Soil Pools Research Articles

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy (MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, and established eighteen 20 ​m ​× ​20 ​m plots in each rainforest. Six nitrogen (N) and phosphorus (P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon (C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall, distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECM-dominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECM-dominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

Invasive snails alter multiple ecosystem functions in subtropical wetlands

Invasive species that compromise ecosystem functioning through direct and indirect (or cascading) pathways are a rising global threat. Apple snails (Pomacea spp.) are semi-aquatic freshwater invaders that have exerted devastating ecological and economic impacts on agricultural wetlands and are emerging as a major threat to the structures and functions of natural wetlands. In this research, we conducted a field mesocosm experiment in subtropical wetlands in Florida, USA to investigate how P. maculata alter a suite of wetland vegetation, water, and soil processes and how these effects vary across wetlands under two different management intensities. Overall, we found that invasive snails substantially decreased aboveground biomass and vegetation cover and exhibited preferential feeding on wetland plant species. In addition, snails increased water nutrients (e.g., total carbon, nitrogen, phosphorous and dissolved solids), but showed minimal impacts on soil pools and processes. While most effects of invasive P. maculata were similar across wetland types, certain responses (e.g., algal biomass) were divergent. Our study provides holistic evidence on multiple direct and indirect consequences of invasive apple snails along the wetland plant-water-soil continuum. By altering plant assemblages and nutrient cycling (e.g., via consumption, egestion, and excretion), P. maculata invasion could hamper vital wetland services, which is concerning for these globally vulnerable ecosystems. Differential snail effects across management intensities further suggest the need for tailored actions to mitigate apple snail impacts and conserve wetland ecosystems.

Spatial Variations in Organic Carbon Pools and Their Responses to Different Annual Straw Return Rates in Surface Paddy Soils in South China

To identify the effects of straw return on different organic carbon pools in surface paddy soils (0–20 cm), a total of 33 soil samples under different annual straw return rates (SRr) was collected, and then the samples were analyzed based on a 100-day incubation. The data from acid hydrolysis-incubation experiments were fitted to a three-pool first-order kinetics model that divided soil organic carbon (SOC) into active (Ca), slow (Cs) and resistant (Cr) pools. The results showed that the mean pool sizes of Ca, Cs, and Cr were 0.27, 10.26, and 13.46 g·kg−1, representing a mean of 1.35%, 41.91%, and 56.74% of the total SOC (TOC), respectively. The SOC pools in the surface paddy soils in Dongxiang had a small Ca pool but had longer mean residence times of the Ca and Cs pools than those in other regions in China. The three carbon pools were less affected by the paddy soil type but showed obvious spatial variations. The SRr contributed a strong positive effect on the variability of Cs and Cr, especially on Cs variability, while it had very little effect on Ca variability. Soil available nitrogen dominated the variability in TOC and Cr compared to the other soil properties. Therefore, the Cs pool is more sensitive than the other carbon pools to long-term straw return.

Effect of land use change on carbon stocks in an agricultural region of southern Benin

AbstractLand use change is one of the most important determinants of carbon storage and dynamics in ecosystems. Areas in the proximity of metropoles undergo land use changes but are poorly studied for their soil and biomass carbon budget, especially in Africa. Close to Benin's economic capital, the Lama Territory located on the Allada Plateau and is subject to high demographic and urbanization pressures. Carbon (C) stocks in the region are likely to be rapidly changing. This research assessed the land use changes and quantified the spatial distribution and variation of C stocks between 2000 and 2018 on the Ferralsols of the study area. Random forest models using spectral bands of LANDSAT images and some spectral indices as predictors were calibrated to classify the land use. C stocks of four C pools (aboveground, belowground biomass, litter, and soil) were mapped with InVEST (integrated valuation of ecosystem services and tradeoffs) model. Land use change occurred in 61% of the Ferralsol area between 2000 and 2018. The surface of forests and crop‐plantation associations decreased in benefit of tree plantations, adult palm groves, and built‐up areas. With the loss of forest surface and the increasing urbanization, C stocks of the region decreased by −218 Gg C with 4% uncertainty (−175 Gg C in soil pools, and − 125 Gg C in aboveground biomass with both 6% uncertainty) between 2000 and 2018. Results highlight: (i) the need for soil C stock accounting to avoid underestimation of C stocks evolution in a rural region; and (ii) the relevance of tree plantations and deforestation control to maintain the C stocks in tropical areas.

