Contrasting species responses to continued nitrogen and phosphorus addition in tropical montane forest tree seedlings

Global changes in nutrient deposition rates are likely to have profound effects on plant communities, particularly in the nutrient‐limited systems of the tropics. We studied the effects of increased nutrient availability on the seedlings of six tree species in montane forests of southern Ecuador in situ. After five years of continued N, P, or N+P addition, naturally grown seedlings of each of the two most common species at each elevation (1000, 2000, and 3000 m asl) were harvested for analyses of leaf morphology, nutrient content, herbivory, and tissue biomass allocation. Most species showed increased foliar N and P concentrations after addition of each respective element. Leaf tissue N:P ratios of >20 in the control plants of all species suggest that P is more growth‐limiting in these forests than N. Leaf morphological responses to nutrient addition were species and nutrient specific, with some species (Hedyosmum purparescens, Graffenrieda emarginata) exhibiting increased specific leaf area (SLA), and others (Graffenrieda harlingii) increased leaf area ratios (LAR). Pouteria torta (1000 m) had lower SLA and LAR after P addition. Increased herbivory was only evident in G. emarginata (after N and N+P addition). Only the species from 3000 m asl modified biomass allocation after nutrient addition. In general, N and N+P addition more strongly affected the species studied at the upper elevations, whereas P addition had a similar range of effects on the species at all elevations. We conclude that the responses of the studied tropical montane forest tree seedlings to chronic N and P addition are highly species‐specific and that successful adaptation to increased nutrient availability will depend on species‐specific morphological and physiological plasticity.     

The ectomycorrhizal fungus Scleroderma bermudense alleviates salt stress in seagrape (Coccoloba uvifera L.) seedlings

The purpose of this study was to test the capacity of the ectomycorrhizal (ECM) fungus, Scleroderma bermudense, to alleviate saline stress in seagrape (Coccoloba uvifera L.) seedlings. Plants were grown over a range (0, 200, 350 and 500 mM) of NaCl levels for 12 weeks, after 4 weeks of non-saline pre-treatment under greenhouse conditions. Growth and mineral nutrition of the seagrape seedlings were stimulated by S. bermudense regardless of salt stress. Although ECM colonization was reduced with increasing NaCl levels, ECM dependency of seagrape seedlings increased. Tissues of ECM plants had significantly increased concentrations of P and K but lower Na and Cl concentrations than those of non-ECM plants. Higher K concentrations in the leaves of ECM plants suggested a higher osmoregulating capacity of these plants. Moreover, the water status of ECM plants was improved despite their higher evaporative leaf surface. The results suggest that the reduction in Na and Cl uptake together with a concomitant increase in P and K absorption and a higher water status in ECM plants may be important salt-alleviating mechanisms for seagrape seedlings growing in saline soils.     

Growth responses of tropical deciduous tree seedlings to contrasting light conditions

Summary The growth responses of seedlings of Amphipterygium adstringens, Caesalpinia eriostachys, and C. platyloba, species associated with undisturbed parts of the tropical deciduous forest in México, and Apoplanesia paniculata and Heliocarpus pallidus, two gap-requiring pioneer species, were determined under contrasting light conditions in a growth chamber experiment. The high (400 mol m^–2 s^–1) and low (80 mol m^–2 s^–1) light treatments correspond to the light available in a medium size gap and underneath the vegetation canopy in the deciduous forest during the rainy season, respectively. Following four destructive harvests the biomass production, relative growth rate, root/shoot ratio, specific leaf area, net assimilation rate, leaf area ratio and light dependency were determined for all species. In the high light treatment all species achieved higher relative growth rates and net assimilation rates than when growing at low light intensity. However, the two pioneer species showed the highest light dependency and were the species more affected by the low light treatment in biomass production. The two Caesalpinia species showed similar growth responses, but C. platyloba was the most shade tolerant species. Plastic adjustments in terms of the specific leaf area were more evident in the two pioneer species.     

