Background and Aims Soil respiration is a major flux in the global carbon cycle. A small change in soil respiration may result in a large increase of atmospheric CO₂. Land conversion has the greatest impact on the terrestrial ecosystems among the components of global change, but the effects on soil respiration are inadequately understood. Our objective was to examine the response of soil respiration to conversion from forests to agricultural lands, using broad-leaved Korean pine forest and reclaimed cropland in the Changbai Mountains.

Methods We used an Infra-red Gas Analyser (IGA) linked to a 50 cm×50 cm×15 cm chamber without a bottom. Three 50 cm×50 cm steel frames were inserted to a soil depth of 3-5 cm in randomly selected plots one day prior to measurement. When measuring, the chamber was put on the steel frame to make a closed container capturing CO₂ from the soil surface and piping the gas of chamber through the IGA. We repeated measurements every 15 days during the growing seasons from 2003 to 2005.

Key Results Diurnal and seasonal variations of soil respiration were mainly affected by soil temperatures. Soil respiration rate reached a maximum around noon in cropland plots, about six hours earlier than that in forest plots. Minimum rates occurred at 5∶00 am in cropland plots and 7∶00-8∶00 am in forest plots. Diurnal variations were driven mostly by temperature. During the growing season, soil respiration had a statistically significant exponential relationship with soil temperatures at 5 cm depth, but was weakly correlated with soil volumetric water contents at 10 cm depth. Although soil temperatures in cropland plots were higher than those in forest plots, soil CO₂ efflux in forest was about twice that in cropland during the growing season (May to September). During the period of measurement, soil respiration rate of cropland ranged from 23.4% to 76.3% that of forest. Therefore, vegetation types were another factor affecting soil respiration due to the change of land-use. Q₁₀ values of soil respiration averaged 2.92 for forest plots and 3.07 for cropland plots, which may be overestimated.

Conclusions Differences in soil respiration rates and patterns between forests and croplands result from changes in abiotic and biotic factors, including soil physicochemical properties, due to land-use change.

Background and Aims Many reports on global change have predicted major change in the temporal and spatial pattern of precipitation, which may have significant effects on temperate grasslands in arid and semi-arid regions. The responses of grasslands to environmental changes, especially amount and timing of precipitation, can be very different. Some studies indicate that drought may result in degradation of ecosystem function in NEE, even changing the ecosystem from a carbon sink to a carbon source.

Methods In order to quantify net ecosystem carbon exchange in Leymus chinensis steppe and its response to precipitation, we used the eddy covariance technique to measure carbon dioxide flux during the 2005 growing season in Xilin River Basin of Inner Mongolia Plateau in 2005. Only 126 mm precipitation fell during this growing season, far less than average; therefore, the steppe was in an extreme drought condition.

Key Results The daily pattern of CO₂ uptake in this drought year was consistent bimodal, with peaks at 8∶00 and 18∶00. In normal years, the bimodal pattern occurred only when soil water stress occurred. Maximum half-hourly average CO₂ uptake was -0.38 mg·m^-2·s^-1 in 2005, which was half that in typical growing seasons. Moreover, the ecosystem was a CO₂ source most of the growing season, releasing about 0.05 mg CO₂·m^-2·s^-1 at nighttime.

Conclusions The seasonal pattern of CO₂ uptake closely followed that of aboveground biomass and was strongly affected by soil temperature and soil water content. The ecosystem emitted 372.56 g CO₂·m^-2 during the growing season in 2005. The partial explanation is that much plant litter accumulated on the ground surface due to enclosure of the grassland since 1979, and this litter decomposed and resulted in a net release of CO₂ to atmosphere.

Background and Aims Most studies of the consequences of enhanced nitrogen deposition on sources and sinks of greenhouse gases have been performed in temperate ecosystems. Little information is available about greenhouse gases and responses to atmospheric nitrogen deposition in subtropical and tropical forests, especially in the forests of China. The objective of this study was to determine soil N₂O emission and its response to simulated N deposition in pine forest (PF), pine-broadleaf mixed forest (MF), and monsoon evergreen broadleaf forest (MEBF) of Dinghushan in subtropical China.

Methods Four N addition treatments (in three replicates) were established in MEBF: Control, Low N (50 kg N·hm^-2·a^-1), Medium N (100 kg N·hm^-2·a^-1) and High N (150 kg N·hm^-2·a^-1), and three treatments were established in MF and PF (Control, Low N and Medium N).

Key Results The effects of nitrogen addition on soil N₂O emission differed by forest type. In MF, no significant differences were found among the three treatments after 3 months. In PF, however, soil N₂O emission rate was significantly higher in Medium plots than that in Low or Control plots, which exhibited no significant difference. In MEBF, soil N₂O emission rate was highest in High N plots and significantly higher in Medium plots than in Low or Control plots, which exhibited no significant difference.

