硅和干旱胁迫对水稻叶片光合特性和矿质养分吸收的影响

硅被认为是植物生长的有益元素,它能增强植物对非生物逆境和生物逆境胁迫的抗性。以抗旱性不同的一对水稻近等基因系w-14-和w-20为实验材料,采用盆栽实验,研究了干旱胁迫下硅处理对水稻生长性状、光合生理特性和矿质养分吸收的影响。结果表明,在正常水分条件下硅处理对水稻的生长及生理特性没有明显影响。干旱胁迫显著降低水稻植株的生长,叶绿素含量、叶绿素荧光参数Fv/Fm及Fv/F0值显著降低,光合作用受到明显抑制。加硅能提高干旱胁迫条件下水稻植株的生物量、水分利用效率、叶片叶绿素含量、净光合速率和蒸腾速率,而气孔导度和细胞间隙CO2浓度则下降。无论干旱与否,施硅后水稻的叶片硅含量均显著上升。两个水稻品系叶片的无机离子含量在干旱胁迫条件下均呈显著增加的趋势,而硅处理后材料w-14的叶片K+、Na+、Ca2+、Mg2+、Fe3+含量分别降低16.38%,24.50%,19.70%,21.52%,18.58%,w-20则分别降低11.64%,12.11%,16.06%,11.11%和19.15%,并使之回复到与对照更接近的水平。研究结果表明了硅提高水稻植株的抗旱性与光合作用的改善和矿质养分的调节有关。     

Plant growth and nutrient uptake characteristics of Fe-deficiency chlorosis susceptible and resistant subclovers

The objective of this study was to evaluate the growth and nutrient-uptake characteristics of Fe-deficiency resistant and susceptible subclover (Trifolium subterraneum L., T. yanninicum Katzn. and Morley, T. brachcalycinum Katzn. and Morley) cultivars on a calcareous soil. Ten subclover cultivars showing varying susceptibilities to Fe-deficiency chlorosis (Karridale, Nangeela, Geraldton, Mt. Barker, Woogenellup, Larisa, Trikkala, Rosedale, Koala and Clare) were grown on a low-Fe, calcareous soil (Petrocalcic Paleustoll) under moist (18% water content, 85% of water holding capacity) and water-saturated conditions using a Cone-tainer^® culture system. Chlorosis and its correlation with growth traits and mineral nutrition of the 10 cultivars were examined. The Fe-deficiency susceptibilities of the 10 cultivars decreased in the above order under the moist condition, but in slightly different order under the saturated condition. Shoot and root dry weights, total dry weight, and root-to-shoot ratio were each negatively correlated with chlorosis under both soil-moisture conditions, as was total shoot content of P, Ca, Fe, Mn and Zn. Shoot P and Fe concentrations were each positively correlated with chlorosis under the moist soil condition. Iron and Cu utilization efficiencies (biomass per unit weight of nutrient) in the shoot were each negatively correlated with chlorosis under the moist soil condition. These results suggest that there may be several characteristics of Fe-deficiency chlorosis resistance in subclovers, such as a more effective soil-Fe mobilizing mechanism(s), more balanced nutrition, lower required Fe concentration in the shoot, higher shoot-Fe utilization efficiency, and higher root/shoot ratio under Fe-deficiency stress conditions.     

供锌条件下碳酸钙对小麦幼苗生长和锌吸收的影响

通过营养液培养试验,研究了供Zn条件下添加CaCO₃对3种基因型冬小麦（远丰998、中育6号、小偃22）幼苗生长及Zn吸收的影响.结果表明,供Zn和添加CaCO₃对小麦幼苗生长量和根冠比均无显著性影响,3种基因型小麦间亦无显著性差异;添加CaCO₃诱发了小麦叶片失绿黄化.无论供Zn还是不供Zn,添加CaCO₃对3种基因型小麦根、茎、叶各部分的Zn含量及累积量均无显著性影响;与不供Zn处理相比,供Zn会大幅度地提高根、茎、叶的Zn含量和累积量,供Zn使3种基因型小麦植株Zn含量分别增加80.0%、104.8%和139.6%,缺Zn敏感型小麦远丰998植株Zn含量和累积量的增加幅度远小于不敏感型小麦中育6号和小偃22.供Zn和添加CaCO₃对小麦幼苗根、茎、叶中P含量均无显著影响,但远丰998小麦根、茎、叶3部分的P含量均明显低于其它两种非敏感型小麦.供Zn使小麦根、茎、叶3部分的P/Zn大幅度降低,添加CaCO₃也使P/Zn呈现降低的趋势.不供Zn条件下添加CaCO₃能诱发小麦失绿黄化,但Zn吸收量未降低.表明在水培条件下,高含量CaCO₃对小麦Zn吸收并未产生明显的抑制作用.     

