Response of hydrology and nutrient losses to different extreme rainfall conditions in a coastal watershed influenced by orchards.

Global warming is altering the frequency of extreme rainfall events and introducing uncertainties for non-point source pollution (NPSP). This research centers on orchard-influenced planting areas (OIPA) in the Wulong River Watershed of Shandong Province, China, which are known for their heightened nitrogen (N) and phosphorus (P) pollution. Leveraging meteorological data from both historical (1989-2018) and projected future periods (2041-2100), this research identified five extreme rainfall indices (ERI): R10 (moderate rain), R20 (heavy rain), R50 (rainstorm), R95p (Daily rainfall between the 95th and 99th percentile of the rainfall), and R99p (>99th percentile). Utilizing an advanced watershed hydrological model, SWAT-CO2, this study carried out a comparison between ERI and average conditions and evaluated the effects of ERI on the hydrology and nutrient losses in this coastal watershed. The findings revealed that the growth multiples of precipitation in the OIPA for five ERI varied between 16 and 59 times for the historical period and 14 to 65 times for future climate scenarios compared to the average conditions. The most pronounced increases in surface runoff and total phosphorus (TP) loss were observed with R50, R95p, and R99p, showing growth multiples as high as 352 and 330 times, and total nitrogen (TN) growth multiples varied between 4.6 and 30.3 times. The contribution rates of R50 and R99p for surface runoff and TP loss in the OIPA during all periods exceeded 55%, however, TN exhibited the opposite trend, primarily due to the dominated NO3-N leaching in the sandy soil. This research revealed how the OIPA reacts to different ERI and pinpointed essential elements influencing water and nutrient losses.

The response of non-point source pollution to climate change in an orchard-dominant coastal watershed.

China is the largest global orchard distribution area, where high fertilization rates, complex terrain, and uncertainties associated with future climate change present challenges in managing non-point source pollution (NPSP) in orchard-dominant growing areas (ODGA). Given the complex processes of climate, hydrology, and soil nutrient loss, this study utilized an enhanced Soil and Water Assessment Tool model (SWAT-CO2) to investigate the impact of future climate on NPSP in ODGA in a coastal basin of North China. Our investigation focused on climate-induced variations in hydrology, nitrogen (N), and phosphorus (P) losses in soil, considering three Coupled Model Intercomparison Project phase 6 (CMIP6) climate scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5. Research results indicated that continuous changes in CO2 levels significantly influenced evapotranspiration (ET) and water yield in ODGA. Influenced by sandy soils, nitrate leaching through percolation was the principal pathway for N loss in the ODGA. Surface runoff was identified as the primary pathway for P loss. Compared to the reference period (1971-2000), under three future climate scenarios, the increase in precipitation of ODGA ranged from 15% to 28%, while the growth rates of P loss and surface runoff were the most significant, both exceeding 120%. Orchards in the northwest basin proved susceptible to nitrate leaching, while others were more sensitive to N and P losses via surface runoff. Implementing targeted strategies, such as augmenting organic fertilizer usage and constructing terraced fields, based on ODGA's response characteristics to future climate, could effectively improve the basin's environment.

Extracellular enzyme stoichiometry and microbial resource limitation following various grassland reestablishment in abandoned cropland.

Grassland restoration in abandoned cropland had great impact on soil enzyme stoichiometry and microbial resource limitation, hence altering carbon (C) sequestration progress in soil depending on soil depth and grassland restoration strategy. It is crucial to understand the microbial resource limitation under various restoration strategies, which could have key implication for optimizing management to improve C sequestration in abandoned cropland. The objective of this study was to examine the changes and key regulators of soil enzyme stoichiometry and microbial resource limitation in different soil depths under different management strategies to restore grassland, namely a) cropland as continuous cropping (CR); b) naturally restored grassland (NR); c) grass-based grassland (GG); d) legume-based grassland (LG); e) grass-legume mixed grassland (MG); and f) grass-based grassland with N fertilization (GF). Results showed that converting cropland into grassland increased absolute soil enzyme activities potential for microbial C, nitrogen (N) and phosphorus (P) acquisition by 5-110 %, 25-132 % and 17-215 %, respectively depending on soil depth and grassland restoration strategy. These enzyme activities increased more in surface soil than subsoil with the conversion of cropland into grassland, especially under LG and GF. The strategies to restore grassland, especially LG and GF, significantly decreased enzymatic C:P and N:P ratios. Microbial C limitation was reduced associated with re-establishment of grassland, exacerbating the P limitation depending on grassland restoration strategies, especially under LG and GF. The shift of relative microbial resource limitation from C to P reduced the microbial C use efficiency, reducing the ecosystem C sequestration potential during the restoration of grassland. It appears that increased biomass input and soil C:P ratio are the key drivers to shift microbial resource limitation from C to P during the restoration of grassland. Thus, a moderate harvest of above-ground biomass with a supplement of P may be necessary for improving the C sequestration potential during the restoration of grasslands, especially in the grass-legume mix or grass-based grassland with N fertilization.

Crop Rotation With Cress Increases Cucumber Yields by Regulating the Composition of the Rhizosphere Soil Microbial Community.

Paddy-upland rotation is an effective agricultural management practice for alleviating soil sickness. However, the effect of varying degrees of flooding on the soil microbial community and crop performance remains unclear. We conducted a pot experiment to determine the effects of two soil water content (SWC) and two flooding durations on the soil microbial community attributes and yield in cucumber. In the pot experiment, cucumber was rotated with cress single (45 days) or double (90 days) under 100 or 80% SWC. Then, the soil microbial were inoculated into sterilized soil to verified the relationship between cucumber growth and microorganisms. The results indicated single cress rotation resulted in a higher cucumber yield than double cress rotation and control. Cress rotation under 80% SWC had higher soil microbial diversity than cress rotation under 100% SWC and control. Flooding duration and SWC led to differences in the structure of soil microbial communities. Under 80% SWC, single cress rotation increased the relative abundance of potentially beneficial microorganisms, including Roseiflexus and Pseudallescheria spp., in cucumber rhizosphere. Under 100% SWC, single cress rotation increased the relative abundance of potentially beneficial bacteria, such as Haliangium spp., and decreased potential pathogenic fungi, such as Fusarium and Monographella spp., compared with double cress rotation and control. Varying degrees of flooding were causing the difference in diversity, structure and composition of soil microbial communities in the cucumber rhizosphere, which have a positive effect on cucumber growth and development.