Contrasting impacts of fertilization on topsoil and subsoil greenhouse gas fluxes in a thinned Chinese fir plantation.

Globally, forest soils are considered as important sources and sinks of greenhouse gases (GHGs). However, most studies on forest soil GHG fluxes are confined to the topsoils (above 20 cm soil depths), with only very limited information being available regarding these fluxes in the subsoils (below 20 cm soil depths), especially in managed forests. This limits deeper understanding of the relative contributions of different soil depths to GHG fluxes and global warming potential (GWP). Here, we used a concentration gradient-based method to comprehensively investigate the effects of thinning intensity (15% vs. 35%) and nutrient addition (no fertilizer vs. NPK fertilizers) on soil GHG fluxes from the 0-40 cm soil layers at 10 cm depth intervals in a Chinese fir (Cunninghamia lanceolata) plantation. Results showed that forest soils were the sources of CO2 and N2O, but the sinks of CH4. Soil GHG fluxes decreased with increasing soil depth, with the 0-20 cm soil layers identified as the dominant producers of CO2 and N2O and consumers of CH4. Thinning intensity did not significantly affect soil GHG fluxes. However, fertilization significantly increased CO2 and N2O emissions and CH4 uptake at 0-20 cm soil layers, but decreased them at 20-40 cm soil layers. This is because fertilization alleviated microbial N limitation and decreased water filled pore space (WFPS) in topsoils, while it increased WFPS in subsoils, ultimately suggesting that soil WFPS and N availability (especially NH4+-N) were the predominant regulators of GHG fluxes along soil profiles. Generally, there were positive interactive effects of thinning and fertilization on soil GHG fluxes. Moreover, the 35% thinning intensity without fertilization had the lowest GWP among all treatments. Overall, our results suggest that fertilization may not only cause depth-dependent effects on GHG fluxes within soil profiles, but also impede efforts to mitigate climate change by promoting GHG emissions in managed forest plantations.

Above- and belowground phenology responses of subtropical Chinese fir (Cunninghamia lanceolata) to soil warming, precipitation exclusion and their interaction.

Plant phenology plays an important role in nutrient cycling and carbon balance in forest ecosystems, but its response to the interaction of global warming and precipitation reduction remains unclear. In this study, an experiment with factorial soil warming (ambient, ambient +5 °C) and precipitation exclusion (ambient, ambient -50 %) was conducted in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. We investigated the effects of soil warming, precipitation exclusion, and their interactions on Chinese fir phenology involving tree height and fine root growth. In the meantime, the impact of tree height growth and related climatic factors on fine root production was also assessed. The results showed that: (1) more variable phenology responses were observed in fine root growth than in tree height growth to the climatic treatments; the duration of fine root growth and tree height growth was significantly reduced by the precipitation exclusion and warming treatment, respectively; phenology differences of fine root and tree height growth caused by the solo warming and precipitation exclusion treatment were further enhanced by the combined treatment; and despite the greater inter-annual phenology stability of tree height growth than that of fine root growth, both of them showed insignificant response to all the climate treatments; (2) asynchrony of phenology between tree height and fine root growth was significantly enlarged by solo warming and precipitation exclusion treatments, and further enlarged by the combined treatment; (3) fine root production was significantly and positively correlated with air, and soil temperature, and tree height growth as well, which was altered by warming and precipitation exclusion treatments. Our results demonstrated that climatic changes significantly and differently alter phenology of, and extend the phenology asynchrony between, above and below ground plant components, and also highlight the climate-sensitive and variable nature of root phenology. Overall, these phenology responses to climatic change may weaken the close link between fine root production and tree height growth, which may result in temporal mismatch between nutrient demand and supply in Chinese fir plantation.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Characteristics of soil nitrogen and phosphorus fractions and microbial traits with increasing stand age in two-layered Cunninghumia lanceolata + Phoebe bournei plantations.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Characterization of hemicellulose in Cunninghamia lanceolata stem during xylogenesis.

