Shuai Zhang

In rocky mountainous regions characterized by shallow, barren soils and water scarcity, non-rainfall water, such as condensation, plays a crucial ecological role in mitigating seasonal drought in forest trees. To enhance the water-use capacity of vegetation, this study utilized a previously developed eco-friendly PVA–CS/SA–Ca²⁺ hydrogel. The primary objective was to elucidate the synergistic mechanisms by which the hydrogel optimizes condensed water utilization and drives the ecophysiological recovery of Pinus tabuliformis and Platycladus orientalis, two keystone afforestation species in northern China. Utilizing a controlled environmental chamber to simulate the condensation and humidification process, the experiment established three treatments: a control group (CK), a pot-sealed group (PS, to isolate soil water absorption), and a hydrogel-amended group (Hydrogel-Root Wrapping, HRW). To comprehensively evaluate the water utilization mechanisms, the amount of condensed water captured by the system was quantified, and hydrogen isotope tracing techniques were employed to precisely track water transport pathways and contribution rates. Concurrently, key physiological parameters were systematically determined, including leaf water potential, stomatal conductance, leaf water content, net photosynthetic rate, and transpiration rate. The results demonstrated the following: (1) the hydrogel significantly enhanced the condensation water capture capacity of the system. The net mass gains of the Pinus tabuliformis and Platycladus orientalis systems under the HRW treatment reached 26.3 g and 32.9 g, respectively, which represented 1.17 and 1.30 times those of the CK treatment, and 1.52 and 1.54 times those of the PS treatment. (2) Isotope tracing confirmed that both tree species possess significant Foliar Water Uptake (FWU) capacity. Following condensation, the δ²H values in the leaves of Platycladus orientalis and Pinus tabuliformis surged to 113.5‰ and 85.3‰, respectively, with stem δ²H values increasing by 31‰ and 22‰ compared to their initial baseline. (3) The introduction of the hydrogel in the HRW treatment provided 11.2% and 10.9% of the stem water supply for Platycladus orientalis and Pinus tabuliformis, respectively, thereby reducing their dependence on soil water by 8.3% and 13.1%. In contrast, there was no significant difference in the fractional contribution of condensation water to stem water between the PS and CK treatments. (4) Regarding physiological responses, the application of the hydrogel material effectively improved the physiological status of the plants. The leaf water potentials of Pinus tabuliformis and Platycladus orientalis increased to −0.15 MPa and −1.32 MPa, respectively. Concurrently, stomatal conductance (3.25 and 3.64 mm·s⁻¹) and leaf water content (58.4% and 67.4%) were significantly higher than those in the other treatments. In summary, the hydrogel can significantly enhance the capture, conversion, and utilization efficiency of condensation water by vegetation, effectively optimizing the water supply dynamics of the system. This provides key theoretical and technical support for ecological afforestation in difficult sites within rocky mountainous areas.

Leaf area index (LAI) is a key vegetation structural parameter widely used to quantify vegetation dynamics. A thorough understanding of its spatiotemporal characteristics and driving mechanisms is essential for sustainable ecosystem management. This study combines LAI and climate remote sensing data with socioeconomic statistics, and uses the Geographically and Temporally Weighted Regression (GTWR) model and geographic detector to identify the key drivers of LAI changes and their spatial differentiation characteristics. The results indicate a significant upward trend in the LAI across the basin, with a markedly higher growth rate after 2000 (0.0123/year) compared to the period before 2000 (0.0028/year). Spatially, before 2000, 57% of the regions showed an increasing trend in LAI, while after 2000, 69% of the regions exhibited an increasing trend in LAI. In terms of temporal LAI dynamics, in the eastern region, the positive promotion effect of the Grain for Green policy (GRGR) was the most significant factor affecting LAI changes. In the central region, the employed population ratio (EPR) emerged as the dominant factor driving LAI increase. In the western region, the negative effect of the urban–rural income ratio (IR) served as the primary driver of LAI change. Regarding the spatial distribution of LAI, both natural and policy factors were statistically significant. Mean precipitation (MP) and mean slope (MS) exerted the most pronounced influences, followed by mean temperature (MT) and GRGR, whereas mean elevation (MD) showed the weakest effect. Notably, socioeconomic factors did not demonstrate statistically significant impacts on the spatial distribution of LAI. This study provides a theoretical foundation for understanding the driving mechanisms of LAI dynamics in the Yellow River Basin and offers scientific support for ecological restoration and sustainable management in the region.

