Rice Ecosystem Research Articles

Balance of humus and nutrients in the meadow-chernozem soil of the rice ecosystem

Balance of humus and nutrients in the meadow-chernozem soil of the rice ecosystem

Paddy Rice Mapping Based on Phenology Matching and Cultivation Pattern Analysis Combining Multi-Source Data in Guangdong, China

Paddy rice mapping is crucial for cultivation management, yield estimation, and food security. Guangdong, straddling tropics and subtropics, is a major rice-producing region in China. Mapping paddy rice in Guangdong is essential. However, there are 2 main difficulties in tropical and subtropical paddy rice mapping, including the lack of high-quality optical images and differences in paddy rice planting times. This study proposed a paddy rice mapping framework using phenology matching, integrating Sentinel-1 and Sentinel-2 data to incorporate prior knowledge into the classifiers. The transplanting periods of paddy rice were identified with Sentinel-1 data, and the subsequent 3 months were defined as the growth periods. Features during growth periods obtained by Sentinel-1 and Sentinel-2 were inputted into machine learning classifiers. The classifiers using matched features substantially improved mapping accuracy compared with those using unmatched features, both for early and late rice mapping. The proposed method also improved the accuracy by 6.44% to 16.10% compared with 3 other comparison methods. The model, utilizing matched features, was applied to early and late rice mapping in Guangdong in 2020. Regression results between mapping area and statistical data validate paddy rice mapping credibility. Our analysis revealed that thermal conditions, especially cold severity during growing stages, are the primary determinant of paddy rice phenology. Spatial patterns of paddy rice in Guangdong result from a blend of human and physical factors, with slope and minimum temperature emerging as the most important limitations. These findings enhance our understanding of rice ecosystems’ dynamics, offering insights for formulating relevant agricultural policies.

Mitigating atmospheric methane emissions from Asian rice fields: a review of potential and promising technical options

Agriculture serves as a significant anthropogenic source of methane emissions. Numerous recent studies have examined the factors influencing methane emissions and have developed emission models. However, there is no a bridging review study related to methene emissions in Asia as one of the primary methane emitters. This review is divided into two manuscripts. In this first manuscript, I explore the process of methane emission and the factors that impact methane production and emissions. Meanwhile, the present state of studies conducted in various Asian countries and knowledge gaps are elaborated in the second manuscript. I elaborate several factors that influence methane production and their roles in the emission process. Further, I highlight that the gas is mostly produced in zero oxygen condition, although, a little concentration of methane also can be generated in oxic condition. This finding provides basic knowledge that contribute to the future research on methane emissions in rice field ecosystems. Eventually, I also explore various recommended technical solutions to reduce the gas emission.

Assessment of rice sheath rot disease risk for its establishment in Southern Coastal states of India

Rice sheath rot (Sarocladium oryzae) is an emerging disease in all rice ecosystems and considered as one of the major threats to rice production. For development of precise management strategies spatial distribution of infection risk is essential to ascertain epidemic nature of the disease. For risk estimation, temperature-based infection model has been designed and disease risk estimated as the monthly cumulative value of the daily infection index. Geo-spatial distribution of infection risk has been assessed for the coastal rice ecosystems based on 39 years of weather data and two years (2018 and 2019) of surveyed ground truth. Infection risk was noted to be higher in kharif than rabi season and the eastern coast was identified as hotspot. Yearly variation estimates has indicated rabi rice is likely to be vulnerable to climate change arising due to temperature rise. Infection risk prediction based on critical weather factor is useful in germplasm, fungicide evaluation along with development of management strategies.

