Nutrient Stocks Research Articles

Microbiome structure and interconnection in soil aggregates across conservation and conventional agricultural practices allow to identify main prokaryotic and fungal taxa related to soil functioning

Under conservation agriculture (CA), soil aggregates physically protect soil organic C, creating microhabitats with heterogeneities in nutrient availability. These may become rich in microbial taxa with structured interconnections, and thus maintain the equilibrium between C sources and sinks. A long-term experiment on tillage and N fertilization was used to investigate the microbiome within small macroaggregates (sM), and within occluded microaggregates (mM). At surface layer, N fertilization was the main determinant of prokaryotic and fungal alpha-diversity in sM and mM, whereas at subsurface tillage intensity was the primary driver. Moreover, although along soil profile a conserved microbial compositional core was found across managements, some taxa were uniquely found in certain treatments and microbiota structure was modified by tillage and N fertilization. Overall sM had a higher diversity of prokaryotes and a lower diversity of fungi than mM. Prokaryotic taxa, such as Actinobacteria, Chloroflexi and Thermomicrobia, and fungi, such as Agaricomycetes, Dydimellaceae, and Mortierellaceae, characterized sM, whereas others prokaryotes (Betaproteobacteria, Sphingobacteriia, Blastocatellia) and fungi (Sordariales, Lasiosphaeriaceae and Glomeraceae) characterized mM. Cross-domain networks were more complex in mM than sM at surface layer, and the opposite occurred at subsurface layer. Some prokaryotic and fungal taxa, retrieved in hubs, were positively linearly related to C cycling and soil structuring (e.g., Chloroflexi and Sordariomycetes). Our results suggest that diversity and structure of microbiome is positively shaped by CA, and there are microbial taxa and network traits suitable as indicators of nutrient stocks and soil structuring under an agriculture focused on soil health.

Effect of the elevated ozone on greening tree species of urban: Alterations in C-N-P stoichiometry and nutrient stock allocation to leaves and fine roots

Anthropogenic ground-level ozone (O3) pollution can alter the phosphorus (P), carbon (C), and nitrogen (N) of terrestrial plants’ ecological stoichiometry, which in turn affects forest productivity, nutrient utilization, and carbon sink capacity. However, there is still quite a lot of uncertainty regarding the impact of high O3 levels on C-N-P stoichiometry in organs with a rapid turnover (i.e., fine roots and leaves) across varied functional types. This study investigated the effects of O3 on the stoichiometry of C-N-P nutrient allocation of stocks to various plant organs, with a special focus on tree species frequently employed for urban greening. The impact of O3 on C-N-P stoichiometry among different functional tree types was subsequently evaluated by reviewing the published literature. Under a pooling of all species, elevated O3 decreased and leaf C and P concentrations increased, thereby decreasing the leaf C: P ratio. Elevated O3 increased the N concentration in fine roots, thereby decreasing the C: N ratio, although no significant impact was observed in leaves. Elevated O3 significantly reduced the leaf stocks of C (CSleaf) and N (NSleaf), however, there was no observed variation in these stocks in fine roots. The content of P, C, and N in fine roots and leaves in evergreen broadleaf species exceeded those in deciduous species. Elevated O3 significantly reduced CSleaf, NSleaf, and PSleaf in deciduous broadleaf species, whereas there was a significant reduction for the same in evergreen species. The literature analysis further demonstrated a larger O3-induced increment in leaf P concentration in deciduous species as compared to evergreen species. Elevated O3 significantly increased the difference in C and N stocks between fine roots and leaves in deciduous broadleaf species, whereas this difference was observed to decrease in evergreen species. The results of this study can facilitate an improved understanding of ecological stoichiometric responses of urban greening tree species under O3 stress and the resulting nutrient use strategies.

