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Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood howsoil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley's P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0--10 cm and soil available P at 0-- 10 cm and 10--20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0--10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO3-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0--10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0--10 cm showed higher contents than those in 10--20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO3-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China. [ABSTRACT FROM AUTHOR]

Cover crops improve soil fertility in orchard ecosystems, however, the response of soil microbial metabolism to fruit tree interactions with cover legumes at different stages of the life cycle remains uncertain, thereby limiting our understanding of the mechanisms that regulate nutrient cycling in orchards with cover crop management. Here, the characteristics of microbial energy (carbon, C) and nutrient (nitrogen, N or phosphorus, P) metabolism in the citrus rhizosphere and bulk soil in orchards were analyzed with two managements, that is, smooth vetch (Vicia villosa Roth var. glabresens Koch) cover and clean tillage, using an extracellular enzymatic stoichiometry model. Microbial C limitation was significantly reduced by cover during the vetch growing season owing to the resulting higher plant root C and soil organic C content. Competition for N between plants and microbes in the bulk soil might lead to significant microbial N limitation in covered orchards during the vetch-decomposition season, presumably owing to a significant increase in citrus root N and a concomitant decrease in bulk soil total N. Partial least squares path modeling showed that citrus root nutrient contents negatively affected microbial C limitation, while soil nutrients negatively affected microbial relative nutrient limitation in covered orchards. Conversely, both effects were reversed by tillage. Smooth vetch cover mitigated microbial C limitation, and the microbial relative N/P limitation was also influenced by the life state of smooth vetch. Our study highlights the importance of changes in microbial metabolism driven by seasonal nutrient dynamics for understanding soil nutrient cycling and optimizing cover-legumes management in orchards. [ABSTRACT FROM AUTHOR]

As a key component of terrestrial ecosystems, soil interacts directly with aboveground vegetation. Evaluating soil quality is therefore of great significance to comprehensively explore the interaction mechanism of this association. The purpose of this study was to fully understand the characteristics of aboveground vegetation, soil quality, and their potential coupling relationship among different forest types in Hunan Province, and to provide a theoretical basis for further exploring the mechanisms underlying soil–vegetation interactions in central China. We have set up sample plots of five kinds of forests (namely broad-leaved forest, coniferous forest, coniferous broad-leaved mixed forest, bamboo forest, and shrub forest) in Hunan Province. To explore the differences of vegetation characteristics and soil physical and chemical properties among the five stand types, variance analysis, principal component analysis, and regression analysis were used. Finally, we explored the coupling relationship between soil quality and aboveground vegetation characteristics of each forest. We found that there were significant differences in soil quality among the forest types, ranked as follows: shrub forest > bamboo forest > broad-leaved forest > mixed coniferous and broad-leaved forest > coniferous forest. In general, there was a negative correlation between vegetation richness and soil quality in the broad-leaved forest and the shrub forest, but they showed a positive correlation in the coniferous forest, the mixed coniferous and broad-leaved forest, and the bamboo forest. As a necessary habitat condition for aboveground vegetation, soil directly determines the survival and prosperity of plant species. These results indicated that for vegetation–soil dynamics in a strong competitive environment, as one aspect wanes the other waxes. However, in a weak competitive environment, the adverse relationship between vegetation and soil is less pronounced and their aspects can promote. [ABSTRACT FROM AUTHOR]

Increasing atmospheric nitrogen (N) deposition has a profound impact on the ecosystem functions and processes. Fine root decomposition is an important pathway for the reentry of nutrients into the soil. However, the effect of N addition on root decomposition and its potential mechanism is not well understood with respect to root branch orders. In this study, we conducted a 30-month decomposition experiment of fine roots under different concentrations of N addition treatments (0, 30, 60, and 90 kg N ha-1 year-1, respectively) in a typical Pinus massoniana plantation in the Three Gorges Reservoir Area of China. In the early stage of decomposition (0-18 months), N addition at all concentrations promoted the decomposition of fine roots, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively. In the late stage of decomposition (18-30 months), high N addition inhibited the decomposition of fine root, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively. At the same time, N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage, whereas high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage. The decomposition constant (k) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities. The higher-order (order 3-4 and order 5-6) fine roots decomposed faster than lower-order (order 1-2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations. In addition, low N (30 kg N ha-1 year-1) treatments decreased soil organic matter content, whereas high N (90 kg N ha-1 year-1) treatment had the opposite effect. All the N treatments reduced soil pH and total P content, indicating that increased N deposition may led to soil acidification. Our findings indicated that the effect of N addition on decomposition varied with the decomposition stages. The decomposition difference between the lowerorder and higher-order fine roots were controlled strongly by the initial chemical quality of the fine roots. This study provides new insights into understanding and predicting possible changes in plant root decomposition and soil properties in the future atmospheric N deposition increase scenarios. [ABSTRACT FROM AUTHOR]

