Species diversity and habitat fragmentation: frogs in a tropical montane landscape in Mexico

We evaluate the alpha (within patch species richness), beta (spatial turnover among patches) and gamma (landscape) diversity of frogs in a tropical montane cloud forest (TMCF) in central Veracruz, Mexico in order to assess (1) the influence of forest fragmentation on frog assemblages, (2) the importance to diversity of the various elements of the landscape matrix, including the shaded coffee plantations and cattle pastures that surround TMCF and (3) to identify the frog guilds most affected by habitat transformation. We sampled ten sites between May 1998 and November 2000: five TMCF fragments and five anthropogenic habitats. For the entire landscape, we registered 21 species belonging to six families. 100% of these were found in the TMCF fragments and 62% in the surrounding mosaic of anthropogenic habitats. Gamma diversity (γ) is determined to a greater extent by species exchange (β) than by local species richness (α). Elevational variation, the degree of conservation of the vegetation canopy and fragment size appear to determine the species diversity of this landscape. Large species, terrestrial species, those whose eggs develop outside water, and those whose larvae develop in the water seemed to be most affected by habitat transformation. On its own, even the largest and most species-rich cloud forest fragment is not capable of preserving the current anuran diversity. Neither are the shaded coffee plantations that are interspersed among and link the patches of TMCF. However together they form a diverse system of habitats crucial to species conservation in this landscape.     

Patterns of species diversity in rural herbaceous communities under different management regimes, Chiba, central Japan

The patterns of plant species diversity in herbaceous vegetation subjected to various human activities were studied in most of the landscape elements in a rural area of Chiba, central Japan. Twenty-eight transects were sampled in four types of human management-regime (cultivation, trampling, mowing, and abandonment) and were grouped into seven vegetation types using TWINSPAN and DCA analyses. The DCA axis 1 arranged all the transects into a successional order along which biomass and the degree of succession increased. Accumulated number of species increased in a stepwise pattern along the DCA axis 1, in which the dominant plant life-forms were replaced from annuals, to perennials and perennials/tree-saplings depending on different management regimes. The unique species which were confined to a certain management regime, were identified in each site. It is suggested that the coexistence of various successional communities under different human management regimes enhance regional species diversity through maintaining these unique species. Among four types of management regime, mowing sites (especially traditional verge meadows) had most abundant unique, rare species specially adapted to regular cutting. It is suggested that maintaining such traditional mown sites is important to conserve the unique biodiversity of the studied area.     

The role of forest structure, fragment size and corridors in maintaining small mammal abundance and diversity in an Atlantic forest landscape

Using the abundance and distribution of small mammals at 26 sites in an Atlantic forest landscape, we investigated how species abundance and alpha and beta diversity are affected by fragment size and the presence of corridors. To account for the variability in forest structure among fragments, we described and minimized the influence of foliage density and stratification on small mammal data. Sites were distributed among three categories of fragment size and in continuous forest. For small and medium-sized categories, we considered isolated fragments and fragments connected by corridors to larger remnants. Small mammal abundance and alpha and beta diversity were regressed against site scores from the first axis of a Principal Component Analysis on forest structure variables. Residuals were used in analyses of variance to compare fragment size and connectivity categories. Forest structure influenced total abundance and abundance of some species individually, but not the diversity of small mammal communities. Total abundance and alpha diversity were lower in small and medium-sized fragments than in large fragments and continuous forest, and in isolated compared to connected fragments. Three species were less common, but none was more abundant in smaller fragments. At least one species was more abundant in connected compared to isolated fragments. Beta diversity showed an opposite relationship to fragment size and corridors, increasing in small and isolated fragments. Results highlight the importance of secondary forest for the conservation of tropical fauna, the hyper-dynamism of small isolated fragments and the potential of corridors to buffer habitat fragmentation effects in tropical landscapes.     

