Growth and Contaminant Removal Effect of Several Plants in Constructed Wetlands

The aim of the present study is to probe the relation between plant growth and its decontamination effect in constructed wetlands. Four species were studied in the small-scale mono-cultured constructed wetlands, which were fed with domestic wastewater. Plant growth indexes were correlated with contaminant removal performance of the constructed wetlands. Wetlands planted with Cyperus flabelliformis Rottb. showed the highest growth indexes such as shoot growth, biomass, root activity, root biomass increment, and the highest contaminant removal rates, whereas wetlands planted with Vetiveria zizanioides L. Nash had the lowest growth indexes and the lowest removal rates. Above-ground biomass and total biomass were significantly correlated with ammonia nitrogen removal, and below-ground biomass with soluble reactive phosphorus removal. Photosynthetic rate had higher correlation with nitrogen removal in these species. Root activity and root biomass increment was more correlated with 5 d biochemical oxygen demand removal. Chemical oxygen demand removal had lower correlations with plant growth indexes. All four species had higher removal rates in summer and autumn. The results suggest that the effect of plant growth on contaminant removal in constructed wetlands were different specifically in plants and contaminants.     

土壤盐分及水分含量对落羽杉幼苗生长的影响

One year old Taxodium distichum seedlings were grown in pots with varied soil water and salt (NaC1) levels (alone and in combination) under greenhouse conditions to determine their effects on the growth and biomass allocation of the seedlings. The results showed that there were significant effects of soft salt and water contents on the relative height growth, relative stem diameter growth, biaomass increment and allocation, shoot/root ratio, seedling survival, ratio of branch to stem area, ratio of leaf mass to stem area, and ratio of leaf mass to branch area. According to the biomass increment, relative height growth and relative stem diameter growth, 20 treatments were classified into 3 groups by means of systematic cluster analysis. The first one was the treatments waterlogging, flooding, waterlogging 0.15% NaC1, flooding 0.15% NaC1, and waterlogging 0.3% NaC1, which had a high growth, the second one was the treatments flooding 0.45% NaC1, flooding 0.3% NaCl, 75% of field capacity, and 75% of field capacity 0.15% NaCl, which had a medium growth, and the last onewas the treatments 50% of field capacity, 50% of field capacity 0.15% Nat1, waterlogging 0.45% Nat1,25% of field capacity, 25% of field capacity 0.15% NaC1, 75% of field capacity 0.3% NaC1, 75% of field capacity 0.45% NaC1, 25% of field capacity 0.3% NaC1, 50% of field capacity 0.3% NaC1, 50% of field capacity 0.45% NaC1, and 25% of field capacity 0.45% NaC1, which had a poor growth.     

Arsenic tolerance, uptake and translocation by seedlings of three rice cultivars

By simulating the anaerobic conditions with agar nutrient solutions, effect of arsenic (As) on the growth and As uptake by hybrid, conventional and glutinous rice cultivars were studied. It showed insignificant effect of As on the root dry weights of three rice cultivars when treated by As of different concentrations. The shoot dry weights of hybrid and glutinous decreased with As concentrations increasing, while low concentrations of As (0.5 mg L^?1) could enhance the growth of conventional rice. Generally, As concentrations in roots and shoots increased as As concentrations of treatment solutions increasing. The root system had strong ability to uptake and accumulate As. The root As concentrations ranged from 156 to 504 mg kg^?1, representing 63.40%–81.90% of the total As concentrations in rice, which were much higher than shoot As concentrations. The fact that the glutinous rice had higher biomass, higher tolerance, and lower As concentrations in its roots and shoots than the other two rice cultivars proved that the glutinous rice was more applicable to As-polluted soils.     

