An Invasive Succulent Plant (Kalanchoe daigremontiana) Influences Soil Carbon and Nitrogen Mineralization in a Neotropical Semiarid Zone

It has long been recognized that plant invasions may alter carbon(C) and nitrogen(N) cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant,Kalanchoe daigremontiana(Crassulaceae), on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes(C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease) between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall,our results showed that C mineralization and transformation of organic compounds to NH_4~+ were favored at sites colonized by K.daigremontiana. With this species, we found the highest cumulative amounts of NH_4~+-N and C and the lowest mineralization time.These results could be explained by higher activities of urease and glucosaminidase in soils under the influence of K. daigremontiana.In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion,invasion of Neotropical semiarid zones by K. daigremontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.     

连续三年添加制革厂堆肥后土壤微生物生物量研究

Brazilian industry produces huge amounts of tannery sludge as residues, which is often disposed by landfilling or land application. However, consecutive amendment of such composted industrial wastes may cause shifts in soil microbial biomass （SMB） and enzyme activity. This study aimed to evaluate SMB and enzyme activity after 3-year consecutive composted tannery sludge （CTS） amendment in tropical sandy soils. Different amounts of CTS （0.0, 2.5, 5.0, 10.0, and 20.0 t ha-1） were applied to a sandy soil. The C and N contents of SMB, basal and substrate-induced respiration, respiratory quotient （qCO2）, and enzyme activities were determined in the soil samples collected after CTS amendment for 60 d at the third year. After 3 years, significant changes were found in soil microbial properties in response to different CTS amounts applied. The organic matter and Cr contents significantly increased with increasing CTS amounts. SMB and soil respiration peaked following amendment with 10.0 and 20.0 t ha-1 of CTS, respectively, while qCO2 was not significantly affected by CTS amendment. However, soil enzyme activity decreased significantly with increasing CTS amounts. Consecutive CTS amendment for 3 years showed inconsistent and contrasting effects on SMB and enzyme activities. The decrease in soil enzyme activities was proportional to a substantial increase in soil Cr concentration, with the latter exceeding the permitted concentrations by more than twofold. Thus, our results suggest that a maximum CTS quantity of 5.0 t ha-1 can be applied annually to tropical sandy soil, without causing potential risks to SMB and enzyme activity.     

Downed logs improve soil properties in old-growth temperate forests of northern Iran

Dead trees, particularly downed logs, play an important role in the dynamics of forest ecosystem. Contribution of decaying wood to C and nutrient pools of forest soils depends on the tree species and degree of wood decay. However, the extent to which the downed logs affect the soil properties of temperate forests has rarely been evaluated. In this study, a mixed beech forest was selected in Liresar region of Mazandaran Province, northern Iran, to investigate if and how the presence of downed logs affected soil quality and function by comparing soils underneath degraded logs and nearby soils of the two dominant tree species(beech and hornbeam). We then explored how these effects occurred as downed logs decomposed by comparing the woods of both tree species at four degrees of decomposition. Degree of decay of downed logs was classified into four classes(DC1–DC4). Eight dead trees of each tree species were selected at the center of each sample plot. Three composite soil samples underneath each decaying log and 100 cm away from a decaying log were collected at two soil depths(0–15 and 15–30 cm) to analyze soil main physicochemical properties and microbial activity. The results revealed that downed logs affected soil physical(5% wetter than control soils), chemical(2% lower pH, 100% increase in organic C and total N in the case of hornbeam, and 2% increase in P), and biological characteristics(soil microbial respiration enhanced by 10%, and microbial biomass C 620 and 351.5 mg kg~(-1) and microbial biomass N 66.47 and 32.18 mg kg~(-1), respectively, in the cases of beech and hornbeam), thus resulting in significantly different soil microsites from those without downed logs. Presence of downed logs increased soil microbial activity and soil fertility as wood decayed. Thus, the presence of downed logs is an important factor influencing forest soils and should be taken into consideration in forest management practices.     