In this study, hemicellulose was isolated from the apical, middle and basal segments of C. lanceolata stem to investigate the dynamic change of its structure during xylogenesis. Results showed that the C. lanceolata hemicellulose is mainly consisted of O-acetylgalactoglucomannan (GGM) which backbone is alternately linked by ß-d-mannopyranosyl (Manp) and ß-d-glucopyranosyl (Glcp) via (1 â†’ 4)-glycosidic bond, while the side chains are α-d-galactopyranosyl (Galp) and acetyl. In addition, 4-O-methylglucuronoarabinoxylan (GAX) is another dominant structure of C. lanceolata hemicellulose which contains a linear backbone of (1 â†’ 4)-ß-d-xylopyranosyl (Xylp) and side chains of 4-O-Me-α-d-glucuronic acid (MeGlcpA) and α-L-arabinofuranose (Araf). The thickness of the cell wall, the ratio of GGM/GAX and the molecular weight of hemicellulose were increased as the extension of growth time. The degree of glycosyl substitutions of xylan and mannan was decreased from 10.34 % (apical) to 8.38 % (basal) and from 15.63 % (apical) to 10.49 % (basal), respectively. However, the total degree of acetylation was enhanced from 0.28 (apical) to 0.37 (basal). Transcriptome analysis showed that genes (CSLA9, IRX9H1, IRX10L, IRX15L, GMGT1, TBL19, TBL25, GUX2, GUX3, GXM1, F8H1 and F8H2) related to hemicellulose biosynthesis are mainly expressed in mature part. This study is of great significance for genetic breeding and high-value utilization of C. lanceolata.

Evaluation of reference genes and characterization of the MYBs in xylem radial change of Chinese fir stem.

The radial change (RC) of tree stem is the process of heartwood formation involved in complex molecular mechanism. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.), an evergreen species, is an important fast-growing timber tree in southern China. In this study, the top four stable genes (IDH, UBC2, RCA and H2B) were selected in RC tissues of 15 years old Chinese fir stem (RC15) and the genes (H2B, 18S, TIP41 and GAPDH) were selected in RC tissues of 30 years old Chinese fir stem (RC30). The stability of the reference genes is higher in RC30 than in RC15. Sixty-one MYB transcripts were obtained on the PacBio Sequel platform from woody tissues of one 30 years old Chinese fir stem. Based on the number of MYB DNA-binding domain and phylogenetic relationships, the ClMYB transcripts contained 21 transcripts of MYB-related proteins (1R-MYB), 39 transcripts of R2R3-MYB proteins (2R-MYB), one transcript of R1R2R3-MYB protein (3R-MYB) belonged to 18 function-annotated clades and two function-unknown clades. In RC woody tissues of 30 years old Chinese fir stem, ClMYB22 was the transcript with the greatest fold change detected by both RNA-seq and qRT-PCR. Reference genes selected in this study will be helpful for further verification of transcript abundance patterns during the heartwood formation of Chinese fir.

Full-length transcriptomic identification of R2R3-MYB family genes related to secondary cell wall development in Cunninghamia lanceolata (Chinese fir).

