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Soil salinization is an increasing global problem, especially in agricultural, coastal, and roadside environments. The increasing intensity of precipitation events due to climate change may be exacerbating these effects, such as through larger pulses of deicing salts entering roadside green stormwater infrastructure (GSI) and stronger coastal storms bringing seawater further inland. Although soils are often amended with biochar to remove pollutants and improve hydraulic properties, it may also mitigate the impact of salinity. Here, we compared the water retention properties and unsaturated hydraulic conductivities of both biochar-amended and unamended GSI soil media with varying salinity levels (1-25 dS m-1, using Na+ salts). The effects of salinity on both matric and osmotic potential included shifts in the plant-available water range, with the magnitude depending on the salt concentration and biochar content. Overall, biochar addition decreased the salinity and improved plant water availability in salt-affected soils. There was an increase in the integral water capacity (which describes the total amount of water the soil media can hold and release to a plant) for biochar-amended saline soils, demonstrating that biochar can reduce the total osmo-matric stress. On a macro scale, the high density of pores in biochar appears to increase soil hydraulic conductivity while reducing osmotic potential by adsorbing salt ions. On a micro scale, the negative surface charge of biochar likely counteracts the impact of the electric double layer of saline soils, reducing the total osmo-matric force on water molecules in soil solution. In effect, this helps the plant's osmotic potential to overcome the forces holding water molecules to soil grains. As soils become more saline due to ongoing climate-related snow events, biochar application might be an effective management technique for roadside and other saline soils. 

Abstract Atmospheric nitrogen (N) deposition and climate change are transforming the way N moves through dryland watersheds. For example, N deposition is increasing N export to streams, which may be exacerbated by changes in the magnitude, timing, and intensity of precipitation (i.e., the precipitation regime). While deposition can control the amount of N entering a watershed, the precipitation regime influences rates of internal cycling; when and where soil N, plant roots, and microbes are hydrologically coupled via diffusion; how quickly plants and microbes assimilate N; and rates of denitrification, runoff, and leaching. We used the ecohydrological model RHESSys to investigate (a) how N dynamics differ between N‐limited and N‐saturated conditions in a dryland watershed, and (b) how total precipitation and its intra‐annual intermittency (i.e., the time between storms in a year), interannual intermittency (i.e., the duration of dry months across multiple years), and interannual variability (i.e., variance in the amount of precipitation among years) modify N dynamics and export. Streamflow nitrate (NO₃⁻) export was more sensitive to increasing rainfall intermittency (both intra‐annual and interannual) and variability in N‐limited than in N‐saturated model scenarios, particularly when total precipitation was lower—the opposite was true for denitrification which is more sensitive in N‐saturated than N‐limited scenarios. N export and denitrification increased or decreased more with increasing interannual intermittency than with other changes in precipitation amount. This suggests that under future climate change, prolonged droughts that are followed by more intense storms may pose a major threat to water quality in dryland watersheds. 

Soil salinization is a global phenomenon that affects large tracts of arid farmland worldwide. It contributes to the loss of soil fertility, declining yields, and – in the most severe cases – land unsuitability for cultivation. Irrigation water applications are both the main cause of and the solution to, anthropogenic (or ‘secondary’) salinization because salt typically enters the soil column as dissolved in irrigation water and leaves it through excess water applications (e.g., leaching). Excess leaching, which places additional water costs in areas affected by water scarcity, can be achieved with different irrigation techniques and practices. Here, by complementing a process-based crop water model with a salt balance of the shallow soil, we investigate the tradeoff between root zone salinization and water conservation to limit withdrawals from the water source. We evaluate how such a tradeoff is achieved under different irrigation technology and excess leaching practices. Considering as a case study the cultivation of tomatoes in Egypt, we find that drip and furrow irrigation allows for better control of salt accumulation, thus preventing crop exposure to salt stress. Drip irrigation achieves this goal with minimal water applications because it maintains the soil wetter. Thus, the (rare) rainfall events find more suitable conditions to drain the excess moisture. Conversely, by using more irrigation water (and ‘less efficiently’), furrow irrigation allows for higher rates of soil drainage and salt leaching. The irrigation schedule typically adopted with sprinkler irrigation allows for soil drying, thus limiting the ability of rainfall events to drain the soil and leach its salts. Collectively, these results highlight the key role of irrigation technology and practices in the management of secondary salinity in dryland agriculture. Specifically, there is a tradeoff between minimizing water use and preventing salt accumulation in the root zone. Drip irrigation exhibits the co-benefit of achieving both goals, while furrow irrigation limits soil salinity at the cost of requiring greater volumes of applied irrigation water. 

