Islands Of Fertility Research Articles

Intensity of ecohydrological interactions in reclaimed Mediterranean slopes: effects of run‐off redistribution on plant performance

ABSTRACTWe have conducted a field experiment to ascertain the role of ecohydrological interactions between run‐off source areas and sink patches in the dynamics of artificial slopes derived from open cast coal mining in central‐eastern Spain. We analysed the effects of run‐off interruption on soil moisture, on the leaf water potential of woody species and on the herbaceous biomass in vegetation patches of three reclaimed slopes subjected to a different disturbance degree resulting from different overland flow volumes running down the slopes. Soil moisture and plant performance were seriously affected by run‐off exclusion, and this effect was more intense as level of disturbance increased. In fact, run‐off redistribution appeared to be determinant for plant performance in the more disturbed slope, whereas the presence of the shrub Genista scorpius appeared to be more determinant for plants in the less disturbed slope. Our results confirm the validity of the Trigger–Transfer–Reserve–Pulse model in artificial slopes during the aggradation process. These results point out the importance of run‐off redistribution between vegetation patches in the evolution of artificial slopes by creating fertility islands that improve the performance of vegetation. Restoration practices in drylands may thus significantly improve if a ‘run‐off expert management’ strategy is adopted. Copyright © 2012 John Wiley & Sons, Ltd.

Hard evidence that heuweltjie earth mounds are relictual features produced by differential erosion

Regularly spaced (over-dispersed, i.e. non-random spacing) non-anthropogenic earth mounds are a surprisingly common occurrence around the world. Their genesis is generally thought to be the consequence of faunal (e.g. fossorial rodents and termites) activities that result in soil translocation towards the mounds. Large (>20m diameter) earth mounds in South Africa, called heuweltjies, are commonly attributed to the activities of the termite Microhodotermes viator. In contrast, it was hypothesised that heuweltjies are the remains of an ancient land surface in which the mound soil volume was protected from erosion by roots of regularly spaced patches of woody shrubs. The heuweltjie soil volumes are at least an order of magnitude larger than the largest verifiable termite nests of the Southern African sub-continent. Large (>2kg) rocks, that could not have been transported onto the mounds by termites or relatively small rodents, are a common feature both on the surface and distributed through the soil volume of the heuweltjies. Furthermore, the mounds sometimes occur on bedrock, conflicting with the notion that termites displaced soil upwards through the soil profile. Soil particle size analysis indicated no strong changes in sand, silt and clay through the profile of the heuweltjie and soil clay was similar between the heuweltjie and surrounding soils. The mounds also showed evidence of down-slope slumping caused by erosion.In areas where water is a constraining resource, vegetation often exhibits striking patterning. Spatial analysis of patches of woody vegetation (‘bush-clumps’) in the region and further afield demonstrated similar densities, sizes and non-random over dispersions as for heuweltjies. It is suggested here that the heuweltjies originated as bush-clumps that protected soil from erosion and resulted in the formation of hardpans (calcrete) due to increased evapotranspiration and reduced leaching of mound soil. During their development these relictual features of the landscape were likely to become ‘islands of fertility’ and, consequently, hotspots for vegetation and secondary faunal activity.

Rhombomys opimus contribution to the “fertile island” effect of tamarisk mounds in Junggar Basin

AbstractFertile islands are created and maintained by a combination of physical and biologically mediated processes. Plants have been shown to be very important in the formation of fertile islands, and recent research indicates that the activities of burrowing animals have a significant influence on the physiochemical properties of soil that can promote the development of fertile islands. In this paper, we chose tamarisk (Tamarix spp.)—a constructive species that grows in the oasis‐desert ecotone, and the great gerbil (Rhombomys opimus)—a widely distributed rodent in Central Asia to study the influence of great gerbils on soil nutrient dynamics in tamarisk mounds. Results indicate that fertile islands exist in tamarisk mounds without burrows of the great gerbil. However, the great gerbil's burrowing activities promote the fertile island effect in tamarisk mounds: soil nutrients under shrubs with great gerbil activity were significantly higher than inter‐mound areas in both surface soil and deep soil from 15 to 50 cm. Available nitrogen in mounds with rodent burrows was over twice as high as in tamarisk mounds without burrows at the same depth. The great gerbil's burrowing activities promote the concentration of soil nutrients in the tamarisk mounds.

