Determination of optimal NH4+/K + concentration and corresponding ratio critical for growth of tobacco seedlings in a hydroponic system.

Inherently, ammonium (NH4 +) is critical for plant growth; however, its toxicity suppresses potassium (K+) uptake and vice-versa. Hence, attaining a nutritional balance between these two ions (NH4 + and K+) becomes imperative for the growth of tobacco seedlings. Therefore, we conducted a 15-day experimental study on tobacco seedlings exposed to different concentrations (47 treatments) of NH4 +/K+ at different corresponding 12 ratios simultaneously in a hydroponic system. Our study aimed at establishing the optimal NH4 +-K+ concentration and the corresponding ratio required for optimal growth of different tobacco plant organs during the seedling stage. The controls were the baseline for comparison in this study. Plants with low or excessive NH4 +-K+ concentration had leaf chlorosis or dark greenish colouration, stunted whole plant part biomass, and thin roots. We found that adequate K+ supply is a pragmatic way to mitigate NH4 +-induced toxicity in tobacco plants. The optimal growth for tobacco leaf and root was attained at NH4 +-K+ concentrations 2-2 mM (ratio 1:1), whereas stem growth was optimal at NH4 +-K+ 1-2 mM (1:2). The study provided an insight into the right combination of NH4 +/K+ that could mitigate or prevent NH4 + or K+ stress in the tobacco seedlings.

Differential Effects of Ammonium (NH4+) and Potassium (K+) Nutrition on Photoassimilate Partitioning and Growth of Tobacco Seedlings.

Plants utilize carbohydrates as the main energy source, but much focus has been on the impact of N and K on plant growth. Less is known about the combined impact of NH4+ and K+ nutrition on photoassimilate distribution among plant organs, and the resultant effect of such distribution on growth of tobacco seedlings, hence this study. Here, we investigated the synergetic effect of NH4+ and K+ nutrition on photoassimilate distribution, and their resultant effect on growth of tobacco seedlings. Soluble sugar and starch content peaks under moderate NH4+ and moderate K+ (2-2 mM), leading to improved plant growth, as evidenced by the increase in tobacco weight and root activity. Whereas, a drastic reduction in the above indicators was observed in plants under high NH4+ and low K+ (20-0.2 mM), due to low carbohydrate synthesis and poor photoassimilate distribution. A strong positive linear relationship also exists between carbohydrate (soluble sugar and starch) and the activities of these enzymes but not for invertase. Our findings demonstrated that NH4+ and K+-induced ion imbalance influences plant growth and is critical for photoassimilate distribution among organs of tobacco seedlings.

Meniscus-Induced Directional Self-Transport of Submerged Bubbles on a Slippery Oil-Infused Pillar Array with Height-Gradient.

Directional manipulation of submerged bubbles is fundamental for both theoretical research and industrial production. However, most current strategies are limited to the upward motion direction, complex surface topography, and additional apparatuses. Here, we report a meniscus-induced self-transport platform, namely, a slippery oil-infused pillar array with height-gradient (SOPAH) by combining femtosecond laser drilling and replica mold technology. Owing to the unbalanced capillary force and Laplace pressure difference, bubbles on SOPAH tend to spontaneously transport along the meniscus gradient toward a higher elevation. The self-transport performances of bubbles near the pillars depend on the complex meniscus shape. Significantly, to understand the underlying transport mechanism, the 3D meniscus profile is simulated by solving the Young-Laplace equation. It is found that the concave valleys formed between the adjacent pillars can change the gradient direction of the meniscus and lead to the varied transport performances. Finally, by taking advantage of a water electrolysis system, the assembled SOPAH serving as a bubble-collecting device is successfully deployed. This work should not only bring new insights into the meniscus-induced self-transport dynamics but also benefit potential applications in the field of intelligent bubble manipulation.

