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Crossing certain aridity thresholds in global drylands can lead to abrupt decays of ecosystem attributes such as plant productivity, potentially causing land degradation and desertification. It is largely unknown, however, whether these thresholds can be altered by other key global change drivers known to affect the water-use efficiency and productivity of vegetation, such as elevated CO2 and nitrogen (N). Using >5000 empirical measurements of plant biomass, we showed that crossing an aridity (1–precipitation/potential evapotranspiration) threshold of ∼0.50, which marks the transition from dry sub-humid to semi-arid climates, led to abrupt declines in aboveground biomass (AGB) and progressive increases in root:shoot ratios, thus importantly affecting carbon stocks and their distribution. N addition significantly increased AGB and delayed the emergence of its aridity threshold from 0.49 to 0.55 (P  < 0.05). By coupling remote sensing estimates of leaf area index with simulations from multiple models, we found that CO2 enrichment did not alter the observed aridity threshold. By 2100, and under the RCP 8.5 scenario, we forecast a 0.3% net increase in the global land area exceeding the aridity threshold detected under a scenario that includes N deposition, in comparison to a 2.9% net increase if the N effect is not considered. Our study thus indicates that N addition could mitigate to a great extent the negative impact of increasing aridity on plant biomass in drylands. These findings are critical for improving forecasts of abrupt vegetation changes in response to ongoing global environmental change. [ABSTRACT FROM AUTHOR]

• Prolonged use or/and partial mulching of plastic films were tested in maize field. • Prolonged use of films acted as no-tillage to achieve higher grain yield and WUE. • Partial mulching enhanced rain infiltration and water storage in deep soil layers. • Both strategies combined to promote soil fertility and AMF rhizospheric effects. • Both strategies reduced plastic film input but maintained high WUE. Reducing the amount of plastic film while maintaining high water use efficiency & soil health is a huge challenge globally. A two-year field investigation showed that full and half plastic film mulching harvested greater in-season rainfall infiltration into soils, and significantly greater grain yield and water use efficiency under the no-tillage conditions than under the tillage conditions. Among the no-tillage treatments, half plastic film mulching resulted in significantly greater soil light fraction organic carbon by 42.7% and particulate organic carbon by 41.2% than full plastic film mulching respectively, due to its enhanced extramatrical hyphal length, glomalin production and root biomass input. Owing to higher water availability, soil nutrient uptake was accordingly enhanced under no-tillage. This phenomenon was tightly correlated with the improved abundance of arbuscular mycorrhizal fungi. Therefore, it might be feasible and efficient to massively reduce plastic mulching but improve water use efficiency and soil health in semiarid environment. [Display omitted] [ABSTRACT FROM AUTHOR]

Ridge-furrow mulching can reduce soil evaporation and conserve rainfall, thereby increasing crop yield and water use efficiency (WUE) in dryland cropping systems. In this study, we collected 837 observations from 50 published papers and used meta-analysis to investigate whether ridge-furrow and mulching practices are equally effective on maize yield, WUE and evapotranspiration (ET) across a range of precipitation and temperature gradients and soil types in China. Five practices were included: (i) straw mulch on flat plots (SMF), (ii) straw mulch on ridge-furrow plots (SMR), (iii) plastic mulch on flat plots (PMF), (iv) plastic mulch on ridge-furrow plots (PMR), and (v) flat plots without mulch, which was used as a control (CK). The meta-analysis showed that both straw mulch and plastic mulch significantly increased maize yields and WUE (except for SMR), and that plastic mulch was more effective than straw mulch in increasing yields, particularly in cold and dry environments. PMR has the highest yields and is more effective in clay loam than in silt loam soils. Straw mulch, but particularly plastic mulch, increased the soil moisture compared to the CK, while plastic mulch increased soil temperature, mainly in spring. However, the positive effect of plastic mulch on maize yield diminished with increasing mean growing-season temperature and precipitation, reaching zero (similar to the CK of no mulch and flat plots) when the growing-season precipitation was greater than 770 mm and the mean growing-season air temperature exceeded 24 °C. The small benefit of straw mulch (on average about 12%) was similar across the precipitation and temperature gradients, including when the benefits of plastic mulch reached zero. While our analysis has shown the benefits of ridge-furrow plastic mulch on yield and water-use efficiency, it has also highlighted the limitations of the benefits. The results provide a guide to the regions where plastic-film mulch and ridge-furrow planting are likely to improve maize yields and regions where the benefits are likely to be limited. [ABSTRACT FROM AUTHOR]

• Leaf iWUE increases but ecosystem WUE decreases with aridity level. • iWUE and ecosystem WUE displayed almost opposite trends in response to abiotic factors. • MAT was the strongest factor in predicting iWUE, whereas the most robust factor in predicting ecosystem WUE was LAI. Water use efficiency (WUE) links carbon and water cycling and has been recognized as important in understanding the carbon-water budget of terrestrial ecosystems. However, there are few studies comparing WUE at leaf and ecosystem levels in response to environmental variables on a global scale. Here, we compare global-scale patterns and the drivers of leaf and ecosystem WUEs and quantify the relative influence of biotic and abiotic factors. Using published world-wide δ13C (carbon stable isotope composition) measurements for 6751 C 3 plant populations from 174 publications, as well as our own measurements of δ13C for 418 C 3 plant populations across drylands in China, and satellite-based datasets of gross primary production and evapotranspiration, we determined global patterns and the drivers of leaf and ecosystem WUEs. Leaf intrinsic WUE (iWUE) and ecosystem WUE displayed almost opposite trends, in response to abiotic factors on a global scale. iWUE was highest in arid regions and lowest in humid regions, whereas ecosystem WUE was lowest in arid regions and highest in humid regions. Phylogeny had a significant effect on iWUE. Mean annual temperature (MAT) was the strongest factor in predicting iWUE, whereas the most robust factor in predicting ecosystem WUE was leaf area index (LAI). The data indicate that the two different responses at the leaf and ecosystem levels must be considered when modeling carbon and water balances in response to climate change. [ABSTRACT FROM AUTHOR]