Seasonal variation of inorganic nitrogen and net mineralization in a salt marsh ecosystem

Inorganic nitrogen pools and net mineralization were estimated in three sites of a Tagus estuary salt marsh in Portugal throughout 1 year. Ammonium (NH₄ ⁺) was the major form of inorganic nitrogen found in the salt marsh soil. Extractable NH₄ ⁺ concentrations showed a marked seasonal pattern with a concentration peak during the hotter months of July/August. The great majority (>99%) of the total nitrogen in the soil was found in sedimented organic matter, not readily available for plant uptake. Net nitrogen mineralization, determined using a field incubation method, showed a peak during the months of June/July which resulted in an increase on nitrogen availability. With the exception of the lower salt marsh, estimated rates of in situ net nitrogen mineralization in the soil during summer were well related to the increase in plant aboveground biomass and plant nitrogen pools, indicating that the process is an important source of available nitrogen for plant uptake and growth. Annual net nitrogen mineralization ranged between 2.4 and 4.5gNm^–2yr^{– 1} being significantly higher for the lower salt marsh site. Rates of net nitrogen mineralization were relatively low during most of the year with a particularly active period from June to August, possibly due to an effect of temperature on soil microbial activity.     

Relationships between <Emphasis Type="Italic">Artemisia ordosica</Emphasis> communities and environmental factors following sand-dune stabilization in the Mu Us desert,northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis (CCA) to examine the relationships between A. ordosica communities and environmental factors at three habitats: semi-fixed dune (SF), fixed dune with low-coverage biological soil crust (F), and fixed dune with high-coverage biological soil crust (FC) in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vegetation–environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0–20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.     

Mangrove species zonation and soil redox state,sulphide concentration and salinity in Gazi Bay (Kenya), a preliminary study

The relationship between soil redox state, sulphide concentration, salinity and spatial patterns of mangrove species distribution was investigated in the mangrove forest of Gazi Bay (Kenya). Field measurements were conducted to examine the relationship between species distribution along a band transect of 280m and soil redox potential (Eh) and sulphide patterns, as well as the indirectly related (through flooding regimes) soil salinity. Of the three major species Avicenniamarina, Ceriops tagal and Rhizophoramucronata present along the transect, only the distribution of the latter correlated with the measured soil variables, R. mucronata being absent from the lessreduced zone with high salinity. Bruguieragymnorhiza and Heritieralittoralis occur in minor populations, they are restricted to the saline, sulphidepoor and lessreduced substrates. From the results it is concluded that soil redox potential (Eh), sulphide concentration and salinity may contribute to structure mangroves through the distribution of dominant species, however in combination with other environmental conditions and processes of vegetation dynamics.     

聚乳酸纤维沙障对植被生长的影响——以巴音温都尔沙漠封禁保护区为例

巴音温都尔沙漠的治理关乎整个河套平原的生态安全,然而,由于降水少,植被盖度低,导致其治理难度大。聚乳酸纤维沙障具有便于移动、使用寿命长、可生物降解无污染的特点,具有较好的发展前景。本研究将聚乳酸纤维沙障应用于巴音温都尔沙漠封禁保护区,并对其影响下植被的盖度、生物量及土壤的水分含量等指标进行为期4 a的监测。结果表明:(1)自沙障布设的第2 a起,沙障内的植被盖度和土壤含水量显著提高(P<0.05);(2)沙障内的植被地上生物量自沙障布设的第2 a起便开始显著增加,而地下生物量自沙障布设的第4 a起才显著增加(P<0.05)。总体来看,聚乳酸纤维沙障可通过提高土壤含水量来促进植被生长,可作为生物固沙难以实施区域的固沙措施,但其效果还有待更长期的研究。     

The effect of Spartina alterniflora Loisel on trace metals accumulation in inter-tidal sediments

