采用室外取样与室内分析结合的方法对祁连山高寒杜鹃灌丛草地不同放牧干扰条件下土壤、根系养分化学计量比进行研究。结果表明: 1)植物群落地下生物量随土层深度增加而迅速减少, 60%~70%根系聚集于0~10 cm土层, 随放牧压力增加活根向土壤深层转移。2)总根系生物量及其C、N、P储量随牧压增加均下降, 重牧与轻牧相比C、N、P养分储量分别下降26%、17%、27%; 表层单位质量活根C含量轻牧最高、N含量中度放牧最高、P含量重牧最高; 死根N、P变化与活根相反。3)随牧压增加土壤有机碳、全氮密度以及N、P速效养分均上升, 全磷含量相对稳定, 但表层全磷含量下降。数据分析得出, 休牧增加了根系生物量的同时, 表层土壤根系的C/N、C/P比值升高, N/P比值降低。说明根系对土壤C积累及养分循环起重要作用, 而生长季休牧有利于高寒灌丛草地土壤养分保持, 这与高寒地区植物生长缓慢特性相适应。
Alpine range is sensitive to global climate change and artificial disturbances and generally adapts to changes in external environment by adjustments in chemical elements. Research on belowground ecosystems is critical for ecological restoration. A combination of field and lab experiments was conducted to study the nutrients characteristics of soils, roots of alpine shrublands in Qilian Mountains under different grazing disturbances. The dynamics of root system phytocoenosis in alpine regions were also analyzed. The results showed that underground biomass of the plant community decreased with increasing soil depth. About 60%~70% of root biomass was concentrated in the 0~10 cm soil layer. Also with increasing grazing intensity, living roots penetrated deeper into the soil. Total root biomass along with carbon, nitrogen and phosphorus contents decreased with increasing grazing intensity. Compared with lightly grazed areas, C, N and P contents in heavily grazed areas decreased by 26%, 17% and 27%, respectively. Per unit mass surface living roots and carbon were highest in lightly grazed areas, nitrogen highest in medium grazed areas and phosphorus highest in heavily grazed areas. Variations in dead root N and P contents were inversely correlated to those in living root N and P contents. With increasing grazing intensity, soil organic carbon, total nitrogen, and available N and P increased. However, the content of total phosphorus remained relatively stable even though surface total phosphorus content decreased. Under non-grazing treatment, root biomass increased, C/N and C/P ratios increased both in surface soils and roots, and N/P ratio decreased, compared with grazing treatments. This implied that roots were vital elements for both soil carbon accumulation and nutrient cycle. Non-grazing in vegetation growth seasons facilitated plant recovery and better growth and high plant nutrient efficiency. Non-grazing during vegetation growth seasons was an effective way of promoting recovery of fragile alpine shrub for high ecological functions and economic values.