Spatial correlogram and spatial correlation index methods were used to analyse the spatial patterns of major vegetation types in the mid-range of the Tianshan Mountains and the relationship between populations and environmental factors. Desert, subalpine meadow and alpine meadow vegetation dominate this area and a number of environmental and climatic factors were used to analyse their distribution. These include 30 years average rainfall, monthly average temperature, elevation and soil nitrogen. The results indicate that elevation and average July temperature were major factors which affected desert population spatial patterns on northern slopes, and with increasing elevation there was a decline in the abundance of plants. Many factors affected plant distribution on the southern slopes, of which nitrogen content was the most important factor. In subalpine meadow vegetation the factors affecting population spatial patterns were CaCO3 content and January temperature (both negatively) and annual rainfall (positively). Many factors worked together on population distributions in alpine vegetation areas, but annual rainfall, January temperature and July temperature were among the most important factors.

Gap-phase replacement of trees was studied in a secondary conifer broad-leaved mixed forest distributed widely in Jinyun Mountain, Chongqing and successional trends in gaps and forest type were predicted. The results show that while Pinus massoniana has an intense reciprocal replacement pattern, Gordonia acuminata, Symplocos setchuanensis and other evergreen broad-leaved tree species display both self replacement and reciprocal replacement patterns. The current tree replacement process in gaps does not appear to act towards the maintenance of the current community composition. The analysis of Markov transition matrix shows that the Pinus massoniana population will lose its dominant position in the future composition of the forest canopy. The whole community is in a succession process from a conifer broad-leaved mixed forest to an evergreen broad-leaved forest.

The stomatal densities of herbarium specimens of Trema angustifolia BL. and T. cannabina Lour were investigated ,and the intrinsic water use efficiency of both species was computed from δ13C values in their leaves. From 1920 to 1990,the stomatal densities of T. angustifolia and T. cannabina reduced by 28 % and 40% respectively, while their intrinsic water use efficiency increased by 20% and 42% respectively. Changes in these parameters with time (and therefore with increasing of atmospheric CO2 concentration)were significant in both species :with stomatal densities declining and water use efficiency increasing with time.

Forest inventory data (FID) are an important resource for compiling accurate information of forest volume at landscape and regional scales, and are useful for understanding the dynamics of forest biomass, net primary production (NPP) and carbon cycling, especially in consideration of compliance with the Kyoto Protocol on greenhouse gas reduction. Field and literature data of Larix forests in China show that the relationships between biomass and volume, net production and net annual biomass increment or net annual volume increment could be expressed as hyperbolic curves for both natural and planted Larix forests. However, the relationship between net production and biomass was not clear. A set of new FID-based biomass models and net production models for both natural and planted Larix forest were developed. These models take into account the change in the ratio of forest biomass and volume with the stand age and the effect of stand age on forest NPP.

The effect of four different water supply levels on the gas exchange processes and photochemical efficiency in PS Ⅱ were investigated in seedlings of Salix psammophila, a dominant shrub in the Maowusu arid sandy region. Increasing water supply levels had a strong influence on diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration (all increasing ) and leaf temperature (decreasing) of the seedlings. The photosynthetic rate of seedlings showed a strong midday depression under low water supply but not under full water supply. Increasing water supply decreased the light compensation point and enhanced the saturation light and apparent quanta efficiency. Water supply significantly influenced photochemical efficiency in PS Ⅱ: maximal fluorescence, variable fluorescence, maximal fluorescence ratio and maximal photochemical efficiency all decreased with declining water supply. Correlation analysis showed that meteorological variables, such as photosynthetic active radiation, air temperature, air saturated water vapour pressure difference, and physiological variables, such as stomatal conductance, leaf temperature, intercellular CO2 concentration, significantly affected the photosynthetic rates of the seedlings under varying water supply conditions.

