Land use change from permanent rice to alternating rice-shrimp or permanent shrimp in the coastal Mekong Delta, Vietnam: Changes in the nutrient status and binding forms

Microbiome analysis reveals the intestinal microbiota characteristics and potential impact of Procambarus clarkii

The intestinal microbiota interacts with the host and plays an important role in the immune response, digestive physiology, and regulation of body functions. In addition, it is also well documented that the intestinal microbiota of aquatic animals are closely related to their growth rate. However, whether it resulted in different sizes of crayfish in the rice-crayfish coculture model remained vague. Here, we analyzed the intestinal microbiota characteristics of crayfish of three sizes in the same typical rice-crayfish coculture field by high-throughput sequencing technology combined with quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme activity, investigating the relationship between intestinal microbiota in crayfish and water and sediments. The results showed that the dominant intestinal microbiota of crayfish was significantly different between the large size group (BS), normal size group (NS), and small size group (SS), where Bacteroides and Candidatus_Bacilloplasma contributed to the growth of crayfish by facilitating food digestion through cellulolysis, which might be one of the potential factors affecting the difference in sizes. Follow-up experiments confirmed that the activity of lipase (LPS) and protease was higher in BS, and the relative expression of development-related genes, including alpha-amylase (α-AMY), myocyte-specific enhancer factor 2a (MEF2a), glutathione reductase (GR), chitinase (CHI), and ecdysone receptor (EcR), in BS was significantly higher than that in SS. These findings revealed the intestinal microbiota characteristics of crayfish of different sizes and their potential impact on growth, which is valuable for managing and manipulating the intestinal microbiota in crayfish to achieve high productivity in practice. KEY POINTS: • Significant differences in the dominant microflora of BS, NS, and SS in crayfish. • Cellulolysis might be a potential factor affecting different sizes in crayfish. • Adding Bacteroides and Candidatus_Bacilloplasma helped the growth of crayfish.

Causes and consequences of tipping points in river delta social-ecological systems

The sustainability of social-ecological systems within river deltas globally is in question as rapid development and environmental change trigger "negative" or "positive" tipping points depending on actors' perspectives, e.g. regime shift from abundant sediment deposition to sediment shortage, agricultural sustainability to agricultural collapse or shift from rural to urban land use. Using a systematic review of the literature, we show how cascading effects across anthropogenic, ecological, and geophysical processes have triggered numerous tipping points in the governance, hydrological, and land-use management of the world's river deltas. Crossing tipping points had both positive and negative effects that generally enhanced economic development to the detriment of the environment. Assessment of deltas that featured prominently in the review revealed how outcomes of tipping points can inform the long-term trajectory of deltas towards sustainability or collapse. Management of key drivers at the delta scale can trigger positive tipping points to place social-ecological systems on a pathway towards sustainable development.

Influence of purple non-sulfur bacterial augmentation on soil nutrient dynamics and rice (Oryza sativa) growth in acidic saline-stressed environments

The aim of the current study was to assess the potency of the exopolymeric substances (EPS)-secreting purple non-sulfur bacteria (PNSB) on rice plants on acidic salt-affected soil under greenhouse conditions. A two-factor experiment was conducted following a completely randomized block design. The first factor was the salinity of the irrigation, and the other factor was the application of the EPS producing PNSB (Luteovulum sphaeroides EPS18, EPS37, and EPS54), with four replicates. The result illustrated that irrigation of salt water at 3-4‰ resulted in an increase in the Na+ accumulation in soil, resulting in a lower rice grain yield by 12.9-22.2% in comparison with the 0‰ salinity case. Supplying the mixture of L. sphaeroides EPS18, EPS37, and EPS54 increased pH by 0.13, NH4+ by 2.30 mg NH4+ kg-1, and available P by 8.80 mg P kg-1, and decreased Na+ by 0.348 meq Na+ 100 g-1, resulting in improvements in N, P, and K uptake and reductions in Na uptake, in comparison with the treatment without bacteria. Thus, the treatments supplied with the mixture of L. sphaeroides EPS18, EPS37, and EPS54 resulted in greater yield by 27.7% than the control treatment.