Conclusions This study suggests that nitrogen addition significantly stimulated soil N₂O emission rates in both MEBF and PF, and its effect generally increased with the levels of nitrogen addition, but there was no such significant effect in MF.

Background and Aims Orchidaceae is one of the largest families of flowering plants, and China is one of its most important centers of diversity, with 171 genera and about 1 247 species. Wild species of this family are considered as a key group for plant conservation. Because we cannot preserve all biota in all areas of distribution, conservation priorities must be set and a minimum number of distribution areas needed to preserve the greatest amount of biodiversity possible must be evaluated. Hainan Island is considered as a typical area in China with a high diversity of wild orchids. Previous studies on Hainan Island have focused on investigations of wild orchid resources, but little information is available on their conservation. Analyses of species diversity and endemism patterns provide vital information for conservation planning. Our goal was to determine priority areas with a diverse wild orchid flora and the minimum number of distribution units needed to protect all wild orchid species on Hainan Island.

Methods The 19 administrative counties of Hainan province were treated as the distribution units. Using data on the distribution of the species obtained from the literature and herbarium specimens, we constructed a presence/absence matrix of 202 wild orchids recorded on Hainan Island. Parsimony analysis of endemicity (PAE) was used to identify hotspots of total diversity and endemism at the distribution unit level, and complementarity analyses were applied to show how the target set of species can be conserved with a minimum number of distribution units.

Key Results The database consisted of 1 182 records in the 19 distribution units. Based on this distribution matrix, the analysis generated 424 equally parsimonious trees, from which a strict consensus cladogram was obtained. According to the floristic similarities among the 19 distribution units based on 202 species of wild orchids, two areas were suggested as priorities: one located in southern Hainan Island, represented by Baoting, Sanya, Lingshui and Qiongzhong, and another in the southwest, represented by Changjiang and Ledong. Bootstrap values were 79% and 69%, respectively. Similar results were obtained by parsimony analysis of endemicity. Units with the most floristic similarities of endemisms were Baoting, Lingshui, Ledong, Sanya, Qiongzhong and Changjiang, but the bootstrap values were low, less than 50%. Complementarity analysis showed that at least ten distribution units are required to protect all wild orchid species; listed in descending order of cumulative numbers, they are Baoting, Sanya, Wuzhishan, Lingshui, Baisha, Ledong, Qiongzhong, Dongfang, Changjiang and Qiongshan. Six are needed to protect 30 endemic species: Lingshui, Baoting, Qiongzhong, Ledong, Sanya and Wuzhishan. These six are included in the ten needed to preserve all wild orchid species. The main difference is the hierarchical arrangement of the units. These results indicated that, at least at distribution unit level, the units important to protect all wild orchid species are also important to preserve the endemic species.

Conclusions An assumption of both parsimony and complementarity analyses is complete knowledge of the distribution of each species in a region, but this is unlikely for wild orchids on Hainan Island. Another problem with our study is that we chose the administrative counties of Hainan Island as the distribution units rather than units based on biogeographic criteria. Despite these limitations, our study provided a baseline set of protected areas for the conservation of wild orchid diversity on Hainan Island that can be supplemented to meet other conservation and socio-economic needs and objectives.

Background and Aims The species diversity of bryophytes in Qinling was rarely studied, especially at different vegetation types. The bryophytes on floor were investigation in Foping Nature Reserve which lies in at the south slope of Qinling. Answers to the following questions were sought. a) What is the composition of bryophytes on floor in Foping Nature Reserve? b) What were the dominant families of bryophytes at there? c) How is the species diversity of bryophytes in Foping Nature Reserve?

Methods A investigation of bryophytes on floor were done in Foping Nature Reserve. The 29 sites were chosen in representative place, and the plots were setted with systematic sampling. The species similarity coefficient, important value and species diversity indexes were examined at different vegetation types.

Key Results A total of 189 floor species belonging to 69 genera of 33 families were founded. Among these species, there are 15 hepatics belonging to 8 genera of 7 families and 174 mosses belonging to 61 genera of 26 families, and Brachytheciaceae is the most dominant family. The species diversity of floor bryophytes is the highest one in deciduous oak forest zone, and it reduced in deciduous birch forest zone, bamboo forest, coniferous forest, rocks in valley, and it is the lowest in Rhododendron shrubs. The similarities between deciduous oak forest zone and deciduous birch forest zone are highest, and the similarities between Rhododendron shrubs and other vegetation types are lowest.

Conclusions It is shown that deciduous oak forest zone is the center of bryophyte diversity and the key area for bryophyte diversity conservation. Rhododendron shrubs have different species from other areas, so it should be paid attention in Foping Nature Reserve at the southern Qinling Mountain.

