草地生态系统生物量在不同气候及多时间尺度上对氮添加和增雨处理的响应

Response of plant biomass to nitrogen addition and precipitation increasing under different climate conditions and time scales in grassland

生产力是草地生态系统重要的服务功能, 而生物量作为生态系统生产力的主要组成部分, 往往同时受到氮和水分两个因素的限制。在全球变化背景下, 研究草地生态系统生物量对氮沉降增加和降水变化的响应具有重要意义, 但现有研究缺乏对其在大区域空间尺度以及长时间尺度上响应的综合评估和量化。本研究搜集了1990-2017年间发表论文的有关模拟氮沉降及降水变化研究的相关数据, 进行整合分析, 探讨草地生态系统生物量对氮沉降和降水量两个因素的变化在空间和时间尺度上的响应。结果表明: (1)氮添加、增雨处理以及同时增氮增雨处理都能够显著地提高草地生态系统的地上生物量(37%, 41%, 104%)、总生物量(32%, 23%, 60%)和地上地下生物量比(29%, 25%, 46%)。单独增雨显著提高地下生物量(10%), 单独施氮对地下生物量影响不显著, 但同时增雨则能显著提高地下生物量(43%); (2)氮添加和增雨处理对草地生态系统生物量的影响存在明显的空间变异。在温暖性气候区和海洋性气候区的草地生态系统中, 氮添加对地上、总生物量及地上地下生物量比的促进作用更强, 而在寒冷性气候区和温带大陆性气候区的草地生态系统中, 则增雨处理对地下、总生物量的促进作用更强; (3)草地生态系统生物量对氮添加和增雨处理的响应也存在时间格局上的变化, 地下生物量随着氮添加年限的增加有降低的趋势, 地上、总生物量及地上地下生物量比则有增加的趋势。增雨年限的增加对总生物量没有明显的影响, 但持续促进地上生物量和地下生物量, 增加地上地下生物量比, 可见长期增氮、长期增雨对地上生物量的促进作用更明显。

Aims Plant biomass accounts for the main part of grassland productivity. The productivity of grassland regarded as one of important ecosystem function is always co-limited by nitrogen and water availability, therefore, how grasslands respond to atmosphic nitrogen (N)addition and precipitation increasing need to be systematically and quantitatively evaluated at different climate conditions and temporal scales.Methods To investigate the impact of nitrogen addition and precipitation increasing on grassland biomass over climate conditions and temproal scales, a meta-analysis was conducted based on 46 papers that were published during 1990-2017 involving 1 350 observations.Important findings Results showed that: (1) N addtion, precipitation increasing and the combinations of these two treatments significantly increased the aboveground biomass (37%, 41%, 104%), total biomass (32%, 23%, 60%) and the ratio of aboveground biomass to belowground biomass (29%, 25%, 46%) in grassland ecosystem.Belowground biomass showed no response to single N addtion, but could be significantly enhanced together with increaseing precipitation; (2) The response of grassland biomass under these N addtion and the increasing of precipitation showed obvious spatial pattern under different climate conditions. The N addition tended to increase more aboveground biomass, total biomass and the ratio of aboveground biomass to belowground biomass under high sites with high mean annual air temperature (MAT) and mean annual precipitation (MAP) while precipitation increasing tended to simulate more belowground biomass and total biomass under low MAT and MAP sites;(3)In addition, the response of grassland biomass under these two global change index showed obvious temporal pattern. With the increase of duration of N addition, the belowgound biomass tended to decrease, while the aboveground biomass, total biomass and the ratio of aboveground biomass to belowground biomass tended to increase under N addition. With the increase of duration of precipitation manipulation, the total biomass showed no response to precipitation increasing, while aboveground biomass, belowground biomass and the ratio of aboveground biomass to belowground biomass tended to be enhanced. The results indicated that aboveground biomass was more likely to be enhanced than belowground biomass under N addition or precipitation increasing in the long term.