Tree seedling development in tropical dry abandoned pasture and secondary forest in Costa Rica

Development of planted seedlings of four canopy tree species in recently abandoned pastures (mown and unmown) and in ca. 40-yr old secondary dry forest in Guana-caste National Park, Costa Rica, was studied from July 1989–June 1992. The species were the light-demanding Cedrela odorata and Swietenia macrophylla, and the shade-tolerant Hymenaea courbaril and Manilkara chicle. Seedling mortality was high and primarily correlated with dry season drought. After the first dry season, M. chicle and C. odorata showed < 5 % survival in the pasture and 20 % in the forest, but after 3 yr survival had decreased to 3% in all plots. Survival of S. macrophylla was highest in the mown pasture (45 % after 3 yr) and lowest in the forest (10 %). For H. courbaril, survival was 40–55 % under all three conditions. Growth rates were low, with a height increment of < 15 cm/yr, possibly due to low precipitation in 1990 and 1991. All species grew taller in the pasture than in the forest. Differences in soil depth, texture and drainage appeared to contribute to variation in the results both within and between plots. Herbivory contributed to the lower survival of C. odorata and S. macrophylla in the forest.     

Behaviour of suspended and sedimentary organic matter in the deltaic areas of the Gulf of Lions (Mediterranean Sea)

The behaviour of organic matter has been approached in two fluvio-marine areas of the Gulf of Lions in the Northwestern Mediterranean Sea: deltas of the Rhône and Têt rivers. Elemental analysis, pyrolysis-gas chromatography-mass spectrometry (main classes of organic compounds) and high performance liquid chromatography (phenolic compounds) enabled to show the fractioning processes and the differentiation of water layers from the river mouth to the open sea. Transitory horizontal and vertical geochemical gradients appeared in the water column. They were more marked in surficial sediments. They underlined the effects of the river inputs which were characterized by high phenol contents. The increase of the marine character towards the open sea was shown by increasing nitrogen-containing compounds. In the Rhône delta, the distribution of the suspended material and organic compounds emphasized the occurrence of a multi-layered water system. In the surficial layers the suspended organic matter was in a little degraded state. On the contrary, the bottom nepheloid contained altered organo-mineral complexes enriched in resistant organic compounds. In the deeper areas of the Lacaze-Duthiers Canyon, in front of the Têt prodelta, the abundance of phytoplanktonic material in the euphotic zone was emphasized by the increase of both nitrogen-containing compounds and aminosugars. In the deeper layers, the suspended material transported by advective currents showed a detrital characteri.e. enriched in clays and in degraded organic matter. The observations carried out in the Rhône delta, the Têt prodelta and the Lacaze-Duthiers Canyon underlined the importance of the general transfer system of suspended material from East to West enhanced by the Liguro-Provençal current.     

The role of mineral compounds and chemical conditions in the binding of phosphate in the Ems estuary

In the Ems estuary the gradients in dissolved phosphorus and iron are non-conservative and opposite. The relations between different mineral compounds, environmental conditions and phosphate concentrations were studied, in an attempt to explain this. Laboratory experiments on water samples from the reaches with high concentrations of phosphate and of suspended matter revealed a low concentration of calcite-bound phosphorus in the middle reaches of the estuary (only 0.07%). Therefore, it is concluded that calcite possibly plays only a modest role in phosphate distribution in the Ems estuary. Further experiments revealed that nearly 70% of the particulate inorganic phosphorus is iron-bound. It is demonstrated that organic coatings on minerals inhibit phosphate release at a low redox potential. Moreover, the organic matter itself contained c. 20% of particulate phosphorus. Approximately 10% of the particulate phosphorus may be associated with clay minerals. It is concluded that in addition to biological processes, the phosphorus associated with ironoxyhydroxides may be crucial for the seasonal variation of the phosphate concentrations in the water.     

Impression Cytology In Patients With Keratoconjunctivitis Sicca

Impression cytology is a simple and painless procedure that allows the collection of the superficial layers of the conjunctival epithelium. Each sample is assigned a grade of epithelial metaplasia, and goblet cell density is calculated in each one. We have studied the superior and temporal bulbar conjuctiva of dry eyes and have compared it with that of normal controls. In normal and dry eyes we find a statistically significant difference both in goblet cell density and grade of metaplasia, between superior and temporal bulbar conjunctiva. the differences in grade of metaplasia and goblet cell density between normal and dry eyes are significant in the superior conjunctiva, but in the temporal conjunctiva we only find significant differences in grade of metaplasia.     

The challenge of estimating kelp production in a turbid marine environment

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (K_d) between 0.28 and 0.87 m⁻¹. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted K_d to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m⁻² seafloor · d⁻¹ for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.     