Background and Aims The dynamics and fractal characteristics of population patterns during vegetation succession are rarely explored. Scale, pattern and process of ecological succession are three intertwined concepts in modern ecology. Succession research will inevitably involve scale and pattern analyses. Fractal theory can be employed as an effective tool for synergic analysis of scale, pattern and successional processes. There are few reports on pattern dynamics of Pinus massoniana, a species that declines during succession in southern China. Five forest communities were selected in Heishiding Nature Reserve, Guangdong Province for a case study. Our objectives were to determine 1) whether results obtained by employing fractal analysis are consistent with those from traditional research where space is substituted for time and 2) the pattern dynamics of P. massoniana and the ecological meaning of the change of fractal characteristics in succession.

Methods For the traditional space-for-time succession approach, we analyzed importance value (IV) and mean diameter at breast height (DBH) of P. massoniana, and the selected forest communities were treated as a time series of five successional stages. The box-counting dimension (Dbox) and information dimension (Dinfo) from fractal theory were employed to analyze the pattern dynamics of P. massoniana.

Key Results Dbox and Dinfo of P. massoniana decreased during succession, in accordance with number of individuals and IV, and the traditional method of substituting space for time was applicable in this study. This demonstrated deteriorating regeneration conditions and decreasing ability of spatial occupation of P. massoniana with succession—thatP. massoniana had a declining population. With its loss of dominance, the community would turn from P. massoniana dominance into a multi-population dominated evergreen broadleaved forest community. The results of fractal analysis were not only consistent with those of the trend analysis of IV and mean DBH, but also yielded more ecological information about scale-related spatial pattern of the population, its degree of spatial occupation and its role in community and regeneration conditions.

Conclusions This study indicated that fractal analysis is an effective approach to study dynamic pattern analysis during forest succession, and the results were more reliable than those obtained by employing only IV and mean DBH in a traditional space-for-time approach.

Background and Aims Secondary evergreen broad-leaf forest is abundant after large-scale destruction of virgin forests in subtropical areas. Restoration depends largely on natural processes, but these rarely have been studied in Daqingshan, Guangxi. We studied population dynamics of second-growth natural forest over 26 years of succession to explore: 1) patterns of variation in population characteristics and interspecific correlations, 2) the zonal climax vegetation type and 3) effective restoration of degraded secondary forest.

Methods We used methods of population ecology to measure and analyze changes in intra-population structure and spatial distribution, in terms of the population type, importance value, niche breath and distribution pattern. The original investigation on this site took place in 1980 and provided the historic data used for our analysis.

Key Results The heliophytes dominant in early succession changed from highly contagious to random distributions, and their niche breaths decreased accordingly. The mesophytes and shade-adapted tree species, however, had the reverse changes, from random to highly contagious, in concomitance with increasing niche breaths. The number of tree species increased from 32 to 65, of which 35 were late-successional, exhibiting rich species diversity. Niche overlap and interspecific association were analyzed to ascertain the mutual adaptation and evolution of species relationships. Values of niche overlap among the light-adapted populations of Castannopsis fleuryi, Aphanamixis grandifolia, etc. generally dropped, while values for mesophytic populations, such as Eurya nitida, Eberhardtia aurata, Schefflera octophylla, Knema guangxiensis, etc., increased slightly. Values for mesophytes partial to the shaded habitats were enhanced greatly and these species have become dominants, e.g., Beilschmiedia percoriacea, Adinandra millettii, Actinodaphne pilosa, etc. Results of interspecific association analysis were consistent with those of niche overlap analysis, i.e., the species pairs with closely positive associations had large niche overlap, indicating that these species tended to utilize environmental resources similarly.

Conclusions This study shows obvious species changes during the natural restoration process, especially in the quantities and distributions of many dominant species. Results indicate that current communities are increasing in ecological stability as the secondary communities approach the zonal climax through natural succession over 26 years.

Background and Aims Canopy gap disturbance drives successional dynamics of forest communities and shapes forest structure, dynamics and biodiversity in the western subalpine region of Sichuan. Gap microenvironment and responses of Abies faxoniana seedlings of different ages have not been investigated.

Methods During the growing seasons of 2002 and 2003, we continuously observed microenvironment (solar radiation and soil temperature at 5 and 15 cm depth) in canopy gaps in Abies faxoniana forest in Wanglang National Nature Reserve, Sichuan Province. We studied the growth of 3-20 year seedlings (basal diameter, height growth and biomass) in gaps and under canopy to determine responses to gaps.

Key Results Total daily solar radiation was slightly higher in gaps than under canopy in June, but was significantly higher than under canopy in July and August. From June to August, total solar radiation was 8.10×MJ·m^-2 and 5.02×MJ·m^-2 in gaps and under canopy, respectively, and average soil temperatures at 5 and 15 cm deep were significantly higher in gaps than under canopy. The basal diameter of 3-8 year Abies faxoniana seedlings in forest gaps was a little smaller than under canopy, but the basal diameter of seedlings 9-20 years was larger in gaps than under canopy. Height growth rate of 3-8 year seedlings was 1.2±0.3 cm·a^-1 and 1.1±0.3 cm·a^-1 in gaps and under canopy, respectively, and for 9-20 years old was 6.2±2.4 cm·a^-1 and 3.0±0.9 cm·a^-1, respectively. The average total biomass of seedlings was a little higher in gaps than under canopy.

