Root growth dynamics of Aleppo pine (Pinus halepensis Mill.) seedlings in relation to shoot elongation, plant size and tissue nitrogen concentration

Large and high nitrogen (N) concentration seedlings frequently have higher survival and growth in Mediterranean forest plantations than seedlings with the opposite traits, which has been linked to the production of deeper and larger root systems in the former type of seedlings. This study assessed the influence of seedling size and N concentration on root growth dynamics and its relation to shoot elongation in Aleppo pine (Pinus halepensis Mill.) seedlings. We cultivated seedlings that differed in size and tissue N concentration that were subsequently transplanted into transparent methacrylate tubes in the field. The number of roots, root depth, and the root and shoot elongation rate (length increase per unit time) were periodically measured for 10 weeks. At the end of the study, we also measured the twig water potential (ψ) and the mass of plant organs. New root mass at the end of the study increased with seedling size, which was linked to the production of a greater number of new roots of lower specific length rather than to higher elongation rate of individual roots. Neither plant size nor N concentration affected root depth. New root mass per leaf mass unit, shoot elongation rate, and pre-dawn ψ were reduced with reduction in seedling size, while mid-day ψ and the root relative growth rate were not affected by seedling size. N concentration had an additive effect on plant size on root growth but its overall effect was less important than seedling size. Shoot and roots had an antagonistic elongation pattern through time in small seedlings, indicating that the growth of both organs depressed each other and that they competed for the same resources. Antagonism between shoot and root elongation decreased with plant size, disappearing in large and medium seedlings, and it was independent of seedling N concentration. We conclude that root and shoot growth but not rooting depth increased with plant size and tissue N concentration in Aleppo pine seedlings. Since production of new roots is critical for the establishment of planted seedlings, higher absolute root growth in large seedlings may increase their transplanting performance relative to small seedlings. The lack of antagonism between root and shoot growth in large seedlings suggests that these plants can provide resources to sustain simultaneous growth of both organs.     

Crassulacean acid metabolism photosynthesis in columnar cactus seedlings during ontogeny: the effect of light on nocturnal acidity accumulation and chlorophyll fluorescence

Columnar cacti have been traditionally classified as crassulacean acid metabolism (CAM) plants, though recent research indicates some cactus seedlings employ the C(3) pathway. To verify this last result, we measured acidity fluctuations for five columnar and one globular cactus species in seedlings from 1 to 48 d old after experimental exposure to 60% and 30% full sunlight, and in adult plants in the field. Using light-response curves of chlorophyll fluorescence, we determined photosynthetic efficiency (ΔF/Fm'), maximum electron transport rate (ETR(max)) and saturating photosynthetically active photon flux density (PPFD(sat)). All seedlings used the CAM pathway from their first day of development, and increases in nocturnal acidity depended on species, light treatment, and age. The CAM pathway was also found in adult plants. Cactus seedlings were able to acclimatize to light conditions by making photochemical adjustments, mainly by modifying the level of light at which photosystem II is saturated (PPFD(sat)). The presence of CAM in the seedlings of columnar cacti increases water-use efficiency and reduces the risk of photoinhibition. This could favor survival in the highly variable light levels characteristic of the desert environments of columnar cacti.     

Mycorrhization and phosphorus nutrition affect water relations and CAM induction by drought in seedlings of Clusia minor

Background and Aims

Crassulacean acid metabolism (CAM) is currently viewed as an adaptation to water deficit. In plants of Clusia minor, which grow mostly on acidic, P-deficient soils, CAM is induced by water deficit. The symbiosis between plants and mycorrhizal fungi alleviates the symptoms of P deficiency and may influence drought resistance. Therefore, the effect of P supply, modified by three different experimental treatments, on the induction of CAM by drought in C. minor was investigated to test the hypothesis that P deficiency will produce greater CAM activity and, in addition, that treatment will modify drought tolerance.

Methods

Seedlings were grown in forest soil sterilized and inoculated with Scutellospora fulgida (SF treatment), sterilized and supplemented with P (Ph treatment) or non-sterilized and containing native mycorrhizae (Nat treatment). Leaf turgor potential (ψ_T) was determined psychrometrically, and CAM activity as nocturnal acid accumulation (ΔH⁺) by titration of dawn and dusk leaf sap.

