黄土高原半干旱区典型草地生态系统CO2交换对刈割的响应

草地生态系统碳循环在全球气候变化中扮演着重要的角色。刈割是实现草地资源合理利用的主要管理措施,但其对草地生态系统碳通量的影响过程和机理尚不清楚。以黄土高原半干旱区典型草地为研究对象,设计刈割和对照两种处理,于2013—2015年对生态系统碳通量各组分,土壤温度和水分进行了测定。结果表明:生态系统碳通量季节性变化均呈明显的单峰模式,以夏季最高,春秋季节最低,但不同组分峰值出现的时间有所不同。刈割使整个试验期土壤呼吸增加了17%,但对总初级生产力(GEP)、生态系统呼吸(Re)和净初级生产力(NEE)的影响不显著。GEP和NEE在正常降水年(2014)高于干旱年(2015),而且其对刈割的响应与降水年型有关。在正常降水年,刈割后GEP和NEE显著减低,而在干旱年显著增加。这些结果表明,降雨年际变化是造成半干旱草地生态系统碳通量变化的主导因素,而刈割增大了这一生态系统的土壤碳排放。

Responses of ecosystem CO2 exchange to clipping in a semi-arid typical grassland on the Loess Plateau

Grassland ecosystem plays an important role in global climate change. Clipping is an effective management practices to realize the rational utilization of grassland resources. However, the responses of grassland ecosystem CO₂ flux to clipping remain unknown. Here, we conducted a 3-year field experiment in a semi-arid typical grassland on the Loess Plateau to examine the effect of clipping on CO₂ flux. Ecosystem carbon dioxide flux components were measured, as well as soil temperature and moisture at the depth of 0-10 cm. The results showed that the seasonal dynamics of CO₂ flux presented a single peak pattern with the highest values in summer and the lowest values in spring and autumn. There was a slight difference in the timing of CO₂ flux peak. During across experimental period, clipping significantly increased soil respiration (Rs) by 17%, but had no significant effects on the gross primary productivity (GEP), ecosystem respiration (Re), and net ecosystem carbon absorption (NEE). The GEP, Re, and NEE in normal rainfall year (2014) were higher than those in dry year (2015). The response of the GEP and the NEE to clipping depended on rainfall type. There was a significant increase of the GEP and the NEE in dry year after clipping, while an opposite trend was found in normal rainfall year. These results suggested that CO₂ flux were mainly determined by the inter-annual rainfall in the semi-arid grassland ecosystems, and clipping could increase the soil CO₂ emission.