High Soil Nutrient Research Articles

Health risk evaluation of heavy metals in green land soils from urban parks in Urumqi, northwest China.

Here, we sampled, tested, and analyzed heavy metals in soil obtained from green land in urban parks of Urumqi. Analysis included soil nutrient contents, particle size distribution, and health risks of heavy metal contaminants. Results showed that (1) organic matter and rapidly available phosphorus contents of all samples ranged from 6.07-58.34 and 6.52-116.15mg/kg, with average values of 31.26 and 36.24mg/kg, respectively; (2) silt (particle size 20-200μm) comprised most of the particle distribution, accounting for 46.56-87.38% of the total, and the remaining particles were clay particles (0-20μm) and sand (200-2000μm); (3) calculations of HQing, HQinh, and HQderm for eight heavy metals in three exposure patterns revealed values less than 1 for children and adults, indicating a level of carcinogenic risk for these heavy metals; and (4) calculating the carcinogenic risks of nickel, chromium, and cadmium through breathing pathway indicating no potential carcinogenic risk for any of the three. This research showed high soil nutrient content, providing fertile ground for plant growth in the green land of these urban parks. However, measures such as using sprinklers and increased green vegetation areas have been proposed to improve soil texture. This research can serve as a reference point for soil environmental protection efforts as well as future plant growth in urban Urumqi parks.

Alien plant invasions in European woodlands

AbstractAimWoodlands make up a third of European territory and carry out important ecosystem functions, yet a comprehensive overview of their invasion by alien plants has never been undertaken across this continent.LocationEurope.MethodsWe extracted data from 251,740 vegetation plots stored in the recently compiled European Vegetation Archive. After filtering (resulting in 83,396 plots; 39 regions; 1970–2015 time period), we analysed the species pool and frequency of alien vascular plants with respect to geographic origin and life‐forms, and the levels of invasion across the European Nature Information System (EUNIS) woodland habitats.ResultsWe found a total of 386 alien plant species (comprising 7% of all recorded vascular plants). Aliens originating from outside of and from within Europe were almost equally represented in the species pool (192 vs. 181 species) but relative frequency was skewed towards the former group (77% vs. 22%) due, to some extent, to the frequent occurrence of Impatiens parviflora (21% frequency among alien plants). Phanerophytes were the most species‐rich life‐form (148 species) and had the highest representation in terms of relative frequency (39%) among aliens in the dataset. Apart from Europe (181 species), North America was the most important source of alien plants (109 species). At the local scale, temperate and boreal softwood riparian woodland (5%) and mire and mountain coniferous woodland (<1%) had the highest and lowest mean relative alien species richness (percentage of alien species per plot), respectively.Main conclusionsOur results indicate that European woodlands are prone to alien plant invasions especially when exposed to disturbance, fragmentation, alien propagule pressure and high soil nutrient levels. Given the persistence of these factors in the landscape, competitive alien plant species with a broad niche, including alien trees and shrubs, are likely to persist and spread further into European woodlands.

Transcriptomic resources for the medicinal legume Mucuna pruriens: de novo transcriptome assembly, annotation, identification and validation of EST-SSR markers