Nutrient status of integrated rice-crayfish system impacts the microbial nitrogen-transformation processes in paddy fields and rice yields

Increasing rice yield is essential for alleviating global food crisis. High soil nutrient level guarantees high rice yields in conventional rice monoculture (RM) systems, but excessive unconsumed nutrients act as pollutants and can even threaten rice growth. The integrated rice-crayfish (IRC) system aims to transfer the excess nutrients from crayfish to paddy fields to improve the comprehensive utilization rate of nutrients and create additional profits, while the responding characteristics of IRC microbial communities in paddy fields and rice yields to the nutrient status remain unclear. Considering the crucial roles of microbiomes in promoting nutrient cycling for crop absorption in rice production progresses, the composition and functional characteristics of soil microbial communities from six IRC farms with variant nutrient statuses in the Yangtze River Delta were surveyed in this study. Compared with RM systems, IRC systems with appropriately improved (p < 0.05) soil quality created favorable nutrient (FN) status accompanied by 15% rice yields increase, while IRC systems with extremely high nutrients (HN) status (p < 0.01) accompanied by 14% rice yields reduction. Soil microbial diversity and network complexity were maintained in FN-IRC systems, but declined in HN-IRC systems, with the Shannon index significantly decreased by 9.2% and network density decreased from 0.135 (in RM) to 0.062. In the FN-IRC systems, the keystone taxa identified by co-occurrence networks displayed inextricably positive correlations with soil nitrification potential (calculated by normalization of amoA gene abundance) and rice yields. While in HN-IRC systems, the large loss of keystone taxa might limit soil nitrogen fixation potential (calculated by normalization of nifH gene abundance), and further rice yields. Our study indicates that soil nutrient management in IRC systems claim attention, and the improvement of nitrogen metabolism is the key to realize agricultural cleaner production.

Occurrence of antibiotics and antibiotic resistance genes in cultured prawns from rice-prawn co-culture and prawn monoculture systems in China

Antibiotics and antibiotic resistance genes (ARGs) in the aquatic environment have raised great concerns, as the deleterious effects of residual antibiotics and the emergence of ARGs are challenges to aquaculture. This study analyzed feed, water, sediment and prawns' tissues from six culture ponds (integrated culture: rice-prawn pond; monoculture: prawn pond) in Tianjin, Northeast China. Eighteen types of antibiotics were detected in all ponds, which conferring to four classes of antibiotics including sulfonamides, tetracyclines, fluoroquinolones, macrolides. The mean log bioaccumulation factor (BAF) values for five antibiotics were analyzed in the hepatopancreas, muscle, and plasma, and we found the maximum Log BAF (1.45) for enrofloxacin in prawn plasma. Correlation analysis of antibiotic concentrations between the plasma and the other two tissues indicated that enrofloxacin, norfloxacin, and erythromycin levels in the hepatopancreas and muscle can be predicted by their plasma concentrations. We also conducted a hazard quotient analysis and found that the risk to human health of eating antibiotic-exposed prawns from the two types of aquaculture method was relatively low. Compared with monoculture, rice-prawn co-culture could significantly decrease the abundance of ARGs; additionally, significant correlations were detected among ARGs, antibiotics, and non-antibiotic environmental factors (e.g., total nitrogen, total ammonia nitrogen, and chemical oxygen demand) in prawn. The present study indicated that the rice-prawn co-culture system is more effective than monoculture for mitigating the bioaccumulation of antibiotics and the occurrence of ARGs in prawn.

Development of top-dressing automation technology for sustainable shrimp aquaculture in India

Globally, the shrimp farming industry faces increasing challenges and pressure to reduce the broken shrimps and maintain a healthier pond environment. Shrimps lack an adaptive immune system to combat invading pathogens due to an imbalance in beneficial gut microbiota. The use of top-dressing agents like probiotics and pond optimizes is an alternative strategy to improve the innate immune system leading produce disease-free shrimp in international markets. The cost of top-dressing agents is accounted for 20% of the production cost and therefore, the development of top-dressing automation technology is important to maintain and improve the financial and environmental viability of shrimp sustainable farming. This perspective described several sensor-based aquaculture technologies for on-farm management systems but sustainability in the aquaculture industry is not yet achieved in practice. The present technology is a new invention to reduce labor and production costs required for reducing bacterial and organic loads in Biofloc shrimp cultures. Aquaculture automation system disperses the top-dressing agents to the shrimp ponds based on the signals received from microbial and environmental sensors. Continuous monitoring of shrimp growth, mortality, immune responses, diseases, and pond water quality parameters will fetch larger profits with additional savings on labor and production costs for sustainable shrimp aquaculture in India.