Does high bicarbonate supply to roots change availability of iron in the leaf apoplast?

The role of the leaf apoplast in iron (Fe) uptake into the leaf symplast is insufficiently understood, particularly in relation to the supposed inactivation of Fe in leaves caused by elevated bicarbonate in calcareous soils. It has been supposed that high bicarbonate supply to roots increases the pH of the leaf apoplast which decreases the physiological availability of Fe in leaf tissues. The study reported here has been carried out with sunflower plants grown in nutrient solution and with grapevine plants grown on calcareous soil under field conditions. The data obtained clearly show that the pH of the leaf apoplastic fluid was not affected by high bicarbonate supply in the root medium (nutrient solution and field experiments). The concentrations of total, symplastic and apoplastic Fe were decreased in chlorotic leaves of both sunflower (nutrient solution experiment) and grapevine plants in which leaf expansion was slightly inhibited (field experiment). However, in grapevine showing severe inhibition of leaf growth, total Fe concentration in chlorotic leaves was the same or even higher than in green ones, indicative to the so-called `chlorosis paradox'. The findings do not support the hypothesis of Fe inactivation in the leaf apoplast as the cause of Fe deficiency chlorosis since no increase was found in the relative amount of apoplastic Fe (% of total leaf Fe) either in the leaves of sunflower or grapevine plants. It is concluded that high bicarbonate concentration in the soil solution does not decrease Fe availability in the leaf apoplast.     

Influence of Norway spruce seedlings on the nutrient availability in mineral soil and forest floor material

A greenhouse experiment was performed to evaluate the effect of Norway spruce (Picea abies (L.) Karst.) seedlings on net nutrient availability in five different growing media containing F- or H-layer and mineral soil originating from a haplic podzol in northern Sweden. The initial total amounts of eight nutrient elements (N, K, P, Ca, Mg, Mn, Fe, Zn) and exchangeable amounts of the same elements were analyzed in pots with or without spruce seedlings. In the planted pots seedling nutrient uptake was also estimated. After 26 weeks, higher net nutrient availability with seedlings was found in 25 out of the 40 (62%) growing media and nutrient element combinations. A positive seedling effect on net nutrient availability might be explained by rhizodeposition stimulating the soil microorganism activity and accelerating the weathering of minerals or by seedling roots promoting the nutrient providing processes through changes in soil chemical and physical properties. Nitrogen availability was primarily affected by what part of the forest floor the growing medium contained although the positive response to seedling presence was apparent. The positive net availability response of P, Ca, Mg, Mn, Fe and Zn to seedling presence was on the other hand relatively strong. In the case of P, K, and Zn the growing medium composition (if the F- and H-layer was pure or mixed with mineral soil) was also an important factor for the estimated net availability. Pure F-and H-layer provided greater P- and K-availability while the availability of Zn increased when mineral soil was added. The influence of growing plants ought to be considered when soil samples are used for assessing the nutrient availability.     

