Fertilizer regime impacts on abundance and diversity of soil fauna across a poplar plantation chronosequence in coastal Eastern China

Microalgae-Based Biotechnology as Alternative Biofertilizers for Soil Enhancement and Carbon Footprint Reduction: Advantages and Implications

Due to the constant growth of the human population and anthropological activity, it has become necessary to use sustainable and affordable technologies that satisfy the current and future demand for agricultural products. Since the nutrients available to plants in the soil are limited and the need to increase the yields of the crops is desirable, the use of chemical (inorganic or NPK) fertilizers has been widespread over the last decades, causing a nutrient shortage due to their misuse and exploitation, and because of the uncontrolled use of these products, there has been a latent environmental and health problem globally. For this reason, green biotechnology based on the use of microalgae biomass is proposed as a sustainable alternative for development and use as soil improvers for crop cultivation and phytoremediation. This review explores the long-term risks of using chemical fertilizers for both human health (cancer and hypoxia) and the environment (eutrophication and erosion), as well as the potential of microalgae biomass to substitute current fertilizer using different treatments on the biomass and their application methods for the implementation on the soil; additionally, the biomass can be a source of carbon mitigation and wastewater treatment in agro-industrial processes.

Ecotoxicological effects of untreated pig manure from diets with or without growth-promoting supplements on Eisenia andrei in subtropical soils

This study aimed to evaluate the effects of untreated pig manure from diets incorporating growth-promoting supplements (antibiotics and Zn oxide) on the survival and reproduction of Eisenia andrei earthworms. The tested manures were obtained from four different groups of pigs fed with four different diets: CS, a diet based on corn and soymeal; TR, a diet based on corn, soymeal, and ground wheat (15%); CSa, a diet based on corn and soymeal + 100 ppm of doxycycline + 50 ppm of colistin + 2500 ppm of Zn oxide; and TRa, a diet based on corn, soymeal, and ground wheat (15%) + 100 ppm of doxycycline + 50 ppm of colistin + 2500 ppm of Zn oxide. The study used two soils representative of the Southern region of Brazil (Oxisol and Entisol). In general, there were no significant differences between the different manures tested in each soil. However, there were differences in the toxicity manure on E. andrei between the soils, and the magnitude of this effect was dependent on the applied dose. In Oxisol, LC₅₀ values were higher than 80 m³ ha^-1, and EC₅₀ varied from 9 to 27 m³ ha^-1. In Entisol, the LC₅₀ values were below the lowest dose tested (< 25 m³ ha^-1), and EC₅₀ remained around 5 m³ ha^-1. It may be possible that the effects observed were attributed to an excess of nitrogen, copper, and zinc, promoted by the addition of the untreated manure and how these factors interacted with soil type.

Nitrogen Enriched Organic Fertilizer (NEO) and Its Effect on Ryegrass Yield and Soil Fauna Feeding Activity under Controlled Conditions

This study aimed to investigate the effects of a new nitrogen-enriched organic-based fertilizer (NEO) on Italian ryegrass (Lolium multiflorum Lam.) yield and soil fauna feeding activity. Nitrogen is transformed from the air to manure by a plasma process. At the farm level, NEO could improve self-sufficiency and sustainability. The work was carried out under controlled conditions in two pot trials. Five fertilization regimes were used: no fertilizer, different amounts of mineral fertilizer, three NEO types, organic fertilizer (untreated manure), and organic fertilizer + different amounts of N in mineral fertilizer, including 14 treatments in trial one and 11 treatments in trial two. Besides evaluating dry matter yields, we utilized the Bait-lamina test system to assess the feeding activity of soil fauna. The results indicated a clear positive impact of nitrogen (N) on ryegrass yield where all fertilizers increased the yield in correspondence with their N availability regardless of the fertilizer type; whereas the yield was highest with mineral fertilizer up to our maximum level of 235 kg N ha−1 in trial one and 175 kg N ha−1 in trial two. The NEO fertilizers yielded in the same range as mineral fertilizers. The same clear pattern was not observed for soil fauna feeding activity. Instead, a tendency was observed where no fertilization tends to give the highest feeding activity. We saw no correlation between the yield and the soil fauna feeding activity. The feeding activity was highest in depth below 5 cm from the soil surface. Feeding activity also increased over time after fertilization. The NEO fertilizers had no more adverse effects on soil fauna feeding activity than other fertilizers. Other factors than fertilization alone are determining the soil fauna feeding activity.

