Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park, Texas

Abstract

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is anticipated to affect biosphere/atmosphere exchanges of both CO(2) and H(2)O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level fluxes of CO(2) and H(2)O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004). In addition, the responses of leaf, soil, and ecosystem fluxes of CO(2) and H(2)O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event. We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO(2) m(-2) s(-1) ground area day(-1). As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO(2) during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem.

Dynamic interactions of ecohydrological and biogeochemical processes in water‐limited systems

“…For example, measuring the responses of leaf, soil, and ecosystem to a 25% increase in precipitation (via manipulation of precipitation) during the summer in the Chihuahuan Desert, researchers found that ecosystem C uptake and soil CO 2 efflux increased following individual watering events despite that measured stomatal conductance remained the same (Patrick et al 2007). However, at the seasonal scale, water additions resulted in an increase in sequestration of atmospheric C and a decrease in soil CO 2 efflux (Patrick et al 2007).…”

“…For example, measuring the responses of leaf, soil, and ecosystem to a 25% increase in precipitation (via manipulation of precipitation) during the summer in the Chihuahuan Desert, researchers found that ecosystem C uptake and soil CO 2 efflux increased following individual watering events despite that measured stomatal conductance remained the same (Patrick et al 2007). However, at the seasonal scale, water additions resulted in an increase in sequestration of atmospheric C and a decrease in soil CO 2 efflux (Patrick et al 2007). While soil CO 2 efflux increased immediately after precipitation and for a few hours (;18 h), once the ecosystem entered an interpulse period and soil moisture decreased, rates of soil CO 2 efflux from wetted plots declined faster than in plots without water addition (Patrick et al 2007).…”

“…However, at the seasonal scale, water additions resulted in an increase in sequestration of atmospheric C and a decrease in soil CO 2 efflux (Patrick et al 2007). While soil CO 2 efflux increased immediately after precipitation and for a few hours (;18 h), once the ecosystem entered an interpulse period and soil moisture decreased, rates of soil CO 2 efflux from wetted plots declined faster than in plots without water addition (Patrick et al 2007). A more recent study demonstrated that soil processes at the landscape level exhibit bidirectional behavior in response to interannual water availability (Riveros-Iregui et al 2012), because lowlands and wet areas of the landscape are favorable for autotrophic and heterotrophic transformation of soil C during dry years whereas uplands and dry areas of the landscape are more favorable during wet years.…”

The impact of invasion and subsequent removal of an exotic thistle, Cynara cardunculus, on CO2 and H2O vapor exchange in a coastal California grassland

“…For example, diel tent-based measurements of NEE in a Chihuahuan desert grassland revealed midday depression of ecosystem CO 2 assimilation with implications for net ecosystem productivity (Patrick et al 2007). Furthermore, daytime measurements of ecosystem respiration may not be representative of nighttime ecosystem respiration, particularly in regards to the contribution of autotrophic respiration (Tang et al 2005).…”

Ecological effects of experimental drought and prescribed fire in a southern California coastal grassland

“…Likewise, by combining evaporation from soil and canopy surfaces with transpiration from stomata, evapotranspiration (ET) is critical in understanding the role of ecosystems in linking the movement of water between the land surface and the atmosphere. Used in a variety of experimental settings, chamber-based measurements have demonstrated the effects of seasonal rainfall (Harpole et al, 2007;Patrick et al, 2007), rainfall timing (Potts et al, 2006) and fire (Prater and DeLucia, 2006) on CO 2 exchange and ET.…”