[Community structure of phyllosphere fungi associated with dominant tree species in a broad-leaved Korean pine forest of Changbai Mountain, Northeast China]

Forest is the main component of terrestrial ecosystems that harbors about 40% of the existing species on the earth. As a vital component of biodiversity, phyllosphere microbes in the canopy play a critical and unique role in maintaining plant health, improving host resistance, and influencing global biogeochemical cycle. However, the studies on the community structure of phyllosphere fungi in natural forests are scarce as compared to that on rhizosphere microbes. Consequently, we know litter about how phyllosphere fungi associates with leaf traits. In this study, we analyzed fungal community composition of canopy leaves of six dominant tree species (i.e., Pinus koraiensis, Tilia amurensis, Quercus mongolica, Acer mono, Fraxinus mandshurica, and Ulmus japonica), in a broad-leaved Korean pine forest of Changbai Mountain Nature Reserve in Jilin Province, using high-throughput sequencing. We compared the differences of phyllosphere fungal community structure and functional groups of different dominant tree species. Moreover, 14 key leaf functional traits of their host trees were measured to investigate the relationships between fungal community composition and leaf functional traits. We found that the dominant phyla and class of phyllosphere fungi were Ascomycota and Basidiomycota, and Dothideomycetes and Taphrinomycetes, respectively. Results of LEfSe analysis indicated that all the tree species except Ulmus japonica had significant biomarkers, such as the Eurotiomycetes of Pinus koraiensis and the Ascomycetes of Quercus mongolica. The main functional groups of phyllosphere fungi were pathotroph. The results of redundancy and envfit analysis showed that functional traits related to plant nutrient acquisition as well as resistance to diseases and pests were the main factors influencing the community structure of phyllosphere fungi.

[Shrub layer structure and species diversity of warm temperate deciduous broadleaved forests of the Qinling Mountains Huangguan plot in China]

Shrub is an important part of forest ecosystem. Exploring the species composition, structure and spatial distribution of shrub layer can lay an important foundation for further clarifying the mechanisms underlying species coexistence, biodiversity maintenance and community succession. In this study, species composition, spatial distribution, and species diversity of shrub layer were analyzed in 25 hm² of Huangguan forest plot. A total of 20716 individual shrubs (with 10463 branches) were recorded in the plot, belonging to 54 species, 45 genera, 28 families. The status of dominant species in the shrub layer was not obvious, with all the importance values being less than 10. The diameter structure of shrub layer vegetation was inverted 'J' type. Shrubs showed aggregated distribution in the plot, with obvious altitude differences in spatial distribution. The diameter structure and spatial distribution of the nine shrub species with the largest abundance in the plot were consistent with the overall situation of shrub layer. With increasing altitude, the Shannon diversity index (H) and Simpson dominance index (D) did not change significantly, while the Pielou evenness index (E) decreased. Those indices decreased with the increases of the abundance of dominant species in tree layer, and E increased with the increase of the number of dominant species in sub-tree layer. The indices of H, D, E were significantly negatively correlated with soil total phosphorus (TP). The H index was significantly positively correlated with soil pH, and the E index was significantly positively correlated with soil total potassium. The shrub layer was rich in species, stable in community structure and well regenerated. The species diversity of shrub layer was mainly affected by the number of dominant species in the tree layer, soil pH, and TP.

[Spatial distribution patterns and intraspecific and interspecific associations of dominant shrub species Lonicera fragrantissima var. lancifolia in Huangguan of Qinling Mountains, China]

In this study, the spatial distribution patterns of individuals with different diameter classes of dominant shrub Lonicera fragrantissima var. lancifolia and the intraspecific and interspecific relationships were analyzed in Qinling Huangguan Plot. The results showed that the diameter class structure of L. fragrantissima var. lancifolia showed a pyramid shape, with a wide bottom and a narrow top. The number of small-diameter class individuals was the largest, showing a good state of renewal and a stable growth, which was conducive to community renewal and succession. Based on Ripley's K function, using univariate and bivariate paired correlation functions, under complete spatial randomness model, heterogeneous Poisson model and antecedent condition model, all individual of the species and their diameter-dividing classes were mainly aggregated, and the aggregation degree decreased with the increases of research scale, and gradually tended to random distribution. Affected by habitat heterogeneity, diffusion restriction and negative density dependence, there was a positive correlation among different intraspecific dia-meter classes, and also a certain degree of no correlation, but without negative correlation. The interspecific relationship was complex. All types of association (no, positive and negative) were observed, but negative association and no association were dominated.

