Responses of root growth of Alhagi sparsifolia Shap. (Fabaceae) to different simulated groundwater depths in the southern fringe of the Taklimakan Desert, China

Alhagi sparsifolia Shap. （Fabaceae） is a spiny, perennial herb. The species grows in the salinized, arid regions in North China. This study investigated the response characteristics of the root growth and the dis- tribution of one-year-old A. sparsifolia seedlings to different groundwater depths in controlled plots. The eco- logical adaptability of the root systems of A. sparsifolia seedlings was examined using the artificial digging method. Results showed that： （1） A. sparsifolia seedlings adapted to an increase in groundwater depth mainly through increasing the penetration depth and growth rate of vertical roots. The vertical roots grew rapidly when soil moisture content reached 3%-9%, but slowly when soil moisture content was 13%-20%. The vertical roots stopped growing when soil moisture content reached 30% （the critical soil moisture point）. （2） The morphological plasticity of roots is an important strategy used by A. sparsifolia seedlings to obtain water and adapt to dry soil conditions. When the groundwater table was shallow, horizontal roots quickly expanded and tillering increased in order to compete for light resources, whereas when the groundwater table was deeper, vertical roots developed quickly to exploit space in the deeper soil layers. （3） The decrease in groundwater depth was probably respon- sible for the root distribution in the shallow soil layers. Root biomass and surface area both decreased with soil depth. One strategy of A. sparsifolia seedlings in dealing with the increase in groundwater depth is to increase root biomass in the deep soil layers. The relationship between the root growth/distribution of A. sparsifolia and the depth of groundwater table can be used as guidance for harvesting A. sparsifolia biomass and managing water resources for forage grasses. It is also of ecological significance as it reveals how desert plants adapt to arid environments.

Diffusion characteristics of oxygenic–thermal coupled airflow in high-altitude sleeping environment

About 1/3 of human life is spent sleeping.The hypoxic and cold environment in high-altitude areas leads to sleep disorders that are more prominently harmful to the human body.To improve the quality of human sleep in high-altitude areas,this study explored the thermal and oxygen environment regulation for plateau sleep.In this study,the influencing factors of the diffusion of oxygenic–thermal coupled airflow were determined through the theoretical analysis of a thermal fluid mechanic jet.This study used computational fluid dynamics(CFD)to investigate the diffusion characteristics of the oxygenic–thermal coupled airflow with a sleeping experiment conducted on the plateau.The results showed that the influence of the thermal plume at 0.1 m near the human face was larger,and the oxygenic–thermal coupled airflow diffusion process was mainly divided into three phases over time.The size and time to stabilize the oxygen volume fraction in the inhalation zone varied between conditions and were strongly influenced by the temperature difference of the supply air.The effects of the thermal and oxygen environment were analyzed using indicators such as facial-area speed ratio,draft risk,and personal oxygen inhalation efficiency.The optimal design strategies were recommended with an outlet air velocity of 1.5 m/s,a temperature difference of 8 K between the outlet airflow and the indoor background air,and an outlet oxygen volume fraction of 30%.The results can provide implications for regulating the thermal and oxygen environment to improve human sleep quality in high-altitude areas.

A novel point source oxygen supply method for sleeping environment improvement at high altitudes

The hypoxic environment at high altitudes causes various sleep disorders.Diffuse oxygen enrichment is an effective way to alleviate sleep disorders and improve the built environment in high altitude areas.In this study,a novel point source local diffuse oxygen supply method was proposed to improve the sleeping oxygen environment.The oxygen supply performance was investigated by the computational fluid dynamics(CFD)method including the oxygen concentration and air velocity distributions.A sleeping experiment was conducted on the plateau to validate the CFD model.The occupied zone including the inhalation zone and the active zone was defined.The results showed that the oxygen concentration showed a rapid rise,then decreased slowly,and finally tended to be stable.The oxygen concentration after stabilization was remarkably influenced by indoor ventilation rate.The sleeping environment’s improvement was examined considering the oxygen enrichment efficiency,uniformity,stability and human comfort demand.The optimal strategies were recommended with a ventilation rate of 1 air change per hour,supplied oxygen concentration of 90%;and jet distance of 0.50 m.The study contributes to improving the oxygen environment and human sleep quality in an effective and energy-saving approach to the sustainable development of buildings in high altitude areas.

Heating load reduction characteristics of passive solar buildings in Tibet,China

China’s Tibet autonomous region has abundant solar energy resources,cold winters,and cool summers.These are ideal conditions for the application of passive solar heating methods.However,differences in climatic conditions and building types can significantly affect passive solar technology’s feasibility,which makes it challenging to promote passive solar buildings in Tibet.In this study,the suitability zone for passive solar technology is categorized based on the sub-zoning indicators for Tibet.By modeling between direct gain windows,Trombe walls,and attached sunspaces,the effect of indoor thermal environments and the capacity for heating load reduction is compared for different passive solar technologies.The climate-difference impact analysis shows that the I-B-1 zone is better suited for passive solar technology than other climate zones.More specifically,this zone has an average energy-saving rate difference of up to 28.61%compared to the II-A-1 zone.The analysis of the impact of building type differences indicates that residential buildings have higher Trombe wall-to-wall ratio limits and more significant potential for energy savings than office buildings.The study also clarifies the implications of Tibet’s climate conditions and building type differences on the effectiveness of passive solar technology.Moreover,it recommends appropriate passive solar technology adoption methods for every climate zone.This study can be used as a reference and engineering guide to improving the indoor thermal environment of Tibetan buildings,tailored to the highly variable local conditions.

Distribution characteristics of indoor oxygen concentration under natural ventilation in oxygen-enriched buildings at high altitudes

Diffuse oxygen supply is an important means to improve the indoor oxygen environment of buildings and ensure physiological and psychological health of immigrants in plateau areas.Existing research on oxygen enrichment strategies at high altitudes has mainly focused on confined spaces under mechanical ventilation,with few studies on the distribution of indoor oxygen concentration under natural ventilation in actual buildings.This study used a verified computational fluid dynamics(CFD)method to investigate the indoor oxygen distribution with practical consideration of natural ventilation at high altitudes.The results showed that the oxygen distribution under wind-driven natural ventilation was more nonuniform than that under buoyancy-driven natural ventilation,with the ratio of local oxygen concentration to overall-mean oxygen concentration,the k value,between 0.8 and 1.3 under wind-driven natural ventilation and between 0.9 and 1.1 under buoyancy-driven natural ventilation.The effects of meteorological condition and oxygen source position on indoor spatial oxygen distribution characteristics were explored with careful examination in human occupied zone under lying,sitting and standing postures.The results can provide implications for effective and energy saving design of indoor oxygen supply system in plateau buildings.

Erratum to: Heating load reduction characteristics of passive solar buildings in Tibet, China

An incorrect Figure 7 was published in the original article.The data for Scenarios A1-A12 were accidentally deleted during typesetting.This erratum provides the correct Figure 7.