Grassland, Soil & Water Research Laboratory, US Department of Agriculture, Agricultural Research Service, Temple, Texas, 76502, USA.
Glob Chang Biol. 2012 Sep;18(9):2813-23. doi: 10.1111/j.1365-2486.2012.02735.x. Epub 2012 Jun 12.
Dynamic global vegetation models simulate feedbacks of vegetation change on ecosystem processes, but direct, experimental evidence for feedbacks that result from atmospheric CO2 enrichment is rare. We hypothesized that feedbacks from species change would amplify the initial CO2 stimulation of aboveground net primary productivity (ANPP) of tallgrass prairie communities. Communities of perennial forb and C4 grass species were grown for 5 years along a field CO2 gradient (250-500 μL L(-1) ) in central Texas USA on each of three soil types, including upland and lowland clay soils and a sandy soil. CO2 enrichment increased community ANPP by 0-117% among years and soils and increased the contribution of the tallgrass species Sorghastrum nutans (Indian grass) to community ANPP on each of the three soil types. CO2 -induced changes in ANPP and Sorghastrum abundance were linked. The slope of ANPP-CO2 regressions increased between initial and final years on the two clay soils because of a positive feedback from the increase in Sorghastrum fraction. This feedback accounted for 30-60% of the CO2 -mediated increase in ANPP on the upland and lowland clay soils during the final 3 years and 1 year of the experiment, respectively. By contrast, species change had little influence on the ANPP-CO2 response on the sandy soil, possibly because Sorghastrum increased largely at the expense of a functionally similar C4 grass species. By favoring a mesic C4 tall grass, CO2 enrichment approximately doubled the initial enhancement of community ANPP on two clay soils. The CO2 -stimulation of grassland productivity may be significantly underestimated if feedbacks from plant community change are not considered.
动态全球植被模型模拟了植被变化对生态系统过程的反馈，但大气 CO2 富集导致反馈的直接、实验证据很少。我们假设，物种变化的反馈将放大高草草原群落地上净初级生产力（ANPP）对 CO2 的初始刺激。在美国德克萨斯州中部，在三种土壤类型上（包括高地和低地粘土壤和沙质土壤），沿田间 CO2 梯度（250-500μL·L-1）生长了多年生草本植物和 C4 草种的群落，为期 5 年。CO2 富集增加了群落 ANPP，幅度为 0-117%，不同年份和土壤的增加幅度不同，并增加了高草物种 Sorghastrum nutans（Indian grass）对三种土壤类型中群落 ANPP 的贡献。CO2 诱导的 ANPP 和 Sorghastrum 丰度变化相关。由于 Sorghastrum 丰度的增加产生了正反馈，在两种粘土壤上，ANPP-CO2 回归的斜率在初始年和最后一年之间增加。这种反馈分别占最后 3 年和实验的最后 1 年，高海拔和低海拔粘土壤上 CO2 介导的 ANPP 增加的 30-60%。相比之下，物种变化对沙质土壤上的 ANPP-CO2 响应几乎没有影响，这可能是因为 Sorghastrum 的增加主要以功能相似的 C4 草种为代价。通过有利于湿润的 C4 高草，CO2 富集使两种粘土壤上群落 ANPP 的初始增强大约增加了一倍。如果不考虑植物群落变化的反馈，对草原生产力的 CO2 刺激可能会被严重低估。
