Leaf ecological stoichiometry and anatomical structural adaptation mechanisms of Quercus sect. Heterobalanus in southeastern Qinghai-Tibet Plateau.

BACKGROUND: With the dramatic uplift of the Qinghai-Tibet Plateau (QTP) and the increase in altitude in the Pliocene, the environment became dry and cold, thermophilous plants that originally inhabited ancient subtropical forest essentially disappeared. However, Quercus sect. Heterobalanus (QSH) have gradually become dominant or constructive species distributed on harsh sites in the Hengduan Mountains range in southeastern QTP, Southwest China. Ecological stoichiometry reveals the survival strategies plants adopt to adapt to changing environment by quantifying the proportions and relationships of elements in plants. Simultaneously, as the most sensitive organs of plants to their environment, the structure of leaves reflects of the long-term adaptability of plants to their surrounding environments. Therefore, ecological adaptation mechanisms related to ecological stoichiometry and leaf anatomical structure of QSH were explored. In this study, stoichiometric characteristics were determined by measuring leaf carbon (C), nitrogen (N), and phosphorus (P) contents, and morphological adaptations were determined by examining leaf anatomical traits with microscopy. RESULTS: Different QSH life forms and species had different nutrient allocation strategies. Leaves of QSH plants had higher C and P and lower N contents and higher N and lower P utilization efficiencies. According to an N: P ratio threshold, the growth of QSH species was limited by N, except that of Q. aquifolioides and Q. longispica, which was limited by both N and P. Although stoichiometric homeostasis of C, N, and P and C: N, C: P, and N: P ratios differed slightly across life forms and species, the overall degree of homeostasis was strong, with strictly homeostatic, homeostatic, and weakly homeostatic regulation. In addition, QSH leaves had compound epidermis, thick cuticle, developed palisade tissue and spongy tissue. However, leaves were relatively thin overall, possibly due to leaf leathering and lignification, which is strategy to resist stress from UV radiation, drought, and frost. Furthermore, contents of C, N, and P and stoichiometric ratios were significantly correlated with leaf anatomical traits. CONCLUSIONS: QSH adapt to the plateau environment by adjusting the content and utilization efficiencies of C, N, and P elements. Strong stoichiometric homeostasis of QSH was likely a strategy to mitigate nutrient limitation. The unique leaf structure of the compound epidermis, thick cuticle, well-developed palisade tissue and spongy tissue is another adaptive mechanism for QSH to survive in the plateau environment. The anatomical adaptations and nutrient utilization strategies of QSH may have coevolved during long-term succession over millions of years.

First report of Dactylonectria pauciseptata causing root rot on Eucalyptus cinerea in China.

