Impacts of cobalt and zinc on improving peanuts nutrient uptake, yield and irrigation water use efficiency under different irrigation levels

The knowledge of proper fertigation across various irrigation levels is necessary for maximizing peanut yield and irrigation use efficiency in arid areas, and it also can effectively alleviate the risk of nutrient deficiency induced by water stress. This study evaluated the effectiveness of cobalt combined with two zinc application methods on peanut nutrient uptake, yield, and irrigation water use efficiency across varying irrigation levels. A split-split plot experiment was carried out in 2021 and 2022. Three peanut gross water requirement (GWR) levels (100%, 80%, and 60%) were designated for main plots. Subplots featured plants treated with either 0 or 7.5 mg L-1 of cobalt. The sub-sub plots assessed chelated zinc effects at rates of 0 and 2 g L-1 via foliar and soil applications. In comparison to the control (100% GWR), nutrient uptake decreased, with sodium being the exception, and there was an increase in soil pH at 60% GWR. The results showed also significant reductions in yield and water use by approximately 60.3% and 38.1%, respectively. At this irrigation level, applying zinc via soil, either alone or combined with cobalt, led to significant yield increases of 89.7% and 191.3% relative to the control. Also, it's crucial to note that cobalt application negatively affected iron and copper at 60% GWR, but this impact was lessened with soil-applied zinc. Hence, under a similar circumstance, treating stressed peanut plants with additional foliar applications of iron + copper and applying zinc via soil, could enhance nutrient uptake and improve yield. On the other hand, at 80% GWR, a combination of foliar-applied zinc and cobalt, had a tremendous impact on the absorption of (nitrogen, phosphorus, magnesium, and zinc), resulting in enhanced agronomic traits and decreased water losses. Additionally, at this irrigation level, foliar zinc application alone yielded a 32.4% increase compared to the 80% GWR control. When combined with cobalt, there was a 70.0% surge in water use. Based on this knowledge, the study suggests using 80% GWR and treating peanut plants with a combination of foliar-applied zinc and cobalt. This strategy aids plants in countering the adverse effects of water stress, ultimately leading to enhanced yield and irrigation water use efficiency.

A combined strategy to mitigate the accumulation of arsenic and cadmium in rice (Oryza sativa L.)

Arsenic and cadmium in rice grain are of growing concern in the global food supply chain. Paradoxically, the two elements have contrasting behaviors in soils, making it difficult to develop a strategy that can concurrently reduce their uptake and accumulation by rice plant. This study examined the combined impacts of watering (irrigation) schemes, different fertilizers and microbial populations on the bioaccumulation of arsenic and cadmium by rice as well as on rice grain yield. Compared to drain-flood and flood-drain treatments, continuously flooded condition significantly reduced the accumulation of cadmium in rice plant but the level of arsenic in rice grain remained above 0.2 mg/kg, which exceeded the China national food safety standard. Application of different fertilizers under continuously flooded condition showed that compared to inorganic fertilizer and biochar, manure addition effectively reduced the accumulation of arsenic over three to four times in rice grain and both elements were below the food safety standard (0.2 mg/kg) while significantly increasing the rice yield. Soil Eh was the critical factor in the bioavailability of cadmium, while the behavior of arsenic in rhizosphere was associated with the iron cycle. The results of the multi-parametric experiments can be used as a roadmap for low-cost and in-situ approach for producing safe rice without compromising the yield.

The fate of amino acid and peptide as affected by soil depth and fertilization regime in subtropical paddies

Amino acids and peptides are important regulators of ecosystem functioning due to their potential role as direct nutrient sources for plants and soil microbes. However, the turnover and driving factors of these compounds in agricultural soils remain poorly understood. This study aimed to reveal the short-term fate of ¹⁴C-labeled alanine and tri-alanine derived C under flooding conditions of the top (0-20 cm) and sub-horizons (20-40 cm) of subtropical paddy soils taken from four long-term (31 years since treatment) nitrogen (N) fertilization regimes (i.e., without fertilization, NPK, NPK with straw return (NPKS) or with manure (NPKM)). Amino acid mineralization was strongly affected by the N fertilization regime and soil depth, while peptide mineralization was only distinct between soil layers. The average half-life of amino acid and peptide in the topsoil was 8 h across all treatments, which was higher than previously reported in uplands. The microbial turnover of amino acid and peptide was 7-10 times slower in the subsoil than in the topsoil, with a half-life of about 2-3 days. The half-life of amino acid and peptide for the respired pool was strongly associated with soil physicochemical characteristics, the total biomass, and the structure of soil microbial communities. The N fertilization regime and soil depth affected the substrate uptake rate by microorganisms, with greater uptake observed in the NPKS and NPKM treatments and the topsoil. Microbial amino acid uptake was correlated with the biomass of total and individual microbial groups, whereas microbial peptide uptake was associated with the soil microbial community structure and physicochemical characteristics. This suggests that there are various pathways of amino acid and peptide use by microorganisms under flooding conditions. We conclude that microbial mineralization of amino acid and its peptide in paddy soils under flooding conditions is slower than in upland soils, and that microbial uptake of these substrates is related to soil abiotic factors and the biomass and structure of soil microbial community. These findings have important implications for understanding nutrient cycling and ecosystem functioning in agricultural soils.