Conclusions Tree seedlings need more illumination with increasing age. Therefore, canopy gaps are an important impetus for growth, forest dynamics and regeneration in subalpine coniferous forest.

Background and Aims Camptotheca acuminata is a special Chinese tree that produces camptothecin (CPT), a monoterpenoid indole alkaloid, which has gained great attention for its remarkable inhibitory activity against tumour cells.

Methods After 70-day growth period,seedlings were inoculated with the arbuscular mycorrhizal (AM) fungi, Glomus manihot (Gm), G. versiforme (Gv), G. etunicatum (Ge), G. diaphanum (Gd), Acaulospora mellea (Am) and A. laevis (Al), respectively.

Key Results We investigated the effects of six species of AM fungi, belonging to two genera, on the growth, absorption of nitrogen and phosphorus in C. acuminata seedlings grown in the greenhouse. All inoculated seedlings were infected by six AM fungi and formed arbuscular mycorrhiza. The seedling growth and nitrogen and phosphorus absorption were affected by the formation of arbuscular mycorrhiza in C. acuminata. The biomass of mycorrhizal seedlings was significantly higher than that of non-mycorrhizal seedlings. For most mycorrhizal seedlings, the ratio of root to shoot was larger than that of the control. Nitrogen contents in Gm, Gv, Ge and Al were significantly lower than in the control. In contrast, phosphorus contents in plant of all mycorrhizal seedlings were higher than in non-mycorrhizal seedlings. Arbuscular mycorrhizal formation also changed the allocation of nitrogen and phosphorus in different organs of seedlings.

Conclusions These patterns suggest that the symbiotic association between C. acuminata roots and AM fungi effectively maintains nutrient homeostasis through changes in physiological properties, including nutrient uptake and allocation.

Background and Aims Rhizomes in clonal plants play a key role in storage and transport of nutrients as well as production of tillers. However, physiological functions of rhizomes in response to abiotic stress are poorly known. We investigated physiological responses of Leymus chinensis to salinity.

Methods We measured the following physiological parameters after 24 h exposure of roots and rhizomes separately and exposure of roots and rhizomes together to 200 mmol·L^-1 NaCl: water and proline content in leaves, K⁺ and Na⁺ content in leaves, roots and rhizomes, and osmolality, net photosynthesis rate and transpiration rate in leaves.

Key Results Net photosynthesis rate and transpiration rate of leaves were significantly (p<0.05) reduced when roots and rhizomes individually and roots and rhizomes together were exposed to NaCl. The same treatments led to increases in osmolality and proline contents in leaves. There was a greater reduction in net photosynthesis rate and transpiration rate of leaves when roots and rhizomes were treated together with NaCl than treated separately. However, when roots and rhizomes were treated with NaCl separately, no significant differences in leaf water content, proline content, net photosynthesis rate and transpiration rate were observed, suggesting that the roots have a similar role to the rhizomes in response to salinity stress inL. chinensis. When roots and rhizomes were treated with NaCl either together or separately, the Na⁺ contents in roots, rhizomes and leaves were higher than those of controls, by contrast, the K⁺ contents were lower than those of controls.

Conclusions Rhizomes of L. chinensis are important in sensing and responding to salinity and have a similar function to that of roots in uptake and translocation of Na⁺ under salinity stress. Because rhizomes have smaller biomass and surface area than root systems, we speculate that rhizomes of L. chinensis may have greater capacity than roots for uptake and translocation of Na⁺ ions under salinity stress.

Background and Aims Cork oak (Quercus variabilis) and China wingnut (Pterocarya stenoptera) are important species in the subtropical riparian and drawdown areas of reservoirs and ponds in China.

Methods We investigated the effect of waterlogging on morphological and physiological characteristics of these species. We measured the maximum net photosynthesis rate (P_max), stomatal conductance (G_s), Chla fluorescence maximum quantum efficiency (F_v/F_m), chlorophyll content and water potential on different days during a period of waterlogging.

Key Results Throughout a 70-day waterlogged period, the survival rates of seedlings of the two species were 100%. The earliest effects of waterlogging were significantly decreased P_max, G_s and F_v/F_m. On the 5th day of waterlogging, F_v/F_m of cork oak and China wingnut decreased to 0.694 and 0.757, respectively. On the 7th day, significant reduction of P_max (cork oak, 39% of control; China wingnut, 42%) and G_s (cork oak, 38.8% of control; China wingnut, 71.9%) were observed. With prolonged waterlogging, P_max, G_s and F_v/F_m recovered gradually to control values in China wingnut, but not in cork oak where values decreased continuously. On the 70th day, P_max of cork oak was reduced by 94.1% of control and F_v/F_m was only 0.537. Waterlogged China wingnut seedlings developed hypertrophied lenticels and adventitious roots at their stem base and exhibited no visible symptoms of injury (neither mortality, leaf chlorosis, leaf necrosis, leaf abscission nor reduced chlorophyll content). However, cork oak showed leaf necrosis with waterlogging. The chlorophyll content of cork oak steadily declined from the 33rd day and the Chla/Chlb ratio also deceased. Predawn leaf water potential was higher in waterlogged cork oak seedlings compared to the control on the 10th and 70th days, but lower in waterlogged China wingnut seedlings. This indicated that water potential changes under waterlogging are species specific.