Effects of Betacyfluthrin + Imidacloprid OD (Solomon) against Major Plant Hoppers on Rice Ecosystem in Burdwan, West Bengal

The current study was conducted to evaluate the effects of three distinct levels of concentration of Betacyfluthrin 90 g l-1 + Imidacloprid 210 g l-1 OD (Solomon) (45 g a.i. ha-1, 60 g a.i. ha-1 and 75 g a.i. ha-1) during kharif 2020 and 2021 against major plant hoppers of rice. White backed plant hopper (Sogatella furcifera) and Brown plant hopper (Nilaparvata lugens) were found as major plant hoppers on rice field. Solomon @ 75 g a.i. ha-1 was recorded significantly efficient against BPH and WBPH in both crop seasons (kharif 2020 and kharif 2021) with highest reduction over control (80.42% & 76.22% and 79.65% & 83.54%, respectively). A noticeably increased yield of rice grains was observed in case of Solomon @ 75 g a.i. ha-1 treatment than in control plot in kharif 2020 (73.78 q ha-1) and kharif 2021 (68.03 q ha-1). Although the natural enemy population in the plots that were treated with Solomon @ 10-30 g a.i. ha-1 had no significant negative impact than the untreated control and other treated plots.

Response of Spider and Epigaeic Beetle Assemblages to Overwinter Planting Regimes and Surrounding Landscape Compositions.

The rotation patterns of summer rice-winter oil seed rape and summer rice-winter fallow are the main planting regimes in the rice ecosystem in southern China. However, the impact of local rotation patterns and landscape factors on the overwintering conservation of predators in spider and epigaeic beetle assemblages remains poorly understood. Here, we investigate the diversity and density of spiders and beetles over two consecutive winters (2019/2020 and 2020/2021), focusing on the impact of two rotation patterns (rice-fallow and rice-oilseed rape) and surrounding landscape compositions on predator diversity. The main findings of our research were that spiders were more abundant and had a higher activity density in the fallow rice fields (FRs) compared to the oilseed rape fields (OSRs), whereas ground beetles exhibited the opposite pattern. Specifically, fallow rice fields supported small and ballooning spiders (e.g., dominant spider: Ummeliata insecticeps), while OSRs supported larger ground beetles (e.g., dominant beetles: Agonum chalcomus and Pterostichus liodactylus). Moreover, the composition of spider assemblages were impacted by semi-natural habitats (SNHs) during overwintering, while ground beetle assemblages were influenced by overwinter planting patterns. Overall, our results suggest that different planting regimes and preserving semi-natural habitats are a strategic way to enhance species diversity and functional diversity of ground predators. It is, therefore, recommended that to conserve and improve predator diversity during overwintering, land managers and farmers should aim to maintain diverse planting regimes and conserve local semi-natural habitats.

Insect Diversity of Some Hybrid Rice Genotypes in Sleman-Yogyakarta Irrigated Agroecosystem

Diversity of insect at the rice field gives a main impact to the stability of ecosystem. Index of diversity reflects the relationship of species abundance in the community. This research was aimed to determine the diversity of insect at some hybrid rice varieties in irrigated rice agroecosystem. Research was conducted in Sleman, Yogyakarta Indonesia from April to August 2018. The experiment was conducted using purposive random sampling. Insect samples were obtained using swing net and visual observation. Diversity index was analysed using Shanon (H), while diversity and uniformity of insect was examined using Evennes index (E). Result showed pest insects found during vegetative stage of rice consist of more species, while lower numbers were found at generative stage with less species. They were belongs to 6 orders (more than 10 families) such as Diptera, Lepidoptera, Coleoptera, Orthoptera, Hemiptera and Hymenoptera. The dominant pest was Cicadellidae, followed by Delphacidae and Alydidae. Based on the diversity data analysis (H), pest insects and natural enemies were between moderate and high, with a range between 1.5 to 2.5. It indicates the rice field ecosystem planted with hybrid rice gave good impact and balance species diversity in the agroecosystem of irrigated rice area in Sleman Yogyakarta.

