Direct and indirect effects of elevated atmospheric CO₂ on net ecosystem production in a Chesapeake Bay tidal wetland

Abstract

The rapid increase in atmospheric CO2 concentrations (Ca ) 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 Ca . 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 Ca (ambient + 340 ppm). Our objectives were to (i) quantify effects of elevated Ca 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 Ca and 2.5 kg m(-2) y(-1) in elevated Ca , for the C3 -dominated community. Similarly, elevated Ca 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 Ca and 1.7 kg m(-2) y(-1) in elevated Ca . 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 Ca , while decreased NEE(night) was associated with lower canopy nitrogen content. These results suggest that rising Ca may increase carbon assimilation in both C3 - and C4 -dominated wetland communities. The challenge remains to identify the fate of the assimilated carbon.

Rising sea level, temperature, and precipitation impact plant and ecosystem responses to elevated CO2 on a Chesapeake Bay wetland: review of a 28‐year study

“…Rubisco, which accounted for a little over 50% of soluble protein in S. olneyi was reduced along with total protein, but there was no effect of elevated CO 2 on the Rubisco as a proportion of total protein (Jacob & Drake, ) suggesting that acclimation was not a property of specific components of photosynthetic carbon reduction but a consequence of reduced protein content. The CO 2 effect on protein was associated with lower nitrogen concentration in plant tissues of 5–30% at midseason (Curtis et al ., ; Erickson et al ., ). Moreover, the reduction in nitrogen was also seen in root tissues of Scirpus C3 as well as shoots of Spartina C4 (Erickson et al ., ).…”

“…Stimulation of shoot density and biomass production by elevated CO 2 (Figs and ) continued throughout the study with periods of very little response preceded and followed by periods of very large response (Erickson et al ., , ). Rasse et al .…”

Nitrogen uptake kinetics and saltmarsh plant responses to global change

“…While the effects of elevated CO 2 on plant productivity are well studied in a variety of ecosystems 19 , 20 including saltmarshes 21 , 22 , our understanding of these responses is primarily based on changes in aboveground biomass, CO 2 assimilation 23 , 24 , and shifts in species composition that reflect competition between plant functional groups 10 . Little attention has been paid to belowground mechanisms such as those associated with N acquisition or how they could be altered by global change.…”

Inter‐annual changes in detritus‐based food chains can enhance plant growth response to elevated atmospheric CO2

“…Plants are the primary link between the atmosphere and biosphere, and rising atmospheric CO 2 is expected to stimulate photosynthesis and plant growth. Evidence from long-term CO 2 enrichment studies suggests that plants can consistently accumulate more carbon in their biomass under elevated compared to current CO 2 conditions (Rasse et al, 2005;Drake, 2014), although these effects are generally more pronounced for plant species that use C 3 compared to C 4 photosynthetic pathways (White et al, 2012;Erickson et al, 2013). This leads to the suggestion that highly productive ecosystems, such as wetlands dominated by C 3 plants, may be a net carbon sink in future atmospheric CO 2 conditions and that wetland conservation may be an effective strategy to mitigate the harmful effects of CO 2 on the global climate (Mcleod et al, 2011).…”