BackgroundThe medicinal legume Mucuna pruriens (L.) DC. has attracted attention worldwide as a source of the anti-Parkinson’s drug L-Dopa. It is also a popular green manure cover crop that offers many agronomic benefits including high protein content, nitrogen fixation and soil nutrients. The plant currently lacks genomic resources and there is limited knowledge on gene expression, metabolic pathways, and genetics of secondary metabolite production. Here, we present transcriptomic resources for M. pruriens, including a de novo transcriptome assembly and annotation, as well as differential transcript expression analyses between root, leaf, and pod tissues. We also develop microsatellite markers and analyze genetic diversity and population structure within a set of Indian germplasm accessions.ResultsOne-hundred ninety-one million two hundred thirty-three thousand two hundred forty-two bp cleaned reads were assembled into 67,561 transcripts with mean length of 626 bp and N50 of 987 bp. Assembled sequences were annotated using BLASTX against public databases with over 80% of transcripts annotated. We identified 7,493 simple sequence repeat (SSR) motifs, including 787 polymorphic repeats between the parents of a mapping population. 134 SSRs from expressed sequenced tags (ESTs) were screened against 23 M. pruriens accessions from India, with 52 EST-SSRs retained after quality control. Population structure analysis using a Bayesian framework implemented in fastSTRUCTURE showed nearly similar groupings as with distance-based (neighbor-joining) and principal component analyses, with most of the accessions clustering per geographical origins. Pair-wise comparison of transcript expression in leaves, roots and pods identified 4,387 differentially expressed transcripts with the highest number occurring between roots and leaves. Differentially expressed transcripts were enriched with transcription factors and transcripts annotated as belonging to secondary metabolite pathways.ConclusionsThe M. pruriens transcriptomic resources generated in this study provide foundational resources for gene discovery and development of molecular markers. Polymorphic SSRs identified can be used for genetic diversity, marker-trait analyses, and development of functional markers for crop improvement. The results of differential expression studies can be used to investigate genes involved in L-Dopa synthesis and other key metabolic pathways in M. pruriens.

The effects of the reverse seasonal flooding on soil texture within the hydro-fluctuation belt in the Three Gorges reservoir, China

PurposeThe formation of the large hydro-fluctuation belt at the altitude of 145–175 m, following the construction of the Three Gorges Dam, developed from the terrestrial system in the Three Gorges reservoir. This research mainly concerned the effects of the resultant reverse seasonal flooding on soil texture.Materials and methodsFour field experimental plots were designed with sample belts and quadrats at the head, middle, and tail sections of the reservoir area. Stratified soil samples were collected, followed by analysis of soil structure and soil grain size of the collected samples.Results and discussionThe reverse seasonal flooding significantly changes texture and nutrient of riparian soil. The percentages of silt and clay formations were greatest at the lower hydro-fluctuation belt, followed by the middle and upper hydro-fluctuation belt, respectively. The percentage of silt and clay particles at 150 m was greater than that of 170 m by 18.12%. Conversely, the percentage of sand particles at the upper hydro-fluctuation belt ranked the highest, and followed by the middle and lower hydro-fluctuation belt, respectively. The percentage of sand particles at 170 m was higher than that at 150 m by 19.72%. Soil texture type changed with increasing altitude gradient, from silt loam, loam, then to sandy loam. Reverse seasonal flooding also promotes silt and clay permeation, and deposition from surface soil to subsurface soil, increasing homogeneity in grain structure between soil layers. This change in soil texture is associated with changes in soil nutrients. The content of soil organic matter, total nitrogen, total phosphorus, and total potassium varied significantly among soil texture types, with loam having the highest soil nutrient concentration and sandy loam having the lowest.ConclusionsThe reverse seasonal flooding promotes the deposition of clay and silt within the hydro-fluctuation belt, inducing the total texture change of loam to silt loam. However, the structures and attributes of soil texture varied along the altitude gradient, as the exposed and submersed season and time span of riparian soil changed with the increase of altitude.

Root order-dependent seasonal dynamics in the carbon and nitrogen chemistry of poplar fine roots

