Growth and Alkaloid Patterns of Roots of Tabernaemontana pachysiphon and Rauvolfia mombasiana as Influenced by Environmental Factors

The influence of environmental factors on the indole alkaloid content and biomass of the roots of Tabernaemontana pachysiphon and Rauvolfia mombasiana, two species of considerable local medicinal use in tropical East Africa, was investigated. Both species, belonging to the Apocynaceae, are frequent constituents of the residual tropical forests, prefering sites of different ecological conditions. Experimental plants, raised from seeds, were grown for 16 months in a temperature- and humidity-controlled greenhouse. Environmental factors at variance were water and nutrient supply, and light intensity. At sufficient water and nutrient supply, the more drought and nutrient shortage-tolerating heliophilous Rauvolfia mombasiana showed increased alkaloid accumulation, concurrently with reduced root biomass. Under the same conditions, the drought-sensitive and higher levels of nutrient-requiring ombrophilous Tabernaemontana pachysiphon produced more root biomass but accumulated less alkaloids in the roots. The results indicate that the accumulation of indole alkaloids in the roots, as well as biomass allocation to the roots, is influenced in an opposite manner by the nutrient and water supply to the heliophilous and the ombrophilous species.     

Effects of light availability on growth, architecture and nutrient content of the seagrass Zostera noltii Hornem

The growth vs. irradiance response of the seagrass Zostera noltii from Cadiz Bay Natural Park (southwestern Spain) was characterised. Plants were exposed along 14 days to different light treatments (1%, 7%, 42% and 100% surface irradiance, SI), using shade screens in an outdoor mesocosm. Growth at 100% SI (1.6 mg DW plant⁻¹ day⁻¹) was lower than that at 42% SI (2.4 mg DW plant⁻¹ day⁻¹), suggesting photoinhibition. The minimum light requirement estimated was 0.8 mol photons m⁻² day⁻¹ (2% SI). Light availability affected the pattern of plant development and the overall plant growth. The contribution of the apical shoots to the aboveground production was nearly constant (c.a. 1.13 cm plant⁻¹ day⁻¹) regardless of the light level (except at 1% SI). In contrast, recruitment and growth of lateral shoots arising from the main rhizome axes accounted for the observed differences in aboveground growth. Rhizome branching was only observed at 42% SI. The possibility of a light threshold for rhizome branching could explain the seasonality of shoot recruitment, as well as the observed decrease in shoot density along depth (or light) gradients in seagrass meadows. Carbon demands at low irradiances (1% and 7% SI) were partially met by mobilization of carbohydrate reserves (sucrose in belowground and starch in aboveground parts). Plant nitrogen content decreased with increasing light, especially in belowground parts, reaching critical levels for growth.     

Three physiological parameters capture variation in leaf respiration of Eucalyptus grandis,as elicited by short‐term changes in ambient temperature,and differing nitrogen supply

We used instantaneous temperature responses of CO₂‐respiration to explore temperature acclimation dynamics for Eucalyptus grandis grown with differing nitrogen supply. A reduction in ambient temperature from 23 to 19 °C reduced light‐saturated photosynthesis by 25% but increased respiratory capacity by 30%. Changes in respiratory capacity were not reversed after temperatures were subsequently increased to 27 °C. Temperature sensitivity of respiration measured at prevalent ambient temperature varied little between temperature treatments but was significantly reduced from ~105 kJ mol^?1 when supply of N was weak, to ~70 kJ mol^?1 when it was strong. Temperature sensitivity of respiration measured across a broader temperature range (20–40 °C) could be fully described by 2 exponent parameters of an Arrhenius‐type model (i.e., activation energy of respiration at low reference temperature and a parameter describing the temperature dependence of activation energy). These 2 parameters were strongly correlated, statistically explaining 74% of observed variation. Residual variation was linked to treatment‐induced changes in respiration at low reference temperature or respiratory capacity. Leaf contents of starch and soluble sugars suggest that respiratory capacity varies with source‐sink imbalances in carbohydrate utilization, which in combination with shifts in carbon‐flux mode, serve to maintain homeostasis of respiratory temperature sensitivity at prevalent growth temperature.     

Growth of a mangrove (Rhizophora apiculata) seedlings as influenced by GA3, light and salinity

The growth performance of Rhizophora apiculata Blume (mangrove) seedlings in the presence and absence of exogenous gibberellic acid (GA3) under different combinations of salinity and light was analyzed. Root and shoot growth responses of 75-day old seedlings in liquid-culture, were measured. It was concluded that light exhibited a significant inhibitory effect on all the growth parameters-number of primary roots, primary root length, shoot elongation, number of leaves, total leaf area; and, the GA3 treatment singly or in combinations with light, showed a significant influence on the total leaf area and primary root length.     