Grazing promotes dung beetle diversity in the xeric landscape of a Mexican Biosphere Reserve

We analyze the impact of grazing on dung beetle diversity at the Barranca de Metztitlán Biosphere Reserve, a xeric ecosystem in central Mexico with a long history of use by humans. We compared the community structure, as well as the alpha and beta diversity between two cover conditions (open and closed vegetation) that represent the impact of grazing within a habitat, and between habitat types (submountainous and crassicaule scrublands). From 576 samples we collected 75,605 dung beetles belonging to 20 taxa. While mean species richness and diversity were different between habitat types, cumulative species richness was not. The effects of grazing on vegetation structure influenced the cumulative species richness and diversity of dung beetles in the submountainous scrubland, where grazing has created land mosaics of a grassland matrix with scrubland patches. This was not the case in the crassicaule scrubland where the impact of grazing is not as evident. Beta diversity significantly responds to the effects of grazing on habitat conditions. We discuss the ecological factors that may promote these responses by landscape diversity components. We also identify the species that could act as useful indicators to monitor the effect of land management on biodiversity. Our results indicate cattle farming maintains a diversified land mosaic, and these areas support more diverse dung beetle ensembles than homogeneous areas of closed, shrubby vegetation cover. Thus, controlled grazing activity could certainly favour the conservation of dung beetle biodiversity and improve ecosystem functioning by maintaining dung decomposition rates.     

Acacia, cattle and migratory birds in southeastern Mexico

Acacia pennatula groves in mid-elevation valleys of southern Mexico supported both the highest density and diversity of migratory birds compared to other habitats in the region. In addition, we found the highest numbers for over half of the common migratory species. Despite the high degree of leaf loss during the late winter, acacia groves do not experience greater declines in insectivorous migratory bird populations than other local habitats. Color-marked individuals of canopy species had a strong tendency to remain resident within a single acacia grove throughout the winter. Management of native acacias on subtropical rangelands for wood products, fodder, and soil improvement would probably directly and indirectly benefit migratory song bird populations. Neotropical acacia woodland is primarily associated with grazing land for livestock which might discourage some from considering acacia management a viable option for migratory bird conservation. However, acacias were probably widespread in recent geologic time under drier conditions with heavy browsing and seed dispersal by a now extinct megafauna. Two observations suggest a foraging advantage for acacia use: the higher density of migratory birds in acacia is a result of higher numbers of canopy insectivores; and acacias are selected by migrants when they occur in mixed habitat. We hypothesize that plant investment in mechanical defenses (thorns) reduces energy available for chemical defenses effective against insect herbivores.     

Physical, chemical and phosphatase activities characteristics in soil-feeding termite nests and tropical rainforest soils

Little is known about the relationship between soil biological function and the physical and chemical characteristics of soil-feeding termite nests in the Lopé tropical rainforest (Gabon). We compared nine soil-feeding termite nests of Cubitermes of different ages (fresh to mature to old) and six surrounding soils that originated from three forests differing with respect to age and vegetative cover according to 14 physical and chemical variables and acid (pH 4) and alkaline (pH 9) phosphatase activities. Physical and chemical variables of the studied samples were influenced by the three factors tested: (1) forest age, (2) termite activity (nest versus soil), (3) termite nest age. Soils from the gallery forest were strongly discriminated from all the other soils studied notably due to their high organic matter contents. All mature nests showed significant increases in K, P, clay and fine silt, pH, and cationic exchange capacity compared to soils. Some nests also had increased amounts of organic matter and larger water retention capacities. Moreover, we observed that with age the termite nests possessed decreased values of these variables from fresh to mature to old. Likewise, phosphatase activities also differed according to the three factors tested. Due to its high organic matter contents, the highest phosphatase activities were noted in the gallery forest. Within each forest, phosphatase activities decreased in mature nests compared to soils and tended to be higher in fresh nests compared to mature nests. These differences might be due to an inhibition by high inorganic P contents, as mature nests were enriched in this element and to the quality of organic matter as nests are built with termite faeces. Termite activity has an important role in influencing physical and chemical variables and phosphatase activities.     

