Interactive effects of α-NAA and UV-B radiation on the endogenous hormone contents and growth of Trichosanthes kirilowii Maxim seedlings

The impact of UV-B radiation on endogenous hormones in plants has recently drawn attention from researchers. The mechanism for reduced stem elongation by UV-B might be due to changes in the phytohormone levels, especially IAA, which plays a role in stem elongation. In this study, effects of UV-B radiation on Trichosanthes kirilowii Maxim (T. kirilowii) seedlings in greenhouse-grown plants were investigated. The results indicated that: (1) In comparison to controls, exposure to 0.029 Jm^?2 s^?1. UV-B radiation led to accumulation of endogenous abscisic acid (ABA) and zeatinriboside (ZR) in the plant contents, and decreased contents of endogenous indole-3-acetic acid (IAA) and gibberellic acid (GA_1/3). Exposure to UV-B radiation reduced the height and leaf area of plants. As a result, total biomass (plant dry weight) was lower. (2) In comparison to controls, addition of 2 mg l^?1 α-naphthaleneacetic acid (α-NAA) slightly increased the contents of IAA, GA_1/3 and ZR, and decreased the content of ABA in leaves. This addition of α-NAA significantly increased plant height and leaf area, but only slightly increased total biomass. (3) Addition of α-NAA to UV-B-exposed plants: increased the content of endogenous IAA, GA_1/3 and ZR; decreased accumulation of endogenous ABA; and increased plant height and leaf area in comparison to plants that only were exposed to UV-B. Moreover, total biomass increased slightly. This suggests that addition of α-NAA may compensate to a certain extent for the lack of IAA resulting from UV-B radiation; it also increases the content of GA_1/3 and ZR, decreases the accumulation of ABA, and promotes the growth of plants.     

Effects of dwarf bamboo (Fargesia denudata) density on biomass, carbon and nutrient distribution pattern

Dense dwarf bamboo population is a structurally and functionally important component in many subalpine forest systems. To characterize the effects of stem density on biomass, carbon and majority nutrients (N, P, K, Ca and Mg) distribution pattern, three dwarf bamboo (Fargesia denudata) populations with different stem densities (Dh with 220 ± 11 stems m^?2, Dm with 140 ± 7 stems m^?2, and Dl with 80 ± 4 stems m^?2, respectively) were selected beneath a bamboo-fir (Picea purpurea) forest in Wanglang National Nature Reserve, Sichuan, China. Leaf, branch, rhizome, root and total biomass of dwarf bamboo increased with the increase of stem density, while carbon and nutrient concentrations in bamboo components decreased. Percentages of below-ground biomass and element stocks to total biomass and stocks decreased with the increase of stem density, whereas above-ground biomass and element stocks exhibited the opposite tendency. Moreover, more above-ground biomass and elements were allocated to higher part in the higher density population. In addition, percentages of culm biomass, above-ground biomass and element stocks below 100 cm culm height (H₁₀₀) increased with the increase of stem density, while percentages of branch and leaf biomass below H₁₀₀ decreased. Pearson’s correlation analyses revealed that root biomass, above-ground biomass, below-ground biomass and total biomass significantly correlated to leaf biomass in H_100?200 and total leaf biomass within high density population, while they significantly correlated to leaf biomass in H_50?150 within low density population. The results suggested that dwarf bamboo performed an efficient adaptive strategy to favor limited resources by altering biomass, carbon and nutrients distribution pattern in the dense population.     

Effects of dwarf bamboo (Fargesia denudata) density on biomass, carbon and nutrient distribution pattern