Fine roots play an important role in above- and belowground carbon (C) allocation in forest ecosystems. However, few studies have focused on the seasonal dynamics of fine roots with different branching orders. The objective of this study is to provide insight to the seasonal heterogeneity in roots of different orders within root hierarchies of poplar trees under different soil conditions. Three plots were established in high (plantation A) and low (plantation B) soil nutrient conditions. Fine roots were sampled in each of four seasons throughout one year. All sampled roots were classified into one to five groups depending on their branching order, and the dry biomass of living roots and the concentrations of C, nitrogen (N) and total non-structural carbohydrate (TNC) were examined. Low order (first- to second-order) roots demonstrated more significant seasonal dynamics than high order roots, and the biomass of first-order fine roots was positively influenced by soil temperature and moisture while the biomass of second-order fine roots was negatively affected by soil nutrient conditions. The different responses of fine roots to environmental fluctuations implied a high division of root function, even within low order roots. The C and N chemistry of poplar fine roots also differed significantly with branching order; element concentrations were lower in low order roots. Principal component analysis indicated that root order explained 98.2% of the variation in fine root chemistry. Moreover, the first-order roots in plantation A had greater C but less TNC concentrations than those in plantation B, suggesting that C allocation in low order roots may be more responsive to soil nutrient conditions. The allocation of C and N also exhibited significant seasonal dynamics (p < 0.05); the TNC concentration was highest in winter, whereas C:N ratios were significantly lower in the summer and fall in each order of fine roots (p < 0.05). All these results suggest that branching order may be related to root growth and photoassimilate allocation, which should receive greater attention in future studies on C and N fluxes in forest ecosystems.

Size-Mediated Interaction between a Cushion Species and Other Non-cushion Species at High Elevations of the Hengduan Mountains, SW China.

Arenaria polytrichoides (Caryophyllaceae) is a common cushion plant occurring at high elevations in the Himalaya-Hengduan Mountains, SW China. It frequently has other non-cushion species growing within its canopy, forming a contrast with the surrounding areas because it creates patches of higher diversity and greater biomass. In this study, we examined the relationship between the cushions and associated non-cushion species along a gradient of cushion size. A total of 200 A. polytrichoides individuals were selected to fit four size classes. Field measurements were carried out to assess canopy structure, functional traits relevant to growth and reproduction, and soil quality below cushions along the size gradient. Furthermore, the size effect of cushions on the richness and abundance of species and biomass production was also examined. All the morphological variables examined exhibited a positive correlation with cushion size, as did the nutrients under cushions. Large and compact cushions were associated with higher soil nutrient contents compared with small and loose cushions. As a result of these biogenic environmental changes, there was a stronger facilitation effect performed by large cushions. Data pertaining to functional traits revealed that large cushions benefit from the enhanced resources within their compact structure and exhibit greater fitness and a higher reproductive output than small cushions. Our data indicated that interactions occur between cushion species and other plants depending on the size of the cushions, probably because of the greater heterogeneity of conditions beneath larger cushions. These findings provide a clear demonstration of the generally overlooked importance of the traits of nurse plants, such as size and age, in terms of their facilitative effects.

Root nutrient concentration and biomass allocation are more plastic than morphological traits in response to nutrient limitation

Understanding the magnitude of phenotypic plasticity within a species is important, particularly when comparing species from diverse habitats or when using traits from global databases. Our objective was to quantify the magnitude of intraspecific variability of fine root, stem, and leaf traits in response to nutrient availability. We measured growth rates and traits from fine roots, stems, and leaves on replicate seedlings of four species grown in two treatments: low and high soil nutrient availability. We used ANOVA to test for effects of fertilizer, species, and their interaction on trait expression, and ranked intraspecific trait variation using the coefficient of variation. Root nutrient concentration, relative growth rate, and biomass allocation exhibited the most plastic responses to nutrient availability. Specific root length, specific leaf area, root diameter, and wood density were the least variable traits within species. Nutrient limitation only induced greater root branching in the non-mycorrhizal Proteaceae species that produced more cluster roots. Woody plants respond to nutrient limitation by increasing root mass fraction, rather than by adjusting root morphology or structure. We urge caution when using root tissue chemistry traits obtained from global databases in local studies, as this is one of the most plastic traits in response to nutrient availability.

