In situ Assemblies of Bacteria and Nutrient Dynamics in Response to an Ecosystem Engineer,Marine Clam Scapharca subcrenata,in the Sediment of an Aquaculture Bioremediation System

The relationships between nutrient dynamics,microbial community,and macrofauna are important in bioremediation systems.In this study,we examined the effects of marine clam Scapharca subcrenata sedimentary activities on the microbial assemblages,benthic nutrient chemistry,and its subsequent remediation impacts on organic effluent in the sediment of an aquaculture wastewater bioremediation system.The results showed that microbial community composition differed significantly in the clam area(ANOSIM,R=0.707,P=0.037).Pyrosequencing of bacterial 16S rRNA gene revealed a total of 48 unique phyla,79 classes,107 orders,197 families,and 321 genera amongst all samples.The most dominant bacterial assemblages were Proteobacteria,Bacteroidetes,Acidobacteria,Firmicutes,Verrucomicrobia,and Actinobacteria,with Bacteroidetes and Firmicutes significantly higher in all treatment samples than control(P<0.001).All dominant phyla in the list were shared across all samples and accounted for 89%(control)and 97%(treatment)of the total 16S rRNA.The nutrient flux rates from the sediments into the water(treatment group)were 51%(ammonium),88%(nitrate),77%(nitrite)and 45%(phosphate)higher,relative to the control implying increased mineralization,degradability,and mobility of the benthic nutrients.Similarly,significantly increased oxygen consumption rates were evident in the clam area signifying improved oxygen distribution within the sediment.The organic effluent contents associated with total-organic matter,carbon,nitrogen,and,phosphate were lower among the clam treatments relative to the control.Our results describe the potential roles and mechanisms contributed by marine bivalve S.subcrenata on benthic-bacterial-community assembly,nutrient balance,and effluent reduction in the sediments of aquaculture wastewaters bioremediation system.

THE SEASONAL DYNAMICS OF NUTRIENT CONTENTS IN MANCHURIA ASH-DAHURIAN LARCH MIXED STAND

The yield increasing mechanism of the manchurian ash (Fraxinus mandchurica) and dahurian larch(Larix gmelini) mixed stand was studied on nutrition status of soil and leaves. The results showed that nutrient contents of leaves and contents of the available nutrients of soil in the mixed and pure stands varied with seasons of the year. The available phosphorus contentS of the soil in the larch belt were much higher than those in the manchurian ash belt during growhg season, with the highest value of 3.5 mg/100g, 2~3 times of the latter. The nitrogen contents of leaves of the manchurian ash trees nearest from dahurian larch belt wer 12.7%~80.8% higher than those of its pure stand, and phosphorus 13.4%~140. 8%. The different uptake thythm of the nutrients modified the interspecific competition. The general conclusion is that the high contents of available phosphorus of the soil in dahurian larch belt improved the growing condition of nearby manhurian ash trees.

Dynamics of Nutrient Accumulation in Maize Plants Under Different Water and N Supply Conditions

The dynamics of accumulations of plant dry matter, nutrient uptake and N fertilizer recovery were studied with different water and N supply, using summer maize (Zea mays L. var. Shandan9) as an indicator crop. The total dry matter (including roots) and N, P, K uptake amounts were continuously increased with plant growth, and their accumulations with time during plant-growing period were shaped in S curves that could be described by exponential regression equations. Differentiating the regression equations fitting the curves over time for first derivatives, the momentary rate was obtained of the dry matter and nutrient uptake. Results show that the dry matter and the nutrient uptake were not in the same rate at all time, but changed from one time to another. Usually, the rate increased rapidly at early stages, and gradually decreased after reaching their peak. Of N, P and K, the uptake rate of N and K was higher, and their increase and decrease were both fast while P was reversed. The time of the maximum absorptive rate appeared earlier for K, followed by N, and then by P. In any case, the maximum nutrient uptake rate appeared earlier than did the dry matter. The momentary N recovery rate was similar in trend to those of dry matter and N uptake, and its maximum recovery rate occurred almost at the same time as its maximum uptake rate. Supplemental irrigation raised the cumulative and momentary rates of N. Although water and N supplies increased dry matter and nutrient uptake rates, they did not alter their changing trends during the plant-growing period.

