Phosphorus limitation induced by nitrogen addition changed soil microbial community structure in a subtropical Pinus taiwanensis forest.

Soil microorganisms play an important role in the biogeochemical cycles of terrestrial ecosystems. How-ever, it is still unclear how the amount and duration of nitrogen (N) addition affect soil microbial community structure and whether there is a correlation between the changes in microbial community structure and their nutrient limi-tation status. In this study, we conducted an N addition experiment in a subtropical Pinus taiwanensis forest to simulate N deposition with three treatments: control (CK, 0 kg N·hm-2·a-1), low N (LN, 40 kg N·hm-2·a-1), and high N (HN, 80 kg N·hm-2·a-1). Basic soil physicochemical properties, phospholipid fatty acids content, and carbon (C), N and phosphorus (P) acquisition enzyme activities were measured after one and three years of N addition. The relative nutrient limitation status of soil microorganisms was analyzed using ecological enzyme stoichiometry. The results showed that one-year N addition did not affect soil microbial community structure. Three-year LN treatment significantly increased the contents of Gram-positive bacteria (G+), Gram-negative bacteria (G-), actinomycetes (ACT), and total phospholipid fatty acids (TPLFA), whereas three-year HN treatment did not significantly affect soil microbial community, indicating that bacteria and ACT might be more sensitive to N addition. Nitrogen addition exacerbated soil C and P limitation. Phosphorus limitation was the optimal explanatory factor for the changes in soil microbial community structure. It suggested that P limitation induced by N addition might be more beneficial for the growth of certain oligotrophic bacteria (e.g. G+) and the microorganisms participating in the P cycling (e.g. ACT), with consequences on soil microbial community structure of subtropical Pinus taiwanensis forest.

[Effects of different carbon addition modes on the soil priming effect of a subtropical Phyllostachys edulis forest under nitrogen deposition]. / æ°®æ²‰é™ä¸‹ä¸åŒç¢³æ·»åŠ æ¨¡å¼å¯¹äºšçƒ­å¸¦æ¯›ç«¹æž—åœŸå£¤æ¿€å‘æ•ˆåº”çš„å½±å“.

Priming effect (PE) plays an important role in regulating terrestrial soil carbon (C) cycling, but the impact of different C addition modes on the PE in subtropical forest ecosystems with increasing nitrogen (N) deposition is unclear. In this study, we investigated the effects of C addition patterns (single or repeated C addition) on soil PE by adding 13C-labeled glucose for 90 d in an incubation experiment with different levels of N application (0, 20, and 80 kg N·hm-2·a-1). The different patterns of glucose addition significantly increased soil organic C (SOC) mineralization and produced positive PE. Single glucose addition resulted in stronger PE than repeated addition. PE was significantly weakened with increasing N application levels, indicating that N deposition inhibited soil excitation in Phyllostachys edulis forests. The cumulative PE was significantly negatively correlated with ß-N-acetylaminoglucosidase (NAG) and peroxidase (PEO) activities, and was significantly positively correlated with microbial biomass P (MBP) and potential of hydrogen (pH). Our findings indicated that, when acting together on soil, N application and C addition could strongly affect soil C stocks by stimulating the mineralization of native soil organic matter in subtropical forests. The findings further indicated that single C addition model might overestimate the effect of exogenous readily decomposable organic C on PE and ignore the effect of N deposition on PE, which in turn would overestimate the mineralization loss of forest SOC.

[Responses of soil microbial carbon use efficiency to short-term nitrogen addition in Castanopsis fabri forest]. / ç½—æµ®æ ²æž—åœŸå£¤å¾®ç”Ÿç‰©ç¢³åˆ©ç”¨æ•ˆçŽ‡å¯¹çŸ­æœŸæ°®æ·»åŠ çš„å“åº”.

