Carbon and nitrogen cycling in North American boreal forests

A model of boreal forest dynamics was adapted to examine the factors controlling carbon and nitrogen cycling in the boreal forests of interior Alaska. Empirical relationships were used to simulate decomposition and nitrogen availability as a function of either substrate quality, the soil thermal regime, or their interactive effects. Test comparisons included black spruce forests growing on permafrost soils and black spruce, birch, and white spruce forests growing on permafrost-free soils. For each forest, simulated above-ground tree biomass, basal area, density, litterfall, moss biomass, and forest floor mass, turnover, thickness, and nitrogen concentration were compared to observed data. No one decay equation simulated forests entirely consistent with observed data, but over the range of upland forest types in interior Alaska, the equation that combined the effects of litter quality and the soil thermal regime simulated forests that were most consistent with observed data. For black spruce growing on permafrost soils, long-term simulated forest dynamics in the absence of fire resulted in unproductive forests with a thick forest floor and low nitrogen mineralization. Fires were an important means to interrupt this sequence and to restart forest succession.     

Laboratory tests carried out onMicrothrix inconspicuella [Lep.: Pyralidae], a biological control agent forEmex australis in Australia

Host specificity tests of the moth,Microthrix inconspicuella Ragonot in Australia, indicated that larvae could feed and develop on young apple leaves. Additional tests in South Africa on leaves and fruit of the 4 apple varieties, Jonathan, Starking (Red Delicious), Granny Smith and Golden Delicious, showed that apples were not a preferred food. Little feeding occurred and pupation happened infrequently. No 2^nd generation resulted whenM. inconspicuella colonies were confined on apple fruit or leaves.      

DOES LIGHT QUALITY AFFECT THE SINKING RATES OF MARINE DIATOMS?1

Although the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experiments in situ is thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell et Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. For T. weissflogii, sinking rates (SETCOL method) were twice as high (～0.2 m·d^?1)for cells grown under red light as for cells grown under white or blue light (～0.08 m·d^?1), but there were no significant differences in carbohydrate content (～105 fg·μm^?3) or silica content (～ 17 fg·μ^?3) to account for the difference in sinking rates. Thalassiosira weissflogii grown under blue light was significantly smaller (495 μm³) than cells grown under red light (661 μm³), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (～0.054 m·d^?1) or silica content (～20 fg·μm^?3) in D. brightwellii grown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm³ than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking rate studies done under white light.     

Effects of fruit fly host, fruit species, and host egg to female parasitoid ratio on the laboratory rearing of Biosteres arisanus

The host suitability of the oriental fruit fly, Bactrocera dorsalis (Hendel), for development of Biosteres arisanus (Sonan), a braconid parasitoid, was compared with three other fruit fly species, namely, Mediterranean fruit fly, Ceratitis capitata Weidemann, melon fly, Bactrocera cucurbitae Coquilett, and Malaysian fruit fly, Bactrocera latifrons (Hendel). In addition, effects of five different fruit species, namely, Carica papaya L. (solo papaya), Musa sapientum (L.) O. Ktze. (apple banana), Mangifera indica (L.) (Haden mango), Terminalia catappa (L.) (false kamani), and Citrus aurantiifolia (Christman) Swingle (common lime), on the parasitization rate of B. dorsalis and sex ratio of parasitoid progenies were evaluated. Effects of host egg to female B. arisanus ratios on parasitoid progeny yields were likewise determined. The host suitability of fruit flies for development of B. arisanus was ranked as: B. dorsalis>C. capitata=B. latifrons=B. cucurbitae. Based on percent parasitization of B. dorsalis, preference of B. arisanus females for host eggs varied with fruit species, however, preferential oviposition displayed by female parasitoids did not influence sex ratios of subsequent parasitoid progenies. Increases in host egg to female parasitoid ratios of 5:1, 10:1, 20:1, 25:1, and 30:1 corresponded with increases in parasitoid progeny yield reaching a plateau at 20:1.     

Shoot regeneration from tissue-cultured leaves of the American cranberry (Vaccinium macrocarpon)

A method for shoot regeneration from leaf explants in two cultivars of cranberry (Vaccinium macrocarpon Ait.) is described. Modified Anderson's medium supplemented with combinations of thidiazuron (TDZ) with or without 1 M NAA (-naphthaleneacetic acid) was used to optimize shoot regeneration. The effect of light or dark incubation was also determined. Maximum regeneration was obtained in the light in the presence of 10 M TDZ and 1 M NAA. While this medium was suitable for leaf explants obtained from shoot cultures, regeneration did not occur from leaves collected from greenhouse-grown plants. Elongation of the regenerated shoot tips did not occur until explants were transferred to growth regulator-free medium at which time only a minority of shoots elongated. Elongated shoots could be dissected away from leaf tissue, rooted easily, and acclimitized to ambient conditions.Abbreviations NAA -naphthaleneacetic acid - TDZ 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea     

Shoot regeneration from mature endosperm of Passiflora foetida

Murashige and Skoog (1962) medium supplemented with 2 M 6-benzylaminopurine (BA) induced adventitious shoots on mature endosperm explants, whilst gibberellic acid (GA₃) and casein hydrolysate stimulated growth and development of these shoot primordia. Plantlets were successfully weaned in vivo. These plants were found to be triploid and flowered, although fruit set was not observed.     

Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa). I. Changes during fruit development

The cytokinin content in fruit tissue of the kiwifruit ( Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) was monitored during fruit development to identify which cytokinins were present and if they were linked with specific stages of fruit growth. Cytokinins were isolated and purified by column chromatography and high-performance liquid chromatography and quantified by radioimmunoassay. A novel HPLC step utilising an amine column was successfully introduced as a preparative step in the separation of the O - and 9-glucosides from the free bases and ribosides. The radioimmunoassay results were validated, and the different cytokinins identified, by gas chromatography-mass spectrometry. Cytokinins detected in fruit included the cytokinin free bases, zeatin and isopentenyladenine, their ribosides, nucleotides and both O - and 9-glucosides. Both qualitative and quantitative changes of the cytokinins occurred during fruit development. A decrease in cytokinin concentration occurred after anthesis (from 342 pmol g⁻¹ fresh weight at anthesis to 41 pmol g⁻¹ fresh weight 27 days after anthesis). A large increase in cytokinin concentration and content per fruit occurred as the fruit reached commercial maturity (to 1900 pmol g⁻¹ fresh weight). Individual cytokinins showed quite different patterns. Zeatin, in particular, showed a peak in concentration (13 pmol g⁻¹ fresh weight) 11 days after anthesis that correlated with the beginning of the cell division phase of fruit growth. The accumulation of cytokinin (mostly zeatin riboside or zeatin nucleotide) in mature fruit may be of significance for the postharvest storage of kiwifruit fruit.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria x ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

Sediment quality assessment in the delta of rivers Rhine and Meuse based on field observations,bioassays and food chain implications

The quality of sediment was assessed in 46 sites in the delta of the rivers Rhine and Meuse (The Netherlands) by means of physical-chemical analysis, field observations on the macrobenthic community structure, accumulation studies and bioassays using Chironomus riparius, Daphnia magna and Photobacterium phosphoreum. The results of chemical analyses were classified using national criteria for sediment quality. Results of field studies and bioassays were classified using criteria derived from research in reference areas or based on data from literature. Risk assessment was carried out according to the sediment quality triad and by means of multi criteria analysis (MCA). The Triad approach was used to demonstrate causal relations between effects on the macrozoobenthos community structure, effects demonstrated in bioassays and sediment pollution. This was done by making a comparison of sediment contamination levels with toxicity data from literature for the test organisms of the bioassays. Using the MCA method, for each site a numerical value was derived for total environmental risk in the present situation, based on observed effects. In this way, a relative risk ranking of all sites was realized. The MCA values for the present situation were also compared with MCA scores based on estimated risks after remediation in 1995, in order to set priorities for sites where remediation is expected to cause a significant reduction in environmental risk. In most of the 46 sites studied so far, the macrofauna community was poorly developed, judged by a low number of benthic species, low abundances and a high dominance of species regarded as relatively tolerant to chemical pollution. In bioassays high sediment toxicity was demonstrated for 24 sites. Using the sediment quality triad approach, 25 sites were identified as areas where pollution can be held responsible for the effects observed in the field. From a comparison of contaminant concentrations in different types of food with maximum tolerable risk levels, and the application of a bioaccumulation model it was concluded that the sediment pollution also implies high risks for plant-, benthos- or fish-eating birds (secondary poisoning of top predators). In the Nieuwe Merwede highest MCA risk scores were found for shallow parts where highly polluted sediments are found. It is concluded that the sediment quality triad and the MCA provide additional information which can be used to establish priorities for remedial action. Based on an ecotoxicological evaluation of the improved quality of new sediments that will be deposited after removal of the polluted sediments in the Nieuwe Merwede, it is concluded that in this upstream part of the Rhine delta remedial action will be effective.     

杨桃果实采后生理研究(综述)

概述了国内外对杨桃果实采后主要营养成分的分析、呼吸、乙烯释放、主要生理病害,并介绍了不同贮藏条件或处理对杨桃果实采后贮藏性影响的研究概况。