Root stoichiometric dynamics and homeostasis of invasive species Phyllostachys edulis and native species Cunninghamia lanceolata in a subtropical forest in China

The community species abundance and diversity declined with bamboo invasion had been widely reported worldwide.However,the physiological strategies used during root competition between native species and invasive bamboo are poorly understood.To clarify the mechanisms underlying such strategies,the stoichiometric dynamics and homeostasis of nitrogen,phosphorus,organic carbon in root orders of Phyllostachys edulis(I du[=Ⅰ-Pe,years 1 and 2];Ⅱdu[=Ⅱ-Pe,years 3 and 4]),Cunninghamia lanceolata in transition and pure forests were analyzed.With increasing intensity of bamboo invasion,N,P,and C content of C.lanceolata root orders declined,N and P content in P.edulis rhizome orders declined,while C increased,the stoichiometric ratios in mixed forest interface mainly increased,and the stoichiometric differences within native and invasive species root orders narrowed.Meanwhile,the stoichiometric homeostasis index(H)of elements in the same root order and even the same elements in different root orders were not consistent.H of most root orders(except some HP)was greater than 4,the H ranked order wasⅠ-Pe>Cl>Ⅱ-Pe in mixed interfaces,and the N:P ratio of most species root orders was greater than 16,despite being affected by invasion.Our research concluded that the bamboo invasion narrows stoichiometric differences within root orders,and the juvenile bamboo rhizome has a stronger capacity for homeostatic regulation than in adult bamboo and C.lanceolata,which is a key determinant of bamboo invasion success.

Litter decomposition and nutrient release for two tropical N-fixing species in Rio de Janeiro,Brazil

Litter production and decomposition are critical to forest productivity,nutrient cycling,and carbon seques-tration in tropical woody ecosystems.However,nutrient release and leaf litter stoichiometry in tropical legume tree plantations over the long term after outplanting are poorly understood or even unknown.Toward improving our under-standing of the pattern of changes in the decomposition of N-fixing leaf litters and their possible impact on carbon stor-age,we measured litter production,mass loss and nutrient release for 240 d during litter decomposition for two tropical legume tree species(Plathymenia reticulata and Hymenaea courbaril),in Rio de Janeiro,Brazil.Litter production for P.reticulata was 5.689 kg ha^(−1) a^(−1) and 3.231 kg ha^(−1) a^(−1) for H.courbaril.The patterns of mass loss rates were similar;however,nutrient release was greater for P.reticulata,while H.courbaril showed immobilization of nutrients,especially for N,which increased by almost 20%in the early phase of decomposition followed by gradual release.Litter from the N-fixing species did differ in nutrient chemistries over time,which was not surprising given that initial nutrient concentrations varied broadly,except for C and P.Most of the nutrient concentrations increased as the remaining litter mass decreased in both species,except for C and K.The C:N and N:P ratios differed between the species,but N:P did not correlate to mass loss.Both species had N-rich leaves,but P.reticulata decomposition was very likely P-limited,while H.courbaril seemed to be co-limited by N and P.The results showed different patterns in nutrient release and the stoichi-ometry involved in the decomposition dynamics of the two tropical N-fixing species,even though they have similar litter decay rates.Both species,but especially P.reticulata,may help re-establish nutrient cycling in disturbed ecosystems.

The Application of Ecosystem Dynamic Model in Xiamen Bay

This paper is to establish a nitrogen and phosphorus nutrients cycle-based numerical model of ecological dynamics for Xiamen Bay on the basis of the existing three-dimensional barocline hydrodynamic model. The calculation results show that the estuarine district of Jiulongjiang estuary has the highest inorganic nitrogen concentration followed by the West Harbor, which demonstrates that Jiulongjiang River is the main input source of inorganic nitrogen in Xiamen Bay. The West Harbor has relatively high concentration of nutrients caused by the huge land pollution emission and its own poor water exchange capacity; while the distribution rules of phytoplankton biomass correspond with those of phosphates, demonstrating Xiamen Bay＇s phytoplankton controlled by phosphorus; the haloplankton biomass differs slightly, presenting the gradual reduction from the interior part to the exterior part of the bay.

