College of Animal Science and Veterinary Medicine, Shanxi Agricultural University, Taigu, China.
State Key Laboratory of Grassland Agro-ecosystems, Lanzhou University, Lanzhou, China.
PLoS One. 2018 Mar 12;13(3):e0194198. doi: 10.1371/journal.pone.0194198. eCollection 2018.
Water use efficiency (WUE) is an important indicator of ecosystem functioning but how ecosystem WUE responds to climate change including precipitation and nitrogen (N) deposition increases is still unknown. To investigate such responses, an experiment with a randomized block design with water (spring snowfall or summer water addition) and nitrogen addition was conducted in a temperate steppe of northern China. We investigated net ecosystem CO2 production (NEP), gross ecosystem production (GEP) and evapotranspiration (ET) to calculate ecosystem WUE (WUEnep = NEP/ET or WUEgep = GEP/ET) under spring snow and summer water addition with or without N addition from 2011 to 2013. The results showed that spring snow addition only had significant effect on ecosystem WUE in 2013 and summer water addition showed positive effect on ecosystem WUE in 2011 and 2013, as their effects on NEP and GEP is stronger than ET. N addition increased ecosystem WUE in 2012 and 2013 both in spring snow addition and summer water addition for its increasing effects on NEP and GEP but no effect on ET. Summer water addition had less but N addition had greater increasing effects on ecosystem WUE as natural precipitation increase indicating that natural precipitation regulates ecosystem WUE responses to water and N addition. Moreover, WUE was tightly related with atmospheric vapor-pressure deficit (VPD), photosynthetic active radiation (PAR), precipitation and soil moisture indicating the regulation of climate drivers on ecosystem WUE. In addition, it also was affected by aboveground net primary production (ANPP). The study suggests that ecosystem WUE responses to water and N addition is determined by the change in carbon process rather than that in water process, which are regulated by climate change in the temperate steppe of northern China.
水分利用效率（WUE）是生态系统功能的一个重要指标，但生态系统 WUE 对气候变化（包括降水和氮（N）增加）的响应仍不清楚。为了研究这种响应，在中国北方的温带草原进行了一项具有随机区组设计的实验，该实验包括水分（春季融雪或夏季补水）和氮添加。我们调查了净生态系统 CO2 产量（NEP）、总生态系统生产力（GEP）和蒸散（ET），以计算 2011 年至 2013 年春季融雪和夏季补水以及是否添加氮的情况下的生态系统 WUE（WUEnep = NEP/ET 或 WUEgep = GEP/ET）。结果表明，春季融雪添加仅在 2013 年对生态系统 WUE 有显著影响，夏季补水在 2011 年和 2013 年对生态系统 WUE 有积极影响，因为它们对 NEP 和 GEP 的影响大于 ET。氮添加增加了 2012 年和 2013 年春季融雪和夏季补水的生态系统 WUE，因为它增加了 NEP 和 GEP，但对 ET 没有影响。与自然降水增加相比，夏季补水对生态系统 WUE 的增加作用较小，而氮添加的增加作用较大，表明自然降水调节了生态系统对水和氮添加的 WUE 响应。此外，WUE 与大气水汽压亏缺（VPD）、光合有效辐射（PAR）、降水和土壤水分密切相关，表明气候驱动因素对生态系统 WUE 的调节作用。此外，它还受到地上净初级生产力（ANPP）的影响。该研究表明，生态系统 WUE 对水和氮添加的响应取决于碳过程的变化，而不是水过程的变化，这是由中国北方温带草原的气候变化决定的。