[Spatial distribution pattern and intraspecific association of dominant species Quercus aliena var. acu-tiserrata in Qinling Mountains, China]

To explore the spatial distribution and intraspecific correlation of Quercus aliena var. acutiserrata, a domi-nant tree species in a 25 hm² plot of warm temperate deciduous broadleaved forest in Qinling Mountains, the pair-correlation function g(r) was used to study the spatial pattern and intraspecific association. The results showed that the diameter class structure of Q. aliena var. acutiserrata was bimodal, with a large proportion of young trees (1 cm≤DBH＜5 cm), indicating an increase population structure with good capability of regeneration. The abundance of middle trees (15 cm≤DBH＜25 cm) was slightly more than that of big trees (25 cm≤DBH＜35 cm) and old trees (DBH≥35 cm), but far less than that of young trees and small trees. The spatial distribution of Q. aliena var. acuteserrata was obviously altitude dependent, which mainly distributed in the middle and high altitude areas. Results of complete spatial randomness (CSR) model analysis showed that young trees, small trees, adult trees, big trees, and old trees were aggregated in the large scale (＜60 m). Heterogeneous Poisson (HP) model was used to eliminate habitat heterogeneity. The results of HP model showed that the individual aggregation degree of each diameter class decreased, indicating that the distribution was affected by habitat heterogeneity. At the small scale (＜40 m), spatial correlation was positively correlated between individuals with small diameter gap, whereas the spatial correlation was negative correlation and no correlation between individuals with large diameter gap. At large scale (>40 m), the spatial correlation was positively correlated between large-diameter individuals, but negatively correlated and unrelated between saplings and other diameter individuals. Our results indicated that biological cha-racteristics of Q. aliena var. acutiserrata and habitat heterogeneity were important drivers for the formation of population spatial pattern.

[Species composition and community structure of warm temperate deciduous broadleaved forests in Huangguan of Qinling Mountains, China]

The Qinling Mountain is a natural boundary between warm temperate zone and subtropical zone. While the China Forest Biodiversity Monitoring Network (CForBio) have basically covered most of the climate regions in China, few plots were located in the climate transition zone. Following the field protocol of CForBio and the Center for Tropical Forest Science (CTFS), a 25 hm²(500 m×500 m) forest plot was established in Huangguan Nature Reserve in Shaanxi Province, China, in 2019. In this study, we analyzed species composition, flora characteristics, diameter class structure, and spatial distribution patterns of dominant tree species based on the data of all woody species with a diameter at breast height (DBH) ≥1 cm. The results showed that there were 75137 woody individuals with DBH ≥1 cm in the plot (95679 when including branching individuals), belonging to 121 species, 83 genera and 44 families. The flora type at the genera level was mainly temperate, accounting for 71.1% of the total genera, and mixed with some tropical components. The dominant species in the community were obvious, with the number of individuals in the top 5 species exceeding 40% of the total number of individuals, the number of individuals in the top 50 species accounting for 95% of the total number of individuals, and the number of individuals in the remaining 61 species being less than 5% of the total. The diameter distribution of all woody indivi-duals in the plot was inverted 'J' type. Spatial distribution patterns varied across the four most abundant species with importance value >5. The degree of aggregation within species decreased with the increases of scales, while the spatial distribution of different species was affected by environmental heterogeneity. Warm-temperate deciduous broadleaved forest in Qinling Mountains had abundant species, stable community structure and good regeneration, reflecting the typical characteristics of the transition from warm temperate zone to subtropical zone. Environmental heterogeneity might be an important factor affecting the spatial distribution of tree species in the plot.