Understory Vegetation Dynamics across a Poplar Plantation Chronosequence in Reclaimed Coastal Saline Soil

Although the understory vegetation abundance, diversity, and composition associated with stand development in natural forests have been well reported, only a few studies have examined the age-related changes of understory vegetation in fast-growing planted forests in reclaimed soils. This study measured the understory vegetation and soil variables in 8-, 12-, and 18-year-old poplar plantations in reclaimed coastal saline soil of Eastern China. This study examined how the abundance, diversity, and composition changed with stand development and the soil variables. Further, structural equation modeling (SEM) was used to evaluate the direct and indirect factors influencing the abundance and plant diversity throughout stand development. Herb abundance was significantly higher in the youngest and oldest stands, whereas shrub abundance was higher in the middle-aged stands. Shannon’s diversity index was significantly higher in the youngest stand for herbs, whereas it was highest in the middle-aged stands for shrubs. A multivariate analysis revealed that the herb and shrub composition were influenced by the stand age, total soil carbon and soil pH. The most parsimonious SEM model showed the negative direct effects of the stand age and the negative indirect effects of the stand age via the soil variables on shrub abundance, shrub diversity, and herb diversity, suggesting that the increase of overstory biomass with the stand age reduces resources available for the understory. Our results revealed that understory diversity and composition might change with stand development mediated by the changes in understory light and soil resources in fast-growing plantations.

Impact of spatial variations in water quality and hydrological factors on the food-web structure in urban aquatic environments

Global aquatic ecosystems are essential to human existence and have deteriorated seriously in recent years. Understanding the influence mechanism of habitat variation on the structure of the food-web allows the effective recovery of the health of degraded ecosystems. Whereas most previous studies focused on the selection of driving habitat factors, the impact of habitat variation on the food-web structure was rarely studied, resulting in the low success rate of ecosystem restoration projects globally. This paper presents a framework for exploring the effects of spatial variations in water quality and hydrological habitat factors on the food-web structure in city waters. Indices for the evaluation of the food-web structure are first determined by integrating model-parameter extraction via literature refinement. The key water quality and hydrological factors are then determined by coupling canonical correspondence analysis with partial least squares regression. Their spatial variation is investigated using spatial autocorrelation. Finally, fuzzy clustering is applied to analyze the influence of the spatial variations in water quality and hydrological factors on the food-web structure. The results obtained in Ji'nan, the pilot city of water ecological civilization in China, show that the Shannon diversity index, connectance index, omnivory index, and the ratio of total primary production to the total respiration are important indicators of food-web structural change. They show that the driving factors affecting the aquatic food-web structure in Ji'nan are hydrological factors (e.g., river width, water depth, and stream flow), physical aspects of water quality (e.g., air temperature, water temperature, electrical conductivity, and transparency), and chemical aspects (e.g., potassium, dissolved oxygen, calcium, and total hardness). They also show that the stability of the food-web is more prone to spatial variations in water quality than in hydrological factors. Higher electrical conductivity, potassium, total hardness, and air temperature lead to deteriorated food-web structures, whereas better transparency improves structure and stability. We found that water and air temperature are the most important factors in the spatial variation of the food-web structure in the study area, followed by total hardness. Transparency is the least important factor. Large disparities and varied spatial distributions exist in the driving effects of water quality and hydrological factors across regions attributable to differences in geographical environments, water salinity (fresh vs. sea water), and environmental factors (e.g., water pollution). The above methods and results serve as a theoretical and scientific basis for a high success rate of aquatic ecosystem restoration projects in the study area and other cities worldwide.