Herpetofauna diversity and microenvironment correlates across a pasture-edge-interior ecotone in tropical rainforest fragments in the Los Tuxtlas Biosphere Reserve of Veracruz, Mexico

We evaluated the relationship between amphibian and reptile diversity and microhabitat dynamics along pasture-edge-interior ecotones in a tropical rainforest in Veracruz, Mexico. To evaluate the main correlation patterns among microhabitat variables and species composition and richness, 14 ecotones were each divided into three habitats (pasture, forest edge and forest interior) with three transects per habitat, and sampled four times between June 2003 and May 2004 using equal day and night efforts. We measured 12 environmental variables describing the microclimate, vegetation structure, topography and distance to forest edge and streams.After sampling 126 transects (672 man-hours effort) we recorded 1256 amphibians belonging to 21 species (pasture: 12, edge: 14, and interior: 13 species), and 623 reptiles belonging to 33 species (pasture: 11, edge: 25, and interior: 22 species). There was a difference in species composition between pasture and both forest edge and interior habitats. A high correlation between distance to forest edge and temperature, understorey density, canopy cover, leaf litter cover, and leaf litter depth was found. There was also a strong relationship between the composition of amphibian and reptile ensembles and the measured environmental variables. The most important variables related to amphibian and reptile ensembles were canopy cover, understorey density, leaf litter cover and temperature.Based on amphibian and reptile affinity for the habitats along the ecotone, species were classified into five ensembles (generalist, pasture, forest, forest edge and forest interior species). We detected six species that could indicate good habitat quality of forest interior and their disappearance may be an indication of habitat degradation within a fragment, or that a fragment is not large enough to exclude edge effects. Different responses to spatial and environmental gradients and different degrees of tolerance to microclimatic changes indicated that each ensemble requires a different conservation strategy. We propose to maintain in the Los Tuxtlas Biosphere Reserve the forest remnants in the lowlands that have gentler slopes and a deep cover of leaf litter, a dense understorey, and high relative humidity and low temperature, to buffer the effects of edge related environmental changes and the invasion of species from the matrix.     

Natural N abundance of plants and soils under different management practices in a montane grassland

The natural ¹⁵N abundance (δ¹⁵N) of different ecosystem compartments is considered to be an integrator of nitrogen (N) cycle processes. Here we investigate the extent to which patterns of δ¹⁵N in grassland plants and soils reflect the effect of different management practices on N cycling processes and N balance. Investigations were conducted in long-term experimental plots of permanent montane meadows with treatments differing in the amount and type of applied fertilizer (0-200 kg N ha⁻¹ yr⁻¹; mineral fertilizer, cattle slurry, stable manure) and/or the cutting frequency (1-6 cuts per season). The higher δ¹⁵N values of organic fertilizers compared to mineral fertilizer were reflected by higher δ¹⁵N values in soils and harvested plant material. Furthermore, δ¹⁵N of top soils and plant material increased with the amount of applied fertilizer N. N balances were calculated from N input (fertilization, atmospheric N deposition and symbiotic N₂ fixation) and N output in harvest. ‘Excess N’—the fraction of N input not harvested—was assumed to be lost to the environment or accumulated in soil. Taking fertilizer type into account, strong positive correlations between δ¹⁵N of top soils and the N input-output balance were found. In plots receiving mineral N fertilizer this indicates that soil processes which discriminate against ¹⁵N (e.g. nitrification, denitrification, ammonia volatilization) were stimulated by the increased supply of readily available N, leading to loss of the ¹⁵N depleted compounds and subsequent ¹⁵N enrichment of the soils. By contrast, in plots with organic fertilization this correlation was partly due to accumulation of ¹⁵N-enriched fertilizer N in top soils and partly due to the occurrence of significant N losses. Cutting frequency appeared to have no direct effect on δ¹⁵N patterns. This study for the first time shows that the natural abundance of ¹⁵N of agricultural systems does not only reflect the type (organic or mineral fertilizer) or amount of annual fertilizer amendment (0-200 kg ha⁻¹ yr⁻¹) but that plant and soil δ¹⁵N is better described by N input-output balances.     

Fruit growth,carbon allocation,and related enzymes in tomato under different irrigation and potassium application regimes

Background

The increasing concentration of atmospheric CO₂ not only affects the growing environment of crops but also aggravates the global greenhouse effect and further aggravates the problem of water shortage. The combined effect of water deficit and potassium (K) application has not been widely studied.

Aims

A pot experiment was conducted to investigate the effect of deficit irrigation (DI) and K application at different growth stages on carbon allocation and enzyme activities related to sugar metabolism.