As an important parameter regulating soil carbon mineralization, microbial carbon use efficiency (CUE) is essential for the understanding of carbon (C) cycle in terrestrial ecosystems. Three nitrogen supplemental levels, including control (0 kg N·hm-2·a-1), low nitrogen (40 kg N·hm-2·a-1), and high nitrogen (80 kg N·hm-2·a-1), were set up in a Castanopsis fabri forest in the Daiyun Mountain. The basic physical and chemical properties, organic carbon fractions, microbial biomass, and enzyme activities of the soil surface layer (0-10 cm) were measured. To examine the effects of increasing N deposition on microbial CUE and its influencing factors, soil microbial CUE was measured by the 18O-labelled-water approach. The results showed that short-term N addition significantly reduced microbial respiration rate and the activities of C and N acquisition enzymes, but significantly increased soil microbial CUE. ß-N-acetyl amino acid glucosidase (NAG)/microbial biomass carbon (MBC), microbial respiration rate, ß-glucosidase (BG)/MBC, cellulose hydrolase (CBH)/MBC, and soil organic carbon content were the main factors affecting CUE. Moreover, CUE significantly and negatively correlated with NAG/MBC, microbial respiration rate, BG/MBC, and CBH/MBC, but significantly and positively correlated with soil organic carbon. In summary, short-term N addition reduced the cost of soil microbial acquisition of C and N and microbial respiration, and thus increased soil microbial CUE, which would increase soil carbon sequestration potential of the C. fabri forest.

[Effects of nitrogen addition on the kinetic parameters of soil acid phosphomonoesterase in a Moso bamboo forest]. / æ°®æ·»åŠ å¯¹æ¯›ç«¹æž—åœŸå£¤é ¸æ€§ç£·é ¸å•é ¯é ¶åŠ¨åŠ›å­¦å‚æ•°çš„å½±å“.

Soil phosphatases are important in the mineralization of organophosphates and in the phosphorus (P) cycle. The kinetic mechanisms of phosphatases in response to nitrogen (N) deposition remain unclear. We carried out a field experiment with four different concentrations of N: 0 g N·hm-2·a-1(control), 20 g N·hm-2·a-1(low N), 40 g N·hm-2·a-1(medium N), and 80 g N·hm-2·a-1(high N) in a subtropical Moso bamboo forest. Soil samples were then collected from 0 to 15 cm depth, after 3, 5 and 7 years of N addition. We analyzed soil chemical properties and microbial biomass. Acid phosphatase (ACP) was investigated on the basis of maximum reaction velocity (Vm), Michaelis constant (Km), and catalytic efficiency (Ka). Results showed that N addition significantly decreased soil dissolved organic carbon (DOC), available phosphorus, and organophosphate content, but significantly increased soil ammonium, nitrate-N content, and Vm. There was a significant relationship between Vm and the concentrations of available phosphorus, organophosphate, and soil DOC. In general, N addition substantially increased Ka, but did not affect Km. The Km value in the high N treatment group was higher than that in the control group after five years of N addition. Km was significantly negatively associated with both available phosphorus and organophosphate. Medium and high N treatments had stronger effects on the kinetic parameters of ACP than low N treatment. Results of variation partition analysis showed that changes in soil chemical properties, rather than microbial biomass, dominated changes in Vm(47%) and Km(33%). In summary, N addition significantly affected substrate availability in Moso bamboo forest soil and modulated soil P cycle by regulating ACP kinetic parameters (especially Vm). The study would improve the understanding of the mechanisms underlying soil microorganisms-regulated soil P cycle under N enrichment. These mechanisms would identify the important parameters for improving soil P cycling models under global change scenarios.

Enzyme stoichiometry evidence revealed that five years nitrogen addition exacerbated the carbon and phosphorus limitation of soil microorganisms in a Phyllostachys pubescens forest.