Eucalyptus cinerea is an evergreen tree in the Myrtaceae. It is native to southern and eastern New South Wales and northern and eastern Victoria, Australia. It was introduced into China in the 1980s (Silva et al. 2011). Because of its unique shape, flexible stems, and rapid growth characteristics, it is widely used in the pulp industry and in decorative materials such as flower bouquets. In July 2022, 5- to 10-year-old E. cinerea showing symptoms of dehydration, withering and yellowing leaves, were found in forests and nurseries in Kunming and Songming, China. More than 37% of the trees showed these symptoms at each location, and disease severity was about 30%. Sixty symptomatic plants were collected from five tree nurseries. Diseased roots with 2-cm-long lesions were soaked in 75% ethanol for 15 s, 0.1% mercuric chloride for 2 min, rinsed with sterilized water, and placed on potato dextrose agar (PDA) at 25℃ for 3 days. Thirty samples were plated, and 21 isolates (YJLGF01 to YJLGF21) obtained, 11 strains with similar colony morphology (including representative strains YJLGF03 to YJLGF05). Three isolates (YJLGF03 to YJLGF05) were obtained by single-spore purification. On PDA, the colonies were circular with fluffy white to light yellow mycelium; the underside was yellowish brown. Conidiophores were bifurcated, with macroconidia borne terminally. The macroconidia were cylindrical with rounded, blunt ends, yellow to transparent, 1 to 3 septate (22.5 to 47.6 × 4.5 to 7.1 µm); microconidia were 0 to 1 septate (12.5 to 19.6 × 4.7 to 6.4 µm). Chlamydospores were spherical, rosary-like, and light yellow. Morphological characteristics were consistent with published descriptions of Dactylonectria pauciseptata (Piperkova et al. 2017). For molecular identification, the internal transcribed spacer (ITS), translation elongation factor 1- alpha (ef1-α) gene, and the beta-tubulin 2 (ß-tub2) gene were amplified and sequenced (ITS accessions OR735053, OR735054, OR735055; ß-tub2 accessios OR757447, OR757448, OR757449; ef1-α accessions OR757450, OR757451, OR757451) using published primers (White et al. 1990; Carbone et al. 1999). A phylogenetic tree was developed by Maximum Parsimony (MP) and Maximum Likelihood (ML) methods. These three isolates fell into the D. pauciseptata clade and were distinguished clearly from other species. Pathogenicity tests were performed using the same three isolates. Each isolate was cultured on PDA, and then subcultured in V8 juice broth on an orbital shaker at 180 RPM for 5 days. Conidia were collected by centrifugation at 6,000 RPM for 5 min, and then resuspended in sterilized distilled water (1×106 conidia/ml). Injured roots of one-year-old E. cinerea were soaked in the spore suspension for 1 h before being transplanted in sterile vermiculite. The plants were incubated at 25℃ with a 12 h photoperiod and 90% humidity. Five plants were inoculated as a group for each treatment and the entire experiment was completed three times. Among the inoculated plants, the incidence of disease development was 100%. A small sot appeared after 4 days, with a water-soaked lesion appearing and gradually expanding during days 5 to 7. After 10 days symptoms of root necrosis were similar to the those observed in the nursery, and aboveground plant parts had yellow, withering leaves and defoliation after 10 to 15 days. Control plants treated with sterile water showed no disease symptoms. The three strains were successfully reisolated from inoculated seedlings and confirmed them using DNA sequencing. No isolates were obtained from the control plants, thus fulfilling Koch's postulates. Dactylonectria pauciseptata was first reported from necrotic tissue of infected grape roots (Schroers et al. 2008). So far, it has been reported in Turkey, Canada, Brazil, Italy, and other countries (Erper et al. 2013; Úrbez-Torres et al. 2014; Santos et al. 2014). Based on our results, E. cinerea is a new host plant of D. pauciseptata in China. This disease is a threat to the nursery production of E. cinerea, potentially leading to a reduction in yields and economic losses.

First report of 'Candidatus Phytoplasma asteris' associated with witches'-broom and plexus bud disease of Cerasus serrula in China.