Key Results

Plant mass and P content were higher in SF and Ph than in Nat seedlings. After 21 d of water deficit, ψ_T increased in SF, decreased in Ph and remained unchanged in Nat, and, after 7 and 14 d of water deficit, ΔH⁺ in Nat was three times higher than at the beginning of drought, whereas in SF and Ph ΔH⁺ was lower than on day 0.

Conclusions

P deficiency in Nat seedlings was ameliorated by inoculation or P addition. The SF and Nat seedlings showed greater tolerance of drought than Ph. P deficiency promoted the induction of CAM by drought in Nat seedlings, whereas P fertilization and mycorrhization did not. Nocturnal acid accumulation was highly and negatively correlated with plant P and N contents, indicating that P and N deficiencies are promoters of CAM in droughted plants of C. minor.Key words: Clusia minor, crassulacean acid metabolism, CAM, mycorrhiza, drought, phosphorus deficiency, nitrogen–water relations     

Slugs, willow seedlings and nutrient fertilization: intrinsic vigor inversely affects palatability

This study evaluates how preference by a generalist slug herbivore Arion subfuscus changes inversely with seedling size across three levels of fertilization for three full‐sib families of willow seedlings. We analyzed seedlings for condensed tannin and protein concentration, and related these data to changes in palatability. In preference tests over time, leaf discs from more fertilized seedlings experienced an extended window of vulnerability compared to discs from less fertilized seedlings, which were also more tannin‐rich. In a whole seedling selection study, slugs readily attacked smaller seedlings (<5 cm) but rarely attacked taller seedlings (>10 cm). However, a general difference in risk of damage close to 50% existed when comparing shorter and taller individuals within each family and level of fertilizer. The decrease in palatability with height of the seedlings was positively correlated with an increase in condensed tannin concentration. We found no effect of seedling size on protein concentration. Akaiki index criterion model comparisons suggested that only main effects were important for explaining seedling choice by slugs as well as the ratio between proteins and condensed tannins. Seedling size, had the largest effect, followed by fertilizer level and family. Surprisingly, seedling size and fertilizer treatment had opposite effects on palatability to slugs. Size decreased probability of damage, whereas fertilization extended the window of susceptibility. Because the seedlings were even‐aged, differences in size are interpreted as differences in growth rate or vigor. The positive phenotypic correlation found between size and tannin production in the less preferred willow seedlings confirms that several plant defense traits may be selected for simultaneously, because fast growth may allow an early development of plant defenses. We discuss these results in the light of plant‐defense theories that predict a negative correlation between the allocation to growth and the production of secondary defense compounds.     

等渗的盐分和水分胁迫对芦荟幼苗生长和离子分布的效应

 研究了等渗透势（-0.44、-0.88 MPa）NaCl和PEG 6000处理对六叶龄芦荟(Aloe vera)幼苗叶片生长速率、干物质积累、电解质渗漏和离子吸收、分配的效应。结果表明: -0.44、-0.88 MPa NaCl和PEG处理10 d均明显抑制芦荟幼苗叶片伸长生长,植株干物质积累速率显著降低, 叶片含水量降低,叶片细胞电解质渗漏率上升。NaCl对芦荟幼苗生长的抑制作用显著大于PEG处理的。不同器官离子含量、根系和叶片横切面X-射线微区分析结果表明, NaCl胁迫导致芦荟体内Na+、Cl－含量显著上升,根中增幅明显高于叶片,其中Cl－尤为显著。NaCl胁迫严重抑制芦荟对K+ 和Ca2+ 的吸收及其向叶片的运输,根、叶K+/Na+、Ca2+/Na+ 比率显著下降,而PEG胁迫对离子平衡的干扰较轻,是芦荟对水分胁迫的适应能力高于盐胁迫的主要原因之一。但芦荟对 -0.44～-0.88 MPa NaCl胁迫仍有一定的适应能力,主要原因是：1) 根系对离子的选择性吸收和运输较强,并随着盐胁迫强度增加其选择性增强; 2) 芦荟叶片中的盐分在贮水组织中显著积累,明显高于其它组织细胞。同时,芦荟是CAM（景天酸代谢）途径植物,蒸腾极小,盐分随蒸腾流进入地上部的机会小。     