Effects, distribution and uptake of silicon in banana (Musa spp.) under controlled conditions

Three contrasted genotypes of Musa spp. (M. acuminata cv Grande Naine, M. acuminata spp. Banksii and M. balbisiana spp. Tani) were grown for 6 weeks under optimal conditions in hydroponics and were submitted to a wide range of Si supply (0–1.66 mM Si) to quantify the Si uptake and distribution in banana, as well as the effect of Si on banana growth. The level of Si supply did not affect plant growth, nor the rate of water and nutrient uptake. The rate of Si uptake and the Si concentration in plant tissues increased markedly with the Si supply. At the highest Si concentrations (1.66 mM), silicon absorption was essentially driven by mass flow of water (passive transport). However, at lower Si concentrations (0.02–0.83 mM), it was higher than its uptake by mass flow and caused the depletion of silicon in the nutrient solution, suggesting the existence of active processes in silicon transport. The distribution of silicon among shoot organs (pseudostem < petiole and midrib < young lamina < old leaf) confirmed the major role of transpiration in silicon accumulation and was not dependent on silicon supply. However, other mechanisms of transport might be operating in the roots and in the petiole and midrib of young leaves, whose silicon concentration was unexpectedly high at low Si supply (0.02 mM) compared to higher levels of Si. The three genotypes did not exhibit consistent differences in their responses to silicon supply.     

Analysis of nutrient deficiencies affecting in vitro growth and development of <Emphasis Type="Italic">Eucalyptus dunnii</Emphasis> Maiden

Although basal medium optimization is a key factor in the success of tissue culture, its mineral composition is frequently disregarded when optimizing in vitro propagation protocols. A previous work on Eucalyptus dunnii micropropagation suggests that excessive callus formation and leaf chlorosis are related to specific nutritional conditions of the basal media. Recently, a novel basal medium based on the mineral nutrient analysis of E. dunnii young stump shoots was developed and successfully tested in plant regeneration and micropropagation of E. dunnii, avoiding all these issues. Considering this basal medium as an ideal growth condition, a mild deprivation of each macro and micronutrient and of the total organic fraction was imposed to E. dunnii in vitro cultures for 30 d. As a result, K, Mg, Mn, Cl, Zn, Mo, Ni or Co deprivation quantitatively affected growth and development of axillary shoots. Moreover, leaf chlorosis and the development of organogenic callus under Fe deficiency, and leaf drop along with shoot tip necrosis under N deficiency were observed. These symptoms suggest that nutrient content in E. dunnii tissues needs to be above 420.3 mg kg^?1 for Fe and 27.7 g kg^?1 for N to avoid the symptoms of leaf chlorosis and shoot tip necrosis. Additionally, the main role of Mn in quantitative responses and the antagonism between ions, especially for Mg/K and Mg/Zn, were denoted by the multivariate analysis. Overall, these results make a relevant contribution to the optimization of in vitro propagation of E. dunnii and other hard-to-propagate related species.     

Zinc, Iron, and Chlorophyll Metabolism in Zinc-toxic Corn

Zinc toxicity and Zn-Fe interactions were studied in corn (Zea mays L. var. Barbecue hybrid) grown in hydroponic culture. High Zn greatly reduced the root and shoot fresh weights; increasing Fe largely, but not completely, restored normal growth. Correlation analyses of root and leaf Zn and Fe contents suggested that Zn may interfere with the translocation of Fe; however, Zn toxicity was not associated with a diminished leaf Fe content. Fe did appear to retard both the absorption and the translocation of Zn. The chlorosis of Zn-toxic plants is not attributable to diminshed total leaf Fe; however, this chlorosis is relieved by increasing nutrient Fe. Zn and Fe probably do interact at some site.     

Influence of varied zinc supply on re-translocation of cadmium (109Cd) and rubidium (86Rb) applied on mature leaf of durum wheat seedlings