The Three Gorges Reservoir (TGR) has made a significant contribution to social and economic development and has vast effects on the aquatic environment. However, reservoirs can also produce a negative impact on the environment. The Three Gorges Dam (TGD) started operation since 2003. TGR operates at a low water level for 145 m during flood season while the water level rises to 175 m during the non-flood season. Water level is an essential hydrological parameter impacting water quality. Continuous and periodical water level change makes the changes of water quality in reservoirs more complicated. This study examined water quality changes in the main channel outflow of the Yangtze River after (TGD) completion and analyzed its relationship with water level fluctuation (WLF). Results showed that water quality indicators (DO, CODMn, and NH3–N) had cyclical changes for hydrological scheduling control, and water quality indicators at different water levels had significant differences, which reflected the response of water quality to reservoir scheduling. According to water quality index, TGR water quality was best at high water level and stayed worst at low water level. Predicting outcomes of the Auto-Regressive Integrated Moving Average model showed water quality would still keep a good level in the future. A comprehensive understanding of temporal variability in water quality and evaluation result will be helpful in investigating water quality at a high precision time for water management. [ABSTRACT FROM AUTHOR]

Carbon assimilation is reduced by stress. Under such conditions, the trade-off between growth and non-structural carbohydrate (NSC) storage becomes crucial for plant survival and continued growth. However, growth and NSC responses to drought and shading in Pinus massoniana Lamb. remain unclear. Here, we investigated the effects of drought, shading, and combined drought and shading on leaf gas exchange parameters, stem basal diameter, plant height, biomass accumulation, and NSC concentration in 2-year old seedlings after a 2 month treatment. The results showed that (1) both drought and shading significantly reduced photosynthetic rate, increment of stem basal diameter and plant height, and biomass accumulation, while NSC concentration increased under drought but decreased under shading; (2) the combined drought-shading treatment had a stronger effect on photosynthetic rate and growth than either stress factor individually, whereas the concentration of NSC did not change significantly; and (3) drought, shading, and their combination had a lower effect on biomass than on NSC partitioning, in which case clear effects were observed. Drought increased NSC proportion in roots by 5.4%; conversely, shading increased NSC proportion in leaves by 3.7%, while the combined treatment increased NSC proportion in roots by 5.1% but decreased it in the leaves by 5.4%. These results suggest that the mechanism inhibiting P. massoniana growth is different under drought and shading conditions according to carbon partitioning. Furthermore, complex environmental stress may lead to different mechanisms of carbon partitioning compared with either dry or shaded environments. Our findings will be helpful in predicting the impact of climate change on P. massoniana growth. [ABSTRACT FROM AUTHOR]