Genetic structure and AFLP variation of remnant populations in the rare plant Pedicularis palustris (Scrophulariaceae) and its relation to population size and reproductive components

We investigated plant reproduction in relation to genetic structure, population size, and habitat quality in 13 populations of the rare biennial plant Pedicularis palustris with 3-28500 flowering individuals. We used AFLP (amplified fragment length polymorphism) profiles to analyze genetic similarities among 129 individuals (3-15 per population). In a cluster analysis of genetic similarities most individuals (67%) were arranged in population-specific clusters. Analysis of molecular variance indicated significant genetic differentiation among populations and among and within subpopulations (P < 0.001). Gene flow (N(e) m) was low (0.298). On average, plants produced 55 capsules, 17 seeds per fruit, and 42 seedlings in the following growing season. The number of seeds per capsule was independent of population size and of genetic variability. In contrast, the number of capsules per plant (P < 0.05) and the number of seedlings per plant (P < 0.05) were positively correlated with population size. The relation between population size and the number of seeds per plant was not significant (P = 0.075). The number of capsules and of seeds and seedlings per plant (P < 0.01) were positively correlated with genetic variability. Genetic variability was independent of actual population size, suggesting that historical population processes have to be taken into account, too. Stepwise multiple regressions revealed additional significant relationships of habitat parameters (soil pH, C:N ratio), vegetation composition, and standing crop on reproductive components. We conclude that populations of P. palustris are genetically isolated and that reproductive success most likely is influenced by population size, genetic variability, and habitat quality. Management strategies such as moderate grazing, mowing, and artificial gene flow should endeavor to increase population size as well as genetic variation.     

On the nature of facultative and constitutive CAM: environmental and developmental control of CAM expression during early growth of Clusia, Kalanchöe, and Opuntia

The capacity to induce crassulacean acid metabolism developmentally (constitutive CAM) and to up-regulate CAM expression in response to drought stress (facultative CAM) was studied in whole shoots of seven species by measuring net CO(2) gas exchange for up to 120 day-night cycles during early growth. In Clusia rosea, CAM was largely induced developmentally. Well-watered seedlings began their life cycle as C(3) plants and developed net dark CO(2) fixation indicative of CAM after the initiation of the fourth leaf pair following the cotyledons. Thereafter, CAM activity increased progressively and drought stress led to only small additional, reversible increases in dark CO(2) fixation. In contrast, CAM expression was overwhelmingly under environmental control in seedlings and mature plants of Clusia pratensis. C(3)-type CO(2) exchange was maintained under well-watered conditions, but upon drought stress, CO(2) exchange shifted, in a fully reversible manner, to a CAM-type pattern. Clusia minor showed CO(2) exchange reponses intermediate to those of C. rosea and C. pratensis. Clusia cretosa operated in the C(3) mode at all times. Notably, reversible stress-induced increases of dark CO(2) fixation were also observed during the developmental progression to pronounced CAM in young Kalancho? daigremontiana and Kalancho? pinnata, two species considered constitutive CAM species. Drought-induced up-regulation of CAM was even detected in young cladodes of a cactus, Opuntia ficus-indica, an archetypal constitutive CAM species. Evidently, the defining characteristics of constitutive and facultative CAM are shared, to variable degrees, by all CAM species.     

DISPERSION OF SEEDLINGS OF THE PRAIRIE COMPASS PLANT,SILPHIUM LACINIATUM (ASTERACEAE)

Although the dispersal of seeds around individual plants (the seed shadow) has frequently been characterized, the dispersion of seedlings around plants (the seedling shadow) has rarely been examined. We mapped 101 and 149 seedlings of the prairie compass plant (Silphium laciniatum) that appeared in our study area in 1987 and 1990 following mass flowering in 1986 and 1989. We also mapped the locations of flowering stems which appeared in 1986 and 1989 and recorded the number of flowerheads at each stem location. The frequency distributions of distance between a seedling and the nearest flowering stem were identical in the 2 years, with a median distance of 1.0 m. The large size and lack of wind-dispersal structures of compass plant seeds (achenes) are responsible for their limited dispersal. From estimates of the total seed production in the study area in 1986 and 1989, we calculated that about 1% of seeds became seedlings in each year. Flowering stem locations with a higher number of flowerheads had a significantly higher density of seedlings around them. This indicates that recruitment to compass plant populations is not a “lottery”; individual plants that produce more seeds produce, on average, more seedlings.     