Sediment capture by vegetation patches: Implications for desertification and increased resource redistribution

Desertification impacts a large proportion of drylands and can be driven by a variety of climate and land use factors. Most conceptual models of desertification include the underlying assumption that when herbaceous cover is reduced, increased erosion from bare patches is redistributed to shrub canopy patches, resulting in self‐reinforcing “islands of fertility.” Notably, however, this underlying assumption has not been explicitly tested with direct field measurements. Here we provide direct measurements of horizontal sediment flux moving into and out of bare‐, herbaceous‐, and shrub‐dominated patch types in a semiarid ecosystem for both simulated and natural dust events, as well as in response to simulated disturbance. Horizontal sediment flux out of the bare patches was ∼20% greater than the herbaceous patches and ∼50% greater than sediment flux out of the shrub‐dominated patches. Differences among vegetation patch types indicate that shrub patches capture more sediment than herbaceous patches and, importantly, that bare patches serve as amplified sediment sources following disturbance. Our results provide explicit support for the pervasive but untested desertification redistribution assumption, highlighting that loss of grass cover is a compounding problem that not only increases dust emissions but also precludes capture, and may have global relevance for coupled human‐environmental systems at risk due to current or potential desertification.

Effect of land management and Prosopis juliflora (Sw.) DC trees on soil microbial community and enzymatic activities in intensive silvopastoral systems of Colombia

Livestock production in Latin America has replaced tropical dry forests with conventional monocultures pastures (CP) that have degraded soils. As an alternative to CP, intensive silvopastoral systems (ISS) have been developed with multi-canopied vegetation that mimics native forest (F). The litter inputs and year-round presence of the tree rhizosphere in ISS, contribute to the formation of “fertile islands,” which is expected to impact biological activity and crop productivity. This study, investigated the impact of the conversion of CP to ISS, as well as the effect of canopy of Prosopis juliflora trees in a chronosequence of ISS (3–15years) on soil microbial communities and the physicochemical properties of soil. FAME (fatty acid methyl ester) profiles indicated that soil microbial community structure and composition shifted depending on land management systems. CP promoted the dominance of G− bacteria, while ISS chronosequence and F favored actinomycetes and fungal biomass (total and arbuscular mycorrhizal fungi). In addition, soil microbial community (FAME profiles) of ISS chronosequence and F were more similar than with CP. An increase in the Cy/pre FAME ratio in CP suggested that the microbial community was under higher stress. The advantage of including trees in pasture systems was reinforced by the observation that FAME biomarkers, enzymatic activities and nutrient status were significantly higher beneath the canopy of P. juliflora. The results indicate that ISS are viable alternatives for improving soil quality and metabolic function, which is reflected in the significant increase in microbial biomass, FAME biomarkers and enzyme activities compared with CP.

Shrub encroachment alters sensitivity of soil respiration to temperature and moisture

A greater abundance of shrubs in semiarid grasslands affects the spatial patterns of soil temperature, moisture, and litter, resulting in fertile islands with potentially enhanced soil metabolic activity. The goal of this study was to quantify the microsite specificity of soil respiration in a semiarid riparian ecosystem experiencing shrub encroachment. We quantified the response of soil respiration to different microsite conditions created by big mesquite shrubs (near the trunk and the canopy edge), medium‐sized mesquite, sacaton bunchgrasses, and open spaces. We hypothesized that soil respiration would be more temperature sensitive and less moisture sensitive and have a greater magnitude in shrub microsites compared with grass and open microsites. Field and incubation soil respiration data were simultaneously analyzed in a Bayesian framework to quantify the microsite‐specific temperature and moisture sensitivities and magnitude of respiration. The analysis showed that shrub expansion increases the heterogeneity of respiration. Respiration has greater temperature sensitivity near the shrub canopy edge, and respiration rates are higher overall under big mesquite compared with those of the other microsites. Respiration in the microsites beneath medium‐sized mesquites does not behave like a downscaled version of big mesquite microsites. The grass microsites show more similarity to big mesquite microsites than medium‐sized shrubs. This study shows there can be a great deal of fine‐scale spatial heterogeneity that accompanies shifts in vegetation structure. Such complexity presents a challenge in scaling soil respiration fluxes to the landscape for systems experiencing shrub encroachment, but quantifying this complexity is significantly important in determining overall ecosystem metabolic behavior.