Understanding local ecosystem dynamics in three provinces of the lowlands of Nepal

Incidences of failure of sustainable ecosystem management policies, especially in the developing world are partly attributable due to a lack of political will and inadequate understanding of ecosystem dynamics (ED) at the local levels. In this study, we endeavor to comprehend the dynamics of two ecosystems - forest and agriculture - by employing a resource-friendly participatory approach based on stake-taking the experiences of indigenous and forest-dependent local stakeholders in three lowland provinces of Nepal and is guided by the theory of socio-ecological concept. An in-depth survey (n = 136) was conducted using semi-structured questionnaires, key informant interviews (n = 9), and focus group discussions (n = 4) for data generation, and generalized linear models were used to test whether understanding of ED is uniform across the socio-ecological landscape. We identified that various attributes of forests and agricultural ecosystems have altered substantially earlier than 30 years (hereafter, earlier decade) relative to the present (hereafter, later decade). Apart from the natural processes including anthropogenic and climatic factors, technological innovations played a significant role in altering ecosystems in the later decade. Understanding of ED among forest-dependent stakeholders significantly varied with respect to gender, occupation, age group, gender-based water fetching responsibility, and water-fetching duration, however, no significant correlation was observed with their level of education across the landscape. The studied ecosystem attributes significantly correlate with water regime changes, signifying that water-centric ecosystem management is crucial. The attributes that observed significant dynamics in the forest ecosystem include changes in forest cover, structure and species composition, the severity of invasive species, wildfires, water regimes, and abundance and behavioral changes in mammals and avifauna. The alteration of crop cultivation and harvesting season which results in a decrease in yield, increased use of chemicals (fertilizers and pesticides), an increase in fallow land, and the proliferation of hybrid variety cultivation in the later decade are significant disparities in the dynamics of the agriculture ecosystem. To withstand the accelerated ED, stakeholders adopt various strategies, however, these strategies are either obtained from unsustainable sources entail high costs and technology, or are detrimental to the ecosystems. In relation, we present specific examples of ecosystem attributes that have significantly experienced changes in the later decade compared to the earlier decades along with plausible future pathways for policy decisions sustaining and stewardship of dynamic ecosystems across the socio-ecological landscape.

How to not trade water for carbon with tree planting in water-limited temperate biomes?

The most widespread nature-based solution for mitigating climate change is tree planting. When realized as forest restoration in historically forested biomes, it can efficiently contribute to the sequestration of atmospheric carbon and can also entail significant biodiversity and ecosystem service benefits. Conversely, tree planting in naturally open biomes can have adverse effects, of which water shortage due to increased evapotranspiration is among the most alarming ones. Here we assessed how soil texture affects the strength of the trade-off between tree cover and water balance in the forest-steppe biome, where the global pressure for afforestation is threatening with increasing tree cover above historical levels. Here we monitored vertical soil moisture dynamics in four stands in each of the most common forest types of lowland Hungary on well-drained, sandy (natural poplar groves, and Robinia and pine plantations) and on poorly drained, silty-clayey soils (natural oak stands and Robinia plantations), and neighboring grasslands. We found that forests on sand retain moisture in the topsoil (approx. 20 cm) throughout the year, but a thick dry layer develops below that during the vegetation period, significantly impeding groundwater recharge. Neighboring sandy grasslands showed an opposite pattern, with often dry topsoil but intact moisture reserves below, allowing deep percolation. In contrast, forests on silty-clayey soils did not desiccate lower soil layers compared neighboring grasslands, which in turn showed moisture patterns similar to sandy grasslands. We conclude that, in water-limited temperate biomes where landscape-wide water regime depends on deep percolation, soil texture should drive the spatial allocation of tree-based climate mitigation efforts. On sand, the establishment of new forests should be kept to a minimum and grassland restoration should be preferred. The trade-off between water and carbon is less pronounced on silty-clayey soils, making forest patches and wooded rangelands viable targets for both climate mitigation and ecosystem restoration.

