Changes In Soil Nutrients Research Articles

ElevatedCO2concentrations reduce C4cover and decrease diversity of understorey plant community in aEucalyptuswoodland

AbstractCompared to tree responses to elevated (e)CO2, little attention has been paid to understorey plant community responses in forest ecosystem studies, despite their critical role in nutrient cycling and the regeneration of overstorey species. Here, we present data on understorey responses from a 3‐year Free‐AirCO2Enrichment experiment in a native, phosphorus‐limitedEucalyptuswoodland in Australia (EucFACE).We conducted repeat surveys of the understorey plant community from 2012 to 2016, recording cover at the species level.Three years ofeCO2significantly decreased the diversity (Shannon‐Weaver; −30%) and species richness (−15%;c. −1 species per 4 m2plot) of graminoid species, and the cover of C4graminoids in both dominant (−38%) and subordinate (−48%) groups, relative to ambient conditions, leading to a significantly lower graminoid C4:C3ratio (−59%) in the understorey plant community. The ratio of C4:C3graminoids was negatively associated with soil nitrogen (N) availability suggesting that previously reportedeCO2‐associated increases in N availability may contribute to (or be a consequence of) shifts in the composition of the graminoid community at the study site. There was, however, no effect ofeCO2on the diversity of forb species, which represented the most species‐rich functional group but onlyc. 1% of the understorey biomass.Synthesis. Our results suggest thateCO2influences competition between C4and C3graminoid species both directly and indirectly via increasing N availability. The shift towards lower C4:C3ratios and enhanced dominance by C3species with their generally higher tissue N concentrations could further change soil nutrient availability and potentially accelerate community succession. Thus,eCO2has altered the diversity and composition of the understorey plant community in this woodland, with the potential for cascading consequences for trophic interactions and ecosystem function.

Remediation of a soil chronically contaminated with hydrocarbons through persulfate oxidation and bioremediation

The impact of remediation combining chemical oxidation followed by biological treatment on soil matrix and microbial community was studied, of a chronically hydrocarbon contaminated soil sourced from a landfarming treatment. Oxidation by ammonium persulfate produced a significant elimination of polycyclic aromatic hydrocarbons (PAHs) and an increase in PAH bioavailability. Organic-matter oxidation mobilized nutrients from the soil matrix. The bacterial populations were affected negatively, with a marked diminution in the diversity indices. In this combined treatment with oxidation and bioremediation working in tandem, the aliphatic-hydrocarbon fractions were largely eliminated along with additional PAHs. The chemical and spectroscopic analyses indicated a change in soil nutrients. In spite of the high residual-sulfate concentration, a rapid recovery of the cultivable bacterial population and the establishment of a diverse and equitable microbial community were obtained. Pyrosequencing analysis demonstrated a marked succession throughout this twofold intervention in accordance with the chemical and biologic shifts observed. These remediation steps produced different effects on the soil physiology. Spectroscopic analysis became a useful tool for following and comparing those treatments, which involved acute changes in a matrix of such chronically hydrocarbon-contaminated soil. The combined treatment increased the elimination efficiency of both the aliphatic hydrocarbons and the PAHs at the expense of the mobilized organic matter, thus sustaining the recovery of the resilient populations throughout the treatment. The high-throughput–DNA-sequencing techniques enabled the identification of the predominant populations that were associated with the changes observed during the treatments.

Remediation of Arsenic-Contaminated Soil Using Alkaline Extractable Organic Carbon Solution Prepared from Wine-Processing Waste Sludge

ABSTRACTPast studies have shown that dissolved organic carbon (DOC) washing can effectively remove heavy metals from contaminated soil. In this study, we used alkaline DOC solutions for remediation of arsenic (As)-contaminated soil (with an initial As concentration in the topsoil of 390 mg kg−1). The removal of As and the change in soil nutrients during DOC washing were studied for 60 min at pH 10 with a 60:1 liquid/soil ratio (v/m). Approximately 88% of As was removed by washing the soil twice using a 3000 mg L−1 DOC solution at 25°C. Following this treatment, the pH of the soil had increased from 5.6 to 9.2; organic carbon content had increased from 3.5% to 4.1%; cation exchange capacity, ammonium-N, and available phosphorus had increased to 2.3, 1.4, and 6.6 times their original levels, respectively; and exchangeable K, Na, Ca, and Mg had increased to 91, 6.1, 4.2, and 2.2 times their original levels, respectively. A sequential extraction investigation revealed that residual As and easily exchangeable As in the fraction were initially 10.2% and 9.2%, respectively, but that the former became the maximum remainder (64%) after the ultimate DOC washing.