Monovalent cation transporters; establishing a link between bioinformatics and physiology

Toxic aluminum (Al) ion is a major constraint to plant growth in acid soils. Aluminum tolerance in wheat (Triticum aestivum L.) is strongly related to the Al-triggered efflux of malate from root apices. A role of the secreted malate has been postulated to be in chelating Al and thus excluding it from root apices (malate hypothesis), but the actual process has yet to be fully elucidated. We measured Al content and root growth during and after Al exposure using seedlings of near-isogenic lines [ET8 (Al tolerant) and ES8 (Al sensitive)] differing in the capacity to induce Al-triggered malate efflux. Aluminum doses that caused 50% root growth inhibition during 24-h exposure to Al in calcium (Ca) solution (0.5 mM CaCl₂, pH 4.5) were 50 μM in ET8 and 5 μM in ES8. Under such conditions, the amount of Al accumulated in root apices was approximately 2-fold higher in ET8 than ES8. Al-treated seedlings were then transferred to the Al-free Ca solution for 24 h. Compared to control roots (no Al pretreatment), root regrowth of Al-treated roots was about 100% in ET8 and about 25% in ES8. The impaired regrowth in ES8 was observed even after 24-h exposure to 2.5 μM Al which had caused only 20% root growth inhibition. The addition of malate (100 μM) during exposure to 50 μM Al in ES8 enhanced root growth 1.6 times and regrowth in Al-free solution 7 times, resulting in similar root growth and regrowth as in ET8. Short-term Al treatments of ES8 for up to 5 h indicated that the Al-caused inhibition of root regrowth started after 1-h exposure to Al. The stimulating effect of malate on root regrowth was observed when malate was present during Al exposure, but not when roots previously exposed to Al were rinsed with malate, although Al accumulation in root apices was similar under these malate treatments. We conclude that the malate secreted from root apices under Al exposure is essential for the apices to commence regrowth in Al-free medium, the trait that is not related to the exclusion of Al from the apices.     

Role of Ca2+ on Growth of Brassica campestris L. and B.juncea (L.) Czern & Coss under Na+ Stress

Root and shoot growth of Brassica campestris L.and B.juncea increased significantly(P0.01) with enhanced Ca2+ treatment along with 60 mM NaCl in the root medium.The maximum fresh mass of shoot and root in B.juncea was recorded at 10 mM Ca2+ concentration.The relative growth rate of shoot of both species reached its maximum at 8 mM of Ca2+ concentration.Average rate of Ca2+ intake(Ca) was higher in B.juncea than B.campestris.In B.juncea,the average transport of Ca2+ to shoot increased by 19%,38%,119%,125% and 169% compared with the control.Furthermore specific utilization rate of Ca2+ was higher in B.juncea than B.campestris.In B.campestris it increased by 9%,32%,41% and 59% at 4,6,8,and 10 mM of calcium in comparison to 2 mM Ca2+ treatment.At 4,6,8 and 10 mM of Ca2+ application,the increase in the leaf area ratio was 10,17,23 and 30%,respectively.In the shoot and root portions of B.campestris and B.juncea,Ca2+ had a linear relationship with potassium and sulfur,whereas it was in antagonism with sodium ion.     

Growth,Nitrogen Uptake and Flow in Maize Plants Affected by Root Growth Restriction

The objective of the present study was to investigate the influence of a reduced maize root-system size on root growth and nitrogen （N） uptake and flow within plants. Restriction of shoot-borne root growth caused a strong decrease in the absorption of root ： shoot dry weight ratio and a reduction in shoot growth. On the other hand, compensatory growth and an increased N uptake rate in the remaining roots were observed. Despite the limited long-distance transport pathway in the mesocotyl with restriction of shoot-borne root growth, N cycling within these plants was higher than those in control plants, implying that xylem and phloem flow velocities via the mesocotyl were considerably higher than in plants with an intact root system. The removal of the seminal roots in addition to restricting shoot-borne root development did not affect whole plant growth and N uptake, except for the stronger compensatory growth of the primary roots. Our results suggest that an adequate N supply to maize plant is maintained by compensatory growth of the remaining roots, increased N uptake rate and flow velocities within the xylem and phloem via the mesocotyl, and reduction in the shoot growth rate.     