Shifts in soil phosphorus fractions during seasonal transitions in a riparian floodplain wetland

Losses of phosphorus from soil to surface waters in agricultural areas have been linked to substantial declines in water quality. Riparian wetlands can potentially intercept phosphorus mobilized from upland soils before it reaches connecting waterways, but the capacity of wetlands to buffer against downstream losses of P is poorly understood, especially in northern temperate zones. In these regions, the spring freshet releases large volumes of water from snowmelt and soil pore water during the time when microbial productivity, which transfers available P into biomass, is low. In addition, losses of P in runoff may be exacerbated by freeze-thaw cycling (FTC) in soil during late winter and early spring through the physical degradation of organic matter. We investigated P dynamics from late fall through spring thaw and into summer to assess P transfers between inorganic, organic and microbial biomass pools, as functions of season and distance from a river. The site is located on the Grand River in southern Ontario, which discharges to Lake Erie, and consists of riparian wetland and wooded areas. Reactive P (Olsen P) and microbial biomass P (PMBIO) increased with distance from the river and varied more over time in the wetland soil compared to the adjacent wooded area, reflecting higher variability in vegetation, topography and hydrology. The positive correlation between microbial biomass P and microbes linked to ammonification supports the release of N and P through mineralization pathways as spring progresses, with microbial biomass decreasing in June as plant growth increases. There was evidence for leaching of Fe and Al, and lower concentrations of total P, in the transect proximate to the river. Seasonal flooding during spring thaw contributed to a pulse of dissolved reactive P, but temperature monitoring showed that the wetland soil did not experience freeze-thaw cycling. Investigation of FTC using wetland soil in mesocosms indicated that multiple FTC (>3) were necessary to increase the pool of reactive soil P, with the highest amount of soil reactive P observed after six FTC, when dissolved reactive P also tended to increase.

Long-term changes in soil composition in unmanaged central European mountain spruce forests after decreased acidic deposition and a bark beetle outbreak

We studied the effect of tree mortality on nutrient concentrations and pools in soils of two unmanaged mountain forest catchments (Plešné, PL; and Čertovo, CT; Czech Republic) recovering from acidification due to decreasing acidic atmospheric deposition since the late 1980s. Both catchments were situated at similar elevation, and before a bark beetle outbreak were covered by healthy mature Norway spruce (Picea abies) forests. However, differing bedrock [granite (PL) vs mica-schist and quartzite (CT)] resulted in lower concentrations of base cations (except for magnesium), but higher concentrations of aluminium and iron oxyhydroxides in the CT soils, enabling higher phosphorus (P) accumulation. Despite these differences, soils were similarly acidic, with pHH2O from 3.5 to 4.3 and cation exchange capacity (CEC) dominated by exchangeable protons (H+ex) and aluminium in both catchments in 2000. In the PL catchment, >75 % of mature spruce trees died after a bark beetle infestation between 2004 and 2008, and all dead biomass was left on site. Forest damage in the CT catchment was minor. Soil concentrations and pools of exchangeable calcium (Ca2+ex), magnesium (Mg2+ex), potassium (K+ex), and H+ex were tightly related to concentrations of organic carbon (C). Following the tree dieback in the PL catchment, we observed significant (p < 0.05) increases in (1) concentrations and pools of Ca2+ex, Mg2+ex, and K+ex, (2) base saturation (from 30 to ∼ 40 %), (3) CEC:C ratios (i.e., CEC of soil organic carbon), (4) pHH2O, (5) mineral P forms, and (6) total nitrogen (N) in the upper (O and A) soil horizons. Similar changes were less pronounced or negligible in the less impacted CT soils. The elevated litterfall after tree dieback, resulting in the increased input of base cations to forest floor and increased CEC of soil organic C, played a more important role in the decreasing acidity of the PL soils than the continuing decrease in acidic deposition.