A Biocompatible Vibration-Actuated Omni-Droplets Rectifier with Large Volume Range Fabricated by Femtosecond Laser.

High-performance droplet transport is crucial for diverse applications including biomedical detection, chemical micro-reaction, and droplet microfluidics. Despite extensive progress, traditional passive and active strategies are restricted to limited liquid types, small droplet volume ranges, and poor biocompatibilities. Moreover, more challenges occur for biological fluids due to large viscosity and low surface tension. Here, a vibration-actuated omni-droplets rectifier (VAODR) consisting of slippery ratchet arrays fabricated by femtosecond laser and vibration platforms is reported. Through the relative competition between the asymmetric adhesive resistance originating from the lubricant meniscus on the VAODR and the periodic inertial driving force originating from isotropic vibration, the fast (up to ≈60 mm s-1 ), programmable, and robust transport of droplets is achieved for a large volume range (0.05-2000 µL, Vmax /Vmin  ≈ 40 000) and in various transport modes including transport of liquid slugs in tubes, programmable and sequential transport, and bidirectional transport. This VAODR is general to a high diversity of biological and medical fluids, and thus can be used for biomedical detection including ABO blood-group tests and anticancer drugs screening. These strategies provide a complementary and promising platform for maneuvering omni-droplets that are fundamental to biomedical applications and other high-throughput omni-droplet operation fields.

Biomimetic Mechanoswitchable Interfaces for High-Performance Spatial Gas Bubble Maneuvering.

The on-demand manipulation of gas bubbles in aqueous ambient environments is fundamental to many fields such as microfluidics and biochemical microanalysis. However, most bubble manipulation strategies are limited to restricted locomotion on the confined surfaces without spatial convenience of transport. Herein, we report a kind of biomimetic bubble manipulator with mechanoswitchable interfaces (MSIs), featuring the advantages of parallel bubble control and spatial maneuvering flexibility. By the synergic action between Janus aluminum membrane and superaerophilic microfiber array, the gas-MSI interfacial adhesion can be reversibly switched to achieve capturing/releasing underwater bubbles. Moreover, the adhesion force of MSI can be readily tuned by diverse experimental parameters including surface roughness, fiber number, diameter, and spacing of the neighboring microfibers, which are further systematically investigated. Relying on this mobile platform, we demonstrate a series of powerful applications including bubble parallel control, bubble array regrouping, arbitrary bubble transport and even manipulating underwater solids through bubbles, which are otherwise challenging for conventional approaches. We envision that this versatile platform will bring new insights into potential applications, such as cross-species sample control and handheld gas microsyringe.

Pitcher plant-bioinspired bubble slippery surface fabricated by femtosecond laser for buoyancy-driven bubble self-transport and efficient gas capture.

Functional materials with specific bubble wettability play an important role in manipulating the behavior of underwater gas bubbles. Inspired by the natural Pitcher plant, we designed a large area lubricated slippery surface (LSS) by femtosecond laser processing for buoyancy-driven bubble self-transport and efficient gas capture. The mechanism of bubble self-transport involves a competition between the buoyancy and the resistance due to drag force and hysteresis. The transportation velocity of the bubbles on the LSS is strongly associated with the surface tension of the lubricants. The lower the surface tension, the higher the sliding velocity. On the basis of sufficient bubble adhesion, the shaped LSS tracks are fabricated to guide the bubble movement and achieve continuous manipulation between bubble merging and detachment. We demonstrate that these designable pathways on the LSS not only manipulate bubble behavior in a two-dimensional space but also realize three-dimensional movement of bubbles on the Mobius-striped LSS. Finally, a gas catcher decorated with large area LSS is manufactured for underwater bubble capture, which maintains a high capture efficiency (more than 90%) with an air output of ∼3.4 L min-1. This finding reveals a meaningful interaction between the underwater bubbles and the LSS surface, accelerating the applications of bubble slippery surfaces in underwater flammable gas collection and tail gas treatment.