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Soil microbial biomass and composition are affected by resource supply and water availability. However, the response of soil microbial communities to nitrogen fertilization under different water availability conditions is unclear. Therefore, this study conducted a 6-year pot experiment comprising five watering regimes (40%, 50%, 60%, 80%, and 100% of field capacity (FC)) and three nitrogen fertilization levels (NH4NO3 solution; 0 [N0], 20 [N1], and 40 [N2] g N m−2 year−1) to investigate soil microbial biomass, composition, and properties. The results indicated that soil microbial biomass and composition were more strongly affected by nitrogen fertilization compared with water regime. Nitrogen fertilization increased soil microbial biomass and altered soil microbial community composition, especially under low soil water availability. Soil microbial biomass was positively linearly associated with soil water regimes under N0, whereas it responded polynomially to soil water regimes under N1 and N2. The maximal soil microbial biomass was observed at FC80 for N1 and FC60 for N2. Furthermore, the biomass of soil microbial groups with high nitrogen and carbon acquisition ability as well as the enzyme activities of carbon and nitrogen cycling (β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, respectively) were stimulated by nitrogen fertilization. Soil microbial biomass was affected directly by nitrogen fertilization and indirectly by nitrogen and water regimes, via altering soil pH, dissolved inorganic nitrogen (NH4+-N and NO3−-N) concentration, and soil organic carbon concentration. This study provides new insights into the effect of interaction between soil nitrogen and water availabilities on soil microbial biomass, composition, and its underlying mechanism. [ABSTRACT FROM AUTHOR]

Pathogenesis-related (PR) proteins are important in plant pathogenic resistance and comprise 17 families, including the PR4 family, with antifungal and anti-pathogenic functions. PR4 proteins contain a C-terminal Barwin domain and are divided into Classes I and II based on the presence of an N-terminal chitin-binding domain (CBD). This study is the first to isolate two PR4 genes, PaPR4-a and PaPR4-b, from Picea asperata, encoding PaPR4-a and PaPR4-b, respectively. Sequence analyses suggested that they were Class II proteins, owing to the presence of an N-terminal signal peptide and a C-terminal Barwin domain, but no CBD. Tertiary structure analyses using the Barwin-like protein of papaya as a template revealed structural similarity, and therefore, functional similarity between the proteins. Predictive results revealed an N-terminal transmembrane domain, and subcellular localization studies confirmed its location on cell membrane and nuclei. Real-time quantitative PCR (RT-qPCR) demonstrated that PaPR4-a and PaPR4-b expression levels were upregulated following infection with Lophodermium piceae. Additionally, PaPR4-a and PaPR4-b were induced in Escherichia coli, where the recombinant proteins existed in inclusion bodies. The renatured purified proteins showed antifungal activity. Furthermore, transgenic tobacco overexpressing PaPR4-a and PaPR4-b exhibited improved resistance to fungal infection. The study can provide a basis for further molecular mechanistic insights into PR4-induced defense responses. [ABSTRACT FROM AUTHOR]

Partial desiccation treatment (PDT) is an effective technology for promoting the germination and conversion of conifer somatic embryos (SEs). PDT, as a drought stress, induces intensive physiological responses in phospholipid metabolism, which are not well understood in the conifer SEs. Here, we integrated lipidomics, transcriptomics and proteomics analyses to reveal the molecular basis of lipid remodeling under PDT in Picea asperata SEs. Among the 82 lipid molecular species determined by mass spectrometry, phosphatidic acid (PA) had a significant effect after PDT and was the most critical lipid in the response to PDT. The transcriptomics results showed that multiple transcripts in the glycerolipid and glycerophospholipid metabolism pathways were differentially expressed, and these included five PLDα1 transcripts that catalyze the conversion of phosphatidylcholine (PC) to PA. Furthermore, the enzyme activity of this phospholipase D (PLD) was significantly enhanced in response to PDT, and PDT also significantly increased the protein level of PLDα1 (MA_10436582g0020). In addition, PA is a key factor in gibberellin, abscisic acid and ethylene signal transduction. One GDI1, one DELLA, three ABI1s, two SnRK2s, one CTR and 12 ERFs showed significantly differential expression between SEs before and after PDT in this study. Our data suggest that the observed increases in the PA contents might result from the activation of PLDα by PDT. PA not only affects the physical and chemical properties of the cell membrane but also participates in plant hormone signal transduction. Our work provides novel insight into the molecular mechanism through which PDT promotes the germination of SEs of coniferous tree species and fills the gap in the understanding of the mechanism of somatic embryo lipid remodeling in response to PDT. [ABSTRACT FROM AUTHOR]