Dense dwarf bamboo population is a structurally and functionally important component in many subalpine forest systems. To characterize the effects of stem density on biomass, carbon and majority nutrients (N, P, K, Ca and Mg) distribution pattern, three dwarf bamboo (Fargesia denudata) populations with different stem densities (Dh with 220 ± 11 stems m^?2, Dm with 140 ± 7 stems m^?2, and Dl with 80 ± 4 stems m^?2, respectively) were selected beneath a bamboo-fir (Picea purpurea) forest in Wanglang National Nature Reserve, Sichuan, China. Leaf, branch, rhizome, root and total biomass of dwarf bamboo increased with the increase of stem density, while carbon and nutrient concentrations in bamboo components decreased. Percentages of below-ground biomass and element stocks to total biomass and stocks decreased with the increase of stem density, whereas above-ground biomass and element stocks exhibited the opposite tendency. Moreover, more above-ground biomass and elements were allocated to higher part in the higher density population. In addition, percentages of culm biomass, above-ground biomass and element stocks below 100 cm culm height (H₁₀₀) increased with the increase of stem density, while percentages of branch and leaf biomass below H₁₀₀ decreased. Pearson’s correlation analyses revealed that root biomass, above-ground biomass, below-ground biomass and total biomass significantly correlated to leaf biomass in H_100?200 and total leaf biomass within high density population, while they significantly correlated to leaf biomass in H_50?150 within low density population. The results suggested that dwarf bamboo performed an efficient adaptive strategy to favor limited resources by altering biomass, carbon and nutrients distribution pattern in the dense population.     

Differential response of leaf gas exchange to enhanced ultraviolet-B (UV-B) radiation in three species of herbaceous climbingplants

We measured diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency in three species of herbaceous climbing plants (Luffa cylindrica, Trichosanthes kirilowii and Dioscorea opposita) exposed to two intensities of UV-B radiation: 3.0 μw cm^?2 (R1) and 8.0 μw cm^?2 UV-B (R2) radiation under ambient growth conditions. Responses differed per species and per treatment. In Luffa all values increased compared to the Control in both treatments, except for stomatal conductance in R2. In Trichosanthes photosynthetic rates and water use efficiency increased, while the transpiration rates decreased under both treatments, and stomatal conductance was lower in R1. In Dioscorea photosynthetic rates and water use efficiency decreased under both treatments, while the transpiration rates and stomatal conductance increased. The results suggested that to some extent increased UV-B radiation was beneficial to the growth of L. cylindrica and T. kirilowii, but detrimental to D. opposita.     

Differential response of leaf gas exchange to enhanced ultraviolet-B (UV-B) radiation in three species of herbaceous climbingplants

We measured diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency in three species of herbaceous climbing plants (Luffa cylindrica, Trichosanthes kirilowii and Dioscorea opposita) exposed to two intensities of UV-B radiation: 3.0 μw cm^?2 (R1) and 8.0 μw cm^?2 UV-B (R2) radiation under ambient growth conditions. Responses differed per species and per treatment. In Luffa all values increased compared to the Control in both treatments, except for stomatal conductance in R2. In Trichosanthes photosynthetic rates and water use efficiency increased, while the transpiration rates decreased under both treatments, and stomatal conductance was lower in R1. In Dioscorea photosynthetic rates and water use efficiency decreased under both treatments, while the transpiration rates and stomatal conductance increased. The results suggested that to some extent increased UV-B radiation was beneficial to the growth of L. cylindrica and T. kirilowii, but detrimental to D. opposita.     

Variations in Growth, Photosynthesis and Defense System Among Four Weed Species Under Increased UV-B Radiation

Weed tolerance of UV-B radiation varies with species, and the radiation could affect weed ecology and management. Variations In growth, photosynthesis and defense system among four important agronomic weeds, Abutllon theophrastl Medlk, Amaranthus retroflexus L., Digitaria sanguinalis （L.） Scop and Chloris virgata Swartz, under Increased UV-B radiation （ambient and increased radiation at 2.7, 5.4 and 10.8 kJ.m^-2.d-1） were studied In the greenhouse experiment. After 2 weeks of radiation, the shoots＇ dry mass decreased with increasing UV-B radiation except for D. sanguinalis. The reduction in biomass was the result of changes in morphology and physiology. Higher levels of UV-B treatment decreased the leaf area, plant height, net photosynthetic rate and chlorophyll contents, while it increased the contents of wax and UV-B absorbing compound in all species, except for A. retroflexus, which did not increase significantly. The activity of superoxide dismutase, catalase, ascorbate peroxide and the content of ascorblc acid changed differently among the weed species as UV-B radiation increased. D. sangulnalls was the most tolerant and A. retroflexus the most sensitive to increased UV-B radiation. The results also show that the two grass species （D. sanguinalis and C. virgata） were more tolerant to UV-B radiation than the two broadleafed species （A. theophrasti and A. retroflexus）. The UV-B absorbing compound and leaf wax played Important roles against UV-B damages in the two grass weeds. The overall results suggest that weed community, competition and management will be altered by continuous ozone depletion.     