BACKGROUND: R2R3-MYB is a class of transcription factor crucial in regulating secondary cell wall development during wood formation. The regulation of wood formation in gymnosperm has been understudied due to its large genome size. Using Single-Molecule Real-Time sequencing, we obtained full-length transcriptomic libraries from the developmental stem of Cunninghamia lanceolata, a perennial conifer known as Chinese fir. The R2R3-MYB of C. lanceolata (hereafter named as ClMYB) associated with secondary wall development were identified based on phylogenetic analysis, expression studies and functional study on transgenic line. RESULTS: The evolutionary relationship of 52 ClMYBs with those from Arabidopsis thaliana, Eucalyptus grandis, Populus trichocarpa, Oryza sativa, two gymnosperm species, Pinus taeda, and Picea glauca were established by neighbour-joining phylogenetic analysis. A large number of ClMYBs resided in the woody-expanded subgroups that predominated with the members from woody dicots. In contrast, the woody-preferential subgroup strictly carrying the members of woody dicots contained only one candidate. The results suggest that the woody-expanded subgroup emerges before the gymnosperm/angiosperm split, while most of the woody-preferential subgroups are likely lineage-specific to woody dicots. Nine candidates shared the same subgroups with the A. thaliana orthologs, with known function in regulating secondary wall development. Gene expression analysis inferred that ClMYB1/2/3/4/5/26/27/49/51 might participate in secondary wall development, among which ClMYB1/2/5/26/27/49 were significantly upregulated in the highly lignified compression wood region, reinforcing their regulatory role associated with secondary wall development. ClMYB1 was experimentally proven a transcriptional activator that localised in the nucleus. The overexpression of ClMYB1 in Nicotiana benthamiana resulted in an increased lignin deposition in the stems. The members of subgroup S4, ClMYB3/4/5 shared the ERF-associated amphiphilic repression motif with AtMYB4, which is known to repress the metabolism of phenylpropanoid derived compounds. They also carried a core motif specific to gymnosperm lineage, suggesting divergence of the regulatory process compared to the angiosperms. CONCLUSIONS: This work will enrich the collection of full-length gymnosperm-specific R2R3-MYBs related to stem development and contribute to understanding their evolutionary relationship with angiosperm species.

Drought stress introduces growth, physiological traits and ecological stoichiometry changes in two contrasting Cunninghamia lanceolata cultivars planted in continuous-plantation soils.

BACKGROUND: The decrease in Cunninghamia lanceolata (Lamb.) production on continuously planted soil is an essential problem. In this study, two-year-old seedlings of two cultivars (a normal cultivar, NC, and a super cultivar, SC) were grown in two types of soil (not planted (NP) soil; continuously planted (CP) soil) with three watering regimes, and the interactive effects on plant growth and physiological traits were investigated in a greenhouse experiment. The water contents of the soil in the control (CK) (normal water content), medium water content (MWC) and low water content (LWC) treatments reached 75-80 %, 45-50 % and 20-25 % of the field water capacity, respectively. RESULTS: The results indicated that the CP soil had a negative effect on growth and physiological traits and that the LWC treatment caused even more severe and comprehensive negative effects. In both cultivars, the CP soil significantly decreased the height increment (HI), basal diameter increment (DI), dry matter accumulation (DMA), net photosynthetic rate (Pn), total chlorophyll content (TChl), carotenoid content (Caro) and photosynthetic nitrogen use efficiency (PNUE). Compared to the NP soil, the CP soil also decreased the proline and soluble protein contents, nitrogen use efficiency (NUE) and phosphorus use efficiency (PUE) and increased the nitrogen:phosphorus ratio in roots, stems and leaves. The LWC treatment decreased growth and photosynthesis, changed ecological stoichiometry, induced oxidative stress, promoted water use efficiency and damaged chloroplast ultrastructure. Significant increases in ascorbate peroxidase (APX), peroxidase (POD), soluble protein and proline contents were found in the LWC treatment. Compared with the NC, the SC was more tolerant to the CP soil and water stress, as indicated by the higher levels of DMA, Pn, and WUE. After exposure to the CP soil and watering regimes, the decreases in biomass accumulation and gas exchange were more pronounced. CONCLUSIONS: The combination of drought and CP soil may have detrimental effects on C. lanceolata growth, and low water content enhances the impacts of CP soil stress on C. lanceolata seedlings. The superiority of the SC over the NC is significant in Chinese fir plantation soil. Therefore, continuously planted soil can be utilized to cultivate improved varieties of C. lanceolata and maintain water capacity. This can improve their growth and physiological performance to a certain extent.

Half-leaf width symmetric distribution reveals buffering strategy of Cunninghamia lanceolata.

