Edaphic Changes Research Articles

Direct characterization of deep soil water depletion reveals hydraulic adjustment of apple trees to edaphic changes

Deep soil water is important for trees to survive droughts in arid and semiarid regions, but often irreversibly decrease as tree age due to limitations in soil infiltration rates and precipitation. How adaptable is the hydraulic system of trees undergoing the depletion of deep soil moisture reserves? To answer this question, we examined 12 traits characterizing the hydraulic structure of apple tree branches along a plantation age gradient (7 - 26 years) under uniform soil and climatic conditions. We found that almost all deep soil available water was consumed (reduced by up to 98%) as apple trees aged, as a result, the fraction of roots located in water deficit layers increased by up to 70%. Reduced water availability in deep soil significantly increased xylem embolism resistance (P50) by 8%, without altering xylem-specific hydraulic conductivity, vessel diameter, or vessel density. A distinct adaptive response to permanently reduced deep soil water availability seems to occur primarily by increasing tree hydraulic safety with no reductions in hydraulic efficiency, through which mechanism trees may acclimatize to deep soil water reduction.

Floristic diversity, composition and dominance across Amazonian forest types respond differently to latitude

AbstractAimThe latitudinal biodiversity gradient is considered a first‐order biogeographical pattern for most taxonomic groups. Latitudinal variation in plant diversity is not always consistent, and this could be related to the particular characteristics of different forest types. In this study, we compare latitudinal changes in floristic diversity (alpha diversity), composition (beta diversity) and dominance across different tropical forest types: floodplain, terra firme and submontane forests.LocationWestern Amazonia (Ecuador, Peru and Bolivia).TaxonWoody plants.MethodsWe inventoried 1978 species and 31,203 individuals of vascular plants with a diameter at breast height ≥ 2.5 cm in 118 0.1‐ha plots over an 1800 km latitudinal gradient in three different forest types. The relationships between alpha diversity, latitude and forest type were analysed using generalised linear mixed models. Semi‐parametric permutational multivariate analysis of variance was used to investigate the effects of latitude and forest type on beta diversity. Dominant species abundances were correlated with non‐metric multidimensional scaling ordination axes to reflect their contributions in shaping changes in beta diversity.ResultsAlpha diversity increased towards equatorial latitudes in terra firme and submontane forests but remained relatively constant in floodplains. Beta diversity of all forest types changed with latitude, although less clearly in floodplains. Also, in floodplain forests, there were fewer dominant species contributing to beta diversity and more species homogeneous along the gradient.Main ConclusionsLatitudinal diversity patterns are manifested in alpha and beta diversity since latitude summarizes climatic and edaphic changes. However, we found different responses of each forest type. In floodplain forests, inundation regime is a stronger predictor than latitude, limiting floristic diversity and composition. Changes in dominant species abundance over gradients explained species composition, but floodplain forests harboured more homogeneous dominant species than well drained forests. It is key to study environmental trends and habitat characteristics of each forest type to understand their species diversity and dominance patterns.

Response of the wheat mycobiota to flooding revealed substantial shifts towards plant pathogens.

Rainfall extremes are intensifying as a result of climate change, leading to increased flood risk. Flooding affects above- and belowground ecosystem processes, representing a substantial threat to crop productivity under climate change. Plant-associated fungi play important roles in plant performance, but their response to abnormal rain events is unresolved. Here, we established a glasshouse experiment to determine the effects of flooding stress on the spring wheat-mycobiota complex. Since plant phenology could be an important factor in the response to hydrological stress, flooding was induced only once and at different plant growth stages, such as tillering, booting and flowering. We assessed the wheat mycobiota response to flooding in three soil-plant compartments (phyllosphere, roots and rhizosphere) using metabarcoding. Key soil and plant traits were measured to correlate physiological plant and edaphic changes with shifts in mycobiota structure and functional guilds. Flooding reduced plant fitness, and caused dramatic shifts in mycobiota assembly across the entire plant. Notably, we observed a functional transition consisting of a decline in mutualist abundance and richness with a concomitant increase in plant pathogens. Indeed, fungal pathogens associated with important cereal diseases, such as Gibberella intricans, Mycosphaerella graminicola, Typhula incarnata and Olpidium brassicae significantly increased their abundance under flooding. Overall, our study demonstrate the detrimental effect of flooding on the wheat mycobiota complex, highlighting the urgent need to understand how climate change-associated abiotic stressors alter plant-microbe interactions in cereal crops.

