青藏高原矮嵩草草甸地下和地上生物量分配格局及其与气象因子的关系

基于2006—2015年青海海北站10年生物量及气候因子监测数据,分析了青藏高原高寒矮嵩草草甸生物量的季节及年际动态,并探讨了气候因子对其影响。结果表明:(1)季节尺度上,高寒矮嵩草草甸地上生物量表现为单峰变化曲线,8月为其峰值点,为(345.72±27.01) g/m~2,代表了高寒草甸的地上净初级生产力。而地下根系的现存量变化较为复杂,其中5—7月呈现持续上升趋势,8月快速下降,之后9月份急剧,且各月份之间未达到显著水平(P0.05);年际尺度上,10年间高寒矮嵩草草甸地上生物量整体呈现波动增加趋势,2014年为其峰值点,达(437.12±32.01) g/m~2。地下生物量呈现波动性变化,变异较大,10年间平均值为(2566.99±138.11) g/m~2;(2)高寒草甸光合产物分配主要分布在地下,80%地下根系生物量分布于地表0—10 cm土层,且不同土层根系生物量占总地下生物量的比值在不同月份较为稳定。(3)气候因子中,大气相对湿度是影响高寒草甸地上生物量大小的主要因素;而气候因子对地下根系生物量的影响极为微弱。研究表明,高寒嵩草草甸对环境变化具有较高的自我调节能力,且高寒草甸的演化受制于人类干扰,而非气候变化。

Allocation patterns of above-and belowground biomass and its response to meteorological factors on an alpine meadow in Qinghai-Tibet Plateau

Qinghai-Tibetan Plateau is the highest and largest plateau on earth, and almost 60% of its area is occupied by natural alpine grassland (alpine steppe and meadow). Owing to its unique climatic conditions, together with little human disturbance, it provides a unique opportunity to test the above-and belowground biomass allocation patterns and its response to meteorological factors. In the past, many studies have been conducted between above-and belowground biomass and environmental factors on alpine meadows in the Qinghai-Tibet plateau, but large uncertainties still exist owing to the difficulty determining belowground biomass. Therefore, the allocation between above-and belowground biomass is still a central issue in plant ecology. In this study, we examined seasonal and interannual variations in biomass based on long-term monitoring data sets. Moreover, a general regression analysis was applied to examine the relationship between above-and belowground biomass and meteorological factors. The results showed that (1) at a seasonal scale, the aboveground biomass showed a unimodal relationship from May to August, with a peak in August (345.7±27.01) g/m² that represented the net primary productivity of alpine meadows, which then decreased from August to September. Thebelowground biomass was relatively complex than the aboveground biomass, which increased from May to July and decreased rapidly in August; no significant difference was observed in the belowground biomass among these months. At an interannual scale, aboveground biomass showed a significant increased trend during 2005-2015, reaching a maximum in 2014(437.12±32.01) g/m². The belowground biomass was relatively stable during 2005-2015, but the year-to-year variations in belowground biomass was larger than that of the aboveground biomass(CV=24.30%); the 10-year average of belowground biomass was (2566.58±138.11) g/m²; (2)the photosynthetic products were mainly distributed in the belowground biomass, with 80% root biomass distributed in the 0-10 cm soil layer. In addition, the distributed fraction was relatively stable across all soil depths (0-10, 10-20, 20-30, and 20-40 cm) among months; (3) the air relatively humidity was the most important factor affecting aboveground biomass, whereas the belowground biomass was less affected by climatic factors. Our results suggest that the alpine meadow ecosystem has a high self-regulation ability against environmental factors, and the evolution of alpine meadows is subject to the interference of human activities rather than climate change.