Soil microorganisms and their diversity are important bioindicators of soil carbon and nutrient cycling. Land use type is a major determining factor that influences soil microbial community composition in floodplain ecosystems. However, how the structure and diversity of soil microbial communities respond to specific changes in land use, as well as the main drivers of these changes, are still unclear. This study was conducted in the Yellow River floodplain to examine the effects of land use type on soil microbial communities. Four land use types (shrubland, farmland, grassland and forest) were selected, wherein shrubland served as the baseline. We measured soil microbial structure and diversity using phospholipid fatty acids (PLFAs). Land use type significantly affected total, bacterial and fungal PLFAs, and the gram-positive/negative bacterial PLFAs. Compared with shrubland, peanut farmland had higher total and bacterial PLFAs and forest had higher fungal PLFAs. Soil pH and phosphorus were the predominate drivers of microbial PLFAs, explaining 37% and 26% of the variability, respectively. Soil total nitrogen and nitrate nitrogen were the main factors increasing microbial community diversity. Peanut farmland had the highest soil carbon content, soil carbon stock, total PLFAs and microbial diversity, suggesting that farmland has great potential as a carbon sink. Our findings indicated that peanut farmland in the Yellow River floodplain is critical for maintaining soil microbial communities and soil carbon sequestration.

Changes in spring and autumn phenology and thus growing season length (GSL) pose great challenges in accurately predicting terrestrial primary productivity. However, how spring and autumn phenology in response to land-use change and nitrogen deposition and underlying mechanisms remain unclear. This study was conducted to explore the GSL and its components [i.e., the beginning of growing season and ending of growing season (EGS)] in response to mowing and nitrogen addition in a temperate steppe on the Mongolia Plateau during 2 years with hydrologically contrasting condition [dry (2014) vs. wet (2015)]. Our results demonstrated that mowing advanced the BGS only by 3.83 days, while nitrogen addition advanced and delayed the BGS and EGS by 2.85 and 3.31 days, respectively, and thus prolonged the GSL by 6.16 days across the two growing seasons from 2014 to 2015. When analyzed by each year, nitrogen addition lengthened the GSL in the dry year (2014), whereas it shortened the GSL in the wet year (2015). Further analyses revealed that the contrasting impacts of nitrogen on the GSL were attributed to monthly precipitation regimes and plant growth rate indicated by the maximum of normalized difference vegetation index (NDV_max). Moreover, changes in the GSL and its two components had divergent impacts on community productivity. The findings highlight the critical role of precipitation regimes in regulating the responses of spring and autumn phenology to nutrient enrichment and suggest that the relationships of ecosystem productivity with spring and autumn phenology largely depend on interannual precipitation fluctuations under future increased nitrogen deposition scenarios.

Variations in soil aggregates and soil organic carbon (SOC) in response to land-use change are important to understanding the carbon cycle in forest ecosystems. However, few studies investigated the effect of forest type on aggregate stability, SOC content, and particulate organic carbon (POC) content. Therefore, we collected soil and fine root samples in two natural forests (Pinus massoniana and Quercus variabilis) and a planted forest (Cunninghamia lanceolata) in a warm temperate–subtropical climate transition zone to analyze the effect of forest type on aggregate stability, SOC content, and POC content. The results showed that the mean weight diameter (MWD) of the soil aggregates was significantly higher in Quercus variabilis and Pinus massoniana forests (62% and 21%, respectively) than in the Cunninghamia lanceolata forest due to higher mycelial length density, mycelial infection rate, and glomalin content. Similarly, the SOC and POC contents were significantly higher in Quercus variabilis and Pinus massoniana forests than in the Cunninghamia lanceolata forest (p < 0.05). The dominant size fraction of aggregate was highly correlated with the carbon fraction content. The SOC and POC contents and fungal traits (mycelial length density, mycelial infection rate, and glomalin content) were significantly positively correlated with the MWD. These results indicated that natural forests had higher aggregate stability than planted forests due to higher SOC content and more favorable fungal traits in the warm temperate–subtropical climate transition zone.

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.