Methods

Tomatoes were transplanted and planted on April 26, 2017 and harvested on August 15, 2017. Four irrigation regimes were implemented with two water levels (full irrigation-W and DI-W/2) in different growth stages, and each water treatment was equally divided into two subgroups: with K (K1) and without K (K0). Fruits from the first to fourth trusses of the tomato plants were sampled. Tomato growth, carbon allocation, and related enzyme activities were measured.

Results

The fresh weight (FW), dry weight, and relative growth rate of dry mass were sensitive to irrigation amount under K fertilization, enhancing the promotion effect of irrigation on fruit. Meanwhile, carbon allocation was sensitive to irrigation amount under K regime. Sucrose synthase (SuSy), acid invertase (AI), and sucrose phosphate synthase (SPS) were also highly sensitive to irrigation amount under K application condition. Starch phosphorylase displayed a quadratic parabola for irrigation amount, and adenosine diphosphate glucose pyrophosphorylase (AGPase) was highly sensitive to irrigation amount without K fertilization. Carbon in the form of other carbohydrates, carbon in the form of soluble sugar (Csol), and fruit water content were the factors that had the greatest influence on the principal components. Classification by K-means algorithm and canonical correlation analysis showed that FW, fructose, sucrose, and starch could be used as significant indicators of the dry matter components of the fruit for the treatment without K. In the case of K regime, SuSy, AGPase, AI, and Csol could be used as a significant indicator of the correlation analysis of carbon metabolism activity.

Conclusions

The factors related to the improvement of fruit quality and carbon allocation by deficient irrigation and K application were explored. Water stress changed the distribution of photosynthetic carbon between starch and soluble sugar. K application further changed the balance between soluble sugars and other compounds. In particular, it significantly increased the carbon content of soluble sugars and decreased that of other compounds. AI and SuSy are key enzymes affecting carbon metabolism under water-deficient conditions.     

不同利用方式下红壤微生物生物量及代谢功能多样性的变化

研究了不同农林利用方式下红壤微生物生物量和代谢功能多样性等土壤质量指标的变化.结果表明:不同利用方式对土壤质量各指标造成了显著的影响;稻田的微生物生物量碳、氮最高,林地和草地微生物生物量次之,旱地的微生物生物量碳、氮最低(分别是稻田利用方式的4.3% 和 13.7%);稻田的微生物代谢功能多样性最高,旱地、林地和草地的细菌代谢功能多样性较低,旱地的真菌代谢功能多样性最低;微生物生物量和代谢功能多样性可以作为反映土壤质量变化的早期敏感的指标,用来衡量管理措施的改变对土壤质量造成的影响.     

Evolution under domestication of correlated characters in populations of Stenocereus stellatus (Pfeiff.) Riccob., under different forms of management in central Mexico: genetic diversity,damage, and defense mechanisms

Genetic Resources and Crop Evolution - Across the process of domestication, human selection produces changes in target attributes as well as changes that are not necessarily desired by humans due...     

Traditional forest management has limited impact on plant diversity and composition in a tropical seasonal rainforest in SW China

In order to determine the impacts of different traditional forest management types on plant diversity of the seasonal tropical rainforests and infer effective conservation strategies, four types of forests with different management histories were studied in Nabanhe National Nature Reserve (NNNR), Xishuangbanna, China. They were: old-growth forest (non-timber product collection allowed), understorey planted old-growth forests, old secondary forests (∼200-years after slash and burn), and young secondary forest (15–50-years after slash and burn). Although human activities affected tree diversity and composition of the forests in NNNR, the forest regeneration potential of the different management systems were good. Even the young secondary forests, that showed the lowest Fisher’s alpha diversity at the plot level, had similar diversity levels to old-growth forest when all plots were combined. Number of red list tree species, timber species, and edible plant species in young secondary forests was as high as those of old-growth forests, and higher than old secondary forests. Additionally, there were a number of vulnerable and endangered species that were more common in the secondary than old-growth forests, indicating the high conservation value of secondary forests. Understorey plantation in old-growth forest, however, impaired regeneration of the climax species. The beneficial effects of traditional forest use depend strongly on its small scale and its close proximity to undisturbed forest, which serves as a species source during secondary forest regeneration. Unfortunately, traditional forest use is now under serious threat by expanding large-scale monoculture rubber plantations.     