Analysis of height growth of dominant trees is crucial for accurate evaluation of site quality and how this influences stand characteristics. This study explores, whether stand origin, tree species composition and stand density influence the growth process of stand dominant height. We used forest resource inventory data from 1283 permanent plots in Sichuan Province, China. Three dominant trees were selected from each permanent plot to calculate the average dominant height and diameter at breast height (DBH). The Chapman-Richards equation was used to construct a dominant height prediction model of each tree species based on DBH. The effects of the stand origin, species composition, and stand density on the upper asymptote parameter a, shape parameter b, and growth rate parameter c were analyzed using a dummy variable method. The results show that there was no statistically significant difference in parameters a, b, and c among different stand origins, species composition, and stand density. The upper asymptote parameters of the stand with a natural origin were greater than stands with an artificial origin. Species composition influenced the parameters among different coniferous species but was associated with large coefficients of variation, especially for broadleaf species. Stand density moderatly influenced the model parameters for all species. With an increase in stand density, the influence of stand density on the model parameters decreased gradually. Our results confirm that the relationship between DBH and height of dominant trees is useful to evaluate site productivity. However, this method has to consider stand origin and differences in stand density and species composition, especially for species with DBHheight relations sensitive to stand conditions. [ABSTRACT FROM AUTHOR]

Partial desiccation treatment ( PDT) stimulates germination and enhances the conversion of conifer somatic embryos. To better understand the mechanisms underlying the responses of somatic embryos to PDT, we used proteomic and physiological analyses to investigate these responses during PDT in Picea asperata. Comparative proteomic analysis revealed that, during PDT, stress-related proteins were mainly involved in osmosis, endogenous hormones, antioxidative proteins, molecular chaperones and defence-related proteins. Compared with those in cotyledonary embryos before PDT, these stress-related proteins remained at high levels on days 7 (D7) and 14 (D14) of PDT. The proteins that differentially accumulated in the somatic embryos on D7 were mapped to stress and/or stimuli. They may also be involved in the glyoxylate cycle and the chitin metabolic process. The most significant difference in the differentially accumulated proteins occurred in the metabolic pathways of photosynthesis on D14. Furthermore, in accordance with the changes in stress-related proteins, analyses of changes in water content, abscisic acid, indoleacetic acid and H2O2 levels in the embryos indicated that PDT is involved in water-deficit tolerance and affects endogenous hormones. Our results provide insight into the mechanisms responsible for the transition from morphologically mature to physiologically mature somatic embryos during the PDT process in P. asperata. [ABSTRACT FROM AUTHOR]

In this study, spruce tree rings from the southern slope of mid-Qinling Mountains were adopted to investigate the characteristics of average minimum temperatures during the past 138 years. Analysis showed that the interannual variability in radial growth of trees was positively correlated with the interannual variability of average minimum temperatures from previous December to current September ( VTM ) in the study area during 1955-2010 ad. Based on the correlation analysis, the VTM were reconstructed for 1876-2013 ad with an explained variance of 42.5 % for the calibration period. Among the 22 dramatic changing years, extreme changes occurred more times when it was cooling, while the warming was comparatively gentle. Both the 10-year filtering of VTM series and the frequency of occurrences for those dramatic changing years showed a relatively stationary variation after the early 1950s. Over the last five decades, the accumulated VTM series showed an obvious warming trend, and the increase of the minimum temperature had contributed to the regional warming. The comparison of VTM and the dryness/wetness indices generally reflected cold-wet and warm-dry climate conditions in the study area. Significant positive correlations between the reconstructed VTM and the gridded minimum temperature indicated a regional representative of the temperature reconstruction, and positive correlations between VTM and sea surface temperature (SST) of the Indian Ocean and western Pacific regions suggested a possible linkage between the VTM variations and the Asian summer monsoon. Synchronous fluctuations in three tree-ring study series and connections of VTM with Arctic oscillation (AO) and El Niño-Southern Oscillation (ENSO) activities suggested that the minimum temperature variations in the TTH area responded sensitively to large-scale climate fluctuations and were the results of atmosphere-ocean interactions. [ABSTRACT FROM AUTHOR]