利手、优势足及扣手的遗传方式初探

采用Slater区分单基因和多基因遗传的计算模式及Smith无偏分析方法对21个家系资料的分析表明：利手、优势足、扣手特征均为常染色体单基因显性遗传,R型为显性性状。虽然环境因素对这类特征的表现也有一定的影响,但遗传因素仍起主要作用。 Abstract:The data of 21 families were analyzed by the method of Slater's calculating model to differentiate between single-gene and multi-gene heredity and by the method of non-deviation analysis.The results showed that the hereditary mode of handedness or preferential foot or hand-clasping is the dominant heredity of single gene of autosome,and the right type of all of them is the dominant character.In a way,although environmental factors affected the phenotypes of these characters,hereditary factors were also the decisive ones.     

Influence of Nitrogen Fertilizer and Endophyte Infection on Ecophysiological Parameters and Mineral Element Content of Perennial Ryegrass

An experiment was designed to determine the effect of the fungal endophyte Neotyphodium Iolii on the growth, physiological parameters and mineral element content of perennial ryegrass （Lolium perennel L.）, when growing at two N supply levels. Endophyte infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected （El） plants accumulated more soluble sugar in the sheath and the root than endophyte-free （EF） plants. Endophyte infection affected mineral element concentrations in the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. El plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both El and EF plants.     

Role of earthworm-straw interactions on phytoremediation of Cu contaminated soil by ryegrass

It is well known that the earthworm's activities can increase the availability of soil nutrients, improve soil structure, and enhance the biomass of plants in uncontaminated soil. Recently, many researchers found that some metal-tolerant earthworms can survive and even change the fractional distribution of heavy metals in contaminated soil. Furthermore, it has been revealed that earthworms are able to increase metal availability, and therefore, accumulate more metals in plants through their burrowing and casting activity. It is clear that the influence of soil animals is an important factor for phyto-remedation that must be taken into account. ~In this article, the authors studied some effects of addition of earthworms (Metaphire guillelmi), corn straw, and in combinations of earthworms and corn straw on the growth and Cu uptake by ryegrass in Cu contaminated pot soils. The experiment consisted of four levels of Cu addition (0, 100, 200, 400 mg·kg?1) and four treatments. The treatments were 1. control (CK); 2.straw mulching only (M); 3. earthworm additions to soil only (E); and 4.straw mulching plus earthworm additions (ME). Each treatment had three replicates. 10 seeds of ryegrass (Lolium multiflorum) were sowed in each pot and harvested after 30 days. After 30 days of incubation, all earthworms were found to be alive and the pot soils were burrowed through by earthworms. Results showed that the biomass of earthworm declined with the increase of the dosage of Cu additions. The biomass of earthworm increased significantly in treatment 4 (ME) as compared with treatment 3 (E). Not only the earthworms could get more food from the straw, but also could counteract some negative effects of Cu on the earthworms. The rates of straw decomposition in ME treatment increased by about 58.11% ?77.32%. The earthworm activities increased root biomass of ryegrass significantly, but did not show the effect on plant root growth. On the contrary, straw enhanced roots biomass significantly instead of shoots biomass. It was also found that the concentration of Cu in the plant shoot and the plant root, as well as plant Cu uptake were enhanced by earthworm's activities and straw mulching. The increased amount by straw mulching was lower than that of earthworms (E). The treatment of the earthworm–straw mulching combinations enhanced plant Cu concentration, and the amount increased by it was lower than that of the earthworm treatment (E) but higher than that of straw mulching treatment (M). The accumulation factors of copper in the shoots of ryegrass were increased by 31.22% ?121.07%, 2.12% ?61.28% and 25.56% ?132.64%, respectively, in treatment 3(E), 2(M), and 4(ME), respectively. In conclusion, the earthworm activities, straw-mulching and their interactions may have potential roles in elevating phyto-extraction efficiency in low to medium level Cu contaminated soil.     