Soil colloidal particles in a subtropical savanna: Biogeochemical significance and influence of anthropogenic disturbances

Soil colloids (diameter < 1000 nm) are comprised mainly of clay minerals and organic matter, and play major roles in determining ion exchange capacity and in regulating key biogeochemical processes. Consequently, it is important to understand how soil colloids and their functions are influenced by land cover and anthropogenic disturbances. In grasslands, savannas, and other dryland ecosystems across the globe, woody plants are encroaching due to livestock grazing, fire suppression, elevated CO2 concentrations, and climate change. These major land cover changes could influence soil colloidal properties, with implications for soil C, N, and P cycles. We assessed how woody encroachment, livestock grazing, and fire interact to influence soil colloidal properties in a juniper-oak savanna. Surface soils (0–10 cm) from the southern Great Plains (Texas, USA) were collected from long-term treatments differing in grazing intensity (none, moderate, and heavy) and fire history. Within each treatment, soil samples were taken under grass, juniper, and oak canopies. Water dispersible soil colloids (WDC, d < 500 nm) were isolated and analyzed by asymmetric flow field-flow fractionation and their P species by liquid-state 31P-nuclear magnetic resonance spectroscopy (31P NMR). Soil beneath oak and juniper canopies had smaller WDC and elevated colloidal organic carbon (OC) and P concentrations, especially in nanocolloid (<30 nm) and fine colloid (30–160 nm) size fractions. Woody encroachment enriched Ca, Fe, Al, Si and Mg in WDC in the ungrazed control, but not in any of the other grazed or burned areas. Colloidal soil P mainly occurred as orthophosphate and orthophosphate diesters, and was present as OC-Ca-P complexes in fine and medium colloid fractions (30–500 nm), while P in the nanocolloid fraction (<30 nm) was in direct association with Ca. Moderate grazing did not affect the retention of colloidal P, while heavy grazing potentially increased the loss risk of colloidal P. Fire accelerated soil P loss from colloid fractions only in woody areas. Our findings highlight that woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils.

Changes in ecosystem nutrient pools through stand development following whole-tree harvesting of jack pine (Pinus banksiana) on sandy, nutrient poor soils in northern Lower Michigan

We used a 10-site, 42-year chronosequence of jack pine (Pinus banksiana) plantations to study the changes in ecosystem nutrient pools following whole-tree harvesting (WTH) on sandy soils. We developed locally-derived allometric equations to predict nutrient contents of jack pine as a function of diameter at breast height and used these to estimate the amount of nitrogen (N), calcium (Ca), potassium (K), magnesium (Mg), and phosphorus (P) stored in aboveground biomass. In addition, we quantified total N, Ca, K, Mg and P in surface organic horizons, plant-available nutrient pools in mineral soils and leaching losses of nutrients for four years post harvest. Finally, we constructed simple input–output nutrient balances accounting for harvest removals at varying ages, post-harvest leaching losses and nutrient inputs from atmospheric deposition and weathering under varying scenarios of harvest intensity and frequency. Nutrient accumulation in aboveground biomass followed a sigmoidal pattern with a period of rapid accumulation between ages 10–20 y, a period of slowing accumulation between 20 and 30 y to an apparent asymptote from 30 y onward. Our estimates of asymptotic aboveground nutrient stocks for these plantations were highest for N (263 kg ha−1), intermediate for K and Ca (112 and 95 kg ha−1) and lowest for Mg and P (22 and 17 kg ha−1). Nutrients in forest floor materials increased from our youngest stand (4 y post harvest) with no signs of slowing accumulation in older stands. We observed weak trends of increasing soil nutrient availability across our chronosequence; however, variability was high both within and among stands. The business-as-usual scenario of WTH and planting on a 50-y rotation had a positive input–output balance for all nutrients with the exception of K, where outputs over this rotation exceeded inputs by 54 kg K ha−1. Shifting to a bole-only harvest improved the nutrient balance for all elements considered and shifted K to a net positive balance of 32 kg K ha−1. Scenarios designed to maximize production of biomass energy with WTH on shorter rotations exacerbated the K imbalance, with net losses of 72 and 63 kg K ha−1 for 30- and 20-y rotations, respectively.