Short-Term Effect of Nitrogen Intensification on Aggregate Size Distribution, Microbial Biomass and Enzyme Activities in a Semi-Arid Soil Under Different Crop Types

There is a lack of quantitative assessments available on the effect of agricultural intensification on soil aggregate distribution and microbial properties. Here, we investigated how short-term nitrogen(N) intensification induced changes in aggregate size distribution and microbial properties in a soil of a hot moist semi-arid region(Bangalore, India). We hypothesised that N intensification would increase the accumulation of macroaggregates 2 mm and soil microbial biomass and activity, and that the specific crop plant sowed would influence the level of this increase. In November 2016, surface(0–10 cm) and subsurface(10–20 cm) soil samples were taken from three N fertilisation treatments, low N(50 kg N ha~(-1)), medium N(75 and 100 kg N ha~(-1) for finger millet and maize, respectively),and high N(100 and 150 kg N ha~(-1) for finger millet and maize, respectively). Distribution of water-stable aggregate concentrations,carbon(C) and N dynamics within aggregate size class, and soil microbial biomass and activity were evaluated. The high-N treatment significantly increased the concentration of large macroaggregates in the subsurface soil of the maize crop treatment, presumably due to an increased C input from root growth. Different N fertilisation levels did not significantly affect C and N concentrations in different aggregate size classes or the bulk soil. High-N applications significantly increased dehydrogenase activity in both the surface soil and the subsurface soil and urease activity in the surface soil, likely because of increased accumulation of enzymes stabilised by soil colloids in dry soils. Dehydrogenase activity was significantly affected by the type of crop, but urease activity not. Overall, our results showed that high N application rates alter large macroaggregates and enzyme activities in surface and subsurface soils through an increased aboveground and corresponding belowground biomass input in the maize crop.     

蚯蚓与黑麦草相互作用对土壤中荧蒽去除的影响

Earthworms can promote the bioremediation of contaminated soils through enhancing plant growth and microorganism development. The individual and combined effects of earthworms and ryegrass (Lolium multiflorum Lam.) on the removal of fluoranthene from a sandy-loam alluvial soil were investigated in a 70-d microcosm experiment. The experiment was set up in a complete factorial design with treatments in four replicates: without earthworms or ryegrass (control, CK), with earthworms only (E), with ryegrass only (P), and with both earthworms and ryegrass (EP). The residual fluoranthene, microbial biomass C, and polyphenol oxidase activity in the soil changed significantly (P<0.01) with time. In general, the residual concentration of fluoranthene in the soil decreased sharply from 71.8-88.7 to 31.7-37.4 mg kg 1 in 14 d, and then decreased gradually to 19.7-30.5 mg kg 1 on the 70th d. The fluoranthene concentration left in the soil was the least with both earthworms and ryegrass, compared to the other treatments at the end of the experiment. Half-life times of fluoranthene in the E, P, and EP treatments were 17.8%-36.3% smaller than that of CK. More fluoranthene was absorbed by earthworms than ryegrass. However, the total amounts of fluoranthene accumulated in both the ryegrass and earthworms were small, only accounting for 0.01%-1.20% of the lost fluoranthene. Therefore, we assumed that microbial degradation would play a dominant functional role in fluoranthene removal from soil. We found that earthworms significantly increased microbial biomass C and polyphenol oxidase activity (P<0.01) in the presence of ryegrass at the end of the experiment. Furthermore, microbial biomass C and polyphenol oxidase activity were significantly (P<0.05) and negatively related to the residual fluoranthene concentration. This implied that earthworms might promote the removal of fluoranthene from soil via stimulating microbial biomass C and polyphenol oxidase activity.     