树干径流对梭梭"肥岛"和"盐岛"效应的作用机制

Spatial heterogeneity is considered to be a ubiquitous feature in natural ecosystems.A typical example of spatial heterogeneity in desert ecosystems is islands.Fertile islands are formed around small shrubs and are important local and regional nutrient reserves that influence community structure and ecosystem function.They alter soil water and nutrient contents which are the primary limiting factors for vegetation structure and production in arid ecosystems.These fertile islands are formed where nutrients accumulate under the shrub canopy.In addition,soil pH and salinity have also been shown to have significant differences between shrub canopies and interspaces.The development of fertile islands is related to a number of factors but in arid land,the stemflow of shrubs could be a significant contributor in their development as well as playing a major role in salinity redistribution.In this study,the distribution patterns of soil salinity and nutrients around individual shrubs and the major influencing factors was investigated using Haloxylon ammodendron Bge.shrubs.The heterogeneity of soil pH,electrical conductivity(EC),soil organic carbon(SOC),total nitrogen(TN),and available phosphorus(AP) was investigated.Soil samples were collected in circles of 2 cm,10 cm,20 cm,30 cm,40 cm and 50 cm radius around the taproot,with eight sampling points in each layer(48 points in total).Results demonstrated that significantly enriched SOC,TN and AP content at the shrub center,which extended to 20—40 cm from the taproot.Conversely,soil pH and EC were significantly lower at 0—25 cm from the taproot,indicating that the fertile island is also an area of low alkalinity/salinity.Water has been regarded as the focus of soil nutrient reduction and redistribution in arid and semiarid regions.Stemflow is considered to be a major source of soil moisture in desert ecosystems,and also a significant influence on runoff generation,soil erosion,groundwater recharge,spatial patterning of soil resources and the distribution of understory vegetation and epiphytes.Therefore,the chemical properties of the shrub stemflow and bulk precipitation were also evaluated in this study to determine the contribution of stemflow to the formation of fertile islands and the distribution of soil salinity.The results revealed the stemflow funneling ratio of H.ammodendron was 46.4 which indicated large amounts of rainwater were accumulated through the shrub stem and consequently,moisture was higher at the shrub center.The chemical properties of stemflow were significantly higher(P0.05) than the bulk precipitation except pH and CO2-3.Compared with bulk precipitation,the accumulation ratios of PO3-4,NO-3,NH+4,K +,Na+,Ca2+,Mg2+,HCO-3,Cl-and SO2-4 in stemflow were from 3.30 to 34.87.This indicates the much higher nutrient and salinity content in stemflow compared with bulk precipitation.There was no difference in pH between bulk precipitation and stemflow.These results demonstrated the fertile island effect of higher nutrients and lower salinity around the taproot likely formed by stemflow.It also demonstrated that stemflow will input nutrients and remove salinity from the soil with increased water infiltration.