Conclusions All results show that cork oak exhibits damage to its photosynthetic apparatus under waterlogging. In contrast, although the photosynthetic apparatus of China wingnut is initially affected, it can recover, indicating that China wingnut seedlings can tolerate prolonged soil waterlogging better than cork oak seedlings. We conclude that it is more suitable to plant China wingnut in the drawdown areas of reservoirs and ponds than cork oak.

Background and Aims Hydraulic redistribution (HR) is an extension of hydraulic lift. The simulation of hydraulic redistribution done by Ryel et al. (2002) indicated that HR is beneficial for transpiration.

Methods Based on the Ryel Model, we first conducted a sensitivity analysis by varying critical parameters of the model. We scaled the model for time steps of 1 hour to 1 day and soil from 10 cm to greater thicknesses by adjusting the necessary parameters. The scaled model was then applied to field observations of Caragana intermedia in Huangfuchuan Watershed of Inner Mongolia to simulate transpiration with and without HR. Daily changes in transpiration were simulated from April to October in 1998 and 1999.

Key Results and Conclusions The ratio of water redistributed by root to transpiration was strongly negative to soil hydraulic conductivity. The ratio also increased when root hydraulic conductivity increased, but gradually approached a limit. Total transpiration with HR increased when root hydraulic conductivity increased <1 cm·MPa ^-1·h^-1 and decreased when it increased >1 cm·MPa ^-1·h^-1. The result of the scaling indicates that it provides a useful approach to incorporating HR into larger models of soil processes. Total transpiration with HR increased 4.4% more than without HR in 1998, in contrast to total transpiration without HR having increased 2.1% more than with HR. This may be related to high precipitation in 1998.

Background and Aims It is important for water conservation that suitable agricultural measures are used to improve the water use efficiency (WUE) of crop production. Water-conserving irrigation has improved WUE of crops, but is difficult to practice in arid and semi-arid areas of Loess Plateau, especially those areas lacking water for irrigation. Therefore, water-conserving agriculture in these areas focuses on increasing the rainfall-use efficiency of crops. This study examines whether root-cutting can increase grain yield and WUE of winter wheat in rain-dependent farmland on Loess Plateau.

Methods The field experiment was conducted in 2004 and 2005 at the Changwu Experimental Station of the Chinese Academy of Sciences. The cultivar of winter wheat was `Changwu135' (Triticum aestivum cv. Changwu135), which is widely used by farmers in the region. Roots were partially cut off vertically to 13 cm depth along two sides, 2 cm away from the main stems at the re-greening stage (March 14, 2004). Soil water content was measured at 10 cm depth intervals at different developmental stages. Root respiration rate was measured at the flowering stage. Grain yield, aboveground biomass, spike number per unit area, grain weight and harvest index were measured at the maturity stage. We studied effects of partial root-cutting on root/shoot ratio (R/S), yield and WUE.

Key Results Partial root-cutting at the re-greening stage of winter wheat significantly decreased upper root biomass: root biomass to 20 cm soil depth at the flowering stage was 249.70 g·m^-2 for root-cutting treatment and 307.52 g·m^-2 for intact plants, and total root biomass was 305.53 g·m^-2 for cutting treatment and 368.73 g·m^-2 for intact plants. Root-cutting reduced root respiration rate by 25.57% compared with intact plants. Spike number was reduced to 590.33 m^-2, compared to 646.33 m^-2 for intact plants, but 1 000 kernel weight increased significantly after partial root-cutting (45.99 g compared to 41.47 g for intact plants), and harvest index also increased. Yield was little affected by root-cutting, but water consumption was greatly reduced. Biomass water use efficiency and yield water use efficiency were increased by 32.52% and 29.98%, respectively, compared with intact plants.

Conclusions Root-cutting reduced the root system of winter wheat, restraining population density which reduced water consumption and improved soil water content after anthesis. It is favorable to grain development in wheat. Root-cutting lowered root respiration rate and decreased the amount of dry matter consumed by the root system, which raised the proportion of dry matter allocated to aboveground organs. Dry weight of shoot was unaffected by root-cutting, but water consumption was greatly reduced. Therefore, WUE of winter wheat can be increased on dry lands by partial root-cutting at the re-greening stage. More study, especially on timing and intensity on root-cutting, is needed to synchronously increase grain yield and WUE of wheat.