The Ecological Differentiation of Particle-Attached and Free-Living Bacterial Communities in a Seasonal Flooding Lake-the Poyang Lake

Particle-attached (PA) and free-living (FL) bacterial communities play essential roles in the biogeochemical cycling of essential nutrients in aquatic environments. However, little is known about the factors that drive the differentiation of bacterial lifestyles, especially in flooding lake systems. Here we assessed the compositional and functional similarities between the FL and PA bacterial fractions in a typical flooding lake-the Poyang Lake (PYL) of China. The results revealed that PA communities had significantly different compositions and functions from FL communities in every hydrological period, and the diversity of both PA and FL communities was affected mainly by the water regime rather than bacterial lifestyles. PA communities were more diverse and enriched with Proteobacteria and Bacteroidetes, while FL communities had more Actinobacteria. There was a higher abundance of photosynthetic and nitrogen-cycling bacterial groups in PA communities, but a higher abundance of members involved in hydrocarbon degradation, aromatic hydrocarbon degradation, and methylotrophy in FL communities. Water properties (e.g., temperature, pH, total phosphorus) significantly regulated the lifestyle variations of PA and FL bacteria in PYL. Collectively, our results have demonstrated a clear ecological differentiation of PA and FL bacterial communities in flooding lakes, suggesting that the connectivity between FL and PA bacterial fractions is water property-related rather than water regime-related.

Natural 15N abundance as an indicator of nitrogen utilization efficiency in rice under alternate wetting and drying irrigation in soils with high clay contents

The ¹⁵N natural abundance is an effective indicator of nitrogen dynamics in plants. The impact of different irrigation regimes as a function of varied soil clay contents on stable nitrogen isotope abundance (δ¹⁵N) in rice remains unknown. Therefore, the response of δ¹⁵N and nitrogen utilization efficiency (NUE) of rice to different combinations of alternate wetting and drying irrigation (AWD) and clay contents were investigated. The study included three AWD regimes, viz. I100, (100 % saturation, 30 mm flooded), I90 (90 % saturation, 30 mm flooded) and I70 (70 % saturation, 30 mm flooded), and three soil clay content treatments, viz. 40 % (S40), 50 % (S50), and 60 % (S60) clay content. Compared with I100, I90 and I70 with high clay content (S60) significantly increased the crack volumes and N leaching losses and reduced the total N accumulation and different forms of NUE of rice plants. The values of δ¹⁵N in above-ground organs and soil were greatly increased by I90 and I70 irrigation regimes compared to I100. An increasing trend of organs δ¹⁵N from root to shoot was found for all three irrigation regimes. Significant negative relationships were found between (i) N partial factor productivity (PFP) and grain ¹⁵N, (ii) PFP and leaf ¹⁵N, and (iii) N harvest index (NHI) and leaf ¹⁵N. These significant negative relationships might contribute to the increased N losses and changed N allocation under AWD with high clay contents. Hence, it is suggested that cracks should be taken into consideration in rice cultivation. Moreover, δ¹⁵N may serve as an effective indicator of NUE in rice grown under AWD irrigation with high clay contents as well as an indirect indicator for assessing the N loss in agro-ecosystems.

The influence of water regime on cadmium uptake by Artemisia: A dominant vegetation in Poyang Lake wetland

An analysis of the influence of water regime on the metal accumulation processes of wetland plants can improve the efficiency of phytoremediation. However, few studies have clearly explored the mechanism of influence of water regime on the process of accumulation of metals by the dominant vegetation in Poyang Lake wetland, the largest freshwater lake in China. The aim of this study was to investigate the influence of water regime (Flooding condition [FC], Dry condition [DC] and alternate dry and flooding condition [DFC]) on the accumulation of cadmium (Cd) by Artemisia selengensis Turcz. ex Bess., a dominant plant in the Poyang Lake wetland. The results indicated that FC treatment significantly enhanced the accumulation of Cd by Artemisia roots compared with DFC and DC treatments. In addition, the DFC treatment significantly increased the translocation of Cd from roots to shoots compared with the FC treatment. A multivariate statistical analysis indicated that the rhizosphere Cd fraction, iron plaque on the root surface and rhizosphere pH directly or indirectly significantly influence the process of accumulation of Cd. The conversion of exchangeable fraction to Fe/Mn oxide bound and organic fraction under the DFC and FC treatments decreased the accumulation of Cd in Artemisia. The formation of increased amounts of iron plaque under the FC treatment may enhance the accumulation of Cd in roots, while it may reduce the translocation of Cd to aboveground tissues. In addition, a higher rhizosphere pH under the FC treatment may promote accumulation of Cd in the root by inducing formation of iron plaque. Similarly, compared with the FC treatment, a lower rhizosphere pH and iron plaque can induce the processes of Cd translocation under the DFC treatment. Based on the bioaccumulation factor, translocation factor and the ratio of root/aerial Cd content, treatment with DC benefited the phytoextraction of Cd, while treatment with DFC and FC enhanced the phytostabilization of Cd by Artemisia. This study provides valuable information for deeply understanding the resilience of wetland ecosystems and for enhancing the phytoremediation with wetland plants using water management.