Enhanced susceptibility to oiling may limit denitrification recovery in marshes subjected to woody encroachment

Coastal salt marshes provide valuable ecosystem services but are subjected to multiple concomitant stressors that may impact their ability to provide those services. Global climate change has led to the poleward expansion of mangroves into salt marshes on each continent where mangroves and marshes co-occur. In the northern Gulf of Mexico, warming winter temperatures have resulted in the expansion of Avicennia germinans (black mangrove) into forb-dominated salt marshes, resulting in a shift in ecosystem structure that can impact the ecosystem services marshes provide, including biogeochemical processes such as nitrogen removal. There have been limited studies addressing how mangrove expansion impacts nitrogen removal rates in salt marshes, but it is possible that mangroves enhance microbial nitrogen removal capacity through more efficient oxygen translocation to sediments. However, mangroves are more sensitive to oiling (such as occurred during the 2010 Deepwater Horizon spill) than marsh plants, such as Spartina alterniflora, which have a higher turnover. Thus, even if they enhance nitrogen removal, if they cannot withstand disturbances such as oiling, there still may be a loss of function associated with woody encroachment. We conducted a field study to assess the impact of woody encroachment in mediating biogeochemical recovery 7 to 8 years after the Deepwater Horizon oil spill. We collected sediments from S. alterniflora- and A. germinans-dominated plots in the Chandeleur Islands (LA, United States), a chain of barrier islands in the northern Gulf of Mexico subjected to a range of oiling following the spill. We compared nitrate reduction rates (denitrification and dissimilatory nitrate reduction to ammonium), microbial community composition, and denitrifier marker gene abundance at sites subjected to light and moderate oiling using a combination of isotope pairing on sediment slurries, 16S sequencing, and qPCR. We predicted that overall, denitrification rates and microbial functional capacity would be enhanced in mangrove-dominated sediments. We also predicted that these enhancements would be diminished at the more intensely oiled site due to the higher susceptibility of A. germinans to oiling. Denitrification potential rates were higher in mangrove sediments at the lightly oiled site, whereas dissimilatory nitrate reduction to ammonium potential rates were higher in marsh sediments. Indicator analysis of 16S rRNA data selected putative sulfur cycling taxa as indicators of marsh sediments, suggesting that changes in oxygen availability associated with encroachment may be driving the differences in process rates. There was no difference in process rates between plant types at the moderately oiled site, where heavily weathered oil residue was still present. Sediment nutrient stocks were lower in moderately oiled mangrove plots than in lightly oiled mangrove plots, suggesting that sediment fertility recovery following the spill may have been slower in the mangroves, contributing to a change in ecosystem function. This study shows that woody encroachment has the potential to impact both the biogeochemical services that marshes provide and their response to and recovery from disturbances.

Aeroponic systems design: considerations and challenges

Controlled Environment Agriculture (CEA) holds promise as a way to intensify current agricultural production systems while limiting pressures on land, water, and energy resources. However, its use has not yet been widely adopted, in part because the engineering design considerations and associated challenges are not well known. This is even more apparent for aeroponics, where the additional cost and complexities in controlling atomization have yet to establish an advantage in scale over simpler hydroponic systems To shed light on these considerations and challenges, an instrumented aeroponic system was prototyped with the goal of creating a quantitative model of growth for various species of leafy greens. As the first consideration, pressure swirl atomizers were paired with a diaphragm-type pressure tank to supply the necessary pressures needed for effective atomization. Secondly, nutrient solution was mixed on-demand from Reverse Osmosis (RO) water and concentrated nutrient stock then pumped into the pressure tank using a positive displacement pump. A bamboo-based substrate that allowed both germination and extended vegetative growth was supported on a stainless steel mesh and PVC frame acting as a grow tray. Finally, a camera microservice platform was developed to quantify plant growth using a computer vision pixel-based segmentation method.

The Influence of Slash Management Practices on Water and Nutrient Dynamics in Longleaf Pine Forests

(1) Silvicultural applications that manipulate woody debris loading and the structural composition of a forest can have both short and long-term effects on biogeochemical cycling. Longleaf pine forests have been the historically dominant community types throughout much of the Southeastern United States. Fire exclusion, hardwood encroachment, and resource exploitation have severely reduced the amount of remaining longleaf pine habitats, making ecological restoration necessary. The silvicultural treatments used to reestablish these communities have been widespread, leading to some skepticism regarding the sustainability of certain restoration practices. (2) This study aimed to understand how overstory manipulation and woody debris management affected soil water retention rates and nutrient availability. Using a randomized complete block design, abiotic responses to biomass harvesting, conventional harvesting, and mastication treatments were measured across a soil moisture gradient in the South Carolina sandhills. (3) Our findings indicate that mastication increased soil moisture retention rates by 37% and 41%, on average, compared to conventional harvesting and biomass harvesting, respectively. (4) Additionally, soil nutrient stocks did not decline following any management practice, indicating that both biomass harvesting and mastication treatments may not necessarily impact site productivity in a negative manner. These findings imply that mastication treatments keep moisture retention high and do not immediately change soil nutrient availability in longleaf pine forests. Long-term vegetation response studies should continue to document successional trends in conjunction with moisture retention rates and long-term nutrient pulsing.