Respiration in mature leaves of Lolium perenne as affected by nutrient supply, cutting and competition

The rate of oxygen uptake was measured on sections of mature leaf tissue derived from two populations of Lolium perenne L. cv. S23, selected for contrasting rates of mature leaf respiration. Under conditions of sufficient nutrient supply, GL72 had a lower rate of respiration and a greater yield than GL66. The populations were exposed to important management variables to investigate their effect on the selection criterion, the two variables being nutrient supply and defoliation. Conditions of low nutrient supply were characterized by a similarity in respiration rate and a change in the regulation of respiration. Enzyme levels, rather than adenylates, controlled respiration. Weekly cutting induced activity of the otherwise latent alternative pathway.     

The nitrogen mineralization rate of legume residues in soil as influenced by their polyphenol,lignin, and nitrogen contents

A 12-week greenhouse experiment was conducted to determine the effect of the polyphenol, lignin and N contents of six legumes on their N mineralization rate in soil and to compare estimates of legume-N release by the difference and ¹⁵N-recovery methods. Mature tops of alfalfa (Medicago sativa L.), round leaf cassia (Cassia rotundifolia Pers., var. Wynn), leucaena (Leucaena leucocephala Lam., deWit), Fitzroy stylo (Stylosanthes scabra Vog., var Fitzroy), snail medic (Medicago scutellata L.), and vigna (Vigna trilobata L., var verde) were incorporated in soil at the rate of 100 mg legume N kg^-1 soil. The medic and vigna were labeled with ¹⁵N. Sorghum-sudan hybrid (Sorghum bicolor, L. Moench) was used as the test crop. A non-amended treatment was used as a control. Net N mineralization after 12 weeks ranged from 11% of added N with cassia to 47% of added N for alfalfa. With the two legumes that contained less than 20 g kg^-1 of N, stylo and cassia, there was net N immobilization for the first 6 weeks of the experiment. The legume (lignin + polyphenol):N ratio was significantly correlated with N mineralization at all sampling dates at the 0.05 level and at the 0.01 level at 6 weeks (r²=0.866). Legume N, lignin, or polyphenol concentrations or the lignin:N ratio were not significantly correlated with N mineralization at any time. The polyphenol:N ratio was only significantly correlated with N mineralization after 9 weeks (r²=0.692). The (lignin + polyphenol):N ratio appears to be a good predictor of N mineralization rates of incorporated legumes, but the method for analyzing plant polyphenol needs to be standardized. Estimates of legume-N mineralization by the difference and ¹⁵N recovery methods were significantly different at all sampling dates for both ¹⁵N-labeled legumes. After 12 weeks, estimates of legume-N mineralization averaged 20% more with the difference method than with the ¹⁵N recovery method. This finding suggests that estimates of legume N available to subsequent crops should not be based solely on results from ¹⁵N recovery experiments.     

Effects of elevated CO2 on growth and carbon/nutrient balance in the deciduous woody shrub Lindera benzoin (L.) Blume (Lauraceae)

We examined the effects of elevated CO₂ on growth and carbon/nutrient balance in a natural population of the deciduous temperate zone shrub Lindera benzoin. Our data concern whole plant, leaf, and stem growth for the first two seasons of a long-term field experiment in which CO₂ levels were manipulated in situ. In addition to growth parameters, we evaluated changes in leaf and stem chemistry, including total nitrogen, nonstructural carbohydrates, and total phenolics. Over the course of this study, L. benzoin appeared to respond to elevated CO₂ primarily by physiological and biochemical changes, with only a slight enhancement in aboveground growth (ramet height). Positive effects on aboveground growth were primarily evident in young (nonreproductive) ramets. Our results suggest that nitrogen limitation may have constrained plants to allocate carbohydrates produced in response to elevated CO₂ primarily to storage and belowground growth, and perhaps to increased secondary chemical production, rather than to increased stem and leaf growth. We discuss our results in terms of changes in carbon/nutrient balance induced by elevated CO₂, and provide predictions for future changes in this system based upon constraints imposed by intrinsic and extrinsic factors and their potential effects on the reallocation of stored reserves.     

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.     