Fine-Scale Spatial Heterogeneity of Resource Modulation in Semi-Arid “Islands of Fertility”

In arid ecosystems, shrub patches are regarded as “islands of fertility,” enriched in resources that facilitate growth of herbaceous vegetation. It is often assumed that the modulation of resources and the effect that it has on herbaceous vegetation are homogeneous within each shrub patch. We examined the modulated resources in terms of their fine-scale spatial extent, level, and response to anthropogenic disturbances, that is, canopy removal and grazing. We defined three patch types—core of shrub patch, periphery of shrub patch, and intershrub patch—and recorded their levels of soil nutrients (organic matter, potassium, phosphorus, nitrate, and ammonium) and temperature regimes, with and without canopy removal, and/or grazing. Overall, our study found higher soil-nutrient contents and lower maximum temperatures at the core of the shrub patch than in the intershrub matrix. However, we also found that resource modulation was not spatially homogeneous within the shrub patch: soil nutrient levels were higher in the core than at the periphery. Anthropogenic disturbances did not affect soil nutrients within the 2-year time scale of our study. Our results emphasize the importance of examining the landscape at the spatial scale of the modulated resources, in order to develop patch management that increases productivity and diversity, and prevents desertification.

Diversity and Activity of Denitrifiers of Chilean Arid Soil Ecosystems

The Chilean sclerophyllous matorral is a Mediterranean semiarid ecosystem affected by erosion, with low soil fertility, and limited by nitrogen. However, limitation of resources is even more severe for desert soils such as from the Atacama Desert, one of the most extreme arid deserts on Earth. Topsoil organic matter, nitrogen and moisture content were significantly higher in the semiarid soil compared to the desert soil. Although the most significant loss of biologically preferred nitrogen from terrestrial ecosystems occurs via denitrification, virtually nothing is known on the activity and composition of denitrifier communities thriving in arid soils. In this study we explored denitrifier communities from two soils with profoundly distinct edaphic factors. While denitrification activity in the desert soil was below detection limit, the semiarid soil sustained denitrification activity. To elucidate the genetic potential of the soils to sustain denitrification processes we performed community analysis of denitrifiers based on nitrite reductase (nirK and nirS) genes as functional marker genes for this physiological group. Presence of nirK-type denitrifiers in both soils was demonstrated but failure to amplify nirS from the desert soil suggests very low abundance of nirS-type denitrifiers shedding light on the lack of denitrification activity. Phylogenetic analysis showed a very low diversity of nirK with only three distinct genotypes in the desert soil which conditions presumably exert a high selection pressure. While nirK diversity was also limited to only few, albeit distinct genotypes, the semiarid matorral soil showed a surprisingly broad genetic variability of the nirS gene. The Chilean matorral is a shrub land plant community which form vegetational patches stabilizing the soil and increasing its nitrogen and carbon content. These islands of fertility may sustain the development and activity of the overall microbial community and of denitrifiers in particular.

Two Islands, One Commodity: Cuba, Java, and the Global Sugar Trade (1790-1930)

Sugar had become, by the eighteenth century, a global commodity. Originating in East Asia, plantations in the Americas fed the growing taste for its use in Europe, with its consumption increasingly popularised. The 1791 Revolution in Saint Domingue (Haiti) and the 1807 British abolition of the slave trade prompted shifts in the epicentres of sugar, the most important of these being arguably to Cuba and Java. These two fertile islands saw the burgeoning development of sugar-plantation systems with major inputs of foreign capital and forced labour. In the process the two islands each, respectively, became central to the very much truncated Spanish and Dutch colonial empires left after the Napoleonic wars and the Latin American wars of liberation; and by the mid-nineteenth century in the case of Cuba, and by the late nineteenth century in the case of Java, they had been catapulted to global sugar pre-eminence. There has been an abundance of study on the two islands each in their own right, but none systematically examines their parallel trajectories. Yet the question arises as to how sugar came to dominate the agriculture, industry and trade of these two islands; and how these two islands in particular, in two different colonial systems and parts of the world, should rise to sugar pre-eminence in the way they did and when they did. Are there connections and similarities between the two that help explain this phenomenon? This article analyses the conditions that led Java and Cuba to become the prime cane-sugar exporters of the nineteenth and early twentieth centuries. Initiative for this came from the linkages between their dominant elites and the transnational, transimperial networks of trade and capital. This furthered the stimulation of technological and scientific innovation in both, enabled not only through the introduction of the latest advances in machinery and method, but also the immigration of technical skilled workers from Europe and North America. New sugar frontiers were opened that offered room for expansion at a time of rapidly growing demand for sugar in Europe; but for this to occur, radical changes needed to be made to the system of land ownership and use. At the same solutions were needed for how to mobilise and control sufficient labour without jeopardising the colonial order. This question eventually came to dominate the political system through which social control could be ensured – particularly, because Cuba and Java came to be ever more closely tied to global capital and trade; and both islands become dominated by sugar while at the same time coming to dominate global sugar production.

