根系是草原生态系统中最重要的碳库之一,分析高寒草甸植物群落生物量和地下不同径级根系碳分配特征及根系的生长特征对降雨变化的响应,有利于了解全球变化背景下高寒草甸植物根系、土壤碳氮循环及其过程。采用微根管技术原位监测5种降雨处理下(增雨50%:1.5P、自然降雨:1.0P、减雨30%:0.7P、减雨50%:0.5P、减雨90%:0.1P)高寒草甸植物群落和根系属性(现存量、生产量、死亡量、根系寿命和周转速率)的变化特征,结果表明:(1)降雨变化对地上植物群落生物量无显著影响,但0.5P和0.1P显著增加禾本科生物量(P<0.05)。(2)总根系现存量在处理间无显著差异,但随着降雨量减少呈先增加后降低的趋势。土层间不同径级根系现存量差异显著,0-10 cm土层1.5P和0.7P1级根现存量显著增加,2级和3级根现存量显著降低;在10-20 cm土层,1.0P2级根系现存量显著高于其余处理(P<0.05)。(3)总根生产量与死亡量随降雨减少而降低,在0-10 cm土层,1.0P总根生产量和死亡量最高,0.1P显著降低了1级根生产量(P<0.05)。(4)0.1P显著增加10-20 cm土层1级根和总根寿命(P<0.05)。(5)根系周转随降雨量减少呈降低趋势,但无显著差异(P>0.05)。(6)结构方程模型进一步表明:根系现存量和生产量受土层和水分的直接影响,土层和养分对根系周转有负效应。综上所述,降雨量的变化并未显著改变地下总根系生物量,但少量降雨变化(0.7P、1.5P)会降低植物对2、3级根生物量的分配,投入更多资源以促进1级根的生长;而水分下降至轻度水分胁迫(0.1P),植物会减少地下各径级根系生物量的分配,保持低根系生物量消耗和低根系生长来维持其正常的生长状态,完成其正常的生态功能。
Root is one of the most important carbon pools in grassland ecosystem. Analyzing the biomass of plant community, the carbon distribution characteristics of roots with different diameters, and the response of root growth characteristics to changing precipitation contributes to understand the carbon and nitrogen cycle and process of roots and soil in an alpine meadow under global change. In this study, we investigated the biomass of plant community and used the minirhizontron technology to investigate changes of root properties (standing crop, production, mortality, life span and turnover) in an alpine meadow, in response to five precipitation gradient, including 90%, 50% and 30% decrease (0.1P, 0.5P, 0.7P), ambient control (1.P) and 50% increase (1.5P). The results showed that: 1) There was no significant effect of precipitation gradient to above-ground biomass, while 0.5P and 0.1P significantly increased the biomass of grass (P<0.05). 2) The total root standing crop was not significant affected by treatments, but increased first and then decreased with precipitation decrease. There were significant differences in response of roots of different diameter classes among soil layers. In 0-10 cm soil layer, the standing crop significantly increased in 1-level roots under 1.5P and 0.7P, however, significantly decreased in 2 and 3-level. In addition, in 10-20 cm soil layer, the standing crop of 2-level roots in 1.0P was significantly higher than that in other treatment (P<0.05). 3) Root production of 1-level roots in the surface layer are significantly reduced under 0.1P, meanwhile, the total production and mortality of 1.0P in the surface layer was significantly higher than that of other treatments (P<0.05). 4) The life span of total roots and 1-level roots in the bottom layer increased under 0.1P (P<0.05). 5) Root turnover decreased with precipitation decrease, but there was no significant difference among treatments. 6) The structural equation model showed that the root standing crop and production were directly affected by the soil layer and water content, besides the root turnover was directly affected by the soil layer and nutrients. In summary, under small range of precipitation change (0.7P, 0.5P), plants would reduce the biomass allocation to fine roots and invest more resources in the growth of 1-level roots; however, under mild water stress (0.1P), the plant would reduce the allocation of underground root biomass in all diameter classes, maintain low biomass consumption and low root growth to maintain its normal growth state, so as to complete its normal ecological function.