Growth and biomass turnover ofHydrocharis dubia L. cultured under different nutrient conditions

Growth of a floating-leaved plant,Hydrocharis dubia L., was examined under varying nutrient conditions between 0.3 and 30 mgN l⁻¹ total inorganic nitrogen.H. dubia plants cultured under the most nutrient-rich condition showed the highest maximum ramet density (736 m⁻²), the highest maximum biomass (80.4 g dry weight m⁻²), and the highest total net production (185 g dry weight m⁻² in 82 days). Plants under nutrient-poor conditions had a relatively large proportion of root biomass and a small proportion of leaves with a long life span. Compared with other floating-leaved and terrestrial plants, the maximum biomass ofH. dubia was relatively small. This, and the rapid biomass turnover, was related to the short life span of leaves (13.2–18.7 days) and large biomass distribution to leaves.     

Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R _Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P _N on a leaf area basis (mean of 9.1–10.1 μmol CO₂ m⁻² s⁻¹) and Chl basis, which correlated well with the higher values of stomatal conductance G _s (range 105–180 mmol m⁻² s⁻¹), as compared to shade leaves (G _s range 25–77 mmol m⁻² s⁻¹; P _N: 3.2–3.7 μmol CO₂ m⁻² s⁻¹). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R _Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R _Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.     

Galerucella nymphaeae (Col., Chrysomelidae) grazing increases Nuphar leaf production and affects carbon and nitrogen dynamics in ponds

Summary The grazing effects of the waterlily beetle Galerucella nymphaeae on Nuphar lutea stands were studied in three ponds in Central Finland. Production of floating leaves of N. lutea and growth in the G. nymphaeae population were investigated in the ponds and bioenergetics of the beetle larvae in the laboratory. Combination of field and laboratory data enabled estimation of the effect of the beetle on the production of floating leaves of N. lutea and the consequences of grazing for the input of detritus from Nuphar into the ponds. Adults and larvae of G. nymphaeae consumed 3.0–6.1% of the net annual floating leaf production during the growing period. In addition to consumption losses, feeding accelerated the degradation rate of the leaves. This was associated with an increased flow of detrital material of Nuphar origin, and also with increased production of floating leaves in the ponds. These increments were estimated to be up to 3 times greater in the presence of grazing than without it. Grazing by G. nymphaeae releases substantial amounts of carbon and nitrogen bound in Nuphar, particularly in ponds with a dense Nuphar vegetation. It is hypothesized that feeding by this beetle may markedly affect the structure and functioning of such small aquatic systems.     

Nitrogen and phosphorus economy of the riparian shrub <Emphasis Type="Italic">Salix gracilistyla</Emphasis> in western Japan

Salix gracilistyla is one of the dominant plants in the riparian vegetation of the upper-middle reaches of rivers in western Japan. This species colonizes mainly sandy habitats, where soil nutrient levels are low, but shows high potential for production. We hypothesized that S.␣gracilistyla uses nutrients conservatively within stands, showing a high resorption efficiency during leaf senescence. To test this hypothesis, we examined seasonal changes in nitrogen (N) and phosphorus (P) concentrations in aboveground organs of S. gracilistyla stands on a fluvial bar in the Ohtagawa River, western Japan. The concentrations in leaves decreased from April to May as leaves expanded. Thereafter, the concentrations showed little fluctuation until September. They declined considerably in autumn, possibly owing to nutrient resorption. We converted the nutrient concentrations in each organ to nutrient amounts per stand area on the basis of the biomass of each organ. The resorption efficiency of N and P in leaves during senescence were estimated to be 44 and 46%, respectively. Annual net increments of N and P in aboveground organs, calculated by adding the amounts in inflorescences and leaf litter to the annual increments in perennial organs, were estimated to be 9.9 g and 0.83 g m⁻² year⁻¹, respectively. The amounts released in leaf litter were 6.7 g N and 0.44 g P m⁻². These values are comparable to or larger than those of other deciduous trees. We conclude that S. gracilistyla stands acquire large amounts of nutrients and release a large proportion in leaf litter.     