Determining the role of richness and evenness in alpine grassland productivity across climatic and edaphic gradients.

Spatial heterogeneity of climatic and edaphic gradients can substantially affect the grassland productivity function. However, few studies have tested the importance of species richness and evenness on regulating grassland productivity across spatial-scale climatic and edaphic changes. This study examines the complex mechanisms by which species richness and evenness regulate productivity in alpine meadow and steppe. We used field survey data to explore above-ground productivity formation and sensitivity to spatial-scale climatic and edaphic response of alpine grassland based on species richness and evenness. Results showed that the growing season solar radiation was the main driving factor of above-ground biomass and was strongly negatively correlated with above-ground biomass. Furthermore, compared with alpine steppe, above-ground biomass in alpine meadow was more responsive to climatic variables, but less responsive to soil variables. Unexpectedly, we found that the regulation patterns of species richness and evenness on above-ground biomass were different in both habitats by a structural equation model analysis. Our study demonstrated that species evenness and richness were both important in co-regulating above-ground biomass in alpine meadow, whereas species richness mattered more than species evenness in regulating above-ground biomass in alpine steppe. Our results offer further support for species richness and evenness co-regulating grassland productivity across spatial-scale climatic and edaphic gradients, which helps maintain the benefits of plant diversity and alpine grassland ecosystems.

Leaf bacterial microbiota response to flooding is controlled by plant phenology in wheat (Triticum aestivum L.)

Leaf microbiota mediates foliar functional traits, influences plant fitness, and contributes to various ecosystem functions, including nutrient and water cycling. Plant phenology and harsh environmental conditions have been described as the main determinants of leaf microbiota assembly. How climate change may modulate the leaf microbiota is unresolved and thus, we have a limited understanding on how environmental stresses associated with climate change driven weather events affect composition and functions of the microbes inhabiting the phyllosphere. Thus, we conducted a pot experiment to determine the effects of flooding stress on the wheat leaf microbiota. Since plant phenology might be an important factor in the response to hydrological stress, flooding was induced at different plant growth stages (tillering, booting and flowering). Using a metabarcoding approach, we monitored the response of leaf bacteria to flooding, while key soil and plant traits were measured to correlate physiological plant and edaphic factor changes with shifts in the bacterial leaf microbiota assembly. In our study, plant growth stage represented the main driver in leaf microbiota composition, as early and late plants showed distinct bacterial communities. Overall, flooding had a differential effect on leaf microbiota dynamics depending at which developmental stage it was induced, as a more pronounced disruption in community assembly was observed in younger plants.

Elevational trends of tree fine root traits in species‐rich tropical Andean forests

With increasing elevation, trees in tropical montane forests have to invest larger fractions of their resources into their fine roots in order to compensate for increasingly unfavorable soil conditions. It is unclear how elevation and related edaphic changes influence the variability in tree fine root traits and belowground functional diversity. We measured six fine root traits related to resource acquisition on absorptive fine roots of 288 trees from 145 species along an elevational gradient from 1000 m to 3000 m a.s.l. in tropical montane forests of the Ecuadorian Andes. We analyzed trait relationships with elevation and soil nutrient availability, and tested whether root functional diversity varied along these gradients. Fine roots at higher elevations and at more nutrient‐poor sites were thicker, had higher tissue densities, and lower specific root length and nutrient concentrations than at lower elevations. These trends were diluted by the coexistence of tree species with a broad range of different root traits within communities particularly towards lower elevations, where root functional diversity was significantly higher. We conclude that nutrient limitation and potentially further adverse conditions at higher elevations are strong environmental filters that lead to trait convergence towards a conservative resource use strategy, whereas different trait syndromes are equally successful at lower elevations.

