Amidst urbanization and industrialization in China, abandoned farmland plays a crucial role in safeguarding plant diversity within agricultural landscapes. This study aimed to examine the patterns of seasonal variation in plant diversity within abandoned farmland habitats in the Huang–Huai Plain region. Nonparametric tests were employed to analyze plant species diversity and phylogenetic diversity across seasons. Redundancy analysis and linear regression were conducted to examine the associations between plant species composition, species diversity, phylogenetic diversity, and soil environmental factors. Our results showed that plant species diversity, richness, and phylogenetic diversity were highest in spring, followed by summer, and lowest in autumn. The phylogenetic structure of plant communities demonstrated a tendency to diverge in spring, become random in summer, and cluster in autumn. Soil available potassium and soil organic matter emerged as important factors influencing plant species composition. The content of soil organic matter and ammonium nitrogen level exhibited a significantly positive correlation with the species diversity and phylogenetic diversity of plants. This study underscores the significance of considering seasonal and temporal scales when investigating plant diversity and provides a theoretical basis for biodiversity conservation in agricultural landscapes.

Riparian woodlands play a significant role in hosting plant diversity and maintaining soil and water resources. However, riparian woodlands are highly sensitive to fluvial and human disturbances, and most are now degraded as a result. In this study, we analyze variation in soil nutrients and plant diversity and their relationships in riparian woodlands along the middle and lower reaches of the Yellow River in China, based on field investigation. Our results indicate that soil nutrient content and plant diversity were lowest in plots located closest to the river. Specifically, we found a hump-shaped relationship with increasing distance from river. This result can be attributed to the intermediate disturbance hypothesis,which explains that species diversity increase at intermediate disturbance levels. However, total species richness within each subzone was greatest close to the river, due primarily to the high level of species turnover observed among plots located closest to the river. Soil nutrients in the riparian woodlands were positively correlated with plant diversity across all distances. Specifically, soil TC, NO3 --N, and A-P contents were significantly correlated with plant species richness and diversity. This relationship also conformed to a hump-shaped response curve between species richness and soil nutrients, though species richness increases with increasing nutrient levels. Results from this study can provide a basis for sustainable management of riparian ecosystems.

Water and sediment regulation aimed at aquatic ecosystems and preserving reservoir capacity to minimize the negative consequences of dams can fundamentally change the distribution of heavy metals (HMs) in the reservoir and downstream reaches. However, the effects of water and sediment regulation on variation in HMs are still poorly understood. In this study, the variations in concentration, contamination, human health risk, potential sources, and influencing factors of the metalloid As and HMs (Cr, Hg, Ni, Pb, and Zn) in surface water in the reservoir and the downstream reach of the Xiaolangdi Dam (XLD) following the operation of the water-sediment regulation scheme (WSRS) were determined. These results indicate that HM concentrations in the two post-WSRS seasons were much lower than the water quality standards, but were significantly increased over time due to the trapping effects of the XLD (p < 0.05, except for Zn). However, As concentration in the reservoir was significantly lower than that observed in downstream reaches, likely due to anthropogenic input from agricultural activities. Meanwhile, HM concentrations varied with distance to the dam, which displayed a distinct accumulation closer to the dam in the post-WSRS II season. The contamination of HMs, the carcinogenic risk of exposure to As, and the noncarcinogenic risks associated with exposure to Hg, Ni, Pb, and Zn via the direct ingestion pathway of drinking water were all within acceptable levels following the WSRS, but increased over time. The carcinogenic risk of Cr in the post-WSRS II season was at an unacceptably high level, particularly at sites near the dam. Hydrological characteristics (water level and flow rate) were the dominant factors in determining the distribution of HMs. These results can provide new insight for a better understanding of the variations in HMs following the water and sediment regulation practices, and guide future management in regulating the trapping effects of dams.

As urbanization and industrialization continue to advance rapidly in China, the issue of farmland abandonment is becoming more prevalent. Nevertheless, this phenomenon is crucial in protecting plant diversity in agricultural landscapes. This study sought to investigate the seasonal variation patterns of plant diversity in abandoned farmland habitats within the Huang-Huai Plain region. The plant community characteristics during spring, summer, and autumn were examined, and the variations in plant species diversity and phylogenetic diversity were analyzed across the different seasons. Spearman correlation analysis was used to explore the interrelationships among various diversity indices, and redundancy analysis and linear regression were employed to examine the connection between plant diversity indices and key soil environmental factors. The results showed that significant seasonal changes occurred in the plant community characteristics of abandoned farmland in the Huang-Huai Plain, with the number of families, genera, and species being highest in spring, followed by summer and autumn. Similarly, plant species diversity, richness index, and phylogenetic diversity were also higher in spring than in summer and autumn. The phylogenetic structure of plant communities tended to diverge in spring, be random in summer, and be clustered in autumn. The phylogenetic diversity and species diversity indexes were strongly associated, and soil organic matter and ammonium nitrogen were significantly positively correlated with plant species diversity and phylogenetic diversity. This study highlights the importance of considering seasonal and temporal scales when studying plant diversity and provides a theoretical basis for biodiversity conservation and agricultural production in the Huang-Huai Plain of China.