海河流域14种农作物对土壤库中磷的输出量和输入量初步研究

 海河流域14种农作物平均含磷量为0.127±0.053%,变化范围0.023—0.214%,不同器官中最高可达0.419%,最低仅为0.019%。对土壤库中磷输出量最大者为谷子,磷可达99.758±56.931kg·ha-1·a-1,其次是玉米和棉花;磷输入量以白薯为最大,为12.557±5.020kg·ha-1·a-1(但包括可食部分块根的输出部分在内),然后是谷子和花生,其余作物均较低,<2kg·ha-1·a-1。具高输出量的作物的部位有玉米、谷子、花生、棉花等果实,谷子、花生、白薯等茎叶;就输入量而言,除白薯为高输入和谷子为低输入类型外,其余均属很低输入型,上述特点揭示了海河流域因作物的收获而大量损失土壤库中的磷,如种植谷子、玉米、棉花等分别以99.758、32.661和26.591kg·ha-1·a-1的速率损失有效态磷。并对不同子流域作物磷的输出(入)量差异以及针对上述问题应采取的对策作了探讨。     

Fine root growth and demographic responses to nutrient patches in four old-field plant species

Proliferation of roots in a nutrient patch can occur either as a result of an increase in root length (morphological response) or by a change in root birth or death rates (demographic responses). In this study we attempted to distinguish between these two mechanisms of response to nutrient patches and to compare the responses of four old-field plant species (two annuals, two perennials). For all four species combined, there were significant increases in root numbers and root length in fertilized patches. Root proliferation in fertilized patches was largely due to increased birth (=branching) rates of new roots. However, there was also a significant increase in root death rates in the fertilized patches which reduced the magnitude of the increase in net root numbers. Plots for individual species suggested they differed in the magnitude and timing of root proliferation in fertilized patches due to differences in root birth and death rates. However, because of the limited sample size in this study, there was only a marginally significant difference among species in root birth rates, and no difference in death rates. Further studies are currently underway to better quantify species differences in the demographic mechanism, as well as magnitude, of response to nutrient patches and if this would affect the ability to exploit small-scale heterogeneity in soil resources.     

Inefficient nitrogen resorption in genets of the actinorhizal nitrogen fixing shrubComptonia peregrina: physiological ineptitude or evolutionary tradeoff?

Nutrient resorption was measured in an actinorhizal nitrogen-fixing shrub,Comptonia peregrina, for five years in the understory of a deciduous oak forest in Rhode Island, USA. Mean resorption of nitrogen was extremely inefficient (11%) compared to most deciduous species (50%+), yet resorption of phosphorus was efficient (53%) and comparable to other species. Of the seven additional nutrients studied, only copper (6%) and zinc (10%) were resorbed from senescing leaves. Resorption of nitrogen (5%–20%) and phosphorus (40%–71%) varied significantly among years. Copper was resorbed from leaves in three years and accreted into leaves in two years. Five-year resorption means differed among individual genets by as much as a factor of 2.5 for nitrogen, and 1.3 for phosphorus. Resorption of nitrogen, copper, and zinc were highly correlated, yet resorption of phosphorus remained autonomous from other nutrients. The ecophysiological tradeoffs inComptonia which have resulted in the cooccurence of actinorhizal nitrogen fixation, inefficient nitrogen resorption, and efficient phosphorus resorption suggest that plant nutrient status does have an impact on resorption efficiency and that the evolution of nutrient conservation strategies is nutrient-specific.     

Utilization of the ambient concentration as a criterion for steady state after exponential growth: Some culture experiments with optimum or suboptimum N nutrition

Culture experiments are described in which Plantago lanceolata L. was grown from seedling till flowering under steady state conditions of optimum or suboptimum nitrate nutrition. In the optimum treatment, plants had free access to nitrate. In two suboptimum treatments, nitrate was added with constant relative addition rates (RAR) of 0.18 or 0.10 d^–1 during the phase of constant relative uptake rates (RUR) of the plants and then with RAR's that were reduced stepwise from 0.18 to 0.07 d^–1 or 0.10 to 0.04 d^–1 when nutrient absorption gradually decreased. Reduction of the RAR's was aimed at maintenance of a balance between RAR and RUR. External nitrate concentrations were measured to monitor the reductions. In the vegetative phase, the relative growth rate (RGR) and the root weight ratio (RWR) of P. lanceolata were constant. In the reproductive phase, RGR's were constant, but lower, and RWR's decreased. Concentrations of organic-N in leaves were stable during the experimental period while those of the peduncles were lower and decreased with time. The ratio of reproductive to vegetative weight increased linearly with time. A number of plant parameters varied with N supply. ei]Section editor: T W Rufty     

Organic matter and nutrient cycling within an endemic birch stand in the Etna massif (Sicily):Betula aetnensis Rafin

At altitudes between 1300 m to 2100 m in the Etna massif (Sicily), an endemic species of theBetula genus,Betula aetnensis Rafin, grows in a well-defined microclimatical context. Aboveground biomass and nutrient content studies within one stand revealed no significant differences from the otherBetula species, normally found in colder more temperate climate regions.Throughout the studied sites, biomass production, nutrient cycling and various structural or physiological characteristics (leaf area index) varied very little.Other researches indicate that the originality ofBetula aetnensis lies more in the histological or anatomical characteristics of its water conducting system which enables the species to adapt to Mediterranean-climate summer droughts in the Etna massif.