Changes in soil water availability and air-temperature impact biomass allocation and C:N:P stoichiometry in different organs of Stylosanthes capitata Vogel

Temperature and soil water availability play important roles in the biogeochemical cycles of essential elements for plant growth, such as carbon (C), nitrogen (N), and phosphorus (P). In this study, we investigated how drought and warming impact C:N:P stoichiometric ratios of different plant organs (leaves, inflorescences, and stems), and biomass allocation and production of a field-grown pasture of Stylosanthes capitata, a tropical forage legume. We evaluated the effects of elevated temperature (+2 °C above ambient temperature) under two conditions of soil water availability, irrigated, and non-irrigated. In general, we observed that different functional plant organs showed distinct responses to drought and warming demonstrating how important is to evaluate different functional plant organs to unravel crop nutrient dynamics. In addition, interactive effects between warming and drought were observed in many situations, highlighting the importance of multifactorial studies. Our data showed that warming produced plants with more inflorescences, decreasing leaf:inflorescence ratio. However, only warming under well-watered conditions improved biomass production (in 38%). Warmed and irrigated plants showed higher stoichiometric homeostasis compared to other treatments. In an opposite direction, drought decreased P concentration and increased N:P ratios in different organs, reducing the stoichiometric homeostasis under both conditions of temperature. We have concluded that warm and well-watered conditions without restrictions in soil nutrient availability can enhance plant production, presumably due to a higher level of stoichiometric homeostasis.

Rice straw biochar mitigated more N2O emissions from fertilized paddy soil with higher water content than that derived from ex situ biowaste

Biochar could mitigate greenhouse gas emissions, especially nitrous oxide (N₂O). Effects of interactions between different biochar and water content on N₂O emissions from rice (Oryza sativa L.) paddy soils have not been thoroughly understood. We evaluated effects of different biochar (derived from Camellia oleifera fruit shell, FS; spent mushroom substrate made of Camellia oleifera fruit shell, MS; rice straw, RS; at the rate of 40 g kg^-1) and water contents (70% and 120% water holding capacity, WHC) on N₂O emissions from rice paddy soil fertilized with nitrogen (N, 0.2 g kg^-1), and examined microbial functional genes associated with N₂O emissions to understand the underlining mechanisms. The results showed that RS biochar was higher in pH, available N, dissolved organic N, and decreased more N₂O emissions from soils with N and 120% WHC treatment relative to MS and FS biochar (by 363% and 200%, respectively). Although RS biochar potentially increased the abundance of ammonia-oxidizing archaea amoA gene (AOA), changes in functional gene abundance did not concur with decreases in N₂O emissions. Instead of changes in microbial communities, the relatively higher pH as well as lower available N and dissolved organic C and N of RS biochar could have contributed to the decrease in N₂O emissions compared with MS and FS biochar. Thereby, the in situ application of rice straw via biochar could be considered in the mitigation of N₂O emissions from fertilized rice paddy soil instead of biochar derived from ex situ feedstock.

The contribution of 137Cs export flux from the Tone River Japan to the marine environment

The contribution of ¹³⁷Cs transport to the marine environment via the Tone River, Japan was investigated. This river has the largest discharge among rivers on the North Pacific side of eastern Japan. The sampling site was located upstream near the river mouth and dissolved and particulate ¹³⁷Cs in the river water was measured during 2014-2015, three years after the Tokyo Electric Power Corporation Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Annual fluxes of total (dissolved and particulate) ¹³⁷Cs with considering desorption of ¹³⁷Cs from riverine particles by change of salinity from the Tone River were similar in both years (78-107 × 10⁹ Bq/y), indicating that about 0.03-0.06% of the estimated total amount of ¹³⁷Cs deposited in the catchment (1.9-2.8 × 10¹⁴ Bq) was transported to the marine environment each year. Although the annual flux was about one order of magnitude lower than the daily direct discharge into the ocean from the FDNPP (800 × 10⁹ Bq/y) during the corresponding period, continuous monitoring of rivers in the southern coastal area of east Japan on the North Pacific side are needed for the effect of ¹³⁷Cs release via the rivers in the Kanto area over the long-term.

