Evapotranspiration and water use efficiency in a Chesapeake Bay wetland under carbon dioxide enrichment

Abstract

Wetlands evapotranspire more water than other ecosystems, including agricultural, forest and grassland ecosystems. However, the effects of elevated atmospheric carbon dioxide (C0 2 ) concentration (C a ) on wetland evapotranspiration (ET) are largely unknown. Here, we present data on 12 years of measurements of ET, net ecosystem C0 2 exchange (NEE), and ecosystem water use efficiency (EWUE, i.e. NEE/ET) at 13:00-15:00 hours in July and August for a Scirpus olneyi (C3 sedge) community and a Spartina patens (C4 grass) community exposed to ambient and elevated (ambient + 340 pmol mol x ) C a in a Chesapeake Bay wetland. Although a decrease in stomatal conductance at elevated C a in the S. olneyi community was counteracted by an increase in leaf area index (LAI) to some extend, ET was still reduced by 19% on average over 12 years. In the S. patens community, LAI was not affected by elevated C a and the reduction of ET was 34%, larger than in the S. olneyi community. For both communities, the relative reduction in ET by elevated C a was directly proportional to precipitation due to a larger reduction in stomatal conductance in the control plants as precipitation decreased. NEE was stimulated about 36% at elevated C a in the S. olneyi community but was not significantly affected by elevated C a in S. patens community. A negative correlation between salinity and precipitation observed in the field indicated that precipitation affected ET through altered salinity and interacted with growth C a . This proposed mechanism was supported by a greenhouse study that showed a greater C a effect on ET in controlled low salinity conditions compared with high salinity. In spite of the differences between the two communities in their responses to elevated C^ EWUE was increased about 83% by elevated C a in both the S. olneyi and S. patens communities. These findings suggest that rising C a could have significant impacts on the hydrologic cycles of coastal wetlands.

ElevatedCO2promotes long‐term nitrogen accumulation only in combination with nitrogen addition

“…It is perhaps more likely that lower canopy‐level transpiration could have reduced bulk flow of deeper (below 80 cm) porewater [] to the surface (Mcdonald et al ., ). Decreased canopy‐level transpiration under elevated CO 2 has been documented in a nearby CO 2 enrichment study in this wetland (Li et al ., ) and live roots extend beyond 80 cm in these plots (personal observation). Although total denitrification rates remain a highly uncertain component of the N cycle at this site, our results suggest that rising CO 2 will not change, let alone increase, N accumulation or retention by strongly N‐limited marshes without additional N inputs.…”

The Impact of Climate, CO2 and Population on Regional Food and Water Resources in the 2050s

“…The magnitude of this physiological forcing depends on the degree of stomatal control over evapotranspiration [23]. A number of field-based experiments have demonstrated the reduction of evapotranspiration in a CO 2 enriched environment [24][25][26]. Reduced evapotranspiration allows a relatively higher proportion of water to form runoff, a renewable water resource.…”

Climate and land use controls over terrestrial water use efficiency in monsoon Asia

“…Associated with the change in land use and cover, land management practices such as irrigation, fertilizer and/or manure application, residue return, and tillage are recognized as important anthropogenic measures to improve crop yield, and hence, modify the carbon, water, and nitrogen cycles in agricultural land Zhang et al, 2006;Lu et al, 2009), which covers around 20% of the total land area in MA. Although a few studies have assessed the impacts of environmental changes on carbon and water interactions Yu et al, 2008;Wang et al, 2008;Li et al, 2010), none of them has addressed the changes in WUE in response to both natural and human perturbations at a regional scale. Thus, an integrated research is needed to understand how these environmental changes interactively affect carbon and water dynamics in MA.…”