陕北黄土高原土壤性质及其生态化学计量的纬度变化特征

为了研究不同纬度下土壤的生态化学计量特征,为黄土高原退化生态系统的植被恢复与重建提供理论依据,通过采集黄土高原陕北地区不同纬度下5 个典型植被区的34 个典型土样,测定并分析土壤养分及生态化学计量指标随纬度和植被的变化特征。结果表明,从南到北土壤碱性逐渐增强;土壤容重逐渐增大;土壤速效钾、硝态氮、铵态氮等速效养分逐渐降低,纬度变异性较大;土壤速效磷纬度变异性小。土壤有机碳、土壤全氮、土壤全磷表现出一致的变化规律,随着纬度的增加逐渐降低,变异性较大,表层土壤大于下层土壤。土壤速效养分也表现出表层土壤大于下层土壤,而土壤容重及土壤pH值表现出下层土壤大于表层土壤。0~5 cm土层土壤的碳氮比(C:N)、碳磷比(C:P)、氮磷比(N:P)分别为8.79~22.00、9.91~35.92、1.06~3.25,5~20 cm土层土壤的分别为8.02~21.03、7.36~24.01、0.82~2.22。土壤的C:N受气候变化影响较小,在黄土高原陕北地区随纬度的升高无明显的变化;而土壤C:P、N:P变异性较大,随着纬度的升高显著下降。随着植被的恢复土壤碳氮磷等养分逐渐累积,森林植被明显高于荒漠植被及沙区植被。土壤有机碳与全氮、全磷之间存在极显著的正相关,C:N 与N:P 存在极显著的正相关,与C:P 存在显著的负相关,C:P 与N:P 存在极显著的正相关。黄土高原土壤C:N较为稳定,不随纬度变化;随着植被的恢复,相对于高纬度地区,低纬度地区更容易缺磷;高纬度地区的植被更容易受到N含量的限制,因此对于该区域应该更加注重N肥的施用。

Ecological Stoichiometry Characteristics and Physical-chemical Properties of Soils at Different Latitudes on the Loess Plateau

The element stoichiometry has been successfully used in indicating community succession and vegetation restoration in recent years. Information about the stoichiometry of soil C, N, and P at different latitudes can help to understand the relationship between vegetation restoration and soil quality, and it is also beneficial to the processes and functions of ecosystem. However, the soil stoichiometry characteristics at different latitudes are poorly documented on the Loess Plateau. To explore the effects of latitudes on ecological stoichiometry of soils in the north of Shaanxi Province on the Loess Plateau, 34 soil sites were sampled from five vegetation zones. Soil organic carbon, total nitrogen, total phosphorus and other properties were analyzed in all soil samples. The results indicated that soil C:N, C:P, N:P ratios varied with latitudes in the range of 8.79-22.00, 9.91-35.92 and 1.06-3.25 in the 0-5 cm soil layer and in range of 8.02-21.03, 7.36-24.01 and 0.82-2.22 in the 5-20 cm soil layer, respectively. Soil C: N ratio did not change much with latitudes. Soil C:P ratio and N:P ratio decreased significantly with the increase of latitude. Soil organic carbon, total nitrogen and total phosphorus were quite consistent with each other in the regular spatial distribution, showing the same trend of declining with the rising of latitude in the studied areas, and their contents were higher in the 0-5 cm soil layer than those in the 5-20 cm soil layer. There were significant positive correlations between soil organic carbon, total nitrogen and total phosphorus. Both soil C:N ratio and C:P ratio were significantly positively correlated to the soil N:P ratio, while the soil C:N ratio was significantly negatively correlated to the soil C:P ratio. Phosphorus was lower in the high latitude areas than that in the low latitude areas. The soil nutrients, such as total nitrogen, phosphorus and soil organic carbon, gradually accumulated with the vegetation restoration, and the contents of these nutrients were significantly higher in forest soil than that in desert and sandy areas. It seemed that the vegetation at higher latitude is more easily limited by nitrogen than that at lower latitude.