Dynamics of soil inorganic nitrogen and their responses to nitrogen additions in three subtropical forests, south China

Three forests with different historical land-use, forest age, and species assemblages in subtropical China were selected to evaluate current soil N status and investigate the responses of soil inorganic N dynamics to monthly ammonium nitrate additions. Results showed that the mature monsoon evergreen broadleaved forest that has been protected for more than 400 years exhibited an advanced soil N status than the pine （Pinus massoniana） and pine-broadleaf mixed forests, both originated from the 1930＇s clear-cut and pine plantation. Mature forests had greater extractable inorganic N pool, lower N retention capacity, higher inorganic N leaching, and higher soil C/N ratios. Mineral soil extractable NH4^＋-N and NO3-N concentrations were significantly increased by experimental N additions on several sampling dates, but repeated ANOVA showed that the effect was not significant over the whole year except NH4^＋-N in the mature forest. In contrast, inorganic N （both NH4^＋-N and NO3^--N） in soil 20-cm below the surface was significantly elevated by the N additions. From 42% to 74% of N added was retained by the upper 20 cm soils in the pine and mixed forests, while 0%-70% was retained in the mature forest. Our results suggest that land-use history, forest age and species composition were likely to be some of the important factors that determine differing forest N retention responses to elevated N deposition in the study region.

Plateau Marsh Methane Oxidation as affected by Inorganic N

In a series of laboratory incubations using soils of two contrasting sitesfrom a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH_4) oxidation rates weremeasured to study the effects of inorganic N inputs on CH_4 oxidation. For adrained site, subsurfacepeat (5--15 cm) at an initial 20 mu L CH_4 L^(-1) showed a significantly different (P < 0.05) CH_4oxidation rate compared to other soil depths, with a maximal rate of 20.9 ng CH_4 gDW (dryweight)^(-1) h^(-1); the underlying mineral soil layers (15--30 and 30--50 cm) also had a strongCH_4 oxidation capacity at about an initial 2 000 mu L CH_4 L^(-1). With a waterlogged site, theCH_4 oxidation rate in an aerobic incubation was significantly greater (P < 0 05) in the surfacesoil layer (0--5 cm) compared to the 15--30 and 30--50 cm depths. There was generally no or a veryweak effect from addition of NO_3^- on CH_4 oxidation. In marked contrast, NH_4^+ salts, such as(NH_4)_2SO_4, NH_4Cl and NH_4NO_3, exhibited strong inhibitions, which varied as a function of theadded salts and the initial CH_4 level Increasing NH_4^+ usually resulted in greater inhibition andincreasing initial CH_4 concentrations resulted in less NH_4^+ inhibition on CH4 oxidation innatural high-altitude, low-latitude wetlands could be as important as has been reported foragricultural and forest soils. The NH_4^+ effects on the CH_4 oxidation rate need to be furtherinvestigated in a wide range of natural wetland soil types.

Moisture-proof and Enhanced Effect of Inorganic Coating on Porous Si_3N_4 Ceramic

Inorganic coating was fabricated on the surface of the porous Si3N4 ceramic by polymer derived（PD） and spraying technology, via using vinyl-polysilazane（PSN-1） as a preceramic polymer and Si3N4 and lithium aluminosilicate（LAS） powders as fillers. The phase and microstructure of the coatings were analyzed by X-ray diffraction（XRD） analysis and scanning electron microscopy（SEM）, respectively. The effect of the coatings on mechanical property and humidity resistance of the porous Si3N4 ceramic was investigated. The experimental results showed that we successfully fabricated the uniform and dense coating which preferably combined with the substrate upon the addition of fillers. The bending strength of the porous Si3N4 ceramic sprayed the coating increased by more than 18%, and the surface hardness increased by 1.7 times. The apparent porosity of the materials reduced by an average of 97.7%, and water absorption was below 0.5%. Therefore, the prepared coating with preferable density had an obviously moisture-proof and enhanced effect on the porous Si3N4 ceramic.

Effect of N and P addition on soil organic C potential mineralization in forest soils in South China

Atmospheric nitrogen deposition is at a high level in some forests of South China. The effects of addition of exogenous N and P on soil organic carbon mineralization were studied to address: (1) if the atmospheric N deposition promotes soil C storage through decreasing mineralization; (2) if the soil available P is a limitation to organic carbon mineralization. Soils (0–10 cm) was sampled from monsoon evergreen broad-leaved forest (MEBF), coniferous and broad-leaved mixed forest (CBMF), and Pinus massoniana...

Effect of N Fertilizers on Root Growth and Endogenous Hormones in Strawberry

Endogenous hormones play an important role in the growth and development of roots. The objective of this research was to study the effect of four types of N fertilizers on the root growth of strawberry (Fragaria ananassa Duchesne) and the endogenous enzymes of indole-3-acetic acid (IAA), abscisic acid (ABA), and isopentenyl adenosine (iPA) in its roots and leaves using enzyme-linked immunosorbent assay. Application of all types of N fertilizers significantly depressed (P ≤ 0.05) root growth at 20 d after transplanting. Application of organic-inorganic fertilizer (OIF) as basal fertilizer had a significant negative effect (P ≤ 0.05) on root growth. The application of OIF and urea lowered the lateral root frequency in strawberry plants at 60 d (P ≤ 0.05) compared with the application of two organic fertilizers (OFA and OFB) and the control (CK). With the fertilizer treatments, there were the same concentrations of IAA and ABA in both roots and leaves at the initial growth stage (20 d), lower levels of IAA and ABA at the later stage (60 d), and higher iPA levels at all seedling stages as compared to those of CK. Thus, changes in the concentrations of endogenous phytohormones in strawberry plants could be responsible for the morphological changes of roots due to fertilization.

