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Water from air: an overlooked source of moisture in arid and semiarid regions.

McHugh TA, Morrissey EM, Reed SC, Hungate BA, Schwartz E - Sci Rep (2015)

Bottom Line: This phenomenon rapidly increased soil moisture and stimulated microbial carbon (C) cycling, and the flux of water vapor to soil had a stronger impact than temperature on microbial activity.In a semiarid grassland, we also observed that non-rainfall water inputs stimulated microbial activity and C cycling.Together these data suggest that, during rain-free periods, atmospheric moisture in drylands may significantly contribute to variation in soil water content, thereby influencing ecosystem processes.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, USA.

ABSTRACT
Water drives the functioning of Earth's arid and semiarid lands. Drylands can obtain water from sources other than precipitation, yet little is known about how non-rainfall water inputs influence dryland communities and their activity. In particular, water vapor adsorption--movement of atmospheric water vapor into soil when soil air is drier than the overlying air--likely occurs often in drylands, yet its effects on ecosystem processes are not known. By adding (18)O-enriched water vapor to the atmosphere of a closed system, we documented the conversion of water vapor to soil liquid water across a temperature range typical of arid ecosystems. This phenomenon rapidly increased soil moisture and stimulated microbial carbon (C) cycling, and the flux of water vapor to soil had a stronger impact than temperature on microbial activity. In a semiarid grassland, we also observed that non-rainfall water inputs stimulated microbial activity and C cycling. Together these data suggest that, during rain-free periods, atmospheric moisture in drylands may significantly contribute to variation in soil water content, thereby influencing ecosystem processes. The simple physical process of adsorption of water vapor to soil particles, forming liquid water, represents an overlooked but potentially important contributor to C cycling in drylands.

No MeSH data available.


Soil CO2 efflux rates across temperature regimes for control and water vapor adsorption treatment.Error bars are standard error for means (n = 5). The effect of water vapor adsorption (percent change relative to control) is shown with white circles.
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f2: Soil CO2 efflux rates across temperature regimes for control and water vapor adsorption treatment.Error bars are standard error for means (n = 5). The effect of water vapor adsorption (percent change relative to control) is shown with white circles.

Mentions: A second laboratory experiment was performed to examine the influence of temperature on water vapor adsorption and the extent to which it regulates soil microbial activity. Field dry soil was incubated for three days under the simulated diurnal temperature fluctuations previously described, or at a constant temperature of either 23 or 40 °C. Water vapor was added to the atmosphere of treatment jars (500 μg fully evaporated into ~1 L headspace), while experimental controls received no water addition. Water vapor adsorption was confirmed by an increase in the gravimetric water content of the soils over the course of the incubation. Relative to their moisture content at the initiation of the experiment (2.3%), the average moisture content of soils in the water vapor adsorption treatment increased by 65.9% for the simulated diurnal treatment, 63.3% for the 23 °C treatment, and 59.9% for the 40 °C temperature regime. Thus, water vapor adsorption occurred under all temperature regimes, and the concomitant increases in CO2 efflux (Fig. 2) indicate that vapor adsorption stimulated soil CO2 production. The effect of water vapor adsorption was significantly greater in soils experiencing simulated diurnal fluctuations (p < 0.0001, Fig. 2). Overall, temperature explained 23% of the variation in soil CO2 efflux rates, while water vapor addition explained 47% (two-way ANOVA). These results suggest that temperature may have opposing effects on microbial activity in dryland soils. On one hand, higher temperatures, which increase molecular diffusion rates, will lead to greater respiration activity but also deplete soils of scarce moisture. On the other hand, colder temperatures will allow more water vapor adsorption, thereby increasing soil moisture and microbial habitat in soil. Maximum respiration rates may be observed when soils are warming up early in the morning, as they still contain moisture trapped through water vapor adsorption, yet are warm enough to support high microbial activity. Others have also observed peaks in respiration during the relatively cool morning hours29, and these results, which challenge commonly held beliefs about the relationship between respiration and temperature, could be explained by the movement of water from air to soil. Future climate conditions could alter the importance of water vapor adsorption in dryland function, not only through changes in precipitation and relative humidity, but also via interactions with temperature.