Parasites structuring ecological communities: The mistletoe footprint in Mediterranean pine forests

Abstract The capacity of parasitic plants in structuring natural communities is increasingly recognized. These plants can affect the structure, composition and productivity of plant communities by modifying the competitive balance between hosts and non‐host species and by altering the quantity and quality of resources entering the soil. Despite the progress made in this field, there is still a lack of integrative studies showing the structuring capacity of parasitic plants in forest ecosystems, where their effect may be less detectable due to the long life span of the system. In this study we evaluate the long‐term impact of Viscum album subsp. austriacum on the woody‐plant community of a Mediterranean pineland. This mistletoe remains several years on the same host, exerting long‐lasting, spatially concentrated effects on community and ecosystem characteristics. Mistletoe concentrates zoochorous seeds and induces changes in the soil fertility and light availability beneath the canopy of parasitized trees, which have the potential to facilitate zoochorous–plant colonization, recruitment, and growth at the same time as it weakens the host. Here, we analyse whether mistletoe‐driven changes could result in a nucleus of zoochorous woody plants nourished by the abundant organic detritus accumulated under the host. We also analyse whether mistletoe effects can expand after host death. We selected unparasitized, parasitized, and dead parasitized Pinus nigra trees, in which we studied the joint effect of mistletoe‐mediated changes in soil nutrient and light availability, with the seed rain, seed predation, seedling establishment, plant recruitment, and plant growth. Light‐ and soil‐nutrient resources were greater under parasitized trees, and intensified after host death. The seed rain was maximum under parasitized trees, where seedling recruitment proved more likely. Sapling density, richness, and growth increased with the development of parasitism. Our findings show that V. album exerts a strong and lasting impact on the structure and dynamics of Mediterranean pinelands, with parasitized trees acting as centres for the establishment and growth of colonizing fleshy‐fruited woody species, which, over the long term, promote vegetation shifts by limiting dominant pine trees and facilitating less represented fleshy‐fruited shrubs. A plain language summary is available for this article.

Understory host plant and insect gall diversity changes across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest

ABSTRACT Topographic gradients in terra firme forests are associated with pronounced changes in soil texture, soil nutrients and distance to the water-table, thereby creating different hydric and nutritional conditions for plants and their associated herbivore community. The aim of this study was to investigate galling species and host plant richness and gall species composition across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest. Nineteen 250 x 3 m plots were randomly sampled in the valley, slope, plateau-slope transition, and plateau habitats in terra firme forests. All individual dicotyledonous plants 1 to 3 meters high were examined for the presence of insect galls. Galling species and host plant richness differed significantly among the studied habitats and were higher in slope habitats (drier habitats), as expected. More humid areas (valleys) showed the lowest richness of galling species, and a lower number of understory host plants. PERMANOVA and PERMDISP results demonstrated that the gall species composition differed significantly in the valley, slope, plateau-slope transition, and plateau areas. However, these structural differences in species composition could be due to unequal dispersion of variability among forest habitats. Our data suggested that spatial heterogeneity, such as a mosaic of local water status and nutrient availability resulting from the topographic conditions, can affect host plants and their associated galling insects.

Wheat cover crop promoted cucumber seedling growth through regulating soil nutrient resources or soil microbial communities?

Although biomass and yield increase of plant following cover crops is often observed in intensive vegetable production systems, clear understanding of the mechanisms driving such stimulatory effects is still poor. Effects of wheat cover crop on cucumber seedling growth were studied by 1) adding nutrients to balance difference in soil nutrients caused by planting wheat, 2) adding activated carbon, residue washing and burning to remove secondary metabolites from root exudates and litter decomposition of wheat, 3) soil sterilization and soil biota inoculation to validate the role of changes in soil biota induced by wheat. Wheat cover crop increased cucumber seedling growth and plant N, P and K concentrations, but decreased soil available N, P, K, Mn and B contents. Cucumber seedling growth decreased after eliminating the difference in soil nutrients, removing secondary metabolites and sterilizing soils. Feedback effects of soil biota on cucumber seedling growth were positive. Wheat cover crop increased the diversity of soil bacterial and fungal community, changed the structure and composition of Pseudomonas spp., and decreased the abundances of Bacillus and Pseudomonas spp. Wheat cover crop promoted cucumber seedling growth by changing soil nutrient availability and regulating soil microbial community diversity.