Soybean residues sequestration affected by different tillage practices and the impacts on soil microbial characteristics and enzymatic activities

A large quantity of leaf litter was left on soil surface after soybean (Glycine max) harvest in the black soil region, northeast of China, where soybean was planted with the largest area. This paper investigated the effects of different fall tillage practices on soybean leaf litter sequestration into soil, and the subsequently durative effects on soil biological and biochemical properties during the next growing season. Two practices were investigated, fall tillage (T) and no fall tillage (NT) after soybean harvest in autumn. Results showed that the residue biomass on soil surface and in subsoil profile (0–20 cm) after soybean harvest was about 1450 kg ha^?1 and 340 kg ha^?1, respectively in October 2006. The residue biomass on soil surface and in subsoil profile was about 84 kg ha^?1, 1581 kg ha^?1 for T, and 423 kg ha^?1, 340 kg ha^?1 for NT respectively in May 2007. It was obvious that T practice can more effectively sequester leaf litter into soil compared to NT. Results also showed that T practices after soybean harvest eminently improved soil microbial carbon biomass and nitrogen biomass contents, and significantly improved soil urease and acid phosphate activities than NT. No significant difference of dehydrogenase activity was found between N and NT. The positive effects of T treatment on Soil microbial properties and soil enzymes activities among the next growing season due to soybean residues sequestration performed durative profit.     

Production of Polyamines Is Enhanced by Endogenous Abscisic Acid in Maize Seedlings Subjected to Salt Stress

It is known that salt stress and exogenously applied abscisic acid （ABA） can enhance the polyamine content in plants and that salt stress itself can lead to an increase in endogenous ABA production. In the present study, the relationships between salt-induced ABA and polyamine accumulation were inves- tigated using ABA-deficient mutant （vp5/vp5） maize （Zea mays L.） seedlings and ABA and polyamine biosynthesis inhibitors. The results show that reduced endogenous ABA levels, as a result of either the mutation or by using a chemical inhibitor （sodium tungstate）, also reduced the accumulation of polyamines in salt-stressed leaves of maize seedlings. The polyamine synthesis inhibitors D-arginine and α- difluoromethylornithine also reduced the polyamine content of the leaves of maize seedling under salt stress. Both ABA and polyamine enhanced the dry weight accumulation of salt-stressed seedlings and also increased the activities of the two dominant tonoplast membrane enzymes, H^＋-ATPase and H^＋-PPase, when plants were under salt stress. The results suggest that salt stress induces an increase in endogenous ABA levels, which then enhances polyamine synthesis. Such responses may increase a plant＇s tolerance to salt.     

Relationship between fresh leaf traits and leaf litter decomposition of 20 plant species in Kerqin sandy land, China

20 plant species (10 monocots and 10 dicots) grown in Kerqin sandy grassland were incubated under indoor conditions to monitor the amount and rate of CO₂ release from the leaf litter. 11 traits of mature fresh leaves including caloric value, contents of Mg, P, N, K, C, C/N, N/P, specific leaf area, dry matter content and leaf surface area were measured to determine the relationship between CO₂ release and leaf characteristics. All those traits have great variation among the 20 species with over 3 fold differences between the maximum and minimum values, and a few traits such as leaf Mg content reached as high as 9 folds. After 28 d's incubation, the average CO₂ release amount from all the species was (4121 ± 1713) μg kg^?1 dry soil. The highest level from Chenopodium acuminatum was (8767 ± 177) μg kg^?1 dry soil, which was 5 folds higher than the lowest level ((1669 ± 47)μg kg^?1 dry soil) from Digitaria sanguinalis. However, CO₂ release rate showed the same trend in all the 20 species, i.e., the leaf litter decomposed faster initially (0–4 d), and gradually slowed down during extended cultural periods. Comparison between monocots and dicots showed that these two taxonomic groups had significant differences in terms of the amount and rate of CO₂ released from leaf litter, and N and C contents, leaf C/N, and dry matter content of mature leaves. Contents of N, C and dry matter, and C/N of mature leaves are significantly correlated with CO₂ release from leaf litter decomposition, which has been revealed by the Pearson correlation test. It can be concluded that these three traits of mature leaves can be used indirectly to predict decomposition rate of the leaf litter.     