Application of an optical nitrate profiler to high-and low-turbidity coastal shelf waters

Here,we report the results of high-resolution nitrate measurements using an optical nitrate profiler(in situ ultraviolet spectrophotometer,ISUS)along transect across a high-turbidity shelf(East China Sea)and a low-turbidity shelf(Chukchi Sea).The ISUS-measured nitrate concentrations closely reproduced the results measured by conventional bottle methods in low-turbidity waters.However,for high-turbidity waters of the East China Sea(salinity<30),a correction factor of 1.19 was required to match the standard bottle measurements.The high-resolution ISUS data revealed subtle spatial variability(e.g.,a subsurface nitrate minimum)that may have been missed if based solely on bottle results.Four main structures of the nitracline on the East China Sea are apparent from the ISUS nitrate profile.High-resolution nitrate data are important for studying nitrate budgets and nutrient dynamics on continental shelves.

Impacts of Soil Fauna on Litter Decomposition at Different Succession Stages of Wetland in Sanjiang Plain,China

Litter decomposition is the key process in nutrient recycling and energy flow. The present study examined the impacts of soil fauna on decomposition rates and nutrient fluxes at three succession stages of wetland in the Sanjiang Plain, China using different mesh litterbags. The results show that in each succession stage of wetland, soil fauna can obviously increase litter decomposition rates. The average contribution of whole soil fauna to litter mass loss was 35.35%. The more complex the soil fauna group, the more significant the role of soil fauna. The average loss of three types of litter in the 4mm mesh litterbags was 0.3-4. l times that in 0.058ram ones. The decomposition function of soil fauna to litter mass changed with the wetland succession. The average contribution of soil fauna to litter loss firstly decreased from 34.96% （Carex lasiocapa） to 32.94% （Carex rneyeriana）, then increased to 38.16% （Calamagrostics angustifolia）. The contributions of soil fauna to litter decomposition rates vary according to the litter substrata, soil fauna communities and seasons. Significant effects were respectively found in August and July on C. angustifolia and C. lasiocapa, while in June and August on C. meyeriana. Total carbon （TC）, total nitrogen （TN） and total phosphorus （TP） contents and the C/N and C/P ratios of decaying litter can be influenced by soil fauna. At different wetland succession stages, the effects of soil fauna on nutrient elements also differ greatly, which shows the significant difference of in- fluencing element types and degrees. Soil fauna communities strongly influenced the TC and TP concentrations of C. meyeriana litter, and TP content of C. lasiocapa. Our results indicate that soil fauna have important effects on litter decomposition and this influence will vary with the wetland succession and seasonal variation.

Effects of Nitrogen Addition on the Mixed Litter Decomposition in Stipa baicalensis Steppe in Inner Mongolia

During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition;N15: 1.5 g N/m2·a;N30: 3.0 g N/m2·a;N50: 5.0 g N/m2·a;N100: 10.0 g N/m2·a;N150: 15.0 g N/m2·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.

Land-Use Change on Soil C and N Stocks in the Humid Savannah Agro-Ecological Zone of Ghana

Land-use conversion and unsustainable farming practices are degrading native forest ecosystems of Ghana’s humid savannah agro-ecological zone. This study assessed the impact of land-use change on soil C and N stocks in different land-use systems and soil types. A total of eighty (80) composite soil samples at two depths (0 - 20 cm and 20 - 50 cm) were sampled from five land use types (Forest, Woodland savannah, Grassland, Fallow and Cropland) for laboratory analyses. Particle size distribution, bulk density, pH, SOC and TN were determined using standard procedures. Results of the study indicated that C and N stocks were significantly lower in croplands (p < 0.05) compared to other land-use systems. There were significant interactions (p < 0.05) within land-use systems, soil types, and soil depth for soil C and N stocks. Acrisol and associated soils had the highest C and N stocks. A strong positive significant correlation (p < 0.05) was observed between C and N stocks with an R2 value of 0.85 and 0.93 for the 0 - 20 and 20 - 50 cm depth, respectively. Soil C and N stocks in the study area were estimated to be 34.56 kg/m2 and 4.63 kg/m2 for soil types and 26.89 kg/m2 and 3.39 kg/m2 for land use types, respectively for the 0 to 50 cm soil depth. Our findings indicated that the conversion of native forest to arable land has significantly reduced soil C and N stocks in the top 50 cm (0.50 m) soil layer by 50.77% and 47.77%, respectively. Therefore, we conclude that land-use change, soil type, and soil depth influenced soil C and N stocks of land-use systems in the humid savannah agro-ecological zone of Ghana.