Effect of varied zinc (Zn) supply (0, 0.1, 1, 5 M) on re-translocation of radio-labeled cadmium (¹⁰⁹Cd) and rubidium (⁸⁶Rb) from mature leaf to root and other parts of shoot was studied in 11-day-old durum wheat (Triticum durum cv. C-1252) plants grown in nutrient solution under controlled environmental conditions. Application of ¹⁰⁹Cd and ⁸⁶Rb was carried out by immersing the tips (3 cm) of mature leaf in radio-labeled solutions for 10 s at three different times over a 42 h period. Differences in Zn supply for 11 days did not affect plant growth nor did it cause visual leaf symptoms, such as necrosis and chlorosis, at either the lowest or the highest Zn supply. Only at the nil Zn supply (0 M), shoot and root dry weights tended to decrease and increase, respectively, causing a lower shoot/root dry weight ratio. Partitioning of more dry matter to roots rather than shoots, a typical phenomena for Zn-deficient plants in nutrient solution experiments, indicated existence of a mild Zn deficiency stress at the nil-Zn treatment. Irrespective of Zn supply, plants could, on average, retranslocate 3.8% and 38% of the total absorbed ¹⁰⁹Cd and ⁸⁶Rb from the treated leaf to roots and other parts of shoots within 42 h, respectively. At nil-Zn treatment, 2.8% of the total absorbed ¹⁰⁹Cd was re-translocated from the treated leaf, particularly into roots. The highest re-translocation of ¹⁰⁹Cd (6.5%) was found in plants supplied with 0.1 M Zn. Increases in Zn supply from 0.1 M reduced ¹⁰⁹Cd re-translocation from 6.5% to 4.3% at 1 M Zn and 1.3% at 5 M Zn. With the exception of the nil-Zn treatment, the proportion of re-translocated ¹⁰⁹Cd was greater in the remainder of the shoot than in the roots. Contrary to the ¹⁰⁹Cd results, re-translocation of ⁸⁶Rb was not (at 0, 0.1 and 1 M Zn), or only slightly (at 5 M), affected by changing Zn supply. The results indicate an inhibitory action of increased concentrations of Zn in shoot tissues on phloem-mediated Cd transport. This effect is discussed in relation to competitive inhibition of Cd loading into phloem sap by Zn.     

三种苦苣苔对石灰土和红壤的适应性分析

为探讨苦苣苔科植物对其岩溶生境的适应性,该研究选取黄花牛耳朵(Primulina lutea)、紫花报春苣苔(Pri.purpurea)和桂林蛛毛苣苔(Paraboea guilinensis)三种苦苣苔科植物,将其栽种在石灰土及红壤两种不同类型的土壤中,观测记录其生长性状并对其叶片元素含量进行测定和比较。植株采集过程中,同时采集自然生境中三种苦苣苔科植物叶片及取样植物基部土壤,并对叶片及土壤元素的含量进行测定,作为今后苗圃试验的参照。结果表明:三种苦苣苔科植物在两种土壤上的生长状况及适应性具有差异,其在石灰土上生长良好,在红壤上生长较差;在两种不同土壤中,除N外,桂林蛛毛苣苔的叶片其他元素(P、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除P外,紫花报春苣苔的叶片其他元素(N、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除N、Cu、Ca外,黄花牛耳朵的叶片元素(P、K、Mn、Mg、Zn)差异极显著(P0.01);三种植物的叶片元素比值,除少数值没有差异外,大部分指标差异都极显著;对叶片元素与栽培土壤元素的相关性分析,发现植物叶片Mn元素与土壤中N、Ca、Mg、Zn、Mn、有机质含量等呈正相关,土壤P元素与叶片中N、P元素呈正相关,而与叶片中Zn元素呈负相关关系。在其他栽培条件一致的条件下,土壤因素及物种差别是造成黄花牛耳朵、紫花报春苣苔和桂林蛛毛苣苔适应性产生差异的主要原因。     

Effect of phosphorus fertilization on water stress in Douglas fir seedlings during soil drying

A growth chamber experiment was conducted to determine if P fertilization to enhance the P nutrition of otherwise N and P deficient Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings reduces water stress in the seedlings during drought periods. Seedlings were grown in pasteurized mineral soil under well-watered conditions and fertilized periodically with a small amount of nutrient solution containing P at either of three levels: 0, 20, or 50 mg P L^-1. By age 6 mo, leaf nutrient analysis indicated that N and P were deficient in control (0 mg P L^-1) seedlings. The highest level of P fertilization, which doubled leaf P concentration, did not affect plant biomass, suggesting that N deficiency was limiting growth. When these seedlings were subjected to drought, there was no effect of P fertilization on leaf water potential or osmotic potential. Furthermore, P fertilized seedlings had lower stomatal conductance and net photosynthesis rate. These results indicate that enhanced P nutrition, in the presence of N deficiency, does not reduce water stress in Douglas fir seedlings during drought periods.     