How the saline water intrusion has reshaped the agricultural landscape of the Vietnamese Mekong Delta, a review

Once a key factor behind Vietnam's successful Doi Moi (restoration) economic reforms, the rice-centered agriculture of the VMD is now confronted by the new pressure of climate change impacts, including the intensifying salinity intrusion (SI). The SI menace has partly triggered the delta-wide emergence of new adaptive livelihood models across the VMD, including the prawn rice rotational crop (PRRC) that is arguably the most prominent. Research on the SI-driving factors is rapidly increasing in numbers, yet little synthesis has been done. Likewise, several studies have investigated the economic benefits of PRRC; less emphasis has placed on environmental and societal aspects, hence the questionable sustainability. This study, therefore, contributes a composite literature review, targeting two SI-related aspects: (i) key factors driving the intensification of SI in recent years across the Mekong Delta, and (ii) current understanding of the sustainability of PRRC. Results from the first review assignment highlight the four key SI-driving factors: riverbed incision, land subsidence, upstream dams, and sea-level rise. Also remarked are the critical absence of studies addressing multiple drivers and the need for a decoupling model to quantify the relative importance of each factor to strategize the adaptive measures. For PRRC, we reveal that while economic benefits have been widely reported, potential negative impacts of this model related to environmental and social aspects are lacking. Therefore, while the lucrative prawn trade might financially benefit the farmers', the economic benefit is marred by the underlying negative environmental impacts and social inequalities, limiting overall sustainability. This study also provides a case study to notify the spatial-temporal trends of PRRC in the last three decades and evaluate the associated geographical and social factors. Kien Giang province was selected as the study site since it is the largest PRRCacross the VMD. The lessons from Kien Giang can also be applied to other transformative agricultural models in both Mekong Delta and other deltas worldwide.

Land-Use and Land-Cover Changes in Dong Trieu District, Vietnam, during Past Two Decades and Their Driving Forces

Land-use and land-cover (LULC) change analyses are useful in understanding the changes in our living environments and their driving factors. Modeling changes of LULC in the future, together with the driving factors derived through analyzing the trends of past LULC changes, bring the opportunity to assess and orientate the current and future land-use policies. As the entryway of Quang Ninh province, Vietnam, Dong Trieu locale has experienced significant LULC changes during the past two decades. In this study, the spatial distribution of six Level I LULC classes, forest, cropland, orchards, waterbody, built-up, and barren land, in Dong Trieu district at 2000, 2010, and 2019 were obtained from Landsat imageries by maximum likelihood technique. The most significant changes observed over the past twenty years are a decrease of barren land (9.1%) and increases of built-up (8.1%) and orchards (6.8%). Driving factor analysis indicated that the changes of cropland and built-up were dependent on distance from road (DFR), distance from main road (DFMR), distance from urban (DFU), distance from water (DFW), elevation, slope, and population density. The changes of forest were dependent on all the driving forces listed above, except DFMR. The orchards mainly appeared near the high-population-density area. The transformation of the waterbody was affected by geography (elevation and slope) and population density. The higher the population density, the less barren the land would appear.

Water and Land as Shared Resources for Agriculture and Aquaculture: Insights from Asia

Although agriculture and aquaculture depend on access to increasingly scarce, shared water resources to produce food for human consumption, they are most often considered in isolation. We argue that they should be treated as integrated components of a single complex system that is prone to direct or indirect tradeoffs that should be avoided while also being amenable to synergies that should be sought. Direct tradeoffs such as competition for space or the pollution of shared water resources usually occur when the footprints of agriculture and aquaculture overlap or when the two practices coexist in close proximity to one another. Interactions can be modulated by factors such as hydropower infrastructure and short-term economic incentives, both of which are known to disrupt the balance between aquaculture and agriculture. Indirect tradeoffs, on the other hand, play out across distances, i.e., when agricultural food sources are diverted to feed animals in aquaculture. Synergies are associated with the culture of aquatic organisms in rice paddies and irrigation waters, seasonal rotations of crop cultivation with aquaculture, and various forms of integrated agriculture–aquaculture (IAA), including jitang, a highly developed variant of pond-dike IAA. Policy decisions, socioeconomic considerations, and technology warrant increased scrutiny as determinants of tradeoffs and synergies. Priority issues for the future include guiding the expansion of aquaculture from its traditional base in Asia, taking advantage of the heterogeneity that exists within both agricultural and aquaculture systems, the development of additional metrics of tradeoffs and synergies, and adapting to the effects of climate change.