Mycorrhizae formation and nutrient uptake of new corn (Zea mays L.) hybrids with extreme canopy and leaf architecture as influenced by soil N and P levels

A study was conducted to evaluate the effect of N and P supply levels on mycorrhizal formation and nutrient uptake in corn hybrids with different architectures and to determine arbuscular mycorrhizal fungal (AMF) development in relation to shoot N/P ratio and shoot:root ratio. Corn pot cultures with a pasteurized medium of two parts sand and one part sandy loam soil were grown in the greenhouse. Marigold plants inoculated or not with Glomus intraradices Schenck & Smith were used to establish an AMF hyphal network in the designated soil pots. Corn hybrids were seeded after removal of the marigold plant. Mycorrhizal colonization of corn hybrids and the quantity of extraradical hyphae produced in soil were greatest at the lowest P level and at the intermediate N level. Root colonization was correlated with shoot N/P ratio only at the intermediate N level. The shoot concentrations of P, Mg, Zn and Cu were significantly higher in mycorrhizal plants than in non-mycorrhizal plants. The corn phenotype with the highest shoot:root ratio had the highest root colonization. The corn hybrid with a leafy normal stature architecture had a greater mycorrhizal colonization than that of other two corn hybrids. This experiment showed that N level in soil influenced shoot N/P ratio, root colonization and extraradical hyphal production, which in turn influenced uptake of other nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biomass and photosynthetic productivity of water hyacinth (Eichhornia crassipes) as affected by nutrient supply and mirid (Eccritotarus catarinensis) biocontrol

The biological control of water hyacinth is affected by water nitrogen and phosphorus content and this was investigated experimentally at five levels of nutrient supply by measuring plant photosynthetic and growth responses, and mirid reproduction and herbivory of nutrient treated plants. Low nitrogen (2–0.2 mg L⁻¹) and phosphorus (0.2–0.01 mg L⁻¹) supply decreased hyacinth photosynthesis, growth and biomass accumulation relative to plants supplied 200 mg L⁻¹ N and 20 mg L⁻¹ P. This effect depended more on nitrogen supply than phosphorus supply. Chlorophyll fluorescence showed that the photosynthetic light reactions of low nutrient plants were affected and leaves had decreased chlorophyll content, density of functional photosystems II and dissipated a greater proportion of absorbed energy as heat. Gas exchange parameters showed reduced carboxylation efficiency, rates of RuBP regeneration and light saturated photosynthetic rates, but not quantum yields. Effects on photosynthesis translated into lower plant dry biomass. Mirid herbivory exacerbated the effects of low nutrients noted for chlorophyll fluorescence, gas exchange parameters and biomass accumulation, however, these effects were not always significant and there was no obvious correlation between the level of nutrients supplied and the effect of mirid herbivory. Low nutrient supply did, however, affect mirid performance reducing the number of adult insects, nymphs and herbivory intensity suggesting that in the long-term mirid populations would be significantly affected by water nutrient status.     

科尔沁沙地沙漠化过程中土壤有机碳和全氮含量变化

通过地面调查,研究了沙漠化对科尔沁沙地农田和草地土壤有机碳和全氮含量的影响.结果表明,随着沙漠化的发展,科尔沁沙地土壤碳、氮含量明显下降.和非沙漠化农田相比,轻度、中度、重度和严重沙漠化农田土壤有机碳和全氮含量分别下降12.3%和15.3%、22.2%和24.7%、39.5%和44.7%、64.4%和63.5%;和非沙漠化草地相比,轻度、中度、重度和严重沙漠化草地土壤有机碳和全氮含量分别下降了56.3%和48.7%、78.4%和74.4%、88.9%和84.6%、91.6%和84.6%.截至2000年,科尔沁沙漠化总面积已经达到50197.5 km2,由于沙漠化而导致的土壤有机碳和全氮损失总量分别为36.39 Mt和7.89 Mt,其中草地分别占91.12%和86.06%,农田分别占8.88%和13.94%.相关分析结果表明,土壤有机碳和全氮的损失主要源于风蚀所引起的土壤粘粉粒的减少.因此,在科尔沁沙地,防治土壤风蚀对于减少农田和草地土壤碳、氮损失极为重要.     