BACKGROUND: Leaf length and width could be a functioning relationship naturally as plant designs. Single-vein leaves have the simplest symmetrical distribution and structural design, which means that fast-growing single-vein species could interpret the scheme more efficiently. The distribution of leaf length and width can be modulated for better adaptation, providing an informative perspective on the various operational strategies in an emergency, while this mechanism is less clear. Here we selected six age groups of Cunninghamia lanceolata pure forests, including saplings, juveniles, mature, and old-growth trees. We pioneered a tapering model to describe half-leaf symmetric distribution with mathematical approximation based on every measured leaf along developmental sequence, and evaluated the ratio of leaf basal part length to total length (called tipping leaf length ratio). RESULTS: The tipping leaf length ratio varied among different tree ages. That means the changes of tipping leaf length ratio and leaf shape are a significant but less-noticed reflection of trees tradeoff strategies at different growth stages. For instance, there exhibited relatively low ratio during sapling and juvenile, then increased with increasing age, showing the highest value in their maturity, and finally decreased on mature to old-growth transition. The tipping leaf length ratio serves as a cost-benefit ratio, thus the subtle changes in the leaf symmetrical distribution within individuals reveal buffering strategy, indicating the selection for efficient design of growth and hydraulic in their developmental sequences. CONCLUSIONS: Our model provides a physical explanation of varied signatures for tree operations in hydraulic buffering through growth stages, and the buffering strategy revealed from leaf distribution morphologically provides evidence on the regulation mechanism of leaf biomechanics, hydraulics and physiologies. Our insight contributes greatly to plant trait modeling, policy and management, and will be of interest to some scientists and policy makers who are involved in climate change, ecology and environment protection, as well as forest ecology and management.

Isolation and screening of multifunctional phosphate solubilizing bacteria and its growth-promoting effect on Chinese fir seedlings.

Phosphorus-solubilizing microorganisms is a microbial fertilizer with broad application potential. In this study, 7 endophytic phosphate solubilizing bacteria were screened out from Chinese fir, and were characterized for plant growth-promoting traits. Based on morphological and 16S rRNA sequence analysis, the endophytes were distributed into 5 genera of which belong to Pseudomonas, Burkholderia, Paraburkholderia, Novosphingobium, and Ochrobactrum. HRP2, SSP2 and JRP22 were selected based on their plant growth-promoting traits for evaluation of Chinese fir growth enhancement. The growth parameters of Chinese fir seedlings after inoculation were significantly greater than those of the uninoculated control group. The results showed that PSBs HRP2, SSP2 and JRP22 increased plant height (up to 1.26 times), stem diameter (up to 40.69%) and the biomass of roots, stems and leaves (up to 21.28%, 29.09% and 20.78%) compared to the control. Total N (TN), total P (TP), total K (TK), Mg and Fe contents in leaf were positively affected by PSBs while showed a significant relationship with strain and dilution ratio. The content of TN, TP, TK, available phosphorus (AP) and available potassium (AK) in the soil increased by 0.23-1.12 mg g-1, 0.14-0.26 mg g-1, 0.33-1.92 mg g-1, 5.31-20.56 mg kg-1, 15.37-54.68 mg kg-1, respectively. Treatment with both HRP2, SSP2 and JRP22 increased leaf and root biomass as well as their N, P, K uptake by affecting soil urease and acid phosphatase activities, and the content of available nutrients in soil. In conclusion, PSB could be used as biological agents instead of chemical fertilizers for agroforestry production to reduce environmental pollution and increase the yield of Chinese fir.

Response of soil chemical properties and enzyme activity of four species in the Three Gorges Reservoir area to simulated acid rain.

