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1.
Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests. 相似文献
2.
The interrelation was studied between the phototransient absorbing maximally at 412 nm (M412) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M412 was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M412 which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M412 was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M412 without affecting the level of M412 which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca2+ and their antagonists La3+ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed. 相似文献
3.
Antonis E. Koromilas 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(3):644-649
Cells employ pro-survival and pro-adaptive pathways to cope with different forms of environmental stress. When stress is excessive, and the damage caused by it is unsustainable, cells engage pro-death pathways, which are in place to protect the host from the deleterious effects of harmed cells. Two important pathways that determine the balance between survival and death of stressed cells are the integrated stress response (ISR) and the mammalian target of rapamycin (mTOR), both of which converge at the level of mRNA translation. The two pathways have established avenues of communication to control their activity and determine the fate of stressed cells in a context-dependent manner. The functional interplay between the ISR and mTOR may have significant ramifications in the development and treatment of human diseases such as diabetes, neurodegeneration and cancer. 相似文献
4.
The microbial metabolism of organic matter (OM) in seagrass beds can create sulfidic conditions detrimental to seagrass growth;
iron (Fe) potentially has ameliorating effects through titration of the sulfides and the precipitation of iron-sulfide minerals
into the sediment. In this study, the biogeochemical effects of Fe availability and its interplay with sulfur and OM on sulfide
toxicity, phosphorous (P) availability, seagrass growth and community structure were tested. The availability of Fe and OM
was manipulated in a 2 × 2 factorial experiment arranged in a Latin square, with four replicates per treatment. The treatments
included the addition of Fe, the addition of OM, the addition of both Fe and OM as well as no addition. The experiment was
conducted in an oligotrophic, iron-deficient seagrass bed. Fe had an 84.5% retention efficiency in the sediments with the
concentration of Fe increasing in the seagrass leaves over the course of the experiment. Porewater chemistry was significantly
altered with a dramatic decrease in sulfide levels in Fe addition plots while sulfide levels increased in the OM addition
treatments. Phosphorus increased in seagrass leaves collected in the Fe addition plots. Decreased sulfide stress was evidenced
by heavier δ34S in leaves and rhizomes from plots to which Fe was added. The OM addition negatively affected seagrass growth but increased
P availability; the reduced sulfide stress in Fe added plots resulted in elevated productivity. Fe availability may be an
important determinant of the impact that OM has on seagrass vitality in carbonate sediments vegetated with seagrasses. 相似文献
5.
A winter bloom dominated by Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle (Bacillariophyceae), a potential domoic acid producer, is reported for the first time in the Aegean Sea, Greece, in a semi-enclosed embayment (Kalloni Gulf) surrounded by agricultural land and drained by intermittent rivers. Abundances of this species in the inner part of the Gulf during February were extremely high (max 1.1 × 107 cells l−1). The species Alexandrium insuetum Balech (Dinophyceae) was also found in considerable cell numbers (max 1.4 × 105 cells l−1) during the bloom and reached up to 40% of the total biovolume. This study demonstrates an evident cause and effect relationship between nutrient inflows originating from agricultural activities in the watershed and the development of a potential HAB. The massive bloom formation was observed soon after an episodic rainfall event during the fertilizer application period (December to February). A bloom was also observed the following year, but it was less pronounced due to the fact that rainfalls were more evenly spaced in time and were of moderate intensity. 相似文献
6.
I. J. Pickering Graham N. George Verena Van Fleet-Stalder Thomas G. Chasteen Roger C. Prince 《Journal of biological inorganic chemistry》1999,4(6):791-794
Received: 2 April 1999 / Accepted: 17 September 1999 相似文献
7.
Kiyohiko Sugano 《化学与生物多样性》2009,6(11):2014-2029
Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed. 相似文献
8.
9.
10.
《Bioscience, biotechnology, and biochemistry》2013,77(8):1872-1875
Rats fed a diet containing β1-4 linked galactooligosaccharides (GOS) (5 g/100 g of diet) absorbed calcium and magnesium more efficiently than those fed the control diet. However, the increment obtained through GOS-feeding was reduced by neomycin sulfate 0.67 g/100 g of diet). Since the decrease in cecal pH in rats fed GOS was suppressed by neomycin-feeding, bacterial action in the digestive tract was considered to be reduced by neomycin-feeding. Our findings suggest that the action of intestinal bacteria is necessary for the effects of GOS. 相似文献