Effects of environmental factor such as climate, topography, vegetation and soil in shelter forests in Three Gorges Reservoir Region on runoff and sediment yields were monitored to identify dominant environmental factors controUing runoff and sediment yields in 15 runoff plots in study area by soil sampling, laboratory analysis, stepwise regression analysis and path analysis, and to establish the main control environmental factors that affect runoff and sediment yields. The results showed that soil bulk density, herbaceous cover, slope, and canopy density were the significant factors controUing runoff, and the direct path coefficient of each factor was ranked as canopy closure (-0.628) > liiter thickness (-0.547) > bulk density (0.509) > altitude (0.289). The indirect path coefficient was ranked as soil bulk density (0.354) > liiter thickness (-0.169) > altitude (0.126) > canopy closure (-0.104). Therefore, canopy closure and liiter thickness mainly had direct eefects on moof, while soil bulk density mainly had indirect eefects through their contributions to other factors. Herbaceous cover, liiter thickness, slope, canopy density, and altitude were the significant factors controlling sediment yields. The direct path coefficient of each factor was ranked as herbaceous cover (-0.815) > liiter thickness (-0.777) > canopy closure (-0.624) > slope (0.620). The indirect path coefficient was ranked as slope (0.272) > liiter thickness (-0.131) > canopy closure (-0.097) > herbaceous cover (-0.084). Therefore, herbaceous cover and liiter thickness mainly had direct effects on sediment yields, while slope manly had indirect effects through their contributions to other factor. All the selected environmental factor jointly explained 85.5% and 78.3% of runoff and sediment yield variability, respectively. However, there were large values of remaining path coefficients of other factors influencing runoff and sediment yields, which indicated that some important factor are not included and should be taken into account. [ABSTRACT FROM AUTHOR]

Several studies have focused on fine roots characteristics because they provide a major pathway for nutrient cycling and energy flow in forest ecosystems. However, few studies have evaluated changes in fine root characteristics according to their diameter. Pinus massoniana forests are the main vegetative component in the Three Gorges Reservoir area and play an important role in providing forest resources and ecological services. Pinus massoniana fine roots were sorted into 0-0.5, 0.5-1, and 1-2 mm diameter classes, and their fine root standing biomass (FRB), necromass, annual production and decomposition rates were determined and correlated with soil characteristics. These fine roots in three diameter classes significantly differed in their initial carbon (C), C/N ratio, FRB, necromass, annual C and N production and decomposition rate. The production and decomposition of these different diameter classes varied significantly with soil variables including soil temperature, moisture, calcium and ammonium concentration but the strength of these interactions varied dependent on diameter class. The very fine roots had a faster decomposition ratio than larger fine roots due to the lower N content, higher C/N ratio and higher sensitivity to soil environmental factors. These results clearly indicate heterogeneity among fine roots of different diameters, and these variations should be taken into account when studying fine root characteristics and their role in the C cycle. [ABSTRACT FROM AUTHOR]

The present study aimed to assess the antihypertensive efficacy and safety of catheter-based radiofrequency renal sympathetic denervation (RSD) in hypertensive dogs. Furthermore, the study investigated the possible antihypertensive mechanism of radiofrequency RSD through measuring the postoperative serum concentrations of angiotensin II (AngII), nicotinamide adenine dinucleotide phosphate oxidase (NADPH-ox), malondialdehyde (MDA), nitric oxide (NO) and endothelial NO synthase (eNOS). A total of 12 beagles were randomly divided into the surgery (n=6) and the sham-surgery groups (n=6). The hypertension model was established using a high-fat diet. The surgery group received catheter-based radio-frequency RSD, while the sham-surgery group only received renal arteriography. Blood pressure was measured prior to the surgery and 3 days, 1 and 2 weeks, and 1, 2 and 3 months after the surgery. The serum concentrations of AngII, NADPH-ox, MDA, NO and eNOS were measured prior to the surgery and 1 week, and 1 and 3 months after the surgery. Following the establishment of the model, the systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) of the surgery and the sham-surgery groups were all significantly increased above the baseline (P<0.05), but there was no significant difference between the two groups. SAP, DAP and MAP in the surgery group at 1 and 3 months after the surgery were significantly decreased compared to the levels measured prior to the surgery and those in the sham-surgery group (P<0.05). Three months after the surgery, the serum creatinine level was normal and renal arteriography did not show renal artery stenosis. Compared to those measured prior to the surgery, the concentrations of serum AngII, NADPH-ox and MDA in the surgery group at 1 week, and 1 and 3 months after the surgery were decreased, while the concentrations of serum NO and eNOS were increased (P<0.05). The above indicators measured at the same time points demonstrated statistically significant differences between the surgery and the sham-surgery groups (P<0.05). In conclusion, catheter-based radiofrequency RSD may inhibit the rennin-angiotensin system and the oxidative stress response, as well as improve vascular endothelial function, thus significantly reducing blood pressure through the reduction of sympathetic activity in hypertensive dogs. [ABSTRACT FROM AUTHOR]