The species composition, height, diameter class structure and tree species diversity were examined in a 1 hm2 plot in old-growth tropical montane rain forest in Bawangling Nature Reserve of Hainan Island. The tree species richness and diversity indexes were high relative to forests in mainland China. Both the numbers of tree species and tree density decreased as height class or diameter class increased, fitting both negative exponential and negative power equations. There was a significant positive correlation between tree species abundance and tree density for trees of different height classes, different diameter classes and for trees in different quadrats in the tropical montane rain forest. At successional maturity, only a small number of species with a small proportion of individuals could reach the canopy layer in the old-growth community.

This paper aims to explore the characteristics of gap disturbances in mixed evergreen/deciduous mountain forests in the Chinese subtropical region. Vegetation plots at Mt. Dalaoling in the Three Gorges region were analyzed according to the quantity, type

The species diversity of 20 broad-leaved deciduous forest communities in the mid- and southwestern parts of the warm-temperate zone were analyzed and compared. The results were as follows: 1) in general, species abundance (Sp) and diversity (D and H′) of herb layers were the highest in most of the 20 forest communities, followed by the shrub and tree layers sequentially; in contrast, the index of Alatalo evenness(Ea) was usually the highest in the shrub layer; 2) communities at the sub-climax stage also showed different trends in diversity among layers--diversity indices (D and H′) were lowest in the tree layers followed the herb and shrub layers sequentially; 3) eveness in different layers were all >0.5 in climax and sub-climax stage communities; 4) using total community importance value (IV) as a measure of the total indices of those communities, it was found that Simpson’s index (D) can be used to describe community stability. That is, early succession stage communities and those distributed in particular habitats have total D lower than or close to 0. 5. On the other hand, in zonal communities--typically highly stable or at a climax stage—have both D>0.5 and total Ea>total D. Communities with total Ea less than or close to their total D have higher species abundance, and are comparatively stable or at the stage just before climax, i.e. sub-climax stage in the sere.

Species richness-abundance relationships in four types of tropical forest (tropical submontane rain forest, tropical montane rain forest, tropical cloud forest and tropical dwarf-forest) were studied at Bawangling National Nature Reserve, Hainan. Four size classes of tree with diameter at breast height (DBH≥1.5, 10, 30 cm respectively) were selected for comparison. The results indicate that the rate of species accumulation is related to the logarithm of number of individuals in each vegetation type, independent of diameter classes. Within samples containing the same number of individuals the rate of species-accumulation decreased from the tropical submontane rain forest, through tropical montane rain forest and tropical cloud forest to the tropical dwarf-forest. For each vegetation type, the proportion of rare species (singleton or doubleton: observed just one or two times respectively in samples) is very high. Their proportion is about 50% of the total species counted in each DBH classes and increases with diameter class. On the other hand, the proportion of species with hundreds of individuals is very low, usually under 1%.

A spatial series representing the temporal sequence of vegetation restoration on Nan’ao island (Guangdong, China) was studied investigating community structure, leaf area index (LAI), biomass, and soil fertility in eight communities in an examination of the process of vegetation restoration on the island. The species richness of the communities in the spatial series proceeded from degraded grassland through artificial forests to secondary forests. The number of the heliophytes in the communities decreased gradually, while mesophytes increased with the process of vegetation restoration. The biomass of degraded grassland, ten-year-old-artificial- forest, fifteen-year-old-artificial-forest and secondary forests were 4.8 t·hm-2, 45 t·hm-2, 100 t·hm-2 and 88 t·hm-2, respectively, while the LAI of this sequence was 1.04, 3.81, 5.89 and 6. 52. The quantity of stand litter also increased as 0.42t·hm-2, 3.20t·hm-2, 3.70t·hm-2and 4.90t·hm-2, respectively. The soil organic matter, total N, available P and exchangeable K were gradually increasing during the process of vegetation restoration. This vegetation restoration pattern was different from that of the mainland due to varying ecological habitat of the island, windiness and storm impact on the island. Most notable was the slower speed of vegetation restoration on the island relative to mainland. In this and similar environments secondary forests represent the pool of species diversity and are very important for sustaining the biodiversity of the island. The paper presents a rational plan for vegetation restoration on the island.