Carbon, nitrogen and phosphorus in volcanic soils following afforestation with native birch (Betula pubescens) and introduced larch (Larix sibirica) in Iceland

Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth) and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed to a slow accumulation of organic matter. Soil N concentrations and soil P_tot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material (400 Mg soil ha⁻¹ in 0–10 cm depth and 600 Mg soil ha⁻¹ in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average 23.6 Mg ha⁻¹ in the upper soil layer and 16.9 Mg ha⁻¹ in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha⁻¹ year⁻¹ in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha⁻¹ in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass of the growing trees. Soil P_tot pools were in average 220 and 320 kg P ha⁻¹ in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence on the availability of N and P to the trees. Responsible Editor: Hans Lambers.     

Biomass Enhancement in Maize and Soybean in Response to Glutamate Dehydrogenase Isomerization

The relationship between nutrient composition, crop biomass, and glutamate dehydrogenase (GDH) isoenzyme pattern was investigated in soybean (Glycine max) and maize (Zea mays) by monitoring the nutrient induced isomerization of the enzyme from the seedling stage to the mature crop. GDH was extracted from the leaves of the plants, and the isoenzymes were fractionated by isoelectric focusing followed by native polyacrylamide gel electrophoresis. The isomerization V_max values for soybean GDH, similar to maize GDH increased curvilinearly from 200 – 400 μmol mg⁻¹ min⁻¹ as the inorganic phosphate nutrient applied to the soil decreased from 50 − 0 mM. In soybean, combinations of N and K, P, or S nutrients induced the acidic and neutral isoenzymes, and gave biomass increases 25 – 50 % higher than the control plant. GDH isoenzymes were suppressed in soybean that received nutrients without N, K, or P and accordingly the biomass was about 30 % lower than the control. Treatment of maize with NPK nutrients increased the GDH V_max values from 138.9 at the vegetative to 256.4 μmol mg⁻¹ min⁻¹ at the reproductive phase, and suppressed the basic isoenzymes, but induced both the acidic and neutral isoenzymes thereby inducing seed production (27.0 ± 1.4 g per plant); whereas both the acidic and basic isoenzymes were suppressed in the control maize, and seeds did not develop. Simultaneous induction of the acidic, neutral, and basic isoenzymes of GDH indicated the occurrence of senescence. Therefore in maize and soybean, the induction of the acidic and basic isoenzymes of GDH led to the enhancement of biomass. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrate reductase activity of two leafy vegetables as affected by nickel and different nitrogen forms

The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO₃ ⁻–N, NH₄ ⁺–N, NH₄NO₃). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in lettuce plants supplied with nitrate nitrogen (NO₃ ⁻–N) or mixed (NH₄NO₃) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants. At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with NO₃ ⁻–N or NH₄NO₃. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the enzyme activity in the roots of NO₃ ⁻-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution contained ammonium nitrogen (NH₄ ⁺–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs, especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated with NH₄ ⁺–N the enzyme activity in roots was even higher than in those supplied with NO₃ ⁻–N.     

Changes in biomass and nutrient content of <Emphasis Type="Italic">Nymphoides hydrophylla</Emphasis> (Lour.) O. Kuntz. in a tropical pond: a comparison with other tropical and temperate species

A study was conducted to ascertain monthly changes in biomass of the plant and nutrient content in various organs of Nymphoides hydrophylla grown in a tropical pond during September 1999–August 2000 in relation to environmental factors. Biomass of N. hydrophylla ranged from 25 to 247 g dry weight m⁻². Among the various organs, leaf blade showed highest nitrogen (3.0–4.6%) and phosphorus content (0.9–2.4%). Comparative data of three Nymphoides species showed that N. peltata, the temperate species, had maximum potential of biomass production while long flowering period, year around growth, higher nitrogen content in various organs and presence of other associated flora were unique features of tropical species (N. hydrophylla and N. indica). Both water temperature and water level together appeared to be the best environmental variables that significantly explained the variability in biomass of N. hydrophylla.     