Cherry blossoms (Cerasus serrula) are native to the temperate zone around the Himalayas in the northern hemisphere, mainly distributed in the west and southwest of China, including Yunnan, Sichuan and Tibet. Cherry has high ornamental, edible and medicinal value. In August 2022, we observed that Cherry trees exhibited witches' broom and plexus bud in Kunming City, Yunan Province, China. The symptoms consisted of many small branches with little leaves at the top of branches, stipule lobation, and clustered adventitious buds that are tumor-like on the branches that usually cannot sprout normally. As disease intensity increased, the branches dried up from the top to the bottom till the death of the whole plant. We named this disease C. serrula witches' broom disease (CsWB). We found CsWB in the areas of Panlong, Guandu, Xishan Districts in Kunming, where more than 17% of the plants we surveyed were infected. We collected 60 samples from across the three districts. These included 15 symptomatic and 5 asymptomatic plants per district. The lateral stem tissues were observed under a scanning electron microscope (Hitachi S-3000N). The nearly spherical bodies were found in the phloem cells of symptomatic plants. Total DNA extraction was conducted from 0.1 g tissue using the CTAB method (Porebski et al. 1997), ddH2O was used as the negative control, and Dodonaea viscose plants with witches' broom symptoms were used as the positive control. The nested PCR was used to amplify the 16S rRNA gene (Lee et al. 1993; Schneider et al. 1993) and PCR amplicon of 1.2 kb were amplified (GenBank accessions: OQ408098; OQ408099; OQ408100). The direct PCR specific to the ribosomal protein (rp) gene yielded amplicons of approximately 1.2 kb with primer pair rp(I)F1A and rp(I)R1A (Lee et a. 2003) (GenBank accessions: OQ410969; OQ410970; OQ410971). The fragment from 33 symptomatic samples was consistent with the positive control, and absent for asymptomatic samples, suggesting an association of phytoplasma with the disease. A BLAST analysis of the 16S rRNA sequences of CsWB phytoplasma showed that it has a 99.76% similarity with Trema laevigata witches' broom phytoplasma (GenBank accession MG755412). The rp sequence shared 99.75% identity with Cinnamomum camphora witches' broom phytoplasma (GenBank accession OP649594). An analysis with iPhyClassifier showed that the virtual RFLP pattern derived from the 16S rDNA sequence shares 99.3% similarity with that of the 'Ca. Phytoplasma asteris' reference strain (GenBank accession: M30790), and the virtual RFLP pattern derived from the fragment is identical (similarity coefficient 1.00) to the reference pattern of 16Sr group I, subgroup B (GenBank accession: AP006628). Thus, CsWB phytoplasma is identified as 'Ca. Phytoplasma asteris'-related strain belonging to sub-group 16SrI-B. The phylogenetic tree was constructed based on 16S rRNA gene and rp gene sequences by using MEGA version 6.0 (Tamura et al. 2013) with neighbor-joining (NJ) method and bootstrap support was estimated with 1000 replicates. The result indicated that the CsWB phytoplasma formed a subclade in 16SrI-B and rpI-B respectively. In addition, the clean 1-year-old C. serrula were tested positive for the phytoplasma using the nested PCR 30 days after being grafted with naturally infected twigs with CsWB symptoms. To the best of our knowledge, Cherry blossoms is a new host of 'Ca. Phytoplasma asteris'-related strains in China. The newly emerged disease is a threat to the ornamental value of cherry blossoms and the production of wood quality.

First report of 'Candidatus Phytoplasma asteris' associated with witches'-broom disease of Pinus yunnanensis in China.

Pinus yunnanensis is an evergreen tree belonging to Pinaceae. The species is distributed in the east of Tibet, southwest of Sichuan, southwest of Yunnan, southwest of Guizhou and northwest of Guangxi. It is an indigenous and pioneer tree species for barren mountain afforestation in southwest China. P. yunnanensis has important value to both the building and medicine industries (Liu et al. 2022). In May 2022, P. yunnanensis showing witches'-broom symptom were found in Panzhihua City, Sichuan Province, China. The symptomatic plants had yellow or red needle, and exhibited plexus bud and needle wither. The lateral buds of infected pines developed into twigs. Some lateral buds grew in clusters and a few sprouted needles (Fig.1). The disease was named the P. yunnanensis witches'-broom disease (PYWB) and was found in some areas of Miyi, Renhe, and Dongqu. More than 9% of the pines showed these symptoms in the three areas surveyed, and the disease was spreading. A total of 39 samples were collected from three areas, including 25 symptomatic plants and 14 asymptomatic plants, respectively. The lateral stem tissues of 18 samples were observed under a scanning electron microscope (Hitachi S-3000N). Spherical bodies were found in the phloem sieve cells of symptomatic pines (Fig.1). Total DNA was extracted from 18 plant samples using the CTAB method (Porebski et al. 1997) and subjected to nested-PCR testing. Double-distilled water and DNA extracted from asymptomatic plants were used as negative controls, and DNA extracted from Dodonaea viscosa affected by the D. viscosa witches'-broom disease was used as positive control. Nested PCR was employed to amplify the pathogen's 16S rRNA gene (Lee et al. 1993; Schneider et al. 1993) and 1.2 kb segment were produced (GenBank accessions OP646619; OP646620; OP646621). PCR specific to the ribosomal protein (rp) gene yielded segment of approximately 1.2 kb (Lee et al. 2003)(GenBank accessions OP649589; OP649590; OP649591). The fragment size from 15 samples was consistent with the positive control, confirming the association of phytoplasma with the disease. A BLAST analysis of the 16S rRNA sequences of P. yunnanensis witches'-broom phytoplasma showed that it shared 99.12% ~99.76% identity with that of Trema laevigata witches'-broom phytoplasma (GenBank accession MG755412). The rp sequence shared 99.84%~99.92% identity with that of Cinnamomum camphora witches'-broom phytoplasma (GenBank accession OP649594). An analysis with iPhyClassifier (Zhao et. 2013) showed that the virtual RFLP pattern derived from OP646621 16S rDNA fragment of PYWB phytoplasma is identical (similarity coefficient 1.00) to the reference pattern of 16Sr group I, subgroup B (OY-M, GenBank accession AP006628). The phytoplasma is identified as a 'Candidatus Phytoplasma asteris'-related strain belonging to sub-group 16SrI-B. Interestingly, compared to AP006628, the virtual RFLP pattern derived from OP646619 and OP646620 fragments exhibit differences in three and one cleavage site, with a similarity coefficient of 0.92 and 0.97, respectively (Fig.2). These strains may represent a new subgroup within the 16Sr group I. The phylogenetic tree was reconstructed based on 16S rRNA and rp gene sequences using MEGA versio6.0 (Tamura et al. 2013). The analysis was conducted using the neighbor-joining (NJ) method with 1,000 replicates of bootstrap analysis. The results indicated that the PYWB phytoplasmas grouped into clades including phytoplasmas belonging to 16SrI-B and rpI-B, respectively (Fig.3). In addition, 2-year-old P. yunnanensis were used for grafting assays in nursery, and the twigs from infected pine under natural conditions were used as a scion, and the phytoplasma were detected using nested PCR after grafting for 40 d (Fig.4). In 2008-2014, P. sylvestris and P. mugo in Lituania had excessive branching symptoms that were attributed to 'Ca. Phtyoplasma Pini' (16SrXXI-A) or asteris' (16SrI-A) strains (Valiunas et al. 2015). In 2015, P. pungens with abnormal shoot branching in Maryland were found to be infected by 'Ca. Phytoplasma pini' strain (16SrXXI-B) (Costanzo et al. 2016). To the best of our knowledge, P. yunnanensis is a new host of 'Ca. Phytoplasma asteris'-related strain (16SrI-B) in China. The newly emerged disease is a threat to pines.