Ecological implications of twentieth century reforestation programs for the urban forests of São Paulo, Brazil: a study based on litterfall and nutrient cycling

The focus of this study was to investigate the wide use of Eucalyptus spp.,an exotic plant with high allelopathic ability,in the reforestation programs of urban parks in São Paulo City,Brazil,over the last century.To understand the implications of using Eucalyptus spp.in the city’s parks,this study aimed to compare nutrient cycling and litter decomposition between a mixed composition of litter(i.e.,native and exotic species)and the litter of a single species(i.e.,Eucalyptus).To accomplish this,newly deciduous leaves were collected from two native and two exotic species that are commonly used in the afforestation of São Paulo as well as from Eucalyptus spp.The mixed composition of litter yielded a higher dry mass loss and return of macro-and micronutrients to the forest floor.The decomposition constant(k)values were 0.00322 and 0.00207 g g^(−1) day^(−1) for the mixed composition and Eucalyptus spp.,respectively.The time required for decomposition of 50 and 95%of deciduous material was 215 and 931 days,respectively,and for the mixed litterfall 334 and 1449 days,respectively,for Eucalyptus spp.Therefore,the mixed litter exhibited greater dry mass loss and nutrient cycling in an urban forest of São Paulo City,since dry mass losses as well as speed and amount of nutrients returned to the forest floor were relatively higher compared to Eucalyptus spp.Nutrient cycling via Eucalyptus spp.litter was less efficient than mixed composition of litter,demonstrating that reforestation programs carried out in the twentieth century using only one species may have had little success.The results of this work emphasize the fact that in urban reforestation programs the City of São Paulo must consider the environmental and biogeographic characteristics of the species employed and use high levels of biodiversity,since the city lies in a megadiverse biome.

Biochar potentially enhances maize tolerance to arsenic toxicity by improving physiological and biochemical responses to excessive arsenate

Metalloid pollution,including arsenic poisoning,is a serious environmental issue,plaguing plant productivity and quality of life worldwide.Biochar,a carbon-rich material,has been known to alleviate the negative effects of environmental pollutants on plants.However,the specific role of biochar in mitigating arsenic stress in maize remains relatively unexplored.Here,we elucidated the functions of biochar in improving maize growth under the elevated level of sodium arsenate(Na_(2)AsO_(4),AsV).Maize plants were grown in pot-soils amended with two doses of biochar(2.5%(B1)and 5.0%(B2)biochar Kg^(−1) of soil)for 5 days,followed by exposure to Na_(2)AsO_(4)(’B1+AsV’and’B2+AsV’)for 9 days.Maize plants exposed to AsV only accumulated substantial amount of arsenic in both roots and leaves,triggering severe phytotoxic effects,including stunted growth,leaf-yellowing,chlorosis,reduced photosynthesis,and nutritional imbalance,when compared with control plants.Contrariwise,biochar addition improved the phenotype and growth of AsV-stressed maize plants by reducing root-to-leaf AsV translocation(by 46.56 and 57.46%in‘B1+AsV’and‘B2+AsV’plants),improving gas-exchange attributes,and elevating chlorophylls and mineral levels beyond AsV-stressed plants.Biochar pretreatment also substantially counteracted AsV-induced oxidative stress by lowering reactive oxygen species accumulation,lipoxygenase activity,malondialdehyde level,and electrolyte leakage.Less oxidative stress in‘B1+AsV’and‘B2+AsV’plants likely supported by a strong antioxidant system powered by biochar-mediated increased activities of superoxide dismutase(by 25.12 and 46.55%),catalase(51.78 and 82.82%),and glutathione S-transferase(61.48 and 153.83%),and improved flavonoid levels(41.48 and 75.37%,respectively).Furthermore,increased levels of soluble sugars and free amino acids also correlated with improved leaf relative water content,suggesting a better osmotic acclimatization mechanism in biochar-pretreated AsV-exposed plants.Overall,our findings provided mechanistic insight into how biochar facilitates maize’s active recovery from AsV-stress,implying that biochar application may be a viable technique for mitigating negative effects of arsenic in maize,and perhaps,in other important cereal crops.