The problem of farmland degradation and air pollution caused by wind erosion and particulate matter emissions is serious. Relying on biological soil crust coverage can effectively inhibit the production of wind erosion materials. However, recent studies have discussed the wind erosion and particulate matter emission processes separately and few studies analyzed both, clarifying the changes in the proportion of particulate matter emissions in the total wind erosion. Aiming at the typical farming-pastoral transition zone in the monsoon climate zone, this study used wind tunnels to analyze the wind erosion and particulate matter emissions of algae crusts and moss crusts for different wind speeds and coverage conditions. Results show that the effects of wind speed and coverage on the total wind erosion of biological soil crusts are similar. However, the emission of particulate matter is particularly sensitive to coverage of biological soil crusts. The proportion of particulate matter emissions in wind erosion decreases with increasing wind speed. According to the trend of the proportion with wind speed, the particle emission capacity of moss crust is directly proportional to the particle size and inversely proportional to the coverage. In contrast, the particle emission capacity of algae crust particles is proportional to the particle size, but the relationship with coverage is not regular. The results of this study can improve the knowledge of the relationship between wind erosion and particulate matter emissions and give relevant information for the management of wind erosion and particulate matter emissions.

The counteractive influence of atmospheric CO2 enrichment and drought stress on tree growth results in great uncertainty in growth patterns of planted forests in cold semi-arid regions. We used tree-ring chronology and carbon isotope analysis to track ecophysiological processes in reaction to environmental factors over the past four decades of Populus simonii plantations in cold semi-arid areas in northern China. Our results showed that the boosting effect of the rising atmospheric CO2 concentration (Ca) on iWUE and stem growth was more significant in declined stands. However, the increased iWUE did not negate tree dieback when water stress was present. Therefore, the BAI and iWUE deviation of different health status trees started from a very early age. Climatic factors showed limited influences on the stem growth of the poplar plantations. The inaccessibility of deep soil water due to site-specific soil conditions rendered the trees exposed to chronic soil water stress and constrained stomatal conductance and reduced the CO2 fertilization effect. Consequently, these stands experienced a lower stem growth rate. In summary, we suggest that soil moisture conditions the iWUE and growth sensitivity to global warming and thus portrays site-specific decline episodes of different degrees in drought-prone areas.