Anthropogenic degradation alter surface soil biogeochemical pools and microbial communities in an Andean temperate forest

Soil microbial communities regulate a myriad of critical biogeochemical functions in forest ecosystems. Anthropogenic disturbances in natural forests could drive major shifts in plant and microbial communities resulting in substantial biogeochemical alterations. We evaluated the effect of anthropogenic disturbances in the soils of Andean temperate forests with different levels of degradation: i) mature forest (MF), ii) secondary forest (SF), iii) degraded forest (DF), and iv) deforested site converted into a prairie (DP). We quantified total soil carbon, nitrogen and phosphorous (TC, TN, and TP), and available nutrient stocks. The soil microbial community structure (i.e., composition, diversity, and abundance) was assessed under each condition from amplicon sequence variants (ASVs) obtained via NGS-Illumina sequencing and subsequent microbiome analysis. There were no significant differences in TC, TN, and TP across the forested states (MF, SF, DF). The deforested site condition presented significantly higher soil TC, TN, and TP and the lowest C:N, C:P, and N:P ratios. The DP soil microbiome was significantly more diverse in bacteria (D′ = 0.47 ± 0.04); and fungi (H′ = 5.11 ± 0.33). The bacterial microbiome was dominated by Proteobacteria (45.35 ± 0.89 %), Acidobacteria (20.73 ± 1.48 %), Actinobacteria (12.59 ± 0.34 %), and Bacteroidetes (7.32 ± 0.36 %) phyla in all sites. The soil fungal community was dominated by the phyla Ascomycota (42.11 ± 0.95 %), Mortierellomycota (28.74 ± 2.25 %), Basidiomycota (24.61 ± 0.52), and Mucoromycota (2.06 ± 0.43 %). Yet, there were significant differences at the genus level across conditions. Forest to prairie conversion facilitated the introduction of exotic bacterial and fungal taxa associated with agricultural activities and livestock grazing (∼50 % of DP core microbiome composed of unique ASVs). For example, the ammonia-oxidizing bacteria community emerged as a dominant group in the DP soils, along with a reduction in the ectomycorrhizal fungi community. The surface soil microbial community was surprisingly resistant to forest degradation and did not show a clear succession along the degradation gradient, but it was strongly altered after deforestation.

Effects of elevated ozone on the uptake and allocation of macronutrients in poplar saplings above- and belowground

Ground-level ozone (O3) is a secondary air pollutant and affects the roots and soil processes of trees. Therefore, O3 can affect the uptake and allocation of nutrients in trees, which merits further clarification. A fumigation experiment with five O3 levels was conducted in 15 open top chambers for two poplar clones, and the concentrations of six macronutrients (N, P, K, S, Ca, Mg) in different organs and leaf positions were determined. Under all O3 levels, the concentration of mobile nutrients (N and P) was higher in upper leaves than in lower leaves, while the non-mobile nutrients (Ca and S) concentration was the opposite. Relative to charcoal filtered ambient air (CF), high O3 treatment (NF60) significantly increased the concentration of mobile nutrients K and Mg in upper leaves by 38 % and 33 %, in lower leaves by 142 % and 65 %, respectively, which suggested the effect of O3 on their concentrations was greater at the lower leaf position than at the upper leaf position. Elevated O3 significantly increased the macronutrient concentrations in most organs. The effects of O3 on nutrient concentrations were attributed using graphical vector analysis, suggested that the increase of nutrient concentration in the shoots was attributed to excessive nutrient stocks, while their increase in root was attributed to the “concentration” effect. Compared to CF, NF60 also reduced the root-to-shoot ratio of N, P, S, K, Ca and Mg stocks by 34 %, 39 %, 37 %, 64 %, 46 % and 42 %, respectively, indicating the allocation of increased nutrients to shoots in response to O3 stress. Changes in the allocation pattern of nutrients in different leaf positions and organs of poplar were primarily in response to O3 stress since these nutrients play important roles in some physiological processes. These results will help improve the plantation nutrient utilization by optimizing fertilizer management regimes under O3 pollution.