Stem tissue phosphorus as an index of the phosphorus status of Banksia ericifolia L. f.

The effects of P fertilizer rate on shoot growth and the total P concentration of the whole shoot, new and mature leaves, symptom leaves and stems of Banksia ericifolia L. f., a P-sensitive species, were investigated in a six month greenhouse pot experiment. Shoot dry weight of plants growing in an Australian sedge peat, coarse sand and perlite potting mix (1:1:1) increased with up to 100 mg P L⁻¹ supplied as a six month controlled release P (0:18:0) fertilizer, but was reduced by toxicity at the highest application rate (200 mg P L⁻¹). Plants receiving this treatment developed chlorotic new and mature leaves. Leaf symptoms observed at rates of 60–100 mg P L⁻¹ were confined to old leaves and were related to the P concentration of the shoot. Growth was not affected at these rates. The P concentration of stems was strongly influenced by P supply. This tissue acted as a sink for excess P, helping to regulate the P concentration of leaves. The approximate range of P concentrations in stem tissue, associated with greater than 90% of maximum shoot dry weight, was 0.5–1.5 g P kg⁻¹ tissue dry weight. This was greater than that calculated for mature leaves (0.5–0.8 g kg⁻¹) or for whole shoots (0.5–1.2 g kg⁻¹). This wider range, and the capacity to store P in excess to requirement, makes the stem a better index tissue for plant P status than either leaves or whole shoots. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chemical and physical-chemical characteristics of dietary fibres from Ulva lactuca (L.) Thuret and Enteromorpha compressa (L.) Grev.

Dietary fibres from Ulva lactuca (L.) Thuret (sea lettuce) and Enteromorpha compressa (L.) Grev. (A.O. nori) were measured according to a ‘standard’ method and a ‘physiological’ protocol simulating the gastric and intestinal environments. U. lactuca contained 15.8–8.0% soluble and 24.2–32.6% insoluble fibres according to the ‘standard’ and ‘physiological’ methods, respectively. For E. compressa, these values were 14.9–15.9 and 21.6–28.7%, respectively. For both algae, the composition suggests that the soluble fibres were xylorhamnoglycuronans sulphates and insoluble fibres were essentially composed of glucans. No marked chemical compositional variation was observed between soluble fractions extracted under the simulated gastric and intestinal conditions. Fibres in both algae are hydrophilic but the water holding capacities were higher after extraction of soluble fibres (5.5–9.5 g g⁻¹ for the dry algae; 14.0–16.0 g g⁻¹ for the standard insoluble fibres). Water soluble fibres demonstrated low intrinsic viscosities at 37 °C in buffers, particularly those from E. compressa (36.0–36.5 ml g⁻¹), and was affected by pH for those of U. lactuca (147.5 ml g⁻¹ at pH 3.0 and 175.0 ml g⁻¹ at pH 7.3).     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg⁻¹ h⁻¹) than standard 5 mg L. obtusata (257 ng N mg⁻¹ h⁻¹) for snails acclimated to 21°C. Comparisons of Q₁₀ values of total weight specific N excretion to Q₁₀ values for weight specific oxygen consumption ({xxV}O₂) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O₂) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O₂ in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Cadmium accumulation in relation to organic acids in leaves of Solanum nigrum L. as a newly found cadmium hyperaccumulator