ICP-OES analysis of total As and Cd in Columbian Oryza sativa L. rice

ABSTRACT Arsenic (As) and cadmium (Cd) are considered toxic elements, even at trace levels. Their accurate quantification in crops can be complex at low levels and due to interference with other elements. The aim of this work was to develop and validate an analytical method for As and Cd quantification in rice stem and grains from the production systems “Irrigated Rice Ecosystems” (IRE) and “Rainfed Rice Ecosystems” (RRE) in Colombia. Mineralisation was carried out by acid digestion using an open system with a heating plate. Metal detection was performed by inductively coupled plasma optical emission spectrometry (ICP‐OES). Method adjustment, calibration, and validation were performed in accordance with AOAC standards, considering sensitivity, precision, accuracy, and selectivity parameters. The obtained method was applied to quantify levels in 259 rice stem and 443 grain samples from IRE and RRE.

A microscopic scenario on recovery mechanisms under waterlogging and submergence stress in rice.

Adaptive traits in rice responding to flooding, a compound stress, are associated with morpho-anatomical and physiological changes which are regulated at the genetic level. Therefore, understanding submergence stress tolerance in rice will help development of adapted cultivars that can help mitigate agricultural losses. Rice is an important dietary component of daily human consumption and is cultivated as a staple crop worldwide. Flooding is a compound stress which imposes significant financial losses to farmers. Flood-affected rainfed rice ecosystems led to the development of various adaptive traits in different cultivars for their optimal growth and survival. Some cultivars can tolerate hypoxia by temporarily arresting elongation and conserving their energy sources, which they utilize to regrow after the stress conditions subside. However, few other cultivars rapidly elongate to escape hypoxia using carbohydrate resources. These contrasting characters are regulated at the genetic level through different quantitative trait loci that contain ERF transcription factors (TFs), Submergence and Snorkels. TFs can simultaneously activate the transcription of various genes involved in stress and development responses. These TFs are of prime importance because the introgressed and near-isogenic lines showed promising results with increased submergence tolerance without affecting yield or quality. However, the entire landscape of submergence tolerance is not entirely depicted, and further exploration in the field is necessary to understand the mechanism in rice completely. Therefore, this review will highlight the significant adaptive traits observed in flooded rice varieties and how they are regulated mechanistically.

Impact of Crude Oil Contamination on Soil Physicochemical Properties around the Sildubi Oil Spill, Borhola, Assam

Crude oil contamination can affect the soil physicochemical properties and it is a serious constraint on the rice ecosystem near the oil drilling sites. The objective of this study was to identify the effects of crude oil contamination through oil exploration on soil health and the horizontal distribution of soil nutrients in rice field soils in the Sildubi area, Jorhat district, Assam. Soil samples were collected at a depth of 0–15 cm from the drilling site and from the four directions (East, West, South and North) in a circular mode with a radius of 500 and 1000m away from the oil spill. Each sample was mounded with four replications. Samples were analyzed for physicochemical properties by using standard methods that reflect soil nutrient status.
 The percentage of organic carbon, organic matter and soil pH are found to be higher at the drilling site compared to the results obtained in the rice field soils, apart by 500 and 1000m from the central zone. Similarly, bulk density, moisture percentage and electrical conductivity were found to be lowest in the soils of the drilling site. In our study, considerable variation in the horizontal distribution of soil nutrients was also observed. The highest P, Ca and nitrogen contents were recorded in the oil-contaminated soils compared to soils collected from 500 and 1000m radius. The total soil Fe was significantly higher in the samples collected at 1000m. Spilled crude oil is certainly responsible for alterations in soil physicochemical properties and the horizontal distribution of some plant-specific nutrients. High concentrations of Fe and P observed due to crude oil contamination have been developing Fe stress situations reducing crop production in nearby agricultural lands.

