Effects of vegetation restoration types on soil nutrients and soil erodibility regulated by slope positions on the Loess Plateau.

Soil degradation is significantly increased driven by soil nutrient loss and soil erodibility, thus, hampering the sustainable development of the ecological environment and agricultural production. Vegetation restoration has been widely adopted to prevent soil degradation given its role in improving soil nutrients and soil erodibility. However, it is unclear which vegetation type has the best improving capacity from soil nutrient and soil erodibility perspectives. This study selected three vegetation restoration types of grasslands (GL), shrublands (SL), and forestlands (FL) along the five slope positions (i.e., top, upper, middle, lower, and foot slope), to investigate the effects of vegetation restoration types on soil nutrients and soil erodibility. All vegetation restoration types were restored for 20 years from croplands (CL). We used comprehensive soil nutrient index (CSNI) and comprehensive soil erodibility index (CSEI) formed by a weighted summation method to reflect the effect of vegetation restoration on the improving capacity of soil nutrient and erodibility. The results showed the vegetation types with the highest comprehensive soil quality index (CSQI) at the top, upper, middle, lower and foot slope were FL (1.92), FL (1.98), SL (2.15), FL (2.37) and GL (3.93), respectively. When only one vegetation type was considered on the entire slope, SL (0.59) and FL (0.59) had the highest CSNI, the SL had the lowest CSEI (0.34) and the highest CSQI (1.89). The CSNI was mainly influenced by soil structure stability index (SSSI), sand content, silt + clay particles, and CSEI was controlled by soil organic matter (SOM), macroaggregates and microaggregates. Moreover, the CSQI was influenced by pH, silt and clay content, and biome coverage (BC). The study suggested the SL were advised as the best vegetation restoration type on the whole slope from improving soil nutrients and soil erodibility.

Indirect regulation of topsoil nutrient cycling by groundwater depth: impacts on sand-fixing vegetation and rhizosphere bacterial communities.

Introduction: The impact of groundwater table depth (GTD) on bacterial communities and soil nutrition in revegetated areas remains unclear. Methods: We investigated the impacts of plant growth and soil physicochemical factors on rhizosphere bacterial communities under different GTD. Results: The four plant growth indices (Pielou, Margalef, Simpson, and Shannon-Wiener indices) and soil water content (SWC) at the Artem and Salix sites all showed a decreasing trend with increasing GTD. Salix had a higher nutrient content than Artem. The response of plant rhizosphere bacterial communities to GTD changes were as follows. Rhizosphere bacteria at the Artem and Salix sites exhibited higher relative abundance and alpha diversity in SW (GTD < 5 m) compared than in DW (GTD > 5 m). Functional microbial predictions indicated that the rhizosphere bacterial communities of Artem and Salix promoted carbon metabolism in the SW. In contrast, Artem facilitated nitrogen cycling, whereas Salix enhanced both nitrogen cycling and phototrophic metabolism in the DW. Discussion: Mantel test analysis revealed that in the SW of Artem sites, SWC primarily governed the diversity of rhizosphere and functional bacteria involved in the nitrogen cycle by affecting plant growth. In DW, functional bacteria increase soil organic carbon (SOC) to meet nutrient demands. However, higher carbon and nitrogen availability in the rhizosphere soil was observed in the SW of the Salix sites, whereas in DW, carbon nutrient availability correlated with keystone bacteria, and changes in nitrogen content could be attributed to nitrogen mineralization. This indicates that fluctuations in the groundwater table play a role in regulating microbes and the distribution of soil carbon and nitrogen nutrients in arid environments.

Spatial-temporal variation, ecological risk, and source identification of nutrients and heavy metals in sediments in the peri-urban riverine system.

A great deal of attention has been directed to the toxicity, enrichment, and accumulation of urban river sediment pollution. To understand the spatial-temporal variation, ecological risk and source of nutrients, and heavy metals in sediments from the Weihe River, the concentrations of total nitrogen (TN), total phosphorus (TP), organic matter (OM), and 10 heavy metals (Cd, Sb, As, Co, Cu, Pb, Ni, Cr, Zn, and Mn) in sediments at 14 sampling sites along the river were investigated. The results showed that nutrients and heavy metals had an interannual decreasing trend, and that the high-value regions were concentrated in urban locations within the study area. Ecological risk assessment results showed that TN was between the security level (no toxic effect) and the lowest level (tolerable for organisms), TP was at the lowest level, and OM was within the security level, all mainly from external sources. The geoaccumulation index (Igeo) and enrichment factor (EF) of 10 heavy metals were all within the unpolluted level, while the pollution load index (PLI) of 12 sampling sites had reached the moderate pollution level. The results of Pearson correlation, principal component analysis, and cluster analysis showed that heavy metals originated mainly from industrial and domestic sources, geochemical environments, and agricultural activities, indicating that heavy metals in the Weihe River sediments were influenced significantly by anthropogenic activities. The results are expected to provide a scientific basis for the development and utilization of the Weihe River water resources.