恢复年限对亚热带次生林土壤化学计量比的影响

Effects of restoration years on soil stoichiometric ratios in subtropical secondary forests

土壤化学计量比是衡量土壤有机质组成及质量的有效指标。多数研究关注土壤碳(C)、氮(N)、磷(P)及化学计量比,而较少关注森林恢复过程中土壤钾(K)、钙(Ca)和镁(Mg)及化学计量比的变化。本研究以亚热带自然恢复的5、8、21、27、40年林分为研究对象,以自然恢复的天然林为对照,分析土壤K、Ca、Mg及化学计量比随林分恢复年限的变化。结果表明:随着土层的加深,土壤C和N含量显著降低,土壤元素化学计量比除K:P、Mg:P和P:Ca外均显著降低。随森林恢复年限的增加,0~10cm土层C和N含量显著增加,10~20cm土层Ca含量显著增加,20~40cm土层全磷含量显著降低,各土层K和Mg含量均无显著变化。随森林恢复年限的增加,0~10cm土层C:Ca、N:Ca、P:Ca显著增加,20~40cm土层C:P、N:P和K:P显著增加,而P:Ca显著降低。所有土层K:P和Mg:P与总磷含量呈显著负相关,C:Ca和N:Ca与矿质氮、有效磷、速效钾含量呈显著正相关。随着次生林恢复年限的增加,研究区土壤普遍受到P限制,恢复后期Ca的限制逐渐增强,进而导致了多种养分元素的限制。

Soil stoichiometric ratios serve as valuable indicators for the composition and quality of soil organic matter. While available studies predominantly examine the soil stoichiometric ratios of carbon(C), nitrogen(N), and phosphorus(P), limited attention has been paid on the influence of forest restoration on soil stoichiometric ratios of potassium(K), calcium(Ca), and magnesium(Mg). We analyzed soil K, Ca, and Mg content, as well as elemental stoichiometric ratios, in secondary forests with varying restoration periods(5, 8, 21, 27 and 40 years) and a natural forest, in order to examine the impact of forest restoration on soil stoichiometry. The results showed that soil C and N contents decreased significantly with increasing soil layers. Soil stoichiometric ratios decreased significantly with increasing soil layers except for K:P, Mg: P, and P:Ca. With the increases of forest restoration years, soil C and N contents significantly increased in 0-10 cm soil layer, Ca content in 10-20 cm soil layer significantly increased, and total P content in 20-40 cm layer significantly decreased. However, soil K and Mg contents in each soil layer did not differ among five restoration ages. With the increases of restoration years, C:Ca, N:Ca and P:Ca in 0-10 cm soil layer significantly increased, and C:P, N:P, and K:P in 20-40 cm soil layer significantly increased, while P:Ca in 20-40 cm soil layer significantly decreased. In all soil layers, K:P and Mg: P were significantly and negatively correlated with soil total P content, and C:Ca and N:Ca were significantly and positively correlated with soil mineral N, available P, and available K content. With the increases of the restoration ages of secondary forests, soils are gradually P-limited and progressively restricted by Ca element in the later years, leading to the limitation of multiple nutrients.