We present the distribution of Cd and Zn in sediment cores taken under Spartina alterniflora Loisel. marsh and compare with adjacent mud flats without plant cover. Vertical distribution of Cd and Zn in the mud flat and S. alterniflora cores were different. From 0 to 5 cm of depth Zn and Cd concentrations did not change with depth in the two cores but were higher in the mud flat. From 5 to 15 cm, corresponding to maximum root biomass under S. alterniflora, Zn and Cd concentrations remained constant in the mud flat cores, but increased by a factor of nearly 4 under S. alterniflora. Below this depth concentrations dropped in both cores. Manganese distribution in S. alterniflora cores suggests that oxides are precipitated at the depth of maximum root biomass. More oxic environment under S. alterniflora (average Eh = +5 mV) with low sulfide concentration (0.58 mg l^-1) relative to the mud flat cores (average Eh = –204 mV; sulfide 47.1 mg l^-1), may favor Fe and Mn oxi-hydroxides precipitation, causing an accumulation of Cd and Zn at the root zone. In the mud flat cores, Zn and Cd highest concentrations were at the sediment water interface, where oxic waters favor their precipitation with Fe and Mn oxi-hydroxides. The results discourages the indiscriminate use of salt marsh sediments in environmental monitoring of trace metals, since the possibility of post-deposition mobilization of trace metals due to root metabolism, will make correlation with trace metal loading rates impossible.     

Spatial pattern of a plant community in a wetland ecosystem in a semi-arid region in northwestern China

The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid and semi-arid regions in northwestern China and the main factors affecting the distribution pattern were studied. The Siertan wetland in the Haba Lake Nature Reserve was the study area. Four transect lines, each about 1 km long, were set up in the growing season along the biotope gradient in four directions: east, northeast, west and northwest. Attributes measured include frequency of occurrence, height, density, coverage, biomass and environmental soil factors. The data were analyzed using a two-way indicative species analysis (TWINSPAN), detrended correspondence analysis (DCA) and Spearman correlation coefficients. On this basis, the vegetation in the Siertan wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh vegetation, mainly distributed in the wetland zone. This type largely contains halophyte and hygric plants and its representative association is Phragmites communis + Kalidium foliatum. The second type was meadow vegetation, distributed in the ecotone. The meadow vegetation species are mainly mesophytic and their representative association is Nitraria tangutorum + Pennisetum flaccidum. The third vegetation type is grassland vegetation, which mainly consists of mesophytic and xerophytes, distributed in the arid grassland zone. The representative association of the third vegetation type is the association of Anaeurolepidium secalium + Saussurea runcinata. Correlation analysis between the axes of DCA and environmental soil factors shows that soil moisture content, organic matter, soil salt content and total nitrogen are the main environmental factors affecting the pattern of vegetation distribution along the biotope gradients from wetland to arid grassland. Other factors affecting the vegetation are microtopography and grazing pressure. Additionally, we have reported modifications and improvements to the importance value methodology. __________ Translated from Journal of Beijing Forestry University, 2008, 30(1): 6–13 [译自: 北京林业大学学报]     

Pathways for resilience in Mediterranean cork oak land use systems

Context

Loss of woodlands and degradation of vegetation and soil have been described for all Mediterranean-type ecosystems worldwide. In the Western Iberian Peninsula, overexploitation of evergreen cork oak land use systems has led to soil erosion, failures in oak recruitment, and loss of forests. Degraded and dry sites are quickly colonised by pioneer heathland rockrose (Cistus spp.) shrubs forming highly persistent patches.

Aims

Although traditionally shrublands have been considered as a transient successional state, we present evidence that they can represent persistent alternative states to former cork oak forests.

Review trends and conclusions

We first describe how Mediterranean vegetation evolved in the Iberian Peninsula and the role of fire and long-term human management as main disturbances. We then discuss alternative pathways through state-and-transition models indicating the ecological and land use variables that halt cork oak regeneration and recruitment and drive vegetation transitions towards persistent shrublands. Unless concerted management actions and restoration programmes are undertaken, the cork oak land use systems will not be sustainable.     

Variations of plant and soil 87Sr/86Sr along the slope of a tropical inselberg

? From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols.

? We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities.

? Granite and atmospheric deposition have ⁸⁷Sr/⁸⁶Sr ratios of 1.3 and 0.71, respectively. The ⁸⁷Sr/⁸⁶Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The ⁸⁷Sr/⁸⁶Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment.

? These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition.