Effects of herbaceous covers and mineral fertilizers on the nutrient stocks and fluxes in a Mediterranean olive grove

The preservation of nutrient capital, soil fertility, and carbon (C) sequestration capacity in Mediterranean olive groves requires evaluation of agricultural practices beyond short-term productivity. We aim to contribute with a mechanistic understanding on the effects that the preservation of herbaceous cover and the use of chemical fertilizers have on the performance of olive trees and on the biogeochemical cycles of the agroecosystem. We compared nutrient fluxes and aboveground leafy stocks in an olive grove that had been organically managed for more than 60 years, in a treatment in which the annual spontaneous herbaceous cover was maintained (H), and after two years of shift to conventional management treatments in which the growth of herbaceous vegetation was avoided by the use of herbicides (NH), and where exclusion of the herbaceous cover is also combined with the supply of mineral fertilizers (NHF). Maintenance of herbaceous vegetation in H contributed to the retention of a high aboveground capital of C and nutrients, particularly nitrogen, (N), phosphorus (P) and potassium (K) that were about 2.9, 3.9 and 7.4 times greater than in NH, respectively. The permanence of herbaceous cover stimulated olive tree leaf litter decomposition rates by about 86 % and increased nutrient release. However, the H treatment led to a 37 % decrease in olive yield and lowered olive foliar N and P content as negative short-term effects. The addition of fertilizers (N, P, K, and Mg) in mineral and solid form in NHF resulted inefficient to improve olive tree nutritional status and olive production, and decelerated olive tree litter decomposition rates by 21 % and nutrient release. The nutrient retention in organic forms in the fast-growing species of herbaceous covers and the progressive nutrient release as litter decomposes may contribute to regulate and better adapt nutrient availability to the nutrient requirements of olive trees.

Temperate fruit farming in fragile lands of the Northwestern Himalayan region: Implications for subsoil nutrient availability, nutrient stock and soil quality

AbstractIn recent years, soil fertility in the Northwestern Himalayan (NWH) region has deteriorated partly due to accelerated soil erosion but mainly due to ineffective nutrient management for field crops. However, it is largely unknown whether long‐term temperate fruit farming has adverse effects on the soil fertility in NWH or not. Therefore, we conducted a study with the purpose of evaluating the impact of different land uses in the NWH ecosystem, namely: peach orchard (PO), apple orchard (AO), fertile‐fallow land (FL), and barren land (BL) on soil physico‐chemical characters, nutrient storage capacity, and soil quality index (SQI), along a soil‐depth gradient. A total of 116 composite soil samples [four treatments (i.e., land uses), 4‐ soil depths (0–0.2, 0.2–0.4, 0.4–0.6, and 0.6–0.8 m) and 5, 9, 9, and 6 replications for PO, AO, FL, and BL systems, respectively] were collected for laboratory analyses. Across depths, the soils under temperate fruit plantations had better soil physical conditions (i.e., lower bulk density and higher porosity) over FL and BL lands. The soils in this study can be categorized as slightly acidic to near neutral in soil reaction. Soils under temperate fruit plantations (PO and AO), averaged over depths, had significantly (p < 0.05) less quantity of soil organic C, available nutrients (i.e., primary‐, secondary‐, and micro‐nutrients), nutrient storage capacity, and indices of soil quality, as compared to FL lands. These unfavourable effects were augmented in subsoils (0.2–0.8 m) than topsoils (0.0–0.2 m) affecting secondary‐ and micro‐nutrients more than primary‐nutrients. Results further revealed that these lands display a less favourable (i.e., very high) C:N ratio that could easily be degraded if brought under intensive farming. Restoration of depleted soil fertility in temperate fruit‐tree‐based ecosystems of NWH could be achieved through incentive‐based building‐up of soil organic matter and adoption of a soil‐test‐based nutrient management regime.

Nutrient stocks, flows and balances for the Bolivian agri-food system: Can recycling human excreta close the nutrient circularity gap?