Changes in natural 15N abundance in paddy soils under different,long-term soil management regimes in the Tohoku region of Japan

Abstract

Long-term temporal changes in natural ¹⁵N abundance (δ¹⁵N value) in paddy soils from long-term field experiments with livestock manure and rice straw composts, and in the composts used for the experiments, were investigated. These field experiments using livestock manure and rice straw composts had been conducted since 1973 and 1968, respectively. In both experiments, control plots to which no compost had been applied were also maintained. The δ¹⁵N values of livestock manure compost reflected the composting method. Composting period had no significant effect on the δ¹⁵N value of rice straw compost. The δ¹⁵N values increased in soils to which livestock manure compost was successively applied, and tended to decrease in soils without compost. In soils to which rice straw compost was successively applied, the δ¹⁵N values of the soils remained constant. Conversely, δ¹⁵N values in soils without rice straw compost decreased. The downward trend in δ¹⁵N values observed in soils to which compost and chemical N fertilizer were not applied could be attributed to the natural input of N, which had a lower δ¹⁵N value than the soils. Thus, the transition of the δ¹⁵N values in soils observed in long-term paddy field experiments indicated that the δ¹⁵N values of paddy soils could be affected by natural N input in addition to extraneous N that was applied in the form of chemical N fertilizers and organic materials.     

Genetic diversity within and among landraces of pearl millet (Pennisetum glaucum) under farmer management in West Africa

The influence of farmer management on pearl millet landrace diversity was determined by evaluating variation in individual farmers' populations from two villages in north-eastern Nigeria. The variability within and between landrace samples was estimated using variation at 163 amplified fragment length polymorphism marker (AFLP) loci. The data indicated that individual farmers' husbandry practices result in the isolation of their own group of ideotypes each in their own unique genetic backgrounds, thereby rendering landrace names inappropriate as indicators of a generic genetic identity. The implications of these findings for sampling strategies for genebanks and regional genetic evaluations are discussed.     

Soil microbial dynamics and genetic diversity in soil under monoculture wheat grown in different long-term management systems

Organic matter incorporation into soil can increase nutrient availability to plants but it can affect soil microbial communities. These in turn influence soil fertility and plant growth. Soil biochemical and microbiological properties are indicators of soil quality, but there is still no consensus as to how these should be used. Recent developments in molecular biology have provided new tools to obtain a view of the whole microbial community. The long-term impact of crop residue management on the microbial biomass, and on the activity and community structure of soil bacteria was evaluated in a clay soil of Southern Italy, where a monoculture of durum wheat (Triticum durum Desf.) was grown in semiarid conditions, and burning or incorporation of post harvest plant residues were typical practices. The role of N-mineral fertilization, simultaneously with the ploughing in of crop residues and during the plant growth cycle was also investigated. Total bacterial counts of viable cells, biomass C, ATP content of soil microorganisms, genetic fingerprinting of the total eubacterial community and of ammonia oxidizers were evaluated. Burning and incorporation did not affect microbial biomass C, ATP content, and total bacterial counts of viable cells although statistically relevant changes were detected among rhizosphere and bulk soil samples regardless of the crop residue management used. Molecular fingerprinting confirmed that: no significant change in the composition and diversity of total bacteria, as well as of ammonia oxidizers was induced by the crop residue managements; that soil bacteria were more sensitive to N fertilizer application during the plant growth cycle; and that rhizosphere soil samples were significantly different from those of the bulk soil. As microbiological and genetic factors related to soil fertility were not affected significantly, the long-term incorporation of crop residues, under the field conditions investigated, is a sustainable practice to manage post-harvest residues.     

