Effects of Elevated Ozone Concentrations on Root Characteristics and Soil Properties of Elaeocarpus sylvestris and Michelia chapensis.

The increasing concentration of surface ozone (O3) was observed during recent decades in the world, which affects tree roots and forest soils. Meanwhile, the impact of ozone on tree roots is greatly affected by soil condition. However, there is a lack of knowledge about the possible effects of ozone on tree roots and soil processes. In this study, The influences of surface ozone (O3) stress on the root biomass, morphology, nutrients, soil properties, and soil enzyme activity of Elaeocarpus sylvestris and Michelia chapensis seedlings were examined at four O3 concentrations (charcoal-filtered air, 1 × O3 air, 2 × O3 air, and 4 × O3 air). Elevated O3 concentrations were found to significantly increase the root C content, N content, C/P ratio, and N/P ratio, and significantly decrease the root biomass, number of root tips, and root C/N ratio of both species. The soil organic matter content, pH, total N content, and urease and catalase activities of both species tended to increase. The limitation in root growth and responses in the root structure of E. sylvestris induced by elevated O3 concentrations led to increased bulk density and decreased soil porosity and void ratio. These profound effects of O3 concentrations on the roots and soil characteristics of these two species underscore the importance of research in O3 science.

Expressed sequence tag analysis of functional genes associated with adventitious rooting in Liriodendron hybrids.

Liriodendron hybrids (Liriodendron chinense x L. tulipifera) are important landscaping and afforestation hardwood trees. To date, little genomic research on adventitious rooting has been reported in these hybrids, as well as in the genus Liriodendron. In the present study, we used adventitious roots to construct the first cDNA library for Liriodendron hybrids. A total of 5176 expressed sequence tags (ESTs) were generated and clustered into 2921 unigenes. Among these unigenes, 2547 had significant homology to the non-redundant protein database representing a wide variety of putative functions. Homologs of these genes regulated many aspects of adventitious rooting, including those for auxin signal transduction and root hair development. Results of quantitative real-time polymerase chain reaction showed that AUX1, IRE, and FB1 were highly expressed in adventitious roots and the expression of AUX1, ARF1, NAC1, RHD1, and IRE increased during the development of adventitious roots. Additionally, 181 simple sequence repeats were identified from 166 ESTs and more than 91.16% of these were dinucleotide and trinucleotide repeats. To the best of our knowledge, the present study reports the identification of the genes associated with adventitious rooting in the genus Liriodendron for the first time and provides a valuable resource for future genomic studies. Expression analysis of selected genes could allow us to identify regulatory genes that may be essential for adventitious rooting.

[Effect of Invasive Herb Species on the Structure of Soil Yeast Complexes in Mixed Forests Exemplified by Impatiens parviflora DC].

Yeast abundance and diversity in a mixed forest sod-podzol soil under Impatiens parviflora DC plants was studied in comparison with unimpaired aboriginal herbaceous plants typical of the Mid-Russian secondary, after-forest meadow. The study was carried out throughout the vegetation period. Standard microbiological plating techniques revealed 36 yeast species. Typical pedobiotic (Cryptococcus podzolicus, Wickerhamomyces anomalus) and eurybiotic yeast species (Rhodotorula mucilaginosa) predominated in both biotopes. The relative abundance of the autochthonous soil yeast species Cryptococcus podzolicus was higher in the soil under aboriginal herbs than under Impatiens parviflora. Sites with aboriginal vegetation were also characterized by high abundance of the pedogamous species Schwanniomyces castelli and Torulaspora delbrueckii. The share of yeastlike Trichosporon fungi with high hydrolytic activity was considerably higher under adventitious plants Impatiens parviflora, as well as in the previously studied soil under Heracleum sosnowskyi.

Benefit of shading by nurse plant does not change along a stress gradient in a coastal dune.