中国木本植物幼苗生长对光照强度的响应

光照是影响植物幼苗生长的重要的环境因子,定量化研究光照对木本植物不同生活型幼苗生长的影响具有重要意义。系统收集了有关光照对我国木本植物幼苗生长影响的国内外文献,采用Meta分析的方法对幼苗的生长效应进行评估。研究结果表明:(1)与全光照下幼苗生长相比,由于遮阴处理对幼苗基径增长量的抑制作用强于对株高增长量的作用,幼苗出现株高基面积比增高的形态特征变化;(2)与灌木相比,乔木树种幼苗对不同光照强度的响应更加敏感;(3)在小于20%和20%—40%全光照条件下,落叶阔叶和常绿阔叶树种幼苗基径均受到显著抑制,而常绿针叶树种的基径并没有受到遮阴的明显抑制;(4)落叶阔叶和常绿阔叶树种的株高基面积比均显著高于全光照,而常绿针叶树种的株高基面积比与全光照相比差异较小。我们的这一研究将有助于更好的理解木本植物幼苗生长对光照的响应机理。     

Identification of a new insertion element, similar to gram-negative IS26, on the lactose plasmid of Streptococcus lactis ML3.

In Streptococcus lactis ML3, the lactose plasmid (pSK08) forms cointegrates with a conjugal plasmid (pRS01). It has been proposed that cointegration is mediated by insertion sequences (IS) present on pSK08 (D. G. Anderson and L.L. McKay, J. Bacteriol. 158:954-962, 1984). We examined the junction regions of the cointegrate pPW2 and the corresponding regions of pSK08 (donor) and pRS01 (target) and identified a new IS element on pSK08 (ISS1S) which was involved in and duplicated during formation of pPW2. ISS1S was 808 base pairs (bp) in size, had 18-bp inverted repeats (GGTTCTGTTGCAAAGTTT) at its ends, contained a single long open reading frame encoding a putative protein of 226 amino acids, and generated 8-bp direct repeats of target DNA during cointegrate formation. An iso-IS element, ISS1T, which is duplicated in some other cointegrate plasmids, was also found on pSK08. ISS1T was also 808 bp in size and was identical to ISS1S in sequence except for 4 bp, none of which altered the inverted repeats or amino acid sequence of the open reading frame. Comparison of ISS1 with gram-negative IS26 revealed strong homologies in size (820 bp), sequence of inverted repeats (GGCACTGTTGCAAA), size of direct repeats generated after cointegration (8 bp), and number, size, and amino acid sequence (44.5% identical) of the open reading of frame.     

檀香幼苗半寄生性初步研究

在不同寄主植物繁殖的基础上,研究了檀香(Santalum album L．)幼苗对寄主植物的半寄生性。檀香种子发芽及幼苗生长初期,并不需要寄主植物的参与,但随后的生长其根系必须寄生于适宜的寄主植物的根上。不同寄主植物对檀香幼苗的生长和吸器的发育影响不同,表现在根寄生吸器的数量、大小和结合的程度上。初步筛选了扶桑(Hibiscus rosa-sinensis)、烂头钵(Phyllanthus reticulatus)等优良的檀香幼苗寄主植物。檀香幼苗根系极不发达,细根缺乏根毛,但其导管非常发达,有利于从寄主根吸收养分和水分。此外还观察了檀香和寄主植物扶桑建立半寄生吸器的过程。     

Phenotypic changes in the fluidity of the tonoplast membrane of crassulacean-acid-metabolism plants in response to temperature and salinity stress

Electron paramagnetic resonance-spectroscopic studies on spin-labeled purified tonoplast membranes showed that in the obligate crassulacean-acid-metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perr. the fluidity of the tonoplast decreased during acclimation to higher temperatures. This phenotypic change in tonoplast fluidity was paralleled by a decrease in the mobilization of malic acid from the vacuoles during CAM in the light. The shift from the C₃ to the CAM mode of photosynthesis in the facultative CAM plant Mesembryanthemum crystallinum L. also led to a decrease in the fluidity of the tonoplast membrane. The results are consistent with the hypothesis that the ability to store malic acid during CAM in the vacuoles depends largely on the actual fluidity of the tonoplast membrane.     