干热河谷植物化学计量特征与生物量之间的关系

了解植物化学计量学特征对生物量变化的响应机制对预测全球变化下植物生产力以及生态系统功能具有重要意义。为了了解干热河谷地区植物化学计量学塑性变化与植物生物量变化的关系, 该研究以当地的典型燥红土为基质, 观察水分、养分以及二者的交互作用对6种植物的生长的促进作用, 并分析这种作用与植物化学计量学特征变化的关系。研究结果显示: 水分、养分、物种及其二元交互作用对植物生长具有显著的作用。养分添加处理增加了32.55%的生物量, 高频次水分处理增加了31.35%的生物量, 水分与养分复合处理下生物量增加了110.60%。植物化学计量学特征的变化与植物生物量对处理的响应具有显著相关性。其中, 植物总体K:Ca、K:Mg、K:Mn、K:Zn、Mg:Mn的变化与植物生物量的变化呈正相关关系, 表明水分和养分处理对植物生长的促进作用影响了植物养分的平衡, 主要的变化趋势是高含量元素与低含量元素的计量比随着生物量的增加而不断增加。此外, 相对于植物生物量变化, 处理类型和物种因素对多数化学计量学特征变化无显著影响, 表明水分和养分处理对化学计量学的影响具有相同的驱动机制, 即通过生物量变化最终影响化学计量学变化。植物生物量对水分和养分的响应可对植物化学计量学特征以及生态系统功能产生深远的影响。     

Soil-plant element relationships in a tundra ecosystem

The objectives of this study were to (1) provide a baseline estimate of soil and plant element concentrations for an intensive research site at Imnavait Creek in northern Alaska, and (2) examine the relationships between soil and plant elements in an arctic ecosystem. Soil and plant element concentrations were highly variable along biotic, spatial, and temporal axes. Deciduous shrubs had higher leaf concentration of N, P. K and Mg, whereas an evergreen shrub had higher leaf concentrations of Ca, Mn, Al and Si. Based on high required solution phase turnover rates, the most likely elemental deficiencies are N > P > K > Ca = Mg. Based on low required solution phase turnover rates and high soil concentrations. Fe, Mn, Zn and Cu deficiencies are unlikely. Manganese could be present in toxic concentrations. The nutrient bottleneck in tundra ecosystems appears to be the rate of nutrient movement to the solution phase.     

Relationships between plant stoichiometry and biomass in an arid-hot valley,Southwest China

Aims The micro-elemental stoichiometry as well as nitrogen (N) and phosphorus (P) plays an important role in ecosystem process. However, the drivers of the variations in these stoichiometric ratios in plants are less explored in compared with N and P. Plant productivity and plant stoichiometry can response simultaneously to environmental changes, such as water and nutrient supply levels. However, the relationships between the changes in plant stoichiometry and biomass were unclear yet although both of them play important roles in ecosystem functioning. Our object was to investigate the changes in plant stoichiometry (including multiple macro- and micro-elements) and in biomass under different nutrient and water supply. Methods We collected seeds from six grass species in an arid-hot valley and performed a nutrient-water addition experiment in 2012 with a complete factorial design (nutrient × water). The concentrations of N, P, K, Ca, Mg, Zn and Mn in different organs and plant biomass were measured. The effects of species, water and nutrient on element concentration and plant biomass were analyzed by three-way ANOVA. Linear regressions were used to test the relationships between changes in plant stoichiometry and changes in biomass after nutrient and water addition. Important findings Nutrient addition increased plant biomass by 32.55% compared with control. High-level water supply increased plant biomass by 31.35% and the combination of nutrient and high-level water addition increased plant biomass by 110.60%. Nutrient, water, species identity and their two-way interactions significantly affected plant biomass. Changes in total plant K:Ca, K:Mg, K:Mn, K:Zn and Mg:Mn were significantly and positively related to changes in plant biomass. The ratio between the concentrations of macro-elements and micro-elements tended to increase with biomass. Species identity and treatment had no effects in most of these relationships, suggesting that the changes in stoichiometry were mostly driven by the variations in biomass. The relationships between changes in stoichiometry and in biomass also occurred in leaves, stems and roots. The covariation between plant stoichiometry and biomass can have profound effects on ecosystem functioning under the global environmental changes.     