Analysis of the current state of nutrient stocks, flows, and balances of a territory is necessary to inform strategies that can transition the agri-food sector to a circular economy model. In this study, we quantified the nitrogen and phosphorus budgets for the Bolivian agri-food system at national and regional scales by way of agro-ecological zoning. We performed nutrient balances to calculate indicators for sufficiency (extent of nutrient deficit/surplus) and circularity (proportion of nutrients recirculated). We also evaluated the potential of renewable stocks (human excreta and livestock manure) to meet nutrient deficits in the system. Our results showed that there are apparent deficits of 32 kt N and 8 kt P in the system that cannot be accounted for using available data. We estimate the real deficits required to bring yields of 45 crops grown in Bolivia to parity with those of neighbouring countries to be 110 kt N and 33 kt P. About 44% of nitrogen and 74% of phosphorus is currently recirculated in the system, with the major nutrient inputs being biological nitrogen fixation, livestock manure, and crop residues. However, nutrient recycling is likely to decrease in the future because the national strategy to address nutrient deficits is to increase domestic production of synthetic fertilisers. Our analysis also shows that there is a sufficient stock of nutrients already available in human excreta (39 kt N and 5 kt P) to cover 100% of the nitrogen deficit and 64% of the phosphorus deficit. The low-altitude zone of Chiquitania-Pantanal alone accounts for 65% of cultivation and 80% of the nutrient demand in the country. Here, export-oriented crops like soybean and sorghum are grown, but less than 25% of the nitrogen is recirculated. In contrast, there are nutrient surpluses of 41 kt N and 34 kt P in agro-ecological zones like the Valleys and Altiplano where traditional agriculture is practiced, and the majority of food is grown for local consumption. Overall, we find that recycling of human excreta, combined with transfer of regional nutrient surpluses, could be an effective strategy to reduce the overall nutrient deficit in the system.

Carbon, Nitrogen, and Phosphorus Stoichiometry and Plant Growth Strategy as Related to Land-Use in Hangzhou Bay Coastal Wetland, China.

Ecological stoichiometry can not only instruct soil nutrient stocks and availability, but also indicated plant growth strategy and adaptability to environmental changes or stress. This study was carried out to examine the plant–soil Carbon (C), Nitrogen (N), and Phosphorus (P) stoichiometry distributions and patterns in three tidal wetlands [mudflat (MF), native Phragmites australis-dominated community wetland (NW), invasive Spartina alterniflora-dominated community wetland (IW)], and one reclaimed P. australis-dominated community wetland (RW) in Hangzhou Bay coastal wetland. The results showed that land-uses have more effect on C and N contents, and C:N and N:P ratios in plant than in soil, P content and C:P ratios more affected by plant organ and soil depth. Compared to land-use, both plant organ and soil depth have stronger effects on C, N, and P stoichiometry. Among tidal wetlands, plant N content and C:P, N:P ratios were significantly higher in NW than in IW. In contrast, plant C, N, and P contents and C:P and N:P ratios were significantly lower in RW, and plant C:N was higher. Soil C, N, and P stocks were similar between tidal wetlands, and were significant higher than those of RW, indicating that reclamation were not beneficial to soil nutrient storage. In the NW, soil N availability was relatively high, and P availability was relatively low; and leaf N:P was 15.33, which means vegetation was co-limited by N and P nutrients. In addition, plants in the NW mainly adopted a conservative growth strategy, with a significantly low aboveground biomass of 1469.35 g·m2. In the RW, soil N availability was relatively low, P availability was relatively high, and leaf N:P was 3, which means vegetation was limited by N nutrient. In addition, plants in the RW mainly adopted a rapid growth strategy, with a significantly high aboveground biomass of 3261.70 g·m2. In the IW, soil N availability was relatively low, soil P availability was relatively high, and leaf N:P was 5.13, which means vegetation was limited by N nutrient. The growth strategy and aboveground biomass (2293.67 g·m2) of the IW were between those of the NW and RW. Our results provide a reference for nutrient management and evaluating the impacts of land-use types on coastal wetland ecosystems.

Modelling and mapping soil nutrient depletion in humid highlands of East Africa using ensemble machine learning: A case study from Rwanda

