Development at the cost of unsustainable degradation of wetlands: Unraveling the dynamics (historic and future) of wetlands in the megacity Dhaka

Despite the recognized role of wetlands in providing ecological benefits for human wellbeing, ∼70% of global wetland ecosystems have been destroyed since the 1990s. Further intensive studies revealed that 3.4 million km2 of natural wetland has declined since 1700. In particular, wetland habitats in the world's megacities have been replaced unsustainably by faster economic, urban, and population growth, and have received less attention in research and policy. However, wetlands degradation in the megacities of developing countries is not quantified and the trends of Land Surface Temperature (LST) are not well understood. Therefore, we are making our first attempt to unravel the historical and future spatiotemporal dynamics of wetlands and the trends of LST in the megacity of Dhaka. The results show that Dhaka lost ∼69% of wetlands and LST has increased between 3.44°C and 9.35°C from 1990 to 2020. An environmental Kuznets curve analysis implies that the point has not yet been reached for wetlands when economic development feeds back to the sustainability of the environment. This assumption coincides with our model-based prediction, as respectively ∼74% and ∼90% of wetlands area of Dhaka city will be decreased by 2050 in Business as Usual (BAU) and development scenarios, whereas, ∼66% of wetlands area will be decreased under conservation scenario over the time period of next 30 (2020 to 2050) years. Our findings suggest that it will be incredibly challenging to restore wetlands to their 1990s condition. Efforts to preserve them should be made, as they potentially provide a nature-based alternative for coping with wetland sustainability and climate change

Diversity of insect and mite species in chili ecosystem: relationship of the major pests with predator and plant damage

The study was carried out with Capsicum frutescens variety BARI Morich 2 to explore the abundance and diversity of insect and mite species harbored in chili ecosystem. The study also determined the relationship of the abundance of major insect and mite pests with predator and chili plant damage index. The chili plants were cultivated in the experimental field of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh and the data of the insect and mite populations were collected at weekly intervals from November 2017 to June 2018. In total 41 insects and one mite species were found in the chili ecosystem where 12 species depicted as pest (three major pests and nine minor pests), 12 species as predator, four species as pollinator and 14 species were found as casual visitor. Insects of the order Hemiptera showed the highest abundance and the ant depicted the top rank with 6.7% abundance of the harbored species. The pest and pollinator species occupied the highest and lowest ranks with 35.4% and 9.3% abundances, respectively. Predator insects revealed the highest diversity and the pollinator category was the most dominant group which has the highest evenness index. The insects of the casual visitor category showed the highest richness index. The population of whitefly was positively correlated with mite, and the abundances of thrips and mite showed significant positive correlation with plant damage index. The abundance of whitefly also showed significant positive correlation with the abundance of dragon fly but negatively associated with the abundance of pirate bug. The abundance of mite had significant negative correlation with the abundance of pirate bug and hover fly, but positively correlated with lady bird beetle. The results indicated that a diversified insect group prevailed in the chili ecosystem, and they had direct linkage with existing predators and plant damage

Productivity and Profitability of Jackfruit-Eggplant Agroforestry System in the Terrace Ecosystem of Bangladesh

Multistoried agroforestry systems as a form of jackfruit-eggplant based is increasingly recognized as a promising option to counteract the catastrophic effects of climate change through providing multifaceted benefits. Unfortunately, farmers of Bangladesh did not manage their jackfruit orchard in a scientific manner. Therefore, the present study was aimed to assess the productivity and profitability of jackfruit-eggplant based agroforestry system after modification from a traditional jackfruit orchard during the period of July 2012 to December 2013. Five treatments covering four orientations of jackfruit tree and an open field was used as a control treatment. To observe the growth and economic performance of the system; soil moisture and temperature, DBH, number of fruits per tree, fruit length, fruit width, fruit weight, total yield, BCR, and LER were calculated following different established methods. The yield of jackfruit dramatically increased by 81% in the agroforestry system in compared to sole cropping, while eggplant shows inverse trend. Soil moisture was high in agroforestry system than that of control plot while soil temperature shows reverse pattern. Indeed, agroforestry system had some negative effects on growth performance of understorey crops. Despite, net return and BCR from jackfruit based agroforestry system were 5.58 lakh and 4.56, which was 66 and 45%, respectively higher than sole cropping systems. The LER of jackfruit-eggplant based agroforestry system was 2.17. Considering the main findings, we can elucidate that jackfruit orchards can be transformed to agroforestry system for maximizing production, generating income and conserving environment

Influence on Water Status, Photosynthesis Rate and Plant Growth of Different Temperatures and Water Regimes during Pod Formation Phase of Mungbean

