Search

[Display omitted] • High soil P content was found in eastern and northern subtropical China. • Soil clay strongly and negatively affected regional-scale variation in soil P. • Humidity index and DBH indirectly affected soil available P via soil clay content. • Extending the rotation period benefits the recovery of soil P availability. Evaluating the environmental effects on soil phosphorus (P) availability is the key to understanding P cycling and regulating forest productivity. However, what and how environmental factors affect soil P availability in regional plantation ecosystems remains unclear. The study evaluated the effects of climatic factors, nitrogen deposition rate, stand attributes, litter characteristics, and soil-associated properties on soil P availability in Masson pine plantations across subtropical China using stepwise regression and structural equation modelling (SEM) analyses. At the 0–20 cm and 20–40 cm soil depths, soil total P ranged from 0.24 to 0.43 g kg−1 and from 0.24 to 0.48 g kg−1, respectively. Similarly, soil available P varied from 0.35 to 7.55 mg kg−1 and from 0.14 to 4.34 mg kg−1, respectively. Soil total and available P had high values in the eastern and northern distribution areas of subtropical China. Soil total P linearly decreased with an increase in bulk density, clay and pH but linearly increased with an increase in DBH. These four factors had a similar contribution (15.5–35.1 %) to soil total P. Soil available P linearly decreased with an increase in bulk density and clay. The relative contribution of clay (48.1–75.7 %) to soil available P was higher than that of bulk density (16.2–33.5 %). Soil total P decreased during the initial 30 years of plantations and then increased. But other variables (e.g., climate, nitrogen deposition, and litter) had no significant impacts on soil P. Overall, the SEM explained 35.4 % and 28.1 % of soil available P variations at the 0–20 cm and 20–40 cm soil depths, respectively, and revealed that clay had strong total effects (β = -0.526 and −0.396) on the soil available P. These results reveal the dominant roles of soil texture (especially clay) in affecting soil P availability in Masson pine plantations and suggest that extending the rotation period benefits soil P recovery in pine plantation ecosystems of subtropical China. [ABSTRACT FROM AUTHOR]

This study aimed to improve runoff simulations and explore deep soil hydrological processes for a watershed in the center of the Loess Plateau (LP), China. This watershed, the Wuding River Basin (WRB), has very complex topography, with soil depths ranging from 0 to 197 m. The hydrological model used for our simulations was the Community Land Model (CLM) version 5 developed by the National Center for Atmospheric Research. Actual soil depths and river channels were incorporated into CLM to realistically represent the physical features of the WRB. Through sensitivity tests, CLM with 150 soil layers produced the most reasonable results and was adopted for this study. Our results showed that CLM with actual soil depths significantly suppressed unrealistic variations of the simulated sub-surface runoff when compared to the default simulations with a fixed soil depth of 8 m. In addition, CLM with higher-resolution soil layering slightly improved runoff simulations, but generated simulations with much smoother vertical water flows that were consistent with the uniform distribution of soil textures in our study watershed. The runoff simulations were further improved by the addition of river channels to CLM, where the seasonal variability of the simulated runoff was reasonably captured. Moreover, the magnitude of the simulated runoff remarkably decreased with increased soil evaporation by lowering the soil water content threshold, which triggers surface resistance. The lowered threshold was consistent with the loess soil, which has a high sand component. Such soils often generate stronger soil evaporation than soils dominated by clay. Finally, with the above changes in CLM, the simulated total runoff matched very closely with observations. When compared with those for the default runoff simulations, the correlation coefficient, root-mean-square error, and Nash Sutcliffe coefficient for the improved simulations changed dramatically from 0.02, 10.37 mm, and -12.34 to 0.62, 1.8 mm, and 0.61. The results in this study provide strong physical insight for further investigation of hydrological processes in complex terrain with deep soils. [ABSTRACT FROM AUTHOR]