Relationship between fresh leaf traits and leaf litter decomposition of 20 plant species in Kerqin sandy land, China

20 plant species (10 monocots and 10 dicots) grown in Kerqin sandy grassland were incubated under indoor conditions to monitor the amount and rate of CO₂ release from the leaf litter. 11 traits of mature fresh leaves including caloric value, contents of Mg, P, N, K, C, C/N, N/P, specific leaf area, dry matter content and leaf surface area were measured to determine the relationship between CO₂ release and leaf characteristics. All those traits have great variation among the 20 species with over 3 fold differences between the maximum and minimum values, and a few traits such as leaf Mg content reached as high as 9 folds. After 28 d's incubation, the average CO₂ release amount from all the species was (4121 ± 1713) μg kg^?1 dry soil. The highest level from Chenopodium acuminatum was (8767 ± 177) μg kg^?1 dry soil, which was 5 folds higher than the lowest level ((1669 ± 47)μg kg^?1 dry soil) from Digitaria sanguinalis. However, CO₂ release rate showed the same trend in all the 20 species, i.e., the leaf litter decomposed faster initially (0–4 d), and gradually slowed down during extended cultural periods. Comparison between monocots and dicots showed that these two taxonomic groups had significant differences in terms of the amount and rate of CO₂ released from leaf litter, and N and C contents, leaf C/N, and dry matter content of mature leaves. Contents of N, C and dry matter, and C/N of mature leaves are significantly correlated with CO₂ release from leaf litter decomposition, which has been revealed by the Pearson correlation test. It can be concluded that these three traits of mature leaves can be used indirectly to predict decomposition rate of the leaf litter.     

Effects of abscisic acid or benzyladenine on pigment contents, chlorophyll fluorescence, and chloroplast ultrastructure during water stress and after rehydration

With the aim to contribute to the elucidation of the role of phytohormones in response of plants to adverse environmental conditions, seedlings of Phaseolus vulgaris, Nicotiana tabacum, Beta vulgaris, and Zea mays were supplied with water, 100 μM abscisic acid (ABA), or 10 μM N⁶-benzyladenine (BA) immediately before imposition of water stress (WS). In all four species, contents of chlorophylls (Chls) and carotenoids were markedly decreased during WS and after rehydration only in plants pre-treated with water but not in those pre-treated with ABA or BA. Contents of pigments of xanthophyll cycle increased during WS more in plants pre-treated with ABA or BA than in those pre-treated with water, but the degree of their de-epoxidation was highest in the later. Similarly, the efficiency of photosystem 2, determined as variable to maximal Chl fluorescence ratio, was not markedly decreased in bean plants pre-treated with ABA or BA in contrast to those pre-treated with water. The imposed WS was not severe enough to damage chloroplast ultrastructure. However, different changes in a size of starch inclusions were observed. In bean plants, the amount of starch increased considerably in plants pre-treated with water, while it decreased in BA pre-treated plants and no change was found in ABA pre-treated ones. The starch content declined under WS in sugar beet and tobacco plants but only moderate changes were found in ABA or BA pre-treated plants. Thus the application of BA and especially of ABA reduced the negative effects of subsequent WS.     