农业土壤中频繁施用有机质提高土壤抑菌作用

Soil-borne plant pathogens are among the most important limiting factors for the productivity of agro-ecosystems.Fungistasis is the natural capability of soils to inhibit the germination and growth of soil-borne fungi in the presence of optimal abiotic conditions.The objective of this study was to assess the effects of different soil managements,in terms of soil amendment types and frequency of application,on fungistasis.For this purpose,a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i.e.,glucose,alfalfa straw and wheat straw).Thereafter,the fungistasis response was assessed on four fungi (Aspergillus niger,Botrytis cinerea,Pyrenochaeta lycopersici and Trichoderma harzianum).Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method.Results showed that irrespective of the fungal species and amendment types,frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration.The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities.This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity.     

七种钾释放动力学方程的比较和动力学参数的应用

Batch equilibrium experiments were conducted to investigate cadmium （Cd） sorption by two permanent-charge soils, a yellow-cinnamon soil and a yellow-brown soil, and two variable-charge soils, a red soil and a latosol, with addition of selected organic acids （acetate, tartrate, and citrate）. Results showed that with an increase in acetate concentrations from 0 to 3.0 mmol L^-1, Cd sorption percentage by the yellow-cinnamon soil, the yellow-brown soil, and the latosol decreased. The sorption percentage of Cd by the yellow-clnnamon soil and generally the yellow-brown soil （permanent-charge soils） decreased with an increase in tartrate concentration, but increased at low tartrate concentrations for the red soil and the latosol. Curves of percentage of Cd sorption for citrate were similar to those for tartrate. For the variable-charge soils with tartrate and citrate, there were obvious peaks in Cd sorption percentage. These peaks, where organic acids had maximum influence, changed with soil type, and were at a higher organic acid concentration for the variable-charge soils than for the permanent charge soils. Addition of cadmium after tartrate adsorption resulted in higher sorption increase for the varlable-charge soils than permanent-charge soils. When tartrate and Cd solution were added together, sorption of Cd decreased with tartrate concentration for the yellow-brown soil, but increased at low tartrate concentrations and then decreased with tartrate concentration for the red soil and the latosol.     

Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan (Carya illinoinensis) orchards in the southwestern region of the United States. Given the paucity of data regarding the effect of indaziflam on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effects of different application rates of indaziflam on soil microbial activity, diversity, and biochemical processes related to nitrogen (N) cycling. During two consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown and treated with indaziflam applied at two different rates (25 and 50 g active ingredient (ai) ha^-1, with the higher rate being slightly lower than the recommended field application rate of 73.1 g ai ha^-1). Soil samples were collected approximately one week before and one week after herbicide application for determination of soil microbial biomass and diversity, N mineralization, and β-glucosaminidase activity. Soil samples collected from the control mesocosms without herbicide application were treated in the laboratory with two rates of indaziflam (75 and 150 g ai ha^-1) to determine the immediate effect on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. The results showed a slight to moderate decrease in microbial diversity (7% in 2015 and 44% in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed in soils from the mesocosms (33%) and soils treated with indaziflam in the laboratory (45%). The mineral N pool was generally dominated by ammonium after indaziflam application, which was consistent with the drastic decrease (75%) in nitrification activity measured in the laboratory experiment. The results of this study indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on soil microbial activity, but may affect N cycling processes.     

Nitrogen Release from Slow-Release Fertilizers in Soils with Different Microbial Activities