PRINCIPLES, PROBLEMS AND PROSPECTS OF IMPLEMENTATION OF ECONOMIC APPROACH TO OPTIMIZATION OF NATURE MANAGEMENT AND NATURE PROTECTION OF PODILLIA REGION

The approaches to the formation of econet relations in Ukraine in the context of the Pan-European strategy for the preservation of biotic and landscape diversity are considered. The basic contradictions in the system of econet relations are highlighted. The essence of the eco-network approach is highlighted on the basis of the materials of the national and regional econet. The polystructurality of econet is noted, their environmental, nature-supporting, and recreational subsystems are analyzed. The identification of the basic elements of the econet should take place against the background of landscape zoning schemes of the territory, so that the natural systems of each landscape region are represented by at least one key territory. Created systems of computer-cartographic models of the Podillya econet and its components; algorithms for multivariate analysis of the NRO and the design of environmental systems of the Podillia region, in which the spatial boundaries of 41 key territories are justified, which will represent the biotic and landscape diversity of 33 landscape areas, areas of connecting territories and their buffer zones. 24 key areas represent landscapes of the zone of deciduous forests; 15 - landscapes of the forest-steppe zone and 2 key territories are confined to the zone of mixed forests. The peculiarities of the eco-network include its complexity and polystructurality with basic nature conservation, nature support and recreational subsystems with a differentiated regime of nature management of the main elements.
 In accordance with the principle of landscape polystructurality, within the territory, it is possible to distinguish landscape territorial structures (LTS) of various types, depending on the structure-forming relations, taken as the basis of this integration. From an environmental point of view, the biocentric-network landscape structure forms the relationship between the areas of natural vegetation (biocenter) and their anthropogenized environment. At the same time, the territorial confinement of biocenters, their compliance with the optimal sizes, functional features, the nature and directions of interrelationships to ensure sustainable functioning were analyzed.
 A complex combination of different-ranked network elements forms spatial polyfunctional storage systems for biotic and landscape diversity. Within the framework of these systems, several types of eco-transforming nodes (EFN) are distinguished: (EFNnl) at the national level, (EFNrl) at the regional level, (EFNll) at the local level. The created schematic map of the biocentric network LTS demonstrates that its elements do not completely cover the territory of the landscape, but form the natural frame of the territory, significantly reduces the probability of population degradation, and reduces the dependence on sharp edaphic changes in individual biocenters. This framework is the basis of the environmental protection and nature-supporting system of the region.
 Key words: eco-network approach, Podillia region, regional eco-network, biocentric-network structure, environmental system.

Soil microbial community response to winter climate change is phylogenetically conserved and highly resilient in a cool-temperate forest

The soil microbial community actively drives biogeochemical cycling even in the plant-dormant season of winter in temperate forests. The northern ecosystems are experiencing considerable winter climate change, which causes the snowpack to become thinner and the soil freeze-thaw cycles to occur more frequently in winter. These climatic and edaphic changes may affect the microbial community function. This study aimed to characterize the soil microbial community's response to winter climate change and its consequences in nitrogen (N) cycling. We conducted a large-scale snow removal experiment in a cool-temperate forest in northern Japan to simulate a winter climate change and assessed the abundance of total bacteria and fungi and ammonia oxidizers and the bacterial community composition throughout a year. This experiment indicated that snowpack decline prolonged the soil freeze-thaw period, which increased the carbon (C) availability to soil microbes in winter. The soil microbial community then sensitively responded by increasing in abundance and shifting the composition based on each taxon's absolute and relative abundances in the way that was phylogenetically patterned, which further activated microbial N cycling. However, the soil microbial community's high resilience driven by the C availability prevented the functional and compositional responses to winter climate change from persisting into the plant-growing season, which left no apparent cascading effect on the soil microbial community and N content during the plant-growing season. This study highlights the sensitive and phylogenetically patterned response of the soil microbial community to the change in soil nutrient availability and its high resilience under winter climate change in a forest.