Mechanism of phosphorus-induced zinc deficiency in cotton. I. Zinc deficiency-enhanced uptake rate of phosphorus

The effect of withholding Zn on the uptake, translocation and accumulation of P was studied in cotton plants ( Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solutions under controlled environmental conditions. The influence of P on the uptake rate, translocation and distribution of ⁶⁵Zn in the plants was also examined. Increasing the P supply resulted in severe Zn deficiency symptoms (interveinal chlorosis) as well as P toxicity symptoms, which were characterized by leaf puckering and grayish-brown marginal necrosis. Zinc deficiency markedly increased the uptake and translocation rates of P over the whole concentration range tested (5x10^-5 to 1.25x10^-3 M ). Uptake and translocation rates of P increased with both level of P and severity of Zn deficiency. This often caused P toxicity symptoms on Zn-deficient leaves. In contrast to P, the concentrations of K and Mg in the leaves were not affected by Zn deficiency. Similar results were obtained for sunflower ( Helianthus annuus L.) and buckwheat ( Fagopyrum esculentum Moench) plants. Higher P concentrations in Zn-deficient leaves or shoots could not be attributed wholly to reduced shoot growth. This was also evident when Zn deficiency was compared with other micronutrient (Fe, Mn, and Cu) deficiencies. Only Zn-deficient plants showed enhanced uptake and translocation of P. In experiments with ⁶⁵Zn, a high P supply did not depress uptake and translocation of Zn. From the results obtained it is concluded that the P-induced Zn deficiency in cotton, as well as in other species, is primarily caused by enhanced P uptake and translocation and not by inhibition of Zn uptake.     

Centelloside accumulation in leaves of Centella asiatica is determined by resource partitioning between primary and secondary metabolism while influenced by supply levels of either nitrogen,phosphorus or potassium

In the present study we aimed to investigate the relevance of either N, P or K supply for herb and leaf yield and for centelloside concentrations in Centella asiatica L. Urban leaves. In this regard, we elucidated the causal relationship between assimilation rate, leaf N, P and K concentrations, herb and leaf production, and centelloside accumulation. The experiments were conducted consecutively in a greenhouse where C. asiatica was grown in hydroponic culture and fertigated with nutrient solutions at either 0, 30, 60, 100 or 150% of the N, P or K amount in a standard Hoagland solution. In general, the increase in N, P or K supply enhanced assimilation rate and herb and leaf yield. However, exceeding specific thresholds, the high availability of one single nutrient caused lower leaf N concentrations and a decline in assimilation rate and plant growth. Irrespective of N, P and K supply, the leaf centelloside concentrations were negatively associated with herb and leaf yield, which is in accordance with the assumptions of the carbon/nutrient balance and the growth differentiation balance hypotheses. Moreover, we found strong negative correlations between saponins and leaf N concentrations, while the respective sapogenins were negatively correlated with K concentrations. Using C. asiatica as model system, our experiments reveal for the first time that the accumulation of saponins and sapogenins is affected by resource allocation between primary and secondary metabolism and that besides carbon, also nutrient availability is relevant for the regulation of the centelloside synthesis. Finally, our results highlight the huge potential of optimized and carefully controlled mineral nutrition of medicinal plants for steering the bio-production of high-quality natural products.     

Limestone gravel as growth medium in hydroponics

Summary Plants were grown in gravel beds of basalt or limestone. With the standard nutrient solution yields for the plants grown in the limestone gravel were very much reduced and the plants were chlorotic. This chlorosis and reduced yields remained even if the gravel was acid or water washed beforehand, or if it was pretreated in high phosphate concentrations.High yields, comparable to those obtained in basalt beds were obtained if phosphate and iron were added in small amounts (0.1mM P, 1 mg/1 Fe) at each irrigation. This technique to avoid lime induced chlorosis can be easily and economically accomplished in hydroponics. It proved successful here with lettuce, cucumber, tomato and eggplants.     