---

Riassunto Sull'Etna, tra 1300 e 2100 m d'altitudine, in una zona microclimaticamente ben definita del versante nordorientale, si rinviene laBetula aetnensis Rafin.Dallo studio della fitomassa e della mineralomassa aerea del bosco di Monte Baracca, è emerso che non vi sono differenze notevoli con le altre specie indagate del genereBetula, più caratteristiche dei climi temperati e freddi.La produzione di biomassa, cosi come la gestione degli elementi nutritivi, è molto simile ai diversi popolamenti già indagati, cosi come certe caratteistiche strutturali e fisiologiche (leaf area index).L'originalità dellaBetula aetnensis è da ricercarsi nel vantaggio che ne ricava, a livello endogeno, sfruttando le caratteristiche istologiche ed anatomiche del suo apparato conduttore, che le consentono un efficace ed eccellente adattamento alle condizioni di siccità estive particolari del clima mediterraneo del vulcano.

     

Filamentous algae in fish ponds of the Třeboň Biosphere Reserve-ecophysiological study

Filamentous algae in eutrophic carp ponds in South Bohemia (Central Europe) were studied from 1988 to 1990. High biomass (490 g DW m^-2) was attained by Cladophora fracta (O. F. Müll. ex Vahl) Kütz. after two months of growth. This marked growth depleted inorganic carbon in the water, but did not decrease the concentration of tissue nutrients. Laboratory measurements of final pH indicate that all the filamentous algae studied, except for Tribonema, are very efficient HCO₃ ^- users. An extremely high pH of 11.6 and oxygen concentration of 32 mg l^-1 were measured in the algal mats. High pH resulted in CaCO₃ precipitation, visible as white incrustations on algal filaments. The amount of precipitated CaCO₃ reached 134 kg ha^-1. After reaching peak biomass, 90% of the Cladophora decomposed over the next 95 days.The highest net photosynthetic rate in C. fracta was measured between pH range 8.5–10.0 and oxygen concentrations of 7–12 mg l^-1. Optimum temperature for photosynthesis was between 17–22°C.     

Partial Resistance to Heterodera avenae in Wheat Lines with the 6M v Chromosome from Aegilops ventricosa

Lines of wheat with the 6M^v chromosome from Aegilops ventricosa display partial resistance to both pathotypes Hal2 and Ha41 of Heterodera avenae. With either pathotype, the effect of this alien chromosome on cyst production, size, and fecundity was expressed in resistance tests. Partial resistance of five 6M^v(6D) substitution lines varied according to the intrinsic cyst-forming capacity of the nematode pathotypes and the recipient germplasms. Such partial resistance can be utilized in wheat breeding lines for integrated management of the cereal cyst nematode.     

Nitrification,denitrification, and related functional genes under elevated CO2: A meta-analysis in terrestrial ecosystems

Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N₂O) emissions mediated by nitrification and denitrification. We conducted a meta-analysis of the effects of elevated CO₂ on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO₂ experiments in terrestrial ecosystems. We investigated the effects of elevated CO₂ alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO₂ of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO₂ increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO₂ increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO₂ also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO₂ was larger at elevated temperature and high N (+62%). Four out of 14 two-way interactions tested between elevated CO₂ and elevated temperature, elevated CO₂ and increased precipitation, and elevated CO₂ and N addition were marginally significant and mostly synergistic. The effects of elevated CO₂ on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta-analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO₂ and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N₂O emissions.     

Microbial nitrogen and phosphorus co-limitation across permafrost region

The status of plant and microbial nutrient limitation have profound impacts on ecosystem carbon cycle in permafrost areas, which store large amounts of carbon and experience pronounced climatic warming. Despite the long-term standing paradigm assumes that cold ecosystems primarily have nitrogen deficiency, large-scale empirical tests of microbial nutrient limitation are lacking. Here we assessed the potential microbial nutrient limitation across the Tibetan alpine permafrost region, using the combination of enzymatic and elemental stoichiometry, genes abundance and fertilization method. In contrast with the traditional view, the four independent approaches congruently detected widespread microbial nitrogen and phosphorus co-limitation in both the surface soil and deep permafrost deposits, with stronger limitation in the topsoil. Further analysis revealed that soil resources stoichiometry and microbial community composition were the two best predictors of the magnitude of microbial nutrient limitation. High ratio of available soil carbon to nutrient and low fungal/bacterial ratio corresponded to strong microbial nutrient limitation. These findings suggest that warming-induced enhancement in soil nutrient availability could stimulate microbial activity, and probably amplify soil carbon losses from permafrost areas.