Exploration of The Species Richness of Butterfly (Hexapoda: Odonata) in The Rice Field Ecosystem of Perian village, Montong Gading, East Lombok

Several Odonata studies on Lombok Island still focus on forest and river habitat types. This causes the diversity of this insect group to be unknown in other habitats such as rice fields. This research aims to explore the richness of dragonfly species in the rice field ecosystem of Perian village, Montong Gading subdistrict, East Lombok district. Sample collection was carried out in May – June 2022. Dragonfly searches were carried out in the morning from 08.00 – 12.00, and in the afternoon from 14.00 – 18.00 on two transects determined purposively. The odonata found were documented using a digital camera, and captured using insect nets. Samples that were successfully collected were identified to the species taxon. The total odonata we found were 2 suborders, 5 families and 11 species. The suborder Zygoptera is the group with the highest species richness. For families, Libellulidae and Coenagrionida are the families with the highest species richness compared to other families. Of the 11 species that we found, 1 species is endemic, namely Euphaea lara lombokensis. Compared with the results of previous research conducted in Suranadi and Batu Bolong River, there are 5 species which are new records. The five species are Copera ciliata, Rhinocypha bisignata, Ischnura senegalensis, Ischnura heterosticta, and Brachythemis contaminata. The results of this study indicate that there are more species from the Odonata order on Lombok Island compared to previous reports.

Central Role of Nitrogen Fertilizer Relative to Water Management in Determining Direct Nitrous Oxide Emissions From Global Rice‐Based Ecosystems

AbstractThe increasing atmospheric nitrous oxide (N2O) concentration stems from the development of agriculture. However, N2O emissions from global rice‐based ecosystems have not been explicitly and systematically quantified. Therefore, this study aims to estimate the spatiotemporal magnitudes of the N2O emissions from global rice‐based ecosystems and determine different contribution factors by improving a process‐based biogeochemical model, TRIPLEX‐GHG v2.0. Model validation suggested that the modeled N2O agreed well with field observations under varying management practices at daily, seasonal, and annual steps. Simulated N2O emissions from global rice‐based ecosystems exhibited significant increasing trends from 0.026 ± 0.0013 to 0.18 ± 0.003 TgN yr−1 from 1910 to 2020, with ∼69.5% emissions attributed to the rice‐growing seasons. Irrigated rice ecosystems accounted for a majority of global rice N2O emissions (∼76.9%) because of their higher N2O emission rates than rainfed systems. Regarding spatial analysis, Southern China, Northeast India, and Southeast Asia are hotspots for rice‐based N2O emissions. Experimental scenarios revealed that N fertilizer is the largest global rice‐N2O source, especially since the 1960s (0.047 ± 0.010 TgN yr−1, 35.24%), while the impact of expanded irrigation plays a minor role. Overall, this study provides a better understanding of the rice‐based ecosystem in the global agricultural N2O budget; further, it quantitively demonstrated the central role of N fertilizer in rice‐based N2O emissions by including rice crop calendars, covering non‐rice growing seasons, and differentiating the effects of various water regimes and input N forms. Our findings emphasize the significance of co‐management of N fertilizer and water regimes in reducing the net climate impact of global rice cultivation.

Inventory of leafhoppers in irrigated rice in Tamil Nadu

Leafhoppers diversity was studied in irrigated rice ecosystems of Cauvery Delta Zone, High Rainfall Zone and Western Zone. Leafhopper assemblage comprised 14 species of Cicadellidae and among them Maiestas dorsalis (Motschulsky) was found to be the most abundant species (35.02%), followed by Cofana spectra (Distant) (23.15%). The order of species diversity in the observed districts were Western Zone (13 species) > High Rainfall Zone (8 species) > Cauvery Delta Zone (4 species). Shannon Weiner Index revealed a higher diversity in High Rainfall Zone and Western Zone (H'= 1.77 > 1.76). Margalef's Index of species richness was observed highest in Western Zone (a = 1.93). Pielou's Evenness Index was found to be almost similar for Western Zone (0.30) and Cauvery Delta Zone (0.29) while High Rainfall Zone exhibited highest evenness (0.37). Jaccard index of similarity of 50% (highest) was observed between Western Zone and Kanyakumari, Cauvery Delta Zone and High Rainfall Zone. Berger-Parker Index of dominance (D) revealed M. dorsalis to be the most dominant in Western Zone (0.25) and Cauvery Delta Zone (0.66) while High Rainfall Zone showed a high dominance of Nephotettix nigropictus (Stål) (0.27). Among the leafhoppers studied Balclutha incisa (Matsumura), Cicadulina bipunctata (Melichar), Empoascanara maculifrons (Motschulsky), Exitianus sp., Thomsonia porrecta (Walker) were recorded for the first time in rice ecosystem of Tamil Nadu. The present study will be a baseline information on the diversity of leafhoppers in irrigated rice of Tamil Nadu and will complement the data collected in the future to gain a holistic understanding on the leafhopper diversity of Tamil Nadu.