Soil respiration of two dominant tundra communities under controlled temperatures in Changbai Mountain, Northeast China

Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO₂ release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370–585 mg kg^?1, total nitrogen was 0.298%–0.468%, and organic matter was 13.5%–17.3%. In Rhododendron community, hydrolizable nitrogen was 445–583 mg kg^?1, total nitrogen was 0.465%–0.696%, and organic matter was 15%–22%. Organic matter within 10 cm depth was 4.07 kg m^?2 in Vaccinium community, and 5.31 kg m^?2 in the other. Temperature-dependent equations indicated that Q₁₀ values in both communities were around 2, with the ranges of 1.81–2.67 in Vaccinium community and 1.67–2.21 in Rhododendron community. The temperature-dependent equation was formed as y = ae^bx, where y is respiration rate (μmol kg^?1 h^?1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52–148 in Vaccinium community and 34–167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg^?1 d^?1) equation was y = 0.021733e^0.084063x for Vaccinium community, and y = 0.023482e^0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57–17.96 g C kg^?1 a^?1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg^?1 a^?1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m^?2, 12 g C m^?2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57–21.15 g C kg^?1 a^?1, with its maximum in May. By the integrated equation, it was 10.35 g C kg?1a^?1or 537 g C m^?2 a^?1. The yearly respiration was 441–544 g C m^?2 a^?1 in Vaccinium community and 449–486 g C m^?2 a^?1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C)^{? 1} a^?1 in Vaccinium community and 101 g C (kg C)^{? 1} a^?1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg?1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg?1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m^?2 a^?1, and the biomass growth was 400 g C m^?2 a^?1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m^?2 a^?1 versus the respiration rate of 486.60 g C m^?2 a^?1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m^?2 a^?1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.     

Soybean residues sequestration affected by different tillage practices and the impacts on soil microbial characteristics and enzymatic activities

A large quantity of leaf litter was left on soil surface after soybean (Glycine max) harvest in the black soil region, northeast of China, where soybean was planted with the largest area. This paper investigated the effects of different fall tillage practices on soybean leaf litter sequestration into soil, and the subsequently durative effects on soil biological and biochemical properties during the next growing season. Two practices were investigated, fall tillage (T) and no fall tillage (NT) after soybean harvest in autumn. Results showed that the residue biomass on soil surface and in subsoil profile (0–20 cm) after soybean harvest was about 1450 kg ha^?1 and 340 kg ha^?1, respectively in October 2006. The residue biomass on soil surface and in subsoil profile was about 84 kg ha^?1, 1581 kg ha^?1 for T, and 423 kg ha^?1, 340 kg ha^?1 for NT respectively in May 2007. It was obvious that T practice can more effectively sequester leaf litter into soil compared to NT. Results also showed that T practices after soybean harvest eminently improved soil microbial carbon biomass and nitrogen biomass contents, and significantly improved soil urease and acid phosphate activities than NT. No significant difference of dehydrogenase activity was found between N and NT. The positive effects of T treatment on Soil microbial properties and soil enzymes activities among the next growing season due to soybean residues sequestration performed durative profit.     

Soil respiration of two dominant tundra communities under controlled temperatures in Changbai Mountain, Northeast China

Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO₂ release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370–585 mg kg^?1, total nitrogen was 0.298%–0.468%, and organic matter was 13.5%–17.3%. In Rhododendron community, hydrolizable nitrogen was 445–583 mg kg^?1, total nitrogen was 0.465%–0.696%, and organic matter was 15%–22%. Organic matter within 10 cm depth was 4.07 kg m^?2 in Vaccinium community, and 5.31 kg m^?2 in the other. Temperature-dependent equations indicated that Q₁₀ values in both communities were around 2, with the ranges of 1.81–2.67 in Vaccinium community and 1.67–2.21 in Rhododendron community. The temperature-dependent equation was formed as y = ae^bx, where y is respiration rate (μmol kg^?1 h^?1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52–148 in Vaccinium community and 34–167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg^?1 d^?1) equation was y = 0.021733e^0.084063x for Vaccinium community, and y = 0.023482e^0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57–17.96 g C kg^?1 a^?1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg^?1 a^?1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m^?2, 12 g C m^?2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57–21.15 g C kg^?1 a^?1, with its maximum in May. By the integrated equation, it was 10.35 g C kg?1a^?1or 537 g C m^?2 a^?1. The yearly respiration was 441–544 g C m^?2 a^?1 in Vaccinium community and 449–486 g C m^?2 a^?1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C)^{? 1} a^?1 in Vaccinium community and 101 g C (kg C)^{? 1} a^?1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg?1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg?1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m^?2 a^?1, and the biomass growth was 400 g C m^?2 a^?1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m^?2 a^?1 versus the respiration rate of 486.60 g C m^?2 a^?1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m^?2 a^?1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.     