Response of soil sulfur availability to elevation and degradation in the Wugong Mountain meadow, China

Vegetation restorations of degraded meadows have been widely implemented. The evaluation of soil nutrient changes as affected by degradation is vital for efficient restorations. However, while macronutrients (nitrogen, phosphorus and potassium) have been widely investigated, sulfur (S) as one important element correlated tightly with other nutrients has not been thoroughly studied. Two studies were conducted to determine changes of sulfur as affected by degradation and elevation gradients. The results showed that available S (AS) changed non-linearly with elevation and the first principal component based on other soil nutrient variables. Soil AS depended on degradation levels and contributed substantially to the separation of meadows with different degradation levels. Moreover, AS responded stronger to changes in elevation gradients and degradation levels compared with other major nutrients. Thereby, AS could be an important nutrient responding to meadow disturbance, which should be considered in future studies on meadow soil nutrients cycling and vegetation restorations. The findings have implications for ecological restoration of degraded meadows with respect to soil nutrient management and conservations.

Plant-soil feedbacks in declining forests: implications for species coexistence.

Plant-soil feedbacks (PSFs) play a relevant role as drivers of species abundance, coexistence, and succession in plant communities. However, the potential contribution of PSFs to community dynamics in changing forest ecosystems affected by global change drivers is still largely unexplored. We measured the direction, strength and nature (biological vs. chemical) of PSFs experienced by coexisting tree species in two types of declining Quercus suber forests of southwestern Spain (open woodland vs. closed forest) invaded by the exotic soil pathogen Phytophthora cinnamomi. To test PSFs in a realistic community context, we focused not only on individual PSFs (i.e., comparing the growth of a tree species on conspecific vs. heterospecific soil) but also calculated net-pairwise PSFs by comparing performance of coexisting tree species on their own and each other's soils. We hypothesized that the decline and death of Q.suber would alter the direction and strength of individual and net-pairwise PSFs due to the associated changes in soil nutrients and microbial communities, with implications for recruitment dynamics and species coexistence. In support of our hypothesis, we found that the decline of Q.suber translated into substantial alterations of individual and net-pairwise PSFs, which shifted from mostly neutral to significantly positive or negative, depending on the forest type. In both cases however the identified PSFs benefited other species more than Q.suber (i.e., heterospecific positive PSF in the open woodland, conspecific negative PSF in the closed forest). Our results supported PSFs driven by changes in chemical soil properties (mainly phosphorus) and arbuscular mycorrhizal fungi, but not in pathogen abundance. Overall, our study suggests that PSFs might reinforce the loss of dominance of Q.suber in declining forests invaded by P.cinnamomi by promoting the relative performance of non-declining coexisting species. More generally, our results indicate an increase in the strength of net PSFs as natural forests become disturbed by global change drivers (e.g., invasive species), suggesting an increasingly important role of PSFs in forest community dynamics in the near future.

Soil nutrient changes induced by the presence and intensity of plateau pika (Ochotona curzoniae) disturbances in the Qinghai-Tibet Plateau, China