Belowground consequences of converting broadleaf to conifer forest: Comparing the fine root systems of European beech and Scots pine

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Fire and herbivory drive fungal and bacterial communities through distinct above- and belowground mechanisms

Fire and herbivory are important natural disturbances in grassy biomes. Both drivers are likely to influence belowground microbial communities but no studies have unravelled the long-term impact of both fire and herbivory on bacterial and fungal communities. We hypothesized that soil bacterial communities change through disturbance-induced shifts in soil properties (e.g. pH, nutrients) while soil fungal communities change through vegetation modification (biomass and species composition). To test these ideas, we characterised soil physico-chemical properties (pH, acidity, C, N, P and exchangeable cations content, texture, bulk density, moisture), plant species richness and biomass, microbial biomass and bacterial and fungal community composition and diversity (using 16S and ITS rRNA amplicon sequencing, respectively) in six long-term (18 to 70 years) ecological research sites in South African savanna and grassland ecosystems. We found that fire and herbivory regimes profoundly modified soil physico-chemical properties, plant species richness and standing biomass. In all sites, an increase in woody biomass (ranging from 12 to 50%) was observed when natural disturbances were excluded. The intensity and direction of changes in soil properties were highly dependent on the topo-pedo-climatic context. Overall, fire and herbivory shaped bacterial and fungal communities through distinct driving forces: edaphic properties (including Mg, pH, Ca) for bacteria, and vegetation (herbaceous biomass and woody cover) for fungi. Fire and herbivory explained on average 7.5 and 9.8% of the fungal community variability, respectively, compared to 6.0 and 5.6% for bacteria. The relatively small changes in microbial communities due to natural disturbance is in stark contrast to dramatic vegetation and edaphic changes and suggests that soil microbial communities, having evolved with disturbance, are resistant to change. This represents both a buffer to short-term anthropogenic-induced changes and a restoration challenge in the face of long-term changes.

Predicting spatial patterns of soil bacteria under current and future environmental conditions

Soil bacteria are largely missing from future biodiversity assessments hindering comprehensive forecasts of ecosystem changes. Soil bacterial communities are expected to be more strongly driven by pH and less by other edaphic and climatic factors. Thus, alkalinisation or acidification along with climate change may influence soil bacteria, with subsequent influences for example on nutrient cycling and vegetation. Future forecasts of soil bacteria are therefore needed. We applied species distribution modelling (SDM) to quantify the roles of environmental factors in governing spatial abundance distribution of soil bacterial OTUs and to predict how future changes in these factors may change bacterial communities in a temperate mountain area. Models indicated that factors related to soil (especially pH), climate and/or topography explain and predict part of the abundance distribution of most OTUs. This supports the expectations that microorganisms have specific environmental requirements (i.e., niches/envelopes) and that they should accordingly respond to environmental changes. Our predictions indicate a stronger role of pH over other predictors (e.g. climate) in governing distributions of bacteria, yet the predicted future changes in bacteria communities are smaller than their current variation across space. The extent of bacterial community change predictions varies as a function of elevation, but in general, deviations from neutral soil pH are expected to decrease abundances and diversity of bacteria. Our findings highlight the need to account for edaphic changes, along with climate changes, in future forecasts of soil bacteria.

Turnover and change in plant species composition in a shielded salt marsh following variation in precipitation and temperature

AbstractQuestionsTemperature and precipitation variation between years may affect plant species composition directly or indirectly. We wish to investigate whether salt marsh edaphic conditions and plant species composition change as a result of climatic variation. Further, whether areas with the largest edaphic variations also experience the largest change in species composition and turnover. Finally, do temperature and precipitation variations change the way the plant community is able to respond to natural edaphic gradients?LocationBygholmengen, a shielded salt marsh in Vejlerne, Denmark, Northern Europe.MethodsBotanical surveys were conducted and soil samples collected from 40 plots during a wet and dry summer to register changes in vegetation cover, species richness composition and edaphic factors (moisture, nutrients, salinity). These data were used to calculate dissimilarities in species composition, temporal turnover and environmental dissimilarity between years. A linear mixed‐effects model was used to link species richness with the measured edaphic factors.ResultsWe found that the precipitation and temperature variations altered the edaphic conditions; furthermore, the vegetation cover and species richness decreased when conditions were dry whereas the number of salt marsh species increased. Further, species composition changed significantly between years, and sampling plots that experienced the least edaphic change also retained more species between years. Species richness responded more to changes in nutrient availability during wet than dry conditions.ConclusionOur results pointed toward the climatic variations, and subsequent change in edaphic conditions, being responsible for the significant change in species composition as areas with the least change in edaphic factors retained most species between years. Dry conditions favored salt marsh‐adapted species and the extent to which increased nutrient levels led to a higher species richness decreased in dry compared to wet conditions.