Elucidating Heavy Metals Concentration and Distribution in Wild Edible Morels and the Associated Soil at Different Altitudinal Zones of Pakistan: a Health Risk Implications Study.

This study evaluates macro-nutrient (MN) and prevailing heavy metal (HM) concentrations in wild edible morels (WEM) species viz., Morchella crassipes, Morchella pulchella, and Morchella eohespera and the associated soil that were collected from different altitudinal zones (Azad Kashmir, Murree, Swat, and Skardu) of Pakistan. A special emphasis on potential health risk analysis for HM in WEM consumption was also explored. In general, MN concentration in fruiting bodies and their associated soil samples were in the following order: potassium (K) > magnesium (Mg) > calcium (Ca) > sodium (Na) and Ca > Mg > K > Na, respectively. The concentration for HM in WEM ranged between 20.0 and 78.0mg/kg, 1.09 and 22.1mg/kg, 2.1 and 22.1mg/kg, 0.26 and 13.1mg/kg, 0.43 and 9.1mg/kg, 1.07 and 7.0mg/kg, 1.01 and 5.4mg/kg, and BDL and 3.1mg/kg for zinc (Zn), copper (Cu), nickel (Ni), manganese (Mn), cobalt (Co), chromium (Cr), lead (Pb), and cadmium (Cd), respectively, and those in underlying soil samples, lowest and highest HM concentration were recorded for Zn (33.7-113.6mg/kg), Cu (13.0-40.8mg/kg), Ni (3.1-23.0mg/kg), Pb (1.3-22.0mg/kg), Co (2.9-5.6mg/kg), Cr (2.7-11.1mg/kg), Mn (2.0-7.1mg/kg), and Cd (1.1mg/kg 7.6). Although, Cd, Pb, and Zn concentrations in some of the WEM samples and Cd in the soil had exceeded the permissible limits set by different organizations. The greater accumulation/or transfer potential for Zn, Co, Ni, and Cu were recorded in WEM from their associated soil. The health risk index (HRI) for HM in all assessed samples of WEM was < 1, predicting no risk to the consuming population. Furthermore, the correlation analyses depicted that the power of hydrogen (pH), low organic matter contents, and sandy texture are likely to be responsible for HM transfer to the lower pool of soil. But the increasing concentration of HM in WEM warrants threats and suggests further monitoring and future policy plan and implementation to avoid the potential health risks via its regular consumption.

The relationship between succession and reclamation of desertified areas in artificial forests of Calligonum spp. in an arid desert of southeastern Iran

This research investigates the association between the succession and restoration of degraded land in the southeast of Iran with artificial Calligonum forests regarding vegetation changes, soil properties, carbon (C) and nitrogen (N) pools in vegetation and soil. Eight forestry sites were selected, aged 1, 4, 6, 9, 11, 16, 25, and 30 years. Observations indicated that vegetation percentage, density, frequency, richness, and diversity of species substantially increased (p &amp;lt; 0.01). The highest percentage of vegetation (80.30%), density (62.70 n ha−1), richness (14.15), and diversity (0.90) was observed in the 30-year site. At the end of the succession phase under study (the 25- and 30-year sites), the variation trend of vegetation was steady. As the age of the forests increased, the soil nutrient values increased significantly during succession (p &amp;lt; 0.01), even though acidity and electrical conductivity (EC) did not change significantly over time (p &amp;gt; 0.01). In the early stages of succession, the soil’s C and N pools (aerial biomass, root, and litter) did not increase significantly (p &amp;gt; 0.01). Over time, however, C and N pools of the soil and plants increased (the highest amounts were seen in the 30-year site). The results indicated a significant difference in the soil and vegetation properties in the forestry sites. In general, planting native species and the succession of vegetation can play an effective role in preserving the environment in degraded lands and increasing the C and N pools.