Decomposition and nitrogen mineralization of <em>Gliricidia sepium</em> leaf green manure under diverse nutrient management strategies in irrigated lowland rice cropping systems in Sri Lanka

The utilization of green manure has become an essential strategy for enhancing soil fertility and substituting synthetic fertilizers. The decomposition and release of nutrients through mineralization processes are influenced by soil microbial activity, which in turn depends on the nutrient management practices employed. depending on nutrient management approaches. The study aimed to investigate the decomposition and N mineralization of Gliricidia sepium leaf green manure in an irrigated lowland rice ecosystem under different nutrient management systems (NMS), for a duration of eight weeks. Litterbags were placed at two soil depths, namely the topsoil, and subsoil, within three NMS; 100% Department of Agriculture (DOA) recommended inorganic fertilizer application (CNM), 50% of DOA recommended inorganic fertilizer combined with the organic fertilizer application (INM), and 100% organic fertilizer application (ONM). The treatments were arranged in a randomized complete block design and litterbags were retrieved weekly to determine dry mass, total N content, and total organic carbon content remaining in the leaves. The rate of decomposition and nutrient release was estimated using an exponential decay equation and analysis of variance was carried out using the repeated measures MIXED model. A consistent biphasic pattern of decomposition and mineralization was observed across all NMS treatments and soil depths, characterized by an initial rapid phase followed by a slower phase. However, significant differences (p<0.05) were observed among the treatments. The ONM treatment combined with topsoil placement exhibited a shorter time for 50% and 80% reduction in biomass and nitrogen content. Approximately 80% of the nitrogen content was released into the soil solution within 4-5 weeks of green manure incorporation, regardless of the nutrient management system employed. These findings suggest that with proper application rates and appropriate depth of placement, Gliricidia sepium green manure can effectively replace a significant portion of mineral nitrogen fertilizer, thereby enhancing nutrient use efficiency in lowland rice-based systems.

Impact of Pesticides on Diversity and Abundance of Predatory Arthropods in Rice Ecosystem

Rice (Oryza sativa) is one of the most important cereal crops with a diverse set of pests and natural enemies. Rice fields often support a high diversity of arthropods which contribute significantly to productivity. This diversity is frequently threatened due to indiscriminate applications of pesticides. Our aim was to emphasize on the predator diversity in agrochemical exposed rice field as well as on the impact of surrounding vegetation on beneficial insect diversity. Natural enemies’ data were recorded from randomly selected 10 quadrates by visual observation from each treatment. A total of 5,590 individuals of predators were observed during the study period which included 27 species belonging to 16 families from five orders of arthropods during the kharif season of rice. Statistically, there were no significant differences between the population of general natural enemies such as Odonata, Coleoptera, Hymenoptera, and Araneae in plots with insecticide and control during the different growth stages of rice cultivation. Diversity indices were almost similar in fields where pesticide was sprayed and not sprayed. Our study concluded that natural enemies are conserved by ensuring crop heterogeneity, growing insect-friendly plants (with high levels of nectar and pollen) as border crops, and judicious application of granule insecticide like cartap hydrochloride in a rice agro-ecosystem.

Effect of different herbicide spray volumes on weed control efficiency of a battery-operated Unmanned aerial vehicle sprayer in transplanted rice (Oryza sativa L.)

