Response of aboveground carbon balance to long-term, experimental enhancements in precipitation seasonality is contingent on plant community type in cold-desert rangelands

Abstract

Semi-arid rangelands are important carbon (C) pools at global scales. However, the degree of net C storage or release in water-limited systems is a function of precipitation amount and timing, as well as plant community composition. In northern latitudes of western North America, C storage in cold-desert ecosystems could increase with boosts in wintertime precipitation, in which climate models predict, due to increases in wintertime soil water storage that enhance summertime productivity. However, there are few long-term, manipulative field-based studies investigating how rangelands will respond to altered precipitation amount or timing. We measured aboveground C pools and fluxes at leaf, soil, and ecosystem scales over a single growing season in plots that had 200 mm of supplemental precipitation added in either winter or summer for the past 21 years, in shrub- and exotic-bunchgrass-dominated garden plots. At our cold-desert site (298 mm precipitation during the study year), we hypothesized that increased winter precipitation would stimulate the aboveground C uptake and storage relative to ambient conditions, especially in plots containing shrubs. Our hypotheses were generally supported: ecosystem C uptake and long-term biomass accumulation were greater in winter- and summer-irrigated plots compared to control plots in both vegetation communities. However, substantial increases in the aboveground biomass occurred only in winter-irrigated plots that contained shrubs. Our findings suggest that increases in winter precipitation will enhance C storage of this widespread ecosystem, and moreso in shrub- compared to grass-dominated communities.

Vegetation and precipitation shifts interact to alter organic and inorganic carbon storage in cold desert soils

“…, Germino and Reinhardt , McAbee et al. ), carbon uptake (McAbee et al. ), and litterfall (Campos et al.…”

“…) and increases in soil heterotrophic activity (McAbee et al. ); the former being the cause and the latter being a symptom of greater N scavenging by soil microbes, with C cycling intimately linked to N availability (Craine et al. ).…”

“…GROW treatments also elicited marginal increases in aboveground net primary production (DORM >GROW ≥ Ambient; Germino and Reinhardt , McAbee et al. ) but simultaneously increased soil respiration (McAbee et al. ).…”

“…), and soil heterotrophic activity (McAbee et al. ). Severely lacking are studies examining the response of soil C throughout the soil profile to long‐term manipulations of rainfall, vegetation, and their interaction in cold desert ecosystems.…”

Controls on gross production in an aspen–sagebrush vegetation mosaic

“…Critical zone (CZ) science is a systems approach for examining the structure and function of the Earth's surface from the top of the plant canopy to the groundwater (Richter & Billings, ), and it provides a framework for understanding the various meteorological, ecological, and geological factors regulating water availability and GEE in arid and semiarid regions. In the northern Great Basin, work emphasizing the ecological and climatic factors governing plant–water relationships often finds that plant growth, leaf‐gas exchange, net ecosystem CO 2 exchange (NEE = GEE minus ecosystem respiration), and GEE are driven by precipitation timing, spring precipitation, or snowpack conditions, and that carbon uptake or plant growth typically increases with greater precipitation amount (Bates, Svejcar, Miller, & Angell, ; Bowling, Bethers‐Marchetti, Lunch, Grote, & Belnap, ; Gilmanov et al, ; Kwon, Pendall, Ewers, Cleary, & Naithani, ; Loik et al, ; McAbee, Reinhardt, Germino, & Bosworth, ; Perfors, Harte, & Alter, ). However, the ability of the soil to store water for dry‐season use (Germino & Reinhardt, ; T. J. Smith et al, ), subsurface water redistribution (McNamara, Chandler, Seyfried, & Achet, ; Seyfried, Grant, Marks, Winstral, & McNamara, ), and snow drifting (Winstral & Marks, ) are important CZ features that create spatially and temporally complex patterns of water availability that often cannot be inferred from microclimate alone.…”