Background and Aims Nitrogen accumulation in cereal crops is a key parameter for assessing plant growth status and predicting grain yield and quality. Non-destructive monitoring and diagnosis of plant nitrogen status is necessary for precise nitrogen management. The present study was conducted to determine the quantitative relationships of leaf nitrogen accumulation to canopy reflectance spectra in both rice and wheat crops.

Methods Ground-based canopy spectral reflectance and nitrogen accumulations in leaves were measured in six field experiments consisting of five different rice cultivars, three different wheat cultivars and varied nitrogen levels across six growing seasons. All possible ratio vegetation indices (RVI), difference vegetation indices (DVI) and normalized difference vegetation indices (NDVI) of sixteen wavebands from the MSR-16 radiometer were calculated. Analyses were made to determine the relationships of seasonal canopy spectral reflectance and all possible vegetation indices to leaf nitrogen accumulations in wheat and rice under different nitrogen treatments and cultivars.

Key Results As expected, nitrogen accumulation in rice and wheat leaves increased with increasing nitrogen fertilization rates. The relationship with canopy reflectance, however, was more complicated. In the near infrared portion of the spectrum (760-1 220 nm), canopy spectral reflectance increased with increasing nitrogen supply, while in the visible region (460-710 nm), canopy reflectance decreased with increasing nitrogen supply. For both rice and wheat, leaf nitrogen accumulation was best evaluated at 810 and 870 nm. Among all possible RVIs, DVIs and NDVIs, RVI(870,660) and RVI(810,660) were most highly correlated with leaf nitrogen accumulation in both rice and wheat. In addition, the correlations of RVI(870,660) and RVI(810,660) to leaf nitrogen accumulation were found to be higher than that of individual wavebands at 810 and 870 nm in both rice and wheat.

Conclusions This study indicated that leaf nitrogen accumulation in both rice and wheat can be monitored with common wavelengths and spectral parameters. In addition, the integrated regression equation could be used to describe the dynamic pattern of change of leaf nitrogen accumulation in both rice and wheat with reflectance spectra parameters, although separate regression functions slightly enhanced prediction accuracy.

Background and Aims Applying different forms of nitrogen is an important method to regulate nitrogen metabolism of wheat. Endogenous plant hormones play an important role in grain filling of wheat. The objectives of this study were to 1) elucidate the effects of nitrogen forms on endogenous hormones content in roots, flag leaves and grains of wheat after anthesis, and 2) find nitrogen application methods for the wheat cultivar `Yumai 49'.

Methods Pot experiments utilizing a sandy loam soil and wheat cultivar 'Yumai 49' were completed during 2003-2005. Nitrogen forms were CONH₄-N (urea), NH₄-N(NH₄HCO₃) and NO₃-N(NaNO₃), and nitrification inhibitor dicyandiamide (DCD) was applied in CONH₄-N and NH₄-N treatments. Spikes of wheat which flowered on same day were marked and roots, flag leaves and grains were sampled at fixed dates. Each sample weighed 0.5 g FW and was stored at -40 ℃. The enzyme-linked immunosorbent assay (ELISA) method was used to determine the content of IAA, GA₃, ABA and ZR.

Key Results Compared with NO₃-N treatment, GA₃ content in CONH₄-N treated flag leaves and IAA and ABA content in grains were higher 5-15 days after anthesis, and the grain-filling rate (GFR) was higher in this period. GA₃ content in CONH₄-N treated roots, IAA and GA₃ content in flag leaves, and ABA content in grains were higher, IAA content in grains was lower 15-25 days after anthesis, and the GFR was lower in this period. Compared with NO₃-N treatment, ZR content in grains was higher 5 days after anthesis in all NH₄-N treatments. IAA and ABA content in grains was lower about 15 days after anthesis, and the GFR was lower in this period. ZR and GA₃ content in roots, IAA and GA₃ content in flag leaves, and ABA and GA₃ content in grains were lower, ABA content in flag leaves and IAA content in grains were higher 15-25 days after anthesis and the GFR was higher in this period. Compared with NO₃-N treatment, the grain weight of wheat was significantly greater in NH₄-N treatment, and grain yield was increased significantly either in NH₄-N or CONH₄-N treatments.

Conclusions This study showed that endogenous hormones in wheat responded differently to nitrogen forms after anthesis. The GFR of wheat regulated by nitrogen forms was realized through the balance of endogenous hormones in roots, flag leaves and grains. We recommend that CONH₄-N or NH₄-N mixed with DCD be applied to wheat cultivar `Yumai 49'.

Background and Aims Mikania micranth is a well-known invasive species. Study of its characteristics will increase our knowledge of invasive mechanisms and management of invasive species. Photosynthesis of leaves is one of the invasive characteristics of M. micranth, but no studies have focused on assimilation characteristics of its stems.

Methods We compared young green stems and mature leaves using the LI-6400 gas exchange and fluorescence system, as well as laser scanning confocal microscopy to observe the distribution of chlorophyll.