The chemical composition in the precipitation is constantly changing, thus acid rain type is gradually changing from sulfuric type to mixed type and then nitric type. The influence of the changing acid rain type on the rhizosphere soil of tree species remains unclear. A pot experiment was performed with two-year-old Pinus massoniana, Cunninghamia lanceolate, Cyclobalanpsis glauca and Phyllostachys edulis seedlings with similar growth condition. Simulated acid rain consists of sulfuric(S/N = 5), mixed(S/N = 1) and nitric(S/N = 0.2) acid rain, and each type acid rain diluted to three acid rain intensity: pH = 2.5, 3.5, 4.5. Soil pH, soil organic matter, cation exchange capacity, the exchangeable Na+, K+, Ca2+, Mg2+ and enzyme activity were inhibited by acid rain intensity, while exchangeable Al3+ and H+ were promoted. Mg2+ was most relevant index to the tolerance to acid rain and the correlation degree of soil chemical index was higher than that of enzyme activity. Response of soil chemical properties differed in tree species under different acid rain types. Soil enzyme activity of Pinus massoniana, Cunninghamia lanceolate, and Phyllostachys edulis reached lowest under nitric acid rain, and that of Cyclobalanpsis glauca reached highest. Rhizosphere soil of Cunninghamia lanceolate is tolerant to sulfuric and nitric acid rain, and that of Cyclobalanpsis glauca is tolerant to mixed acid rain.

The Transcriptome of Cunninghamia lanceolata male/female cone reveal the association between MIKC MADS-box genes and reproductive organs development.

BACKGROUND: Cunninghamia lanceolata (Chinese fir), a member of the conifer family Cupressaceae, is one of the most popular cultivated trees for wood production in China. Continuous research is being performed to improve C. lanceolata breeding values. Given the high rate of seed abortion (one of the reasons being the failure of ovule and pollen development) in C. lanceolata, the proper formation of female/male cones could theoretically increase the number of offspring in future generations. MIKC MADS-box genes are well-known for their roles in the flower/cone development and comprise the typical/atypical floral development model for both angiosperms and gymnosperms. RESULTS: We performed a transcriptomic analysis to find genes differentially expressed between female and male cones at a single, carefully determined developmental stage, focusing on the MIKC MADS-box genes. We finally obtained 47 unique MIKC MADS-box genes from C. lanceolata and divided these genes into separate branches. 27 out of the 47 MIKC MADS-box genes showed differential expression between female and male cones, and most of them were not expressed in leaves. Out of these 27 genes, most B-class genes (AP3/PI) were up-regulated in the male cone, while TM8 genes were up-regulated in the female cone. Then, with no obvious overall preference for AG (class C + D) genes in female/male cones, it seems likely that these genes are involved in the development of both cones. Finally, a small number of genes such as GGM7, SVP, AGL15, that were specifically expressed in female/male cones, making them candidate genes for sex-specific cone development. CONCLUSIONS: Our study identified a number of MIKC MADS-box genes showing differential expression between female and male cones in C. lanceolata, illustrating a potential link of these genes with C. lanceolata cone development. On the basis of this, we postulated a possible cone development model for C. lanceolata. The gene expression library showing differential expression between female and male cones shown here, can be used to discover unknown regulatory networks related to sex-specific cone development in the future.

Effects of LED photoperiods and light qualities on in vitro growth and chlorophyll fluorescence of Cunninghamia lanceolata.

BACKGROUND: Cunninghamia lanceolata (C. lanceolata) is the main fast-growing timber species in southern China. As an alternative to conventional lighting systems, LED has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The application of LED can provide rapid propagation of C. lanceolata in vitro culture. RESULTS: We applied two-factor randomized block design to study the effects of LED photoperiods and light qualities on the growth and chlorophyll fluorescence of C. lanceolata in vitro culture plantlets. In this study, plantlets were exposed to 20 µmol·m- 2·s- 1 irradiance for three photoperiods, 8, 16, and 24 h under the three composite lights, 88.9% red+ 11.1% blue (R/B), 80.0% red+ 10.0% blue+ 10.0% purple (R/B/P), 72.7% red+ 9.1% blue+ 9.1% purple+ 9.1% green (R/B/P/G), as well as white light (12.7% red+ 3.9% blue+ 83.4% green, W) as control. The results showed that: (1) Plant height, dry weight, rooting rate, average root number, length, surface area and volume, chlorophyll, and chlorophyll fluorescence parameters were significantly affected by photoperiods, light qualities and their interactions. (2) Plantlets subjected to photoperiod 16 h had longer root, higher height, rooting rate, root number, and the higher levels of chlorophyll, chlorophyll a/b, Y (II), qP, NPQ/4 and ETRII compared to photoperiods 8 h and 24 h, while Fv/Fm during photoperiod 16 h was lower than 8 h and 24 h. Plantlets exposed to R/B/P/G generated more root and presented higher chlorophyll, Fv/Fo, Y (II), qP, and ETRII than W during photoperiods 8 and 16 h. (3) Total chlorophyll content and ETRII were significant correlated with rooting rate, root length and root volume, while Fv/Fm and ETRII were significant correlated with plant height, average root number and root surface area. (4) 16-R/B/P/G is best for growing C. lanceolata plantlets in vitro. CONCLUSIONS: This study demonstrated the effectiveness of photoperiods and light qualities using LEDs for micropropagation of C. lanceolata. The best plantlets were harvested under 16-R/B/P/G treatment. And there was a correlation between the growth and the chlorophyll and chlorophyll fluorescence of their leaves under different photoperiod and light quality. These results can contribute to improve the micropropagation process of this species.