Isotopic determination with molecular emission using laser-induced breakdown spectroscopy and laser-induced radical fluorescence

Molecular emission can be used for isotopic analysis in laser-induced breakdown spectroscopy (LIBS) due to its large isotopic shift. However, spectral weakness and interference have become the main flaws in molecular isotopic analysis, causing deterioration of quantitative accuracy and sensitivity. Here, to overcome these problems, laser-induced radical fluorescence (LIRF) was applied to enhance the molecular spectra and eliminate the spectral interference. The root mean square errors of cross validation (RMSECVs) of boron and carbon isotopes (¹¹BO, ¹⁰BO, ¹²CN, and ¹³CN) improved to 2.632, 5.721, 5.990, and 1.543 at.%, as compared with 16.96, 35.79, 57.10, and 13.89 at.%, respectively, obtained in the case without LIRF. The limits of detection (LoDs) of ¹¹BO, ¹⁰BO, ¹²CN, and ¹³CN were 0.9858, 0.8470, 1.606, and 1.193 at.%, respectively. This work demonstrates the feasibility of LIBS-LIRF to achieve isotopic determination with high accuracy and sensitivity.

One-point and multi-line calibration method in laser-induced breakdown spectroscopy

The calibration-free laser-induced breakdown spectroscopy (CF-LIBS) and its variations are low cost, short time consumption, and high adaptability. However, seeking a more flexible and simple quantitative analysis method remains a challenge. A one-point and multi-line calibration (OP-MLC) was presented as a simple quantitative analysis method of LIBS. The results showed that OP-MLC-LIBS method can achieve quantitative analysis using only one standard sample, and the average relative errors (AREs) are 9, 22, 21 and 36% for Mn, Cr, Ni and Ti elements in six tested low-alloy steel samples, respectively. The method requires neither a large number of standard samples nor complicated calculations, which provides a flexible and low-cost quantitative analysis approach for development and application of LIBS.

Determination of boron with molecular emission using laser-induced breakdown spectroscopy combined with laser-induced radical fluorescence

Boron is an essential element for industry, but it is hard to accurately and rapidly determine high boron content with conventional laser-induced breakdown spectroscopy (LIBS), due to the matrix and self-absorption effect. Using molecular emission is an alternative method for boron content analysis, but its weak spectra are major challenges. Here, boron monoxide (BO) radicals were used to establish calibration assisted by LIBS and laser-induced radical fluorescence (LIBS-LIRF). Two types of BO radical excitations, vibrational ground state excitation (LIRFG) and vibrational excited state excitation (LIRFE), were compared. The results showed that LIRFG achieved better sensitivity with a limit of detection of 0.0993 wt.%, while the LIRFE was more accurate with a root mean square error of cross validation of 0.2514 wt.%. In conclusion, this work provided a potential approach for molecular emission analysis with LIBS-LIRF.

Investigation on self-absorption at reduced air pressure in quantitative analysis using laser-induced breakdown spectroscopy

The self-absorption at reduced air pressure for quantitative analysis of Mn and Cu elements in steel using laser-induced breakdown spectroscopy was investigated. The calibration curves of Mn and Cu elements at the air pressures of 100, 80, 50, 20, and 1 kPa were studied. The results show that, the nonlinearity of calibration curves which caused by self-absorption effects at atmosphere could be significantly improved by reducing the air pressure to 1 kPa, and the coefficients of determination (R²) of linear calibration curves of Mn and Cu lines are all higher than 0.99. The further study explored that the reason for the improvement was that the induced plasma became low density and the self-absorption coefficient was close to 1 when the air pressure reduced to 1 kPa.

