The influence of the frequency of periodic disturbances on the maintenance of phytoplankton diversity

The influence of periodic disturbances of various frequency on the maintenance of the phytoplankton diversity was studied by semicontinuous competition experiments. Disturbances consisted of dilution events, which meant both addition of fresh nutrients and elimination of organisms. The intervals between dilution events varied from 1 to 14 days. Diversity was found to increase with increasing intervals between disturbances. coexisting species belonged to different strategy types: (a) species with rapid growth under enriched conditions, (b) species with good competitive abilities under impoverished conditions, (c) species with the ability to build up storage pools of the limiting nutrient. An increase of the number of coexisting species over the number that would have coexisted in steady state was only found when the interval exceeded one generation time.     

Phosphorus deficiency induced by nitrogen input in Douglas fir in the Netherlands

Summary A re-examination of earlier NPK fertilization experiments in Douglas fir stands on sandy soils shows the effects of high nitrogen input by air pollution during the last 10–15 years on plant nutrition at these sites. In 1960, experimental plots showed a positive growth reaction to nitrogen, phosphorus, and potassium fertilization. All suffered from severe phosphorus deficiency in 1984, low phosphorus in the needles was invariably accompanied by a high nitrogen content, with all N/P ratios between 20 and 30. The same conclusion emerges from an independent investigation of nutrient status of a selection of Douglas fir stands. Hence, if stand productivity and a balanced nutrient status of the trees is to be maintained, the increase in atmospheric input of nitrogen calls for supplementary fertilization. Given the current N/P ratios in the needles, a positive growth response to phosphorus fertilization is to be expected.     

营养膜无土栽培技术

前言营养膜技术(Nutrient Film Technique简称NFT)是国外广泛采用的一种特殊的无土栽培方法。它是将植物栽植在一个狭长的不透水的营养槽中,槽中有缓慢流动的营养液。植物根系的一部分浸没在营养液中,一部分露在空气中,植物从这种小环境中吸收水、营养物和氧气。由于这种方法采用很薄一层营养液在根际周围流动,裸露的根     

The effect of air-borne ammonium sulphate onPinus nigra var.maritima in the Netherlands

Summary As a result of air pollution, considerable deposition of ammonium sulphate occurs on vegetation and soil in the vicinity of chicken farms and fields dressed with animal slurry. A clear relation exists between this ammonium sulphate deposition and the distance to certain agricultural activities. Field investigations and ecophysiological experiments both show that the needles ofPinus nigra var.maritima (Ait.) Melville take up ammonium and excrete potassium, magnesium and calcium. This often results in potassium and/or magnesium deficiencies and may lead to premature shedding of needles. The high levels of nitrogen in the needles are strongly correlated to fungal diseases.Whether the observed cation leaching will result in disturbed nutrient budgets depends mainly on soil conditions. Leaching of K, Mg and Ca from the soil, caused by ammonium sulphate, may further inhibit nutrient uptake.Field investigations show a clear correlation between increased ratios of NH₄ to K, Mg and Ca in the soil solution and the damage to pine forests.     

Leaf phosphorus fractionation and growth responses to phosphorus of the forage legumes Trifolium repens, T. dubium and Lotus pedunculatus

'Grasslands Huia' white clover ( Trifolium repens L.), 'Grasslands Maku' lotus ( Lotus pedunculatus Cav.) and suckling clover ( T. dubium Sibth) were grown in a controlled environment at various levels of P supply. Dry weights and the concentration of inorganic-, lipid-, ester- and residual-P in trifoliate leaves were measured. Lotus grew better than white or suckling clover at low P. White clover and lotus responded steeply to increased P and had similar shoot dry weights at high P. Suckling clover had lower shoot weights than the other species at all P levels. The superior growth of lotus at low levels of p was probably due to better root growth and P uptake. Lotus had higher shoot P concentrations at low levels of P but lower concentrations than the others at high levels. White clover and suckling clover had similar shoot P concentrations at all levels of supply. In white and suckling clover total leaf P concentration rose with P supply. Of the P fractions, inorganic-and residual-P showed the largest rises in concentration. The increases in lipid- and ester-P were smaller. Increases in lotus leaf P were small, primarily because of the relatively small rises in inorganic- and residual-P. White clover is a vigorous species but requires high levels of P for best growth. Suckling clover has a relatively small response to improvements in P availability. The behaviour of the various P fractions is similar to that in white clover. Lotus grows well at low P but also shows rapid growth at high P supply. Whether efficiency is defined as the ability to extract P from the environment or to maintain low internal P concentration, lotus makes efficient use of P over the whole range of P supply.     

Root development and configuration in intensively managed radiata pine plantations

Summary In south-east Australia, where radiata pine (Pinus radiata D. Don) is grown on sandy soils low in nutrients and short of water, early establishment, and rapid growth to canopy closure lead to increased productivity. At this stage demands for nutrients and water are high, and trees respond vigorously to silvicultural inputs.For several months after transplanting in winter roots are confined within a narrow planting wedge, low temperature restricts new root growth and slows recovery from water stress in plants. From spring, depending upon the configuration and vigour of the roots transplanted, lateral roots extend radially throughout the soil.Although there were small decreases in concentration of roots radially from the stems of very young trees, such spatial differences disappeared between ages 2 and 3, so that rooting density was independent of distance from the stem. The pattern of vertical distribution of lateral roots was not influenced by age and 80–90% of the lateral roots were within the top 30 cm soil. Roots developed rapidly as the trees grew towards canopy closure, but in general the rooting densities of these pines are among the lowest reported for plants. In rapidly growing trees approaching canopy closure, the secondary thickening of the lateral roots was sufficient to double the weight of roots without altering root length.Knowledge about root growth and root configuration during the early phase of plantation development will assist management decisions where intensive silviculture is practiced, and hence ensure the most efficient use of nutrients and water.     