Resource requirements of four freshwater diatom taxa determined by in situ growth bioassays using natural populations from alpine lakes

We performed a series of in situ batch culture experiments to assess the resource requirements of common diatom taxa in alpine lakes of the central Rocky Mountains of North America. While physiological data are available on the resource requirements of some of these taxa, it is unclear whether intraspecific generalizations can be made across aquatic systems due to the potential development of ecotypes. In these experiments, we used amended lake water for a culture medium and natural diatom populations. Growth kinetics were determined for Asterionella formosa Hassall, Fragilaria crotonensis Kitton, Staurosirella pinnata (Ehr.) Williams and Round and Tetracyclus glans (Ehr.) Mills. Staurosirella pinnata, a historically abundant alpine diatom, had very low N and P requirements. Asterionella formosa and F. crotonensis, generally considered meso- or eutrophic species, exhibited low P requirements if N and Si were in moderate supply. Tetracyclus glans had the highest Si requirement. These experiments reveal that the recent changes in diatom community structure in these alpine lakes may be driven by changes in nutrient supply. We suggest that local diatom taxa and a natural culturing medium should be used to obtain more representative algal physiological data from a particular area.     

Phosphorus–zinc interactions in cotton: consequences for biomass production and nutrient‐use efficiency in photosynthesis

The fragmentary information on phosphorus (P) × zinc (Zn) interactions in plants warrants further study, particularly in plants known for their high P and Zn requirements, such as cotton (Gossypium hirsutum L.). The objective of this study was to investigate the effect of P × Zn interactions in a modern cultivar of cotton grown hydroponically. Biomass, mineral nutrition and photosynthetic parameters were monitored in plants receiving contrasting combinations of P and Zn supply. Root biomass, length and surface area were similar in plants with low P and/or low Zn supply to those in plants grown with high P and high Zn supply, reflecting an increased root/shoot biomass quotient when plants lack sufficient P or Zn for growth. Increasing P supply and reducing Zn supply increased shoot P concentrations, whilst shoot Zn concentrations were influenced largely by Zn supply. A balanced P × Zn supply (4 mM P × 4 μM Zn) enabled greatest biomass accumulation, while an imbalanced supply of these nutrients led to Zn deficiency, P toxicity or Zn toxicity. Net photosynthetic rate, stomatal conductance, transpiration rate and instantaneous carboxylation efficiency increased as P or Zn supply increased. Although increasing P supply reduced the P‐use efficiency in photosynthesis (PUEP) and increasing Zn supply reduced the Zn‐use efficiency in photosynthesis (ZnUEP), increasing Zn supply at a given P supply increased PUEP and increasing P supply at a given Zn supply increased ZnUEP. These results suggest that agricultural management strategies should seek for balanced mineral nutrition to optimize yields and resource‐use efficiencies.     

Performance of Sparganium emersum Rehm. shoots in response to sediment quality

Biomass, dry matter production, nutrient (N, P, K, Ca, Mg) contents and accumulation were studied in Sparganium emersum Rehm. in Southern Bohemia, Czech Republic. The aim was to determine the species' relationship to sediment quality and water flow and to estimate its nutrient uptake from sediments. The plants were sampled from six field sites, and one cultivation experiment was carried out. In the field, dry weight, shoot length and leaf number related to one another, while probably responding to nutrient supply both from water and sediment, while leaf width seemed to be correlated with other environmental factors. In the experiment, all measured growth parameters, except for the number of leaves, reflected sediment quality. The standing stocks of N, P and K reflected best the sediment nutrient contents in the field, both in running and standing water, but the stocks were generally higher in running water. In the experiment, all the measured growth parameters were correlated with sediment nutrient contents, and for N and P they were also with these nutrient contents in the plants. Nutrient removal from the rooting media was substantial for nitrogen. S. emersum was found to grow well in sediments rich both in mineral nutrients and organic matter.