Water from air: an overlooked source of moisture in arid and semiarid regions.

McHugh TA, Morrissey EM, Reed SC, Hungate BA, Schwartz E - Sci Rep (2015)

Soil CO2 efflux rates across temperature regimes for control and water vapor adsorption treatment.Error bars are standard error for means (n = 5). The effect of water vapor adsorption (percent change relative to control) is shown with white circles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561883&req=5

f2: Soil CO2 efflux rates across temperature regimes for control and water vapor adsorption treatment.Error bars are standard error for means (n = 5). The effect of water vapor adsorption (percent change relative to control) is shown with white circles.
Mentions: A second laboratory experiment was performed to examine the influence of temperature on water vapor adsorption and the extent to which it regulates soil microbial activity. Field dry soil was incubated for three days under the simulated diurnal temperature fluctuations previously described, or at a constant temperature of either 23 or 40 °C. Water vapor was added to the atmosphere of treatment jars (500 μg fully evaporated into ~1 L headspace), while experimental controls received no water addition. Water vapor adsorption was confirmed by an increase in the gravimetric water content of the soils over the course of the incubation. Relative to their moisture content at the initiation of the experiment (2.3%), the average moisture content of soils in the water vapor adsorption treatment increased by 65.9% for the simulated diurnal treatment, 63.3% for the 23 °C treatment, and 59.9% for the 40 °C temperature regime. Thus, water vapor adsorption occurred under all temperature regimes, and the concomitant increases in CO2 efflux (Fig. 2) indicate that vapor adsorption stimulated soil CO2 production. The effect of water vapor adsorption was significantly greater in soils experiencing simulated diurnal fluctuations (p < 0.0001, Fig. 2). Overall, temperature explained 23% of the variation in soil CO2 efflux rates, while water vapor addition explained 47% (two-way ANOVA). These results suggest that temperature may have opposing effects on microbial activity in dryland soils. On one hand, higher temperatures, which increase molecular diffusion rates, will lead to greater respiration activity but also deplete soils of scarce moisture. On the other hand, colder temperatures will allow more water vapor adsorption, thereby increasing soil moisture and microbial habitat in soil. Maximum respiration rates may be observed when soils are warming up early in the morning, as they still contain moisture trapped through water vapor adsorption, yet are warm enough to support high microbial activity. Others have also observed peaks in respiration during the relatively cool morning hours29, and these results, which challenge commonly held beliefs about the relationship between respiration and temperature, could be explained by the movement of water from air to soil. Future climate conditions could alter the importance of water vapor adsorption in dryland function, not only through changes in precipitation and relative humidity, but also via interactions with temperature.

Bottom Line: This phenomenon rapidly increased soil moisture and stimulated microbial carbon (C) cycling, and the flux of water vapor to soil had a stronger impact than temperature on microbial activity.In a semiarid grassland, we also observed that non-rainfall water inputs stimulated microbial activity and C cycling.Together these data suggest that, during rain-free periods, atmospheric moisture in drylands may significantly contribute to variation in soil water content, thereby influencing ecosystem processes.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, USA.

ABSTRACT
Water drives the functioning of Earth's arid and semiarid lands. Drylands can obtain water from sources other than precipitation, yet little is known about how non-rainfall water inputs influence dryland communities and their activity. In particular, water vapor adsorption--movement of atmospheric water vapor into soil when soil air is drier than the overlying air--likely occurs often in drylands, yet its effects on ecosystem processes are not known. By adding (18)O-enriched water vapor to the atmosphere of a closed system, we documented the conversion of water vapor to soil liquid water across a temperature range typical of arid ecosystems. This phenomenon rapidly increased soil moisture and stimulated microbial carbon (C) cycling, and the flux of water vapor to soil had a stronger impact than temperature on microbial activity. In a semiarid grassland, we also observed that non-rainfall water inputs stimulated microbial activity and C cycling. Together these data suggest that, during rain-free periods, atmospheric moisture in drylands may significantly contribute to variation in soil water content, thereby influencing ecosystem processes. The simple physical process of adsorption of water vapor to soil particles, forming liquid water, represents an overlooked but potentially important contributor to C cycling in drylands.

No MeSH data available.