Growth response of Afzelia africana Sm. seedlings to ectomycorrhizal inoculation in a nutrient-deficient soil

 The growth and mineral nutrition responses of seedlings of two provenances of Afzelia africana Sm. from Senegal and Burkina Faso, inoculated with four ectomycorrhizal (ECM) fungi (Scleroderma spp. and an unidentified isolate) from the same regions were assessed in a pot experiment in a savanna ECM-propagule-free soil deficient in NPK. There was little variation in the ability of the different fungal species to colonize roots of either provenance of A. africana or to produce external hyphal in soil. Root colonization by ECM fungi and their hyphal development were not related to mineral nutrition or ECM dependency. Differences in P, N, Mg and Ca concentrations in the leaves of inoculated and non-inoculated Afzelia seedlings were not always associated with production of biomass. Only leaf K concentration increased in both provenances after ECM inoculation. However, the Burkina Faso provenance responded better to inoculation with the two fungal isolates than the Senegal provenance in terms of biomass production. This was due to stimulation of root dry weight of the Burkina Faso provenance. Therefore, the hypothesis arises that non-nutritional rather than nutritional effects explain the contribution of ECM inoculation to the growth of A. africana seedlings. Accepted: 27 April 1999     

Characteristic responses of three tropical legumes to the inoculation of two species of VAM fungi in Andosol soils with different fertilities

The growth and mineral nutrition responses were evaluated of three tropical legumes, cowpea (Vigna unguiculata L. cv Kuromame), pigeonpea [Cajanus cajan L. (Millsp.) cv ICPL 86009] and groundnut (Arachis hypogaea cv Nakateyutaka) inoculated with two different species of VAM fungi, Glomus sp. (Glomus etunicatum-like species) and Gigaspora margarita, and grown in Andosols with different fertilities [Bray II-P: topsoil (72 ppm), subsoil (<0.1 ppm)]. Percent fungal root colonization was high in cowpea and groundnut but relatively low in pigeonpea in both soil types. Despite the low rate of root infection, significant growth responses were produced, especially in the inoculated pigeonpea plant. In all legumes, shoot dry matter production was favoured by the inoculations. Increases in shoot biomass due to mycorrhizae were greater in the subsoil than in the topsoil. Mycorrhization raised shoot concentrations of P and Ca (in cowpea and groundnut) and P and K (in pigeonpea) in the topsoil. Whereas the P concentration in shoots in the subsoil was not positively affected by VAM fungi, particularly in cowpea and pigeonpea, the concentration of K in such plants was significantly increased by VAM treatment. The results also showed that mycorrhizal enhancement of shoot micronutrient concentrations was very rare in all plants, with negative effects observed in certain cases. Cu concentration, in particular, was not affected by VAM formation in any of the plants, and Mn and Fe in pigeonpea and groundnut, respectively, remained the same whether plants were mycorrhizal or not. In both soils the three legumes responded to Glomus sp. better than to Gigaspora margarita, and the effects of the VAM fungi on each of the crops relative to the controls were greater in the subsoil than in the topsoil. However, shoot growth of groundnut was not affected as much as cowpea and pigeonpea by the type of soil used. In spite of the relatively low infection of its root, pigeonpea was generally the most responsive of the three legume species in terms of mycorrhizal/nonmycorrhizal ratios.     

Effect of time of inoculation on in vitro ectomycorrhizal colonization and nodule initiation in Acacia holosericea seedlings

The complex interactions that occur in systems with more than one type of symbiosis were studied using one isolate of Bradyrhizobium sp. and the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch inoculated on to the roots of Acacia holosericea A. Cunn. ex G. Don in vitro. After a single inoculation with Bradyrhizobium sp., bacteria typically entered the roots by forming infection threads in the root hair cells via the curling point of the root hair and/ or after intercellular penetration. Sheath formation and intercellular penetration were observed on Acacia roots after a single inoculation with Pisolithus tinctorius but no radial elongation of epidermal cells. Simultaneous inoculation with both microorganisms resulted in nodules and ectomycorrhiza on the root system, occasionally on the same lateral root. On lateral roots bearing nodules and ectomycorrhiza, the nodulation site was characterized by the presence of a nodule meristem and the absence of an infection thread; sheath formation and Hartig net development occurred regularly in the region of the roots adjacent to nodules. Prior inoculation with Bradyrhizobium sp. did not inhibit ectomycorrhizal colonization in root segments adjacent to nodules in which nodule meristems and infection threads were clearly present. Conversely, in ectomycorrhizae inoculated by bacteria, the nodule meristem and the infection thread were typically absent. These results show that simultaneous inoculation with both microorganisms inhibits infection thread development, thus conferring an advantage on fungal hyphae in the competition for infection sites. This suggests that fungal hyphae can modify directly and/or indirectly the recognition factors leading to nodule meristem initiation and infection thread development.     