The influence of various cadmium concentrations on organic acid levels in leaves of the Cd hyperaccumulator, Solanum nigrum L. and a closely related species, Solanum melongena L., were investigated. In particular, the relationship of organic acids with Cd accumulation in the two plants was investigated. The results showed that Cd accumulation in the shoots of S. nigrum was significantly higher than that of S. melongena. The accumulation of Cd in the leaves of S. nigrum ranged from 2.0 to 167.8 μg g⁻¹ dry weight (DW), but only from 1.2 to 64.0 μg g⁻¹ DW in S. melongena. Solanum melongena was considerably less tolerant to Cd than S. nigrum. Approximately 20% of the total Cd in S. nigrum leaves was water-soluble, suggesting that some accumulated Cd was associated with water-soluble compounds such as organic acids. Malic acid in the leaves of S. nigrum was the most abundant organic acid [up to 115.6–145.7 μmol g⁻¹ fresh weight (FW)], but this acid was not significantly affected by the Cd concentration in soil. However, the level of malic acid in S. melongena plants was much lower, only 16.3–75.4 μmol g⁻¹ FW. The significant positive correlations between total Cd and water-soluble Cd concentrations and both acetic and citric acid concentrations in the leaves of S. nigrum were observed. In contrast, there was no correlation between concentrations of the two acids and Cd concentrations in the leaves of S. melongena. These results indicated that acetic and citric acids in the leaves of S. nigrum might be related to its Cd hyperaccumulation.     

Nutrient leaching in dry heathland ecosystems: effects of atmospheric deposition and management

Atmospheric nutrient deposition has contributed to widespread changes in sensitive seminatural ecosystems throughout Europe. For an understanding of underlying processes it is important to quantify input–output flows in relation to ongoing atmospheric inputs and current management strategies. In this study we quantified losses of N, P, Ca, Mg, and K via leaching in heathland ecosystems (Lüneburger Heide, NW Germany) as a function of current deposition rates and different management measures (mowing, prescribed burning, choppering, sod-cutting) which aim to prevent shrub and tree encroachment. Leaching was only moderately related to atmospheric input rates, indicating that leaching was mostly affected by internal turnover processes. Leaching significantly increased for most of the nutrients after the application of management measures, particularly in the choppered and sod-cut plots. However, atmospheric nutrient inputs exceeded leaching outputs for most of the nutrients, even in the plots subjected to management. Despite high deposition rates (20–25 kg N ha⁻¹ year⁻¹), retention of atmospheric N input ranged between 74% and 92% in the control plots. In the treated plots, N retention decreased to 59–80%. However, in the study area mean N leaching in the controls has almost doubled since 1980 and currently amounts to 3.7 kg ha⁻¹ year⁻¹, indicating an early stage of N saturation. Our study provides evidence that leaching did not compensate for atmospheric nutrient deposition, particularly as regards N. Management, thus, will be an indispensable tool for the maintenance of the low-nutrient status as a prerequisite for the long-term preservation of heathland ecosystems.     

Excess irradiance causes early symptoms of senescence during leaf expansion in photoautotrophically <Emphasis Type="Italic">in vitro</Emphasis> grown tobacco plants

Photosynthetic parameters, growth, and pigment contents were determined during expansion of the fourth leaf of in vitro photoautotrophically cultured Nicotiana tabacum L. plants at three irradiances [photosynthetically active radiation (400–700 nm): low, LI 60 μmol m⁻² s⁻¹; middle, MI 180 μmol m⁻² s⁻¹; and high, HI 270 μmol m⁻² s⁻¹]. During leaf expansion, several symptoms usually accompanying leaf senescence appeared very early in HI and then in MI plants. Symptoms of senescence in developing leaves were: decreasing chlorophyll (Chl) a+b content and Chl a/b ratio, decreasing both maximum (F_V/F_M) and actual (Φ_PS2) photochemical efficiency of photosystem 2, and increasing non-photochemical quenching. Nevertheless, net photosynthetic oxygen evolution rate (P _N) did not decrease consistently with decrease in Chl content, but exhibited a typical ontogenetic course with gradual increase. P _N reached its maximum before full leaf expansion and then tended to decline. Thus excess irradiance during in vitro cultivation did not cause early start of leaf senescence, but impaired photosynthetic performance and Chl content in leaves and changed their typical ontogenetic course.     