Soil microbial activity is recognized as an important factor affecting nitrogen (N) release from slow-release fertilizers. However,studies on the effect of size and activity of soil microflora on fertilizer degradation have provided contrasting results. To date, no clear relationships exist between soil microbial activity and the release of N from slow-release fertilizers. Hence, the aim of this study was to better understand such relationships by determining the release of N from three slow-release fertilizers in soils with different microbial activities. Soils were amended with urea-formaldehyde (UF), isobutylidene diurea (IBDU), and crotonylidene diurea (CDU). Urea, a soluble fertilizer, was used as the control. Fertilized soil samples were placed in a leaching system, and the release of N was determined by measuring ammonium-N and nitrate-N concentrations in leachates during 90 d of incubation. Non-linear regression was used to fit N leaching rate to a first-order model. In all the treated soils, N was released in the order: urea (89%–100%) IBDU (59%–94%) UF (46%–73%) CDU (44%–56%). At the end of incubation, N released from CDU did not differ (P 0.05) among soils. On the contrary, UF and IBDU released significantly lower (P 0.05) amounts of N in the soil with higher microbial activity and lower pH.The rate constant (K_0) for UF was lower (P 0.05) in the soil with lower pH. Taken together, our results indicated that soil microbial size and microbial activity had a marginal effect on fertilizer mineralization.     

长期重金属胁迫下的土壤微生物特征: 沈阳张士污灌区的案例研究

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City, China, an area with a 30-year irrigation history with heavy metal-containing wastewater. The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress. In light of the National Environmental Quality Standards of China, the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu, even though wastewater irrigation ceased in 1993. Soil metabolic quotient （qCO2） had a significant positive correlation, while soil microbial quotient （qM） had a negative correlation with content of soil heavy metals. Soil microbial biomass carbon （MBC） had significantly negative correlation with Cd, but soil substrate~induced respiration （SIR）, dehydrogenase activity （DHA）, cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content. Soil nutrients, except for phosphorous, showed positive effects on soil microbial characteristics, which to a certain degree obscured the adverse effects of soil heavy metals. Soil Cd contributed more to the soil microbial characteristics, but qM and qCO2 were more sensitive and showed persistent responses to heavy metals stress. It could be concluded that qM and qCO2 can be used as bioindicators of heavy metal pollution in soils.     

Some effects of mound-building termites on the soils of a semi-arid area of Kenya

The nutrient status of soils from Macrotermes termite mounds, in and around Kajiado District, reflects that of the subsoils more closely than in some other studies, notably Watson (1977). Consequently the growth of vegetation on and around mounds was not noticeably enhanced, except in grasslands and in higher rainfall areas. There was no evidence that mounds acted as wicks. Mound soils contained greater concentrations of calcium, magnesium and potassium than subsoils in almost all cases where subsoil values were low, suggesting that the termites’ activities enhanced the nutrient status of mound soils. The nutrients were probably derived from their food, and the effects increased in some cases by their selection of clay on clay-poor soils. Nevertheless, the overall effects of Macrotermes on rangeland soils are probably small. The distribution of Macrotermes is remarkably unaffected by soil types; they construct mounds on almost all soils except those consisting largely of montmorillonite.     

Use of RAPD markers for the study of microbial community similarity from termite mounds and tropical soils

In this study, we test the use of the RAPD (Random Amplified Polymorphic DNA) molecular markers as a way to estimate the similarity of the microbial communities in various termite mounds and soils. In tropical ecosystems, termite activities induce changes in the chemical and physical properties of soil. The question then arises as to whether or not termites affect the presence of natural microbial communities. Successful 16S rDNA amplifications provided evidence of the occurrence of bacterial DNA in termite constructions including both soil feeder and fungus grower materials. A phenetic dendrogram using the similarity distance calculated from pairwise data including 88 polymorphic RAPD markers was reconstructed and bootstrap scores mapped. The microbial communities of the mounds of the four soil-feeding termites were clustered in the same clade, while those of the mounds of the fungus-growing species were distinct like those of control soils. Microbial changes in nests result from termite building behavior, depending on whether they include feces in their constructions for soil-feeders or use saliva as particle cement for fungus-growers. It is argued that RAPDs are useful markers to detect differences in microbial community structure not only between termitaries and control soils but also between mounds of soil-feeders.     