Despite the recognized importance of root exudation to soil biogeochemical processes and soil function in forest ecosystems, few studies have investigated the impact of quantity and stoichiometry of root exudation on soil nitrogen (N) transformations. In addition, the potential mechanism of how climate warming influences soil N cycling via root-soil interactions remains unclear. We performed an experiment in which in situ root exudates were collected from Picea asperata seedling to examine the response of root carbon (C) & N exudation rates and the C: N ratio stoichiometry along with the soil N transformation rates to warming using infrared heaters in the Eastern Tibetan Plateau. The results showed that warming enhanced root C exudation rates (ug C g −1 root biomass h −1 ), with higher C: N ratio stoichiometry simultaneously. Experimental warming also significantly increased the soil net mineralization rates, net nitrification rates, and denitrification rates. Then, we conducted an in vitro experiment in which three bacterial strains ( Bacillus subtilis , Nitrobacter hamburgensis , and Brachymonas denitrificans ) representing ammonifiers, nitrifiers, and denitrifiers, respectively, were cultured with exudates as the culture media. The results indicated that root exudates collected in warmed plots significantly stimulated the growth of the three soil N transformation bacteria, compared with the treatments in control plots. Collectively, our results, to some degree, evidence a linkage that climate warming-induced changes in C fluxes and C: N ratio stoichiometry of root exudation stimulated the growth and reproduction of soil N transformation bacteria, consequently accelerating the soil organic matter decomposition and soil N transformations. [ABSTRACT FROM AUTHOR]

Abstract: Previous research on the effects of tree species on soil processes has focused primarily on the role of leaf litter inputs and relatively few studies have considered the importance of plant roots and their associated ecological processes, especially under climate change. We therefore conducted an experiment to compare the impacts of two coniferous species via roots on soil N transformations and their responses to experimental warming using infrared heaters in the Eastern Tibetan Plateau. The infrared heater on average enhanced both air temperature and soil temperature by 2.0 °C and 3.7 °C, respectively. Warming did not affect soil organic C (SOC), total N (TN), microbial biomass C (MBC) and N (MBN), or their ratios (MBC/MBN) in both coniferous species plots. Effects of experimental warming on soil N availability varied with tree species and sampling dates. There were higher and lower concentrations in the Picea asperata than in the Abies faxoniana plots irrespective of warming treatment or sampling date, possibly caused by higher gross nitrification and denitrification rates in the P. asperata. Experimental warming significantly increased the net mineralization, net nitrification and denitrification rates on most sampling times in both species plots. Responses of gross nitrification to experimental warming significantly differed between the two species, and depended strongly on seasons. Gross nitrification and denitrification rates were markedly greater in the P. asperata than in the A. faxoniana plots, with P. asperata being more sensitive than A. faxoniana in response to experimental warming. Differences in the root morphology (i.e., root length, root type) and activity (i.e., root exudation, fine root vigor) between the two species could be largely responsible for the variation in the soil N cycling and its response to experimental warming. Taken together, our results indicate that tree species can differ in their effects on soil transformations and nutrient availability via roots and associated microbial processes. Further research is required regarding the exact mechanisms of tree species effects via roots on soil processes and function under climate change. [Copyright &y& Elsevier]

The impacts of global climatic change on belowground ecological processes of terrestrial ecosystems are still not clear. We therefore conducted an experiment in the subalpine coniferous forest ecosystem of the eastern edges of the Tibetan Plateau to study roots of Picea asperata seedlings and rhizosphere soil responses to soil warming and nitrogen availability from April 2007 to December 2008. The seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0 or 25 g myear N). We used a free air temperature increase from an overhead infrared heater to raise both air and soil temperature by 2.1 and 2.6°C, respectively. The results showed that warming alone significantly increased total biomass, coarse root biomass and fine root biomass of P. asperata seedlings. Both total biomass and fine root biomass were increased, but coarse root biomass was significantly decreased by nitrogen fertilization and warming combined with nitrogen fertilization. Warming induced a prominent increase in soil organic carbon (SOC) and NO-N of rhizosphere soil, while nitrogen fertilization significantly decreased SOC and NH-N of rhizosphere soil. The warming, fertilization and warming × N fertilization interaction decreased soil microbial C significantly, but substantially increased soil microbial N. These results suggest that nitrogen deposition combined with warmer temperatures under future climatic change possibly will have no effect on fine root production of P. asperata seedlings, but could enhance the nitrification process of their rhizosphere soils in subalpine coniferous forests. [ABSTRACT FROM AUTHOR]

