【大气CO2增加对湿地净生产力的直接和间接影响】John E. Erickson¹² Gary Peresta¹ Kathryn J. Montovan²³ Bert G. Drake^1*. Direct and indirect effects of elevated atmosphericCO₂on net ecosystem production in a Chesapeake Bay tidal wetland.Global Change BiologyVolume 19Issue 11 pages 3368–3378 November 2013

Abstract

The rapid increase in atmospheric CO₂ concentrations (C_a) has resulted in extensive research efforts to understand its impact on terrestrial ecosystems especially carbon balance. Despite these efforts there are relatively few data comparing net ecosystem exchange of CO₂ between the atmosphere and the biosphere (NEE) under both ambient and elevated C_a. Here we report data on annual sums of CO₂ (NEE_net) for 19 years on a Chesapeake Bay tidal wetland for Scirpus olneyi (C₃ photosynthetic pathway)- and Spartina patens (C₄ photosynthetic pathway)-dominated high marsh communities exposed to ambient and elevated C_a (ambient + 340 ppm). Our objectives were to (i) quantify effects of elevated C_a on seasonally integrated CO₂ assimilation (NEE_net = NEE_day + NEE_night kg C m⁻² y⁻¹) for the two communities; and (ii) quantify effects of altered canopy N content on ecosystem photosynthesis and respiration. Across all years NEE_net averaged 1.9 kg m⁻² y⁻¹ in ambient C_a and 2.5 kg m⁻² y⁻¹ in elevated C_a for the C₃-dominated community. Similarly elevated C_a significantly (P < 0.01) increased carbon uptake in the C₄-dominated community as NEE_net averaged 1.5 kg m⁻² y⁻¹ in ambient C_a and 1.7 kg m⁻² y⁻¹ in elevated C_a. This resulted in an average CO₂ stimulation of 32% and 13% of seasonally integrated NEE_net for the C₃- and C₄-dominated communities respectively. Increased NEE_day was correlated with increased efficiencies of light and nitrogen use for net carbon assimilation under elevated C_a while decreased NEE_night was associated with lower canopy nitrogen content. These results suggest that rising C_a may increase carbon assimilation in both C₃- and C₄-dominated wetland communities. The challenge remains to identify the fate of the assimilated carbon.

【高纬度生态系统中土壤-植物N过程】Sean M. Schaeffer^12* Elizabeth Sharp³ Joshua P. Schimel¹ Jeffery M. Welker³. Soil–plant N processes in a High Arctic ecosystem NW Greenland are altered by long-term e