Dispersed ice of permafrost peatlands represents an important source of labile carboxylic acids, nutrients and metals

Thawing of frozen organic and mineral soils and liberation of organic carbon (OC), macro- and micro-nutrients and trace elements from pore ice in high latitude regions represent a potentially important but poorly quantified retroactive linkage to climate warming. This is especially true for permafrost peatlands, occupying a sizable proportion of all permafrost territories and presenting a large and highly vulnerable stock of soil OC which can be subjected to fast thawing at currently circum-zero temperatures. The conventional method of assessing the labile water-soluble fraction of permafrost soils is aqueous extraction from dried soil. However, this technique does not allow collecting native ice present in soil pores and is therefore likely to underestimate or overestimate the pool of labile soil C and nutrients. Here, we present results of direct pore ice analyses performed on native peat cores from the western Siberia Lowland in comparison to the water extraction (10 and 100 gdry peat L-1) of soluble components from the same peat subjected to freeze drying. Aqueous leachates of permafrost peat from both thawed (0–45 cm) and frozen (45–130 cm) layers yielded high concentrations of DOC, nutrients, carboxylic acids and trace metals, comparable or higher to those in peat porewater and dispersed peat ice. We found strong (a factor of 3 to 30) enrichment in the frozen part of the core (below 45 cm, which is active layer depth) in dissolved OC, many carboxylates (acetate, formate, lactate, butyrate, propionate, pyruvate), inorganic nutrients (Si, P, N) and trace elements (Fe, Al, Mn, Zn, Sr and Ba). The dispersed ice which is present in peat below active layer represents highly labile reservoir of organic and inorganic nutrients which should be considered in permafrost thaw scenarios.

Impacts of the US southeast wood pellet industry on local forest carbon stocks

We assessed the net impacts of a wood-dependent pellet industry of global importance on contemporaneous local forest carbon component pools (live trees, standing-dead trees, soils) and total stocks. We conducted post-matched difference-in-differences analyses of forest inventory data between 2000 and 2019 to infer industrial concurrent and lagged effects in the US coastal southeast. Results point to contemporaneous carbon neutrality. We found net incremental effects on carbon pools within live trees, and no net effects on standing-dead tree nor soil pools. However, we found concurrent lower carbon levels in soils, mixed effects associated with increased procurement pressures and large mill pelletization capacity, and possible spillover effects on standing-dead tree carbon pools beyond commercial procurement distances. There is robust evidence that although some trade-offs between carbon pools exist, the wood pellet industry in this particular context and period has met the overall condition of forest carbon neutrality.

Effect of Tree Leaf Litterfall on available Nutrients and Organic Carbon Pools of Soil

A study was conducted to investigate the effect of leaf litterfall of shelterbelt, Azadirachta indica, Ailanthus excels and Prosopis cineraria and control (devoid of trees) on available nutrients and organic carbon pools of soil from 3 distances (2, 5 and 10m) The total litterfall during the study period ranged between 1712 and 4126kg/ha and it was found maximum in the month of January and it was minimum in February in different plantations. Annual litterfall showed considerable variation among different plantations. Litter accumulation under the different plantations canopy was highest in the shelterbelt followed by Prosopis cineraria and lowest in the Azadirachta indica. There was improvement in soil organic carbon, dissolved organic carbon, microbial biomass carbon, available macro (N, P and K) and micronutrients (Zn, Fe, Mn and Cu) tree species when compared to field without trees. Significant improvement in soil organic carbon (0.14 to 0.26 %), available N (55.9 to 116.6kg/ha) P (9.6 to 13.6kg/ha) and K (188.9 to 248.3kg/ha) was observed under these tree species compared to field without trees. The content of Zn, Cu, Fe and Mn and was 15, 25, 40 and 51 percent, respectively higher under these tree species than the control field. The amount of nutrients returned to the soils through litter was significantly highest at 2m distance under different plantations. The present study indicated that these available nutrients and organic carbon pools improved significantly across the different land use system. Due to intensive cultivation and monocropping, the fertility of soil is deteriorating day by day. Simultaneously it is creating a pressure on the natural resources like soil because the population is increasing day by day. Therefore, it is wise to use degraded and problematic soil for cultivation. Agroforestry systems have been recognized as an alternative for the rehabilitation of degraded areas and it provides ecosystem services and reduces human impacts on natural forests (Nair et al., 2009). Tree based land use systems have special role in reclamation of wastelands, use of poor-quality waters, organic carbon build up and moderating climate change related risks. In areas of Haryana and Rajasthan trees like Prosopis cineraria, Azadirachta indica and Ailanthus excels are more beneficial under adverse environments due to their drought hardiness, resistance to inhospitable climate and assured economic returns. These tree species can be grown on soils having poor fertility, moisture deficit and high soil temperature.

