栓皮栎地上部分构型及生物量分配

研究秦岭南坡商洛地区不同径级栓皮栎的地上部分构型、生物量及其分配和构型与生物量的关系.结果表明： 不同径级栓皮栎地上部分构型与生物量的分配存在差异.随着径级的增大,栓皮栎树高、胸径和冠幅逐渐增大;平均递减率先增大后减小;栓皮栎总体分枝率和逐步分枝率先增加后下降;不同径级栓皮栎垂直方向上的比叶面积为0.02～0.03,叶重比、叶面积指数和叶面积比的较大值在径级为Ⅰ、Ⅱ、Ⅲ时出现于树干中、上部,在径级为Ⅳ、Ⅴ、Ⅵ时出现在树干中部,径级进一步增大则在垂直方向上出现2个峰值,分别位于树干中下部和中上部.栓皮栎地上部分生物量中,树干生物量占71.8%～88.4%,枝生物量占5.8%～19.6%,叶生物量占4.2%～8.6%.随着径级的增大,树干生物量所占比例先减小后增大,而枝、叶生物量所占比例呈先增大后减小再增大的趋势.栓皮栎地上部分生物量与树高、胸径、冠幅和逐步分枝率(R_2∶1)呈显著正相关,与总体分枝率和逐步分枝率(R_3∶2)呈正相关趋势,但相关性不显著.树干生物量、地上总生物量与树干递减率呈负相关趋势,枝生物量、叶生物量与树干递减率呈正相关趋势,但相关性均不显著.     

The spores of Pteris cretica complex (Pteridaceae-Pteridophyta) in America

Spore morphology in the Pteris cretica complex, including Pteris brasiliensis, P. ciliaris, P. cretica, P. denticulata var. denticulata, P. denticulata var. tristicula, P. ensiformis, P. multifida and P. mutilata was examined using light and scanning electron microscope. The spores are trilete, triangular to circular in shape, with an equatorial thickening (= cingulum). Equatorial diameter ranges from 29 to 69 μm, and polar diameter from 18 to 53 μm. Exospore is proximally verrucate and distally rugate, with the exception of Pteris ensiformis, which has cones on both polar faces. Perispore is generally less than 1 μm thick, apparently single-layered in section, and translucent under light microscope. Spheroids were frequently observed on the surfaces of both perispore and exospore. Hyaline spores lacking cingulum were found in all specimens. Pteris brasiliensis, P. cretica and P. denticulata exhibit pronounced polymorphism and, in addition to trilete spores these taxa also produce atypical spores such as tetralete, monolete and intermediate types.     

Metabolic adaptation of Pteris vittata L. gametophyte to arsenic induced oxidative stress

The sporophyte and gametophyte of Pteris vittata are arsenic hyperaccumulators, however, little is known about the mechanism by which the gametophyte deals with this toxic element. An in vitro system (spores grown in arsenic amended nutrient media) was used to investigate the impact of arsenic on growth of the gametophyte and the role of antioxidative systems in combating As-stress. When mature spores of P. vittata were grown in medium amended with 0-50 mg kg(-1) of arsenic (as arsenate), the arsenic concentration in the gametophyte increased, with increasing arsenate in the media, but did not inhibit the spore germination and biomass development. Increases in the level of antioxidant enzymes, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and glutathione-Stransferase) and of ascorbic acid and glutathione probably enabled the gametophyte to withstand the oxidative stress caused by arsenate.     

Arsenic hyperaccumulation in the Chinese brake fern (Pteris vittata) deters grasshopper (Schistocerca americana) herbivory

Brake fern, Pteris vittata, not only tolerates arsenic but also hyperaccumulates it in the frond. The hypothesis that arsenic hyperaccumulation in this fern could function as a defense against insect herbivory was tested. Fronds from control and arsenic-treated ferns were presented to nymphs of the grasshopper Schistocerca americana. Feeding damage was recorded by visual observation and quantification of the fresh weight of frond left uneaten and number of fecal pellets produced over a 2-d period. Grasshopper weight was determined before and after 5 d of feeding. Grasshoppers consumed significantly greater amounts of the frond tissue, produced more fecal pellets and had increased body weight on control plants compared with grasshoppers fed arsenic-treated ferns. Very little or none of the arsenic-treated ferns were consumed indicating feeding deterrence. In a feeding deterrent experiment with lettuce, sodium arsenite at 1.0 mm deterred grasshoppers from feeding whereas 0.1 mm did not. In a choice experiment, grasshoppers preferred to feed on lettuce dipped in water compared with lettuce dipped in 1.0 mm sodium arsenite. Our results show that arsenic hyperaccumulation in brake fern is an elemental defense against grasshopper herbivory.     

A Critical Review of the Arsenic Uptake Mechanisms and Phytoremediation Potential of Pteris vittata

The discovery of the arsenic hyperaccumulator, Pteris vittata (Chinese brake fern), has contributed to the promotion of its application as a means of phytoremediation for arsenic removal from contaminated soils and water. Understanding the mechanisms involved in arsenic tolerance and accumulation of this plant provides valuable tools to improve the phytoremediation efficiency. In this review, the current knowledge about the physiological and molecular mechanisms of arsenic tolerance and accumulation in P. vittata is summarized, and an attempt has been made to clarify some of the unresolved questions related to these mechanisms. In addition, the capacity of P. vittata for remediation of arsenic-contaminated soils is evaluated under field conditions for the first time, and possible solutions to improve the remediation capacity of Pteris vittata are also discussed.     

Phytoremediation of arsenic contaminated soil by Pteris vittata L. I. Influence of phosphatic fertilizers and repeated harvests

A greenhouse experiment was conducted to evaluate the effectiveness of diammonium phosphate (DAP), single superphosphate (SSP) and two growing cycles on arsenic removal by Chinese Brake Fern (Pteris vittata L.) from an arsenic contaminated Typic Haplustept of the Indian state of West Bengal. After harvest of Pteris vittata the total, Olsen's extractable and other five soil arsenic fractions were determined. The total biomass yield of P. vittata ranged from 10.7 to 16.2 g pot(-1) in first growing cycle and from 7.53 to 11.57 g pot(-1) in second growing cycle. The frond arsenic concentrations ranged from 990 to 1374 mg kg(-1) in first growing cycle and from 875 to 1371 mg kg(-1) in second growing cycle. DAP was most efficient in enhancing biomass yield, frond and root arsenic concentrations and total arsenic removal from soil. After first growing cycle, P. vittata reduced soil arsenic by 10 to 20%, while after two growing cycles Pteris reduced it by 18 to 34%. Among the different arsenic fractions, Fe-bound arsenic dominated over other fractions. Two successive harvests with DAP as the phosphate fertilizer emerged as the promising management strategy for amelioration of arsenic contaminated soil of West Bengal through phyotoextraction by P. vittata.