Acclimation responses of macaw palm seedlings to contrasting light environments

Meta-analysis revealed the factors affecting the functions of ecological floating bed in removing nitrogen and phosphorus from eutrophic water

Ecological floating bed (EFB) has been widely used to remove nitrogen and phosphorus from eutrophic water. However, its effects on nitrogen and phosphorus removal are different in various studies. Presently it has not been systematically clear what factors produce effects on EFB removing nitrogen and phosphorus from eutrophic water. In this study, we performed a meta-analysis of 169 articles to discuss the effects of EFB characteristics and experimental conditions on EFB removing nitrogen and phosphorus. Results showed that EFB generally decreased nitrogen and phosphorus concentrations in eutrophic water regardless of EFB characteristics and experimental conditions. EFB showed better effects on simultaneously removing TN, NH4+-N, and TP when it had one of the characteristics: constructed by monocots, 2-3 plant species, an area of 1.1-3.0 m2, and the coverage of 21%-40%. However, NO3--N removal by EFB was complicated due to the effects of nitrification and denitrification. Moreover, EFB plant density also showed different effects on nitrogen and phosphorus removal. Experimental conditions produced evident effects on EFB removing nitrogen and phosphorus, and it showed better effects under one of the conditions: water temperature of 16-25℃, experimental duration of 31-60 days, long hydraulic retention time, and aeration. This study indicates that EFB can significantly remove nitrogen and phosphorus from eutrophic water, and it is an effective technology to control water eutrophication, but the effects of EFB characteristics and environmental conditions on EFB function should be considered in application.

Response of blueberry photosynthetic physiology to light intensity during different stages of fruit development

To investigate the response of blueberry photosynthetic physiology to different light intensities during different stages of fruit development. In this study, four light intensity treatments (25%, 50%, 75% and 100% of full light) were set up to study the change rule of photosynthetic pigment content and photosynthetic characteristics of 'O'Neal' southern highbush blueberry leaves during the white fruiting stage (S1), purple fruiting stage (S2) and blue fruiting stage (S3) under different light intensity environments, and to explore the light demand and light adaptability of blueberry during different developmental stages of the fruit. The results showed that the chlorophyll and carotenoid contents of blueberry leaves showed an increasing trend with decreasing light intensity at all three stages of fruit development. The total chlorophyll content of blueberry leaves at 25% light intensity increased by 76.4% compared with CK during the blue fruiting stage; the maximum net photosynthetic rate (Pmax), light compensation point (LCP), light saturation point (LSP), rate of dark respirations (Rd), inter-cellular CO2 concentration (Ci), stomatal conductance (Gs), transpiration rate (Tr), net photosynthesis rate (Pn), and chlorophyll a/b showed a decreasing trend with decreasing light intensity. The Pn of blueberry leaves was highest under full light conditions at all three stages, and the Pn at 25% light intensity decreased by 68.5% compared with CK during the white fruiting stage Reflecting the fact that blueberries can adapt to low-light environments through increases in chlorophyll and carotenoids, but reduced light intensity significantly inhibited their photosynthesis. The photosynthetic physiology of blueberry showed a consistent pattern at all three stages, but there were some differences in the changes of photosynthetic parameters at different stages. The results of the study can provide theoretical references for the selection of sites and density regulation in blueberry production.

Photon spectra effects tested on the vegetal model Allium cepa

The use of artificial light sources in plants is considered a type of photobiomodulation (PBM), a trend in agriculture and food industries, aiming at decontamination, pest control, and increased production yield. However, literature lacks a broader assessment to address the effects of photon light spectra on plant characteristics. Here, we aimed to describe the effects of visible light, infrared, and ultraviolet light upon Allium cepa, a known bioindicator, under various light doses. Samples irradiated under visible and infrared light did not show cytotoxicity, genotoxicity, or mutagenicity in any of the evaluated doses. Light induction at 460 and 635 nm significantly stimulated root development of the test organism. In contrast, 254 nm irradiation proved to be cytotoxic, genotoxic, and mutagenic. This work reveals and quantifies the spectral response of A. cepa seeds, suggesting that it can be proposed as a model for future research on mechanisms of PBM in plants.