Soil nutrient depletion is one of the major causes of high yield gaps and nutrient deficiencies in East Africa highlands, including Rwanda. This research sought to determine the current soil nutrient balance and its spatial variation in 10 Rwandan agro-ecological zones. Soil nitrogen (N), phosphorus (P) and potassium (K) depletion in croplands were calculated using data from 455 field trials of the Optimizing Fertilizer Recommendations in Africa (OFRA) project in Rwanda. Calculated soil nutrient balances (NPK) and 15 environmental covariates were used to calibrate soil nutrient depletion models using ensemble machine learning (EML) and 10-fold cross-validation. In the 2019–2020 growing season, annual N and K depletions were 33.6 kg N ha−1 yr−1 and 71.0 kg K ha−1 yr−1, with a positive P balance of 2.30 kg P ha−1 yr−1. High soil nutrient uptake and high soil nutrient loss due to erosion and leaching were two main causes of NPK depletion. Spatial variations of NPK balance were influenced by soil nutrient stocks, soil erosion, elevation, rainfall, soil texture, and soil bulk density. The 10-fold cross-validation showed that coefficients of determination (R2) of NPK models were 62%, 58%, and 58%, respectively. Compared to single models, ensemble machine learning improved NPK model accuracy up to 5%. Our research revealed that soil nutrient depletion was highest in the northwest and lowest in the southeast of the study area. We conclude that increasing soil nutrient inputs without reducing soil nutrient loss due to soil degradation will not decrease soil nutrient depletion in Rwanda and ensemble machine learning outperforms single models in predicting soil nutrient balance. Thesolutiontoreducehighsoilnutrientdepletionin all agro-ecological zones of Rwanda would be to prioritize soil and water conservation measures and increase soil nutrient inputs.

Extreme Nitrate Deficits in the Western Arctic Ocean: Origin, Decadal Changes, and Implications for Denitrification on a Polar Marginal Shelf

AbstractThe western Arctic Ocean is known to be nitrate deficient relative to phosphate but the decadal trend and the processes contributing to the deficit are not clear. To investigate changes in this extreme nitrate deficit of over 10 μmol/kg and its causal mechanisms, nutrient concentrations were examined along a transect spanning the Bering Basin, the Bering–Chukchi Shelf, and the western Arctic Ocean Basin over the last two decades (1994–2018). The results show that the extreme nitrate deficit has extended to greater depths and further north during the past two decades, which coincided with the expansion of Pacific water in the western Arctic Ocean. Subsurface nutrient stocks in the basin areas appear to have increased, but are accompanied by a larger nitrate deficit, which may be due to stronger shelf denitrification. This nitrate loss (∆N) caused by shelf denitrification was estimated to be 7.3 ± 0.1 μmol/kg during the interval 2012–2018, which was ∼10% higher than that in 1994. This suggests an intensification of denitrification on this marginal shelf under climatic and environmental change in the Arctic Ocean.

Blue carbon and nutrient stocks in salt marsh and seagrass from an urban African estuary

Halophytes in estuaries are effective sinks of carbon, nitrogen, and phosphorus. Blue carbon (BC) is carbon stored in coastal habitats such as mangroves, salt marshes and seagrass. The objectives of this study were to firstly assess the biomass and sediment C stocks in salt marsh (Spartina maritima and Salicornia tegetaria) and seagrass (Zostera capensis) habitats of the Swartkops Estuary, South Africa. Secondly, we applied the nutrient pollutant indicator (NPI) to assess the nutrient status of the estuary. Six replicate sediment cores of 1 m (summer) and 0.5 m (winter) per plant species were collected at six sites. Six replicates for biomass of each species were harvested at each site during summer and winter. Biomass and nutrient dynamics showed that there were distinct seasonal differences in the magnitude of C, N, and P stored in the plants. The sediment was the dominant C pool and differed spatially with creek sites storing more C. Out of the three species, S. maritima stored the most C (224 ± 19.1 Mg C ha−1 in sediment, 16.7 ± 1.2 Mg C ha−1 in biomass), followed by S. tegetaria (207 ± 3.5 Mg C ha−1 in sediment, 4.3 ± 0.4 Mg C ha−1 in biomass) and Z. capensis (180 ± 18.4 Mg C ha−1 in sediment, 2.1 ± 0.7 Mg C ha−1 in biomass). The N:biomass ratios were low in both seasons for Z. capensis, S. maritima and S. tegetaria (0.08, 0.02 and 0.04, respectively) indicating consistent eutrophic conditions in the estuary. Resultantly, the plants displayed a significantly lower below-ground standing biomass highlighting the potential variations of BC storage in eutrophic estuaries.