The activity and stoichiometry of soil extracellular enzyme can provide a good indication for changes in soil nutrient availability and microbial demands for nutrients. However, it remains unclear how would nitrogen (N) deposition affect nutrient limitation of microbes in subtropical forest soils. We conducted a 5 years N addition experiment in a subtropical Phyllostachys pubescens forest. The soil nutrients and enzyme activities associated with carbon (C), N, and phosphorus (P) cycles were measured. We also examined the nutrient distribution of microorganisms using enzyme stoichiometry and vector analysis. The results showed that N addition significantly decreased the contents of soil soluble organic C and available P and increased that of available N. Furthermore, N addition significantly decreased ß-N-acetyl-glucosaminidase (NAG) activity and NAG/ microbial biomass carbon (MBC), and increased acid phosphatase (ACP) and ACP/MBC. The low and moderate N addition levels significantly increased enzyme C/P, vector length, and vector angle, but significantly decreased enzyme N/P. Results of redundancy analysis showed that the change in soil enzyme activity and enzymatic stoichiometry were mainly driven by soil available P content under N addition. In summary, N addition altered the microbial nutrient acquisition strategy, which increased nutrient allocation to P-acquiring enzyme production but reduced that to N-acquiring enzyme production. Moreover, N addition exacerbated the C and P limitation of soil microorganisms. Appropriate amount of P fertilizer could be applied to improve soil fertility of subtropical P. pubescens forest in the future.

Removal of heavy metals from contaminated paddy soils using chemical reductants coupled with dissolved organic carbon solutions.

General acid washing is commonly used to treat heavy metal-contaminated soils, but it is sometimes difficult to achieve remediation aims in severely polluted soils. If we expose the surfaces of Fe oxide minerals to reductive dissolution during washing treatment, more of the metals initially adsorbed to these surfaces will be liberated, which may encourage the removal of heavy metals. Initially, the metal extraction capabilities of nine chemical reductants were compared in ten soil samples polluted by Cr, Cu, Zn, and Ni. Sodium dithionite (Na2S2O4) and ferrous sulfate (FeSO4) were screened for subsequent intensive research. In summary, the Na2S2O4 solutions had higher Cr, Cu, and Zn removal rates than either the FeSO4 or acid solution. Application of dissolved organic carbon (DOC) further increased the removal of heavy metals by complexation. About 15%, 86%, 32%, and 52% of the Cr, Cu, Zn, and Ni, respectively, were removed from the representative soil (M-2) by two-stage washing using 0.2 M Na2S2O4 coupled with 1,500 mg L-1 DOC solution at pH 2.0. Meanwhile, most soil fertility was preserved: ammonium nitrogen was increased 3.9 times; the increase in exchangeable potassium was 33%; and the reduction in available P was only 10%.

[Responses of soil phosphorus fractions and microorganisms to nitrogen application in a subtropical Phyllostachys pubescen forest]. / 亚热带毛竹林土壤磷组分和微生物对施氮的响应.

Phosphorus (P) is an important nutrient for plant and microbial growth. Soil P availabi-lity is poor in subtropical areas. Long-term heavy nitrogen (N) deposition might further reduce P availability. The experiment was performed in a Phyllostachys pubescens forest in Daiyun Mountain. The effects of N application on soil basic physical and chemical properties, soil P fractions, microbial biomass, and acid phosphomonoesterase activity were analyzed after three years of N application. The results showed that N application significantly increased NO3--N content and thus soil N availability, while it significantly reduced the percentage of decomposable organic P to total P, with the ratio of carbon (C) to organic P being over 200. The soil microbial biomass C, microbial biomass P, acid phosphomonoesterase, and the ratio of microbial biomass N to microbial biomass P and microbial biomass C to microbial biomass P were increased as the N application rate increased. There was a significant negative correlation between the percentage of decomposable organic P to total P and microbial biomass P. Consequently, N application enhanced soil P limitation and increased microbial P demand.

[Effects of nitrogen deposition on the concentration and spectral characteristics of dissolved organic matter in soil in Moso bamboo plantations.] / æ°®æ²‰é™å¯¹æ¯›ç«¹æž—åœŸå£¤å¯æº¶æ€§æœ‰æœºè´¨æ•°é‡ä¸Žå ‰è°±å­¦ç‰¹å¾çš„å½±å“.