The effect of spray volume on weed control in transplanted rice ecosystems using the Unmanned aerial vehicle (UAV) needs to be better understood for management in the advancements of UAV-based spraying technology. The present study aimed to find out the influence of varied spray volumes of 15 L/ha, 20 L/ha and 25 L/ha using the UAV and 500 L/ha using a Knapsack sprayer (KS) to compare the weed density, weed dry matter and weed control efficiency and yield in transplanted rice (Oryza sativa L.). Pre-emergence (PE) application of Pyrazosulfuron-ethyl at 25 g a.i./ha at three days after transplanting (DAT) and post-emergence (PoE) application of Bis-pyribac sodium at 25 g a.i./ha at 25 DAT were used as herbicide treatments. The results revealed that varied spray volumes significantly influenced the weed density, dry matter, and weed control efficiency of the UAV and KS. Application of herbicides using KS (500 L/ha) and UAV (25 L/ha) had better control on the weeds by reducing weed density and dry matter at 20, 40, and 60 DAT, with no significant difference. Higher grain yield and straw yield were recorded in KS (500 L/ha) and UAV (25 L/ha), with no significant difference. However, applying 25 L/ha had better weed control efficiency and higher yield, possibly due to optimum deposition. Considering the low volume application of UAV (25 L/ha) as compared with KS (500 L/ha), it is better to go for the optimal application of 25 L/ha, which is an energy-efficient and cost-effective, labour-saving approach compared to KS.

Toxicity of insecticides to wolf spider (Pardosa pseudoannulata) and rice leaf folder (Cnaphalocrocis medinalis): assessing the risk of insecticides on spiders in the rice ecosystem

Chemical insecticides complemented with the natural enemies result in successful pest management in crop fields. Hence, knowing the impact of insecticides on natural enemies present in the rice ecosystem is essential. The wolf spider (Pardosa pseudoannulata), a predator of plant hoppers and young larva of leaf folders and stem borers in rice ecosystem, plays an important role in pest suppression. The effect of certain efficacious insecticides, commonly used in rice on P. pseudoannulata through contact toxicity was evaluated and compared with its toxicity to rice leaf folder (Cnaphalocrosis medinalis). Calculations of median lethal doses (LD50) for adult spiders revealed deltamethrin as a highly toxic chemical with an LD50 of 0.055 × 10−3 µg spider−1 followed by clothianidin (0.001 µg spider−1) at 48 h after treatment. Chlorantraniliprole was found to be highly toxic to C. medinalis larvae (LD50 = 0.001 µg larvae−1) followed by deltamethrin (0.009 µg larvae−1). Based on the risk assessment estimator selectivity ratio, which compares the LD50 of pest and predator, acephate and chlorantraniliprole were found to be safe by causing low mortality. However, when the LD90 of the pest was subjected to probit substitution, acephate, and chlorpyrifos were relatively less toxic to the predator. The hazard ratio, which takes into account the realistic field dose, revealed that chlorantraniliprole and acephate were safe for P. pseudoannulata. Most of the insecticides commonly used in agriculture negatively affect spiders, with few exceptions like chlorantraniliprole and acephate with minimum contact toxicity.

Biodiversity of herbivorous insects in rice organic and inorganic ecosystem

Since many years, presence and activities of herbivorous insect very crucial in the agricultural ecosystem. Purpose of the research is to study biodiversity of herbivorous insect in the rice organic and inorganic ecosystem. The research was conducted in Salassae village, Bulukumba Regency, South Sulawesi from June to August 2021. The herbivorous insect from organic and inorganic ecosystem was carried out and identified at the Pest Laboratory, Department of Plant Pest and Diseases, Faculty of Agriculture, Hasanuddin University Makassar. The places used in the research divided into organic and inorganic rice ecosystem, with measurement 25 m x 25 m, respectively. The insect samples collected used ubinan system methods with diagonal intersection applied for pitfall trap. The samples from organic and inorganic ecosystem analyzed by Shannon-Wiener Index Diversity. The result of Shannon-Wiener Index was showed the higher number of herbivorous insects in the inorganic rice ecosystem (H’ = 1.71) with population about 391 individual (51%). In contrast, result of organic ecosystem (H’ = 1.68) lower than inorganic. Conclusion of the research: 1) the higher number of herbivorous insects in the inorganic rice ecosystem (H’ = 1.71), the lowest result from organic ecosystem (H’ = 1.68); 2) the highest rice harvest higher the organic ecosystem (297 kg) and the lowest in the inorganic (279.2 kg).