Rice-crayfish co-culture increases microbial necromass' contribution to the soil nitrogen pool

The rice-crayfish co-culture (RC) is a putative sustainable agricultural system. However, studies on the ecological effects of long-term RC systems were still lacking. Here, we compare enzymatic stoichiometry, microbial necromass, and microbial community between the RC and rice monoculture systems (RM). Soil enzymatic stoichiometry analysis showed that after transformation from RM to RC for about three years, ammonium nitrogen (NH4+-N) availability increased to depress relative N-acquiring enzyme production, especially for leucine aminopeptidase. The contents of microbial necromass increased approximately onefold in the RC system, making microbial necromass' contribution to the soil nitrogen (N) reach up to 46.72%. Elevation in NH4+ decreased N-acquiring enzyme, and a relatively more effective C acquisition likely benefited microbial necromass retention and production in the RC system. This study highlights that the rice-crayfish co-culture could modify the N pool of the surface paddy soil.

Effects of 12-Year Nitrogen Addition and Mowing on Plant-Soil Micronutrients in a Typical Steppe.

Changes in soil micronutrient availability may have adverse consequences on grassland productivity, yet it’s still largely unclear how concurrent human practices, such as fertilization and mowing, affect micronutrient cycling in the plant-soil systems. Here, we measured six essential micronutrient (Fe, Mn, Cu, Zn, Co and Mo) contents in both plant pool (separated as aboveground plant parts, litter, and belowground roots) at the community level and soil pool (0−10 cm depth) after 12-year consecutive nitrogen (N) addition (0, 2, 10, and 50 g N m−2 year−1) and mowing in a typical steppe of the Mongolian Plateau. The results show that (i) medium-N (10 g m−2 year−1) and high-N (50 g m−2 year−1) addition rates significantly increased contents of soil-available Fe (+310.0%, averaging across the two N addition rates), Mn (+149.2%), Co (+123.6%) and Mo (+73.9%) irrespective of mowing treatment, whereas these addition treatments usually decreased contents of soil total Fe (−8.9%), Mn (−21.6%), Cu (−15.9%), Zn (−19.5%), Co (−16.4%) and Mo (−34.7%). (ii) Contents of Fe in aboveground plant parts, litter, and roots significantly decreased, whereas plant Mn increased with N addition. Contents of above ground plant Cu, Zn, Co, and Mo significantly decreased at high-N addition rate, whereas contents of micronutrients in roots and litters, except for Fe, generally increased with N addition. Moreover, the total amount of micronutrients in the plant pool (contents × biomass) significantly increased at the medium-N addition rate but decreased at the high-N addition rate. All N addition rates significantly enlarged the pool of litter micronutrients, and roots could hold more micronutrients under N addition, especially combined with mowing treatment. Importantly, although mowing could regulate the effects of N addition on variables (i) and (ii), the effects were weaker overall than those of N addition. (iii) Changes in root micronutrients, except for Mn, could explain corresponding changes in plant micronutrients (R2: 0.19−0.56, all p < 0.01), and significant linear correlations were also observed between soil-available Fe and Fe in plant and roots. Aboveground plant Mn was significantly correlated with soil-available Mn, while Co and Mo in roots were also significantly correlated with soil-available Co and Mo. These results indicate that soil micronutrient supply capacity may decrease due to a decrease in total micronutrient contents after long-term N addition and mowing. They also suggest that different magnitude responses of soil micronutrients in plants (i.e., litters, roots) and soil should be considered when comprehensively examining nutrient cycling in grassland ecosystems.

