长期氮添加对内蒙古典型草原植物地上、地下生物量及根冠比的影响

Effects of long-term nitrogen addition on community aboveground and belowground biomass and their ratio in a typical steppe of Inner Mongolia

氮沉降的增加显著改变了生态系统功能和过程。大量研究表明,氮添加会提高生态系统生产力,然而,大部分研究集中在地上生物量,对地下生物量以及根冠比的研究较少。我们在内蒙古典型草原进行了7年的氮添加实验,设置6个氮添加水平,分别是N0(0)、N1(5.6 g N·m^-2)、N2(11.2 g N·m^-2)、N3(22.4 g N·m^-2)、N4(39.2 g N·m^-2)、N5(56 g N·m^-2),测定植物地上和不同土层(0~10、10~30、30~50和50~100 cm)地下生物量并计算根冠比,研究不同氮添加水平对植物地上、地下生物量和根冠比的影响。结果表明:(1)与对照相比,低氮添加水平(N1和N2)未显著增加地上生物量,高氮添加水平(N3~N5)显著增加了地上生物量(96%~117%),且各高氮添加水平间差异不显著;(2)不同氮添加水平下,植物地上生物量的氮响应效率(NRE)均大于0且呈下降趋势,相邻氮添加水平的NRE差值(ΔNRE)仅在N3水平下显著增加,说明地上生物量在N3水平下达到饱和;(3)氮添加未显著改变不同土层以及整个土壤剖面上的地下生物量,且对各土层地下生物量的占比情况无显著影响;(4)与对照相比,N1和N2未显著改变植物的根冠比,N3~N5显著降低了植物根冠比。综上所述,氮沉降增加会提高植物地上生物量,对不同土层根系的影响比较复杂,需要更多的研究来明确地下生产力对氮沉降增加的响应规律。

The increase of nitrogen deposition has significantly altered ecosystem functions and processes.Numerous studies showed that nitrogen addition could increase ecosystem productivity.However,most of these studies focused on aboveground biomass,much less on the belowground biomass and root:shoot ratio.We conducted a 7-year nitrogen addition experiment in a typical steppe in Inner Mongolia.Six treatments were set up in 2006,namely N0(0),N1(5.6 g N·m^-2),N2(11.2 g N·m^-2),N3(22.4 g N·m^-2),N4(39.2 g N·m^-2),N5(56 g N·m^-2).Aboveground biomass and belowground biomass in soil depths of 0-10,10-30,30-50 and 50-100 cm of plant communities were measured in 2012.We examined the responses of aboveground and belowground biomass and their ratio to nitrogen addition.The results showed that:(1)Low nitrogen addition levels(N1 and N2)did not significantly affect aboveground biomass.High nitrogen addition levels(N3-N5)significantly increased aboveground biomass(96%-117%),with no significant difference across the high nitrogen addition levels.(2)Under different nitrogen addition levels,the nitrogen response efficiency(NRE)of aboveground biomass was all greater than 0 and showed a downward trend.The difference in NRE(ΔNRE)increased significantly only at the level of N3,indicating that aboveground biomass reached saturation at the level of N3;(3)Nitrogen addition did not affect 0-100 cm belowground biomass,and kept consistent in all four soil layers(0-10,10-30,30-50 and 50-100 cm).N addition did not affect the proportion of belowground biomass in each soil layer.(4)N1 and N2 did not significantly change the root-shoot ratio,but N3-N5 did.These results suggest that increased nitrogen deposition has a Pofitive effect on aboveground biomass.The effects of increased nitrogen deposition on plant roots in different soil layers varied greatly.More researches are needed to clarify the effects of increased nitrogen deposition on belowground productivity.