Sensitive determinations of Cu, Pb, Cd, and Cr elements in aqueous solutions using chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy

In this study, chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy (CR-SENLIBS) was for the first time applied to improve the detection sensitivities of trace heavy metal elements in aqueous solutions. Utilizing chemical replacement effect, heavy metal ions in aqueous solution were enriched on the magnesium alloy surface as a solid replacement layer through reacting with the high chemical activity metallic magnesium (Mg) within 1 minute. Unitary and mixed solutions with Cu, Pb, Cd, and Cr elements were prepared to construct calibration curves, respectively. The CR-SENLIBS showed a much better detection sensitivity and accuracy for both unitary and mixed solutions. The coefficients of determination R² of the calibration curves were above 0.96, and the LoDs were of the same order of magnitude, i.e., in the range of 0.016-0.386 μg/mL for the unitary solution, and in the range of 0.025-0.420 μg/mL for the mixed solution. These results show that CR-SENLIBS is a feasible method for improving the detection sensitivity of trace element in liquid sample, which definitely provides a way for wider application of LIBS in water quality monitoring.

Background removal in soil analysis using laser- induced breakdown spectroscopy combined with standard addition method

The matrix effect of powder samples, especially for soil samples, is significant in laser-induced breakdown spectroscopy (LIBS), which affects the prediction accuracy of the element concentration. In order to reduce this effect of the soil samples in LIBS, the standard addition method (SAM) based on background removal by wavelet transform algorithm was investigated in this work. Five different kinds of certified reference soil samples (lead (Pb) concentrations were 110, 283, 552, 675, and 1141 ppm, respectively) were used to examine the accuracy of this method. The root mean square error of prediction (RMSEP) was more than 303 ppm by using the conventional calibration method. After adoption of SAM with background removal by wavelet transform algorithm, the RMSEP was reduced to 25.7 ppm. Therefore, the accuracy of the Pb element was improved significantly. The mechanism of background removal by wavelet transform algorithm based on SAM is discussed. Further study demonstrated that this method can also improve the predicted accuracy of the Cd element.

Acidity measurement of iron ore powders using laser-induced breakdown spectroscopy with partial least squares regression

Laser-induced breakdown spectroscopy (LIBS) with partial least squares regression (PLSR) has been applied to measuring the acidity of iron ore, which can be defined by the concentrations of oxides: CaO, MgO, Al₂O₃, and SiO₂. With the conventional internal standard calibration, it is difficult to establish the calibration curves of CaO, MgO, Al₂O₃, and SiO₂ in iron ore due to the serious matrix effects. PLSR is effective to address this problem due to its excellent performance in compensating the matrix effects. In this work, fifty samples were used to construct the PLSR calibration models for the above-mentioned oxides. These calibration models were validated by the 10-fold cross-validation method with the minimum root-mean-square errors (RMSE). Another ten samples were used as a test set. The acidities were calculated according to the estimated concentrations of CaO, MgO, Al₂O₃, and SiO₂ using the PLSR models. The average relative error (ARE) and RMSE of the acidity achieved 3.65% and 0.0048, respectively, for the test samples.

[Species composition and community structure of a spruce-fir forest and a larch forest on the northern slope of Changbai Mountains, Northeast China]

Spruce-fir forest is the best protected forest vegetation, while larch forest is intrazonal vegetation on the northern slope of Changbai Mountains. To further understand their species composition and community structure, we established a 4 hm2 forest permanent plot in each of these two forests in 2010. All free-standing plant species with DBH (diameter at breast height) ≥ 1 cm were mapped, tagged, and identified to species. The results showed that there were 9257 stems belonging to 8640 genotype individuals, 22 species, 6 genera and 12 families in the spruce-fir forest plot, while 4060 stems belonging to 3696 genotype individuals, 22 species, 8 genera and 16 families in the larch forest plot. Species composition in the two plots was very similar. Most of the species belonged to the Changbai Mountains plant flora. The analysis of species' importance values showed that there were dominant species in both communities. The spruce-fir forest was dominated by Abies nephrolepis and Larix olgensis, whose importance values accounted for 38.7% and 23.9% of the sum of importance values over all species in the plot, respectively. The larch forest was dominated solely by L. olgensis, whose importance value accounted for 61.9% of the sum of importance values over all species in the plot. Both forests were in good condition of regeneration and showed a reversed 'J' type in tree size distributions, at community level. However, different species showed different shapes in size distribution in the two forests. A. nephrolepis showed a reversed 'J' type size distribution in the spruce-fir forest, while L. olgensis with DBH ≥ 10 cm showed a hump-shaped distribution in the larch forest. Spatial distribution patterns of the main species changed differently with size class and spatial scales. Common species had different spatial distribution patterns in the two plots.