Simulated Nitrogen Deposition Decreases the Ratios of Soil C to P and N to P, Changes Soil Enzyme Activity, and Reduces Soil Microbial Biomass in Paddy Soil in Southern China

There have been few studies on the impact of nitrogen deposition on paddy field ecosystem; therefore, we evaluated the effects of different N deposition levels (0, 40, and 120 kg N·ha−1) with the conventional nitrogen rate (180 kg N·ha−1) on rice field ecosystem through two-season experiments. The results showed that 40 and 120 kg·ha−1 nitrogen deposition had no significant effect on rice yield, although the rice grains per panicle and the 1000-grain weight increased. The 40 and 120 kg·ha−1 nitrogen deposition levels had no significant effect on rice and soil total carbon/total nitrogen (TC/TN) in the two-season experiment; however, 40 and 120 kg·ha−1 nitrogen deposition significantly increased TP content of the rice root and soil in a short time, and continuous 120 kg·ha−1 nitrogen deposition significantly decreased TP content of the rice root and significantly increased TP content of the rice stem. In addition, nitrogen deposition significantly reduced total carbon/total phosphorus (TC/TP) and total nitrogen/total phosphorus (TN/TP) in the soil. The activities of soil acid phosphatase (S-ACP), β-glucosidase (S-β-GC), and N-acetyl-β-D-glucosidase (S-NAG) increased under 40 kg·ha−1 nitrogen deposition, while the activities of S-β-GC and S-NAG decreased under 120 kg·ha−1 nitrogen deposition compared with 40 kg·ha−1. The microbial carbon, microbial nitrogen, microbial phosphorus, and fungal microbial biomass reduced under 40 and 120 kg·ha−1 nitrogen deposition. These findings suggest that, under short-term N deposition, rice and soil can adjust the C, N, P, and even the nutrient balance by themselves; however, continuous nitrogen deposition may have adverse reactions to microorganisms, thereby disrupting this balance and ultimately leading to the deterioration of paddy soil environment and a reduction in rice yield in the long term.

Changes in soil stoichiometry, soil organic carbon mineralization and bacterial community assembly processes across soil profiles

Soil organic carbon (SOC) mineralization is essential to biogeochemical recycling in terrestrial ecosystem. However, the microbial mechanisms underlying the nutrient-induced SOC mineralization remain uncertain. Here, we investigated how SOC mineralization was linked to microbial assembly processes as well as soil nutrient availability and stoichiometric ratio in a paddy rice ecosystem at four soil profile levels. Our results showed a sharp decrease in SOC mineralization from topsoil (112.61–146.34 mg CO2 kg−1 day−1) to subsoil (33.51–61.41 mg CO2 kg−1 day−1). High-throughput sequencing showed that both abundance and diversity of specialist microorganisms (Chao1: 1244.30–1341.35) significantly increased along the soil profile, while the generalist microorganisms (Chao1: 427.67–616.15; Shannon: 7.46–7.97) showed the opposite trend. Correspondingly, the proportion of deterministic processes that regulate specialist (9.64–21.59 %) and generalist microorganisms (21.17–53.53 %) increased and decreased from topsoil to subsoil, respectively. Linear regression modeling and partial least squares path modeling indicated that SOC mineralization was primarily controlled by the assembly processes of specialist microorganisms, which was significantly mediated by available soil C:N:P stoichiometry. This study highlighted the importance of soil stoichiometry-mediated bacterial community assembly processes in regulating SOC mineralization. Our results have an important implication for the integration of bacterial community assembly processes into the prediction of SOC dynamics.