Key Results Electron transport rate (ETR) and actual photochemical efficiency of system Ⅱ (Φ_PSⅡ) of stems and leaves were positively correlated (0.97), suggesting similar photosynthetic structure in stems and leaves. The gas exchange rate under constant conditions was stable for leaves but fluctuating for stems, possibly because of the pore factor of stems. Under the same area and saturated light (PPFD=2 000 μmol·m ^-2·s^-1), the ETR of leaves was 42.44 μmol·m ^-2·s^-1 and the ETR of stems was 30.32 μmol·m ^-2·s^-1. However, under the same area and low light (PPFD=10 μmol·m ^-2·s^-1), the Φ_PSⅡ of leaves was 0.69 and the Φ_PSⅡ of stems was 0.57. The electron transport rate in stems was 4.24 per unit SPAD, 2.3 times that of leaves. Actual photochemical efficiency of system Ⅱ was 0.08 per unit SPAD, 3 times that of leaves. Our research also indicated that light adaptive ability was better in stems than in leaves. Chlorophyll existed mainly in two tissues: cortex and around vascular bundles. It is possible that there are different chlorophyll functions in different tissues.

Conclusions This study indicates that photosynthesis occurred in young green stems of M. micrantha and the instantaneous efficiency of light utilization in stems was higher than in leaves. Results were unclear regarding the function of chlorophyll in different tissues.

Background and Aims Phosphorus(P)deficiency is one of the main factors that influence plant productivity in agricultural and forestry systems. Fertilization and soil improvement are the primary practices used to meet the P demands of crops in traditional agriculture and of trees in forestry management. Chinese fir (Cunninghamia lanceolata), a fast-growing, evergreen coniferous tree with high yield and quality of wood, is the most important tree species of timber plantations in subtropical China. Since Chinese fir plantations range from about 20° to 30° N in latitude and 100° to 120° E in longitude, there are many different genotypes of Chinese fir among the forests in south China. Therefore, it is possible to select the Chinese fir clone with high phosphorus use efficiency.

Methods Based on the pot experiment under the different phosphorus deficiency stress (heavy, medium, slight phosphorus deficiency and normal phosphorus supply), the dry matter accumulation, phosphorus absorption efficiency, and phosphorus use efficiency of eight different Chinese fir clones were analyzed to compare their phosphorus characteristics.

Key Results There were significant differences in the dry matter accumulation, phosphorus absorption efficiency and phosphorus use efficiency among different clones under phosphorus stress. The dry matter accumulation and phosphorus absorption efficiency of different clones decreased whereas phosphorus use efficiency increased with increasing phosphorus stress. The dry matter accumulation of Clone 8, 9, 24 and 37 were influenced by phosphorus stress less than those of the other clones. Phosphorus stress significantly afftected the dry matter accumulation of Clone 23. Higher phosphorus absorption and use efficiency in Clone 8, higher phosphorus absorption efficiency in Clone 24 and 37, and higher phosphorus use efficiency Clone 9 were found under phosphorus stress. However, the phosphorus absorption efficiency and phosphorus use efficiency of Clone 23 were lower than those of the other 7 clones.

Conclusion High phosphorus absorption and use efficiency of Chinese fir are the major adaptive strategy under environment with low phosphorus availability.

Background and Aims This study was conducted to examine the pollination characteristics of Eremurus anisopterus, an ephemeroid plant in Gurbantunggut Desert in Xinjiang, China.

Methords An integratve approach combining investigation in field with analysis in lab was adopted. Pollen traps were usded to measure air-borne pollen loads, and artificial isolation experiments were applied to test the potentiality of cross-pollination or apomixes.

Key Results Duration of flowering of Eremurus anisopterus varied from late April to middle May. Anthesis of a single flower often lasted for 1 d. However, if the daily maximum air temperature was under 20 ℃, the anthesis of a single flower could be prolonged to 2 d. Pollen-dispersion period of single flower could last for 4 to 5 h from 10∶30 to 15∶00 local time with the duration of pollen dispersion for single anther approximately 40 min. The heterotypical maturation of stamina could significantly prolonged the pollen-dispersion period of a single flower, suggesting an adaptation to the habitat ofE. anisopterus in the desert where the pollinators were not reliable. The timing of blossom of the ephemeroid plant showed close correlations with wind velocity, habit and characteristics of the pollinators in the desert. Pollens of the plant might spread over 70 m by wind with approximately 60% of the pollens fallen within 20 m away from the plant. Insects, especially bee, hover fly, flesh fly, mason bee and Halictus sp. were very important pollination medium. Visitors, such as bee and hover fly, usually landed at the yellowish green spot on the tepal, and then entered the flower along the purple vein on the pink tepals. The yellowish green spot might be a mimetic structure to nectar that could attract insects to visit, which was also the result of the long-period adaptation of the plant to its sandy desert habitat. Higher visiting frequency was reached between 10∶30 and 13∶30. The P/O ofE. anisopterus (6 164) suggested the species was of cross-pollination characteristic according to Cruden's criterion. However, artificial isolation experiment showed that E. anisopterus was self-compatible, which might act as a compensation mechanism for the inadequate outbreeding chances in the desert habitat. The fact that there was no seed set in bagged emasculated flowers indicated that there was no apomixes occur.

