Effects of root zone temperature on aluminium toxicity in two cultivars of spring wheat with different resistance to aluminium

Manifestations of aluminium (Al) toxicity in two cultivars of wheat ( Triticum aestivum L. cvs Kadett [relatively Al-resistant] and WW 20299 [relatively Al-sensitive]) were investigated at two root zone temperatures (RZT) that may occur in the field. The plants were grown for 9 days at 10 or 25°C RZT. Mineral nutrients other than CaSO₄ were supplied daily in exponentially increasing amounts to meet the demand of the plants. Al was added as Al₂(SO₄)₃ at the beginning of the culture period at concentrations ranging from 0 to 100 μ M . pH was kept constant at 4.1. Experimental data were analysed for interactions between Al and RZT on a fresh weight basis by the nonlinear Weibull function. Cultivar Kadett, when grown at 25°C RZT, was more resistant to Al than when grown at 10°C RZT. Cultivar WW 20299 was equally sensitive to Al at 10 and 25°C RZT but generally more sensitive to Al than cv. Kadett. It is suggested that cv. Kadett, in contrast to cv. WW 20299, possesses a mechanism for Al resistance that is less effective at 10°C than at 25°C RZT and therefore may be metabolically dependent. In roots, the concentrations of K, P, Mg and Ca were not negatively affected by Al or by RZT. In shoots of both cultivars the concentrations of Ca and Mg became comparatively low when the plants were treated with Al or at low RZT, the effect being larger for Ca than for Mg. At 10°C RZT under Al stress, the Ca concentrations in shoots approached the critical concentration where growth may be inhibited. As no Al was detected in the shoots, it is suggested that Al in the roots inhibits shoot growth by reducing transport of Ca from roots to shoots.     

The effect of soil pH on the ability of ectomycorrhizal fungi to increase the growth of Eucalyptus globulus Labill.

We examined the effect of two levels of soil pH (5 and 6) on the ability (effectiveness) of ectomycorrhizal fungi to increase the growth of Eucalyptus globulus Labill. at a deficient supply of P. Plants were inoculated with one of six fungal isolates [Laccaria laccata (Scop. ex Fr.) Berk. and Br. (isolates A and B), Pisolithus tinctorius (Pers.) Coker and Couch (isolates A and B), Descolea maculata Bough. and Mal. and Setchelliogaster sp. nov.] and were grown in a P-deficient sand, in pots, in a temperature-controlled glasshouse. Seedlings were harvested 89 days after planting and were assessed for dry matter production, tissue P concentrations, ectomycorrhizal colonization of roots and hyphal development in soil.Uninoculated plants had less than 5% of their fine root length colonized by ectomycorrhizal fungi. In contrast, inoculated plants had 30% or greater of their fine root length ectomycorrhizal. Inoculation increased the uptake of P and growth of plants for all isolates and at both levels of soil pH, although growth responses to inoculation were greater at pH 6, particularly for the two L. laccata isolates. Isolates which colonized roots most extensively increased plant growth to the greatest extent. D. maculata was the most effective fungal isolate at pH 5, and both D. maculata and L. laccata A were most effective at pH 6. The effects of soil pH on plant growth were also related to some extent to the effects of soil pH on colonized root length. Growth responses to inoculation were related less well to hyphal development in soil. The L. laccata isolates formed more hyphae in soil (on a per pot, per m of fine root, and per m of colonized fine root basis) than other fungal isolates, but were not always more effective in increasing plant grown.     

Photosynthesis in leaves and siliques of winter oilseed rape (Brassica napus L.)

The rate of photosynthesis and its relation to tissue nitrogen content was studied in leaves and siliques of winter oilseed rape (Brassica napus L.) growing under field conditions including three rates of nitrogen application (0, 100 or 200 kg N ha^-1) and two levels of irrigation (rainfed or irrigated at a deficit of 20 mm). The predominant effect of increasing N application under conditions without water deficiency was enhanced expansion of photosynthetically active leaf and silique surfaces, while the rate of photosynthesis per unit leaf or silique surface area was similar in the different N treatments. Thus, oilseed rape did not increase N investment in leaf area expansion before a decline in photosynthetic rate per unit leaf area due to N deficiency could be avoided. Much less photosynthetically active radiation penetrated into high-N canopies than into low-N canopies. The specific leaf area increased markedly in low light conditions, causing leaves in shade to be less dense than leaves exposed to ample light. In both leaves and siliques the photosynthetic rate per unit surface area responded linearly to increasing N content up to about 2 g m^-2, thus showing a constant rate of net CO₂ assimilation per unit increment in N (constant photosynthetic N use efficiency). At higher tissue N contents, photosynthetic rate responded less to changes in N status. Expressed per unit N, light saturated photosynthetic rate was three times higher in leaves than in silique valves, indicating a more efficient photosynthetic N utilization in leaves than in siliques. Nevertheless, from about two weeks after completion of flowering and onwards total net CO₂ fixation in silique valves exceeded that in leaves because siliques received much higher radiation intensities than leaves and because the leaf area declined rapidly during the reproductive phase of growth. Water deficiency in late vegetative and early reproductive growth stages reduced the photosynthetic rate in leaves and, in particular, siliques of medium- and high-N plants, but not of low-N plants.     