Role of earthworm-straw interactions on phytoremediation of Cu contaminated soil by ryegrass

It is well known that the earthworm's activities can increase the availability of soil nutrients, improve soil structure, and enhance the biomass of plants in uncontaminated soil. Recently, many researchers found that some metal-tolerant earthworms can survive and even change the fractional distribution of heavy metals in contaminated soil. Furthermore, it has been revealed that earthworms are able to increase metal availability, and therefore, accumulate more metals in plants through their burrowing and casting activity. It is clear that the influence of soil animals is an important factor for phyto-remedation that must be taken into account. ~In this article, the authors studied some effects of addition of earthworms (Metaphire guillelmi), corn straw, and in combinations of earthworms and corn straw on the growth and Cu uptake by ryegrass in Cu contaminated pot soils. The experiment consisted of four levels of Cu addition (0, 100, 200, 400 mg·kg?1) and four treatments. The treatments were 1. control (CK); 2.straw mulching only (M); 3. earthworm additions to soil only (E); and 4.straw mulching plus earthworm additions (ME). Each treatment had three replicates. 10 seeds of ryegrass (Lolium multiflorum) were sowed in each pot and harvested after 30 days. After 30 days of incubation, all earthworms were found to be alive and the pot soils were burrowed through by earthworms. Results showed that the biomass of earthworm declined with the increase of the dosage of Cu additions. The biomass of earthworm increased significantly in treatment 4 (ME) as compared with treatment 3 (E). Not only the earthworms could get more food from the straw, but also could counteract some negative effects of Cu on the earthworms. The rates of straw decomposition in ME treatment increased by about 58.11% ?77.32%. The earthworm activities increased root biomass of ryegrass significantly, but did not show the effect on plant root growth. On the contrary, straw enhanced roots biomass significantly instead of shoots biomass. It was also found that the concentration of Cu in the plant shoot and the plant root, as well as plant Cu uptake were enhanced by earthworm's activities and straw mulching. The increased amount by straw mulching was lower than that of earthworms (E). The treatment of the earthworm–straw mulching combinations enhanced plant Cu concentration, and the amount increased by it was lower than that of the earthworm treatment (E) but higher than that of straw mulching treatment (M). The accumulation factors of copper in the shoots of ryegrass were increased by 31.22% ?121.07%, 2.12% ?61.28% and 25.56% ?132.64%, respectively, in treatment 3(E), 2(M), and 4(ME), respectively. In conclusion, the earthworm activities, straw-mulching and their interactions may have potential roles in elevating phyto-extraction efficiency in low to medium level Cu contaminated soil.     

甘蔗生物量育种的ADGE遗传分析

对甘蔗11个亲本品种及不完全双列杂交(NCdesignⅡ)遗传设计的30个组合的F1代实生苗生物量进行加性-显型-随机环境效应模型(ADGE)分析。结果表明:甘蔗的生物量性状遗传主要是由基因的加性、显性及加性×环境互作效应共同决定的,但基因的加性效应作用较大;甘蔗杂交亲本对其后代表型的遗传作用主要为母本的遗传效应影响;甘蔗生物量性状都具有较高的广义遗传率(h2B)和狭义遗传率(h2N),且h2B>h2N,说明了对甘蔗生物量性状在选育种早期阶段的选择效果好;通过对亲本的加性基因随机效应分析的综合,较优良的甘蔗亲本有粤糖72/426、粤糖79/177、粤糖85/177、ROC24和ROC25;根据杂交组合显性随机效应分析,认为粤糖72/426×ROC16、粤糖79/177×ROC24、粤糖79/177×ROC23及粤糖80/101×ROC22是较优良的高生物量甘蔗杂交组合,可以应用于甘蔗的高生物量育种。     

Physiological basis of reduced Al tolerance in ditelosomic lines of Chinese Spring wheat

