Calcium, potassium, and magnesium cycling in aMexican tropical dry forest ecosystem

We estimated the fluxes, inputs and outputs of Ca, K,and Mg in a Mexican tropical dry forest. The studywas conducted in five contiguous small watersheds(12–28 ha) gauged for long-term ecosystem research. A total of five 80 × 30 m plots were used for thestudy. We quantified inputs from the atmosphere,dissolved and particulate-bound losses, throughfalland litterfall fluxes, and standing crop litter pools. Mean cation inputs for a six-year period were 3.03 kg/ha for Ca, 1.31 kg/ha for K, and 0.80 kg/ha for Mg. Mean outputs in runoff were 5.24, 2.83, and 1.79 kg/ha, respectively. Calcium, K, and Mgconcentrations increased as rainfall moved through thecanopy. Annual Ca return in the litterfall (11.4 g/m²) was much higher than K (2.3 g/m²)and Mg (1.6 g/m²). Litterfall represented 99%of the Ca, 84% of the Mg, and 53% of the K, totalaboveground return to the soil. Calcium concentrationin standing litter (3.87%) was much higher than K(0.38%) and Mg (0.37%). These concentrations werehigher (Ca), lower (K), or similar (Mg) to those inlitterfall. Residence times on the forest floor were0.86, 1.17, and 1.77 yr for K, Mg, and Carespectively. Compared to the residence time fororganic matter at the site (1.31 yr), these resultssuggest slow mineralization for Ca in this ecosystem. Budget estimates were calculated for a wet and a dryyear. Results indicated that nutrients accumulated inthe dry but that nutrients were lost during the wetyear. Comparison of Ca, K, and Mg losses in streamwater with the input rates from the atmosphere for thesix-year period show that inputs are lower thanoutputs in the Chamela tropical dry forestecosystem.     

Litterfall and nutrient dynamics in a montane moist evergreen broad-leaved forest in Ailao Mountains,SW China

Montane moist evergreen broad-leaved forest, dominated byLithocarpus and Castanopsis species,is the most extensive stand of subtropical mountain in Yunnan Province, SWChina. Litter production, standing crop of litter on forest floor and nutrientreturn patterns were studied over nine years (1991–1999) in a stand ofprimary evergreen broad-leaved forest in northern crest of the Ailao MountainRange. There were significant yearly variations in litter production, which ismainly related with the masting year of canopy species, and exceptionalphysicalevents (strong winds and snow) in the natural forest. The mean annual smalllitterfall is 7.12 t ha^–1 yr^–1ofwhich leaf litter account for 65% of the total litterfall. The seasonality ofsmall litterfall was bia-modal, with the main one in the late dry season(April–May) and a lesser one in early winter (October–November).Decomposition quotient value was relatively low with 0.58 for total smalllitterfall. Mean large-wood ( 2.5 cm in diameter) ranged from0.21 to 1.41 t ha^–1 yr^–1 with amean of 0.52 t ha^–1 yr^–1.Concentrations of most elements in leaf and twig were slightly greater in wetmonths than dry months, except for C and K. Woody litter had low N and Pconcentrations compared with the leaf and reproductive parts. Nutrient returntothe soil through small litterfall decrease in the orderC>N>Ca>K>Mg>Mn>Al>P>Fe, while nutrient reserve inlitteron the forest floor was in the declining sequenceC>N>Ca>K>Mg>P>Fe>Al>Mn.     

Inhibition of DNA-ethidium bromide intercalation due to free radical attack upon DNA

Summary The fluorescent intercalation complex of ethidium bromide (ETB) with DNA was used as a probe to compare the effects of various radicals with respect to impairment of the DNA base-pair region.OH radicals inhibit up to 0.7 dye intercalations perOH at low salt concentration, and for various oxidizing species the effect decreases in the orderOH > Br ₂ ^– > N ₃ > $$ " align="middle" border="0"> (SCN) ₂ ^–. DNA impairment by theOH product of Met-Gly is comparable to that of N ₃ , but no effect was found due to the interaction between DNA and Lys-Tyr-Lys phenoxyl radicals. The reducing speciese _aq ^– , H, O ₂ ^–, and CO ₂ ^– hardly affect the DNA-ETB intercalation.     