Abstract An overlooked phenomenon is a potential increase in the distribution and abundance of plants with the highly water-usage-efficient crassulacean acid metabolism (CAM). In the present article, we critically analyze recent research to investigate to what extent and why CAM plants may have recently expanded their range and abundance under global change. We discuss the ecophysiological and evolutionary mechanisms linked with CAM succulence and the drivers underlying potential CAM expansion, including drought, warming, and atmospheric carbon dioxide enrichment. We further map the biogeographic pattern of CAM expansion and show that some CAM plants (e.g., Cylindropuntia, Opuntia, and Agave) are expanding and encroaching within dryland landscapes worldwide. Our results collectively highlight the recent expansion of CAM plants, a trend that could be sustained under increasing aridity with climate change. We recommend that CAM expansion be evaluated in a data-model integrated framework to better understand and predict the ecological and socioeconomic consequences of CAM expansion during the Anthropocene. 

Abstract Wind erosion and dust emissions affect regions of the world with sparse vegetation cover or affected by agricultural practices that expose the soil surface to wind action. Although several studies have investigated the impact of soil moisture, land use and land cover on soil susceptibility to wind erosion and dust emissions, the effect of surface soil salinity and sodicity on dust emissions, remains poorly understood. Salt accumulation in agricultural soils is a major concern in agroecosystems with high evaporative demand, shallow water tables or irrigated with water rich in dissolved solids. Recent studies have focused on the effect of soil salinity on soil erodibility in dry atmospheric conditions, while the effect of soil salinity and sodicity in more humid conditions still needs to be investigated. Here we use wind tunnel tests to study the effect of high atmospheric humidity on wind erodibility and particulate matter emissions under saline and sodic conditions. We find that the threshold velocity for wind erosion significantly increases with increasing soil salinity and sodicity, provided that the soil crust formed by soil salts is not disturbed. Indeed, with increasing soil salinity, the formation of a soil crust of increasing strength is observed, leading to an increase in the threshold wind velocity and a consequent decrease in particulate emissions. Interestingly, after the threshold velocity was exceeded, soil crusts were readily ruptured by saltating sand grains resulting in comparable or sometimes even higher particulate matter emissions in saline and sodic soils compared to their untreated (‘control’) counterparts which can be explained by salinity‐induced aggregation and sodicity‐driven clay dispersion effects. Lastly, understanding the role of atmospheric humidity under changing climate scenarios will help to modulate the wind erosion processes in saline‐sodic soils and will help mitigate better dust emissions and soil management policies in arid and semi‐arid climate zones. 

Abstract Plants with crassulacean acid metabolism (CAM) are increasing in distribution and abundance in drylands worldwide, but the underlying drivers remain unknown. We investigate the impacts of extreme drought and CO₂enrichment on the competitive relationships between seedlings ofCylindropuntia imbricata(CAM species) andBouteloua eriopoda(C₄grass), which coexist in semiarid ecosystems across the Southwestern United States. Our experiments under altered water and CO₂water conditions show thatC. imbricatapositively responded to CO₂enrichment under extreme drought conditions, whileB. eriopodadeclined from drought stress and did not recover after the drought ended. Conversely, in well‐watered conditionsB. eriopodahad a strong competitive advantage onC. imbricatasuch that the photosynthetic rate and biomass (per individual) ofC. imbricatagrown withB. eriopodawere lower relative to when growing alone. A meta‐analysis examining multiple plant families across global drylands shows a positive response of CAM photosynthesis and productivity to CO₂enrichment. Collectively, our results suggest that under drought and elevated CO₂concentrations, projected with climate change, the competitive advantage of plant functional groups may shift and the dominance of CAM plants may increase in semiarid ecosystems.