Photosynthesis and photoinhibition after night chilling in seedlings of two tropical tree species grown under three irradiances

We investigated the physiological effect of night chilling (CN) on potted seedlings of two tropical tree species, Calophyllum polyanthum and Linociera insignis, in Xishuangbanna, southwest China. Seedlings grown under 8, 25, and 50 % daylight for five months were moved to a 4–6 °C cold storage house for three consecutive nights, and returned to the original shaded sites during the day. CN resulted in strong suppression of photosynthesis and stomatal conductance for L. insignis, and reduced photorespiration rates, carboxylation efficiency, and maximum photochemical efficiency of photosystem 2 (PS2) at dawn and midday for both species. CN increased dawn and midday rates of non-photochemical quenching, and the contents of malondialdehyde and H₂O₂ for both species. CN also induced inactivation or destruction of PS2 reaction centres. The impacts of CN on tropical seedlings increased with the number of CN. Shading could significantly mitigate the adverse effects of CN for both species. After 3-d-recovery, gas exchange and fluorescence parameters for both species returned to pre-treatment levels in most cases. Thus CN induced mainly stomatal limitation of photosynthesis for L. insignis, and non-stomatal limitation for C. polyanthum. C. polyanthum was more susceptible to CN than L. insignis. Fog, which often occurs in Xishuangbanna, could be beneficial to chilling sensitive tropical seedlings in this area through alleviating photoinhibition or photodamage by reducing sunlight.     

Dormancy inDioscorea: Differences of temperature responses in seed germination among six Japanese species

Effects on seed germination of temperatures ranging from −2 C to +29 C were tested inDioscorea nipponica, D. tokoro, D. japonica, D. tenuipes, D. septemloba andD. quinqueloba which orginate in the temperate zone; they are distributed from northern cold areas to southern warm areas approximately in this order in Japan. After water imbibition of these seeds, chilling induced full germination, and high temperatures over 23 C induced a secondary dormancy, but sensitivities to the chilling and to the high temperatures differed with species. Cold-climate species germinated rapidly at higher temperatures after a short-term chilling or even without chilling, whereas warm-climate species required chilling of a rather long period for germination; thus, among 6 species tested, favourable temperatures for germination and climatic temperatures of distribution area were conversely correlated. Seeds ofD. tokoro andD. japonica collected from several populations grown in different climates were also tested for germination at 11 to 29 C; seeds from warm climates germinated rather slowly compared to seeds from cold climates. These inte- and intra-specific adaptation manners in the temperature members of the genusDioscorea are entirely different from those of many other plant genera reported by some workers.     

Root responses of flood-tolerant and flood-sensitive tree species to soil redox conditions

Summary Under controlled rhizotron conditions, roots of Taxodium distichum L., Quercus lyrata Walt, and Q. falcata var. pagodaefolia Ell. were subjected to low soil redox potentials. Root elongation was inhibited at low soil redox potentials. In T. distichum, redox potentials below +200 mV resulted in a significant inhibition of root elongation. In Q. falcata var. pagodaefolia and Q. lyrata, redox potentials below +350 mV resulted in complete cessation of root growth. Studies on root anatomy indicated that low soil redox potenials resulted in a changed cellular structure in the cortex of T. distichum. However, little change was noted in stress roots of oak species. Alcohol dehydrogenase activity in T. distichum roots was approximately doubled compared to control plants, indicating stimulated alcoholic fermentation. In T. distichum, alcoholic fermentation and anatomical changes contribute to flood tolerance but oak species lack these characteristics.     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