Contrasting oxygen-effects in the inactivation of ribonuclease A by N 3 ⋅ , (SCN) 2 ⋅ − and⋅OH radicals

Summary N ₃ exhibits higher efficiency thanOH in the inactivation of RNase in de-acerated (neutral) aqueous solution. In O₂-saturated solution theOH-induced inactivation is enhanced, but N ₃ and (SCN) ₂ ^– become remarkably inefficient. Our results suggest that semi-oxidized tyrosine, the predominant initial defect induced by N ₃ and (SCN) ₂ ^– but not byOH, can be re-reduced upon reaction with O ₂ ^– or cysteine.     

Interactions of growth inhibitory factor with hydroxyl and superoxide radicals

To show the effects of growth inhibitory factor (Cu₄Zn₃MT-III) involved in the scavenging of reactive oxygen species (ROS), a pulse radiolytic study was employed using N₂O-saturated Cu₄Zn₃MT-III aqueous solutions. It was demonstrated that the oxidizing OH radical efficiently reacted with Cu₄Zn₃MT-III by forming a thiyl radical RS with a second-order constant of 1.46×10¹¹ mol l^–1s^–1, which was determined by competition kinetics against KSCN. The thiyl radical RS reacted rapidly and reversibly with a thiolate in Cu₄Zn₃MT-III to form radical anion RSSR ^– with a constant of 1.65×10⁹ mol lL^–1s^–1 per thiolate, while the constant of the decay of this radical anion was 2.72×10⁵ s^–1, and the equilibrium constant of the formation for RSSR ^– was 6.08×10³ mol^–1 l. These values were close to those of Cd₅Zn₂MT-II. The SOD activity of Cu₄Zn₃MT-III to quench O₂ ^–was assayed by the riboflavine-methionine-nitrobluetetrazolium (NBT) method which catalyzed the dismutation of superoxide (O₂ ^–) at pH 7.8 with an IC₅₀ value of 1.50×10^–6 M for Cu₄Zn₃MT-III and 1.62×10^–6 M for Cd₅Zn₂MT-II. Additionally, the down-regulation of GIF may be a main factor in the decrease of the scavenging ability for the free OH and O₂ ^–radicals, which is possibly associated with the pathogenesis of neurodegenerative disease.     

Dual Role of Superoxide Radicals in the Chilling-Induced photoinhibition in Maize Seedlings

Maize (Zea mays) seedlings were exposed for 6 h to strong irradiance (1 000 mol m^–1 s^–1 of PPFD) at 5, 12, 17, or 25 °C, followed by an exposure to the darkness for 6 h at 22 °C. Leaf chlorophyll fluorescence, net photosynthetic rate (P _N), and the amount of superoxide radicals (O₂ ^–) in relation to chilling-induced photoinhibition were investigated. During the photophase, a good correlation (r=–0.879) was observed between _PS2 (relative quantum efficiency of PS2 electron transport) and the amount of O₂ ^–. Treatment with exogenous O₂ ^– reduced the P _N and _PS2 as the chilling stress did, that was inhibited by specific scavenger of O₂ ^–. Hence chilling-induced photoinhibition might be due to the production of O₂ ^–. In contrast, in the dark period, P _N and _PS2 of the seedlings treated with the exogenous O₂ ^– were enhanced, but they were inhibited by the specific scavenger of O₂ ^–, showing the photoprotective role of O₂ ^– in the recovery phase. Furthermore, in terms of the effect of exogenous O₂ ^– on the xanthophyll cycle, the O₂ ^– production suggested a promotion effect for the de-epoxidation of violaxanthin during the photophase, the epoxidation of zeaxanthin at the dark stage, and the increase of the xanthophyll pool both in the photophase and dark phase, resulting in an enhancement of the ability of non-photochemical quenching to avoid or alleviate the damage to photosynthetic apparatus.     