First report of 'Candidatus Phytoplasma asteris' associated with witches'-broom disease of Cinnamomum camphora in China.

Camphor tree (Cinnamomum camphora) has a wide distribution in the world and is mainly distributed in the South and southwest in China. It can be used as both a wood and a medicine, with high value in industry, medicine, and ecology. In May 2022, it was observed that the approximately ten to fifteen years old Camphor trees were exhibiting witches'-broom, small leaf morphology and chlorosis, and leaf drop in Panzhihua City, Sichuan Province, China. The witches'-broom symptoms consisted of many small branches with little leaves at the top of branches. It was named C. camphora witches'-broom disease (CCWB) and was found in some areas of Miyi, Yanbian, Renhe Xiqu and Dongqu counties. More than 28% of the plants were infected on the five areas surveyed. Total 100 samples were collected from five areas, with 15 symptomatic plants and 5 asymptomatic plants each area. The lateral stem tissues were observed under a scanning electron microscope (Hitachi S-3000N). The nearly spherical bodies were found in the phloem sieve cells of symptomatic plants. Total DNA extraction was conducted from 0.1 g tissue using the CTAB method (Porebski et al. 1997), ddH2O was used as the negative control, and Dodonaea viscose witches'-broom disease plants were used as the positive control. The nested PCR was employed to amplify the 16S rRNA gene (Lee et al. 1993; Schneider et al. 1993) and PCR amplicon of 1.2 kb were amplified (GenBank accessions OP662614; OP662615; OP662616). The direct PCR specific to the ribosomal protein (rp) gene yielded amplicons of approximately 1.2 kb with primer pair rp(I)F1A and rp(I)R1A (Lee et al. 2003) (GenBank accessions OP649592; OP649593; OP649594). The fragment from 25 symptomatic samples was consistent with the positive control, and asymptomatic plants were negative, confirming an association of a phytoplasma with the disease. A BLAST analysis of the 16S rRNA sequences of CCWB phytoplasma showed that it has a 99.44% similarity with Trema laevigata witches'-broom phytoplasma (GenBank accession MG755412). The rp sequence shared 99.59% identity with rapeseed phyllody phytoplasma (GenBank accession CP055264). An analysis with iPhyClassifier showed that the virtual RFLP pattern derived from the query 16S rDNA fragment of CCWB phytoplasma is most similar to the reference pattern of the 16Sr group I, subgroup B (OY-M, GenBank accession AP006628). The phytoplasma is identified as 'Ca. Phytoplasma asteris'-related strain belonging to sub-group 16SrI-B. The phylogenetic tree was constructed based on 16S rRNA gene and rp gene sequences by using MEGA version 6.0 (Tamura et al. 2013) with neighbor-joining (NJ) method and bootstrap support was estimated with 1000 replicates. The result indicated that the CCWB phytoplasma formed a subclade in 16SrI-B and rpI-B respectively. In addition, the plants were positive for the phytoplasma using nested PCR after grafting for 30 d in nursery conditions. It is noteworthy that the plants were seriously damaged by aphid, Psyllidae and Ceroplastes. It is speculated that the insects of Homoptera typically transmit phytoplasmas by feeding on plant sap, thus it is necessary to control aphids in order to control the C. camphora witches'-broom disease. To the best of our knowledge, Camphor tree is a new host plant of 'Ca. Phytoplasma asteris' in China. The newly emerged disease is a threat to Camphor tree production.

