Abstract: Effective biodiversity conservation requires reasonable targeted regionalization, and insufficient data and unclear targets often lead to conservation biases and deficiencies. So, we explored quantitative and representative methods to delineate freshwater biodiversity regions. We established a river-lake network model as the mask of the Yangtze River Basin. Based on field samplings and the literatures, we filtered the environmental variables by principal component analysis, and identified key factors to distribution of fish functional group and macroinvertebrate taxonomic group by Mantel test, then conducted species distribution models using maximum entropy modeling. We delineated biodiversity regionalization using the binary data of high suitability in the hydrological units (HUs) by spatial cluster analysis, then calculated Jaccard dissimilarity index (βdissim) among all HUs. Proportion of vegetation and waterbody type are key to the distribution of annelids and mollusks, while distribution of arthropods depend more on bioclimatic and topographic variables. For fish, topographic and hydrological variables were more important. We have delineated seven freshwater biodiversity regions (HWR, HDR, WSR, DQR, QWR, LXR and FPR). The βdissim of fish is the highest in LXR and FPR, while for macroinvertebrates, it is the highest in HWR. Species distribution models could compensate for the scarce and uneven data. Single target, and region delineation based on provincial administration or subbasins are insufficient for biodiversity conservation. Transition zones and confluent regions exhibit higher species richness and beta diversity, while these regions are often overlooked. We hope the method could serve as a reference to realize comprehensive of systematic conservation planning for biodiversity conservation.

Converting alfalfa (Medicago sativa L.) into cropland (rotation cropland, RC) is a common way of land use to reuse degraded alfalfa pasture. However, it is a big challenge for RC to achieve high productivity and maintain high soil organic carbon (SOC) achieved by previous alfalfa. Here, we conducted a nine-year field experiment, with continuous cropland (CC) under plastic film mulching as reference, to evaluate soil moisture restoration, crop productivity, and SOC in RC also under plastic film mulching, in the case of fertilization and non-fertilization, respectively. SOC and total soil N in the alfalfa pasture before conversion were 12.3% and 7.7% higher, but the available P and inorganic-N were 59.2% and 71.5% lower than in CC, respectively. The crop yield and biomass were not significant between RC and CC following the second year of conversion in both fertilization and without fertilization cases. The SOC and total soil N in RC with fertilization were similar to the previous alfalfa pasture throughout the nine-year experiment, while decreased in RC without fertilization by 8.3% and 7.5% after the nine years. Soil moisture in RC at 0-0.6 m restored to the level of CC only one year after the conversion, and restored from 77.6% and 56.2% of CC to 95.3% and 69.2% at 0.6-2 and 2-5 m through nine-years after conversion. These findings help to dispel the worries about the long-term low production and rapid decline of SOC in RC and support for sustainable high-productivity and high SOC sequestration in dryland farming.

The long-term planting of alfalfa (Medicago sativa L.) gradually reduces the yield and causes severe soil desiccation in semiarid areas. Converting alfalfa pasture into cropland (rotation cropland, RC) is a common way of land use to restore soil moisture. However, it is a challenge for RC to achieve high productivity and maintain high soil organic carbon (SOC) achieved by previous alfalfa. Here, we conducted a nine-year field experiment, with continuous cropland (CC) under plastic film mulching as reference, to evaluate soil moisture restoration, crop productivity, and SOC in RC also under plastic film mulching, in the case of fertilization and non-fertilization, respectively. After the long-term alfalfa pasture was converted to RC, Soil moisture at the upper 2 m profile, especially the upper 0.6 m, restored rapidly to the levels like the CC. The crop yield and biomass were not significant between RC and CC following the second year of conversion in both fertilization and without fertilization cases. The SOC content in RC without fertilization decreased gradually with the conversion years. However, it had no significant difference in RC with fertilization with the previous alfalfa pasture throughout the nine-year experiment. These findings imply that fertilization allowed the RC under plastic film mulching to keep similar productivity to CC and maintain SOC continuously the same as the previous alfalfa pasture while gradually restore soil moisture. This study provided promising adaptive management for increasing agricultural carbon sequestration and crop productivity in semi-arid Loess Plateau and other similar areas.