The subtropical zone in China is one of the regions most affected by nitrogen deposition. Soil dissolved organic matter (DOM) is considered to be an important indicator of soil organic matter. Nitrogen deposition may alter the quality and quantity of soil DOM by changing soil microbial activity. In this study, we explored the effects of nitrogen addition on soil DOM content, its spectral characteristics and microbial extraceller enzyme activity in the Moso bamboo plantations by setting control (CT), low-nitrogen (LN), and high-nitrogen (HN) addition levels for three-year nitrogen addition. The results showed that there was no significant change in soil pH, dissolved organic carbon, dissolved organic nitrogen, and aroma index following nitrogen addition, while the humification index increased significantly, microbial enzyme activities increased first and then decreased with the increases of nitrogen addition. Fourier transform infrared spectroscopy results showed that soil DOM had similar absorption peaks in seven regions, and that the absorption peaks of 1000 to 1260 cm-1 were the strongest, indicating an enhanced amount of polysaccharides, alcohols, carboxyl acids, and esters after nitrogen addition. The results of three-dimensional fluorescence spectroscopy showed that soil DOM structure significantly changed following nitrogen addition, with a decrease in low-molecular substances such as protein-like substances and microbial metabolites and a significant increase in high-molecular substances such as humus-like substances. In general, nitrogen addition made soil nitrogen compatible with microbial requirements. Microorganisms decompose substances that were easily degraded in DOM. The structure of soil DOM was more complex after nitrogen addition. Therefore, short-term nitrogen deposition might be conducive to preserving soil fertility.

[Characteristics of soil phosphorus fractions of different vegetation types in subtropical forests and their driving factors.] / äºšçƒ­å¸¦ä¸åŒæ¤è¢«ç±»åž‹åœŸå£¤ç£·ç»„åˆ†ç‰¹å¾åŠå ¶å½±å“å› ç´ .

Soil P fraction, microbial biomass P (MBP), and activities of acid phosphomonoesterase (ACP) and phosphodiesterase (PD) were analyzed under evergreen broad-leaved forest, mixed forest and coniferous forest in Daiyun Mountains. The results showed that labile-P comprised only 1.0%-4.5% of soil total phosphorus (TP). The ratio of soil carbon to organic phosphorus (C:Po) was >200, indicating phosphorus limitation across the three vegetation types. Organic phosphorus (Po) was a significant fraction of soil P, which accounted for 44.8%-47.1% and 28.6%-30.6% of TP in A and B horizons, respectively. Results from the redundancy analysis showed that the changes in P fractions were mainly driven by PD in the A horizon and by ACP in the B horizon. Moreover, the activities of PD and ACP had a significant negative correlation with Po. The results suggested that phosphorus deficiency occurred in the three vegetation types, and that PD and ACP could play major roles in the depletion of soil Po in response to phosphorus limitation in subtropical forests.

[Effects of precipitation reduction on the composition and stability of soil organic matter in a young Cunninghamia lanceolata plantation.] / 减少降雨对杉木幼林土壤有机质组分及稳定性的影响.

It is hard to predict the response of soil organic matter (SOM) to global climate change due to its heterogenous chemical structure. With the development of molecular techniques to identify the structure, sources and stages of SOM degradation, long-standing questions regarding the composition and stability of SOM might be resolved. To investigate the effects of changes in precipitation patterns on the stability of SOM, we analyzed the specific compositions and extent of degradation of SOM using biomarkers, in a young Cunninghamia lanceolata plantation after reducing 50% of precipitation (P) for two years. The results showed that precipitation reduction (P-treatment) significantly reduced the levels of free lipids. Relative to control (CT), P-treatment decreased short-chain n-alkanoic acids (C16-18) and terpenoids and steroids by 62.8% and 19.1%, respectively. However, P-treatment did not significantly change the concentrations of other aliphatic compounds. Although there was no observable difference in the total lignin content between treatments, P-treatment significantly reduced the acid to aldehyde ratios for syringyl [(Ad/Al)s] and vanillyl [(Ad/Al)v]. Thus, the labile compositions of SOM were accelerated to decomposition under rainfall pattern change. Although the recalcitrant compositions (lignin) were relatively stable, their long-term stability should be further monitored.