The integrated use of excreta-based vermicompost and inorganic NP fertilizer on tomato (Solanum lycopersicum L.) fruit yield, quality and soil fertility

PurposeA field study was conducted at Dire Dawa, Eastern Ethiopia, with an objective to find out an optimum combination of inorganic (NP) fertilizer and excreta-based vermicompost for best economic yield and quality of tomato and to assess their effect on selected physico-chemical properties of amended soil after crop harvest.MethodsThe experiment consisted of eight treatments where the mineral (NP) fertilizer and the excreta-based vermicompost were combined in different proportions being arranged in a completely randomized block design replicated three times.ResultsGrowth, yield and quality attributes of tomato as well as the post-harvest soil nutrient status were markedly influenced by the nutrient treatments. The highest values for the various growth, yield and quality attributing parameters were recorded for the treatment combination consisting 75% of the recommended rate of NP fertilizer + 11.25 ton ha−1 vermicompost (T6), this treatment was also observed to have the highest net benefit with acceptable economic return as well as a fairly high residual soil nutrient status. Following this treatment, is the integration of 50% of recommended rate of NP fertilizer + 7.5 ton ha−1 vermicompost (T3) which surpassed the sole mineral fertilizer and vermicompost in terms of the crop’s yield and its economic return.Conclusion25–50% of the recommended rate of chemical fertilizer can be supplemented through vermicompost. However, in order to generate more reliable information, there is a need to conduct more such studies using more integration ratios of these nutrient sources (NP fertilizer and vermicompost) at various soil and agro-climatic conditions.

The effect of riparian restoration on channel complexity and soil nutrients

Restoration of riparian vegetation may reduce nutrient and sediment contamination of waterways while potentially enhancing stream channel complexity. Accordingly, the present study used a paired-site approach to investigate the effects of mature regrowth riparian vegetation on river channel morphology and soil nutrients (i.e. nitrogen and phosphorus), comparing four sites of degraded (pasture) and reforested reaches. A revised rapid assessment of riparian condition (RARC) was used to validate the site pairings. Riparian soil nutrient and elemental geochemistry were compared between paired sites, along with two parameters of channel width complexity and two for channel slope complexity. The RARC analysis confirmed the validity of the paired site design. The elemental geochemistry results indicated that underlying geology may affect the paired site analyses. Reaches with mature regrowth vegetation had greater channel width complexity but no difference in their riverbed slope complexity. In addition, degraded reaches had higher soil nutrient (i.e. nitrogen and phosphorus) concentrations, potentially indicative of the greater nutrient retention of pasture grass sites compared with mature regrowth forested reaches with less ground cover. Overall, the present study indicates that restoring mature regrowth riparian vegetation may increase river channel width complexity, although it may require canopy management to optimise the nutrient retention potential necessary to maximise the effect of riparian restoration strategies on freshwater environments.

A Forest Tent Caterpillar Outbreak Increased Resource Levels and Seedling Growth in a Northern Hardwood Forest.

In closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics. Crown defoliation by insects, however, may also influence understory resource levels and thus forest dynamics. We evaluate the effect of a forest tent caterpillar outbreak on understory light availability, soil nutrient levels and tree seedling height growth in six sites with contrasting levels of canopy defoliation in a hardwood forest in northern lower Michigan. We compared resource levels and seedling growth of six hardwood species before, during and in the three years after the outbreak (2008–2012). Canopy openness increased strongly during the forest tent caterpillar outbreak in the four moderately and severely defoliated sites, but not in lightly defoliated sites. Total inorganic soil nitrogen concentrations increased in response to the outbreak in moderately and severely defoliated sites. The increase in total inorganic soil nitrogen was driven by a strong increase in soil nitrate, and tended to become stronger with increasing site defoliation. Seedling height growth increased for all species in the moderately and severely defoliated sites, but not in lightly defoliated sites, either during the outbreak year or in the year after the outbreak. Growth increases did not become stronger with increasing site defoliation, but were strongest in a moderately defoliated site with high soil nutrient levels. Growth increases tended to be strongest for the shade intolerant species Fraxinus americana and Prunus serotina, and the shade tolerant species Ostrya virginiana. The strong growth response of F. americana and P. serotina suggests that recurring forest tent caterpillar outbreaks may facilitate the persistence of shade intolerant species in the understory in the absence of canopy gaps. Overall, our results suggest that recurrent canopy defoliation resulting from cyclical forest insect outbreaks may be an additional driver of dynamics in temperate closed-canopy forests.