Translocation and effectiveness of foliar-fertilized boron in broccoli plants of varying boron status

The translocation and effectiveness of foliar-fertiilized boron (B) was investigated in broccoli plants supplied via the root system with luxury, sufficient or deficient levels of B. ¹⁰B-enriched boric acid was applied three times to lower leaves, beginning one week prior to inflorescence emergence, and the shoot and floret yields, as well as the ¹⁰B and ¹¹B contents or concentrations of xylem sap, phloem exudate and various plant parts, were determined three weeks after inflorescence emergence. The amount of ¹⁰B translocated in phloem from fed leaves to the remainder of the shoot did not exceed 0.5%, of that supplied, but it was inversely related to plant-B status. The partitioning of translocated ¹⁰B to florets (16–30%) and the degree of enhancement in floret yield (28–75%) was also inversely related to plant-B status. It is concluded that foliar-B fertilization may be more effective for preventing B deficiency than soil-derived B in leaves.Abbreviations ¹⁰B/¹¹B mass isotopes of boron - DM dry matter - FF foliar fertilization - RF root fertilization     

Marcescence and senescence in a submediterranean oak (Quercus subpyrenaica E.H. del Villar): photosynthetic characteristics and nutrient composition

We have studied some characteristics of marcescent leaves (withered retained leaves) and senescent leaves in Quercus subpyrenaica, a tree species that plays a major role in the climatic transition forests between temperate and mediterranean environments in north-eastern Spain. Leaves were taken from the upper and lower halves of the tree crown, both in the south- and north-exposed parts of the tree. Leaves receiving low photosynthetic photon flux density (PPFD) undergo autumnal senescence, which is associated with decreases in photosynthetic pigments and decreases in the chlorophyll a to chlorophyll b ratio. Leaves receiving higher PPFD underwent senescence at a later date. Leaves situated in the upper, south-exposed part of the tree, which receive the highest PPFD, showed no signs of senescence and remained photosynthetically active for a longer period of time, marcescence occurring suddenly at the end of the season. Marcescence is unlikely to cause an improvement in nutrient recycling, since the removal of nutrients proceeded similarly in marcescent and senescent leaves. Marcescence may increase the time-span of the assimilation capacity for a significant period of time during September and October, when high light intensities and mild temperatures occur. The phenomena triggering marcescence may be related to low temperatures.     

A geographically-based study of shell shape in small rough periwinkles

A study using principal component analysis and discriminant analysis was carried out on shell shape variation in 3093 specimens of rough periwinkles, 2500 of which were below 5.5 mm in columella length, from around the North Atlantic. Using a combination of colour plus sculpture, and life history trait, the snails were classified by inspection and examination into Littorina nigrolineata, L. arcana, L. saxatilis and L. neglecta. Principal component analyses indicated that similar aspects of variation were important in the different taxa, but these were sometimes of differing levels of importance between L. saxatilis and L. neglecta. Crossvalidation in a discriminant analysis showed classification of shells larger than 5.5 mm to have at least an 88% accuracy. That of shells below 5.5 mm showed an accuracy of 49% in L. arcana, increasing to 54% in L. saxatilis and 63% in L. neglecta, with 76% accuracy for small L. nigrolineata. This last was a special case as only one site was sampled, therefore comparative data are not available. This geographically-based study reveals that L. neglecta is more homogeneous over its range than recently reported by other workers and shows greater differences from L. saxatilis than the latter does from either L. nigrolineata or L. arcana. Size effects do not account for these differences because L. neglecta is morphometrically distinct from both large and small L. saxatilis. Furthermore, small, mid-shore L. saxatilis classify with large high-shore L. saxatilis in discriminant analysis, not with L. neglecta. These results provide evidence that the taxon L. neglecta is more distinct than has sometimes been suggested.     