Multi-decadal patterns of vegetation succession after tundra fire on the Yukon-Kuskokwim Delta, Alaska

Alaska’s Yukon-Kuskokwim Delta (YKD) is one of the warmest parts of the Arctic tundra biome and tundra fires are common in its upland areas. Here, we combine field measurements, Landsat observations, and quantitative cover maps for tundra plant functional types (PFTs) to characterize multi-decadal succession and landscape change after fire in lichen-dominated upland tundra of the YKD, where extensive wildfires occurred in 1971–1972, 1985, 2006–2007, and 2015. Unburned tundra was characterized by abundant lichens, and low lichen cover was consistently associated with historical fire. While we observed some successional patterns that were consistent with earlier work in Alaskan tussock tundra, other patterns were not. In the landscape we studied, a large proportion of pre-fire moss cover and surface peat tended to survive fire, which favors survival of existing vascular plants and limits opportunities for seed recruitment. Although shrub cover was much higher in 1985 and 1971–1972 burns than in unburned tundra, tall shrubs (>0.5 m height) were rare and the PFT maps indicate high landscape-scale variability in the degree and persistence of shrub increase after fire. Fire has induced persistent changes in species composition and structure of upland tundra on the YKD, but the lichen-dominated fuels and thick surface peat appear to have limited the potential for severe fire and accompanying edaphic changes. Soil thaw depths were about 10 cm deeper in 2006–2007 burns than in unburned tundra, but were similar to unburned tundra in 1985 and 1971–1972 burns. Historically, repeat fire has been rare on the YKD, and the functional diversity of vegetation has recovered within several decades post-fire. Our findings provide a basis for predicting and monitoring post-fire tundra succession on the YKD and elsewhere.

A new forest vegetation type in Sri Lanka: Dry Canal-associated Evergreen Forest

During the Kingdom of Polonnaruwa (11-14th Century AD), irrigation infrastructure and agricultural development in Sri Lanka were at their zenith. Irrigation system also consisted of canals conveying water from the Mahaweli River to distant farmlands. One such irrigation canal, presently within the Somawathiya National Park (SNP), supplied water from the river to a cascade of small tanks and farmlands as far as Kalu Ganga that divides Polonnaruwa and Trincomalee Districts on the Mahaweli Left Bank. The perennial presence of water during use, and subsequent disuse of the canal for centuries, since the fall of the Kingdom, evidently has caused edaphic, hydrological, microclimatic, biological and ecological changes that seem to have transformed vegetation existed during pre-Polonnaruwa and Polonnaruwa Periods in this part of the dry zone. Along the present day ruins of this ancient irrigation canal exists a unique zone of forest vegetation which has not been hitherto identified or recorded. This special forest formation which is anthropogenic in origin is here described as a new forest vegetation type in Sri Lanka and named Dry Canal-associated Evergreen Forest (DCEF) which closely resembles a river forest (Dry Riverine Evergreen Forest (DREF)), which in contrast is a natural vegetation formation.

Cambios edáficos provocados por el uso de abonos de origen natural en una región cafetalera de Veracruz, México.

Mexico is an important producer of organic coffee worldwide. A sector of coffee growers in the municipality of Ixhuatlán del Café, Veracruz, Mexico, use organic amendments as edaphic improvers. Hypothetically, the contributions of these organic fertilizers cause edaphic changes that improve coffee production. Therefore, the objective of this study was to determine changes in soil chemical fertility caused by incorporating fertilizer mixtures made from organic sources, as well as their contribution to improving yield. To verify this hypothesis, four organic fertilizers formulated from dolomite lime, coffee pulp (PC), biol (fermented liquid fertilizer) and a soil improver called PSD® were added to a Cromic Luvisol (cutanic) soil. After three, six and nine months, the contribution of the treatments to the soil variables organic matter, pH, electrical conductivity, nitrogen, phosphorus, and interchangeable bases (K, Ca, Mg, Na) were determined. In parallel, yield was evaluated. The results indicate that six months after application of the treatments, the greatest depletion of the organic sources added occurs, coinciding with a greater release of the nutrients. The dose of 300 g of dolomite lime tree-1 supplied (Treatment 1) was insuff icient to neutralize the strong initial soil acidity (pH 4.3). The coffee pulp and biol utilized are organic fertilizers that, because of their C: N ratio of less than 16, are of rapid mineralization and slightly increased levels of nitrogen, phosphorus and interchangeable bases, reaching only low or moderately low levels. The dolomite lime and PCD® of Treatment 4 improved the pH, Ca and Mg, although these changes are not reflected in increased coffee yield.

