Biomedical subjects

Youzhi Han

Publications and source records attributed to Youzhi Han.

5 recordsLinked to original sources

PubMed2006

[Distribution patterns of Fraxinus mandshurica root biomass, specific root length and root length density].

Employing soil core method, an investigation in Maoershan Experiment Station was made on the root biomass, specific root length (SRL), and root length density (RLD) of Fraxinus mandshurica plantation (17 yr) within a growth season in stand level. The results showed that the total root biomass was 1,637 g x m(-2), in which, living biomass accounted for 85%, and necrotic biomass was 15%. In the living biomass, coarse roots (5 approximately 30 mm in diameter) had the highest percentage (69.95 %), followed by fine roots (< 1 mm in diameter) (13.53 %), medium roots (2 approximately 5 mm in diameter) (7.21%), and small roots (1 approximately 2 mm in diameter) (9.31%). Among the four diameter classes, fine roots had a higher SRL (32.20 m x g(-1)), while coarse roots had a lower one (0.08 m x g(-1)). The total RLD in living biomass was 6,602.54 m x m(-2) in stand level, among which, fine root accounted for 92.43%, and the others was less than 8%. Fine root biomass and RLD had a positive correlation with soil available nitrogen, while no significant correlation was found between SRL and soil available nitrogen.

Biomass↗

PubMed2006

[Application of minirhizotron in fine root studies].

Due to the production, death, and decomposition of fine root, its turnover plays an important role in carbon allocation and nutrient cycling in terrestrial ecosystems. Some methods such as sequential root coring, compartmental flow model, and ingrowth core have been widely used in collecting root biomass data and estimating fine root turnover, but failed in monitoring the dynamics of fine root due to its simultaneous production and death. Minirhizotron is a nondestructive in situ method for studying the dynamics of fine root, which allows the simultaneous measurement of fine root growth and mortality. This paper reviewed the application of minirhizotron in fine root studies, with the focus on minirhizotron tube installation, image collection, data extraction, and calculation parameters. In a case study, the total fine root length, fine root length density per unit volume, fine root length density per unit area, fine root biomass density, and fine root production and mortality of Fraxinus mandshurica and Larix gmelini were calculated, and the results showed that minirhizotron method was feasible in studying the processes of fine root development, eclipse, death, and decomposition. The factors affecting fine root measurement and its precision mainly included the quality and quantity of tube installation, sampling interval and quantity, and analysis technique of images, etc. Soil texture, tube material, and disturbance of light on root were also the factors affecting the precision of the method. How to improve the measurement precision of minirhizotron would be the critical problem in future study.

Fraxinus↗

PubMed2006

[Root decomposition and nutrient release of Fraxinus manshurica and Larix gmelinli plantations].

A two-year buried bag experiment with different sizes of Fraxinus mandshurica and Larix gmelinii roots showed that the coarse (5 to approximately 10 mm), medium (2 to approximately 5 mm) and fine ( <2 mm) roots of F. mandshurica had an annual decomposition coefficient of 0.3649, 0.4381 and 0.2720, while those of L. gmelinii had the coefficient of 0.1967, 0.1955 and 0.2464, respectively. During root decomposition, large amounts of carbon and nutrients released. After buried into soil for 150 days, more than 90% of soluble sugar in all sizes of the two species roots was released, and about 40%, 71% and 95% of potassium was released from the coarse and medium, and fine roots of F. mandshurica, and all sizes of L. gmelinii roots, respectively. In the second year of the experiment, about 50% of nitrogen and 40% of phosphorus were released from the coarse and medium roots of the two species, and 60% of nitrogen and phosphorus were released from their fine roots. In the study of forest ecosystem's carbon and nutrient cycles, root decomposition shouldn't be ignored.

Carbon↗

PubMed2003

[Quantification comparison of spatial pattern of soil seed bank of Fraxinus mandshurica in two stands].

The spatial pattern of soil seed bank of Fraxinus mandshurica were examined by geostatistics in two stands with different densities, tree species composition and ground plants, in the Northeast of China. A sampling grid of 559 points, at each point a sample was located, was established according to regular grid design at three spatial scales (cell size were 0.5 m x 0.5 m, 1 m x 1 m, and 2 m x 2 m) in each plot. Spatial pattern were quantified by using semivariance analysis, fractal dimension and Kriging maps. The object of this paper is to quantify the spatial pattern of seed bank, to compare its variations between two stands, and to explore what sort of mechanism would control its variations. The results indicated seed distribution showed appreciable heterogeneity within stand and clearly difference between the two stands. In plot 1 (mixed stand), seed bank, with a mean of 158.1 +/- 96.7 seeds.m-2, higher sill (C0 + C = 0.549) and 4.25 m scales, has a stronger spatial pattern. There were a high autocorrelated variation (89.4%) and lowly random variation (10.6%) at this scale. However, at scale from 5 m to 31.3 m, its autocorrelated variation ranged 51.4%-69.8% and random variation ranged 30.2%-47.6%, also has distinctly mosaic patterns. Fractal dimension (D) analysis showed that the D values was relatively lower(1.728-1.865), their coefficient of variation only about 26.7%-68.35%, indicated that there was a high self-similarity of patch shapes of seed bank. In plot 2 (pure stand), with a mean of 57.4 +/- 44.7 seed.m-2, and lower sill (C0 + C = 0.125), spatial patterns were not so strong as plot 1, which has a smaller scale (2.59 m). Its spatially autocorrelated variation was 56.8% and randomly variation was 43.2%. Over the scale there were no clearly autocorrelated spatial patterns. Fractal dimension analysis showed higher D value (1.906-1.960), and their coefficient of variation varying wildly (69.51%-134.14%), implying highly random variation and more complex patch shapes. The differences of spatial pattern of seed bank between the two stands were likely to be due to spatial heterogeneity at the level of stands.

Seeds↗

PubMed2002

[Spatial heterogeneity and forest regeneration].

The research on spatial heterogeneity is meaningful for forest regeneration dynamics, which is a critical part in the forest ecosystem dynamics. Traditionally, forestry scientists are mainly concentrated their attention to the studies on the process of regeneration. However forests are spatiotemporal heterogeneous. In regeneration, there exists an ecological dynamic process at temporal scale, but also a heterogeneous pattern at spatial scale. Almost of the factors influencing forest regeneration, including both botic and abotic environment, both natural and human disturbances, and both characteristics of tree species and response of tree species to different disturbance agents, are spatially heterogeneous. Discussion on spatial heterogeneity and its effect on regeneration is indispensable for the understanding of the pattern, process and mechanism of forest regeneration. Main research contents and viewpoints of spatial heterogeneity in forest regeneration were summarised on the basis of available literature, and sources of spatial heterogeneity in the process of regeneration were analysed. The response of species to spatial heterogeneity, small-scale spatial heterogeneity and regeneration dynamics, spatial heterogeneity of lights in stand and regeneration pattern, and correlative relationships between the scales of soil heterogeneity and regeneration heterogeneity were reviewed.

Trees↗