To improve the efficient use of nitrogen and decrease the environmental pollution of N losses, a novel and biodegradable composite hydrogel was prepared by chemical cross-linking synthesis using gelatin (Gel), chitosan (CS) and polylactic acid (PLA) as raw materials. Urea as the nitrogen source was loaded into this new biodegradable hydrogel using the solution immersion method. The chemical structures of the composite hydrogels were characterized and their properties were analyzed by XRD and XPS. The regulation of urea loading and the swelling behavior of the composite hydrogel under different temperature conditions were investigated; the release behavior and release model of the composite hydrogel in the aqueous phase was explored. The results show that the loading of urea is controllable in aqueous urea solution with different concentrations. In the water phase, it shows a three-stage sustained release behavior, that is, the initial release rate of urea is relatively fast, and the medium release rate of urea gradually slows down, and finally the nutrient release rate tends to be flat. The release behavior in the water phase fits to the Ritger–Peppas model. Within 10 min, 180 min and 900 min, the cumulative nutrient release rate of gelatin/chitosan/PLA-urea (GCPU) composite hydrogel is 20%, 70% and 86%, respectively. Compared with pure urea, The urea diffusion time of GCPU was extended by 1350-times. In addition, the GCPU also has good water absorption and water retention properties, in which average water content can reach as high as 4448%. All of the results in this work showed that GCPU hydrogel had good water absorption and retention and N slow-release properties, which are expected to be widely used in sustainable agriculture and forestry, especially in arid and degraded land.

Hydrogels are highly hydrophilic polymers that have been used in a wide range of applications. In this study, we prepared PVA–CS/SA–Ca²⁺ core–shell hydrogels with bilayer space by cross-linking PVA and CS to form a core structure and chelating SA and Ca²⁺ to form a shell structure to achieve multiple substance loading and multifunctional expression. The morphology and structure of core–shell hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The factors affecting the swelling properties of the hydrogel were studied. The results show that the PVA–CS/SA–Ca²⁺ hydrogel has obvious core and shell structures. The SA concentration and SA/Ca²⁺ cross-linking time show a positive correlation with the thickness of the shell structure; the PVA/CS mass ratio affects the structural characteristics of the core structure; and a higher CS content indicates the more obvious three-dimensional network structure of the hydrogel. The optimal experimental conditions for the swelling degree of the core–shell hydrogel were an SA concentration of 5%; an SA/Ca²⁺ cross-linking time of 90 min; a PVA/CS mass ratio of 1:0.7; and a maximum swelling degree of 50 g/g.

Since the establishment of blown sand physics, surface roughness has been widely used in current research to indicate the ability of a surface to resist wind erosion and to evaluate the windproof effect of protective measures. However, since the calculation of surface roughness can result in different values and its applicability is poor, there are disadvantages to its use. Therefore, it is proposed that the boundary layer displacement thickness should be used rather than roughness as an indicator to solve such problems. To analyze the new indicator’s accuracy and applicability when evaluating the effect of protective measures, a wind tunnel simulation experiment on a typical mechanical protection measure commonly used for sand control in China was conducted. Indicators of roughness and boundary layer displacement thickness were compared in evaluating the windproof performance of a Salix psammophila sand barrier of differing heights, side lengths, and porosities. The wind speed acceleration rate and effective protection area, which can directly reflect the protective effect of a sand barrier, were analyzed as evaluation criteria. The results show that roughness can only reflect the influence of height on the windbreak effect of sand barriers, whereas the boundary layer displacement thickness accurately showed the influence of height, side length, and porosity on the windproof effect of the sand barriers. Compared with roughness, the boundary layer displacement thickness was more strongly correlated with the effective protection area. Therefore, the boundary layer displacement thickness, rather than roughness, should be used as a new indicator when evaluating the windproof effect of protective measures.

Due to their simple layout and adaptability to various environments, straw checkerboards are widely used to control windblown sand in China. To fully understand the wind proofing and sand-fixing benefits of different board specifications, and to determine the restorative effects of straw checkerboard, we tested different sizes of checkerboard, determined their performance as a windbreak and in trapping shifting sand, and constructed models based on wind tunnel tests, enabling the wind speed flow field to be analysed. We also sampled the soil in areas where straw checkerboards had been established for several years and analysed the trends in soil physical and chemical properties over time. We found that all sizes of straw checkerboard effectively reduced the wind speed near the surface and formed a protected area, with the best protective effect achieved for a one-meter board. All sizes of straw checkerboard effectively intercepted windblown sand to form surface accumulation, with the one-meter board again showing the best performance. The use of a straw checkerboard also effectively improved the physical and chemical properties of soil and promoted ecological restoration. These results indicate that straw checkerboards are a low-cost engineering measure that could play an important role in desertification control and the ecological restoration of sandy land ecosystems.