Asymmetric pruning reveals how organ connectivity alters the functional balance between leaves and roots of Chinese fir.

The functional balance between leaves and roots is believed to be mediated by the specific location of shoots and roots, i.e. differences in transport distances and degrees of organ connectivity. However, it remains unknown whether the adaptive responses of trees to biomass removal depend on the relative orientation of leaf and root pruning. Here, we applied five pruning treatments to saplings of Cunninghamia lanceolata (Chinese fir) under field and glasshouse conditions, namely no pruning (control), half of lateral branches pruned, half of lateral roots pruned, half of the branches and roots pruned on the same side of the plant, and half of the branches and roots pruned on opposite sides of the plant. The effects of pruning on the growth, carbon storage and allocation, and physiology of leaves and fine roots on the same and opposite sides of the plant were investigated. Compared with the effect of root-pruning on leaves, fine roots were more limited by carbon availability and their physiological activity was more strongly reduced by shoot pruning, especially when branches on the same side of the plant were removed. Pruning of branches and roots on the opposite side of the plant resulted in the lowest carbon assimilation rates and growth among all treatments. The results of a stable-isotope labeling indicated that less C was distributed to fine roots from the leaves on the opposite side of the plant compared to those on the same side, but N allocation from roots to leaves depended less on the relative root and leaf orientation. The results collectively indicate that the functional responses of C. lanceolata to pruning are not only determined by the source-sink balance model but are also related to interactions between leaves and fine roots. We argue that the connectivity among lateral branches and roots depends on their relative orientation, which is therefore critical for the functional balance between leaves and fine roots.

Metabolomic Analysis of Pollen Grains with Different Germination Abilities from Two Clones of Chinese Fir (Cunninghamia lanceolata (Lamb) Hook).

Pollen grains produce certain metabolites, which can improve or inhibit germination and tube growth. Metabolomic analysis of germinating and growing Chinese fir pollen has not been reported. Therefore, this study aimed to analyse metabolites changes, content and expression in the germinating pollen of Chinese fir. To understand the metabolic differences, two clones from Chinese fir were selected. Metabolomics analyses were performed on three stages (1-, 24- and 48-h) during in vitro pollen germination. The metabolites profiles at different time points were analyzed by using liquid chromatography-mass spectrometry. The results showed that 171 peaks were screened; the corresponding differential metabolites of 121 peaks were classified into nine types of substances. The expression of metabolites showed significant differences across and between clones, and the variation was evident at all germination stages. The expression was obvious at the early stage of germination, which differed clearly from that of the late stage after pollen tube growth. Moreover, the metabolites were mainly enriched in 14 metabolic pathways. Pollen germination and tube growth and metabolites expressions changed per incubation time. Since this work is preliminary, we suggest further investigations to understand the relationship between the differential metabolites and pollen development, and factors affecting pollen germination process.

Effects of sulfuric, nitric, and mixed acid rain on Chinese fir sapling growth in Southern China.