The "Kluge-Lüttge Kammer": a preliminary evaluation of an enclosed, Crassulacean acid metabolism (CAM) Mesocosm that allows separation of synchronized and desynchronized contributions of plants to whole system gas exchange

Crassulacean acid metabolism (CAM) is recognized as a photosynthetic adaptation of plants to arid habitats. This paper presents a proof-of-concept evaluation of partitioning net CO2 exchanges for soil and plants in an arid, exclusively CAM mesocosm, with soil depth and succulent plant biomass approximating that of natural Sonoran Desert ecosystems. We present the first evidence that an enclosed CAM-dominated soil and plant community exposed to a substantial day/night temperature difference (30/20 degrees C), exhibits a diel gas exchange pattern consisting of four consecutive phases with a distinct nocturnal CO2 uptake. These phases were modulated by plant assimilation and soil respiration processes. Day-time stomatal closure of the CAM cycle during phase III was used to eliminate aboveground photosynthetic assimilation and respiration and thereby to estimate belowground plant plus soil respiration. Rapid changes in temperature appeared to synchronize single plant gas exchange but individual plant gas exchange patterns were desynchronized at constant day/night temperatures (25 degrees C), masking the distinct mesocosm pattern. Overall, the mean carbon budget of this CAM model Sonoran Desert system was negative, releasing an average of 22.5 mmol CO2 m-2 d-1. The capacity for nocturnal CO2 assimilation in this exclusively CAM mesocosm was inadequate to recycle CO2 released by plant and soil respiration.     

Comparison of biomass allocation in ectomycorrhizal and nonmycorrhizal Douglas fir seedlings of similar nutrition and overall size

Biomass allocation in 6-month-old ectomycorrhizal Douglas fir seedlings was compared to that in nonmycorrhizal seedlings of the same age, nutrient status and total biomass. Seedlings colonized by Rhizopogon vinicolor had the same distribution of biomass between roots, stems and needles, but only 56% of the total length of roots (including mycorrhizal branches) compared to nonmycorrhizal seedlings. Laccaria laccata had no effect on distribution of biomass or root length of seedlings. The results for Rhizopogon provide direct evidence that the process of ectomycorrhizal colonization can significantly affect plant biomass allocation by one or more mechanisms not directly related to altered nutrition or overall plant size.     

Drought-stress-induced up-regulation of CAM in seedlings of a tropical cactus, Opuntia elatior, operating predominantly in the C3 mode

Immediately after unfolding, cotyledons of the tropical platyopuntoid cactus, Opuntia elatior Mill., exhibited a C(3)-type diel CO(2) exchange pattern characterized by net CO(2) uptake in the light. Significant nocturnal increases in titratable acidity typical of crassulacean acid metabolism (CAM) were not detected at this early developmental stage. As cotyledons matured and the first cladode (flattened stem) developed, features of CAM were observed and the magnitude of CAM increased. Nonetheless, in well-watered seedlings up to 10 cm tall, C(3) photosynthetic CO(2) fixation in the light remained the major pathway of carbon fixation. Reduced soil water availability led to an up-regulation of net dark CO(2) fixation and greater nocturnal increases in tissue acidity, consistent with facultative CAM. These observations demonstrate that C(3) photosynthesis, drought-stress-related facultative CAM, and developmentally controlled constitutive CAM can all contribute to the early growth of O. elatior. The strong C(3) component and facultative CAM features expressed in young O. elatior contrast with mature plants in which obligate CAM is the major pathway of carbon acquisition.     

