Strengthen sunflowers resilience to cadmium in saline-alkali soil by PGPR-augmented biochar

In the center of the Nile Delta in Egypt, the Kitchener drain as the primary drainage discharges about 1.9 billion m3 per year of water, which comprises agricultural drainage (75 %), domestic water (23 %), and industrial water (2 %), to the Mediterranean Sea. Cadmium (Cd) stands out as a significant contaminant in this drain; therefore, this study aimed to assess the integration of biochar (0, 5, and 10 ton ha-1) and three PGPRs (PGPR-1, PGPR-2, and PGPR-3) to alleviate the negative impacts of Cd on sunflowers (Helianthus annuus L.) in saline-alkali soil. The treatment of biochar (10 ton ha-1) and PGPR-3 enhanced the soil respiration, dehydrogenase, nitrogenase, and phosphatase activities by 137 %, 129 %, 326 %, and 127 %, while it declined soil electrical conductivity and available Cd content by 31.7 % and 61.3 %. Also, it decreased Cd content in root, shoot, and seed by 55.3 %, 50.7 %, and 92.5 %, and biological concentration and translocation factors by 55 % and 5 %. It also declined the proline, lipid peroxidation, H2O2, and electrolyte leakage contents by 48 %, 94 %, 80 %, and 76 %, whereas increased the catalase, peroxidase, superoxide dismutase, and polyphenol oxidase activities by 80 %, 79 %, 61 %, and 116 %. Same treatment increased seed and oil yields increased by 76.1 % and 76.2 %. The unique aspect of this research is its investigation into the utilization of biochar in saline-alkali soil conditions, coupled with the combined application of biochar and PGPR to mitigate the adverse effects of Cd contamination on sunflower cultivation in saline-alkali soil.

Partial Substitution of Urea with Biochar Induced Improvements in Soil Enzymes Activity, Ammonia-Nitrite Oxidizers, and Nitrogen Uptake in the Double-Cropping Rice System

Biochar is an important soil amendment that can enhance the biological properties of soil, as well as nitrogen (N) uptake and utilization in N-fertilized crops. However, few studies have characterized the effects of urea and biochar application on soil biochemical traits and its effect on paddy rice. Therefore, a field trial was conducted in the early and late seasons of 2020 in a randomized complete block design with two N levels (135 and 180 kg ha^-1) and four levels of biochar (0, 10, 20, and 30 t ha^-1). The treatment combinations were as follows: 135 kg N ha^-1 + 0 t B ha^-1 (T1), 135 kg N ha^-1 + 10 t B ha^-1 (T2), 135 kg N ha^-1 + 20 t B ha^-1 (T3), 135 kg N ha^-1 + 30 t B ha^-1 (T4), 180 kg N ha^-1 + 0 t B ha^-1 (T5), 180 kg N ha^-1 + 10 t B ha^-1 (T6), 180 kg N ha^-1 + 20 t B ha^-1 (T7) and 180 kg N ha^-1 + 30 t B ha^-1 (T8). The results showed that soil amended with biochar had higher soil pH, soil organic carbon content, total nitrogen content, and mineral nitrogen (NH₄⁺-N and NO₃^--N) than soil that had not been amended with biochar. In both seasons, the 20 t ha^-1 and 30 t ha^-1 biochar treatments had the highest an average concentrations of NO₃^--N (10.54 mg kg^-1 and 10.25 mg kg^-1, respectively). In comparison to soil that had not been treated with biochar, the average activity of the enzymes urease, polyphenol oxidase, dehydrogenase, and chitinase was, respectively, 25.28%, 14.13%, 67.76%, and 22.26% greater; however, the activity of the enzyme catalase was 15.06% lower in both seasons. Application of biochar considerably increased the abundance of ammonia-oxidizing bacteria (AOB), which was 48% greater on average in biochar-amended soil than in unamended soil. However, there were no significant variations in the abundances of ammonia-oxidizing archaea (AOA) or nitrite-oxidizing bacteria (NOB) across treatments. In comparison to soil that had not been treated with biochar, the average N content was 24.46%, 20.47%, and 19.08% higher in the stem, leaves, and panicles, respectively. In general, adding biochar at a rate of 20 to 30 t ha^-1 with low-dose urea (135 kg N ha^-1) is a beneficial technique for improving the nutrient balance and biological processes of soil, as well as the N uptake and grain yield of rice plants.