The proximity of adult neighbors often increases the performance of woody seedlings under harsh environmental conditions but this nurse plant effect becomes less intense when abiotic stress is alleviated, as predicted by the stress gradient hypothesis (SGH). Although some studies have tested how the net nurse effect is changed by stress, few studies have tested how the mechanism that drives the facilitative effect of nurse responds to changes in stress. We conducted field experiments in a subtropical coastal dune to test if shading drives the known nurse effect of adults of the tree Guapira opposita on seedling performance of another tree species, Ternstroemia brasiliensis. We transplanted T. brasiliensis seedlings to three neighbor environments: under a G. opposita crown, under artificial shade and without neighbor as a control. Furthermore, assuming that proximity to the seashore correlates with stress intensity, we tested if the potential shade-driven facilitation became less intense as stress decreased. Regardless of the proximity to the seashore, after a year, the survival of T. brasiliensis seedlings was twice as high when the seedlings were under G. opposita or under artificial shade compared to the control, indicating that the nurse effect is driven by shade and that this facilitation mechanism is constant along the stress gradient. However, G. opposita and artificial shade had a negative effect on seedlings growth. Overall, our results showed that the facilitation mechanism behind the nurse effect did not wane as the stress was reduced. Furthermore, in spite of the potential costs in terms of biomass production, our study highlights the potential of nurse plants and artificial shade as techniques to improve the survival of transplanted seedlings used in the restoration of degraded shrubland coastal dunes.

Functional trait trade-offs for the tropical montane rain forest species responding to light from simulating experiments.

Differences among tropical tree species in survival and growth to light play a key role in plant competition and community composition. Two canopy species with contrasting functional traits dominating early and late successional stages, respectively, in a tropical montane rain forest of Hainan Island, China, were selected in a pot experiment under 4 levels of light intensity (full, 50%, 30%, and 10%) in order to explore the adaptive strategies of tropical trees to light conditions. Under each light intensity level, the pioneer species, Endospermum chinense (Euphorbiaceae), had higher relative growth rate (RGR), stem mass ratio (SMR), specific leaf area (SLA), and morphological plasticity while the shade tolerant climax species, Parakmeria lotungensis (Magnoliaceae), had higher root mass ratio (RMR) and leaf mass ratio (LMR). RGR of both species was positively related to SMR and SLA under each light level but was negatively correlated with RMR under lower light (30% and 10% full light). The climax species increased its survival by a conservative resource use strategy through increasing leaf defense and root biomass investment at the expense of growth rate in low light. In contrast, the pioneer increased its growth by an exploitative resource use strategy through increasing leaf photosynthetic capacity and stem biomass investment at the expense of survival under low light. There was a trade-off between growth and survival for species under different light conditions. Our study suggests that tree species in the tropical rainforest adopt different strategies in stands of different successional stages. Species in the earlier successional stages have functional traits more advantageous to grow faster in the high light conditions, whereas species in the late successional stages have traits more favorable to survive in the low light conditions.

[Responses of Manglietia glauca growth to soil nutrients and climatic factors].

Tree height and diameter of breast height (DBH) as growth characteristics of Manglietia glauca introduced from Vietnam were measured at many sites in south China and responses of M. glauca growth to soil nutrients and climatic factors were analyzed in this study. Annual average increments of tree height and DBH among different planted sites had significant differences. Annual average increments of tree height and DBH had significant positive correlation with soil total N and P, available N and P, but no significant correlation with soil organic matter, total K, available K, indicating that soil N and P contents could be the main affecting factors for the growth of M. glauca. Annual average increment of tree height had significant difference, but annual average increment of DBH had no significant difference at different altitudes. Annual average increment of tree height increased with the altitude from 150 to 550 m, the maximum was at the altitude of 550 m, and then it decreased. It indicated that the most appropriate altitude for M. glauca introduction is 550 m. Annual average increments of tree height and DBH had significant negative correlation with annual average temperature and > or = 10 degrees C accumulated temperature, and significant positive correlation with annual average precipitation, suggesting that annual mean temperature, > or = 10 degrees C accumulated temperature and annual average precipitation could be the main climatic factors influencing the growth of M. glauca.

[Litter decomposition of dominant plant species in successional stages in mid-subtropical zone].