In vitro plant regeneration of Aristolochia indica through axillary shoot multiplication and organogenesis

Protocols for in vitro plant regeneration via axillary and adventitious shoot regeneration were established in an important medicinal plant, Aristolochia indica L. (Aristolochiaceae). Basal Murashige and Skoog's (MS) medium supplemented with 0.54 μM α-naphthaleneacetic acid (NAA) and 13.31 μM benzyladenine (BA) induced the maximum number of shoots (45-50) from shoot tip and nodal segment cultures. Phenolic accumulation in leaf and internodal stem derived callus cultured in MS medium containing NAA or 2,4-dichlorophenoxyacetic acid and BA or kinetin was controlled by the addition of 1.0 mg l^-1 phloroglucinol (PG) to the callus induction medium. Basal medium supplemented with 2.69 μM NAA, 13.31 μM BA and 1.0 mg l^-1 PG induced the best results in terms of shoot bud regeneration from leaf derived callus. Direct de novo development of shoots from leaf segments was achieved using 13.31 μM BA along with 50 mg l^-1 activated charcoal. The microshoots were rooted in White's medium supplemented with 2.46 μM indolebutyric acid. More than 85% of rooted plants survived in the soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reviewing the Technical Designs for Experiments with Ultraviolet-B Radiation and Impact on Photosynthesis,DNA and Secondary Metabolism

The ultraviolet-B(UV-B) portion of sunlight has received much attention in the last three decades,because radiation from this spectral region increases due to the stratospheric ozone depletion,which results from increases of chlorofluorocarbons in the atmosphere.Plant responses to UV-B exposure vary greatly and the interpretation of and comparison between studies is hindered,mainly by the contrasting experimental conditions used and interactive factors such as low light levels and possible artifacts due to the artificial experimental conditions.It seems likely that increases in solar UV-B radiation of the magnitude anticipated under current stratospheric ozone projections will not significantly inhibit photosynthesis and cause DNA damage in plants.This is in part due to the wellevolved protection mechanisms present in most plant species.One of the significant plant responses to UV-B is changes in foliar secondary chemistry,which could be translated into significant effects at higher trophic levels through plant-herbivore interactions and decomposition.Enhanced UV-B radiation due to stratospheric ozone depletion could also cause morphological changes that would affect competitive interactions,especially if contrasting UV-B sensitivity exists among the competitors.     

Effect of salinity, gibberellic acid and Azospirillum inoculation on growth and nitrogen uptake of Zea mays

Pot experiments were conducted to evaluate the possible interaction of salinity (osmotic potential -0.3, -0.9 and -1.2 MPa) and occurrence of Azospirillum lipoferum or exogenous gibberellic acid (GA₃) (100 μg g^-1) on growth and some physiological parameters of maize. ¹⁵N-uptake as well as the percentage of nitrogen derived from ¹⁵N-fertilizer were decreased by increasing the NaCl concentrations and completely inhibited at concentrations corresponding to osmotic potentials -0.9 and -1.2 MPa. The percentage of nitrogen originating from N₂ fixation was significantly correlated to the total counts of Azospirillum cells that colonized the histosphere. At high NaCl concentrations although no significant changes in N % in shoot dry mass either in inoculated or uninoculated plants were observed, the total N-yield [mg(N) pot^-1] was decreased. Fresh and dry shoot mass significantly increased by Azospirillum inoculation. Azospirillum and GA₃ treatments were positively correlated with most of the parameters analysed. Azospirillum inoculation or GA3 application at NaCl concentrations up to -1.2 MPa significantly increased the chlorophyll, K, Ca, soluble saccharides and protein contents as compared with control plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Responses of <Emphasis Type="Italic">Nigella sativa</Emphasis> to foliar application of gibberellic acid and kinetin

Foliar sprays of water or 1, 10 and 100 μM aqueous solutions of gibberellic acid (GA₃) or kinetin (KIN) were applied to 40-d-old plants of Nigella sativa (L.) to study their effects on net photosynthetic rate, nitrogen metabolism, and the seed yield. 10 μM solutions of both the hormones, especially GA₃, appreciably increased the activities of nitrate reductase and carbonic anhydrase, chlorophyll and total protein contents and net photosynthetic rate in the leaves, along with capsule number and seed yield plant⁻¹, at harvest.     