Seedling responses of four Australian tree species to toxic concentrations of manganese in solution culture

Little is known about the responses of Australian plants to excess metal, including Mn. It is important to remedy this lack of information so that knowledgeable decisions can be made about managing Mn contaminated sites where inhabited by Australian vegetation. Acacia holosericea, Melaleuca leucadendra, Eucalyptus crebra and Eucalyptus camaldulensis were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Mn treatments viz., 1, 8, 32, 128, 512 and 2048 M. The order of tolerance to toxic concentrations of Mn was A. holosericea E. crebra < M. leucadendra < E. camaldulensis, the critical external concentrations being approximately 5.1, 5.0, 21 and 330 M, respectively. The critical tissue Mn concentrations for the youngest fully expanded leaf and total shoots were, respectively, 265 and 215 g g^–1 DM for A. holosericea, 445 and 495 g g^–1 DM for M. leucadendra, 495 and 710 g g^–1 DM for E. crebra and 7230 and 6510 g g^–1 DM for E. camaldulensis. The high tolerance of E. camaldulensis (as opposed to the sensitivity of E. crebra) to excess Mn raises concern about fauna feeding on the plant and is consistent with hypotheses suggesting the Eucalyptus subgenus Symphomyrtus is particularly tolerant of stress, including excess Mn. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the management of Mn toxic sites.     

Fruit size in a tropical tree species: variation,preference by birds,and heritability

Ocotea tenera (Lauraceae), an understory bird-dispersed tree, produces single-seeded fruits that vary in diameter from 1.4 to 2.4 cm. Much of the variation within a population at Monteverde, Costa Rica occurred within individual trees. The relative size of fruits produced by different trees remained generally constant over an 11-year period despite slight differences between years in the average size of fruits produced by a given tree.Fruit-eating birds could thus express their preferences for particular fruit size characteristics by choosing among trees that have distinct distributions of fruit diameters, and between individually variable fruits within trees. In a field study of individually marked fruits, birds removed 46.2% of fruits; the rest of the fruits were destroyed by invertebrate (25.3%) and vertebrate (4.3%) pulp-feeders or aborted by the plant after remaining ripe but uneaten for as long as 100 days (24.2%). The four major avian seed dispersers of O. tenera each have gape widths exceeding all but the largest fruits. Birds preferred plants with greater-than-average-sized fruits; within trees, they favored larger fruits, apparently because net pulp mass increases with fruit diameter. Fruits that ripened early in the season were more likely to be removed and were removed more quickly than late-ripening fruits.Based on mother-offspring regressions of mean fruit size, the phenotypic variation in fruit diameter in O. tenera is highly heritable, indicating the potential for an evolutionary response to selection by birds. Nonetheless, directional selection on fruit size or shape is likely to be inconsistent, constrained by genetic correlations, and weak compared to selection on traits like fecundity or phenology.     

Contrasting mechanisms of secondary metabolite accumulation during leaf development in two tropical tree species with different leaf expansion strategies

Young leaves of most species experience remarkably higher herbivore attack rates than mature leaves. Considerable theoretical effort has focused on predicting optimal defense and tradeoffs in defense allocation during leaf expansion. Among others, allocation to secondary chemistry may be dependent on growth constraints. We studied flavanoid production during leaf development in two species of Inga (Fabaceae: Mimosoideae) with different expansion strategies: Inga goldmanii, a species with slowly expanding young leaves, and Inga umbellifera, a species with fast-expanding young leaves. In these two species, the most abundant and toxic class of defensive compounds is flavanoids (which include tannins). We measured their concentration by leaf dry weight, their total content per leaf, their HPLC chemical profile and their toxicity to a generalist herbivore at different expansion levels. Although in both species the flavanoid concentration decreased with increasing leaf expansion, that decrease was twice as pronounced for I. umbellifera as it was for I. goldmanii. I. umbellifera leaves produced flavanoids only during the first half of their development while I. goldmanii leaves continued production throughout. The changes in flavanoid HPLC profiles and toxicity were also more dramatic for I. umbellifera, which had different flavanoids in young than in mature leaves. Relative to I. umbellifera, I. goldmanii showed smaller changes in both flavanoid composition and toxicity in the transition from young to mature leaves. These results indicate that, even though young leaves suffer higher rates of attack and are predicted to have better chemical defenses than mature leaves, growth constraints may modulate defense allocation and thus, evolution of defense strategies.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Soil modification by different tree species influences the extent of seedling ectomycorrhizal infection