Effect of Biochar on Rhizosphere Soil Microbial Diversity and Metabolism in Tobacco-Growing Soil

In this study, four different biochar application rates and a control were set up using indoor potted tobacco, to study the effects of biochar on the microbial diversity and metabolism of tobacco-growing soil. The five treatments were as follows: control—0% biochar (w/w) + 26 g fertilizer/pot; biochar treatments—1% biochar (w/w) + 26 g fertilizer/pot, 2% biochar (w/w) + 26 g fertilizer/pot, 3% biochar (w/w) + 26 g fertilizer/pot, and 4% biochar (w/w) + 26 g fertilizer/pot. We found that biochar increases the microbial diversity of soils and simultaneously changes the microbial community structure. Under the influence of biochar, soil urease activity increased by 18%, invertase activity increased by 23.40%, polyphenol oxidase activity increased by 59.50%, and catalase activity increased by 30.92%. Biochar also significantly increased the microbial biomass carbon and nitrogen content of the soil. Soil microbial biomass nitrogen had a positive correlation on bacterial diversity, with the highest coefficient, while soil microbial biomass carbon had a positive correlation on fungal diversity, with the highest coefficient. The microbial diversity and metabolic capacity of soil are improved under the influence of biochar, and soil enzyme activity and microbial biomass carbon and nitrogen have positive impacts on soil microbial diversity.

Latitudinal shifts of soil microbial biomass seasonality

Soil microbes ultimately drive the mineralization of soil organic carbon and thus ecosystem functions. We compiled a dataset of the seasonality of microbial biomass carbon (MBC) and developed a semi-mechanistic model to map monthly MBC across the globe. MBC exhibits an equatorially symmetric seasonality between the Northern and Southern Hemispheres. In the Northern Hemisphere, MBC peaks in autumn and is minimal in spring at low latitudes (<25°N), peaks in the spring and is minimal in autumn at mid-latitudes (25°N to 50°N), while peaks in autumn and is minimal in spring at high latitudes (>50°N). This latitudinal shift of MBC seasonality is attributed to an interaction of soil temperature, soil moisture, and substrate availability. The MBC seasonality is inconsistent with patterns of heterotrophic respiration, indicating that MBC as a proxy for microbial activity is inappropriate at this resolution. This study highlights the need to explicitly represent microbial physiology in microbial models. The interactive controls of environments and substrate on microbial seasonality provide insights for better representing microbial mechanisms in simulating ecosystem functions at the seasonal scale.

Hyphae move matter and microbes to mineral microsites: Integrating the hyphosphere into conceptual models of soil organic matter stabilization

Associations between soil minerals and microbially derived organic matter (often referred to as mineral-associated organic matter or MAOM) form a large pool of slowly cycling carbon (C). The rhizosphere, soil immediately adjacent to roots, is thought to control the spatial extent of MAOM formation because it is the dominant entry point of new C inputs to soil. However, emphasis on the rhizosphere implicitly assumes that microbial redistribution of C into bulk (non-rhizosphere) soils is minimal. We question this assumption, arguing that because of extensive fungal exploration and rapid hyphal turnover, fungal redistribution of soil C from the rhizosphere to bulk soil minerals is common, and encourages MAOM formation. First, we summarize published estimates of fungal hyphal length density and turnover rates and demonstrate that fungal C inputs are high throughout the rhizosphere-bulk soil continuum. Second, because colonization of hyphal surfaces is a common dispersal mechanism for soil bacteria, we argue that hyphal exploration allows for the non-random colonization of mineral surfaces by hyphae-associated taxa. Third, these bacterial communities and their fungal hosts determine the chemical form of organic matter deposited on colonized mineral surfaces. Collectively, our analysis demonstrates that omission of the hyphosphere from conceptual models of soil C flow overlooks key mechanisms for MAOM formation in bulk soils. Moving forward, there is a clear need for spatially explicit, quantitative research characterizing the environmental drivers of hyphal exploration and hyphosphere community composition across systems, as these are important controls over the rate and organic chemistry of C deposited on minerals.

UK Government Policy and the Transition to a Circular Nutrient Economy

The “circular economy” is an increasingly influential concept linking economic and environmental policy to enable sustainable use of resources. A crucial although often overlooked element of this concept is a circular nutrient economy, which is an economy that achieves the minimization of nutrient losses during the production, processing, distribution, and consumption of food and other products, as well as the comprehensive recovery of nutrients from organic residuals at each of these stages for reuse in agricultural production. There are multiple interconnecting barriers to transitioning from the current linear economic system to a more circular one, requiring strongly directional government policy. This paper uses interpretive policy analysis to review six UK government strategies to assess their strengths and weaknesses in embracing nutrient circularisation. Our analysis highlights the acute underrepresentation of the circular nutrient economy concept in these strategies as well as the potential to reorient the current policy towards its development. We find significant barriers to transition presented by ambiguity in key policy terms and proposals, the use of inappropriate indicators, the lack of a systematic approach to key sustainability objectives, and the presence of a “techno-optimist imaginary” throughout the strategies. We develop these findings to make recommendations to help integrate definitions, objectives, and activities across the policy domains necessary for the operational development of a circular nutrient economy.