Consistent effects of eastern subterranean termites (Reticulitermes flavipes) on properties of a temperate forest soil

Termites inhabit a large portion of land covered by temperate forests. Climate warming and urbanization will likely extend their range and increase their densities in these ecosystems but, compared to their tropical counterparts, little is known about their effects on soil properties and processes. If temperate termites have the strong ecosystem engineering effects of tropical termites, then knowledge of their ecology and impacts will be vital for predicting how temperate systems respond to environmental change. We investigated how feeding and tunneling by the eastern subterranean termite, Reticulitermes flavipes, affected wood decomposition and soil properties under decaying wood. Twelve laboratory microcosms filled with mineral soil and with wood blocks of four common temperate tree species, received R. flavipes soldiers and workers at field densities, with an additional five termite-free microcosms serving as controls. After 25 weeks, the effects of termites on wood mass loss, and on carbon and nitrogen dynamics, differed across tree species, yet their effects on soil properties were consistent regardless of wood type. Microbially-available carbon in soil was 20% higher with termites and soil moisture content 20% lower. Soil pH was more acid with termites and their effects on soil microbial biomass were positive but non-significant. These soil responses were consistent regardless of the wood species, suggesting that termite effects on soil are dictated largely by their activity within the soil matrix and not by their feeding rate on specific wood substrates. These results are among the first to quantify the effects of temperate forest termite activity on soil properties, demonstrating the potential for these termites to shape biogeochemical cycling and plant communities through their alteration of the soil environment.     

Soil genesis and heterogeneity of phosphorus forms and carbon below mounds inhabited by primary and secondary termites

Termite activities are known to significantly influence small-scale soil properties in tropical savannas. The lateral and vertical extent of the alterations to the nest's surrounding, and particularly resulting impacts on diagnostic soil horizons remain largely unresolved until today. We examined the effects of mound-building termites on soil genesis and constitutive chemical soil properties in and below their nests. Two transects to a soil depth of 100 cm were dug below three younger mounds of Cornitermes silvestrii (the primary nest builder), three older mounds in which C. silvestrii had died out and which were secondarily colonized mainly by Nasutitermes kemneri, and three reference sites in the Brazilian Cerrado. The samples were characterized by standard procedures for soil classification; in addition, phosphorus extractions were conducted on selected samples using NaHCO₃ for labile P forms, and concentrated HCl for stable P forms. This data set was then used to build calibration models for the prediction of labile and stable inorganic (P_i) and organic (P_o) P forms, as well as for contents of organic carbon (OC), for the remaining samples applying mid-infrared spectroscopy in combination with partial least squares regression (MIRS-PLSR). We can show that the termite influence on the soil was sufficiently large to change diagnostic characteristics of the soils under termite mounds. The MIRS-PLSR predictions were suitable for quantifying organic carbon and most of the labile and stable phosphorus fractions. They showed an enrichment of OC, NaHCO₃-P_o and NaHCO₃-P_i contents in nests inhabited by primary and secondary termites by factors of 1.6–2.0 and 1.4–1.5, respectively. The soils surrounding the nests had higher contents of OC and NaHCO₃-P under both nest types vertically down to 30 cm below the lower nest border, and OC and NaHCO₃-P_i contents were elevated at minimum to a lateral distance of 60 cm away from the nest border. As the pattern of HCl_conc-P_i, which comprised 95% of total P, showed no variations, we conclude that the higher NaHCO₃-P_i amount was formed in termite nests by changing the availability of the more stable HCl_conc-P_i. In contrast to the contents, the OC and NaHCO₃-P stocks below the mounds inhabited by primary termites were comparable to those inhabited by secondary ones, because the bulk density of the secondarily inhabited nests was elevated. This was due to a transport of clay-rich material from the subsurface argic horizons into the nests. Here, the secondary termites even reverted the lessivation observed in the reference soils and under mounds inhabited by primary termites, thus causing the soil types to change from Alisols and Acrisols to the properties of Umbrisols.     