Antifungal action and induction of resistance by Bacillus sp. strain YYC 155 against Colletotrichum fructicola for control of anthracnose disease in Camellia oleifera.

Anthracnose disease caused by Colletotrichum fructicola is a serious disease that can afflict Camellia oleifera. Biological control is a rapidly growing approach for the management of plant diseases. In this study, we investigated the bio-control efficiency and the defense responses of an endophytic Bacillus tequilensis strain YYC 155, which was isolated from the root nodules of the Crotalaria pallida against anthracnose disease, caused by C. fructicola in C. oleifera. B. tequilensis YYC 155 exhibited significant inhibitory activity against anthracnose disease, caused by C. fructicola in C. oleifera. YYC 155 can secrete extracellular hydrolases, such as chitinase and ß-1, 3-glucanase, which produce lipopeptides that are antimicrobial and forms strong biofilms. In addition, in treatment with YYC 155, the cell membranes of C. fructicola were injured and the leakage of cell contents from the mycelia of the pathogen was increased. Spraying 1 × 107 cells mL-1 bacterial suspension of YYC 155 on C. oleifera leaves enhanced the activity of key enzymes in C. oleifera associated with the phenylpropanoid pathway and increased the content of phenolic compounds and flavonoids. Results of our study indicate that B. tequilensis YYC 155 may potentially represent an effective biocontrol agent against anthracnose disease in C. oleifera.

Effects of repeated drought stress on the physiological characteristics and lipid metabolism of Bombax ceiba L. during subsequent drought and heat stresses.

BACKGROUND: Trees of Bombax ceiba L. could produce a large number of viable seeds in the dry-hot valleys. However, the seedling regeneration of the species is difficult in these areas as mild drought often occur repeatedly which might be followed by heat stress. However, how the repeated drought affects the subsequent drought and heat tolerance of B. ceiba is not clear. In this study, chlorophyll fluorescence, soluble sugar content and lipid metabolism were measured for the drought-treated seedlings and heat-treated seedlings with or without drought hardening. RESULTS: Neither the first nor third dehydration treatments affected the photosynthetic activity and soluble sugar content of B. ceiba seedlings. However, they differentially affected the fluidity of the local membranes and the levels of diacylglycerol and phosphatidic acid. Heat shock severely decreased the photosynthetic efficiency but drought priming reduced the effects of heat shock. Moreover, heat shock with or without drought priming had differential effects on the metabolism of soluble sugars and some lipids. In addition, the unsaturation level of membrane glycerolipids increased following heat shock for non-drought-hardened seedlings which, however, maintained for drought-hardened seedlings. CONCLUSIONS: The results suggest that two cycles of dehydration/recovery can affect the metabolism of some lipids during the third drought stress and may enhance the heat tolerance of B. ceiba by adjusting lipid composition and membrane fluidity.

Development and characterization of novel EST-SSR markers for Speranskia tuberculata (Euphorbiaceae).