     

A soil seed bank in a mature conifer plantation and establishment of seedlings after clear-cutting in southwest Japan

Compositions and spatial distribution patterns of buried viable seeds, and demographic transition from buried viable seeds to seedlings after clear-cutting were examined in a 75-year-old conifer plantation in southwest Japan. A part of the plantation was cleared in December 1997 and study plots were set up on a cleared site and a preserved site. Soil samples (a total of 105 l for the preserved plot and 90 l for the cleared plot) were collected from surface soils in spring 1998 and were incubated in a greenhouse for 120 days. There were an estimated 1064 buried viable seeds per square meter from 67 species in the preserved plot and 1754 seeds/m² from 53 species in the cleared plot. The soil seed bank was from mostly low density species with some high density species, and contained many pioneer species that were absent in the floor vegetation. Buried viable seeds were clumped together, especially in gravity-dispersal species. Although plenty of buried viable seeds were pooled in the soil, few seedlings emerged on the forest floor. In contrast, a number of seedlings, including many pioneer species, emerged in the cleared plots, showing a positive correlation between seed weight and germination rate. It is assumed that dominance of the seedlings established after clear-cutting depends on germination rates and/or growth rates of the seedlings rather than the initial density of buried viable seeds. These results suggest strong contribution of the soil seed bank to the establishment of the secondary vegetation after disturbance in a mature conifer plantation.     

Sediment mixing and accumulation in a mangrove ecosystem: evidence from 210Pb, 234Th and 7Be

210Pb, 234Th and 7Be activities were measured to establish sediment accumulation rates, estimate sediment mixing rates, and determine the depth of the sediment mixed layer in the Sepetiba Bay mangrove ecosystem near Rio de Janeiro City, Brazil. Three sediment cores were collected from Enseada das Garças, a typical exposed tidal flat region with a sequence of sedimentary features. The seaward edge of this sequence is a mud flat with the landward portion covered with Spartina alterniflora followed by mangrove vegetation. An additional core was collected on an overwash island near Barra de Guaratiba, which is cover with mangroves without a mud flat or Spartina alterniflora sequence. Sediment accumulation rates were determined to range up to 1.8cm/yr with the Spartina alterniflora having the maximum rate. Mixing rates were estimated for the Spartina alternifloracore at 40cm2/yr based on 210Pb and 7Be from the upper mixed region of the core. The 234Th activity in this core suggested that either mixing or the input of 234Th were not in steady state. The sediment mixed region depth ranged from 4cm to greater than 30cm. At the Enseada das Garças site the mixing depth decreased in the landward direction (i.e. mud flats > 30cm, Spartina alterniflora 11cm, mangroves 4cm). Along with this decrease in sediment mixing depth was a shift from physical to biological mixing. The Barra de Guaratiba core had a sediment mixed layer of 13cm as a result of physical and intense biological activity.     

毛乌素盐渍化沙地不同亚环境土壤差异性浅析

以毛乌素盐渍化沙地典型的裸沙丘、放牧草地和人工灌木林地下的土壤为研究对象,通过野外实地观测、采样和室内实验,对土壤含水率、全盐量、pH值、有机质、土壤容重进行测定分析。结果表明：人工植被样地的土壤容重、土壤盐分、土壤pH值明显低于坡后丘间草地、坡前丘间地、迎风坡坡中、迎风坡坡底、迎风坡坡顶、沙脊线处。植被恢复对降低土壤盐分、土壤容重和土壤pH值有一定积极作用。同时发现人工植被样地对提高土壤有机质也有一定的影响作用,人工植被样地土壤有机质含量达到0.60%,而坡前丘间地仅为0.27%。     

临泽县不同土壤类型肥力分析

对临泽县主要土壤类型的有机质，全氮，全磷，速效钾，速效磷，全盐量，ph值进行了化验分析。分析结果表明不同类型的土壤肥力差异较明显，沼泽泥炭土，灌耕厚立土的养分含量最高，灌耕厚平土次之，流动风沙土最差。全县土壤肥力属偏下水平，土壤均呈偏碱性，速效钾含量较高，在农业生产中应施磷肥，不施或少施钾肥。     