Established vegetation can facilitate the ectomycorrhizal infection of seedlings, but it is not known whether this interaction is limited by the phylogenetic relatedness of trees and seedlings. We use a series of bioassay experiments to test whether soil modification by different ectomycorrhizal tree species causes different levels of seedling infection, whether the extent of seedling infection is a function of the relatedness of tree and seedling, and whether the effect of trees on seedlings is mediated by biotic or abiotic soil factors. We found that soils from under different tree species do vary in their mycorrhizal infectiveness. However, this variation is not related to the genetic relatedness of trees and seedlings but instead, appears to be an attribute of the overstory species, irrespective of seedling species, mediated through a suite of humus- and base-cation-related abiotic effects on soils. Modification of abiotic soil properties by overstory trees should be considered as an important factor in the effect of different overstory trees on the extent of seedling mycorrhizal infection.     

Seedling responses of three Australian tree species to toxic concentrations of zinc in solution culture

A frequently desired outcome when rehabilitating Zn toxic sites in Australia is to establish a self-sustaining native ecosystem. Hence, it is important to understand the tolerance of Australian native plants to high concentrations of Zn. Very little is known about the responses of Australian native plants, and trees in particular, to toxic concentrations of Zn. Acacia holosericea, Eucalyptus camaldulensis and Melaleuca leucadendra plants were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Zn treatments viz., 0.5, 5, 10, 25, 50 and 100 M. The order of tolerance to toxic concentrations of Zn was E. camaldulensis> A. holosericea> M. leucadendra, the critical external concentrations being approximately 20, 12 and 1.5 M, respectively. Tissue Zn concentrations increased as solution Zn increased for all species. Root tissue concentrations were higher than shoot tissue concentrations at all solution Zn concentrations. The critical tissue Zn concentrations were approximately 85 and 110 g g^–1 DM for M. leucadendra, 115 and 155 g g^–1 DM for A. holosericea and 415 and 370 g g^–1 DM for E. camaldulensis for the youngest fully expanded leaf and total shoots, respectively. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the rehabilitation of potentially Zn toxic sites.     

The effect of ectomycorrhizal fungi on Zn uptake and distribution in seedlings of Pinus sylvestris L

Seedlings of pine, infected with two different ectomycorrhizal fungi, Suillus bovinus (Fr.) O. Kuntze and an unidentified isolate (BP), were exposed to various external Zn concentrations. An additional strain of S. bovinus, cultured on a Zn-enriched medium, was also used. The effect of mycorrhizal associations on Zn uptake and distribution within the plant was determined by AAS.The results show that nonmycorrhizal seedlings have the capability to control the uptake and translocation of Zn to the shoot until the external Zn concentration reaches a threshold level, where no limitation of uptake is possible. Excess Zn is accumulated in the root system to protect the shoot against toxic tissue concentrations. The effect of an ectomycorrhizal infection on Zn uptake and distribution depends on (1) the fungal species (2) the external concentration and (3) the Zn content of the fungal culture medium. Under conditions of low external Zn supply, especially a mycorrhizal infection with S. bovinus led to an increased Zn uptake in root and needles of Pinus sylvestris. Under high external conditions the mycobionts varied considerably in their capability to reduce the transport of Zn to the shoot. Only by an infection with S. bovinus the plant was able to maintain the shoot tissue concentration on a low level. This effect can be enhanced by pretreatment of S. bovinus with high Zn concentrations.     

