally across the plot at depths of 0-10, 10-20, 20-30, 30-50, 50-100, 100-150, and 150-200 cm. The cored samples from the same depth in each plot were mixed, and all samples were then transferred to the laboratory for further analyses. Prior to the analysis, samples were air-dried, ground to powder, and passed through a 0.25-mm sieve. The SOC content was determined using the potassium dichromate-sulfuric acid oxidation method. The N and P contents were determined using the perchloric acid sulfate cooking method. A FOSS-8400 fully automated Kjeldahl analyzer was used for N quantification. The STC and N contents were also determined using an elemental analyzer. The main results were as follows: (1) SOC and STC contents were linearly correlated (P < 0.0001), and the relationship between SOC and STC could be fitted using the same curve for the two forest types. The relative SOC and SIC contents were stable within a specific soil type from the same area, independent of forest type; (2) in general, the SOC:N ratio was approximately 10, but the STC:N ratio increased with increasing soil depth, and stabilized gradually (saturation curve); and (3) the soil N:P ratio decreased with an increase in soil depth (power law curve). These results provide basic information for the clarification of stoichiometry characteristics in relation to vegetation type and soil depth in this region.