The antioxidative ability of four subtropical forest plants, Schima superba,Castanopsis fissa (tree species), and Psycotria rubra,Ardisia quinguegona (shrub species) growing under different light intensities was studied. Potted seedlings were grown in three light treatments: natural sunlight (100%), and shading to 36% and 16% of natural sunlight. Young trees growing in natural forest in deep shade (8% and 3% sunlight) and at an artificially open site (sparsely cut) were also tested. Changes in the contents of ascorbic acid (AsA), glutathione (GSH) and the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD) were analyzed in leaves sampled in summer and winter. Under natural light conditions, the two shrub species showed higher antioxidative ability, with a high amount of AsA and high activities of APX, SOD relative to the tree species. The levels of AsA, GSH, APX and SOD decreased with declining light intensity in four species, but the antioxidative ability response to changing light intensity was greater in the shrub species. A close positive correlation between AsA, APX and SOD was observed across changing light intensities, indicating a good coordination of antioxidative metabolism in these woody plants. The results were somewhat different in summer and winter, showing that in addition to the important role of light intensity, other environmental factors, such as temperature may also be involved in the development and regulation of plant antioxidative ability.

Field- and limited soil cylinder-cultivation of widely grown maize cultivars released from 1950s to 1990s in China was conducted in order to investigate differences in the growth of the root system through space and time. Dry matter accumulation of maize roots agreed with a Vapor Pressure Model. Root weight of 1990s cultivars increased rapidly as plants grew and a long period of high root weight continued from anthesis until maturity; this trend became more evident with deeper soil. 1990s maize cultivars root weight in 40-100 cm soil depth were 75% and 1060% higher than those of 1970s and 1950s, respectively; the proportion of roots in this layer was also much higher. The percentage of roots that were located within a horizontal area 0-10 cm soil from the plant center was also higher than in cultivars of 1970s and 1950s. We conclude that the historical development in maize cultivars has led to increased vertical extension and horizontal contraction.

Variation in mating system and genetic diversity of seed samples collected 3 years before and 3 years after thinning were examined in a clonal seed orchard of Pinus tabulaeformis Carr. in Liaoning province. Allozyme markers with 10 loci were used in the study of genetic diversity. The multilocus outcrossing, selfing and inbreeding rates of the seed orchard before thinning in 1993 were 0.962, 0.038 and 0.141 respectively. The multilocus outcrossing rate in the thinned seed orchard in 1996 and 2000 decreased to 0.795 and 0.801 respectively. At the same time the multilocus selfing rate increased to 0.205 and 0.199 and the genetic diversity indices A and P decreased to different degrees after thinning. The results showed that thinning based on phenotype had a strong influence on mating system but a lesser effect in genetic diversity indices. Factors influencing the mating system and genetic diversity are also discussed.

Seasonal and diurnal variations in zeaxanthin content of Kobresia humilis and Polygonum viviparum took the form of a monotonic curve, which was closely related to the seasonal and diurnal changes in solar radiation in Haibei Research Station.

This 1998 research found that the structure of the Miyun reservoir phytoplankton community was of a diatom-green algae type, and the cell density is 358.76 ×104·L-1. The nutritive peculiarity belongs to responding type of phytoplankton. From 1988 to 1998, the total nitrogen of water body increased by 48.7% and total phosphorus of water body increased by 31.2%. Over this period the cell density of phytoplankton also increased by 41.7%. The water body of the lake has reached a medium level of nutrition and eutrophic phytoplankton, (e. g. Scenedesmus obliquus (Turp.) Kütz. , Microcystis aeruginosa Kütz. and Chroococcus limneticus Lemm. ) are now common in the lake. The water body, which supplys water for Beijing, is approaching a eutrophic condition. In order to maintain the water quality and production of Miyun reservoir, it is essential that the water environment of the valley is protected and the vegetation cover of the valley is increased.

The fact that species are not equally important for the functioning of ecosystems is now widely recognised. With the presumed significance of keystone species in ecosystems, it is assumed that if we can distinguish the keystone species of an ecosystem and the mechanism through which they affect ecosystem processes, we will have obtained the most useful information on the functioning of the ecosystem. This information would be of great benefit to managers, especially when the keystone species itself is a target for management. Thus when considering biodiversity conservation, the term "keystone species" has been introduced by conservationists and ecologists to protect ecosystem functioning more efficiently with the protection of keystone species. In this paper, we reviewed the advances in researches on keystone species, and concluded the possible approach to determine quantitatively the keystone species in an ecosystem, and the significant, but limited, application of keystone species in biodiversity conservation.