PREMISE OF THE STUDY: The first set of expressed sequence tag-simple sequence repeat (EST-SSR) markers were developed and characterized for Speranskia tuberculata (Euphorbiaceae), a traditional medicinal plant endemic to northern China, to explore the effects of recent habitat fragmentation on the genetic diversity and structure of this species. METHODS AND RESULTS: In this study, a total of 18 novel polymorphic microsatellite (EST-SSR) markers were developed for S. tuberculata using high-throughput transcriptome sequencing. Analysis of 24 individuals of S. tuberculata from four natural populations revealed their robust polymorphic reliability. The number of alleles per locus ranged from two to 11, while the expected and observed heterozygosity per marker varied from 0.187 to 0.827 and 0.042 to 0.917, respectively. Of these markers, 13 showed good amplification results in the closely related species S. cantonensis. CONCLUSIONS: These newly generated SSR markers are expected to provide novel tools for genetic studies of S. tuberculata, which will contribute to the conservation and sustainable use of the species' wild genetic resources.

RNA-seq Reveals Complicated Transcriptomic Responses to Drought Stress in a Nonmodel Tropic Plant, Bombax ceiba L.

High-throughput transcriptome provides an unbiased approach for understanding the genetic basis and gene functions in response to different conditions. Here we sequenced RNA-seq libraries derived from a Bombax ceiba L. system under a controlled experiment. As a known medicinal and ornamental plant, B. ceiba grows mainly in hot-dry monsoon rainforests in Southeast Asia and Australia. Due to the specific growth environment, it has evolved a unique system that enables a physiologic response to drought stress. To date, few studies have characterized the genome-wide features of drought endurance in B. ceiba. In this study, we first attempted to characterize and identify the most differentially expressed genes and associated functional pathways under drought treatment and normal condition. Using RNA-seq technology, we generated the first transcriptome of B. ceiba and identified 59 differentially expressed genes with greater than 1,000-fold changes under two conditions. The set of upregulated genes implicates interplay among various pathways: plants growth, ubiquitin-mediated proteolysis, polysaccharides hydrolyzation, oxidative phosphorylation and photosynthesis, etc. In contrast, genes associated with stem growth, cell division, fruit ripening senescence, disease resistance, and proline synthesis are repressed. Notably, key genes of high RPKM levels in drought are AUX1, JAZ, and psbS, which are known to regulate the growth of plants, the resistance against abiotic stress, and the photosynthesis process. Furthermore, 16,656 microsatellite markers and 3,071 single-nucleotide polymorphisms (SNPs) were predicted by in silico methods. The identification and functional annotation of differentially expressed genes, microsatellites, and SNPs represent a major step forward and would serve as a valuable resource for understanding the complexity underlying drought endurance and adaptation in B. ceiba.

Development and characterization of EST-SSR markers in Bombax ceiba (Malvaceae).

PREMISE OF THE STUDY: Bombax ceiba (Malvaceae), commonly known as silk cotton tree, is a multipurpose tree species of tropical forests. Novel expressed sequence tag-simple sequence repeat (EST-SSR) markers were developed and characterized for the species using transcriptome analysis. METHODS AND RESULTS: A total of 33 new EST-SSR markers were developed for B. ceiba, of which 13 showed polymorphisms across the 24 individuals from four distant populations tested in the study. The results showed that the number of alleles per polymorphic locus ranged from two to four, and the expected heterozygosity and observed heterozygosity per locus varied from 0.043 to 0.654 and from 0 to 0.609, respectively. CONCLUSIONS: These newly developed EST-SSR markers can be used in phylogeographic and population genetic studies to investigate the origin of B. ceiba populations. Furthermore, these EST-SSR markers could also greatly promote the development of molecular breeding studies pertaining to silk cotton tree.

[Kapok capsule formation and fiber development process in Yuanjiang dry-hot valley].