Impacts of Fire and Invasive Species on Desert Soil Ecology

A review of literature shows that both fire and invasive species may cause changes in biological, chemical, and physical properties of desert soils . Although soil may recover from the impacts of fire during succession, these changes are permanent under persistent invasive species. The most severe effects of fire occur under high temperatures with high fuel buildup and soil moisture that conducts heat downward. Deserts typically have low fuel mass and low soil moisture, both conditions that would contribute to lower impacts of fire than in mesic soils. Soil is a good insulator , so soil microorganisms will survive a few centimeters deep even in hot surface fires. Immediately postfire there is often an increase in mineral nitrogen (N) and a decrease in soil carbon (C) and organic N, but these changes are often minimal in desert soils, except under fertile shrub islands that have higher fuel loads and fire temperature. Both hot and cold deserts have experienced slow recovery of native shrubs and increased growth of invasive grasses following fire. Invasive species may either increase or decrease soil N and C depending on fire temperature and site and species characteristics. Mineralization and fixation of N are often high enough after fire that subsequent productivity balances N losses. The elimination of islands of fertility coupled with postfire erosion may be a major impact after fire in grass-invaded shrub lands. In the long term, the interaction of fire and invasive species may result in more frequent fires that eliminate fertile islands and reduce the productivity of deserts. Managers may use fire as a tool to control desert invasives without the concern that N will be irrevocably lost, but this must be done judiciously to avoid eliminating shrubs and further increasing invasive species. La revisión de literatura demuestra que tanto el fuego como las especies invasoras pueden causar cambios en las propiedades biológicas, químicas y físicas de los suelos del desierto. Mientras que el suelo puede recuperarse del impacto del fuego durante la sucesión, las especies invasoras producen cambios permanentes. Los efectos más severos del fuego ocurren bajo temperaturas altas con una alta acumulación de combustible y con una humedad del suelo que conduce el calor hacia abajo. Los desiertos tienen típicamente una humedad y masa de combustible baja, ambas condiciones podrían contribuir a un menor impacto del fuego en suelos mésicos. El suelo es un buen aislador, así que los microorganismos del suelo pueden sobrevivir a pocos cm de profundidad incluso en fuegos superficiales calientes. A menudo, inmediatamente después del fuego hay un incremento en nitrógeno mineral (N) y una disminución en el carbón del suelo (C) y N orgánico, pero estos cambios son a menudo mínimos en los suelos del desierto, con excepción de debajo de los arbustos en las islas fértiles que tienen cargas de combustibles y temperaturas más altas. Tanto los desiertos calientes como los desiertos fríos han experimentado una recuperación muy lenta de arbustos nativos y un incremento en el crecimiento de gramíneas invasivas después de los fuegos. Las especies invasivas pueden incrementar o disminuir el N y el C del suelo dependiendo de la temperatura del fuego, así como las características de las especies y del sitio. La mineralización y la fijación del N son a menudo bastante altos después del fuego que la productividad subsecuente estabiliza las pérdidas de N. La eliminación de las islas de fertilidad unida con la erosión después del fuego puede ser un impacto importante después del fuego en pastizales invadidos por arbustivas. A largo plazo la interacción del fuego y las especies invasivas puede dar lugar a fuegos más frecuentes que eliminen las islas fértiles y reduzcan la productividad de los desiertos. Los manejadores del recurso pueden utilizar fuego como una herramienta para controlar las especies invasivas del desierto sin la preocupación que la pérdida del N sea para siempre, pero esto puede hacerse cautelosamente evitando la eliminación de los arbustos y fomentando un incremento en las especies invasoras.

