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

Abstract

Dryland ecosystems are experiencing shifts in rainfall and plant community composition, which are expected to alter cycling and storage of soil carbon (C). Few experiments have been conducted to examine long‐term effects on (1) soil organic C (SOC) pools throughout the soil profile, and (2) soil inorganic C (SIC) pools as they relate to dynamic changes in C storage and climate change. We measured SOC and SIC from 0 to 1 m beneath plants and in adjacent interplant microsites following nearly 20 yr of experimental manipulations of plant community (native sagebrush steppe or monoculture of exotic crested wheatgrass) and the amount and timing of water availability (ambient, or doubling of annual rainfall in the dormant, DORM, or growing, GROW, season). Under sagebrush plants, GROW increased both SOC and SIC pools, resulting in total carbon (TC) pools 15% greater than plots receiving ambient precipitation, while DORM decreased SOC and SIC pools, decreasing TC pools 20% from ambient. Under crested wheatgrass plants, GROW increased SOC by 73% but decreased SIC by 11% relative to ambient, netting no change in TC pools, while DORM SIC pools were 5% greater than ambient, with no significant increase in either SOC or TC pools. GROW significantly increased TC pools for interplant microsites, regardless of vegetation treatment. At the community scale and summing C pools weighted by percent patch cover, patterns of TC pool were similar to plot measurements. Our findings suggest that sagebrush communities can become a net C source to the atmosphere with increases in dormant season rainfall rather than a C sink as previously predicted. We also provide evidence of SIC as an important and dynamic C sequestration mechanism in drylands. Consideration of vegetation type, all or most of the soil profile, and both organic and inorganic C pools are all important to accurately predict C sequestration with changing climate and disturbance in drylands.

Microbial residues as indicator for inorganic carbon transition to organic carbon in coastal saline soils

“…Along the natural salinity gradient, the SIC was higher at low salinity, < 6suggesting that salinity stress influences SIC cycling (Wang et al, 2019). SIC has two potential determinants: (1) uptake and deposition of atmospheric CO 2 by base cation (Xie et al, 2009;Raheb et al, 2017), and (2) re-distribution of respired CO 2 among microorganisms and roots (Huber et al, 2019). pH markedly influences the magnitude of SIC, soil acidity at low pH results in SIC loss, and soil alkalinity at high pH increases atmospheric and soil CO 2 absorption of base cations (Liu et al, 2020a;Raza et al, 2020).…”

Interannual climate variability mediates changes in carbon and nitrogen pools caused by annual grass invasion in a semiarid shrubland

“…Huber et al (2019) also found that increases in winter rainfall can turn soil under sagebrush plants into a net C source. In stages III and IV, litter C:N ratio was not a significant part of the model, perhaps because the litter layer was composed mainly B. tectorum detritus, and the C:N ratio did not differ between years.…”

“…In semiarid shrubland systems of the western United States, invasion by herbaceous species can interact with drought to reduce an ecosystem's capacity to sequester C (Esch et al, 2019). A. tridentata communities are a C sink during the growing season and this is amplified with increased summer precipitation (Germino et al, 2015;Huber et al, 2019). However, they may become a source with increases in dormant season precipitation (Huber et al, 2019).…”

“…However, they may become a source with increases in dormant season precipitation (Huber et al, 2019). While plants are dormant, the accelerated microbial C mineralization triggered by precipitation generates inorganic C that is susceptible to leaching or atmospheric losses via respiration (Huber et al, 2019), without being offset by the C assimilation resulting from plant growth. A. tridentata typically grows in neutral to slightly alkaline soils (Hooker et al, 2008), and in alkaline soils, some of the inorganic C may be composed of carbonates which can also be lost via leaching, only to accumulate at the bottom of hillslopes (Johnson et al, 2014).…”

Microbial residues as the nexus transforming inorganic carbon to organic carbon in coastal saline soils

“…Plant-assimilated inorganic C (i.e., CO 2 ) is the major SOC source that atmospheric and soil-released CO 2 fixed via photosynthesis contributes to the SOC pool through litter and root inputs (Fig. 1; Le Quéré et al, 2018;Huber et al, 2019). Few studies have reported that microorganisms can also utilize inorganic C to maintain cell proliferation and growth (Zamanian et al, 2016;, whether microorganisms convert SIC to SOC remains unclear owing to the lack of a microbial indicator between SIC…”