Microhabitat heterogeneity promotes soil fertility and ground-dwelling arthropod diversity in Mediterranean wood-pastures

Mediterranean wood-pastures are extensive agroforestry systems that hold great ecological, social and cultural values, which consist of mixtures of grassland, scattered trees and shrubs, primarily used for livestock grazing. For centuries, low-intensity management in these landscapes has resulted in multiple microhabitats that favour biodiversity and are considered key elements for the long-term persistence of wood-pastures. However, the relative contribution of each microhabitat type to wood-pasture biodiversity and functioning remains poorly studied. We investigated the impact that different wood-pasture microhabitats have on soil chemical fertility and the decomposition food web. We analysed the two main microhabitats that make wood-pastures up – open grasslands and isolated trees – and three additional “litter-trapping” microhabitats – shrubs scattered in the grassland matrix, canopied shrubs and piles of pruning debris—in terms of soil chemical properties (organic matter content, total N, C:N ratio, available P, and exchangeable base cations), collembolan and dipteran (mostly detritivores) abundance, and carabid (seed-eaters and predators) and staphylinid (mostly predators) beetle abundance, body size, biomass, species richness and composition. Grasslands were the most different microhabitats, with the lowest soil nutrient content and particular carabid and staphylinid species composition. Trees had the highest soil fertility levels and abundance of Diptera and staphylinids, and held unique staphylinid assemblages. “Litter-trapping” microhabitats had medium to high soil nutrient values and shared a distinct staphylinid assemblage compared to grasslands and trees. Besides, scattered shrubs provided shelter for large-sized carabid and staphylinid predators, while canopied shrubs held the highest carabid abundance and biomass. “Litter-trapping” microhabitats retained tree leaves that would otherwise be lost to the wood-pasture, recovering nutrients to the system, and provided new habitat, shelter and food for detritivores and unique predator assemblages. “Litter-trapping” microhabitats thus enhanced soil fertility and the decomposition process, at the same time as increased the abundance and diversity of the communities of ground-dwelling detritivores and predators inhabiting wood-pastures. These findings confirmed that microhabitat heterogeneity resulting from low-intensity management is essential to maintain both the primary production and the biodiversity conservation value of wood-pastures.

Corn Grain Yield and Soil Properties after 10 Years of Broiler Litter Amendment

Use of broiler litter (BL) nutrients for crop production benefits crops, soils, and aids in disposing manure. Understanding corn (Zea mays L.) grain production and soil properties resulting from long‐term BL amendment helps establish a sustainable manure‐based corn production with low environmental risk potential. This study conducted at Bowling Green, KY, during 2005 to 2015 examined effects of supplying N requirement of corn grain crop monoculture by broiler litter (full broiler litter, FBL), 1:1 mixture of BL and inorganic N (half broiler litter rate, HBL), and chemical fertilizer (CF) on corn grain yield and post‐harvest soil properties under no‐till (NT) and conventional tillage (CT). The FBL produced significantly higher grain yield (10.1 Mg ha−1) than the HBL (9.6 Mg ha−1), but similar to CF (9.8 Mg ha−1). The FBL soils had greater cation exchange capacity (CEC), organic matter (OM), and total nitrogen (TN) (15.5 cmol kg−1; 45 and 2.9 g kg−1) than the HBL (12.3 cmol kg−1; 42.3 and 2.4 g kg−1) and CF (10.1 cmol kg−1; 35.5 and 1.7 g kg−1). The FBL and HBL soils had 478 and 270 mg P kg−1; 15.7 and 9.6 mg Cu kg−1; 40.9 and 21.1 mg Zn kg−1 levels, respectively. Soil pH increased in the FBL, but decreased in CF. Soil nutrient aggregation rate was greater in the NT. Having lower soil nutrient accumulation than FBL and equivalent grain production potential as CF, HBL offers a better option for corn grain production with BL than by FBL.Core Ideas This study examined effects of long‐term broiler litter amendment on corn grain yield and post‐harvest soil properties. Broiler litter at full and half rates has similar corn grain production potential as chemical fertilizer. Broiler litter induced high soil nutrient levels, but levels elevated by half litter rate was not environmentally significant. No‐till and conventional tillage treatments have similar agronomic benefits and environmental risks.