This study explored the capsule formation and fiber development process of kapok which is a tree in Yuanjiang dry-hot valleys (DHV) using the methods of paraffin section and scanning electron microscopy. The result showed that formation process of kapok capsule can be divided into four stages: the capsule formation within 5 days after anthesis (DAA), the capsule mass period from 5 to 35 DAA, the capsule dehydration period from 35 to 50 DAA, and the capsule bursting period after 50 DAA. The kapok fiber was developed via endocarp cells differentiation (0-2 DAA), swelling (2-5 DAA), bulging (5-10 DAA), fiber elongating (10-40 DAA), and divorcing from pericarp (40-50 DAA). During the development, the length and projection width of fiber increased as a power function, and their daily average growth rates reached .the maximums at 20 DAA. Fiber fresh mass substantially increased and then reduced, and the daily average growth rate reached the maximum in the period from 25 to 30 DAA. Fiber dry mass gradually increased and reached the maximum growth rate in the period from 20 to 25 DAA. The seed and fiber continually increased their mass after 30 DAA, but the pericarp mass declined with its dehydration and aging. Compared with cotton, it was easy to separate fiber from kapok capsule inner wall because of small adhesion power between kapok fiber and capsule inner wall. The period from 5 to 35 DAA was critical for the fiber development and growth. Therefore, water and fertilizer management should be concentrated at this stage. The capsule should be harvested at 50 DAA because the fiber began to divorce from the pericarp.

Mycorrhizas alter nitrogen acquisition by the terrestrial orchid Cymbidium goeringii.

BACKGROUND AND AIMS: Orchid mycorrhizas exhibit a unique type of mycorrhizal symbiosis that occurs between fungi and plants of the family Orchidaceae. In general, the roots of orchids are typically coarse compared with those of other plant species, leading to a considerably low surface area to volume ratio. As a result, orchids are often ill-adapted for direct nutrient acquisition from the soil and so mycorrhizal associations are important. However, the role of the fungal partners in the acquisition of inorganic and organic N by terrestrial orchids has yet to be clarified. METHODS: Inorganic and amino acid N uptake by non-mycorrhizal and mycorrhizal Cymbidium goeringii seedlings, which were grown in pots in a greenhouse, was investigated using a (15)N-labelling technique in which the tracer was injected at two different soil depths, 2·5 cm or 7·5 cm. Mycorrhizal C. goeringii seedlings were obtained by inoculation with three different mycorrhizal strains isolated from the roots of wild terrestrial orchids (two C. goeringii and one C. sinense). KEY RESULTS: Non-mycorrhizal C. goeringii primarily took up NO3(-) from tracers injected at 2·5-cm soil depth, whereas C. goeringii inoculated with all three mycorrhiza primarily took up NH4(+) injected at the same depth. Inoculation of the mycorrhizal strain MLX102 (isolated from adult C. sinense) on C. goeringii roots only significantly increased the below-ground biomass of the C. goeringii; however, it enhanced (15)NH4(+) uptake by C. goeringii at 2·5-cm soil depth. Compared to the uptake of tracers injected at 2·5-cm soil depth, the MLX102 fungal strain strongly enhanced glycine-N uptake by C. goeringii from tracers injected at 7·5-cm soil depth. Cymbidium goeringii inoculated with CLB113 and MLX102 fungal strains demonstrated a similar N uptake pattern to tracers injected at 2·5-cm soil depth. CONCLUSIONS: These findings demonstrate that mycorrhizal fungi are able to switch the primary N source uptake of a terrestrial orchid, in this case C. goeringii, from NO3(-) to NH4(+). The reasons for variation in N uptake in the different soil layers may be due to possible differentiation in the mycorrhizal hyphae of the C. goeringii fungal partner.

[Limiting factors of waste land revegetation in indigenous zinc smelting areas of western Guizhou].

With indigenous zinc smelting waste residue, contaminated soil and background soil as test substrates, a pot experiment was conducted to study the growth characteristics of Lolium perenne and Trifolium pretense on these substrates. The results showed that the major limiting factors of waste land revegetation in indigenous zinc smelting areas of western Guizhou were the salt-alkali stress and the lower contents of organic matter, total N, available N and total K. The heavy metals in waste residue had a high concentration, but their available forms only occupied a small proportion, with low toxicity to plant but having potential harmful risk. Contaminated soil had lower concentrations of heavy metals than waste residue, but its contained heavy metals were more in available form. The constraints of revegetation on contaminated soil were the toxicity of heavy metals and the low contents of available P and K. Mixing contaminated soil with zinc smelting waste residue could be one of the effective approaches for the substrate amendment in indigenous zinc smelting areas.