3D-Reconstruction of a Giant Posidonia oceanica Beach Wrack (Banquette): Sizing Biomass, Carbon and Nutrient Stocks by Combining Field Data With High-Resolution UAV Photogrammetry

Beach wracks are temporary accumulations of vegetal detritus that can be found along coastlines all over the world. Although beach wracks are often perceived as a nuisance for beach users, they play a crucial ecological role in carbon and nutrient connectivity across ecosystem boundaries, especially when they reach a relevant size, as in the case of the wedge-shaped seagrass accumulations called banquette. In this study, three-dimensional mapping of a giant Posidonia oceanica banquette was carried out for the first time using high-resolution UAV photogrammetry combined with field sampling and compositional and chemical analysis. The combined approach allowed a reliable estimation of the amount and spatial distribution of both vegetal biomass and sedimentary mass, as well as of total carbon, nitrogen and phosphorus content, revealing that i) banquette act as a sediment trap and represent hot spots of seagrass biomass and carbon accumulation; ii) banquette thickness, rather than the distance from the sea, influences the spatial distribution of all variables. Moreover, high-resolution digital elevation models (DEM) revealed discontinuous patterns in detritus accumulation resulting in an unknown banquette type here termed “Multiple Mega-Ridge banquette” (MMR banquette). On the one hand, this study highlighted the high potential of the UAV approach in very accurately 3D mapping and monitoring of these structures, with relevant implications for ecosystem service estimation and coastal zone management. On the other hand, it opened new questions about the role played by temporary beach wracks and, in particular, by P. oceanica banquette in the blue carbon exchange across land-ocean boundaries.

Long Term Benefits of Legume Based Cropping Systems on Soil Health and Productivity. An Overview

Increasing land-use pressure and monoculture coupled with inadequate restorative practices pose threat to sustainability, nutrient uptake of crops often exceeds replenishment causing fertility deterioration. Imbalanced and indiscriminate use of fertilizers deteriorates soil health and factor productivity. Long-term impacts on soil nutrient stocks influence the sustainability of crop production are major gains of regular inclusions of legume in a cropping system. Inclusion of green gram in potato cultivation increased organic carbon and nutrients than non-legume based potato cropping systems. Legume-based cropping systems increased soil C and N stock than only cereal based cropping system. Maize intercropped with velvet-bean recorded higher productivity compared with pure maize and pure maize with mineral fertilizers. Bulk density of soil in glyricidia + maize system was lower compared to sole maize and maize grass fallow. Intercropping with glyricidia, glyricidia pruning incorporated into the soil optimized the cation exchange capacity in soil than sole maize system. Higher grain yield of finger millet and sustainable yield index were observed in green leaf manuring. Due to socioeconomic and environmental benefits, legumes could be introduced in cropping systems to reduce external inputs and increase crop diversity. They also found to perform well in conservation systems, intercropping systems, which are very important in developing nations. Legumes fix nitrogen from the atmosphere and aid in the cycle of soil nutrients and water retention. Because of their many uses, legumes have a lot of potential for conservation agriculture, as they can be used as a growing crop or as crop residue.

Accumulated litter, nutrient stock and decomposition in an Atlantic Forest fragment

Litter dynamics is one of the fundamental processes for the growth and maintenance of native forest fragments, being considered the main pathway for nutrient cycling in forests. Therefore, studies on accumulated litter and nutrient content provide information for a better understanding of nutrient dynamics. The aim of the study was to evaluate leaf litter and nutrient stock in different seasons and the instantaneous rate of decomposition in an Atlantic Forest Fragment over two years. Litter sampling was carried out in 12 permanent plots with dimensions of 20 m x 50 m. Litter dry mass and nutrient concentration were determined. The average annual accumulation of litter was 5269 kg ha-1. There was no statistically significant difference in the amount of litter between seasons. There was a statistically significant difference in the contents of N, P, K Ca and Mg between the different seasons. Nutrient stocks were 123.3, 92.8, 13.2, 11.8, 9.6, 3.0 kg ha-1 year-1 for Ca, N, Mg, S, K and P respectively. The total of nutrients in the accumulated litter was 253.7 kg ha-1 year-1. The litter renewal time was 281 days. The times required for 50% and 95% litter decomposition were 196 and 850 days. The average litter stocks, nutrients and decomposition are in line with other studies, indicating that the Atlantic Forest fragment seasonal semi-deciduous presents indicators of nutrient cycling. These results show that the ecosystem is sustainable from the point of view of cycling and nutrient release.
 Keywords: ecosystem functions, nutrient cycling, secondary succession.