The litters of seven tree species representing the dominant plant species in three main successional stages in subtropical China, i.e., Pinus massoniana in early successional forests, Schima superba and Cinnamanun camphora in transitional forests, and Castanopsis eyeri, Cyclobalanopsis gracilis, Cyclobalanopsis glauca, and Michelia chapensis in late successional forests, were collected, and their decomposition rates were measured with litterbags. The results showed that M. chapensls and C. gracilis had the highest litter decomposition rate (k = 1.12 and 0.89, respectively), followed by C. camphora and S. superba (k = 0.61 and 0.55, respectively), and P. massoniana (k = 0.51), indicating that there was a trend of litter decomposition rate being increased with succession stage. Litter decomposition rate had significant correlations with the litter' s initial P, N, and lignin contents, lignin/N ratio (P < 0.01), and C/N ratio (P < 0.05), suggesting that the initial P, N, and lignin contents and lignin/N ratio of leaf litter could be the good indictors of litter decomposition rate.

Essential oil composition of Laurus nobilis L. of different growth stages growing in Iran.

The chemical variations of the essential oil from the aerial parts of Laurus nobilis L. (Lauraceae) have been studied. Plant material has been harvested at each phenological status (vegetative, before anthesis, full flowering and seed-bearing). The oils were obtained by hydrodistillation of the air-dried samples. Analysis by GC and GC-MS of the essential oils has allowed to identify 39 compounds. The main compounds were 1,8-cineole, trans-sabinene hydrate, alpha-terpinyl acetate, methyl eugenol, sabinene, eugenol and alpha-pinene.

Embryogenesis and seed development in Sinomanglietia glauca (Magnoliaceae).

The development of the floral bud, especially the ovule and seed coat, of Sinomanglietia glauca was observed. Floral buds were covered by eight to nine hypsophyll pieces. The hypsophyll nearest the tepal was closed completely and characterized by two arrays of densely stained cells with dense cytoplasm, which split longitudinally at flowering. The perianth consisted of 16 tepals arranged in three whorls. The gynoecium was composed of numerous apocarpous carpels; the ovule was anatropous with two integuments. Embryogenesis was of the Polygonum type, and the endosperm was nuclear. The inner integument degenerated during seed development. The seed of S. glauca had an endotestal seed coat comprised of a sclerotic layer derived from the inner adaxial epidermis of the outer integument and a sarcotesta derived mainly from the middle cells between the inner and outer epidermis of the outer integument. The embryo developed normally, so embryogenesis is not the cause of difficult regeneration.

[Soil properties and water holding capacites of Michelia macclurei, Schima superba and Castanopis fissa stands].

The study showed that the soil density, total porosity, natural water capacity and capillary moisture capacity were 1.19 g x cm(-3), 56.73%, 15.7% and 43.2% in Michelia nacclurei stand, 1.26 g x cm(-3), 54.18%, 13.0% and 37.8% in Schima superb stand, and 1.06 g x cm(-3), 60.74%, 19.4%, and 45.8% in Castanopsis fissa stand, respectively. Soil water holding capacity and aeration were good in Castanopsis fissa stand but bad in Schima superba stand, whereas Michelia macclurei stand had a medium water holding capacity and a bad aeration. The water holding capacity of litter per tree was in order of Michelia nuacclurei (20 kg) > Castanopsis fissa (15 kg) > Schima superba (8 kg), whereas that of litter in stand was Castanopsis fissa (17 t x hm(-2)) > Michelia macclurei (16 t x hm(-2)) > Schima superba (13 t x hm(-2)). The nutrient storage of litter per tree was 112.71, 31.20 and 87.30 g in Michelia macclurei, Schima superba and Castanopsis fissa stands, respectively, and that of litter in stand was 84.35,51.86 and 98.11 kg x hm(-2), respectively. The soil in the three stands was strong acidic, and the content of soil organic matter, total N, total P, total K, alkalized N, available P and available K was 18.43 g x kg(-1), 0.69 g x kg(-1), 0.17 g x kg(-1), 5.83 g x kg(-1), 45.67 mg x kg(-1), 0.83 mg x kg(-1) and 23.13 mg x kg(-1) in Michelia macclurei stand, 13.40 g x kg(-1), 0.68 g x kg(-1), 0.20 g x kg(-1), 12.32 g x kg(-1), 40.78 mg x kg(-1), 0.85 mg x kg(-1) and 90.63 mg x kg(-1) in Schima superba stand, and 28.50 g x kg(-1), 0.97 g x kg(-1), 0.23 g x kg(-1), 18.77 g x kg(-1), 73.40 mg x kg(-1), 1.45 mg x kg(-1) and 66.50 mg x kg(-1) in Castanopsis fissa stand, respectively. Soil bacteria accounted for > 94% of soil microbes, and their individuals were 41 x 105, 34 x 104 and 5.3 x 104 g(-1) in Michelia macclurei, Schima superba and Castanopsis fissa stands, respectively. The activities of soil urease, catalase and phosphatase in Castanopsis fissa stand were the greatest among the three stands, while soil cellulase activity in Michelia macclurei stand was greater than that in other two stands. In a word, soil fertility of Castanopsis fissa stand was the highest among three test stands.