The nitrification inhibitor 3,4,-dimethylpyrazole phosphate strongly inhibits nitrification in coarse-grained soils containing a low abundance of nitrifying microbiota

The effectiveness of the nitrification inhibitor 3,4,-dimethylpyrazole phosphate (DMPP) on sandy soils containing low nitrifying microbial abundance has not been established. Two coarse-grained soils, representative of Western Australia’s agricultural zones, were incubated with 100mgNkg–1 soil, added as either urea, urea+DMPP or urea+nitrapyrin as an alternative nitrification inhibitor for comparative purposes. Ammonium (NH4+) and nitrate (NO3–) concentrations, potential nitrification rates (PNR) and the abundance of ammonia-oxidising bacteria (AOB) and archaea (AOA) were measured over time. Interactions between soil type and inhibitor type altered the extent of nitrification observed in these soils. When N was supplied as urea alone, NH4+-N concentrations decreased from 100mgNkg–1 soil to approximately 20mgNkg–1 soil in the high nutrient soil (Williams) and approximately 60mgNkg–1 soil in the low nutrient soil (Vasse). These differences were reflected in AOB abundance, which was higher (~105genecopiesg–1 soil) in Williams soil than in Vasse soil (&lt;104genecopiesg–1 soil). This difference could have been attributable to differences in soil pH between Williams and Vasse (5.4 vs 4.0 respectively) and/or copper (Cu) availability (~1.5 vs ~0.5mgCukg–1 soil respectively), both of which have been demonstrated to reduce AOB abundance or limit nitrification. On the Williams soil, DMPP limited nitrification, resulting in approximately 80mgNkg–1 soil being retained as NH4+-N. Nitrapyrin was similarly effective for the first 56 days of incubation, but declined considerably in effectiveness between Days 56 and 100. Changes in soil nitrification rates were accompanied by changes in AOB abundance, which was below 103genecopiesg–1 soil when nitrification was impaired. Both DMPP and nitrapyrin inhibit nitrification via chelating Cu and, because these soils contained low Cu concentrations, it may be possible that interactions between DMPP, naturally low abundance of AOB and low Cu availability facilitated the long-term inhibition of nitrification in these soils.

Aspect and slope as determinants of vegetation composition and soil properties in coastal forest backdunes of Eastern Cape, South Africa

AbstractCoastal sand dune ecosystems are subjected to many stress and disturbance factors that are particularly high in the foredunes compared to the backdunes. Although a few studies have been conducted on eastern coastline sand dunes of South Africa, none have examined the relationship between aspect and slope on vegetation composition and soil properties of coastal forest backdunes. Vegetation and soil sampling were conducted in 11 transects, each with four plots measuring 10 × 10 m, located on the seaward and landward sides and on middle and lower slopes of backdunes of Bathurst coastal forest. A total of 39 species were identified, of which 23 were trees and shrubs, thirteen were forbs and three were grasses. The data show that both aspect and slope had limited influence on vegetation community assemblage and soil properties, but had significant effects on individual species distribution. There was a grass‐dominated community on the middle slope and a tree‐ and shrub‐ dominated community on the lower slope. These two plant communities act as the required coastal forest ecosystem engineer driving variability in soil properties between the slopes, the most prominent being high soil nutrients and moisture in the lower slopes compared to the middle slopes.

Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2 exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO2 uptake was high, the annual budget of −229 ± 7 ± 49 g C m−2 y−1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.

Water track distribution and effects on carbon dioxide flux in an eastern Siberian upland tundra landscape

Shrub expansion in tundra ecosystems may act as a positive feedback to climate warming, the strength of which depends on its spatial extent. Recent studies have shown that shrub expansion is more likely to occur in areas with high soil moisture and nutrient availability, conditions typically found in sub-surface water channels known as water tracks. Water tracks are 5–15 m wide channels of subsurface water drainage in permafrost landscapes and are characterized by deeper seasonal thaw depth, warmer soil temperatures, and higher soil moisture and nutrient content relative to adjacent tundra. Consequently, enhanced vegetation productivity, and dominance by tall deciduous shrubs, are typical in water tracks. Quantifying the distribution of water tracks may inform investigations of the extent of shrub expansion and associated impacts on tundra ecosystem carbon cycling. Here, we quantify the distribution of water tracks and their contribution to growing season CO2 dynamics for a Siberian tundra landscape using satellite observations, meteorological data, and field measurements. We find that water tracks occupy 7.4% of the 448 km2 study area, and account for a slightly larger proportion of growing season carbon uptake relative to surrounding tundra. For areas inside water tracks dominated by shrubs, field observations revealed higher shrub biomass and higher ecosystem respiration and gross primary productivity relative to adjacent upland tundra. Conversely, a comparison of graminoid-dominated areas in water tracks and inter-track tundra revealed that water track locations dominated by graminoids had lower shrub biomass yet increased net uptake of CO2. Our results show water tracks are an important component of this landscape. Their distribution will influence ecosystem structural and functional responses to climate, and is therefore of importance for modeling.

Chemically and biologically-mediated fertilizing value of manure-derived biochar

This study evaluates the potential of manure-derived biochars in promoting plant growth and enhancing soil chemical and biological properties during a 150day pot experiment. Biochars from pyrolysis of poultry litter (PL) and swine manure (SM) at 400 and 600°C, and a commonly available wood chip (WC) biochar produced at high temperature (1000°C) were incorporated to silt-loam (SL) and sandy (SY) soils on a 2% dry soil weight basis. Ryegrass was sown and moisture was adjusted to 60% water filled pore space (WFPS). The PL400 and SM400 biochars significantly increased (p<0.05) shoot dry matter (DM) yields (SL soil) and enhanced nitrogen (N), phosphorus (P) and potassium (K) uptake by the plants in both soils, compared to the Control. All biochars significantly increased the soil carbon (C) contents compared to the Control. Total N contents were significantly greater for PL400 and PL600 treatments in both soils. The dehydrogenase activity (DA) significantly increased for PL400 and SM400 treatments and was positively correlated with the volatile matter (VM) contents of the biochars, while β-glucosidase activity (GA) decreased for the same treatments in both soils. All biochars significantly shifted (p≤0.05) the bacterial community structure compared to the Control. This study suggests that pyrolysis of animal manures can produce a biochar that acts as both soil amendment and an organic fertilizer as proven by increased NPK uptake, positive liming effect and high soil nutrient availability, while WC biochar could work only in combination with fertilizers (organic as well as mineral).

Soil Nitrogen Status Modifies Rice Root Response to Nematode-Bacteria Interactions in the Rhizosphere.