Accuracy improvement of quantitative analysis in laser-induced breakdown spectroscopy using modified wavelet transform

A modified algorithm of background removal based on wavelet transform was developed for spectrum correction in laser-induced breakdown spectroscopy (LIBS). The optimal type of wavelet function, decomposition level and scaling factor γ were determined by the root-mean-square error of calibration (RMSEC) of the univariate regression model of the analysis element, which is considered as the optimization criteria. After background removal by this modified algorithm with RMSEC, the root-mean-square error of cross-validation (RMSECV) and the average relative error (ARE) criteria, the accuracy of quantitative analysis on chromium (Cr), vanadium (V), cuprum (Cu), and manganese (Mn) in the low alloy steel was all improved significantly. The results demonstrated that the algorithm developed is an effective pretreatment method in LIBS to significantly improve the accuracy in the quantitative analysis.

[Woody plant species composition and community structure in residual fragments of broad-leaved Korean pine mixed forests in Changbai Mountains area]

The broad-leaved Korean pine mixed forest represents the typical vegetation type of the eastern mountain area in Northeast China. However, due to the interference of human activities, the natural broad-leaved Korean pine forest only distributes in some residual fragments with unequal areas in Changbai Mountains and Small Hinggan Mountains. To compare and analyze the similarities and differences of broad-leaved Korean pine mixed forests in the different areas, we established six forest plots following the field protocol of the 50 hm2 forest plot in Panama (Barro Colorado Island, BCI) in 2012 in Changbai Mountain National Nature Reserve in Jilin Province and the eastern mountain area in Liaoning Province. All free-standing plant species with DBH (diameter at breast height) > or = 1 cm were mapped, tagged and identified to species. The results showed that there were 69 woody species in the six plots, comprising 42 genera and24 families. Aceraceae was the most species-rich family in all six plots. Most species belonged to the plant type of North Temperate Zone, with a minor subtropical plant species component. The statistics of species abundance, basal area, mean DBH, and importance value showed that there were obviously dominant species in each community. The DBH distribution of all individuals showed a reversed "J" type. However, the percentage of individuals in small size-class and large size-class varied in the six communities, which indicated that these communities were at different successional stages. Ranked by the importance value, the DBH distribution of the top three species in the six plots showed four distribution types: reversed "J" distribution, reversed "L" distribution, unimodal distribution, and partial peak distribution. Spatial distribution patterns of the main species in the six plots changed differently with species and size-class, and the distribution patterns of the same species varied in the different plots.

Accuracy improvement on polymer identification using laser-induced breakdown spectroscopy with adjusting spectral weightings

A new approach to polymer identification by laser-induced breakdown spectroscopy (LIBS) with adjusting spectral weightings (ASW) was developed in this work aiming at improving the identification accuracy. This approach has been achieved through increasing the intensities of specific characteristic spectral lines which are important to polymer identification but difficult to be excited. Using the ASW method, the identification accuracies of all 11 polymers were increased to nearly 100%, while the accuracies of PE, PU, PP and PC were only 98%, 74%, 90% and 98%, respectively, without using the ASW method.