Characteristics of Organic Phosphorus Pool in Soil of Typical Agriculture Systems in South China

Organic phosphorus (P) is an important potential source of plant P nutrition in agro-ecosystems. It was hypothesized that the soil organic P pools were distinguished one from another by different land-utilization patterns. A total of 38 sites were sampled, to clarify the organic P pool and its distribution in paddy fields, vegetable fields, and orchards. Soil organic P fractions, including labile organic P (LOP), moderately labile organic P (MLOP), moderately resistant organic P (MROP) and highly resistant organic P (HROP) were examined. Results showed that the soil total P (TP) and available P (AP) concentration have enhanced by 138% and 1559%, respectively, over the last four decades. The soil total organic P (TOP) accounted for 21.4% of the TP pool. Soil MLOP dominated the organic P reservoir, irrespective of land-planting pattern. Soil organic P fractions ranked as MLOP &gt; MROP &gt; HROP &gt; LOP. The highest accumulations of TP, AP and TOP were in the vegetable fields, followed by orchards and paddy fields. The vegetable fields had higher LOP and MLOP levels than those of the paddy fields and orchards, whereas the paddy fields exhibited higher concentrations of MROP, and HROP. Soil pH, organic matter and available nitrogen all contributed to the buildup of the organic P pool. It was suggested that soil organic P should be considered preferentially in the management of the plant P nutrient in regional planting systems.

THE POTENTIAL SOIL ORGANIC CARBON STOCKS IN MANGROVE AREAS OF SINJAI DISTRICT, SOUTH SULAWESI, INDONESIA

The soil pool is the primary sink for carbon in mangrove wetlands and plays a major role in mitigating climate change. However, aquaculture pond expansions go further to disrupt carbon storage in mangroves. The aim of this study is to estimate the stock of soil organic carbon (SOC) in the mangrove area of South Sulawesi, Indonesia. The mangroves of Sinjai District in South Sulawesi are a disturbed region with no previous study on SOC stock. We implemented a line transect method at five study sites, collected 15 soil cores at a depth of 0–15 cm, 15–30 cm, and 30–50 cm, and performed soil analysis using the Loss on Ignition method. We find that the mean value of SOC stock is 413.10±12.37 Mg C ha–1. More attention to the conservation and restoration of lost mangrove areas is a high priority. It may also increase the stock of SOC to mitigate climate change. This study will help to preserve the remaining mangroves.

Elucidating the impact of boron fertilization on soil physico-chemical and biological entities under cauliflower-cowpea-okra cropping system in an Eastern Himalayan acidic Inceptisol.

Information on the role of boron (B) on soil physico-chemical and biological entities is scarce, and the precise mechanism in soil is still obscure. Present field investigation aimed to assessing the implication of direct and residual effect of graded levels of applied-B on soil biological entities and its concomitant impact on crop productivity. The treatments comprised of five graded levels of B with four replications. To assess the direct effect of B-fertilization, cauliflower was grown as a test crop wherein, B-fertilization was done every year. For assessment of succeeding residual effects of B-fertilization, cowpea and okra were grown as test crops and, B-fertilization was phased out in both crops. The 100% recommended dose of NPK (RDF) along with FYM was uniformly applied to all crops under CCOCS. Results indicated that the direct effect of B had the edge over residual effect of B in affecting soil physico-chemical and biological entities under CCOCS. Amongst the graded levels of B, application of the highest B level (2 kg ha-1) was most prominent in augmenting microbiological pools in soil at different crop growth stages. The order of B treatments in respect of MBC, MBN, and soil respiration at different crop growth stages was 2.0 kg B ha-1 > 1.5 kg B ha-1 > 1.0 kg B ha-1 > 0.5 kg B ha-1 > 0 kg B ha-1, respectively. Moreover, maximum recoveries of potentially mineralizable-C (PMC) and potentially mineralizable-N (PMN) were noticed under 2 kg B ha-1. Analogous trend was recorded in soil microbial populations at different crop growth stages. Similarly, escalating B levels up to 2 kg B ha-1 exhibited significantly greater soil enzymatic activities viz., arylsulphatase (AS), dehydrogenase (DH), fluorescein diacetate (FDA) and phosphomonoesterase (PMA), except urease enzyme (UE) which showed an antagonistic effect of applied-B in soil. Greater geometric mean enzyme activity (GMEA) and soil functional diversity index were recorded under 2 kg B ha-1 in CCOCS, at all crop growth stages over control. The inclusive results indicated that different soil physico-chemical and biological properties CCOCS can be invariably improved by the application of graded levels of B up to 2 kg B ha-1 in an acid Inceptisol.