Potential of Crotalaria species as green manure crops for the management of pathogenic nematodes and beneficial mycorrhizal fungi

On the basis of preliminary experiments, some Crotalaria species from Senegal were investigated to determine (1) their susceptibility to Meloidogyne javanica and M. incognita compared to a sensitive host (tomato), (2) their mycorrhizal and rhizobial responses, and (3) the effect of their cultivation on the mycorrhizal soil infectivity. The nematode invasion rates on Crotalaria spp. ranked from 0.17 to 7.17% and from 0.58 to 5.25%, respectively, for M. incognita and M. javanica, vs. 97% and 77% on tomato. Moreover, the inoculated J2 which invaded tomatoes developed into adult females, while those on Crotalaria spp. rarely developed beyond the third stage, confirming that all Crotalaria spp. evaluated are non hosts or poor hosts. In two other experiments, Crotalaria spp. were inoculated with an arbuscular mycorrhizal fungus (Glomus intraradices). Mycorrhization was generally well developed among Crotalaria species, and mycorrhizal colonization enhanced mainly phosphorus content of shoot tissues and always significant plant growth. Inoculation with both rhizobial isolates and Glomus intraradices enhanced growth and nodule formation on some Crotalaria species. The data recorded in both experiments showed, for the first time, that Crotalaria spp. are highly mycorrhiza dependent, some of them reaching more than 90% mycorrhizal dependency. Among Crotalaria species, twelve were used in two different experiments. A significant correlation was obtained between their mycorrhizal dependencies calculated on the shoot dry mass recorded in each experiment. Crotalaria spp. could be used as pre-crops for providing green manure while at the same time decreasing the level of detrimental nematodes and increasing the level of beneficial mycorrhizal fungi.     

Factors affecting the initiation and growth of aboveground adventitious roots in a tropical cloud forest tree: an experimental approach

Some of the proximate factors that would induce aboveground stems to produce adventitious roots were investigated experimentally on Senecio cooperi, a tropical cloud forest tree. Stem segments were air-layered with different treatments to promote root formation, and the number of roots initiated and rates of root growth were monitored for 20 weeks. Treatments were the application of wet epiphytes or dry epiphytes plus associated humus, sponges wetted with either water or nutrient solutions, or dry sponges. Controls (stem segments with nothing applied) were also monitored. Numbers of adventitious roots formed and rates of subsequent root growth differed among treatments. Wet epiphyte/humus and nutrient solutions were most effective in producing roots, which suggests that epiphytes and the nutrients they intercept and retain within the canopy may cue adjacent host tissue to exploit this resource.     

金银花容器苗对干旱胁迫下接种根际促生细菌的生理响应

在盆栽试验条件下,以金银花容器苗为试材,研究了不同干旱强度下接种蜡样芽孢杆菌(Bacillus cereus)L90对植物生理特征的影响。结果表明:随着干旱胁迫强度的增加,金银花容器苗的光合速率和气孔导度逐渐降低;而干旱环境下接种L90可显著提高气孔导度,缓解干旱胁迫对净光合速率的抑制;且干旱强度增加,缓解效果增强。接种B.cereus L90可显著抑制干旱胁迫下金银花容器苗PSⅡ最大光化学效率、实际光化学效率和光化学猝灭系数的降低,抑制非光化学猝灭系数的升高。虽然L90并没有提高对照处理中光合色素的绝对含量,但可显著抑制干旱环境下金银花叶片中光合色素的分解。干旱显著降低了金银花叶片中细胞分裂素含量,增加了脱落酸(ABA)的含量;在干旱胁迫下,接种L90可显著提高叶片中细胞分裂素的含量,并可促使根部产生的ABA运输到叶片中。干旱胁迫程度较轻时,L90对金银花容器苗的相对含水量和相对电导率影响不显著;而在重度干旱时,同对照相比,干旱及接种L90处理的相对含水量分别降低20.56%和10.21%,相对电导率分别提高31.42%和16.08%,接种L90处理的变化幅度明显较小。因此,干旱生境下接种B.cereus L90,可增加叶片中细胞分裂素含量,抑制光合色素的分解及光合能力的下降,提高金银花容器苗在干旱环境中的适应能力。