Effects of arbuscular mycorrhizal inoculation and phosphorus supply on the growth and nutrient uptake of Kandelia obovata (Sheue, Liu & Yong) seedlings in autoclaved soil

National Natural Science Foundation of China [2013CB956504, 31170471, 31370516]This study evaluated the interactive effect of arbuscular mycorrhizal fungi (AMF) inoculation and exogenous phosphorus supply on soil phosphotases, plant growth, and nutrient uptake of Kandelia obovata (Sheue, Liu & Yong). We aimed to explore the ecophysiological function of AMF in mangrove wetland ecosystems, and to clarify the possible survival mechanism of mangrove species against nutrient deficiency. K. obovata seedlings with or without AMF inoculation (mixed mangrove AMF), were cultivated for six months in autoclaved sediment medium which was supplemented with KH2PO4 (0, 15, 30, 60, 120 mg kg(-1)). Then the plant growth, nitrogen and phosphorus content, root vitality, AMF colonization and soil phosphatase activity were analyzed. The inoculated AMF successfully infected K. obovata roots, developed intercellular hyphae, arbuscular (Arum-type), and vesicle structures. Arbuscular mycorrhizal fungi colonization ranged from 9.04 to 24.48%, with the highest value observed under 30 and 60 mg kg(-1) P treatments. Soil P supply, in the form of KH2PO4, significantly promoted the height and biomass of K. obovata, enhanced root vitality and P uptake, while partially inhibiting soil acid (ACP) and alkaline phosphotase (ALP) activities. Without enhancing plant height, the biomass, root vitality and P uptake were further increased when inoculated with AMP, and the reduction on ACP and ALP activities were alleviated. Phosphorus supply resulted in the decrease of leaf N-P ratio in K. obovata, and AMF inoculation strengthened the reduction, thus alleviating P limitation in plant growth. Arbuscular mycorrhizal fungi inoculation and adequate P supply (30 mg kg(-1) KH2PO4) enhanced root vitality, maintained soil ACP and ALP activities, increased plant N and P uptake, and resulted in greater biomass of K. obovata. Mutualistic symbiosis with AMF could explain the survival strategies of mangrove plants under a stressed environment (waterlogging and nutrient limitation) from a new perspective. (C) 2013 Elsevier B.V. All rights reserved

The short-term effect of cadmium on low molecular weight organic acid and amino acid exudation from mangrove (Kandelia obovata (S, L) Yong) roots

The aim of this study was to evaluate short-term concentration and time effects of cadmium on Kandelia obovata (S., L.) Yong root exudation, thereby evaluating and predicting the ecophysiological effects of mangrove to heavy metals at the root level. Mature K. obovata propagules were cultivated in a sandy medium for 3 months, and then six concentrations of Cd (0, 2.5, 5, 10, 20, and 40 mg L-1) were applied. After exposure time of 24 h and 7 days, respectively, the root exudates of K. obovata were collected and low molecular weight organic acids (LMWOAs) and amino acids of which were analyzed. In addition, we measured glutathione, soluble protein content, and Cd concentration in the plant. We found 10 and 15 types of LMWOAs and amino acids in root exudates of K. obovata with total concentrations ranging from 29.54 to 43.08 mg g(-1) dry weight (DW) roots and from 737.35 to 1,452.46 ng g(-1) DW roots, respectively. Both of them varied in quality and quantity under different Cd treatment strengths and exposure times. Oxalic, acetic, l-malic, tartaric acid, tyrosine, methionine, cysteine, isoleucine, and arginine were dominant. Both LMWOAs and amino acids excreted from K. obovata roots play a key role in Cd toxicity resistance. The responsiveness of amino acids was less than that of LMWOAs. We suggest that the ecological effect of root-excreted free amino acids in the rhizosphere is mainly based on the role of nutrients, supplemented with detoxification to heavy metals

The short-term effect of cadmium on low molecular weight organic acid and amino acid exudation from mangrove (Kandelia obovata (S, L) Yong) roots