Dinitrogen-fixation by three neotropical agroforestry tree species under semi-controlled field conditions

Cultivating dinitrogen-fixing legume trees with crops in agroforestry is a relatively common N management practice in the Neotropics. The objective of this study was to assess the N₂ fixation potential of three important Neotropical agroforestry tree species, Erythrina poeppigiana, Erythrina fusca, and Inga edulis, under semi-controlled field conditions. The study was conducted in the humid tropical climate of the Caribbean coastal plain of Costa Rica. In 2002, seedlings of I. edulis and Vochysia guatemalensis were planted in one-meter-deep open-ended plastic cylinders buried in soil within hedgerows of the same species. Overall tree spacing was 1 × 4 m to simulate a typical alley-cropping design. The ¹⁵N was applied as (NH₄)₂SO₄ at 10% ¹⁵N atom excess 15 days after planting at the rate of 20 kg [N] ha⁻¹. In 2003, seedlings of E. poeppigiana, E. fusca, and V. guatemalensis were planted in the same field using the existing cylinders. The ¹⁵N application was repeated at the rate of 20 kg [N] ha⁻¹ 15 days after planting and 10 kg [N] ha⁻¹ was added three months after planting. Trees were harvested 9 months after planting in both years. The ¹⁵N content of leaves, branches, stems, and roots was determined by mass spectrometry. The percentage of atmospheric N fixed out of total N (%N_f) was calculated based on ¹⁵N atom excess in leaves or total biomass. The difference between the two calculation methods was insignificant for all species. Sixty percent of I. edulis trees fixed N₂; %N_f was 57% for the N₂-fixing trees. Biomass production and N yield were similar in N₂-fixing and non-N₂-fixing I. edulis. No obvious cause was found for why not all I. edulis trees fixed N₂. All E. poeppigiana and E. fusca trees fixed N₂; %N_f was ca. 59% and 64%, respectively. These data were extrapolated to typical agroforestry systems using published data on N recycling by the studied species. Inga edulis may recycle ca. 100 kg ha⁻¹ a⁻¹ of N fixed from atmosphere to soil if only 60% of trees fix N₂, E. poeppigiana 60–160 kg ha⁻¹ a⁻¹, and E. fusca ca. 80 kg ha⁻¹ a⁻¹.     

The Status and Characteristics of Eutrophication in the Yangtze River (Changjiang) Estuary and the Adjacent East China Sea, China

Eutrophication has become increasingly serious and noxious algal blooms have been of more frequent occurrence in the Yangtze River Estuary and in the adjacent East China Sea. In 2003 and 2004, four cruises were undertaken in three zones in the estuary and in the adjacent sea to investigate nitrate (NO₃–N), ammonium (NH₄–N), nitrite (NO₂–N), soluble reactive phosphorus (SRP), dissolved reactive silica (DRSi), dissolved oxygen (DO), phytoplankton chlorophyll a (Chl a) and suspended particulate matter (SPM). The highest concentrations of DIN (NO₃–N+NH₄–N+NO₂–N), SRP and DRSi were 131.6, 1.2 and 155.6 μM, respectively. The maximum Chl a concentration was 19.5 mg m⁻³ in spring. An analysis of historical and recent data revealed that in the last 40 years, nitrate and SRP concentrations increased from 11 to 97 μM and from 0.4 to 0.95 μM, respectively. From 1963 to 2004, N:P ratios also increased from 30–40 up to 150. In parallel with the N and P enrichment, a significant increase of Chl a was detected, Chl a maximum being 20 mg m⁻³, nearly four times higher than in the 1980s. In 2004, the mean DO concentration in bottom waters was 4.35 mg l⁻¹, much lower than in the 1980s. In comparison with other estuaries, the Yangtze River Estuary was characterized by high DIN and DRSi concentrations, with low SRP concentrations. Despite the higher nutrient concentrations, Chl a concentrations were lower in the inner estuary (Zones 1 and 2) than in the adjacent sea (Zone 3). Based on nutrient availability, SPM and hydrodynamics, we assumed that in Zones 1 and 2 phytoplankton growth was suppressed by high turbidity, large tidal amplitude and short residence time. Furthermore, in Zone 3 water stratification was also an important factor that resulted in a greater phytoplankton biomass and lower DO concentrations. Due to hydrodynamics and turbidity, the open sea was unexpectedly more sensitive to nutrient enrichment and related eutrophication processes.     