From forest to agroforest and logger to agroforester: a case study

This paper examines interactive change and adaptation of human and natural systems in two pioneer forest settlements in the Philippines. The forest ecosystem was converted by logging, further resource extraction by settlers, and cultivation — factors usually associated with systems degradation. Natural succession, however, was rapid because of high rainfall and abundant forest seed stocks; and because of high rainfall, weeds, insect pests, and poor soil — annual cereal and cash cropping was not profitable or sustainable and farmers turned to root and mixed perennial cropping. This naturally developing, more sustainable agroforestry was initially financed by boom-and-bust incomes from small scale logging and charcoal making, and took place in spite of the settlers' formation of factions and an us before them attitude towards resource use.     

Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest,northern Ethiopia

Arbuscular mycorrhiza fungi(AMF) are vital in the regeneration of vegetation in disturbed ecosystems due to their numerous ecological advantages and therefore are good indicators of soil and ecosystem health at large. This study was aimed at determining how the seasonal, vegetation cover density, edaphic and anthropogenic factors affect AMF root colonization(RC) and spore density(SD)in Desa'a dry Afromontane forest. AMF RC and SD in the rhizosphere of five dominant woody species, Juniperus procera, Olea europaea, Maytenus arbutifolia, Carissa spinarum and Dodonaea angustifolia growing in Desa'a forest were studied during the rainy and the dry seasons in three permanent study vegetation cover density plots(dense, medium, and poor). Each plot(160 x40 m~2) has two management practices(fenced and unfenced plots) of area. A 100 g sample of rhizosphere soil from moisturefree composite soil was used to determine spore density.Spore density ranged from 50 to 4467 spores/100 g soil,and all species were colonized by AMF within a range of 4–95%. Glomus was the dominant genus in the rhizosphere of all species. Vegetation cover density strongly affected SD and RC. The SD was significantly higher(p 0.05) in the poor vegetation cover density than in the other two and lowest in the dense cover; root colonization showed the reverse trend. Management practices significantly(p 0.05) influenced AMF SD and RC, with the fenced plots being more favoured. Seasons significantly(p 0.05) affected RC and SD. More RC and SD were observed in the wet period than the dry period. Correlating AMF SD and RC with soil physical and chemical properties showed no significant difference(p 0.05) except for total nitrogen. Disturbance, vegetation cover density, season and total nitrogen are significant factors that control the dynamics and management interventions to maintain the forest health of dry Afromontane forests.     

Plant growth,biomass production and soil water dynamics in a shifting dune of Indian desert

A study was carried out to find suitable species and its combined surface vegetation with the aim of fast stabilization of dune and production of fuel and fodder from this highly stressed site. Seedlings of Acacia tortilis, Prosopis juliflora and Calligonum polygonoides species were planted on shifting dune and micro-windbreaks were erected to protect the seedlings from the drifting sand. Cassia angustifolia and Cenchrus ciliaris were sown as treatment (vegetation type) to develop undercanopy vegetation. Vegetation types had no significant (P>0.05) effect on the growth of the species. However, growth of species differed significantly (P<0.001) and P. juliflora was the best performer to cover soil in a best way. C. polygonoides produced the highest biomass in the form of fuelwood utilizing minimum amount of soil water. There was an increase in SOM and soil available NH₄-N due to plantation and vegetation type treatments. C. polygonoides with C. ciliaris was the best combination for fuel and fodder production, whereas combination with C. angustifolia was the best to control sand drift. Sowing of undershrubs and grass of local importance can also be done in advance to control the sand drift and burial of the planted seedlings. It will help in the improvement of soil conditions and control the sand drift when the seedlings attain greater height leaving bare the undercanopy soil.     