Tracing Carbon Metabolism with Stable Isotope Metabolomics Reveals the Legacy of Diverse Carbon Sources in Soil.

Tracking the metabolic activity of whole soil communities can improve our understanding of the transformation and fate of carbon in soils. We used stable isotope metabolomics to trace 13C from nine labeled carbon sources into the water-soluble metabolite pool of an agricultural soil over time. Soil was amended with a mixture of all nine sources, with one source isotopically labeled in each treatment. We compared changes in the 13C enrichment of metabolites with respect to carbon source and time over a 48-day incubation and contrasted differences between soluble sources (glucose, xylose, amino acids, etc.) and insoluble sources (cellulose and palmitic acid). Whole soil metabolite profiles varied singularly by time, while the composition of 13C-labeled metabolites differed primarily by carbon source (R2 = 0.68) rather than time (R2 = 0.07), with source-specific differences persisting throughout incubations. The 13C labeling of metabolites from insoluble carbon sources occurred slower than that from soluble sources but yielded a higher average atom percent (atom%) 13C in metabolite markers of biomass (amino acids and nucleic acids). The 13C enrichment of metabolite markers of biomass stabilized between 5 and 15 atom% 13C by the end of incubations. Temporal patterns in the 13C enrichment of tricarboxylic acid cycle intermediates, nucleobases (uracil and thymine), and by-products of DNA salvage (allantoin) closely tracked microbial activity. Our results demonstrate that metabolite production in soils is driven by the carbon source supplied to the community and that the fate of carbon in metabolites do not generally converge over time as a result of ongoing microbial processing and recycling. IMPORTANCE Carbon metabolism in soil remains poorly described due to the inherent difficulty of obtaining information on the microbial metabolites produced by complex soil communities. Our study demonstrates the use of stable isotope probing (SIP) to study carbon metabolism in soil by tracking 13C from supplied carbon sources into metabolite pools and biomass. We show that differences in the metabolism of sources influence the fate of carbon in soils. Heterogeneity in 13C-labeled metabolite profiles corresponded with compositional differences in the metabolically active populations, providing a basis for how microbial community composition correlates with the quality of soil carbon. Our study demonstrates the application of SIP-metabolomics in studying soils and identifies several metabolite markers of growth, activity, and other aspects of microbial function.

Irrigation water quality, gypsum, and city waste compost addition affect P dynamics in saline-sodic soils

The amendments used for sodicity reclamation also profoundly influence P dynamics and leaching losses. This study characterized the effect of irrigation water quality on P dynamics and leaching from saline-sodic soil during reclamation utilizing gypsum alone or in combination with manure and city compost. Changes in properties of unleached and leached soils were fitted with labile P pools using redundancy analysis. The relation between leachate properties and P loss was explained by means of monitoring leachate properties up to ten pore volumes. During incubation, the water-extractable P (PH2O) concentration was greater than Olsen's P (PNaHCO3) in all treatments. The PNaHCO3 decreased in proportion to the amount of gypsum applied. Applying the organics with gypsum increased the PNaHCO3, PH2O, and organic P concentration compared to gypsum alone. The labile P pools in soil were positively correlated with HCO3− content (r = 0.39–0.77; P < 0.05) of leached and unleached soils. Adding gypsum and compost caused a 10–14% decrease in cumulative P leaching. The cumulative P leaching were greater with rainwater compared to saline water of SAR (sodium adsorption ratio) 5 and 15. The CO32−, HCO3−, pH, and SO42–content of the leachate explained about 71% variability in total P leaching (adj. R2 = 0.71; P < 0.001). This study concludes that low electrolyte water had a greater risk of P leaching and associated environmental pollution. Leaching of the saline–sodic soil amended with gypsum and city waste compost with low SAR saline water can reduce P leaching compared to good quality rainwater.