Effect of light intensities on the photosynthesis, growth and physiological performances of two maple species

Photoinhibition decreases photosynthetic capacity and can therefore affect the plant survival, growth, and distribution, but little is known about how it affects on kindred tree species. We conducted field experiments to measure the photosynthetic, growth and physiological performances of two maple species (Acer mono and A. pseudosieboldianum) seedlings at four light intensities (100%, 75%, 55%, and 20% of full light) and evaluated the adaptability of seedlings. We found that: (1) A. mono seedlings have larger light saturated photosynthetic rates (A _max), the light saturation point (LSP), and lower light compensation point (LCP) than A. pseudosieboldianum seedlings, thus indicating that the former has a stronger light utilization ability. (2) A. mono seedlings under 75% light intensity and had higher seedling height (SH), basal stem diameter (BSD), leaf number (LN), leaf area per plant (LAPP) and total dry weight (TDW), while A. pseudosieboldianum seedling at 55% light intensity displayed greater growth advantages, which agreed with their response of light saturated photosynthetic rate. Morphological plasticity adjustments such as decreased root shoot ratio (RSR) and increased specific leaf area (SLA) showed how seedlings adapt to weak light environments. (3) 100% and 20% light intensities increased the malondialdehyde (MDA) content of two maple seedlings, indicating that very strong or very weak light could lead to the imbalance of reactive oxygen species (ROS) metabolism. The regulation of antioxidant enzyme activities such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the content of osmoregulation substances such as free proline and soluble protein, are the main mechanisms of plant adaptation to light stress. Although both A. mono and A. pseudosieboldianum are highly shade tolerant, subtle differences in the photosynthetic, morphological and physiological traits underpinning their shade tolerance suggest A. pseudosieboldianum has the advantage to deal with the light threat. Future studies should focus on the expression level of photosynthesis-related genes and cell, to better understand the adaptation mechanism of plants to light variation which facilitates forest development, either natural or via silvicultural practices. This information expands our understanding of the light-regulating mechanism of trees, which contributes to develop management practices to support natural forest regeneration.

Estimating Light Acclimation Parameters of Cucumber Leaves Using Time-Weighted Averages of Daily Photosynthetic Photon Flux Density

Leaves acclimate to day-to-day fluctuating levels of photosynthetic photon flux density (PPFD) by adjusting their morphological and physiological parameters. Accurate estimation of these parameters under day-to-day fluctuating PPFD conditions benefits crop growth modeling and light environment management in greenhouses, although it remains challenging. We quantified the relationships between day-to-day PPFD changes over 6 days and light acclimation parameters for cucumber seedling leaves, including leaf mass per area (LMA), chlorophyll (Chl) a/b ratio, maximum net photosynthetic rate (P _nmax), maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (V _cmax), and maximum rate of electron transport (J _max). The last two parameters reflect the capacity of the photosynthetic partial reactions. We built linear regression models of these parameters based on average or time-weighted averages of daily PPFDs. For time-weighted averages of daily PPFDs, the influence of daily PPFD was given a specific weight. We employed three types of functions to calculate this weight, including linear, quadratic, and sigmoid derivative types. We then determined the trend of weights that estimated each parameter most accurately. Moreover, we introduced saturating functions to calibrate the average or time-weighted averages of daily PPFDs, considering that light acclimation parameters are usually saturated under high PPFDs. We found that time-weighted average PPFDs, in which recent PPFD levels had larger weights than earlier levels, better estimated LMA than average PPFDs. This suggests that recent PPFDs contribute more to LMA than earlier PPFDs. Except for the Chl a/b ratio, the average PPFDs estimated P _nmax, V _cmax, and J _max with acceptable accuracy. In contrast, time-weighted averages of daily PPFDs did not improve the estimation accuracy of these four parameters, possibly due to their low response rates and plasticity. Calibrating functions generally improved estimation of Chl a/b ratio, V _cmax, and J _max because of their saturating tendencies under high PPFDs. Our findings provide a reasonable approach to quantifying the extent to which the leaves acclimate to day-to-day fluctuating PPFDs, especially the extent of LMA.

Increased soybean tolerance to water deficiency through biostimulant based on fulvic acids and Ascophyllum nodosum (L.) seaweed extract

To meet the growing demand for soybean it is necessary to increase crop yield, even in low water availability conditions. To circumvent the negative effects of water deficit, application of biostimulants with anti-stress effect has been adopted, including products based on fulvic acids and Ascophyllum nodosum (L.) seaweed extracts. In this study, we determined which formulation and dosage of a biostimulant is more efficient in promoting the recovery of soybean plants after stress due to water deficit. The experiment was conducted in a greenhouse, in a double-factorial randomized block design with two additional factors, four repetitions and eleven treatments consisting of three biostimulant formulations (F1, F2 and F3), and three dosages (0.25; 0.50 and 1.0 kg ha-1); a control with water deficit and a control without water deficit. Soybean plants were kept at 50% of the pot's water capacity for three days, then rehydrated and submitted to the application of treatments with biostimulant. After two days of recovery, growth, physiological, biochemical and yield parameters were evaluated. All plants that received the application of the biostimulant produced more than the water-stressed control plants. The biostimulant provided higher photosynthetic rates, more efficient mechanisms for dissipating excess energy and higher activities of antioxidant enzymes. Plants treated with biostimulant were more efficient in the recovery of the metabolic activities after rewatering, resulting in increased soybean tolerance to water deficit and reduced yield losses. The best result obtained was through the application of formulation 2 of the biostimulant at a dosage of 0.25 kg ha-1.