Aluminum tolerance was assessed in the moderately Al-tolerant wheat (Triticum aestivum L.) cultivar Chinese Spring and a set of ditelosomic lines derived from Chinese Spring. Three ditelosomic lines lacking chromosome arms 4DL, 5AS and 7AS, respectively, exhibited decreased Al tolerance relative to the euploid parent Chinese Spring based on reduced root growth in Al-containing solutions. The physiological basis of the reduced Al tolerance was investigated. Measurements by inductively coupled argon plasma mass spectroscopy of root apical Al accumulation demonstrated that two of these three lines had a decreased ability to exclude Al from the root apex, the site of Al phytotoxicity. As Al-induced malate exudation has been suggested to be an important physiological mechanism of Al tolerance in wheat, this parameter was quantified and malate exudation was shown to be smaller in all three deletion lines compared with Chinese Spring. These results suggest that the decreased Al tolerance in at least two of the three ditelosomic lines is due to the loss of different genes independently influencing a single Al-tolerance mechanism, rather than to the loss of genes encoding alternative Al-tolerance mechanisms. Received: 3 July 2000 / Accepted: 9 August 2000     

Genetic aspects of aluminum tolerance in sorghum

To obtain crops tolerant to aluminum (Al) toxicity in acid soils, several methods have been used to screen different plant species and genotypes to this production constraint. Little is known about the effect of the method on genetic analyses and breeding method suggested. Three genetic studies were conducted to examine evaluation method on inheritance and gene action of sorghum [Sorghum bicolor (L.) Moench] to Al toxicity as measured by seedling dry matter production.Results of acid soil and solution culture studies indicated that tolerance to Al toxicity was inherited as a dominant character. Narrow-sense heritability estimates in the greenhouse acid-soil study were low for shoot and root dry matter production. Six of the same hybrids tested in solution culture produced high additive-genetic variance and had narrow-sense heritability estimates of 72% for shoot and 65% for root DM yields. Griffing's diallel analysis showed that seven of nine restorer lines had substantially higher specific than general combining ability variances for both root and shoot dry matter yields.Inconsistencies between the acid soil and solution culture techniques showed that different genetic responses to the treatments were being measured. The solution culture study indicated to the plant breeder that genes conditioning Al tolerance could be incorporated into pure lines while the greenhouse acid-soil study would predict that this would not be possible. The diallel study of plants grown in solution culture showed that developing both Al-tolerant varieties and hybrids would be possible depending upon Al-tolerant germplasm used. Acid-soil field studies of actual genetic gain for Al to lerance are needed.     

Development of root biomass in an Eucalyptus globulus plantation under different water and nutrient regimes

The distribution along the soil profile of Eucalyptus globulus root biomass was followed in a plantation in central Portugal at 1, 2 and 6 years after planting, using an excavation technique. The experimental design consisted of a control (C) and 3 treatments: application of solid fertilizers twice a year (F), irrigation without the application of fertilizers (I) and irrigation combined with liquid fertilizers (IL). Below- and above-ground biomass decreased as follows: IL>I>F>C. So, water stress limited growth more severely than nutrient stress. The roots rapidly colonized the top soil volume (0–20 cm depth) during the first year after planting. Fine root biomass 6 years after planting was 2.2, 1.8 and 1.6 times higher in IL treatment than it was respectively in control, and in F and I treatments. The distribution of fine roots along the soil profile 6 years after planting was more even in IL compared to the other treatments. However, fine roots in the top soil were more concentrated along the tree rows in the irrigated treatments than in the others. The proportion of below-ground biomass relative to the total tree biomass and the root/shoot ratio were higher in C than in the treatments at early growth stages. This pattern was not so clear 6 years after planting, due to the increased proportion of the tap root relative to total biomass, especially in the IL treatment.     

The species richness–biomass relationship in herbaceous plant communities: what difference does the incorporation of root biomass data make?