The aim of this study was to evaluate short-term concentration and time effects of cadmium on Kandelia obovata (S., L.) Yong root exudation, thereby evaluating and predicting the ecophysiological effects of mangrove to heavy metals at the root level. Mature K. obovata propagules were cultivated in a sandy medium for 3 months, and then six concentrations of Cd (0, 2.5, 5, 10, 20, and 40 mg L-1) were applied. After exposure time of 24 h and 7 days, respectively, the root exudates of K. obovata were collected and low molecular weight organic acids (LMWOAs) and amino acids of which were analyzed. In addition, we measured glutathione, soluble protein content, and Cd concentration in the plant. We found 10 and 15 types of LMWOAs and amino acids in root exudates of K. obovata with total concentrations ranging from 29.54 to 43.08 mg g(-1) dry weight (DW) roots and from 737.35 to 1,452.46 ng g(-1) DW roots, respectively. Both of them varied in quality and quantity under different Cd treatment strengths and exposure times. Oxalic, acetic, l-malic, tartaric acid, tyrosine, methionine, cysteine, isoleucine, and arginine were dominant. Both LMWOAs and amino acids excreted from K. obovata roots play a key role in Cd toxicity resistance. The responsiveness of amino acids was less than that of LMWOAs. We suggest that the ecological effect of root-excreted free amino acids in the rhizosphere is mainly based on the role of nutrients, supplemented with detoxification to heavy metals

Kandelia obovata (S, L) Yong tolerance mechanisms to Cadmium: Subcellular distribution, chemical forms and thiol pools

National Natural Science Foundation of China [31170471, 30970527, 30710103908, 30970526, 31000244]In order to explore the detoxification mechanisms adopted by mangrove under cadmium (Cd) stress, we investigated the subcellular distribution and chemical forms of Cd, in addition to the change of the thiol pools in Kandelia obovata (S., L.) Yong, which were cultivated in sandy culture medium treated with sequential Cd solution. We found that Cd addition caused a proportional increase of Cd in the organs of K. obovata. The investigation of subcellular distribution verified that most of the Cd was localized in the cell wall, and the lowest was in the membrane. Results showed sodium chloride and acetic acid extractable Cd fractions were dominant. The contents of non-protein thiol compounds, Glutathione and phytochelatins in K. obovata were enhanced by the increasing strength of Cd treatment. Therefore, K. obovata can be defined as Cd tolerant plant, which base on cell wall compartmentalization, as well as protein and organic acids combination. (C) 2012 Elsevier Ltd. All rights reserved

Kandelia obovata (S, L) Yong tolerance mechanisms to Cadmium: Subcellular distribution, chemical forms and thiol pools

In order to explore the detoxification mechanisms adopted by mangrove under cadmium (Cd) stress, we investigated the subcellular distribution and chemical forms of Cd, in addition to the change of the thiol pools in Kandelia obovata (S., L.) Yong, which were cultivated in sandy culture medium treated with sequential Cd solution. We found that Cd addition caused a proportional increase of Cd in the organs of K. obovata. The investigation of subcellular distribution verified that most of the Cd was localized in the cell wall, and the lowest was in the membrane. Results showed sodium chloride and acetic acid extractable Cd fractions were dominant. The contents of non-protein thiol compounds, Glutathione and phytochelatins in K. obovata were enhanced by the increasing strength of Cd treatment. Therefore, K. obovata can be defined as Cd tolerant plant, which base on cell wall compartmentalization, as well as protein and organic acids combination. 漏 2012 Elsevier Ltd

Research on the nitrogen cycle in rhizosphere of Kandelia obovata under ammonium and nitrate addition

National Important Scientific Research Program of China [2013CB956504]; National Natural Science Foundation of China [31370516, 31170471, 31000244]The present study investigated nitrogen process in rhizosphere of Kandelia obovata under nitrogen input. Results showed that nitrogen additions significantly increased 4 kinds of enzyme activities (Urease, Nitrate reductase, Nitrite reductase and hydroxylamine reductase). The pH value increased to 7.1 under ammonium addition, but decreased to 6.9 under nitrate addition. Potential Nitrification Intensity (PNI) increased 200-1500% compared with control under ammonium addition, and Potential Denitrification Intensity (PDI) increased more than 200% under nitrate addition. Ten types of organic acids were detected from root exudates, which mainly included oxalic acid, tartaric acid, formic acid, acetic acid, and citric acid. The abundance of 5 kinds of microbial functional groups (nifH, AOA, AOB, nirS, nirK) responded differently. Total nitrogen in organs of K. obovata increased more than 200%. This indicated that nitrogen additions accelerated the transformation of nitrogen directly and stimulated the exudation of root exudates and 5 kinds of genes indirectly. (C) 2013 Elsevier Ltd. All rights reserved