Growth and survival performance of the gametophyte of Gigartina skottsbergii (Rhodophyta, Gigartinales) under defined nutrient conditions in laboratory culture

Gigartina skottsbergii is a commercially important carrageenan producer that has been suffering severe extraction pressure in Chile’s Magellan Region and Cape Horn Archipelago since 1998. In order to create baseline information for its cultivation and repopulation, we studied the effects of agricultural fertilizers on growth of G. skottsbergii early developmental stages. The culture media utilized were: a) seawater + Bayfoland, b) seawater + Superphosphate, c) seawater + Urea, d) seawater + Provasoli and e) seawater as a control. The culture conditions were: a) 12L:12D photoperiod; b) temperature 8 ± 1°C and c) irradiance at 45 μmol photons m⁻² s⁻¹. After 60 days, higher relative growth rates between treatments were observed; the treatments that included Bayfoland and Provasoli showed greater growth (382 ± 55 and 378 ± 50 μm, respectively,) compared to Superphosphate (88 ± 16 μm), control (78 ± 10 μm) and Urea (70 ± 11 μm) treatments, after 81 days. The Urea treatment and the control had inhibitory effects on G. skottsbergii germlings growth and survival, as evidenced by progressive loss of pigmentation and death after 60 days. These results showed that Bayfoland was an excellent alternative to develop cultures.     

Response of nutrient dynamics of decomposing pine (Pinus massoniana) needles to simulated N deposition in a disturbed and a rehabilitated forest in tropical China

The effects of simulated N deposition on changes in mass, C, N and P of decomposing pine (Pinus massoniana) needles in a disturbed and a rehabilitated forest in tropical China were studied during a 24-month period. The objective of the study was to test the hypothesis that litter decomposition in a disturbed forest is more sensitive to N deposition rate than litter decomposition in a rehabilitated forest due to the relatively low nutrient status in the former as a result of constant human disturbance (harvesting understory and litter). The litterbag method and N treatments (control, no N addition; low-N, 5 g N m⁻² year⁻¹; medium-N, 10 g N m⁻² year⁻¹) were employed to evaluate decomposition. The results revealed that N addition increased (positive effect) mass loss rate and C release rate but suppressed (negative effect) the release rate of N and P from decomposing needles in both disturbed and rehabilitated forests. The enhanced needle decomposition rate by N addition was significantly related to the reduction in the C/N ratio in decomposing needles. However, N availability is not the sole factor limiting needle decomposition in both disturbed and rehabilitated forests. The positive effect was more sensitive to the N addition rate in the rehabilitated forest than in the disturbed forest, however the reverse was true for the negative effect. These results suggest that nutrient status could be one of the important factors in controlling the response of litter decomposition and its nutrient release to elevated N deposition in reforested ecosystems in the study region.     

Effects of temperature experienced during embryonic development on biomass and C and N composition at hatching in Palaemon serratus (Pennant, 1777)

In decapod crustaceans, the conditions experienced during embryonic development trigger phenotypic plasticity of the larvae at hatching. The objective of this study was to test the effects of temperature during embryonic development of Palaemon serratus on the phenotypic plasticity of hatching larvae. We incubated egg-bearing females from eggs laying to hatching at four temperatures (10, 15, 18 and 20°C). Weight, carbon and nitrogen contents were measured on newly laid eggs and on freshly hatched larvae. The duration of embryonic development was negatively correlated with incubation temperature. At 20°C, all females abandoned their eggs during development. Incubation temperature had no effect on the weight and the percentage of N of the larvae at hatching, while it did affect their percentage of C and their C/N ratio. Embryos incubated at 10°C seemed to produce larvae with fewer lipid reserves than those incubated at 15 and 18°C. They probably overconsumed their lipid reserves to compensate for the metabolic losses due to the low temperature. These results provide information on the link between maternal investment per egg and larval development in P. serratus.     

Seasonal variation in primary production of a large high altitude tropical lake (Lake Tana,Ethiopia): effects of nutrient availability and water transparency

Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May–November) and daily resuspension of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m⁻³ to 8.5 mg m⁻³ (mean: 4.5 mg m⁻³) in the offshore zone. Primary production was measured using the light–dark bottles technique. We incubated only at three depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably also frequently missed P _max. Gross primary production in the openwater averaged 2.43 g O₂ m⁻² d⁻¹ and ranged between 0.03 g O₂ m⁻² d⁻¹ and 10.2 g O₂ m⁻² d⁻¹; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season (Oct–Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing P _max. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs. The higher primary production in the inshore zone is probably the result of the daily water column mixing (Z _mix ≥ Z _t) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of matter between the first and second trophic level of the Lake ecosystem will be poor.     