Ectomycorrhizal fungal communities in alpine relict forests of Pinus pumila on Mt. Norikura, Japan.

Ectomycorrhizal (ECM) symbioses are indispensable for the establishment of host trees, yet available information of ECM symbiosis in alpine forests is scarce. Pinus pumila is a typical ice age relict tree species in Japan and often forms monodominant dwarf vegetation above the tree line in mountains. We studied ECM fungi colonizing P. pumila on Mt. Norikura, Japan, with reference to host developmental stages, i.e., from current-year seedlings to mature trees. ECM fungal species were identified based on rDNA ITS sequences. Ninety-two ECM fungal species were confirmed from a total of 2480 root tips examined. Species in /suillus-rhizopogon and /wilcoxina were dominant in seedling roots. ECM fungal diversity increased with host development, due to the addition of species-rich fungal lineages (/cenococcum, /cortinarius, and /russula-lactarius) in late-successional stages. Such successional pattern of ECM fungi is similar to those in temperate pine systems, suggesting the predominant role of /suillus-rhizopogon in seedling establishment, even in relict alpine habitats fragmented and isolated for a geological time period. Most of the ECM fungi detected were also recorded in Europe or North America, indicating their potential Holarctic distribution and the possibility of their comigration with P. pumila through land bridges during ice ages. In addition, we found significant effects of soil properties on ECM fungal communities, which explained 34.1% of the total variation of the fungal communities. While alpine vegetation is regarded as vulnerable to the ongoing global warming, ECM fungal communities associated with P. pumila could be altered by the edaphic change induced by the warming.

A climosequence of chronosequences in southwestern Australia

SummaryTo examine how climate affects soil development and nutrient availability over long timescales, we studied a series of four long‐term chronosequences along a climate gradient in southwestern Australia. Annual rainfall ranged from 533 to 1185 mm (water balance from −900 to +52 mm) and each chronosequence included Holocene (≤ 6.5 ka), Middle Pleistocene (120–500 ka) and Early Pleistocene (∼2000 ka) dunes. Vegetation changed markedly along the climosequence, from shrubland at the driest site to Eucalyptus forest at the wettest. Soil pH was similar in the youngest soil of each chronosequence, although the carbonate and P contents of the parent sand declined from dry to wet along the climosequence, presumably linked to variation in offshore productivity. Despite this, soil development and associated nutrient status followed remarkably consistent patterns along the four chronosequences. Pedogenesis involved decalcification and secondary carbonate precipitation in Holocene soils and leaching of iron oxides from Middle Pleistocene soils, leading ultimately to bleached quartz sands in the oldest soils. Along all chronosequences soil pH and total P declined, whereas C:P and N:P ratios increased, which is consistent with the predicted change from N to P limitation of vegetation during ecosystem development. The expected unimodal pattern of leaf area index was most pronounced along wetter chronosequences, suggesting an effect of climate on the expression of retrogression. The four chronosequences do not appear to span a pedogenic climate threshold, defined as an abrupt change in soil properties across a relatively small change in climate, because exchangeable phosphate and base cations declined consistently during long‐term pedogenesis. However, the proportion of total P in organic form was greater along wetter chronosequences. We conclude that soil and nutrient availability on the coastal sand plains of southwestern Australia change consistently during long‐term pedogenesis, despite marked variation in modern vegetation and climate. The four chronosequences provide a rare soil‐age × climate framework within which to study long‐term ecosystem development.Highlights We describe four long‐term coastal dune chronosequences spanning a climate gradient in a global biodiversity hotspot. Pedogenesis involves depletion of phosphorus and cations linked to decalcification and subsequent podsolization. Climate has relatively little effect on patterns of nutrient availability during ecosystem development along the climosequence. The age by climate framework enables study of effect of edaphic change on above‐ and below‐ground communities.

Long-term effects of grazing and topography on extra-radical hyphae of arbuscular mycorrhizal fungi in semi-arid grasslands.