The plateau pika (Ochotona curzoniae), one of the main bioturbators, creates extensive disturbances in the soil of the alpine meadow of the Qinghai-Tibet Plateau (QTP). This study investigated the effects of the presence and intensity of plateau pika disturbances on the main soil nutrients of the Kobresia pygmaea meadow across three study sites in the QTP by using the method of counting the active burrow entrance densities of plateau pika in the field as a representation of the disturbance intensity. Our results showed that the presence of plateau pika significantly increased the soil total nitrogen (TN), soil organic carbon (SOC) and total phosphorus (TP) concentrations and decreased the available phosphorus (AP) concentrations across the three study sites. The presence of plateau pika increased the NO3−-N and NH4+-N concentrations in Luqu County and Maqu County, but had no significant effect on these concentrations in Gonghe County. The soil TN, SOC and TP concentrations showed a downward parabola and the NO3−-N, NH4+-N and AP concentrations showed an upward parabola as the intensity of the disturbances increased in Luqu County and Maqu County. These soil nutrients had a threshold (inflection point) of 475 (475±90) burrow entrances per ha. However, the soil TN, SOC and TP concentrations increased linearly while the NO3−-N, NH4+-N and AP concentrations decreased linearly with the increasing intensity of disturbances in Gonghe County (≤512 burrow entrances per ha). These results implied that the soil nutrient changes induced by plateau pika disturbances are not only related to their presence but are also related to the intensity of the disturbances, and that the most appropriate disturbance intensity (475 (475±90) burrow entrances per ha) of plateau pika was beneficial to the storage of soil carbon and nitrogen in the alpine meadow in the QTP.

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.

Changes in soil nutrients after 10 years of cattle manure and swine effluent application

Application of cattle manure and swine effluent to cropland builds nutrient pools, affects soil quality, and increases crop productivity. The objective of the present study was to evaluate the rate of change in soil nutrient concentration and soil chemical properties due to cattle manure and swine effluent application. The study was conducted from 1999 to 2008 near Tribune, KS, with 10 treatments (three levels each of cattle manure and swine effluent [P, N, and 2N], three levels of N fertilizer, and a control). Soil NO3-N, P, K, micronutrients, pH, and EC were measured annually. Swine P treatment resulted in significantly greater NO3-N concentration in most years compared with all other treatments, followed by the Cattle 2N and Swine 2N treatments. The cattle treatments, in the order Cattle 2N>Cattle N>Cattle P, built the total N, soil P, and total C level significantly over the years compared with all other treatments. Soil pH did not change over time for most treatments except for the Swine P and Swine 2N treatments. Soil K, Cl, Fe, Zn, and Cu concentration increased significantly in cattle and swine treatments in 2008 compared with their initial level in 1999, and compared with check and inorganic fertilizer treatments. A significant build up in soil nutrients due to cattle and swine nutrient application suggests that they are good sources of many essential nutrients, in places where nutrients are limiting, but can cause excessive accumulation and increased environmental risk. A quick build up from Cattle 2N and Swine P applications calls for lower rates and periodic soil tests to determine need for further applications.

Fortified cassava peel compost amendment for Amaranthus: Influence on plant growth, nutrients uptake and on soil nutrient changes

ABSTRACTNutrient supply through organic sources usually requires fortification for timely and optimum release of plant nutrients to achieve optimum crop performance. A pot experiment was conducted in a screen house to determine the optimum rate of cassava peel compost (CPC) fortification that supports optimum Amaranthus (Amaranthus cruentus L.) plant nutrient contents and residual soil nutrient contents. A compost of cassava peel and poultry manure was applied at 2.5; 5.0 and 7.5 t ha−1each complemented with either 25 or 50 kg nitrogen (N), using nitrogen, phosphorus and potassium (NPK) 20-10-10 at 2 weeks before sowing Amaranthus. An unfertilized treatment served as control. Seeds were sown in plastic containers with a surface diameter of 24 cm filled with 5 kg soil, with a drain underneath. Seedlings were thinned to 4 plants/pot 2 weeks after planting. Plants were harvested at 5 weeks by ratooning and plant re-growth also harvested after 5 weeks. Soil pH was lower with high rates of 5.0 and 7.5 t ha−1 CPC while the organic matter content was increased with increased CPC rate. Soil N was reduced but reflected in increased plant shoot and root N, with compost application. Soil P was generally increased but was not reflected in plant contents. Soil K contents were reduced and were reflected in increased plant contents. Application of 2.5 t ha−1 CPC, fortified with either 25 or 50 kg N ha−1 gave the optimum Amaranthus shoot nutrient contents with optimum residual soil nutrient contents.