Fine Root Biomass Mediates Soil Fauna Community in Response to Nitrogen Addition in Poplar Plantations (Populus deltoids) on the East Coast of China

Soil fauna is critical for maintaining ecosystem functioning, and its community could be significantly impacted by nitrogen (N) deposition. However, our knowledge of how soil-faunal community composition responds to N addition is still limited. In this study, we simulated N deposition (0, 50, 100, 150, and 300 kg N ha−1 year−1) to explore the effects of N addition on the total and the phytophagous soil fauna along the soil profile (0–10, 10–25, and 25–40 cm) in poplar plantations (Populus deltoids) on the east coast of China. Ammonium nitrate (NH4NO3) was dissolved in water and sprayed evenly under the canopy with a backpack sprayer to simulate N deposition. Our results showed that N addition either significantly increased or decreased the density (D) of both the total and the phytophagous soil fauna (Dtotal and Dp) at low or high N addition rates, respectively, indicating the existence of threshold effects over the range of N addition. However, N addition had no significant impacts on the number of groups (G) and diversity (H) of either the total or the phytophagous soil fauna (Gtotal, Gp and Htotal, Hp). With increasing soil depth, Dtotal, Dp, Gtotal, and Gp largely decreased, showing that the soil fauna have a propensity to aggregate at the soil surface. Htotal and Hp did not significantly vary along the soil profile. Importantly, the threshold effects of N addition on Dtotal and Dp increased from 50 and 100 to 150 kg N ha−1 year−1 along the soil profile. Fine root biomass was the dominant factor mediating variations in Dtotal and Dp. Our results suggested that N addition may drive changes in soil-faunal community composition by altering belowground food resources in poplar plantations.

The effects of drought and nutrient addition on soil organisms vary across taxonomic groups, but are constant across seasons

Anthropogenic global change alters the activity and functional composition of soil communities that are responsible for crucial ecosystem functions and services. Two of the most pervasive global change drivers are drought and nutrient enrichment. However, the responses of soil organisms to interacting global change drivers remain widely unknown. We tested the interactive effects of extreme drought and fertilization on soil biota ranging from microbes to invertebrates across seasons. We expected drought to reduce the activity of soil organisms and fertilization to induce positive bottom-up effects via increased plant productivity. Furthermore, we hypothesized fertilization to reinforce drought effects through enhanced plant growth, resulting in even drier soil conditions. Our results revealed that drought had detrimental effects on soil invertebrate feeding activity and simplified nematode community structure, whereas soil microbial activity and biomass were unaffected. Microbial biomass increased in response to fertilization, whereas invertebrate feeding activity substantially declined. Notably, these effects were consistent across seasons. The dissimilar responses suggest that soil biota differ vastly in their vulnerability to global change drivers. Thus, important ecosystem processes like decomposition and nutrient cycling, which are driven by the interdependent activity of soil microorganisms and invertebrates, may be disrupted under future conditions.

Changes in Soil Arthropod Abundance and Community Structure across a Poplar Plantation Chronosequence in Reclaimed Coastal Saline Soil

Poplar plantations have the capacity to improve the properties of soils in muddy coastal areas; however, our understanding of the impacts of plantation development on soil arthropods remains limited. For this study, we determined the community dynamics of soil dwelling arthropods across poplar plantations of different ages (5-, 10-, and 21-years) over the course of one year in Eastern Coastal China. The total abundance of soil arthropods differed with stand development. Further, there were some interactions that involved the sampling date. On average, total abundance was highest in the 10-year-old stands and lowest in the 5-year-old stands. Total abundance exhibited strong age-dependent trends in June and September, but not in March or December. The abundance of Prostigmata and Oribatida increased in the 5- to 21-year-old stands, with the highest levels being in the 10-year-old stands. The abundance of Collembola increased with stand development; however, the stand age had no significant impact on the abundance of epedapic, hemiedaphic, and euedaphic Collembola. Order richness (Hill number q = 0) curve confidence intervals overlapped among three stand ages. Shannon and Simpson diversity (Hill numbers q = 1 and q = 2) differed between 10- and 21-year-old stand age. They showed almost similar trends, and the highest and lowest values were recorded in the 21- and 10-year-old stand ages, respectively. Permutational multivariate analysis of variance demonstrated that composition also varied significantly with the sampling date and stand age, and the 10-year-old stands that were sampled in June stood well-separated from the others. Indicator analysis revealed that Scolopendromorpha and Prostigmata were indicators in June for the 10-year-old stands, while Collembola were indicators for the 21-year-old stands sampled in September. Our results highlight that both stand development and climate seasonality can significantly impact soil arthropod community dynamics in the reclaimed coastal saline soils of managed poplar plantations.