The influence of acid rain on plant growth includes direct effects on foliage as well as indirect soil-mediated effects that cause a reduction in root growth. In addition, the concentration of NO3- in acid rain increases along with the rapid growth of nitrogen deposition. In this study, we investigated the impact of simulated acid rain with different SO42-/NO3- (S/N) ratios, which were 1:0, 5:1, 1:1, 1:5 and 0:1, on Chinese fir sapling growth from March 2015 to April 2016. Results showed that Chinese fir sapling height growth rate (HGR) and basal diameter growth rate (DGR) decreased as acid rain pH decreased, and also decreased as the percentage of NO3- increased in acid rain. Acid rain pH significantly decreased the Chlorophyll a (Chla) and Chlorophyll b (Chlb) content, and Chla and Chlb contents with acid rain S/N 1:5 were significantly lower than those with S/N 1:0 at pH 2.5. The chlorophyll fluorescence parameters, maximal efficiency of Photosystem II photochemistry (Fv/Fm) and non-photochemical quenching coefficient (NPQ), with most acid rain treatments were significantly lower than those with CK treatments. Root activities first increased and then decreased as acid rain pH decreased, when acid rain S/N ratios were 1:1, 1:5 and 0:1. Redundancy discriminant analysis (RDA) showed that the Chinese fir DGR and HGR had positive correlations with Chla, Chlb, Fv/Fm ratio, root activity, catalase and superoxide dismutase activities in roots under the stress of acid rain with different pH and S/N ratios. The structural equation modelling (SEM) results showed that acid rain NO3- concentration and pH had stronger direct effects on Chinese fir sapling HGR and DGR, and the direct effects of acid rain NO3- concentration and pH on HGR were lower than those on DGR. Our results suggest that the ratio of SO42- to NO3- in acid rain is an important factor which could affect the sustainable development of monoculture Chinese fir plantations in southern China.

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A field mesocosm experiment with Chinese fir (Cunninghamia lanceolata) seedlings was conducted in Chenda State-Owned Forest Farm, Sanming, Fujian Province. The effects of soil warming (ambient +5 ℃) on specific respiration rates and nonstructural carbohydrate (NSC) concentrations in fine roots were measured by the ingrowth core method, to reveal the belowground responses and the adaptability of Chinese fir to global warming. The results showed that soil warming caused significant changes of fine root NSC in the second year. The NSC and starch concentrations in 0-1 mm fine roots, and the NSC and sugar concentrations in 1-2 mm fine roots decreased signifi-cantly in January. The NSC, sugar and starch concentrations in 0-1 mm roots and the starch concentration in 1-2 mm roots increased in July. Soil warming had no significant effect on fine root NSC in the third year. The specific root respiration rate of the 0-1 mm roots significantly increased in July of the second year but significantly decreased in July of the third year in the warmed plots. Compared with the 0-1 mm roots, soil warming had no significant effect on the specific root respiration rate of the 1-2 mm roots. In conclusion, the responses of fine root respiration to soil warming depended on the duration of warming. Fine root respiration partly acclimated to soil warming with increasing duration of soil warming, which kept fine root NSC being relatively stable.

A More Comprehensive Community of Ammonia-Oxidizing Archaea (AOA) Revealed by Genomic DNA and RNA Analyses of amoA Gene in Subtropical Acidic Forest Soils.