Chemical,physical and micromorphological properties of termite mounds and adjacent soils along a toposequence in Zona da Mata,Minas Gerais State,Brazil

Little is known about the effects of neotropical mound-building termites in soil chemical and physical properties. The influence of soil termite activity on soil characteristics was studied by assessing chemical, physical and micromorphological properties of a toposequence of Latosols (Oxisols). Soil samples were collected from the walls and inner parts of termite mounds and also from adjacent soil. A high diversity of termite genera was found in the mounds along the toposequence, together with the inquiline termites and other soil-dwelling arthropods. Chemical analyses showed that pH and the contents of organic C and N, P, Ca and Mg were significantly higher in termite mounds compared with adjacent areas, with an inverse trend for Al content. Significant differences in pH and exchangeable Al were observed between soil and mound across the slopes. The mound density across the landscape was higher at the upper slope segment, followed by the hill top, middle slope and lower slope segments. Considering a lifespan of 30 years and dimensions of termite mounds found in the toposequence we conclude that the textural and chemical uniformity of Latosols may be increased, following the pedobiological turnover during mound building, with local rates varying from 2.1 to 7.5 m³ ha^− 1.     

Effects of termites on the physical and chemical properties of the acid sandy soils of southern Nigeria

Abstract

This study was aimed at characterizing the effects of the activity of termites of the genus Nasutitermes on the physico‐chemical properties of the acid sandy soils of southern Nigeria. Selected morphological properties of the termite mounds were measured in the field. Outside portions of the termite mound and surface (0–15 cm) soil were collected and analyzed for some physical and chemical properties. Results obtained showed a density of 112 mounds ha^‐1 with average height of 0.85 m. There were significantly higher proportions of clay, silt, and organic carbon, and higher pH, exchangeable potassium (K), calcium (Ca), magnesium (Mg), available phosphorus (P), effective cation exchange capacity and base saturation in the mounds of the Nasutitermes than in the surrounding topsoil. Mounds of Nasutitermes termites, if returned to the soil, could improve the properties of the soil in areas where termites occur in large numbers.     

Impact of subterranean fungus-growing termites (Isoptera, Macrotermitiane) on chosen soil properties in a West African savanna

Fungus-growing termites (Isoptera, Macrotermitinae) play an important role in tropical ecosystems in modifying soil physical properties. Most of the literature regarding the impact of termites on soil properties refers to termite epigeous mounds. In spite of their abundance and activity in African savannas, few studies deal with the properties of underground nest structures (fungus-comb chambers) built by subterranean Macrotermitinae termites. We tested whether these termites significantly modify the soil physico-chemical properties within their nests in a humid tropical savanna and whether these effects are different for two termite species with differing building behaviour. Termite-worked soil material was collected from fungus-comb chamber walls of two widespread species: Ancistrotermes cavithorax, which builds diffuse and ephemeral nests and Odontotermes nr pauperans, which most often builds concentrated and permanent nests for a comparatively much longer period of time. Neither species influenced soil pH but both significantly modified soil texture and C-N content in their nest structures. A strong impact on clay-particle size was also detected but no significant differences in clay mineralogy. Thus Odontotermes has a greater effect on soil properties, that could be explained by its building behaviour and the concentration in space of its nest units. Therefore, spatial pattern and life-span of fungus-comb chambers should be an important parameter to be considered in the functional role of subterranean Macrotermitinae termites in the savanna.     

Tree species effects on soil enzyme activities through effects on soil physicochemical and microbial properties in a tropical montane forest on Mt. Kinabalu, Borneo