Grazing and topography have drastic effects on plant communities and soil properties. These effects are thought to influence arbuscular mycorrhizal (AM) fungi. However, the simultaneous impacts of grazing pressure (sheepha-1) and topography on plant and soil factors and their relationship to the production of extra-radical AM hyphae are not well understood. Our 10-year study assessed relationships between grazing, plant species richness, aboveground plant productivity, soil nutrients, edaphic properties, and AM hyphal length density (HLD) in different topographic areas (flat or sloped). We found HLD linearly declined with increasing grazing pressure (1.5-9.0 sheepha-1) in sloped areas, but HLD was greatest at moderate grazing pressure (4.5 sheepha-1) in flat areas. Structural equation modeling indicates grazing reduces HLD by altering soil nutrient dynamics in sloped areas, but non-linearly influences HLD through plant community and edaphic changes in flat areas. Our findings highlight how topography influences key plant and soil factors, thus regulating the effects of grazing pressure on extra-radical hyphal production of AM fungi in grasslands. Understanding how grazing and topography influence AM fungi in semi-arid grasslands is vital, as globally, severe human population pressure and increasing demand for food aggravate the grazing intensity in grasslands.

Reduction of soil erosion and mercury losses in agroforestry systems compared to forests and cultivated fields in the Brazilian Amazon

In addition to causing physical degradation and nutrient depletion, erosion of cultivated soils in the Amazon affects aquatic ecosystems through the release of natural soil mercury (Hg) towards lakes and rivers. While traditional agriculture is generally cited as being among the main causes of soil erosion, agroforestry practices are increasingly appreciated for soil conservation. This study was carried out in family farms of the rural Tapajós region (Brazil) and aimed at evaluating soil erosion and associated Hg release for three land uses. Soils, runoff water and eroded sediments were collected at three sites representing a land cover gradient: a recently burnt short-cycle cropping system (SCC), a 2-year-old agroforestry system (AFS) and a mature forest (F). At each site, two PVC soil erosion plots (each composed of three 2 × 5 m isolated subplots) were implemented on steep and moderate slopes respectively. Sampling was done after each of the 20 rain events that occurred during a 1-month study period, in the peak of the 2011 rain season. Runoff volume and rate, as well as eroded soil particles with their Hg and cation concentrations were determined. Total Hg and cation losses were then calculated for each subplot. Erosion processes were dominated by land use type over rainfall or soil slope. Eroded soil particles, as well as the amount of Hg and cations (CaMgK) mobilized at the AFS site were similar to those at the F site, but significantly lower than those at the SCC site (p < 0.0001). Erosion reduction at the AFS site was mainly attributed to the ground cover plants characterizing the recently established system. Moreover, edaphic change throughout AFS and F soil profiles differed from the SCC site. At the latter site, losses of fine particles and Hg were enhanced towards soil surface, while they were less pronounced at the other sites. This study shows that agroforestry systems, even in their early stages of implementation, are characterized by low erosion levels resembling those of local forest environments, thus contributing to the maintenance of soil integrity and to the reduction of Hg and nutrient mobility.

Consistent effects of nitrogen fertilization on soil bacterial communities in black soils for two crop seasons in China

Long-term use of inorganic nitrogen (N) fertilization has greatly influenced the bacterial community in black soil of northeast China. It is unclear how N affects the bacterial community in two successive crop seasons in the same field for this soil type. We sampled soils from a long-term fertilizer experimental field in Harbin city with three N gradients. We applied sequencing and quantitative PCR targeting at the 16S rRNA gene to examine shifts in bacterial communities and test consistent shifts and driving-factors bacterial responses to elevated N additions. N addition decreased soil pH and bacterial 16S rDNA copy numbers, and increased soil N and crop yield. N addition consistently decreased bacterial diversity and altered bacterial community composition, by increasing the relative abundance of Proteobacteria, and decreasing that of Acidobacteria and Nitrospirae in both seasons. Consistent changes in the abundant classes and genera, and the structure of the bacterial communities across both seasons were observed. Our results suggest that increases in N inputs had consistent effects on the richness, diversity and composition of soil bacterial communities across the crop seasons in two continuous years, and the N addition and the subsequent edaphic changes were important factors in shaping bacterial community structures.