Amendment of Acid Soils with Crop Residues and Biochars

The liming potential of some crop residues and their biochars on an acid Ultisol was investigated using incubation experiments. Rice hulls showed greater liming potential than rice hull biochar, while soybean and pea straws had less liming potential than their biochars. Due to their higher alkalinity, biochars from legume materials increased soil pH much compared to biochars from non-legume materials. The alkalinity of biochars was a key factor affecting their liming potential, and the greater alkalinity of biochars led to greater reductions in soil acidity. The incorporation of biochars decreased soil exchangeable acidity and increased soil exchangeable base cations and base saturation, thus improving soil fertility.

Correlation Between CO_2 Efflux and Net Nitrogen Mineralization and Its Response to External C or N Supply in an Alpine Meadow Soil

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.

Changes in Soil Physicochemical Properties Following Land Use Change from Paddy Fields to Greenhouse and Upland Fields in the Southeastern Basin of Dianchi Lake,Yunnan Province,China

Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collected from a flat lowland area mainly used for agricultural production fields in the southeastern basin of Dianchi Lake. Analyses of the soil samples indicated that the greenhouse soils were characterized by a lower organic matter content, lower pH, and higher soluble nutrients than the paddy soils in the area. The lower organic matter content of the greenhouse soils was ascribed to environmental or management factors rather than the clay content of the soil. Accumulation of soluble nutrients, especially inorganic N, was due to over-application of fertilizers, which also caused soil acidification. The average amount of readily available N, P, and K accumulated in the greenhouse soils was estimated to be equal to or higher than the annual input of these nutrients as a fertilizer, indicating that a reduction in fertilizer application was possible and recommended. In contrast, a very low available Si content was observed in the paddy soils, suggesting the need for Si application for rice production.

Effects of different forms of nitrogen addition on microbial extracellular enzyme activity in temperate grassland soil

Background:Nitrogen(N)deposition alters litter decomposition and soil carbon(C)sequestration by influencing the microbial community and its enzyme activity.Natural atmospheric N deposition comprises of inorganic N(IN)and organic N(ON)compounds.However,most studies have focused on IN and its effect on soil C cycling,whereas the effect of ON on microbial enzyme activity is poorly understood.Here we studied the effects of different forms of externally supplied N on soil enzyme activities related to decomposition in a temperate steppe.Ammonium nitrate was chosen as IN source,whereas urea and glycine were chosen as ON sources.Different ratios of IN to ON(Control,10:0,7:3,5:5,3:7,and 0:10)were mixed with equal total amounts of N and then used to fertilize the grassland soils for 6 years.Results:Our results show that IN deposition inhibited lignin-degrading enzyme activity,such as phenol oxidase(POX)and peroxidase(PER),which may restrain decomposition and thus induce accumulation of recalcitrant organic C in grassland soils.By contrast,deposition of ON and mixed ON and IN enhanced most of the C-degrading enzyme activities,which may promote the organic matter decomposition in grassland soils.In addition,theβ-N-acetyl-glucosaminidase(NAG)activity was remarkably stimulated by fertilization with both IN and ON,maybe because of the elevated N availability and the lack of N limitation after long-term N fertilization at the grassland site.Meanwhile,differences in soil pH,soil dissolved organic carbon(DOC),and microbial biomass partially explained the differential effects on soil enzyme activity under different forms of N treatments.Conclusions:Our results emphasize the importance of organic N deposition in controlling soil processes,which are regulated by microbial enzyme activities,and may consequently change the ecological effect of N deposition.Thus,more ON deposition may promote the decomposition of soil organic matter thus converting C sequestration in grassland soils into a C source.

The effect of modified layers on the performance of inverted ZnO nanorods/MEH-PPV solar cells

We fabricate inverted organic/inorganic hybrid solar cells based on vertically oriented ZnO nanorods and polymer MEH-PPV. The morphology of ZnO nanorods and ZnO nanorods/MEH-PPV hybrid structure is depicted by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscope (AFM), respectively. It is observed that ZnO nanorods array grows primarily aligned along the perpendicular direction of the ITO substrate. The MEH-PPV molecule does not enter the interspace between ZnO nanorods completely according to SEM picture. It results in the small and bad contact area between ZnO nanorods and MEH-PPV. To improve the photovoltaic performance, we also fabricate another kind of photovoltaic (PV) device modified by N719 dye, and exploit the effect of N719. After the modification of ZnO nanorods by N719, not only Jsc increases from 0.257 mA/cm2 to 0.42 mA/cm2, but also Voc enhances from 0.37 V to 0.42 V. Insert LiF buffer layer between MEH-PPV and anode, Jsc of 1.05 mA/cm2 is obtained, and it is 2.5 times that the device without LiF.