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are the main nitrifiers which are well studied in natural environments, and AOA frequently outnumber AOB by orders especially in acidic conditions, making AOA the most promising ammonia oxidizers. The phylogeny of AOA revealed in related studies, however, often varied and hardly reach a consensus on functional phylotypes. The objective of this study was to compare ammonia-oxidizing communities by amoA gene and transcript based on both genomic DNA and RNA in extremely acidic forest soils (pH <4.5). Our results support the numerical and functional dominance of AOA over AOB in acidic soils as bacterial amoA gene and transcript were both under detection limits and archaeal amoA, in contrast, were abundant and responded to the fluctuations of environmental factors. Organic matter from tree residues was proposed as the main source of microbial available nitrogen, and the potential co-precipitation of dissolved organic matter (DOM) with soluble Al3+ species in acidic soil matrix may further restrict the amount of nitrogen sources required by AOB besides NH3/NH4+ equilibrium. Although AOA were better adapted to oligotrophic environments, they were susceptible to the toxicity of exchangeable Al3+. Phylotypes affiliated to Nitrososphaera, Nitrososphaera sister group, and Nitrosotalea were detected by amoA gene and transcript. Nitrosotalea devantaerra and Nitrososphaera sister group were the major AOA. Compared to the genomic DNA data, higher relative abundances of Nitrososphaera and Nitrososphaera sister group were recognized in amoA transcript inferred AOA communities, where Nitrosotalea relative abundance was found lower, implying the functional activities of Nitrososphaera sister group and Nitrososphaera were easily underestimated and Nitrosotalea did not attribute proportionally to nitrification in extremely acidic soils. Further comparison of the different AOA community compositions and relative abundance of each phylotypes revealed by amoA genes and transcripts make it possible to identify the functional AOA species and assess their ecological role in extremely acidic soils.

Soil microbial community structure and catabolic activity are significantly degenerated in successive rotations of Chinese fir plantations.

This study examined the hypotheses that soil microbial community composition and catabolic activity would significantly degenerated by consecutive monoculture in Chinese fir plantations. The phospholipid fatty acids (PLFA) and community level physiological profiles (CLPP) methods were used to assess the variations of soil microbial community among the first rotation Chinese fir plantation (FCP), the second rotation plantation (SCP) and the third rotation plantation (TCP). The total content of PLFA biomarkers was highest in FCP, followed by SCP, and TCP was the least detected. Conversely, the fungi/bacteria ratio significantly increased in the SCP and TCP soils. The average well-color development (AWCD) values significantly decreased (FCP > SCP > TCP). However, the sum of AWCD values of amino acids, carboxylic acids and phenolic compounds were higher significantly in the SCP and TCP soils than FCP soils, suggesting that the microflora feeding on acids gradually became predominant in the continuous monoculture plantation soils. Soil C/N ratio was one of the most important factors to soil microbial diversity. Both the PLFA and CLPP results illustrated the long-term pure plantation pattern exacerbated the microecological imbalance in the rhizospheric soils of Chinese fir, and markedly decreased the soil microbial community diversity and metabolic activity.

Optimization of hormone combinations for root growth and bud germination in Chinese fir (Cunninghamia lanceolata) clone leaf cuttings.

In order to ascertain the optimal hormone combination for Chinese fir (Cunninghamia lanceolata) leaf cuttings, an L16(4)4 orthogonal test of 6-benzylaminopurine (6-BA), 1-naphthaleneacetic acid (NAA), and indole-3-butyric acid (IBA) (0, 10, 30, or 50 mg · L-1 of each exogenous hormone) immersion for 5, 10, 15, or 20 min was conducted. Callus initiation rate and rooting promotion rate were mainly affected by treatment time, root length increase by 6-BA concentration, and bud germination rate and plantlet formation rate by NAA concentration. The expected optimal combination for callus initiation rate was 50 mg · L-1 6-BA + 0 mg · L-1 NAA + 30 mg · L-1 IBA + 10 min; for rooting promotion rate, it was 0-10 mg · L-1 6-BA + 10 mg · L-1 NAA + 30 mg · L-1 IBA + 20 min; for bud germination rate, it was 50 mg · L-1 6-BA + 0-10 mg · L-1 NAA + 0-30 mg · L-1 IBA + 20 min; and for seedling formation rate for No. 4, it was 10 mg · L-1 6-BA + 10 mg · L-1 NAA + 0 mg · L-1 IBA + 20 min. Light microscopy image analysis revealed that a cluster of primordial cells was produced 40 days after cutting, and mastoid cells developed into peninsula cells in calli that were cultured for 50 days.