Wheat plants (Triticum aestivum L. ) was grown in pots at three water levels (80%, 60% and 40% field water capacity) and three CO2 concentrations (350, 550 and 700 parts per million by volume (μmol·mol-1)) in open-top chambers (OTC). Leaf stomata characteristics were observed and measured. Drought and CO2 enrichment both influenced not only the leaf stomatal densities but also their distribution. Drought increased the abaxial stomatal densities while high CO2 decreased these densities. The variations of the stomatal distributions were diminished under drought and high CO2 treatments. Different temperatures also influenced the stomatal densities and distributions under constant water levels and CO2 concentrations.

Approximately maximum photosynthetic rate was attained in leaves of Musa paradisiaca grown in NO3--N, NH4+-N and NH4NO3-N. UV-B radiation induced decreases of photosynthetic rate, apparent quantum yield and efficiency of energy conversion in plants grown with all three nitrogen sources, but to different degrees. Exposure to UV-B radiation resulted in lower levels of leaf dry mass per area and leaf nitrogen content per unit leaf dry mass and a slightly elevated level of chlorophyll content. Higher levels of Vcmax and J max were found in plants grown with NH4+-N relative to either NO3-N, or NH4NO3-N. A stronger decrease in Vcmax and Jmax was observed in plants grown in NH4+-N with exposure to UV-B radiation, indicating a greater sensitivity to UV-B radiation. UV-B radiation induced a change in the carbon: hydrogen and carbon: nitrogen ratios and may induce a change in nitrogen utilization, carbon and nitrogen metabolism and acid-base regulation. Decreases in the partitioning coefficient for leaf nitrogen in Rubisco and in bioenergetics were found with increasing exposure to UV-B radiation which may cause a decrease in the synthesis of these compositions and in photosynthetic rate. The results show that plants grown in different nitrogen-sources had the ability to vary their responses to UV-B radiation. NH4+-N supply may act to increase relative photosynthetic parameters and may be capable of being subjected to more severe UV-B radiation impact. Lower sensitivity to UV-B radiation may occur for nitrogen limited plants or those with NH4NO3-N as a major nitrogen-source.

The effect of varying temperature on the growth of Dendrobium nobile Lindl. was studied under different light intensities. In the tillering stage,Dendrobium nobile was treated with different temperatures (15℃,20℃ , 25℃, 30℃ and 35℃) in different light intensities (80 μmol·m-2·s-1, 160 μmol·m-2·s-1,320μmol·m-2 ·s-1 and 640μmol·m-2·s-1). Growth and metabolism of D. nobile peaked at 25-30℃ in 80 μmol·m-2·s-1 and 20-25℃ in 160 μmol·m-2·s-1 light intensity. At 320 μmol·m-2·s-1 and 640 μmol·m-2·s-1 of light, D. nobile growth was highest at 25℃. At all light intensities, temperatures of 20℃ and 25℃ had a significant positive effect on reproductive capacity, while fresh weight production was strongest at 25℃. The MDA content initially declined with increasing temperature, but increased again with the higher temperatures. The reverse trend was observed in chlorophyll, soluble protein and total sugar content. The MDA content was lowest and chlorophyll,soluble protein and total sugar content was highest in the 25℃ treatment. Net photosynthetic rate followed the same patterns as that of chlorophyll content. However, dark respiratory rate was improved with increasing temperature under each of the light intensities. These observed patterns of physiological and biochemical changes in D. nobile indicate that while higher temperatures and lower light conditions resulted in an increase in the plant height, the fresh weight and growth mass was significantly negatively correlated to the content of MDA(r80＝-0.9082、r160＝-0.9816、r320＝-0.8075、r640＝-0.8586) but positively related to the content of total sugar (r80＝0.7673、r160＝0.8892、r320＝0.8179、r640＝0.9278);the growth mass showed corresponding changes with the soluble protein and chlorophyll content and photosynthetic rate. Optimal temperature for D. nobile growth is approximately 25 ℃ across the varied light intensities.