Re-vegetation processes in cutaway peat production fields in Estonia in relation to peat quality and water regime

Eighty-one cutaway peat production fields with a total area of about 9000 ha exist and were studied in Estonia in 2005-2015. Only a very small number of the fields (seven) have been restored-either afforested or used for growing berries. The re-vegetation of Estonian cutaway peat production fields is mainly the result of natural processes, which are generally very slow due to an unfavourable water regime or a too thin remaining peat layer. The fields are mostly covered by cotton grass and birches. Often sparse vegetation covers 15-20% of a peat field, but some fields have turned into heaths or grasslands with plant coverage up to 60%. However, due to changes in environmental (mainly hydrological) conditions and peat characteristics (mainly peat type), these areas can also be new niches for several species. A number of moss species new to or rare in Estonia, e.g. Pohlia elongata, Ephemerum serratum, Campylopus introflexus and Bryum oblongum, were recorded.

Combination of wet irrigation and nitrification inhibitor reduced nitrous oxide and methane emissions from a rice cropping system

To conserve water resources and guarantee food security, a new technology termed as "wet irrigation" is developed and practiced in rice fields; thus, its impact on radiative forcing derived from nitrous oxide (N2O) and methane (CH4) emissions merits serious attention. Dicyandiamide (DCD), a kind of nitrification inhibitor, is proposed as a viable means to mitigate greenhouse gas (GHG) emission while enhancing crop productivity. However, little is known about the response of GHG emission and grain yield to DCD application in a rice system under wet irrigation. In these regard, effects of water regime and DCD application on CH4 and N2O emissions, grain yield, global warming potential (GWP), and greenhouse gas intensity (GHGI) from rice fields were studied. For this study, a field experiment, designed: Treatment II (intermittent irrigation), Treatment WI (wet irrigation), Treatment IID (II plus DCD), and Treatment WID (WI plus DCD), was conducted in Jurong, Jiangsu Province, China, from 2011 to 2012. Relative to Treatment II, Treatment WI decreased CH4 emission significantly by 49-71 % while increasing N2O emission by 33-72 %. By integrating CH4 and N2O emissions and grain yield, Treatment WI was 20-28 and 11-15 % lower than Treatment II in GWP and GHGI, respectively. The use of DCD under wet irrigation reduced N2O emission significantly by 25-38 % (p < 0.05) and CH4 emission by 7-8 %, relative to Treatment WI, resulting in a decline of 18-30 % in GWP. Due to the increase in N use efficiency, maximal grain yield (6-7 %) and minimal GHGI (22-34 %) was observed in Treatment WID. These findings indicate that combined application of N fertilizer and DCD is a win-win strategy in water-saving high-yield rice production with less GHG emission.

Impact of water regimes on an experimental community of four desert arbuscular mycorrhizal fungal (AMF) species, as affected by the introduction of a non-native AMF species

Field studies have revealed the impact of changing water regimes on the structure of arbuscular mycorrhizal fungal (AMF) communities, but it is not known what happens to the abundance of individual AMF species within the community when the water conditions in the rhizosphere change. The behavior of four AMF species isolated from the Arabian desert (Diversispora aurantia, Diversispora omaniana, Septoglomus africanum, and an undescribed Paraglomus species) was investigated when assembled in microcosms containing Sorghum bicolor as host plant, and treated with various water regimes. Furthermore, the impact of invasion of these assemblages by Rhizophagus irregularis, an AMF species widely used in commercial inocula, was studied. The abundance of each AMF species in sorghum roots was measured by determining the transcript numbers of their large ribosomal subunit (rLSU) by real-time PCR, using cDNA and species-specific primers. Plant biomass and length of AMF extraradical hyphae were also measured. The abundance of each AMF species within the sorghum roots was influenced by both the water regime and the introduction of R. irregularis. Under dry conditions, the introduction of R. irregularis reduced the total abundance of all native AMF species in roots and also led to a reduction in the amount of extraradical mycelium, as well as to a partial decrease in plant biomass. The results indicate that both water regime and the introduction of an invasive AMF species can strongly alter the structure of an AMF native assemblage with a consequent impact on the entire symbiotic mycorrhizal relationship.