So far, in all studies on the much-discussed hump-backed relationship between plant community productivity and species richness, productivity has been assessed through plant shoot biomass, i.e. it has been ignored that frequently most of the biomass is produced below ground. We revisited the 27 grassland and forest field-layer communities, studied earlier by Zobel and Liira, to sample root biomass, plant total biomass and root/shoot allocation, and learn how the incorporation of below-ground biomass data would affect the shape of the hump-backed relationship. In order to avoid scaling artefacts we estimated richness as the average count of species per 500 plant ramets (absolute richness). We also included relative richness measures. Relative richness was defined as richness per 500 ramets/size of the actual species pool (the set of species present in the community), relative pool size was defined as size of the actual species pool/size of the regional species pool (the set of species available in the region and capable of growing in the given community).
The biomass-absolute richness relationship was humped, irrespective of the biomass measure used, the hump being most obvious when plant total biomass was used as the independent variable. Evidently, the unimodal richness–productivity curve is not a sampling artefact, as suspected by Oksanen. However, relative richness was not related to community biomass (above-ground, below-ground or total). The hump-backed curve is shaped by the sizes of actual species pools in communities, implying that processes which are responsible for small-scale diversity pattern mainly operate on the community level.
Neither absolute nor relative richness were significantly related to root/shoot allocation. The presumably stronger (asymmetric) shoot competition at greater allocation to shoots appears not to suppress small-scale richness. However, there is a significant relationship between relative pool size and root/shoot allocation. Relatively more species from regional species pools are able to enter and persist in communities with more biomass allocated into roots.     

Physiological and genetic analyses of aluminium tolerance in rice, focusing on root growth during germination

Aluminium (Al) ion limits root growth of plants in acidic soils, and rice exhibits the highest level of Al-tolerance among graminous crops. To elucidate Al-tolerance mechanisms in rice, response to Al was compared between rice (Oryza sativa L., cv. Nipponbare) and wheat (Triticum aestivum L., cv. ET8), focusing on seminal root growth at seedling stage and germination stage. At seedling stage, rice and wheat were similarly sensitive to Al in both dose- and time-dependent manner during a 24-h Al exposure. On the contrary, at germination stage, rice was more tolerant to Al than wheat, and wheat roots displayed the loss of plasma membrane integrity more extensively than rice. A rice mutant exhibiting Al hypersensitivity at germination stage was obtained by screening 42,840 R2 progeny derived from the regenerated R0 plants of Nipponbare and thereafter confirmation of the mutant phenotype in R3 progeny. At germination stage, root growth of the mutant was strongly inhibited in the presence of Al but not in the absence of Al. However, at seedling stage, root growth of the mutant and wild type was similarly tolerant to Al. Taken together, we conclude that rice possesses Al-tolerant function that is under genetic control and specifically operates for root growth at germination stage, making rice more tolerant to Al than wheat.     

Mineral nutrition and growth of tropical maize as affected by soil acidity

Soil constraints linked to low pH reduce grain yield in about 10% of the maize growing area in tropical developing countries. The aim of this research was to elucidate the reasons for this maize yield reduction on an oxisol of Guadeloupe. The field experiment had two treatments: the native non-limed soil (NLI, pH 4.5, 2.1 cmol Al kg^–1, corresponding to 20% Al saturation), and the same soil limed 6 years prior to the experiment (LI, pH 5.3, 0 cmol Al kg^–1). The soils were fertilized with P and N. The above-ground biomass, root biomass at flowering, grain yield and yield components, leaf area index (LAI), light interception, radiation-use-efficiency (RUE), P and N uptake, soil water storage, and soil mineral N were measured during the maize cycle. The allometric relationships between shoot N concentration, LAI and above-ground biomass in LI were similar to those reported for maize cropped in temperate regions, indicating that these relationships are also useful to describe maize growth on tropical soils without Al toxicity. In NLI, soil acidity severely affected leaf appearance, leaf size and consequently the LAI, which was reduced by 60% at flowering, although the RUE was not affected. Therefore, the reduction in the above-ground biomass (30% at flowering) and grain yield (47%) were due to the lower LAI and light interception. At flowering, the root/shoot ratio was 0.25 in NLI and 0.17 in LI, and the root biomass in NLI was reduced by 64% compared to LI. Nitrogen uptake was also reduced in NLI in spite of high soil N availability. Nevertheless, shoot N concentration vs aboveground biomass showed a typical decline in both treatments. In NLI, the shoot P concentration vs above-ground biomass relationship showed an increase in the early stages, indicating that P uptake and root-shoot competition for the absorbed P in the early plant stages controlled the establishment and the development of the leaf area.     