Beyond bulk: Density fractions explain heterogeneity in global soil carbon abundance and persistence

Understanding the controls on the amount and persistence of soil organic carbon (C) is essential for predicting its sensitivity to global change. The response may depend on whether C is unprotected, isolated within aggregates, or protected from decomposition by mineral associations. Here, we present a global synthesis of the relative influence of environmental factors on soil organic C partitioning among pools, abundance in each pool (mg C g^-1  soil), and persistence (as approximated by radiocarbon abundance) in relatively unprotected particulate and protected mineral-bound pools. We show that C within particulate and mineral-associated pools consistently differed from one another in degree of persistence and relationship to environmental factors. Soil depth was the best predictor of C abundance and persistence, though it accounted for more variance in persistence. Persistence of all C pools decreased with increasing mean annual temperature (MAT) throughout the soil profile, whereas persistence increased with increasing wetness index (MAP/PET) in subsurface soils (30-176 cm). The relationship of C abundance (mg C g^-1  soil) to climate varied among pools and with depth. Mineral-associated C in surface soils (<30 cm) increased more strongly with increasing wetness index than the free particulate C, but both pools showed attenuated responses to the wetness index at depth. Overall, these relationships suggest a strong influence of climate on soil C properties, and a potential loss of soil C from protected pools in areas with decreasing wetness. Relative persistence and abundance of C pools varied significantly among land cover types and soil parent material lithologies. This variability in each pool's relationship to environmental factors suggests that not all soil organic C is equally vulnerable to global change. Therefore, projections of future soil organic C based on patterns and responses of bulk soil organic C may be misleading.

Multiple distinct, scale-dependent links between fungi and decomposition

Decomposition has historically been considered a function of climate and substrate but new research highlights the significant role of specific micro-organisms and their interactions. In particular, wood decay is better predicted by variation in fungal communities than in climate. Multiple links exist: interspecific competition slows decomposition in more diverse fungal communities, whereas trait variation between different communities also affects process rates. Here, we paired field and laboratory experiments using a dispersal gradient at a forest-shrubland ecotone to examine how fungi affect wood decomposition across scales. We observed that while fungal communities closer to forests were capable of faster decomposition, wood containing diverse fungal communities decomposed more slowly, independent of location. Dispersal-driven stochasticity in small-scale community assembly was nested within large-scale turnover in the regional species pool, decoupling the two patterns. We thus find multiple distinct links between microbes and ecosystem function that manifest across different spatial scales.

Response of carbon and microbial properties to risk elements pollution in arctic soils

A 180-day incubation study was conducted to evaluate the effects of risk elements (REs) on organic carbon use and microbial activities in organic soils in the Arctic during the summer snowmelt period. Soils were artificially spiked with Cd, Pb, Cr, Ni, Cu, As, and a combination of these REs according to the levels measured in Arctic soils from REs-polluted industrial sites. During the incubation period, microbial activities and microbial biomass carbon (MBC) formation were inhibited, and microbial quotient (qCO2) values were relatively high in the spiked soils indicating that more energy was used by microbes for maintenance under REs stress. Meanwhile, microbial metabolism was significantly restrained. Microbial Specific phospholipid fatty acids (PLFAs) were reduced in RE spiked soils relative to the control, especially in the As- and multi-RE-spiked soils. The abundance of both fungi and bacteria was reduced in response to RE amendments by 14-24% and 1-55%, respectively. PLFA biomarkers indicated a shift in soil microbial community structure and activities influenced by REs, consequently having a negative effect on soil organic carbon degradation. This study addresses the knowledge gap regarding the alternation of biochemical reactions in Arctic soils under anthropogenic REs with relevant contamination levels.

Elemental stoichiometry (C, N, P) of soil in the Yellow River Delta nature reserve: Understanding N and P status of soil in the coastal estuary

The Yellow River Delta Nature Reserve (YNR), which includes two separated regions: part of the old Yellow River Delta (OYD) and part of the current Yellow River Delta (CYD), was established to protect coastal wetlands in the coastal estuary. A total of 120 plots were sampled in the YNR in April 2016, and the spatial patterns of soil C, N and P contents and their stoichiometric ratios (C:N (R_CN), C:P (R_CP) and N:P (R_NP)) were studied and interpolated using the Ordinary Kriging method. Results indicated that the soil elemental contents and stoichiometric ratios showed high spatial heterogeneity and large variations. The mean C:N:P ratio (R_CNP) was ~ 64.7:2.3:1 in OYD, and ~ 64.5:2.0:1 in CYD, respectively, and a well-constrained R_CP ratio ~ 65:1 was found in the 0-50 cm soil depth within the YNR. N showed greater variation than C and P. Furthermore, N contents in the 0-5 cm soil layer of OYD were significantly higher than that of CYD (F = 4.79, p = 0.03); R_CN in 0-5 cm, 5-10 cm layers of OYD was significantly lower than those in the same layers of CYD (F = 4.75, p = 0.03; F = 5.18, p = 0.02, respectively). R_NP in 0-5 cm soil layer of OYD was notably higher than that of CYD (F = 4.88, p = 0.03). These results were due to the combined actions of sedimentation, reclamation and fertilization. Finally, we concluded that a longer reclamation and fertilization history led to decreased R_CN in coastal estuary soils, confirmed that the soil of the YNR exhibits N limitation, and suggested that the soil R_CN and R_NP could be good indicators of the anthropogenic improvement status during soil development in this coastal estuary.