Nodulation,accumulation and redistribution of nitrogen in soybean (Glycine max (L.) Merrill) as influenced by seed inoculation and scheduling of irrigation

Summary A field experiment was conducted on soybean (Glycine max (L.) Merrill) with a view to find out the effect of seed inoculation and scheduling of irrigation on nodulation, accumulation and re-distribution of nitrogen in plant tops and soil. The eight treatment combinations consists of two seed inoculations,viz. uninoculated and inoculated with rhizobium culture, and four irrigation schedules,viz. irrigation water to the cumulative pan evaporation (IW/CPE) ratio of 0.5, 0.7, 0.9 and a control (rainfed). Seed inoculation by, rhizobium culture increased the number, dry-weight and N content of nodules per plant. Inoculation of seeds also increased the N accumulation rate in plant top and it was 2.48 kg/ha/day during the flower-initiation to the pod-initiation stage (30–60 days interval). At harvest, 32.2, 47.8 and 26.2 kg N/ha was re-distributed from the stems, leaves and pods-wall of inoculated plants to the grains, respectively. A total of 186.5 kg N/ha was harvested and 64.7 kg N/ha, was accumulated in soil under the inoculated condition.Scheduling of irrigation at 0.7 IW/CPE proved better, than other irrigation schedules and helped in increasing the nodulation, nitrogen accumulation and grain yield. As compared to control, 8.4, 17.8 and 18.4 kg more of N/ha was redistributed from the stems, leaves and pods-wall respectively when the irrigations were scheduled at 0.7 IW/CPE ratio. Under this irrigation schedule the total N harvest was 200.1 kg/ha while the total N increased by 55.9 kg over that present in soil at the time of sowing.     

Bacterial abundance and production in river sediments as related to the biochemical composition of particulate organic matter (POM)

The major proportion of heterotrophic activity in running waters islocalized on the solid surfaces of sediments in the benthic and hyporheic zoneand is dominated by microorganisms. However, this assertion is based on thestudies of small streams, and little is known about the microbial metabolism oforganic matter in river ecosystems. We therefore explored the relationshipsbetween bacterial abundance and production and the gradients of organic matterquality and quantity in sediments of a sixth-order lowland river (Spree,Germany). We found vertical gradients of detrital variables (particulateorganicmatter (POM), particulate organic carbon (POC), nitrogen (PN), and protein) andof bacterial variables (abundance, production, turnover time, and proportion ofbacterial carbon in total POC) in two different sediment types. These gradientswere steeper in stratified sediments than in the shifting sediments. Detritalvariables correlated strongly with bacterial abundance and production. The bestcorrelation was found for detrital variables indicating substrate quantity andquality (r_S = 0.90 for PN with abundance). Although bacterialbiomasscomprised only 0.7% of the POC (1.9% of PN, 3.4% of the protein) in sediments,the turnover of sedimentary organic carbon was fast (median = 62d), especially in the shifting sediments. Our findings demonstratethat sediment dynamics significantly foster organic carbon metabolism in riversystems. Thus, these sediments, which are typical for lowland rivers, stronglyinfluence the metabolism of the whole ecosystem.     

Growth of Escherichia coli O157:H7 in bruised apple (Malus domestica) tissue as influenced by cultivar, date of harvest, and source

Four of five apple cultivars (Golden Delicious, Red Delicious, McIntosh, Macoun, and Melrose) inoculated with Escherichia coli O157:H7 promoted growth of the bacterium in bruised tissue independent of the date of harvest (i.e., degree of apple ripening) or the source of the apple (i.e., tree-picked or dropped fruit). Apple harvest for this study began 4 September 1998 and ended 9 October, with weekly sampling. Throughout this study, freshly picked (<2 days after harvest) McIntosh apples usually prevented the growth of E. coli O157:H7 for 2 days. Growth of E. coli O157:H7 did occur following 6 days of incubation in bruised McIntosh apple tissue. However, the maximum total cell number was approximately 80-fold less than the maximum total cell number recovered from Red Delicious apples. When fruit was stored for 1 month at 4 degrees C prior to inoculation with E. coli O157:H7, all five cultivars supported growth of the bacterium. For each apple cultivar, the pH of bruised tissue was significantly higher and degrees Brix was significantly lower than the pH and degrees Brix of undamaged tissue regardless of the source. In freshly picked apples, changes in the pH did not occur over the harvest season. Bruised Golden Delicious, McIntosh, and Melrose apple tissue pHs were not significantly different (tree-picked or dropped), and the degrees Brix values of McIntosh, Macoun, and Melrose apple tissue were not significantly different. Single-cultivar preparations of cider did not support growth of E. coli, and the cell concentration of inoculated cider declined over an 11-day test period. The rate of decline in E. coli cell concentration in the McIntosh cider was greater than those in the other ciders tested. The findings of this study suggested that the presence of some factor besides, or in addition to, pH inhibited E. coli growth in McIntosh apples.