Diagnosis of zinc deficiency in seedlings of a tropical eucalypt (Eucalyptus urophylla S. T. Blake)

A glasshouse experiment was undertaken to establish the internal Zn requirement for shoot growth of Eucalyptus urophylla, a fast-growing commercial plantation species widely planted in tropical regions of the world. A Zn-deficient sand was supplemented with ten rates of Zn and seedlings were harvested after three months. In Zn-deficient plants the new growth was dwarfed with small, necrotic leaves and short internodes. Foliar Zn concentrations declined markedly with leaf age in both Zn-deficient and Zn-adequate plants. The critical Zn concentration for the diagnosis of Zn deficiency also fell with leaf age. Zinc concentrations in the youngest fully expanded leaf ranged from 8–11 g Zn g^–1 dry weight in plants with severe symptoms to 30–37 g Zn g^–1 dry weight in non-deficient plants. The critical Zn concentration for the diagnosis of Zn deficiency at 90% of maximum shoot growth in the same leaf was 21 g Zn g^–1 dry weight. This value is nearly twice that reported for several other species of eucalypts and may indicate a higher internal demand for Zn in tropical than in temperate eucalypts.     

The influence of stand development on nutrient demand,growth and allocation

As an even-aged stand develops growth is concentrated first on leaves and fine roots, as a result nutrient accumulation is very rapid. During this early stage there is a distinct species effect whereas later nutrient uptake becomes a function of growth rate irrespective of species. Once canopy is closed up to two thirds of the nutrients required for growth can be obtained by retranslocation from older or dying tissues, an efficient conservation mechanism that leads to a reduction in the demands that are further reduced by the cycle through the litter layer. In consequence nutritional problems are most likely in the early years while the green crown is being constructed. Later in the rotation problems are unlikely unless nutrient cycles are disturbed, for example by thinning or as a result of excessive accumulation of humus. The eventual clear felling is a major disruption to nutrient cycles. Accelerated litter decomposition can lead to leaching losses, although this can be short lived, and burning if practised can have a major impact on poor sites. Nutrient loss in material removed from the felling site, whether or not harvested, is not high but is much increased if crowns are removed, particularly for the heavily crowned species. The importance of such loss clearly varies with site but may be significant for more than just loss of nitrogen, with loss of calcium, phosphorus or even organic matter per se all being possibly causes of worry.     

Phytosiderophore release in relation to micronutrient metal deficiencies in barley

Phytosiderophore release occurs under both iron and zinc deficiencies in representative Poaceae and has been speculated to be a general adaptive response to enhance the acquisition of micronutrient metals. To test this hypothesis, phytosiderophore (PS) release rates from barley (Hordeum vulgare cv. CM72) subjected to deficiencies of Fe, Zn, Mn, and Cu were compared using chelator-buffered nutrient solutions. PS release rates were determined at two day intervals during onset and development of deficiency symptoms. Plant dry matter yields and nutrient concentrations, measured at three time points were used to construct growth curves for calculation of PS release per unit root mass and estimation of critical internal nutrient levels associated with PS release. In comparison to trace metal-sufficient control plants, dry matter production was markedly reduced in the Zn, Mn, and Cu deficiency treatments, with final relative yields of 49, 61, and 34%, respectively. Relative yields for Fe-deficient plants grown at three suboptimal Fe levels ranged from 95 to 33% of control, and provided a basis for comparison of PS release rates by Zn-, Mn-, and Cu-deficient plants at similar levels of growth inhibition. Under Fe deficiency, PS release increased with severity of the deficiency as measured by foliar Fe concentration, yield reduction, and chlorosis. Changes in PS release rates over time suggested a cyclical pattern that may be regulated by Fe concentration in the plant shoot. The highest rate of PS release (35 mol g^–1 root dw 2 h^–1) was measured after 10 days of growth at pFe 19, whereas control plants adapted for growth at pFe 17 released only 2 to 3 mol g^–1 root dw 2 h^–1. In a second experiment, maximum PS release rates for barley subjected to Zn, Mn, and Cu deficiencies were only 2.6, 2.5 and 1 mol g^–1 2 h^–1, respectively and were only slightly elevated over those of the control plants (ca. 1 mol g^–1 root dw 2 h^–1) grown at pFe 16.5. Moreover, enhanced PS release under Zn deficiency occurred much later, after the deficiency had already caused severely reduced growth. The results suggest that phytosiderophore release in this barley cultivar is a specific response to Fe deficiency and is not significantly induced in response to deficiencies of other trace metals.     

水分胁迫和氮素营养对小麦根苗生长及水分利用效率的效应

采用目前生产上广泛种植的小麦品种小偃６号,在一种特制木盒中土培,研究了水分胁迫和氮素营养对小麦根系和幼苗生长及水分利用效率（ＷＵＥ）的效应。小麦根系生长在双层尼龙网之间,土壤中的水分和养分可以被正常吸收,但主根和侧根不能穿过。结果表明：在土壤含水量为田间持水量的４０％－７０％范围内,随着土壤干旱程度的增加,小麦根长（ＲＬ）、根干重（ＲＤＷ）、叶面积（ＬＡ）和ＷＵＥ显著降低。氮肥的效应更为复杂。随着