Forest floor mass,litterfall and nutrient return in Central Himalayan high altitude forests

Dynamics of forest floor biomass, pattern of litter fall and nutrient return in three central Himalayan high elevation forests are described. Fresh and partially decomposed litter layer occur throughout the year. In maple and birch the highest leaf litter value was found in October and in low-rhododendron in August. The relative contribution of partially and more decomposed litter to the total forest floor remains greatest the year round. The total calculated input of litter was 627.7 g m^-2 yr^-1 for maple, 477.87 g m^-2 yr^-1 for birch and 345.9 g m^-2 yr^-1 for low-rhododendron forests. 49–61% of the forest floor was replaced per year with a subsequent turnover time of 1.6–2.0 yr. The annual nutrient return through litter fall amounted to (kg ha^-1 yr^-1) 25.5–56.1 N, 2.0–5.4 P and 9.9–23.3 K. The tree litter showed an annual replacement of 26–54% for different nutrients and it decreased towards higher elevation. The nutrient use efficiency in terms of litter produced per unit of nutrient was higher in present study compared to certain mid- and high-elevation forests of the central Himalaya.     

Polysaccharide-enriched fraction isolated from Duchesnea chrysantha protects against oxidative damage

Reactive oxygen species (ROS)-related oxidative damages have been implicated in a wide variety of the pathological processes such as atherosclerosis, inflammation and carcinogenesis. A polysaccharide-enriched fraction (PEF) was isolated from Duchesnea chrysantha, a herbaceous plant, and its antioxidant activity was demonstrated using several assay systems in vitro. The PEF effectively inhibited Cu²⁺-stimulated low density lipoprotein oxidation in a concentration-dependent way and retarded the conjugated diene formation with the enhancement of the lag phase during oxidation. An assay for DNA strand breaks showed that PEF strongly protected DNA against damage caused by UV or by OH or O₂ ^– generated in the metal-catalyzed oxidation system. PEF effectively inhibited Nitroblue Tetrazolium reduction mediated by O₂ ^– in a dose-dependent manner. It also competed with 2-deoxy-d-ribose in absorbing OH generated by -irradiation (600 Gy) and thus inhibited the formation malondialdehyde. In conclusion, these evidences indicate that PEF may act as an antioxidant to scavenge O₂ ^–, OH or LO₂ directly. Our findings suggest the possibility that it may play a role as a potential therapeutic antioxidant in treatment of oxidative damage-derived diseases.     

Litter Decomposition and Nutrient Release in a Tropical Seasonal Rain Forest of Xishuangbanna,Southwest China1

We studied litter decomposition and nutrient release in a tropical seasonal rain forest of Xishuangbanna, Southwest China. The monthly decay rates (k) of leaf litter ranged from 0.02 to 0.21/mo, and correlated with rainfall and soil moisture. Annual k values for leaf litter (1.79/yr) averaged 4.2 times of those for coarse wood (2.5–3.5 cm in diameter). The turnover coefficients of forest floor mass (annual litterfall input/mean floor mass) were: 4.11/yr for flowers and fruits, 2.07/yr for leaves, and 1.17/yr for fine wood (≤2 cm in diameter), with resident time decreasing from fine woods (0.85 yr) to leaves (0.48 yr) and to flower and fruits (0.24 yr). Nutrient residence times in the forest floor mass were ranked as: Ca (1.0 yr) > P (0.92 yr) > Mg (0.64 yr) > N (0.36 yr) > K (0.31 yr). Our data suggest that rates of litter decomposition and nutrient release in the seasonal rain forest of Xishuangbanna are slower than those in typical lowland rain forests, but similar to those in tropical semideciduous forests.     

Carbonate bioformations around underwater freshwater springs in the north-eastern Adriatic Sea

Large carbonate, bryozoan-serpulid constructions, made by Pentapora fascialis and Salmacina dysteri respectively, were found around karstic freshwater springs, called vruljas, in the Senj Archipelago (Velebit Channel, Croatia). In June 2002, several sites were investigated by SCUBA divers on the rocky cliffs of Grmac and dralova at depths ranging from 19 to 32 m. Mean colony diameter decreased with increasing distance from the vruljas: in the vicinity the mean diameter was 65.8±21 cm, at 2-m distance it was 40.4±8.2. Carbonate contribution was to a great extent due to the bryozoan (5,784±1,186 gm^–2 CaCO₃) rather than to the serpulid (383±218 gm^–2 CaCO₃). P. fascialis carbonate standing stock was remarkably high if compared with data from literature for shallow carbonate producers. The bryozoan-serpulid constructions can be indicated as important, even if localised, contributions to the carbonate budget in the Adriatic Sea.