Gas exchange and photosynthesis nutrient use efficiency were studied in leaves of Panicum miliaceum grown in heterogeneous (patchy) nutrient environments (HNEs). HNEs had a significant influence on gas exchange in the leaves of this species, but this effect varied among growth stages. In pre-reproductive stage individuals, photosynthetic rate (Pn), transpiration rate (E), and stomatal conductance (gs) decreased with increasing total nutrient availability in HNEs, while water use efficiency increased. These trends were reversed in the seed maturation stage. There was a significant correlation between gas exchange (Pn, E, gs) and leaf nitrogen (N). However, no such correlation was found between gas exchange and leaf phosphorus (P) or leaf potassium (K). Both P and K use efficiency were significantly affected by HNEs, but photosynthetic N use efficiency was not.

In the long-term interactions with its pathogenic rust fungus Uromyces trifolii-repentis, Trifolium repens has evolved two genotypes of clones: resistant and susceptible clones. Two questions were addressed in this study. Firstly, whether the susceptible

Wild soybean is the progenitor of soybean, sharing the gene pool of soybean. In this paper structure and geographical distributions of the natural populations of wild soybean in Hebei Province were analyzed using some important quantitative traits. Coefficients of variation within populations were greatest for 100-seed weight (46 % ) followed by fat content (17 % ), flowering time (10.3 % ) and protein content (4.7% ). Within-population mean flowering times were related to latitudes, but 100-seed weight, fat and protein contents were not. Every population had some individual plants with outstanding differences in character performances that had virtually been caused by the accumulation of gene frequencies for quantitative characters. It was observed that there were different genotypes for genetic flexibility in flowering photoperiodic response, although the populations had always been subjected to the same photoperiodic induction. A similarity analysis of the natural populations indicated a relationship between the quantitative structures of populations and their geographic and ecological distribution areas--showing distinct ecological groups in wild soybean.

The causes and mechanisms of shrub invasion in natural grassland, and the impact on soil resource (soil moisture and available nutrients) heterogeneity caused by shrub invasion of natural grassland are reviewed as are biogeochemical ecosystem processes and the relationship between soil heterogeneity and land degradation in semi-arid areas. Periodic drought and human activity are the two main factors promoting shrub invasion in semiarid areas. Temporal and spatial heterogeneity of soil resources increased with shrub invasion: as soil moisture and available nutrients accumulate under the shrub canopy forming an ‘island of fertility’. Both physical and biological factors show increasing heterogeneity with shrub establishment. Temporal and spatial heterogeneity of soil resources at the patch scale contribute to the initiation of soil erosion and consequent land degradation. Grass and shrub patch mosaic landscapes have low stability and have the highest likelihood of future land degradation. Hence, shrub invasion and shrub density in communities in natural grassland in semi-arid areas should be controlled to prevent soil erosion. Multi-scale analysis of the causes of soil resource heterogeneity in ecosystem are helpful in revealing the mechanisms of land degradation in semi-arid areas.

Field observations of CH4 and CO2 concentration down soil profiles in the major grassland communities of Xilin River Basin of Inner Mongolia in 1999 indicate that the distribution of methane through the soil profile was different from that of carbon dioxide. Methane concentration decreased gradually with soil depth while the concentration of carbon dioxide showed a strongly increasing trend. On the other hand, methane concentration in the soil of meadow steppe, Leymus chinensis steppe and Stipa grandis steppe, a series driven by moisture gradients in Xilin River Basin, differed significantly with seasonal variation. Variation in the time scale of impacts may partially account for the result that there was no significant effect of grazing on CH4 and CO2 concentration in the grassland soil.