It has been hypothesized that faunal activity in the rhizosphere influences root growth via an auxin-dependent pathway. In this study, two methods were used to adjust nematode and bacterial populations within experimental soils. One is “exclusion”, where soil mixed with pig manure was placed in two bags with different mesh sizes (1mm and 5μm diameter), and then surrounded by an outer layer of unamended soil resulting in soil with a greater populations of bacterial-feeding nematodes (1mm) and a control treatment (5μm). The second method is “inoculation”, whereby autoclaved soil was inoculated with bacteria (E. coli and Pseudomonas) and Nematodes (Cephalobus and C. elegans). In order to detect the changes in the rice’s perception of auxin under different nutrient and auxin conditions in the presence of soil bacterial-feeding nematodes, responses of soil chemistry (NH4+, NO3- and indole acetic acid (IAA)), rice root growth and the expression of an auxin responsive gene GH3-2 were measured. Results showed that, under low soil nutrient conditions (exclusion), low NO3- correlated with increased root branching and IAA correlated with increased root elongation and GH3-2 expression. However, under high soil nutrient conditions (inoculation), a high NH4+ to NO3- ratio promoted an increase in root surface area and there was an additional influence of NH4+ and NO3- on GH3-2 expression. Thus it was concluded that soil bacterial-feeding nematodes influenced soil nutritional status and soil IAA content, promoting root growth via an auxin dependent pathway that was offset by soil nitrogen status.

Evolutionary Divergences in Root Exudate Composition among Ecologically-Contrasting Helianthus Species.

Plant roots exude numerous metabolites into the soil that influence nutrient availability. Although root exudate composition is hypothesized to be under selection in low fertility soils, few studies have tested this hypothesis in a phylogenetic framework. In this study, we examined root exudates of three pairs of Helianthus species chosen as phylogenetically-independent contrasts with respect to native soil nutrient availability. Under controlled environmental conditions, seedlings were grown to the three-leaf-pair stage, then transferred to either high or low nutrient treatments. After five days of nutrient treatments, we used gas chromatography-mass spectrometry for analysis of root exudates, and detected 37 metabolites across species. When compared in the high nutrient treatment, species native to low nutrient soils exhibited overall higher exudation than their sister species native to high nutrient soils in all three species pairs, providing support for repeated evolutionary shifts in response to native soil fertility. Species native to low nutrient soils and those native to high nutrient soils responded similarly to low nutrient treatments with increased exudation of organic acids (fumaric, citric, malic acids) and glucose, potentially as a mechanism to enhance nutrition acquisition. However, species native to low nutrient soils also responded to low nutrient treatments with a larger decrease in exudation of amino acids than species native to high nutrient soils in all three species pairs. This indicates that species native to low nutrient soils have evolved a unique sensitivity to changes in nutrient availability for some, but not all, root exudates. Overall, these repeated evolutionary divergences between species native to low nutrient soils and those native to high nutrient soils provide evidence for the adaptive value of root exudation, and its plasticity, in contrasting soil environments.

Evolutionary divergences in root system morphology, allocation, and nitrogen uptake in species from high- versus low-fertility soils.

Root morphology and nutrient uptake processes are essential for acquisition of mineral resources from soil. However, our understanding of how root form and function have diverged across environments is limited. In this study, we addressed hypotheses of adaptive differentiation using three pairs of Helianthus species chosen as phylogenetically-independent contrasts with respect to native soil nutrients. Under controlled environmental conditions, root morphology, allocation, and nitrogen (N) uptake (using a 15N tracer) were assessed for seedlings under both high and low N treatments. Species native to low nutrient soils (LNS) had lower total root length than those native to high nutrient soils (HNS), reflecting the slower growth rates of species from less fertile environments. Contrary to expectations, species did not consistently differ in specific root length, root tissue density, or root system plasticity, and species native to LNS had lower root:total mass ratio and higher 15N uptake rates than species native to HNS. Overall, these evolutionary divergences provide support for adaptive differentiation among species, with repeated evolution of slow-growing root systems suited for low resource availability in LNS. However, species native to LNS maintain a high capacity for N uptake, potentially as a means of maximising nutrient acquisition from transient pulses.