Effects of different temperatures and water regimes on soil and leaf water potential, photosynthesis, growth and dry matter production of mungbean during pod formation were examined in the phytotron growth chambers of the Kyushu University, Japan. Temperatures were 15, 20, 25 and 30℃ and water regimes were well irrigation and light irrigation. Almost all parameters (except root dry weight) of mungbean were much reduced in the light irrigated pots than those in the well irrigated pots irrespective of temperature gradients except 15℃. Effects of different temperature gradients were more pronounced in photosynthesis, plant height, number of pods per plant, total dry matter and dry matter accumulation in pods in the well irrigated pots; and soil water potential, leaf water potential, leaf area per plant and root dry matter in the light irrigated pots. In the well irrigated condition, 25℃ was found to be the most favorable for growth and development of mungbean, but in the light irrigated condition no definite temperature was found to be most favorable in all cases. It may be suggested that for getting higher photosynthesis, growth and dry matter production in mungbean an adequate soil moisture accompanied with 25℃ is the best environment for the plant

Coastal Erosion and Human Perceptions of Revetment Protection in the Lower Meghna Estuary of Bangladesh

This study investigates coastal erosion, revetment as a shoreline protection strategy, and human perceptions of revetments in the Lower Meghna estuary of the Bangladesh where new revetments were recently constructed. Questions addressed were: (1) How do rates of shoreline change vary over the period 2011–2019? (2) Did new revetments effectively halt erosion and what were the magnitudes of erosion change? (3) How have erosion rates changed for shorelines within 1 km of revetments, and (4) How do households perceive revetments? High-resolution Planet Lab imagery was used to quantify shoreline change rates. Analysis of household survey data assessed human perceptions of the revetment’s desirability and efficacy. Results revealed high rates of erosion for 2011–2019 with declining erosion after 2013. New revetments effectively halted erosion for protected shorelines. Significant spatial trends for erosion rates existed for shorelines adjacent to revetments. Survey respondents overwhelmingly had positive attitudes about a desire for revetment protection; however, upstream respondents expressed a strong majority perception that revetment acts to make erosion worse. Highlights of the research include integration of remote sensing with social science methods, the timing of the social survey shortly after revetment construction, and results showing significant erosion change upstream and downstream of new revetments

Water Relation, Gas Exchange Characteristics and Yield Performance of Selected Mungbean Genotypes under Low Soil Moisture Condition

Among the environmental constraints, the growth and yield of crops are seriously impaired by moisture stress. With this view, an experiment was conducted to observe genotypic differences in water relation, gas exchange characteristics and yield performance of mungbean under low soil moisture conditions. Experimental variables consisted of five drought tolerant genotypes (G88, G108, G141,varietiesG186), one susceptible genotype (G43) and two standard check variety (BU mug 5, Binnamoog-8) which assigned to two moisture regimes viz., water regime A ((80 to 90% field capacity (FC)) and water regime B (40 to 50% FC). Results showed that water saturation deficit, water uptake capacity and transpiration rate were the lowest in tolerant genotypes G88 followed by genotypes G141, while those were the highest in susceptible genotype G43 under low soil moisture conditions. Contrarily, the highest amount of relative water content and water retention capacity were found in tolerant genotypes G141, G108 and G88 and the lowest was recorded in susceptible genotype G43 under low soil moisture conditions. In the case of the photosynthetic rate and stomatal conductance, the tolerant genotype G141, G88 and G108 showed the higher values at moisture stress condition. The highest total chlorophyll content and proline content were also found in tolerant genotype G88 followed by G141 and G108, and the lowest was found in susceptible genotype G43 under moisture stress conditions. Irrespective of genotypes, moisture stress significantly decreased the yield attributes and yield of mungbean genotypes. However, the highest seed yield per plant (12.11 g) was found in tolerant genotype G88 under low soil moisture conditions because of its lowest reduction rate of yield attributes under moisture stress. Similar responses were also observed in tolerant genotypes G141 and G108. Therefore, the genotypes G88, G108 and G141 showed better performance in the case of water relation and gas exchange characteristics which might be contribute to higher yield of those genotypes

Chitosan biopolymer promotes yield and stimulates accumulation of antioxidants in strawberry fruit.

Strawberry is a well-known source of natural antioxidants with excellent free radical scavenging capacity. This study determined the effects of chitosan application in field condition on plant growth, fruit yield and antioxidant activities in strawberry fruit. Foliar applications of chitosan on strawberry significantly increased plant growth and fruit yield (up to 42% higher) compared to untreated control. Increased fruit yield was attributed to higher plant growth, individual fruit weight and total fruit weight/plant due to the chitosan application. Surprisingly, the fruit from plants sprayed with chitosan also had significantly higher contents (up to 2.6-fold) of carotenoids, anthocyanins, flavonoids and phenolics compared to untreated control. Total antioxidant activities in fruit of chitosan treated plants were also significantly higher (ca. 2-fold) (p< 0.05) than untreated control. To the best of our knowledge, this is the first report of chitosan applied on field plants providing significant improvement of both yield and health benefiting biochemical contents in strawberry fruit. Further study on the elucidation of mechanisms involved with enhancement of growth, yield and biochemical contents by chitosan is needed to promote sustainable production of strawberry