Long-term monitoring of microbial biomass, N mineralisation and enzyme activities of a Chernozem under different tillage management

 We investigated the influence of tillage (conventional, minimum and reduced) on selected soil microbial properties of a fine-sandy loamy Haplic Chernozem over a period of 8 years. The microbial biomass and soil microbial processes were affected mostly by type of tillage and to a lesser extent by the date of soil sampling. Whereas xylanase activity was significantly higher in the 0 to 10-cm soil layer of the reduced and minimum tillage systems within the first year of the experiment (protease and phosphatase activities were significantly higher in the second year), significant treatment effects on microbial biomass, N mineralisation and potential nitrification were observed after a 4-year period. The slow response of substrate-induced respiration to the change in type of tillage may have been due to the differences in the biomass C turnover rates. After a 4-year period, the stratification of the soil microbial biomass within the profile of reduced and minimum tillage systems was probably responsible for the more intensive soil microbial processes near the soil surface compared with conventional tillage. In the 20 to 30-cm layer, N mineralisation, potential nitrification and xylanase activity in the conventional treatment were significantly higher than in the minimum and reduced tillage plots due to buried organic materials. Discriminant analysis underlined the similarity of the enzyme activity patterns in the top layer of the reduced and minimum tillage treatments, and in both layers of the conventional tillage system. The trend towards a significant increase in functional diversity caused by reduced tillage became obvious within the first year of the experiment, and this effect was still manifest after 8 years. All relationships suggested that there were differences in available resources (e.g. organic matter) along the sequence of different tillage systems; this was reflected in part by enhanced enzymatic and microbial activities in the soil layers. In conclusion, this study showed that soils affected by tillage may be classified on the basis of their functional diversity. Therefore, the soil microbial properties chosen for microbiological soil monitoring (microbial biomass, N mineralisation and enzyme activities involved in C, N and P cycling) provide a reliable tool with which to estimate early changes in the dynamics and distribution of soil microbial processes within soil profiles. Received: 3 February 1998     

Fungal diversity in agricultural soil under different farming management systems,with special reference to biocontrol strains of Trichoderma spp.

Fungal communities and their dynamics were investigated in relation to season, soil type and farming management practice. The research was done using soils from high- (H) and low-yield areas (L) of a field site cultivated with winter wheat under two different farming management systems (precision farming, P; conventional farming, C) over the vegetation period. Fungal diversity was analysed by cultivation-independent methods [direct extraction of DNA from soil followed by PCR amplification of a subunit of the 18S rDNA and fingerprinting (DGGE)] as well as cultivation-dependent techniques (isolation of pure cultures). The comparisons of the PCR amplicons by DGGE patterns showed no differences between the different sampling sites and no influence of the farming management systems. Only small differences were observed over the vegetation period. For cultivation purposes active hyphae were isolated using a soil-washing technique. The resulting isolates were subcultured and grouped by their morphology and genotype. In contrast to the cultivation independent approaches, clear site-specific and seasonal effects on the fungal community structure could be observed. However, minor effects of the different farming management techniques applied were visible for active populations. These results clearly indicate that the potential fungal community (including spores), investigated by the cultivation-independent approach, is almost entirely uninfluenced by the investigated factors, whereas active populations show a clear response to environmental changes. The most abundant group consisting of Trichoderma species was investigated in more detail using strain-specific genotype based fingerprinting techniques as well as a screening for potential biocontrol activity against the wheat pathogen Fusarium graminearum. The genotypic distribution as well as the potential biocontrol activity revealed clear site-specific patterns.     

Establishment of protected areas in different ecoregions, ecosystems, and diversity hotspots under successive political systems

Protected areas are valuable tools for nature conservation but the effectiveness of reserve networks must be monitored continuously. Knowing the history of the establishment of protected areas can help to improve future conservation. We explore how different ecoregions, ecosystems and diversity hotspots have been incorporated in protected areas in Estonia during the last century. We found that the average rate of establishment of protected areas has been surprisingly constant despite profound changes in political systems. However, establishment of protected areas has varied regionally; an agricultural region in south-east Estonia has seen less protection, partly due to lower biodiversity. Wetland ecosystems were initially more placed under protection, whereas recently semi-natural grasslands have gained more attention. In contrast, farmland is under-protected. Surprisingly, biodiversity hotspots were no more protected than the national average. We consider how the development of a protected area network has been influenced by individual persons and public opinion under successive political systems. We suggest that simultaneous gap analysis of ecoregions, ecosystems and diversity hotspots provides a more complete picture than examining a single aspect. Therefore this study can be used as a model for other regions.