The short-term effects of two levels of air temperature (ambient and warmed) and light (full light and ca. 10% of full light regimes) on the early growth and physiology of Picea asperata and Abies faxoniana seedlings was determined using open-top chambers (OTC). The OTC manipulation increased mean air temperature and soil surface temperature by 0.51°C and 0.34°C under the 60-year plantation, and 0.69°C and 0.41°C under the forest opening, respectively. Warming, with either full-light or low-light conditions, generally caused a significant increase in plant growth, biomass accumulation, and stimulated photosynthetic performance of P. asperata seedlings. However, the warming of A. faxoniana seedlings only significantly increased their growth under low-light conditions, possibly as a result of photoinhibition caused by full light, which may shield and/or impair the effects of warming manipulation, per se, on the growth and physiological performance of A. faxoniana seedlings. In response to warming, P. asperata seedlings allocated relatively more biomass to roots and A. faxoniana more to foliage under similar environments. This might provide A. faxoniana with an adaptive advantage when soil moisture was not limiting and an advantage to P. asperata if substantial moisture stress occurred. Warming markedly increased the efficiency of PSII in terms of the increase in F v/ F m and photosynthetic pigment concentrations for the two conifer seedlings, but the effects of warming were generally more pronounced under low-light conditions than under full-light conditions. On balance, this study suggested that warming had a beneficial impact on the early growth and development of conifer seedlings, at least in the short term. Consequently, warming may lead to changes in forest regeneration dynamics and species composition for subalpine coniferous ecosystems under future climate change. [ABSTRACT FROM AUTHOR]

Dragon spruce (Picea asperata Mast.) is widely planted on clear-cuts from natural subalpine coniferous forests in western Sichuan. To assess the natural regeneration potential of this species in spruce plantations of different ages, field studies on the seed rain, seed bank, and seedling recruitment were conducted in 20-year, 30-year, and 60-year plantations, and in a retained natural forest ca. 150 years old for comparison. Moreover, a series of temperature and light regimes were also designed in March 2003 to test germination/dormancy responses of the P. asperata seeds to different conditions. In the plantations considered, both the densities of seed rain and soil seed bank increased with increasing stand age, whereas they were both low beneath the natural forest partially due to low adult density of P. asperata adult trees. P. asperata has a transient seed bank, and ca. 60% of seeds were found in the litter layer. Seed decay and seed predation were the two most important factors affecting soil seed bank dynamics, which caused a number of seed losses from the soil. Only a small fraction germinated and produced seedlings, and the indices of the losses from the seed bank via germination in the 30-year plantation, 60-year plantation and natural forest were 4.75, 5.10, and 2.80%, respectively. High seedling mortality was observed after seedling emergence, and most of the germinated seedlings died out within one growing season. The P. asperata seeds showed a high percent germination and no significant differences under most light and temperature regimes except for full sunlight or temperature below 5°C. In conclusion, despite a substantial number of seed produced, the high depletion of soil seed, the low seedling output, and high seedling mortality may obscure the natural regeneration potential of this tree species. [ABSTRACT FROM AUTHOR]

Abstract: The genetic structure and diversity of natural populations of Picea asperata Mast. were investigated based on seven microsatellite loci. For a total of 300 individuals from 10 populations sampled, a moderate to high level of genetic diversity was observed at population levels with the number of alleles per locus (A) ranging from 6.86 to 11.86 (average 10.89), the proportion of polymorphic loci (P) equaling 100.0%, and the expected heterozygosity (He) ranging from 0.409 to 0.440 (average 0.426). The proportion of genetic differentiation present among populations accounted for 22.3% of the whole diversity. Such extensive inter-population differentiation detected in P. asperata could have resulted from several factors, including restricted gene flow between populations. In fact, the estimate of gene flow obtained in the study was low (Nm=0.871). Habitat fragmentation caused by human disturbances may be a factor attributing to the low level of gene flow and high genetic differentiation among populations. Our results suggest that microsatellite markers are powerful high-resolution tools for the accurate assessment of population genetic parameters, which are greatly needed in the conservation genetics of P. asperata. [Copyright &y& Elsevier]