[Soil quality assessment of forest stand in different plantation esosystems].

After a clear-cutting of the first generation Cunninghamia lanceolata plantation in 1982, three plantation ecosystems, pure Michelia macclurei stand (PMS), pure Chinese-fir stand (PCS) and their mixed stand, were established in spring 1983, and their effects on soil characteristics were evaluated by measuring some soil physical, chemical, microbiological and biochemical parameters. After 20 years' plantation, all test indices showed differences among different forest management models. Both PMS and MCM had a favorable effect on soil fertility maintenance. Soil quality assessment showed that some soil functions, e.g., water availability, nutrient availability, root suitability and soil quality index were all in a moderate level under the mixed and pure PMS stands, whereas in a relatively lower level under successive PCS stand. The results also showed that there existed close correlations between soil total organic C (TOC), cation exchange capacity (CEC), microbial biomass-C (Cmic) and other soil physical, chemical and biological indices. Therefore, TOC, CEC and Cmic could be used as the indicators in assessing soil quality in this study area. In addition, there were also positive correlations between soil microbial biomass-C and TOC, soil microbial biomass-N and total N, and soil microbial biomass-P and total P in the present study.

Influence of elevated CO2 and mycorrhizae on nitrogen acquisition: contrasting responses in Pinus taeda and Liquidambar styraciflua.

An understanding of root system capacity to acquire nitrogen (N) is critical in assessing the long-term growth impact of rising atmospheric CO2 concentration ([CO2]) on trees and forest ecosystems. We examined the effects of mycorrhizal inoculation and elevated [CO2] on root ammonium (NH4+) and nitrate (NO3-) uptake capacity in sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.). Mycorrhizal treatments included inoculation of seedlings with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith in sweetgum and the ectomycorrhizal (EM) fungus Laccaria bicolor (Maire) Orton in loblolly pine. These plants were then equally divided between ambient and elevated [CO2] treatments. After 6 months of treatment, root systems of both species exhibited a greater uptake capacity for NH4+ than for NO3-. In both species, mycorrhizal inoculation significantly increased uptake capacity for NO3-, but not for NH4+. In sweetgum, the mycorrhizal effect on NO3- and NH4+ uptake capacity depended on growth [C02]. Similarly, in loblolly pine, the mycorrhizal effect on NO3- uptake capacity depended on growth [CO2], but the effect on NH4+ uptake capacity did not. Mycorrhizal inoculation significantly enhanced root nitrate reductase activity (NRA) in both species, but elevated [CO2] increased root NRA only in sweetgum. Leaf NRA in sweetgum did not change significantly with mycorrhizal inoculation, but increased in response to [CO2]. Leaf NRA in loblolly pine was unaffected by either treatment. The results indicate that the mycorrhizal effect on specific root N uptake in these species depends on both the form of inorganic N and the mycorrhizal type. However, our data show that in addressing N status of plants under high [CO2], reliable prediction is possible only when information about other root system adjustments (e.g., biomass allocation to fine roots) is simultaneously considered.