Growth and nutrition of birch seedlings in relation to potassium supply rate

Summary Growth of hydroponically cultivated birch seedlings (Betula pendula Roth.) at sub- and supra-optimum potassium supply rates was investigated. Potassium was supplied either as a relative addition rate (r _k = 5, 10, 15 and 20% increase day^-1) or as fixed concentrations (0.2, 3, 6, 12 and 15 mM) in the culture solution. After an acclimation period the growth rate of the seedlings in the suboptimum treatments reached values close to the treatment variable, the relative rate of K-addition. Deficiency symptoms, in the form of chlorosis and necroses along the leaf margins, developed initially in all suboptimum treatments, but very few new symptoms appeared once the seedlings had reached the phase of steady-state nutrition and growth. At supra-optimum K-supply levels, i.e. at 0.2–15 mM K in the culture solution, no symptoms of deficiency or toxicity developed, and the relative growth rate of the seedlings remained maximum. The relative growth rate of the seedlings was linearly related to the plant K-status for K contents ranging from 0.2 to 1.0% of dry weight (DW). At higher internal K-concentrations, 1.0–3.0% DW, no further increase in relative growth rate was achieved. A shortage of K resulted in a decrease in the net assimilation rate. This effect was counterbalanced by the absence of shift in he leaf weight ratio as well as by the production of relatively thin leaves. The fraction of dry matter allocated to roots decreased in K-limited plants, as did the leaf contents of soluble carbohydrates and starch.     

沙地云杉苗期生长与干物质生产关系的研究

本文用不同_的模型定量地研究了沙地云杉苗期的生长规律、季节动态及不同生长时期干物质在各器官之间的分配规律。1)1年生幼苗一直保持较高的生长速度,根生长尤为迅速。5年生幼苗在接近生长上限时,增长越来越慢。2)根、茎、叶干物质的生产符合理查德模型;根、茎、叶干重与全株干重之百分比表现出不同的变化趋势,反映了于物质在各器官中的分配规律。3)不同年度各器官的干重变化反映了由于自疏造成的叶的脱落和部分枝的脱落情况。4)各模型的相关系数几乎都达到了极显著的水平。     

Maize Rabl7 overexpression in Arabidopsis plants promotes osmotic stress tolerance

Rabl7 is a Late Embryogenesis Abundant (LEA) protein from maize, which accumulates largely during embryogenesis and also in vegetative tissues when subjected to stress conditions. We have analysed the effect of Rab 17 expression under a constitutive promoter in vegetative tissues of transgenic Arabidopsis thaliana plants. These transgenic plants have higher sugar and proline contents, and also higher water loss rate under water stress. In addition, these plants are more tolerant than non-transformed controls to high salinity and recover faster from mannitol treatment. Our results point to a protective effect of Rabl7 protein in vegetative tissues under osmotic stress conditions.     

Relations between stomatal closure, leaf turgor and xylem vulnerability in eight tropical dry forest trees

This study examined the linkage between xylem vulnerability, stomatal response to leaf water potential (Ψ_L), and loss of leaf turgor in eight species of seasonally dry tropical forest trees. In order to maximize the potential variation in these traits species that exhibit a range of leaf habits and phenologies were selected. It was found that in all species stomatal conductance was responsive to Ψ_L over a narrow range of water potentials, and that Ψ_L inducing 50% stomatal closure was correlated with both the Ψ_L inducing a 20% loss of xylem hydraulic conductivity and leaf water potential at turgor loss in all species. In contrast, there was no correlation between the water potential causing a 50% loss of conductivity in the stem xylem, and the water potential at stomatal closure (Ψ_SC) amongst species. It was concluded that although both leaf and xylem characters are correlated with the response of stomata to Ψ_L, there is considerable flexibility in this linkage. The range of responses is discussed in terms of the differing leaf‐loss strategies exhibited by these species.     

Occurrence of Verticillium fungicola var. fungicola on Agaricus bitorquis Mushroom Crops in Spain

Diseased fruit bodies of Agaricus bitorquis, with similar symptoms to those caused by dry bubble on Agaricus bisporus, were observed in some Spanish crops during summer 1999. Isolates of Verticillium fungicola from A. bitorquis and A. bisporus were submitted to different temperatures and to prochloraz–Mn sensitivity tests. All the isolates collected from A. bitorquis and A. bisporus were identified as V. fungicola var. fungicola. Artificial infections of A. bisporus and A. bitorquis with V. fungicola var. fungicola are also described in the present study. The appearance of natural infections of V. fungicola var. fungicola in A. bitorquis crops could well be due to the growing temperatures used in Spain, which are considerably below those used in other countries.