[Effects of nitrogen deposition on diversity and composition of soil bacterial community in a subtropical Cunninghamia lanceolata plantation.] / ä¸­äºšçƒ­å¸¦åœ°åŒºæ°®æ²‰é™å¯¹æ‰æœ¨å¹¼æž—åœŸå£¤ç»†èŒç¾¤è½å¤šæ ·æ€§åŠç»„æˆçš„å½±å“.

The increasing rate of atmospheric nitrogen (N) deposition has become the focus of research attention. Soil bacterial community plays an important role in soil nutrient cycling. We stimulated N deposition at the Forest Ecosystem of Fujian Normal University and Global Change Research Station in Chenda Town, Sanming City in the Fujian Province of China. We examined the effect of N deposition on the structure and composition of soil bacterial community using 16S rDNA amplification sequencing. The results showed that short-term addition of N had no significant effect on the soil bacterial diversity and composition, but high N treatment significantly affected therelative abundance of individual bacterial species, which increased the abundance of Copiotrophic group and decreased that of the corresponding Oligotrophic group, indicating that changes in soil bacterial nutrient strategies were driven by the availability of nutrients. Enhanced understanding of the responses of soil bacterial community and nutrient distribution pattern to rapid N deposition could improve the prediction ability about the future environment.

Kinetic and thermodynamic studies on removal of Cu(II) from aqueous solutions using soil nanoclays.

Soil clays (< 2,000 nm) (SC) and soil nanoclays (< 100 nm) (SNC) were used as adsorbents for removal of Cu(II) from aqueous solution. The experiments were conducted with variables including pH, interaction time, concentration of Cu(II) and temperature. Four kinetic models have been employed to investigate adsorption mechanisms, and the experimental data more closely resemble a second-order process of the kinetic model. Adsorption studies on soil nanoclays have been shown to be highly effective in removing of Cu(II) from aqueous solution. This adsorbent is widely available as a natural material, is mechanically stable and, most importantly, it is environmentally appealing. The maximum Cu(II) adsorption capacity of soil nanoclays (31.7 mg/g) is more than three times higher than natural soil clays (10.2 mg/g). Our study demonstrates that soil nanoclays can be used effectively for removal of Cu(II) from aqueous systems to achieve environmental cleaning purposes.

Some selected heavy metal concentrations in water, sediment, and oysters in the Er-Ren estuary, Taiwan: chemical fractions and the implications for biomonitoring.

Studies of heavy metal contamination and ecological risk in estuaries are an important emerging area of environmental science. However, there have been few detailed studies of heavy metal contamination that concern the spatial variation of heavy metal levels in water, sediment, and oyster tissue. Because of the effective uptake of heavy metals, cultured oysters are a cheap and effective subject for study. This study, conducts an experiment in the Er-Ren river to examine the biological uptake of heavy metals in farmed, cultured oysters. The distribution of copper, zinc, lead, cadmium, and arsenic concentrations in water, sediment, and oysters from the Er-Ren river is also evaluated. By sequential extraction of the sediments, the following order of mobilities is found for heavy metals Pb > Cd > As > Zn > Cu. The highest percentages of heavy metals are found in the residual phase. The mean uptake rates for young oysters are 7.24 mg kg(-1) day(-1) for Cu and 94.52 mg kg(-1) day(-1) for Zn, but that for adult oyster is 10.79 mg kg(-1) day(-1) for Cu and 137.24 mg kg(-1) day(-1) for Zn. With good policies and management, the establishment of cultured oyster frames in these contaminated tributaries and near shore environments is a potential method for removing Cu and Zn and protecting the coast.