高寒草甸矮生嵩草种群根系周转率沿土壤水分梯度的变化

Variations of root turnover rate of Kobresia humilis populations along a soil moisture gradient in an alpine meadow

根系周转率可以衡量植物根系的更新能力,对土壤含水率变化的响应敏感。在藏东南东达山高寒草甸选择5个土壤水分梯度设置样地,第Ⅰ、Ⅱ土壤水分梯度为湿润生境(土壤含水率>25%),第Ⅲ~Ⅴ土壤水分梯度为干旱生境(土壤含水率<25%)。分别于2017年与2021年取样,分析矮生嵩草(Kobresia humilis)种群根系周转率在生境干旱化过程中的动态。结果表明:1)随土壤含水率的降低,种群盖度显著下降(P<0.05),地下芽库密度在各土壤水分梯度间差异显著(P<0.05),但与土壤含水率之间的相关性不显著(P>0.05);湿润生境中,两个年度根系生物量的季节动态变化一致,而干旱生境的季节动态变化无规律。2)两个年度根系净增长量、周转率均与土壤含水率极显著正相关(P<0.01),干旱生境中根系周转率年际差异显著(P<0.05)。3)根系主要由细根(直径≤1 mm)组成,在各土壤水分梯度的占比均大于80%,所占比例与土壤含水率显著正相关(P<0.05),细根周转率显著大于粗根(直径>1 mm)(P<0.05)。4)根系周转率与种群盖度显著正相关,根系周转率年际差异与盖度年际差异、地下芽库密度显著负相关(P<0.05)。生境干旱化过程中,矮生嵩草根系更新能力减弱,且根系生物量季节动态、周转率在年际间的差异增大,这种波动不利于种群的生长与更新,干旱胁迫使植物种群稳定性存在下降的风险。

Root turnover rate can measure the renewal capacity of plant roots and is sensitive to changes in soil moisture.Five sample plots were set up along the natural soil moisture gradient in an alpine meadow,the Dongda Mountains,southeastern Tibet.The soil moisture plotsⅠandⅡare wet habitats(soil moisture>25%),whereas the plotsⅢ~Ⅴare arid habitats(soil moisture<25%),and were sampled in 2017 and 2021 to analyze the dynamics of root turnover rate of Kobresia humilis populations during habitat aridification.The results showed that 1)the population coverage decreased significantly with the decrease of soil moisture(P<0.05)and the density of bud bank varied significantly among soil moisture levels(P<0.05),but the correlation with soil moisture was not significant;in the wet habitat,the seasonal dynamic changes of root biomass were consistent in both years,while they were irregular in the arid habitat.2)Net root growth and turnover rate were significantly and positively correlated with soil moisture in both years(P<0.01),with significant interannual differences in root turnover rate in the arid habitat(P<0.05).3)The root system consisted mainly of fine roots(diameter≤1 mm),which accounted for>80%of the total roots in soil,and the proportion was significantly positively correlated with soil moisture(P<0.05).The turnover rate of fine roots was significantly greater than that of coarse roots(diameter>1 mm)in each site(P<0.05).4)Root turnover was significantly and positively correlated with population coverage(P<0.05),and inter-annual differences in root turnover were significantly and positively correlated with inter-annual differences in coverage and underground density of bud bank(P<0.05).During habitat aridification,the root renewal capacity of K.humilis was reduced,and the seasonal dynamics of root biomass and inter-annual variation in turnover rate increased.These fluctuations were not conducive to the growth and renewal of the population,and drought stress increased the risk of a decrease in community stability.