Short-term Impacts of Tillage and Fertilizer Treatments on Soil and Root Borne Nematodes and Maize Yield in a Fine Textured Cambisol

Conservation agriculture (CA) based on the principles of minimum soil disturbance, crop residue retention, and crop rotation has been the focus of intensive research in recent years. A study was carried out to determine the effects of tillage and fertilizer on the population densities of plant-parasitic nematodes in maize. Three tillage regimes, (i) basin planting, (ii) rip line seeding, and (iii) conventional tillage, were combined with four fertilizer regimes: (i) no-fertilizer, (ii) low fertilizer rate, (iii) medium fertilizer rate, and (iv) high fertilizer rate. The experiment was arranged as a split plot in randomized complete block design, replicated three times with tillage as the main plot factor and fertilizer as the sub-plot factor. The study was conducted on fine-textured Cambisol soils at Chinhoyi University of Technology farm, Zimbabwe, over two cropping seasons between December 2014 and April 2016. Eight plant-parasitic nematode genera were observed belonging to five groups based on their feeding sites: (i) sedentary endoparasites ( Meloidogyne and Rotylenchulus ), (ii) migratory endoparasites ( Pratylenchus ), (iii) semi-endoparasites ( Scutelonema and Helicotylenchus ), (iv) ectoparasites ( Xiphinema and Trichodorus ), and (v) algal, lichen or moss feeders ( Tylenchus ). In both cropping seasons, semi-endoparasitic nematodes were double under rip line seeding and triple under basin planting compared to conventional tillage. Basin planting had higher plant-parasitic nematode richness than rip line seeding. Nematode densities did not have a measurable effect on maize grain yield. Maize grain yield was higher in rip line seeding (37%) and planting basins (52%) than conventional tillage during 2014/15 cropping season. On the other hand, during 2015/16 cropping season, maize grain yield was 78% and 113% higher in rip line seeding and basin planting, respectively, compared to conventional tillage. The results show that under the environmental and edaphic conditions of this specific study site, semi-endoparasitic nematodes were higher under rip line seeding and basin planting compared to conventional tillage. The authors conclude that (i) plant-parasitic nematode genera exhibited differential responses to different tillage systems but were not affected by fertilizer application, and (ii) in the present study, maize grain yield response under different tillage and fertilizer regimes was overall not related to nematode population density and composition.

Impacts of carbon nanomaterials on the diversity of microarthropods in turfgrass soil

Nanoscale materials have been produced with unprecedented speed due to their widespread use, and they may eventually be released into the environment. As effective adsorbents for heavy metals, carbon nanomaterials can be used to immobilize metals in contaminated soil, but little information is available regarding their effects on soil microarthropods. This study was designed to investigate the influence of three types of carbon nanomaterials, graphene (G), graphene oxide (GO) and carbon nanotubes (CNTs) on soil microarthropod communities under turfgrass growth conditions. The application of carbon nanomaterials resulted in increased abundance of all soil microarthropods, especially in the GO and CNT treatments. GO also significantly increased the abundances of multiple trophic functional groups, including predators, detritivores, herbivores and fungivores. Further, the dominant genera varied among the treatments. Herbivorous microarthropods predominated in the control, whereas predatory species predominated in the carbon nanomaterial treatments. Carbon nanomaterials also increased the total taxonomic richness, Shannon diversity index, and dominance index of the microarthropod community, but they decreased the evenness index. Higher diversity of soil microarthropods indicates an environment suitable for soil mesofauna and for enhanced decomposition and nutrient cycling in the soil food web.