Effects of Variation in Tamarix chinensis Plantations on Soil Microbial Community Composition in the Middle Yellow River Floodplain.

Floodplains have important ecological and hydrological functions in terrestrial ecosystems, experience severe soil erosion, and are vulnerable to losing soil fertility. Tamarix chinensis Lour. plantation is the main vegetation restoration measure for maintaining soil quality in floodplains. Soil microorganisms are essential for driving biogeochemical cycling processes. However, the effects of sampling location and shrub patch size on soil microbial community composition remain unclear. In this study, we characterized changes in microbial structure, as well as the factors driving them, in inside- and outside-canopy soils of three patch sizes (small, medium, large) of T. chinensis plants in the middle Yellow River floodplain. Compared with the outside-canopy soils, inside-canopy had higher microbial phospholipid fatty acids (PLFAs), including fungi, bacteria, Gram-positive bacteria (GP), Gram-negative bacteria (GN), and arbuscular mycorrhizal fungi. The ratio of fungi to bacteria and GP to GN gradually decreased as shrub patch size increased. Differences between inside-canopy and outside-canopy soils in soil nutrients (organic matter, total nitrogen, and available phosphorus) and soil salt content increased by 59.73%, 40.75%, 34.41%, and 110.08% from small to large shrub patch size. Changes in microbial community composition were mainly driven by variation in soil organic matter, which accounted for 61.90% of the variation in inside-canopy soils. Resource islands could alter microbial community structure, and this effect was stronger when shrub patch size was large. The results indicated that T. chinensis plantations enhanced the soil nutrient contents (organic matter, total nitrogen, and available phosphorus) and elevated soil microbial biomass and changed microbial community composition; T. chinensis plantations might thus provide a suitable approach for restoring degraded floodplain ecosystems.

Effects of vegetation patterns on soil nitrogen and phosphorus losses on the slope-gully system of the Loess Plateau.

The slope-gully system, the erosion unit on the Loess Plateau, suffers from severe soil erosion and loss of soil nutrients. Restoring vegetation can effectively reduce soil erosion, thereby reducing the loss of nitrogen and phosphorus. In the Loess Plateau, owing to the shortage of water resources and the adverse effects of over-revegetation, the restoration of vegetation in large areas is limited. To efficiently prevent the loss of soil nutrients and reduce non-point source pollution, vegetation patterns need to be reasonably restored. However, it is currently not clear as to how this can be achieved. Different slope-gully systems were established in this study, including pattern A (no vegetation), pattern B (up-slope vegetation), pattern C (middle-slope vegetation), and pattern D (down-slope vegetation). Then, the effects of vegetation patterns on soil total nitrogen (TN) and soil total phosphorus (TP) losses associated with runoff and sediment processes was quantitatively evaluated through the simulated rainfall. The results showed that (1) vegetation pattern markedly affected the yields of runoff, sediment, soil nitrogen, and soil phosphorus, resulting in the following order: pattern A > pattern B > pattern C > pattern D. (2) The correlation between TN and runoff was higher than that between TN and sediment; conversely, TP was more strongly correlated with sediment than with runoff. (3) Nitrogen loss with runoff was the main source of TN (58.76-90.74%), while phosphorus loss with sediment was the main source of TP (48.51-89.30%). Compared with other vegetation patterns, the down-slope can more effectively reduce the yields of runoff and sediment, thereby reducing the loss of TN and TP. Therefore, it was suggested that the lower part of the slope should be considered when revegetating.