Root Morphology Was Improved in a Late-Stage Vigor Super Rice Cultivar

This study aimed to test the hypothesis that root morphology might be improved and consequently contributing to superior post-heading shoot growth and grain yield in late-stage vigor super rice. A pot experiment was carried out to compare yield attributes, shoot growth and physiological properties and root morphological traits between a late-stage vigor super rice cultivar (Y-liangyou 087) and an elite rice cultivar (Teyou 838). Grain yield and total shoot biomass were 7–9% higher in Y-liangyou 087 than in Teyou 838. Y-liangyou 087 had 60–64% higher post-heading shoot growth rate and biomass production than Teyou 838. Average relative chlorophyll concentration and net photosynthetic rate in flag leaves were 7–11% higher in Y-liangyou 087 than in Teyou 838 during heading to 25 days after heading. Y-liangyou 087 had 41% higher post-heading shoot N uptake but 17–25% lower root biomass and root-shoot ratio at heading and maturity than Teyou 838. Specific root length and length and surface area of fine roots were higher in Y-liangyou 087 than in Teyou 838 at heading and maturity by more than 15%. These results indicated that root-shoot relationships were well balanced during post-heading phase in the late-stage vigor super rice cultivar Y-liangyou 087 by improving root morphology including avoiding a too great root biomass and developing a large fine root system.     

Density-dependent Mortality Induced by Low Nutrient Status of the Substrate

The hypothesis that changing the fertility level of the substratewould change the self-thinning line (different slope or intercept)followed by high-density populations was tested by sowing populationsof Ocimum basilicum L. at two densities on a soil-based pottingmix adjusted to three fertility levels (F0, F1 and F2). Fertilitylevel significantly affected the slope of the thinning linesfor both shoot and root biomass. For shoot biomass, more mortalityoccurred per unit increase in biomass as fertility level declined(the slope of the thinning line became flatter). The slope ofthe log shoot biomassvs. log density relationship was -0.5 atthe F2-, zero at the F1-, and 0.94 at the F0-fertility. Forthe log root biomassvs. log density lines, slopes were zeroat the F2- and F0-fertility levels, and -0.32 at F1. Packingof shoot biomass into canopies of individual plants correlatedwell with observed exponents of self-thinning lines at the F2-and F1-fertility level. Plants at the F2-fertility level requiredmore canopy space to support a given shoot biomass than plantsat F1, indicating that shoot competition was more intense atthe F2-fertility level for a given biomass. Leaf area indexand size inequality also increased with fertility level fora given shoot biomass. Density-dependent mortality in populationsgrown at the F0-fertility level was highly unusual in havinga positive slope for the shoot biomass vs. density relationship.Shoot growth per plant was static as density declined in theF0-populations; however, root growth per plant increased. Allmeasurements of shoot growth (mass, height, canopy extension,leaf area) remained static in the F0-populations: root massand length increased in comparison. It is argued that root competitionbecame sufficiently intense to cause the density-dependent mortalityseen at the F0-fertility level, with little contribution ofshoot competition to mortality. Copyright 1999 Annals of BotanyCompany Ocimum basilicum, self-thinning, root competition, shoot competition, fertility level and competition, density-dependent mortality, allometric self-thinning.