Root growth and litter decomposition in a coffee plantation under shade trees

In a non-fertilized coffee plantation under shade trees the root biomass was excavated to estimate its distribution in the soil profile. One third of total fine (less than 1 mm) roots was found in the first 10 cm of soil; the cumulative total to 30 cm reached 73%. A highly variable and transient amount of fine roots colonized the litter layer. Root production both in the litter and in the first 7.5 cm of mineral soil was estimated from sequential samplings and was 10 g m^–2 yr^–1 and 660 g m^–2 yr^–1 respectively. The decomposition rate of weighed averages of litter fractions in the coffee plantation, calculated as the ratio of litter fall rate to the amount found in the soil was k=4.8. Shade tree leaves, the major component of litter descomposed slower than coffee leaves and these slower than flowers and fruits. Litter bag experiments showed considerable slower rates when mesh was 0.03 mm than 0.5 mm. Nitrogen and phosphorous showed increases in concentrations as decomposition progressed while potassium, calcium and magnesium followed a decrease in concentration that paralleled that of dry weight loss. In comparing the decomposition rate for litter with or without coffee roots growing in the bags, a tendency to show faster decomposition rates was found for the treatment with roots. These differences were however, only significant for one month for shade tree leaves litter. Nitrogen amounts remaining in shade tree leaves litter was lower in the treatment with roots that without roots. Potassium concentration in roots was positively correlated with potassium concentration in decomposing leaf litter where roots were growing. These results suggest that while roots growing attached to decomposing litter had little or no effect in speeding the decomposition process, the superficial roots seem to play an important role in absorbing very efficiently the mineralized nutrients from litter. The anatomical study of roots showed that the plantation is intensely infected with V-A mycorrhiza. External mycorrhizal hyphae did not to play a role in attachment of roots to decomposing litter while root hairs were found to grow in profusion on root surfaces oriented toward litter.     

Plant-soil interactions in primary succession at Hawaii Volcanoes National Park

Summary Plant nutrient status and physiological processes were examined in relation to soil nutrient characteristics under individuals of five species colonizing a young cinder deposit in Hawaii Volcanoes National Park. Two exotic species, Buddeleja asiatica and Myrica faya, had high photosynthetic rates and high nitrogen concentrations and relatively easily decomposed leaves; soils under them had high concentrations of nitrogen, cations, and organic matter and high rates of net nitrogen mineralization. At the other extreme, the natives Metrosideros polymorpha and Vaccinium reticulatum had low plant concentrations and photosynthetic rates, and low concentrations and turnover rates of N in the soil. Thus, a strong correlation exists between soil processes and plant processes, suggesting a positive feedback cycle.     

Rapid loss of phosphorus from dying ryegrass roots: the chemical components involved

Summary Lolium perenne was grown in solution culture with either ample or deficient phosphate supply (high-P and low-P plants). The concentration in the roots of phosphorus as water-soluble compounds, phospholipid and insoluble residue was measured. A supplementary experiment showed that the concentration of each component in the roots of low-P plants was similar to that in plants grown in P-deficient soil. The time-course of the decline of each P component was determined in roots detached from the shoot and left hanging in solution. During the three weeks residue P concentration in the roots declined little. In contrast, both types of root lost about three-quarters of their lipid P in the first week. Low-P roots lost little of their water-soluble P. High-P roots contained much more water-soluble P and lost much of it during the first two weeks. By the end of three weeks their water-soluble P content was levelling out at a value similar to that in low-P roots, suggesting a non-labile pool. The rapid loss of lipid P from low-P roots comprised more than half of their total loss, and the possible ecological significance of this is discussed.     

天祝高寒珠芽蓼草甸群落的热值和营养成分的初步研究

 本文报告了甘肃天祝高寒珠芽蓼(Polygonum viviparum)草甸群落地上及地下四部分生物量的热值和营养成分动态,并对其放牧利用的价值进行了总的评价。 6—9月现存量的热值平均为18330焦／克干物质,或20279焦／克去灰分物质,较立枯物+凋落物、活根、死根的平均值为大;死根略大于活根。在珠芽蓼及其他大多数植物种子成熟期的8月下旬,现存量的热值最大,其他三部分的热值变化也有其各自的特点。现存量6—9月的平均营养成分以绝对干重计为：粗蛋白13.52%,粗脂肪2.25,粗纤维22.99,无氮浸出物51.88,粗灰分9.61(其中钙1.627,磷0.164);在时间变化上四部分各有其特点。根据地形、植物组成、产量、易食性、适口性、热值和营养成分等综合条件,认为珠芽蓼草甸是良好的放牧地。