Rehabilitation of a tailing dam at Shimen County, Hunan Province: Effectiveness assessment

This study was conducted to assess the effectiveness of phytoremediation on a tailing dam located in Shimen County, Hunan Province. Quadrat survey method was employed to investigate and sample the dominant plant species growing on the rehabilitated tailing dam. The fertilities of the soils were assessed, and concentrations of arsenic and other heavy metals in the plant and soil samples were measured. The results showed that no difference was found on the effect of soil capping with top and non-topsoils for rehabilitation of plants on the tailing dam. After rehabilitation, stable vegetation coverage types were established, 39 plant species were found to grow on the tailing dam, and the minimal area for plant communities was 30 m². The dominant plant species were planted Pteris vittata and natural colonizing Miscanthus sinensis. The contents of organic matter, nitrogen and phosphorus in the soils were low, while the potassium content was at a middle level; however, plots where Legumina plants grew were found to have higher level of nitrogen and phosphorus in the growing soils. Arsenic (As) and Cadmium (Cd) concentrations in the soils were 8 and 7 times of the grade III value of the National Standard for Soil Quality (GB15618-1995), respectively; while in tailings these were 81 and 68 times. The available As concentration in the soils ranged as 3.7–29.5 mg kg^?1, whereas the available As concentration in tailings was as high as 61.1 mg kg^?1. Concentrations for most of the heavy metals were in the normal range of terrestrial higher plants, except As and Cd in P. vittata and M. sinensis, and As in the roots of M. sinensis. It is concluded that phytoremediation project has reduced the ecological and health risks caused by the tailing dam to the ambient environment. However, the plants growing on the tailing dam which contained high As and Cd should be kept from entering into food chain in order to protect the health of local residents.     

Stomatal movement in response to long distance-communicated signals initiated by heat shock in partial roots of Commelina communis L.

The systematic or long-distance signal transmission plays crucial roles in animal lives. Compared with animals, however, much less is known about the roles of long-distance signal communication in plant lives. Using the model plant Commelina communis L., we have probed the root to shoot communication mediated by heat-shock signals. The results showed that a heat shock of 5 min at 40℃ in partial roots, i.e. half or even 1/4 root system, could lead to a significant decrease in stomatal conductance. The regulation capability depends on both heat shock temperature and the amount of root system, i.e. with higher temperature and more roots stressed, the leaf conductance would decrease more significantly. Interestingly, the stomatal regulation by heat shock signal is in a manner of oscillation: when stomata conductance decreased to the lowest level within about 30 min, it would increase rapidly and sometimes even exceed the initial level, and after several cycles the stomata conductance would be finally stabilized at a lower level. Feeding xylem sap collected from heat-shocked plants could lead to a decrease in stomata conductance, suggesting that the heat shock-initiated signal is basically a positive signal. Further studies showed that heat shock was not able to affect ABA content in xylem sap, and also, not able to lead to a decrease in leaf water status, which suggested that the stomatal regulation was neither mediated by ABA nor by a hydraulic signal. Heat shock could lead to an increase in xylem sap H₂O₂ content, and moreover, the removal of H₂O₂ by catalase could partially recover the stomatal inhibition by xylem sap collected from heat-shocked plants, suggesting that H₂O₂ might be able to act as one of the root signals to control the stomatal movement. Due to the fact that heat-shock and drought are usually two concomitant stresses, the stomatal regulation by heat-shock signal should be of significance for plant response to stresses. The observation for the stomatal regulation in an oscillation manner by presently identified new signals should contribute to further understanding of the mystery for the pant systematic signaling in response to stresses.