Influence of the Application of Non-Hazardous Sewage Sludge on the Evolution of Soil Carbon Pool and Carbon Pool Management Index

The products of non-hazardous commercial sewage sludge were utilized in the accordance of the national standard in the experiment with sandy fluvo-aquic soil under wheat-maize rotation system during 2013 to 2015. The experiment focused on the effects of the use of non-hazardous sewage sludge on soil carbon pool and carbon pool management index to provide theoretical and technical basis for the resource utilization of non-hazardous sewage sludge. The results showed that compared with CK, soil amended sludge significantly improved soil total organic carbon (TOC), soil microbial biomass carbon (SMBC), labile organic carbon (LOC),and dissolved organic carbon (DOC) to 8.40-14.74 g·kg-1, 164.45-257.45 mg·kg-1, 3.58-4.88 g·kg-1and 81.16-101.58 mg·kg-1, soil amended sludge significantly enhanced SMBC, LOC and DOC by 84.00%-188.07%, 26.26%-58.03%, and 109.58%-185.39% (P<0.05) respectively, and 45 t·hm-2 sewage sludge (W3) had the most significant impact on soil carbon pool. The soil microbial entropy (SMBC/TOC), and utilization of labile organic carbon (LOC/TOC) increased by 8.02%-2.77% and 13.75%-46.48% respectively, and the utilization of dissolved organic carbon (DOC/TOC) significantly decreased by 153.45%-195.40% (P<0.05). SMBC/TOC, LOC/TOC, and DOC/TOC declined in treatments of soil amended sludge due to increased application of sewage sludge, which indicated that soil amended with 45 t·hm-2 of the sewage sludge improved the content of stable carbon resulting in the decease of the ratio. L and LI decreased with the increasing amount of sewage sludge indicating that soil amended with 45 t·hm-2 of the sewage sludge improved the content of stable carbon and was conducive to the accumulation of organic carbon. Soil amended with sludge significantly increased carbon pool management index (CMPI) by 153.45%-195.40% (P<0.05), and W3 had the most significant effect on CMPI. Compared with TOC, CMPI could be more sensitive and direct to reflect the dynamic changes of soil nutrients and carbon pools through the correlation analysis and redundancy analysis. In summary, the application of 15-45 t·hm-2 sewage sludge could significantly enhance the soil carbon pool and carbon pool management index, especially 45 t·hm-2 sewage sludge (W3).

Nutritive Value and Nutrient Uptake of Summer‐Active and Summer‐Dormant Tall Fescue under Different Broiler Litter Rates

Core Ideas The nutrient value of broiler litter in tall fescue was compared with NPK fertilizer. Nutrient uptake was similar between a summer‐dormant and two summer‐active ecotypes. Flecha summer‐dormant produced more forage in early season that was less digestible. A rate of 9.0 Mg litter per ha appeared to optimize forage yield and nutritive value. Recommendations are provided for minimizing excess manure nutrients in tall fescue. Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] responds to broiler litter fertilization; however, data concerning the summer dormancy trait are not available. This 3‐yr study (2006–2008) determined the nutrient value of litter compared with commercial fertilizer (CF) and associated changes in soil nutrients as affected by degree of fescue summer dormancy. Litter rates of 0, 4.5, 9.0, 13.4, and 17.9 Mg ha−1 yr−1 (as‐is moisture basis) and CF (2:1:2 ratio of N/P2O5/K2O, respectively) were split‐applied in autumn and spring, and forage was harvested at early, mid‐, and late season. At early and mid‐season harvests, forage digestibility exceeded 708 g kg−1 and cultivar Flecha summer‐dormant had greater dry matter (DM) yield, less crude protein (CP) and similar uptake of N and P, as compared with cultivars Jesup and Kentucky 31 summer‐active tall fescue. Phosphorus uptake increased linearly from 2 to 19 kg ha−1 across litter rates and was approximately 17 kg ha−1 with CF. Per megagram (Mg) of applied litter, ranking of slopes for cumulative DM and nutrient uptake in 2008 was Kentucky 31 &gt; Flecha &gt; Jesup and slope for CP was least in Flecha. While 9.0 Mg litter ha−1 appeared to be the optimum rate to achieve high nutritive value and DM yield, soil test P in 2008 was lower (P &lt; 0.05) with CF or 0 Mg litter ha−1 than 4.5 or 9.0 Mg litter ha−1 (approximately 33.5 vs. 57.5 mg kg−1). Flecha summer‐dormant appeared to offer an early season productivity benefit and annual nutrient uptake comparable to summer‐active tall fescue.