Dinitrogen‐fixing Acacia species from phosphorus‐impoverished soils resorb leaf phosphorus efficiently

Nitrogen (N) and phosphorus (P) resorption from senescing leaves were studied, and the contribution of N and P cycling through litterfall to soil nutrient patchiness was investigated for four Acacia species in the Great Sandy Desert in north-western Australia. N and P concentrations of mature and recently shed leaves were analysed and compared; soils under the canopies of the shrubs and soils in gaps (open areas) between the shrubs were also analysed and compared for N and P concentrations. Mature leaf P concentrations of the plants were considerably lower than the global average values, and N : P ratios of mature leaves were high. Plants derived 0-75% of their leaf N from symbiotic N(2)-fixation. N-resorption efficiency was between 0 and 43%, and P-resorption efficiency was between 32 and 79%; all plants were more efficient at P resorption than at N resorption, and litter N : P ratios were significantly higher than mature leaf N : P ratios. Soils of the study sites were P-impoverished. Total soil N and P concentrations were higher under the canopy than in gaps, but bicarbonate-extractable P concentration was higher in gaps. Nutrient cycling through litterfall results in soil nutrient patchiness and forms 'islands of fertility' under the canopies of the shrubs.

The effect of long-term exposure to elevated CO2on nitrogen gas emissions from Mojave Desert soils

[1] In arid regions, emissions of nitrogen (N) gases are important to long-term soil fertility and regional atmospheric chemistry, making alterations in N gas emissions an important aspect of ecosystem response to climate change. Studies at the Nevada Desert FACE Facility suggest that rising atmospheric CO2 concentrations impact ecosystems N dynamics in the Mojave Desert; our objective was to identify whether those responses translate into changes in trace N gas emissions. We measured soil fluxes of reactive N gases (NO, NOy, NH3) and N2O in plots receiving long-term fumigation with ambient and elevated (550 ppm) CO2. Reactive N gas emissions were significantly lower under elevated CO2 during high soil moisture conditions in the spring and fall. The strongest responses occurred in the islands of fertility created by the dominant shrub Larrea tridentata, where fluxes were 3–5 ng N m−2 s−1 lower in elevated CO2 plots. Changes in total N gas emissions were driven by reduced NO and NH3 emissions, with smaller changes in NOy efflux and little to no production of N2O. Lower N gas emissions under elevated CO2 reflect changes in plant and microbial demand for N, suggesting increased uptake or immobilization coupled with decreased rates of N mineralization and nitrification. This response of N gas efflux to elevated CO2 in the growing season suggests that in deserts, elevated CO2 promotes ecosystem retention of N during periods of peak biological demand. Concomitantly, exposure to elevated CO2 alters inputs of new reactive gases into the atmosphere, potentially impacting local atmospheric processes.

Facilitative effects of shrubs in shifting sand on soil macro-faunal community in Horqin Sand Land of Inner Mongolia, Northern China

Shrubs can create “fertile islands” with improved soil and microclimatic conditions surrounded by a low-nutrient matrix in arid and semi-arid areas. But the relationship of sandy-soil adapted shrubs ( Caragana microphylla and Salix gordejevii) with the structure of soil macro-faunal assemblages is largely unknown in Horqin Sand Land, Northern China. The environmental variables and soil macro-faunal community were investigated under shrubs and in the open spaces between shrubs in this study. Environmental parameters (soil water, temperature, pH, EC, total organic carbon and nitrogen) indicated a significant alteration of the soil environment under shrubs in comparison with that in the open spaces. Significantly larger shrub canopy size and greater height were found for S. gordejevii than for C. microphylla. The microhabitats under shrubs maintained significantly higher abundance, group richness and diversity of soil macro-faunal communities in comparison with those in the open spaces, with a higher abundance and group richness but lower diversity under the legume C. microphylla than under S. gordejevii. Further, data for the different faunal groups characterized specific responses to varying microhabitats under shrubs. Results implied that soil microhabitats under shrubs, in addition to shrub characteristics, could facilitate macro-fauna assemblages and diversity in shifting sand lands, which by feedback is beneficial for recovery, conservation and sustainable management in a sandy ecosystem.