[Spatial autocorrelation of genetic structure of Prunus padus population in broadleaved Korean pine forest of Changbai Mountains]

All 396 Prunus padus individuals of the population with DBH (diameter at breast height) > or = 1 cm were sampled in a 25 hm2 broadleaved Korean pine forest plot of Changbai Mountains and divided into three DBH classes: 1-3 cm, 3-10 cm, and >10 cm. They were then genotyped using microsatellite loci. The spatial autocorrelation of their genetic structure was analyzed at different distance classes and life stages. The results showed that positive autocorrelation mainly occurred at scales less than 70 m, while negative autocorrelation occurred at scales larger than 110 m. The spatial genetic structure (SGS) at different life stages was similar due to limited pollen/seed dispersal and asexual reproduction. No significant self-thinning occurred in the studied population.

Accuracy improvement of quantitative analysis by spatial confinement in laser-induced breakdown spectroscopy

To improve the accuracy of quantitative analysis in laser-induced breakdown spectroscopy, the plasma produced by a Nd:YAG laser from steel targets was confined by a cavity. A number of elements with low concentrations, such as vanadium (V), chromium (Cr), and manganese (Mn), in the steel samples were investigated. After the optimization of the cavity dimension and laser fluence, significant enhancement factors of 4.2, 3.1, and 2.87 in the emission intensity of V, Cr, and Mn lines, respectively, were achieved at a laser fluence of 42.9 J/cm(2) using a hemispherical cavity (diameter: 5 mm). More importantly, the correlation coefficient of the V I 440.85/Fe I 438.35 nm was increased from 0.946 (without the cavity) to 0.981 (with the cavity); and similar results for Cr I 425.43/Fe I 425.08 nm and Mn I 476.64/Fe I 492.05 nm were also obtained. Therefore, it was demonstrated that the accuracy of quantitative analysis with low concentration elements in steel samples was improved, because the plasma became uniform with spatial confinement. The results of this study provide a new pathway for improving the accuracy of quantitative analysis of LIBS.

[Short-term death dynamics of trees in natural secondary poplar-birch forest in Changbai Mountains of Northeast China]

Taking the 5 hm2 sampling plot in the natural secondary poplar-birch forest in Changbai Mountains as test object, and based on the two census data in 2005 and 2010, an analysis was made on the main tree species composition and quantity, size class distribution of dead individuals, and regeneration characteristics of the main tree species in different habitat types of the plot in 2005-2010. In the five years, the species number of the individuals with DBH> or = 1 cm increased from 46 to 47, among which, 3 species were newly appeared, and 2 species were disappeared. The number of the individuals changed from 16509 to 15027, among which, 2150 individuals died, accounting for 13% of the whole individuals in 2005, and 668 individuals were newly increased. The basal area of the trees increased from 28.79 m2.m-2 to 30.55 m2.m-2, with that of 41 species increased while that of 6 species decreased. The decrease of the basal area of Betula platyphylla and Populus davidiana accounted for 72.3% of the total decrease. Small individuals had higher mortality, as compared with large ones, and the mortality of the individuals with DBH<5 cm occupied 65% of the total. B. platyphylla and P. davidiana contributed most in the dead individuals with large DBH. No difference was observed in the tree mortality among different habitat types, but the mortality of the individuals with different size classes showed greater variation.

[Species composition, structure, and spatial distribution of shrubs in broad-leaved Korean pine (Pinus koraiensis) mixed forest in Changbai Mountains]

Based on the shrub census of 600 quadrats (5 mx5 m) in a 25 hm2 plot of broad-leaved Korean pine mixed forest in Changbai Mountains, this paper analyzed the species composition, structure, and spatial distribution of shrubs in the forest. A total of 18 shrub species, including 6435 shrub individuals and 11369 stems, were found in the census, with Philadelphus schrenkii, Corylus mandshurica, and Acer barbinerve being the dominant species. P. schrenkii had the highest amounts of individuals and stems, occupying 40.6% and 33.4% of the total, respectively. There existed great differences in the clumpy ratio, stem number per clump, crown size, and basal diameter among the shrub species, and the height of different shrub species also varied significantly, with obvious vertical stratification observed in the community. The dominant species P. schrenkii had a wide distribution, while Sorbaria sorbifolia, Spiraea chamaedryfolia, S. salicifolia, and Euonymus pauciflorus had obvious heterogeneous distributions.