Depletion of carbohydrate reserves limits nitrate uptake during early regrowth in Lolium perenne L.

The mechanisms linking C/N balance to N uptake and assimilation are central to plant responses to changing soil nutrient levels. Defoliation and subsequent regrowth of grasses both impact C partitioning, thereby creating a significant point of interaction with soil N availability. Using defoliation as an experimental treatment, we investigated the dynamic relationships between plant carbohydrate status and NO3--responsive uptake systems, transporter gene expression, and nitrate assimilation in Lolium perenne L. High- and low-affinity NO3- uptake was reduced in an N-dependent manner in response to a rapid and large shift in carbohydrate remobilization triggered by defoliation. This reduction in NO3- uptake was rescued by an exogenous glucose supplement, confirming the carbohydrate dependence of NO3- uptake. The regulation of NO3- uptake in response to the perturbation of the plant C/N ratio was associated with changes in expression of putative high- and low-affinity NO3- transporters. Furthermore, NO3- assimilation appears to be regulated by the C-N status of the plant, implying a mechanism that signals the availability of C metabolites for NO3- uptake and assimilation at the whole-plant level. We also show that cytokinins may be involved in the regulation of N acquisition and assimilation in response to the changing plant C/N ratio.

Optimizing Utilization of Palm Oil Mill Effluent and its Influences on Nutrient Availability and Soil Organic Matter on Ultisols

Optimizing the utilization of agroindustrial organic waste such as palm oil mill effluent (POME) can prevent environment pollution and soil nutrient cycling can be a valuable alternative to improve soil quality. The objective of this study was to evaluate the changes of soil organic fractions and nutrients after application of treated palm oil mill effluent. The treatments consisted of control and effluent application at rates of 5, 10, 15 and 20 ton ha -1 . The treatments were arranged in a completely randomized design with three replications. Application of effluent significantly increased total organic C, labile organic C, humic acid C, pH, total N, available P, and exchangeable K. A significant reduction of exchangeable Al also occurred with effluent application. The increases of total organic C and labile organic were found with the application of 20 t ha -1 of effluent, but the increase was not significant compared to the effluent application at rates of 10 and 15 t ha -1 . Sensitivity indexes of total organic C, labile organic C and humic acid C following effluent application were 24-66%, 103-197% and 95-114% respectively in which labile organic C showed the highest sensitivity index. Total organic C, labile organic C and humic acid were positively correlated with increasing rates of effluent application. Labile organic C revealed the strongest relationship (R 2 =0.91) with effluent application compared to total organic C (R 2 =0.88) and humic acid (R 2 =0.67). A significant increase of total N was only found by the effluent application at rate of 20 t ha -1 . Significant increases in available P and exchangeable K occurred at rate of 10, 15 and 20 t ha -1 . It can be concluded that the increase in soil organic carbon levels was related to the amount of organic (effluent) input added to the soil. In addition, the application of treated effluent can improve soil pH and nutrient availability.

Wildfire impact: Natural experiment reveals differential short-term changes in soil microbial communities

A wildfire which overran a sensor network site provided an opportunity (a natural experiment) to monitor short-term post-fire impacts (immediate and up to three months post-fire) in remnant eucalypt woodland and managed pasture plots. The magnitude of fire-induced changes in soil properties and soil microbial communities was determined by comparing (1) variation in fire-adapted eucalypt woodland vs. pasture grassland at the burnt site; (2) variation at the burnt woodland-pasture sites with variation at two unburnt woodland-pasture sites in the same locality; and (3) temporal variation pre- and post-fire. In the eucalypt woodland, soil ammonium, pH and ROC content increased post-fire, while in the pasture soil, soil nitrate increased post-fire and became the dominant soluble N pool. However, apart from distinct changes in N pools, the magnitude of change in most soil properties was small when compared to the unburnt sites. At the burnt site, bacterial and fungal community structure showed significant temporal shifts between pre- and post-fire periods which were associated with changes in soil nutrients, especially N pools. In contrast, microbial communities at the unburnt sites showed little temporal change over the same period. Bacterial community composition at the burnt site also changed dramatically post-fire in terms of abundance and diversity, with positive impacts on abundance of phyla such as Actinobacteria, Proteobacteria and Firmicutes. Large and rapid changes in soil bacterial community composition occurred in the fire-adapted woodland plot compared to the pasture soil, which may be a reflection of differences in vegetation composition and fuel loading. Given the rapid yet differential response in contrasting land uses, identification of key soil bacterial groups may be useful in assessing recovery of fire-adapted ecosystems, especially as wildfire frequency is predicted to increase with global climate change.