Effect of Caragana tibetica nebkhas on sand entrapment and fertile islands in steppe–desert ecotones on the Inner Mongolia Plateau, China

Phytogenic mounds (nebkhas) formed by shrubs are a common phenomenon in arid and semi-arid areas and play important roles in preventing soil erosion and nutrient loss. One feature of nebkhas is the development of fertile islands. We investigated whether fertile islands were present inside and underneath Caragana tibetica-formed nebkhas in the northwest portion of the Ordos on the Inner Mongolia Plateau, China, and if such a fertile island effect increased with the age of the nebkhas. We also analyzed the spatial heterogeneity of the soil properties and quantified the amount of sand trapped by C. tibetica. The morphometric characteristics of C. tibetica nebkhas were investigated in a 4.5 ha area. Soil samples were collected inside, underneath and outside of the nebkhas and the soil organic matter (SOM), total phosphorus (TP), soil moisture (SM) and soil texture were determined. The SOM, TP and SM inside and underneath nebkhas at later stages of growth were higher than those at smaller, younger growth stages, which in turn were higher than those outside the nebkhhas. Inside the nebkhas at the establishment and early growth stages, SOM and TP first increased and then decreased with increasing soil depth, but SM steadily increased. The amount of sand trapped by C. tibetica per unit area was 0.0313 m3m−2. Nebkhas of C. tibetica primarily accumulated fine sand, which accounted for 74% of the soil, and is significantly higher than that outside the nebkhas. Caragana tibetica significantly increased sand entrapment, and fertile islands are formed inside and underneath C. tibetica nebkhas.

Arbuscular mycorrhizal fungi host preference and site effects in two plant species in a semiarid environment

Arid environments are characterized by a patchy distribution of resources (soil nutrients and water availability) which often accrue under or around shrubs. These so-called ‘fertile islands’ have high levels of organic matter, nutrients, and mycorrhiza inocula. Interactions between arbuscular mycorrhizal fungi (AMF) communities and plants, as well as their distribution, are poorly known in these ecosystems, although elsewhere their relevance in ecosystem function is well known. Here, we characterized the AMF community colonizing roots of two plant species, Ballota hirsuta and Lobularia maritima, growing in both patches and open areas. We found differences between AMF genetic composition of communities associated with the two plant species, suggesting specificity. The similarity of AMF colonizing roots of the same plant species was higher in open areas than in patches, while there were differences in AMF genetic richness and diversity between target species in open areas. These data provide new information on the specificity of AMF–plant interactions in patchy environments, and suggest a control of AMF on plant population and community dynamics in arid ecosystems.

Ant community structure under Retama sphaerocarpa shrubs in a semi‐arid environment

AbstractThe Tabernas Desert (Spain) is an emblematic area as it constitutes, strictly speaking, the only European desert. Under the canopy of one of the dominant shrub species, Retama sphaerocarpa, there are different microhabitat conditions that encourage the growing of a dense understory of herbs (fertile islands). However, these changes may not be enough to be also reflected in the fauna. Studying ants as bioindicators, we found higher densities of individuals and species richness below the canopy than outside it. However, while the density of individuals increased from outside the canopy to the inner position under the shrubs, species richness increased from the inner to the border position under the canopy and abruptly decreased outside it. This is because the inner positions were usually monopolized by dominant ants with populous nests that feed on aphid honeydew, such as Monomorium subopacum or Tapinoma nigerrimum. Granivorous species (genus Messor) were usually found in intermediate positions under the canopy, taking advantage of the better microclimatic conditions but close to the grass for feeding. Among the most abundant species, the only one found mainly outside the influence of the retama shrubs was the thermophilic insectivorous Cataglyphis ibericus.

Can biosolids compost improve, in the short term, native vegetation and soils fertility in burned Nothofagus pumilio forest in Patagonia, Argentina?