[Effects of precipitation and interspecific competition on Quercus mongolica and pinus koraiensis seedlings growth]

Aiming at the variation of precipitation pattern caused by global warming, a field simulation experiment was conducted to study the effects of 30% increase (+W) and decrease (-W) of precipitation on the morphology, growth, and biomass partitioning of mono- and mixed cultured seedlings of Quercus mongolica and Pinus koraiensis, the two dominant tree species in temperate broad-leaved Korean pine mixed forest in Changbai Mountains. Comparing with monoculture, mixed culture increased the canopy width and main root length of Q. mongolica seedlings, but decreased the basal diameter, plant height, leaf number, and dry masses of root, stem, leaf and whole plant of P. koraiensis seedlings significantly. Treatment (-W) increased the stem/mass ratio while decreased the main root length of Q. mongolica seedlings, and decreased the main root length, leaf number, dry masses of leaf and whole plant, and leaf/mass ratio, while increased the stem/mass ratio of P. koraiensis seedlings significantly, compared with treatment CK. Treatment (+W) had no significant effect on these indices of the two species. At early growth stage, interspecific competition and precipitation pattern had significant effects on the morphology and growth of the seedlings, and the responses were much stronger for P. koraiensis than for Q. mongolica.

[Sensitivity of parameters in net primary productivity model of broadleaf-Korean pine mixed forest]

PnET-II (photosynthesis and evapotranspiration) model is an ecosystem process model, which requires extensive input parameters, including vegetation parameters, soil parameters and climate parameters, to simulate net primary productivity (NPP). This study estimated the total and wood (stem and branch) NPPs of Korean pine and broadleaf species in Fenglin Natural Reserve, and examined the responses of the NPPs to the variations of the input parameters in PnET-II model. The simulation results indicated that among the vegetation parameters in PnET-II model, the variation of canopy parameters, had greater effects on the simulated NPPs of Korean pine and broadleaf species, and the response of Korean pine's total NPP to vegetation parameters was larger than that of broadleaf species'. The variation of soil water holding capacity (WHC) had smaller effects on the NPPs of Korean pine and broadleaf species, and the response of Korean pine's NPP to the WHC was somewhat smaller than that of broadleaf trees'. In climate scenarios, the variation of air temperature had the greatest effects on the simulated NPP of Korean pine and broadleaf trees, followed by precipitation and radiation. Different climate scenarios had different effects on the predicted results. The total and wood NPPs of Korean pine and broadleaf trees had different responses to the input parameters.

[Seasonal dynamics and spatial distribution patterns of herbs diversity in broadleaved Korean pine (Pinus koraiensis) mixed forest in Changbai Mountains]

In this paper, the species composition, seasonal dynamics, and spatial distribution patterns of herbs were examined in a 25 hm2 broadleaved Korean pine (Pinus koraiensis) mixed forest plot in Changbai Mountains. The results showed that the plot had a relatively high herbaceous richness, with 102 species belonging to 40 families and 84 genera, and the Shannon index, Simpson index, and Pielou index was 3.52, 0.96 and 0.75, respectively. The three indices varied dramatically with growth season, whereas the species abundance decreased linearly from early spring to autumn. The species richness and abundance showed irregular distribution, indicating that herbaceous species were microenvironment-dependent. Slope aspect had significant effects on herbaceous species richness and abundance. Northern and eastern slopes had higher species richness and abundance in early spring than southern and western slopes, whereas it was in adverse in late summer and autumn.

Oval-like hollow intensity distribution of tightly focused femtosecond laser pulses in air

The propagation of a tightly focused femtosecond laser pulse in air has been investigated. Unlike long-distance self-guided propagation of short laser pulses, a novel oval-like hollow distribution of the laser intensity is observed in the experiments and reproduced by the numerical simulations. The formation of the hollow structures can be explained by the interplay between ionization-induced refraction and Kerr self-focusing.