Effects of long-term experimental warming on plant community properties and soil microbial community composition in an alpine meadow

Climate change is likely to alter the relative abundances of plant functional groups and the interactions between plants and soil microbes that maintain alpine meadow ecosystems. However, little is known about how warming-induced alterations to aboveground biomass (AGB) affect soil nutrients and microbial communities. We investigated plant community characteristics in 2002-2009 and analyzed soil properties and the soil microbial community in 2007-2009 to study the effects of warming in Qinghai Province, China. Sampling involved the use of warmed open top chambers, the monitoring of plant community characteristics, the quantification of total and available amounts of soil nutrients, and the evaluation of microbial community composition using phospholipid fatty acid (PLFA) analysis. Experimental warming initially significantly increased the number of plant functional groups and plant community AGB; however, plant community diversity and species richness decreased. Nevertheless, all these variables stabilized over time. Fungal and bacterial abundance, total nitrogen, available nitrogen and soil organic matter increased with warming, while microbial PLFAs decreased. These findings demonstrated that climate change drivers and their interactions may cause changes in soil nutrients and the abundance and content of soil microbial PLFAs. Elevated temperature has strong effects on aboveground grass biomass. Surface conditions and disturbance affect the soil microbial communities of deep soil layers.

Realistic soil-heating gradient temperature linearly changes most of the soil chemical properties

ABSTRACTSoil heating is a key factor in changing the biological and physicochemical properties of soil. Extensive experiments have been conducted to identify the heating effects on soil properties. However, selecting temperature and time of exposure are critical in laboratory experiments. Herein, a realistic soil-heating gradient was applied to detect soil nutrient changes. This realistic soil-heating gradient is adequate to linearly change most of the soil chemical properties (~70% of the nutrient evaluated). Overall, peak temperature is more important in inducing chemical changes in the soil than time of exposure is. Furthermore, nutrient release is closely connected to the gradient temperature and groups of nutrients are either released or depleted at certain heating temperatures. Soil organic matter (SOM) begins to be depleted at a low temperature of 250°C. In addition, its reduction affects, to the same extent, the cation exchange capacity. Overall, the moderate temperature of 350°C results in optimum improvement of soil nutrients.

Frequent fires reduce the nutritional quality of Sorghum stipoideum seed, a keystone food resource for the Gouldian finch (Erythrura gouldiae)

Fire is a pervasive feature of the tropical savannas of northern Australia. Increasingly extensive and intensive fires have had an adverse effect on grass layer diversity. Reduced grass species diversity and abundance are important correlates of the decline of granivores in these tropical savannas. The Gouldian finch (Erythrura gouldiae), an endangered species that is endemic to northern Australia, is particularly vulnerable to changes to the grass layer as its diet comprises only grass seed, and it relies mostly on Sorghum stipoideum during the breeding season. Although this annual grass species is abundant at breeding sites, the finches do not always choose to breed at these sites, raising the possibility that seed quality may vary from year to year. This study examines the effect of fire (time since last fire; fire frequency) on soil fertility and seed nutritional quality. We hypothesise that recently burnt sites produce a flush of soil nutrients and Sorghum stipoideum seed at these sites is of higher nutritional quality. Furthermore, we posit that frequently burnt sites become depleted of soil nutrients and their seeds are of lower nutritional quality. There was a significant increase in inorganic nitrogen in soils following a fire, but no notable change in other soil nutrients. Contingent on this increase in soil inorganic nitrogen, seed nutrient levels, particularly essential proteins, were greater at sites that were recently, but infrequently burnt. Fires appear to affect soil nitrogen and in turn seed nutrition, providing a plausible explanation for why Gouldian finches choose recently, but infrequently burnt breeding sites.