Harvesting rate of the termite,Drepanotermes tamminensis (Hill) within native woodland and shrubland of the Western Australian wheatbelt

The Western Australian termite,Drepanotermes tamminensis (Hill), harvests various plant materials according to biomass availability. The main litter components harvested by this termite in a woodland dominated byEucalyptus capillosa are bark and leaves of the major tree species, while in shrubland dominated byAllocasuarina campestris, shoots of this species are taken. Harvesting mainly occurs during the autumn (April–May) and spring (September–October) seasons. The commencement and duration of harvesting appears to depend partly on weather conditions, with harvesting taking place at temperatures between 15 and 25°C after periods of rain. This species of termite harvests approximately 15.6 g m⁻² year⁻¹ and 3.2 g m² year⁻¹ (dry weight of plant material) in the woodland and shrubland, respectively.     

Macronutrient content in leaves of bean plants (Phaseolus vulgaris,L.) grown with differents rates of N/S as fertilizers

Summary The effect of increasing rates of nitrogen (N) and sulphur (S) as fertilizers on the yield, leaf area and N, P, S, Ca, Mg, NO₃ ⁻ and SO₄ ⁼ content in leaves of bean (Phaseolus vulgaris, L.) were studied in a hydroponic culture experiment under greenhouse conditions. Bean plants responded significantly to all treatments with differents N/S ratios. When plants grew with high N/S ratios, the leaf content of N, Ca and NO₃ ⁻ increased while the content of K, P and SO₄ ⁼ decreased. However, optimal yield and leaf area were not obtained. Optimal leaf and fruit dry matter was obtained at N/S ratio value of 1.41. When lower N/S rates were used, optimal leaf and fruit dry matter was only observed when the leaf N/S ratio was between 15 and 16. At high sulphate levels in the nutrient solution there is no interaction with nitrate which is easily observed, resulting in an increase in yield. An interaction between nitrate and sulphate in the nutrient solution was found at a N/S ratio of 0.81 which produced in leaves a synergic effect between P-K, an antagonistic effect between N-P and N-K and a lower yield. This research was supported by Fundacion ‘Ramon Areces’.     

Why does photosynthesis decrease with needle age in Pinus pinaster?

Rates of photosynthesis vary with foliage age and typically decline from full-leaf expansion until senescence occurs. This age-related decline in photosynthesis is especially important in species that retain foliage for several years, yet it is not known whether the internal conductance to CO₂ movement (g _i) plays any role. More generally, g _i has been measured in only a few conifers and has never been measured in leaves or needles older than 1 year. The effect of ageing on g _i was investigated in Pinus pinaster, a species that retains needle for 4 or more years. Measurements were made in autumn when trees were not water limited and after leaf expansion was complete. Rates of net photosynthesis decreased with needle age, from 8 μmol m⁻² s⁻¹ in fully expanded current-year needles to 4.4 μmol m⁻² s⁻¹ in 3-year-old needles. The relative limitation due to internal conductance (0.24–0.35 out of 1) was in all cases larger than that due to stomatal conductance (0.13–0.19 out of 1). Internal conductance and stomatal conductance approximately scaled with rates of photosynthesis. Hence, there was no difference among year-classes in the relative limitations posed by internal and stomatal conductance or evidence that they cause the age-related decline in photosynthesis. There was little evidence that the age-related decline in photosynthesis was due to decreases in contents of N or Rubisco. The decrease in rates of photosynthesis from current-year to older needles was instead related to a twofold decrease in rates of photosynthesis per unit nitrogen and V _cmax/Rubisco (i.e., in vivo specific activity).