Tree species influence on the soil mineralization process can regulate overall nutrient cycling in a forest ecosystem, which may occur through their effects on substrate quality, soil physicochemical properties and soil microbial community. We investigated tree species effects on soil enzyme activities in a tropical montane forest on Mt. Kinabalu, Borneo. Specifically, we analyzed C- and P-degrading enzyme activities, as well as the relationships among the enzyme activities, soil physicochemical properties, substrate quality (C, N, and P concentrations), and microbial composition in the top 5 cm soils beneath conifers (Dacrycarpus imbricatus and Dacrydium gracilis) and broadleaves (Lithocarpus clementianus, Palaquium rioence, and Tristaniopsis clementis). Activities of acid phosphatase and β-d-glucosidase were significantly different among the tree species. Soil moisture, total C and N content and microbial lipid abundance (a proxy for microbial composition) could influence the enzyme activities although the relative contributions of microbial composition to the enzyme activities might be smaller. A higher acid phosphatase activity beneath Dacrydium than those beneath the other tree species can compensate for a lower concentration of P in available fractions beneath Dacrydium. This localized mineralization activity could subsequently influence soil nutrient availability in this forest.     

Contributions of ant mounds to soil carbon and nitrogen pools in a marsh wetland of Northeastern China

Ant mounds often occur at high densities in marsh wetlands. However, little information is available regarding their impacts on soil nutrient pools in these ecosystems. We studied C_org, dissolved organic carbon (DOC), total nitrogen (TN), NO₃⁻ and NH₄⁺ concentrations in above-ground ant mounds and in soils under mounds for three ant species (Lasius flavus, Lasius niger and Formica candida), and estimated their contribution to the total soil nutrient pools in a marsh wetland. Ant impacts were greatest in above-ground soils. All measured nutrient concentrations in above-ground mounds were significantly higher than the average values in reference soils (upper 25 cm). However, except for DOC, no significant differences for nutrient concentrations existed between soils under mounds and reference soils. The impacts of ant mounds on soil C and nutrient concentrations varied by ant species. L. niger above-ground mounds stored less C_org, TN and NO₃⁻ than F. candida and L. flavus mounds, or reference soils. At the ecosystem scale, soils in above-ground mounds and under ant mounds all contained less C_org per hectare than the reference soils. Total amounts in nutrient pools from mounds of the three ant species comprised from 5.3% to 7.6% of the total in natural marsh soils. More importantly, ant mounds increased the spatial heterogeneity of nutrient pools. Thus, ant mounds can be important to a fully integrated understanding of the structure and function of wetland nutrient cycles and balances.     

Functional diversity of soil microbial community,rock phosphate dissolution and growth of Acacia seyal as influenced by grass-, litter- and soil-feeding termite nest structure amendments

We tested termite mound materials belonging to different feeding groups: Cubitermes (soil-feeder), Trinervitermes (grass-feeder) and Macrotermes (litter-feeder), as natural microbial inoculum to promote plant growth and increase nutrient supplies from soil organic matter and inorganic amendments (rock phosphate), through their effects on soil microorganisms (functional diversity of soil microflora, arbuscular mycorrhizal fungi, rhizobia, fluorescent pseudomonads, actinomycetes and saprophytic fungi). Experiments were made in a pot experiment with Acacia seyal, a leguminous tree abundant in West Africa, with a sandy soil amended or not with rock phosphate. Results indicated a stimulation of plant growth with Cubitermes and Trinervitermes mound powder (plant height and shoot biomass), similar to what was obtained with rock phosphate alone. Leaf content in N was also increased in the termite treatments (except in Macrotermes soil), whereas mycorrhizal colonization was inhibited as compared to the control. The development of saprophytic fungi was significantly higher in the soils amended with rock phosphate and this effect was hypothesized to be related to the production of large quantities of oxalic acid by fungal populations. The fluorescent pseudomonad populations notably increased in the soils dually amended with mound powders and rock phosphate, and this could be due to the fact that some species of this bacterial group are able to dissolve rock phosphate. The organic and inorganic amendments decreased the soil catabolic evenness in all the mound powder treatments. Among the mound materials tested, Cubitermes mound powder had the most promising effect, especially on SIR response to oxalate. It is concluded that soils amended both with rock phosphate and Cubitermes mound soil could promote the development of microbial communities, which could help to metabolize this compound and consequently enhance plant growth.