In the Patagonian Andean forests, wildfires principally have an anthropic origin and constitute one of the most important disturbances. They lead to severe losses of soil fertility and vegetation; particularly compromising the regeneration of native vegetation. Organic amendments can facilitate the regeneration of vegetation, enhancing principally soil fertility conditions. Our objective was to evaluate the effects of biosolids compost application as a tool for recovering soil fertility and regenerating vegetation in burnt areas of a Nothofagus pumilio forest along two growing seasons. Considering the National Park status of the study area, low rates (2 kg m-2) of biosolids compost application were used to minimize the polluting effect of this amendment. We considered two types of microsites, with and without litter accumulation, in order to test whether biosolids application had a differential effect related to microsite type. Soil properties, composition and cover vegetation were evaluated. We concluded that biosolids compost application improved some of the physical-chemical, chemical and biological soil properties but did not contribute, over a period of almost two growing seasons, to vegetation recovery. These results confirm that organic amendment application may be used as an initial restoration strategy at microsite level in burnt N. pumilio forests related principally to a beneficial effect on soil fertility. The creation of fertility islands can be a valid restoration strategy, but mechanisms to increase the reinstallation of native vegetation should be also applied.

Spatial heterogeneity of soil chemical properties at fine scales induced by Haloxylon ammodendron (Chenopodiaceae) plants in a sandy desert

AbstractSpatial heterogeneity is considered a ubiquitous feature in natural ecosystems. Fertile islands represent a typical example for such heterogeneity in desert ecosystems. The soil pH and salinity also show significant heterogeneity in fertile islands. To investigate the distribution of soil salinity and nutrients around individual shrubs and the major factors influencing their distribution, an experiment was conducted at the scale of the rhizosphere, root system, and individual for Haloxylon ammodendron (C. A. Mey.) Bunge (Chenopodiaceae) shrub in the Gurbantünggüt Desert. Specifically, the heterogeneity of the following soil chemical parameters was evaluated: pH, electrical conductivity (EC), soil organic carbon (SOC), total nitrogen (TN), and available phosphorus (AP). The chemical properties of the shrub stemflow were also evaluated to determine its contribution to the formation of fertile islands and the distribution of soil salinity. The results revealed great variance in the soil pH and EC at the rhizosphere and root system scales, indicating that a single root or root system exerts a great effect on soil pH and salinity. At the individual scale, the content of SOC, TN, and AP was significantly enriched in the layers adhering to the taproot, and this enrichment extended 20–40 cm from the taproot. Conversely, the soil pH and EC were significantly lower from the taproot to 10–25 cm away from the root, indicating that the fertile island is also an island of low alkalinity/salinity. Comparison of the chemical properties of stemflow and bulk precipitation revealed a higher content of chemical elements (except pH and CO32−) in the stemflow, indicating that the fertile island and lower pH and EC in this island were likely formed by the effects of stemflow. Specifically, stemflow brings in water and nutrients, while reducing the salt levels. Overall, the high nutrients and low alkalinity/salinity island created around the taproot favor the growth of the plants.

Shrubs influence arbuscular mycorrhizal fungi communities in a semi-arid environment

Interactions between arbuscular mycorrhizal fungi (AMF) and plants are essential components of ecosystem functioning; however, they remain poorly known in dry ecosystems. We examined the relationship between seven shrub species and their associated AMF community in a semi-arid plant community in southern Spain. Soil characteristics and plant physiological status were measured and related to AMF community composition and genetic diversity by multivariate statistics. We found differences in AMF communities in soils under shrubs and in gaps among them, whereas no differences were detected among AMF communities colonizing roots. Soil nutrients content drove most of the spatial variations in the AMF community and genetic diversity. AMF communities were more heterogeneous in fertile islands with low nitrogen-to-phosphorus ratio and vice versa. AMF genetic diversity increased in soils limited by phosphorus and with high soil organic matter content, while AMF genetic diversity increased in roots growing in soil not limited by phosphorus. Overall, we could not find a clear link between plant performance and the associated AMF community. Our findings show that different shrub species generate islands of fertility which differ in nutrient content and, therefore, support different AMF communities, increasing AMF diversity at the landscape level.