Effect of coppice conversion into high forest on soil organic C and nutrients stock in a Turkey oak (Quercus cerris L.) forest in Italy

In forest ecosystems, a variety of abiotic and biotic soil forming factors drives soil organic matter (SOM) and nutrients cycling with a profitable outcome on climate change mitigation. As a consequence, type and intensity of forest management, through its impact on carbon (C) and nutrient soil stocks, can be considered as an additional soil forming force. In this study, we investigated the influence of the coppice conversion into high forest on pedogenesis and on soil C and nutrient (N, P, Ca, Mg, and K) stocks, fifty years later the beginning of the conversion-cycle. The trial was established in a Turkey oak forest historically managed under the coppice system in central Italy. Specifically, we considered tree population density (natural evolution – control, moderate thinning, heavy thinning) where soil samples were collected according to genetic horizon to estimate C, N, and P stocks both in the forest floor and at fixed depth intervals (0–30, 30–50 and 50–75 cm). Further, the stocks of exchangeable Ca, Mg, and K were also assessed for the mineral layers. The results showed that litter and the upper layer of mineral soil (0–30 cm) contained a similar quantity of C (about 74–83 Mg ha-1), independently of the trials and no differences were observed also in the whole soil stocks (about 192–213 Mg ha−1). The comparison of the mean stocks calculated per 1-cm of thickness of organic (O), organo-mineral (OM), and mineral (M) layers, although it did not display any difference among trials (excepted for P and Mg), showed a similar capability of the organo-mineral horizons to store C and nutrients compared with the organic ones (e.g., about 6–12 Mg ha−1, 0.3–0.5 Mg ha−1 and 0.5–1.5 kg ha−1 for C, N and P, respectively). Our findings showed that thinning operated on Turkey oak coppice did not affect soil capacity to store C and nutrients. These results suggested that the forest ecosystem itself is the main soil forming force and this is consistent with the target of adopting forest management able to control the global C cycle through the storage of SOM in the mineral soil rather than in forest floor, where SOM turnover is faster.

Phosphorus Concentrations and Stocks in Different Soil Classes, Uses and Coverages in Agreste Pernambucano, Brazil

Changes in land use cause a mosaic of areas in the landscape with different uses and coverage. This condition compromises soil nutrient stocks, especially phosphorus (P). In this sense, this study aimed to determine the concentrations of extractable and total phosphorus in 04 soil classes (Yellow Argisol, Litholic Neosol, Entisol and Planosol), 04 uses and covers (Open Native Caatinga, Dense Native Caatinga, Agriculture and Pasture) of the soil, in 04 depths (0-10, 10-20, 20-30 and 30-40 cm). To determine the extractable P, the Mehlich 1 and colorimetric reading were used. Total phosphorus was determined by sulfur digestion and colorimetry. The results of extractable and total P concentrations were higher for the Argisol and Planosol classes. It was observed that there were reductions in extractable P concentrations between the soil layers as the soil profile deepened. Depths between 0-20 cm generally showed higher concentrations of extractable and total phosphorus in agriculture. Among the four soil classes studied, the highest average values of extractable and total P stocks occurred in Litholic Neosols and Planosols, mainly due to agricultural use. P deficiency has been a limiting factor to agricultural productivity and, especially in the Agreste region of Pernambuco, where the main soil classes under natural cover have low levels of available and total P.

Do agrosystems change soil carbon and nutrient stocks in a semiarid environment?

Ecological processes, such as net primary production, root system development, organic matter mineralization, nutrient removal and fertilizer application interfere in gains and losses of C and nutrients (N, P, K, Ca and Mg) in soils. Herein, we studied how five rainfed livestock and four irrigated agricultural systems affected soil C and nutrient stocks in a semi-arid environment. Soil concentrations, stocks, gains and losses of the nine land-uses were compared to those of the preserved native deciduous forest (Caatinga) along the top 1 m soil layer. Open Caatinga used as pasture, gliricidia and leucaena fields maintained the stocks of most nutrients. The shallower roots of buffel grass and prickly pear led to C (7 and 18%) and N (7 and 20%, respectively) losses, and P, Ca and Mg accumulations in the deeper layers. Irrigated crops reduced soil C and N stocks. C losses in irrigated maize and beans fields (23%) were lower than in rainfed fields in the region, while those in mango fields were large (70 and 66%). Fertilization in beans and grapes increased soil P and K stocks. Knowledge of stock changes allows proper system management to reduce the negative impacts of land-use change and promote sustainable production.