Ecophysiology of Crassulacean Acid Metabolism (CAM)

BACKGROUND AND SCOPE: Crassulacean Acid Metabolism (CAM) as an ecophysiological modification of photosynthetic carbon acquisition has been reviewed extensively before. Cell biology, enzymology and the flow of carbon along various pathways and through various cellular compartments have been well documented and discussed. The present attempt at reviewing CAM once again tries to use a different approach, considering a wide range of inputs, receivers and outputs. INPUT: Input is given by a network of environmental parameters. Six major ones, CO(2), H(2)O, light, temperature, nutrients and salinity, are considered in detail, which allows discussion of the effects of these factors, and combinations thereof, at the individual plant level ('physiological aut-ecology'). RECEIVERS: Receivers of the environmental cues are the plant types genotypes and phenotypes, the latter including morphotypes and physiotypes. CAM genotypes largely remain 'black boxes', and research endeavours of genomics, producing mutants and following molecular phylogeny, are just beginning. There is no special development of CAM morphotypes except for a strong tendency for leaf or stem succulence with large cells with big vacuoles and often, but not always, special water storage tissues. Various CAM physiotypes with differing degrees of CAM expression are well characterized. OUTPUT: Output is the shaping of habitats, ecosystems and communities by CAM. A number of systems are briefly surveyed, namely aquatic systems, deserts, salinas, savannas, restingas, various types of forests, inselbergs and paramós. CONCLUSIONS: While quantitative census data for CAM diversity and biomass are largely missing, intuition suggests that the larger CAM domains are those systems which are governed by a network of interacting stress factors requiring versatile responses and not systems where a single stress factor strongly prevails. CAM is noted to be a strategy for variable, flexible and plastic niche occupation rather than lush productivity. 'Physiological syn-ecology' reveals that phenotypic plasticity constitutes the ecophysiological advantage of CAM.     

Treatment with 24-epibrassinolide,a brassinosteroid,increases the basic thermotolerance of Brassica napus and tomato seedlings

Brassinosteroids are plant growth-promoting compounds that exhibit structural similarities to animal steroid hormones. Recent studies have indicated that brassinosteroids are essential for proper plant development. In addition to a role in development, several lines of evidence suggest that brassinosteroids exert anti-stress effects on plants. However, the mechanism by which they modulate plant stress responses is not understood. We show here that Brassica napus and tomato seedlings grown in the presence of 24-epibrassinolide (EBR) are significantly more tolerant to a lethal heat treatment than are control seedlings grown in the absence of the compound. Since a preconditioning treatment of seedlings was not required to observe this effect, we conclude that EBR treatment increases the basic thermotolerance of seedlings. An analysis of heat shock proteins (HSPs) in B. napus seedlings by western blot analysis indicated that the HSPs did not preferentially accumulate in EBR-treated seedlings at the control temperature. However, after heat stress, HSP accumulation was higher in EBR-treated than in untreated seedlings. The results of the present study provide the first direct evidence for EBR-induced expression of HSPs. The higher accumulation of HSPs in EBR-treated seedlings raises the possibility that HSPs contribute, at least in part, to thermotolerance in EBR-treated seedlings. A search for factors other than HSPs, which may directly or indirectly contribute to brassinosteroid-mediated increase in thermotolerance, is underway.     

Functional constraints of CAM leaf anatomy: tight cell packing is associated with increased CAM function across a gradient of CAM expression

Increased cell size, increased leaf succulence, reduced intercellular air space (IAS), and reduced surface of mesophyll exposed to IAS (L(mes)/area) are traits associated with the Crassulacean acid metabolism (CAM) photosynthetic pathway. An examination was carried out to determine whether these anatomical and structural traits are related to the degree of CAM function in eight CAM species, as measured by CO(2) assimilation during the CAM and C(3) phases. Increased cell size and leaf succulence were not closely related to the degree of CAM function, indicating that succulence beyond a certain threshold does not enhance CAM function. Reduced IAS and L(mes)/area were positively related to CAM function, and negatively related to C(3) function. These results indicate that reduced IAS and L(mes)/area are beneficial for CAM function through the reduction of CO(2) efflux and the improvement of carbon economy. However, reduced IAS and L(mes)/area limit C(3) photosynthesis, potentially mediating a bimodal distribution of weak and strong CAM species with high and low IAS and L(mes)/area values, respectively.