浅谈宾川县生态环境状况及建设措施

宾川县生态环境状况恶化的趋势未被遏制住，主要表现在：旱涝灾害趋于频繁，水土流失严重，泥石流成灾，泥沙淤塞河床和库塘。主要原因是受干热河谷气修、地形地质及土壤、植被和人为因素的影响。根据国家生态环境建设的要求及宾川县的实际，采取生物措施，水土保持工程措施和农艺措施相结合的治理方法。     

The productivity of salt marsh vegetation at Tollesbury,Essex, and Stiffkey,Norfolk, England

This study presents data on the biomass and net aerial primaryproductivity (NAPP) of two contrasting East Anglian salt marshes.One site was at Tollesbury, Essex where the marshes are of theestuarine type and are subject to marsh degradation and erosionwhile the other site was 130 km to the north at Stiffkey, Norfolkwhere the barrier-type marshes are still actively developing withno signs of erosion. The NAPP was determined by the method ofSmalley with quadrats being harvested monthly with replacement.At the lowest levels at Tollesbury there was Pioneer Marshwhich was dominated by a mixture of Salicornia spp. and Astertripolium. At higher levels at Tollesbury there was LowerMarsh which was dominated by a mixture of Atriplex portulacoides andPuccinellia maritima. Over the four years of the studyPuccinellia became the dominant species following a markeddecrease in the extent and vigour of Atriplex. At Stiffkey theMiddle Marsh was at a much higher level and the vegetation waspredominantly a short dense sward with Atriplex portulacoides,Puccinellia maritima and Limonium vulgare together with smallerquantities of Armeria maritima and Plantago maritima. The meanNAPPs over three years of the Pioneer and Lower Marsh atTollesbury (467 & 519 g m^-2 yr^-1respectively) were similar butin 1993 the NAPPs recorded at Tollesbury were higher than thoserecorded at Stiffkey (625 & 583 compared with 458 g m^-2yr^-1).Smalleys method is difficult to apply to communities wherespecies dominance is variable, especially when dominance isshared between species with markedly different growth patterns.The results for NAPP obtained from the salt marshes at Tollesburyand Stiffkey are discussed in relation to results obtained byother workers from comparable areas in England and theNetherlands. Attention is also drawn to the possibly largerbelow-ground component of production that is frequentlyoverlooked. The importance of salt marshes in relation to othercoastal communities lies in the export of a proportion of theorganic matter produced and this mainly depends on theabove-ground production.     

First report of identification and molecular characterization of <Emphasis Type="Italic">Tuber aestivum</Emphasis> in Iran

During June 2013 to March 2014, several visits were made to the truffle-bearing areas of Kermanshah province, Iran. In this study, two specimens associated with roots of oak (Quercus brantii Lindl.) were identified as Tuber aestivum Vittad based on morphological and cytological characteristics. Internal transcribed spacer (ITS) region was amplified by PCR using primer pair ITS1/ITS4 and the sequences were analyzed. Phylogenetic trees constructed based on ITS sequences revealed that all Iranian specimens were in the same branch in a clade with T. aestivum reported from others. All T. aestivum sequences, including Iranian specimen, showed an average of 97 % similarity (ranged from 96 to 100 %). The results of physico-chemical analyses on soil samples collected from oak forest indicated that T. aestivum was prevalent in the sandy soil with rather low phosphorus concentration, low in organic matter, and high CaCo₃. To our knowledge, this is the first report of T. aestivum and its host plant from Iran.     

Influence of several tree traits on rainfall partitioning in temperate and boreal forests: a review

? In forests, rainfall is partitioned into intercepted water (IW), throughfall (TF) and stemflow (SF). We reviewed the majority of published works comparing water flows among tree species in temperate and boreal forests to test the effect of several tree traits on water flows.

? We hypothesized that water flows differed between evergreen and deciduous species, and according to successional status and bark roughness. We also investigated that water flows would be explained by stand variables such as basal area.

? Linear mixed models fitted on reviewed data showed that evergreens had a lower TF than deciduous trees (decrease of 13.9% of total precipitation year-round and 8.4% over the growing period). Similar results were found for conifers compared to broadleaves. TF also declined with the successional status from pioneer to late-successional tree species. SF decreased with bark roughness from smoother to rougher bark. Evergreens had water flows that were dependent on age of the stand, especially for TF which increased by 15.6% of total precipitation from young to adult forests.

? The large scale of TF differences between tree genera together with specific transpiration amounts and rooting features highlighted in other studies should result in significant differences in soil water content among tree species. This may have consequences on stand fitness and growth, and understory vegetation.