[Some ideas about ecological assets assessment]

Ecological assets assessment is of great significance in building harmonious society and implementing scientific concept of development. Based on the achievements in ecological assets assessment research, the concept and scope of ecological assets were re-examined, and the contents of ecological assets assessment were summarized in this paper. It was considered that ecosystem quality, ecosystem pressure and ecological assets value should be the focus in assessing ecological assets. With the ecological assets assessment on forest ecosystem as an example, some referenced indicators and calculation models were given. By the end of the paper, some suggestions on the further study were presented.

[Spatial distribution patterns and associations of Pinus koraiensis and Tilia amurensis in broad-leaved Korean pine mixed forest in Changbai Mountains]

Based on the investigation data from a 25 hm2 broadleaved Korean pine (Pinus koraiensis) mixed forest plot in Changbai Mountains of China, the dominant species Korean pine and Tilia amurensis were chosen as research objects. One point pattern analysis method, O-ring statistics, was used to analyze the spatial patterns of the species in three vertical layers, i. e., overstory, midstory and understory layers, and the spatial associations of intra- and inter-species between different vertical layers were studied. The results showed that P. koraiensis and T. amurensis were clumped at smaller scales. Higher layers tended to be randomly or regularly distributed, while lower layers tended to be aggregated at smaller scales. The aggregation degree decreased with canopy height. P. koraiensis stems in overstory layer were significantly positively associated to the stems in midstory layer at scales < 11 m, and T. amurensis in overstory layer showed negatively correlation with that in midstory and understory layers. There was generally a positive correlation between the two species, but the association varied among different layers. No significant correlation was observed between P. koraiensis stems in overstory layer and T. amurensis in three layers. P. koraiensis stems in midstory layer showed slightly negative correlation with T. amurensis in the same layer at scales > 4 m, but no significant association to T. amurensis in understroy layer. T. amurensis in overstory layer was significantly positively associated to P. koraiensis in midstory layer at scales < 100 m.

Porcine dermal collagen as a wound dressing for skin donor sites and deep partial skin thickness burns

Collagen was extracted by pepsin digestion from porcine skin, and collagen membrane was prepared by salt precipitation. The porcine collagen membrane was evaluated as a burn wound dressing in deep partial skin thickness burn wounds in rats. Burn wounds, 4 x 4 cm, were inflicted by exposure of skin to 75 degrees C for 15 s followed by de-epithelialization. Wound healing was assessed by planimetry of epithelialization on day 10 after injury. Open wounds exhibited 24 per cent of wound area re-epithelialized. Collagen membrane dressing significantly improved the healing to 69 per cent of wound area (P < 0.0001). In a completely separate experiment, the porcine collagen membrane was applied as a wound dressing to the donor sites of burn patients, and its effect on wound healing was compared with that of a petroleum jelly gauze dressing. The donor sites covered with petroleum jelly gauze had re-epithelialized by an average of 14.5 days (ranging from 13 to 16 days) after wounding. The wounds dressed with collagen membrane demonstrated a significant increase in the healing rate. Complete re-epithelialization was observed by 10.3 days (ranging from 10 to 12 days) after wounding (P < 0.0001).

Coverage of full skin thickness burns with allograft inoculated with autogenous epithelial cells

Since the supply of unburned autograft skin may be insufficient to cover very extensive burns, we have prepared allograft skin inoculated with a suspension of uncultured autogenous epithelial cells and grafted this material on to full skin thickness loss wounds. There was a satisfactory 'take' and permanent healing of this mixture of heterogeneous dermis and autogenous epidermis in two out of four patients. In this preliminary report we describe the clinical and histological observations which indicate that in the two patients with successful graft 'take' the epithelial cells proliferated and formed a continuous pale-coloured layer on top of the heterogeneous dermis between 30 and 40 days after application.