Conclusions This study suggests that E. anisopterus might adapt the not-reliable pollinator habitat by self-compatible and lengthening pollen-dispersion period of single flower.

In-stream wood is defined as dead wood (>10 cm diameter and >1 m length) in the stream channel. In-stream wood is a common, but important structural component in forest streams, particularly in relatively small creeks. Through review of research from the last 30 years (mainly from North America), we synthesize information on in-stream wood ecological functions (on channel morphology, nutrient cycling, sediment storage, aquatic habitat and biodiversity), dynamics, spatial variation and relationship between in-stream wood (loadings and distribution) and disturbance (natural and human-caused). We also present wood management paradigms and future research directions.

Much research has demonstrated that in-stream wood has important ecological functions for aquatic ecosystems. In-stream wood can significantly change channel morphology through its role in intercepting sediments and water flow as well as stabilizing stream banks. Many aquatic habitat features such as pool, cover and substrate are positively related to in-stream wood characteristics. In-stream wood also affects nutrient cycling through its decomposition and interception of fine organic materials (e.g., tree needles and branches). Because of these ecological functions, in-stream wood supports greater aquatic biodiversity and productivity. However, its ecological significance largely depends on types of forested watersheds and sizes of streams. As stream sizes increase, wood loading and its influence generally decrease. The size of individual wood pieces, however, increases with increasing stream size. In-stream wood also has large temporal variations or dynamics which are mainly driven by large-scale catastrophic forest disturbance (i.e., fire, windthrow, etc). Understanding spatial and temporal variations and differences between natural and human disturbances is important for protecting and maintaining wood ecological functions. We provide suggestions for future in-stream wood ecological research in China.

Ecological complexity has received increasing attention in recent years. Structural complexity is one of the most important parts of ecological complexity. This paper reviews the literature on the development of concepts and measures of community structure. Findings indicate that currently used methods can be classified into three groups: measures based on biodiversity, algorithmic complexity and geometrical properties. The many measures based on biodiversity are commonly used. The algorithmic method is new and has not been widely used. It represents the complexity of community structure by the difference of mean length of Huffman code of community attributes and 12th order of Rényi entropy. The methods based on geometrical properties are also commonly used, employing fractal dimension as the most important index. A common problem for all these methods is the difficulty of comparing community complexity with different complexity measures. Also, these methods weakly discriminate among different structures. For the methods based on biodiversity, it is difficult to objectively determine weights of the attributes used. For the algorithmic complexity based methods, the ecological meanings of the measures are still uncertain. Some of them are closely correlated with biodiversity indices, and the others need field testing. Future studies should focus on the following: 1) Determine algorithmic measures with high discriminant ability that differ from biodiversity indices both in concept and values. Because many algorithmic measures have been widely used in fields other than ecology, interesting results could be generated when applying these measures to description of complexity of community structure. 2) Objectively determine weights of attributes with ecological meaning used in complexity measures, a problem that exists in biodiversity and algorithmic measures that use multiple attributes. 3) Connect measures of structural complexity with functions and processes, a critical goal in the study of complexity of community structure.

Vegetation-climate relationship at the species level has always been a popular research topic in ecology. This review paper summarizes early research and recent research advances on plant species-climate relationship in China and in the world. Especially since the 1980s, when global change study started and rapidly developed, research has focused on relationship between plant species' geographical distribution and climate. During the past two decades, predictive models on species' potential geographical distributions have been well developed. These include statistical models (e.g., correlative models including bioclimatic envelope or climatic envelope models, regression models including generalized linear and generalized additive models, rule-based models including classification and regression tree analysis and artificial neural network, as well as ecological niche models and climatic response models) and mechanistic models (e.g., the STASH model on the basis of BIOME1 biogeographical model, FORSKA forest gap model, the process-based phenology model PHENOFIT, and a model based on water balance, temperature and plant phenology). We compare the advantages and disadvantages of different models, synthesize predictions on the future distribution of plant species in different regions and introduce China's studies about the potential and future distributions of selected plant species. This review provides background knowledge in order to more precisely model and predict the future change of plant species under global change.

Plant reproductive traits are key characteristics for predicting the impacts of global changes on plant community, agro-ecosystem and plant ecological fitness. This review seeks to integrate current results about the effects of elevated CO₂ on plant reproductive traits in detail based on the existing experimental data in the past few decades. Earlier investigations demonstrate that elevated CO₂ advances the flowering time through increasing relative growth rate and accelerating developmental process. All the numbers of flowers, fruits, and seeds, the mass of seed as well as the production of pollen and nectar of plants have been found to be stimulated by CO₂ enrichment. It is further revealed that the increase in plant yields results largely from an increase in seed number rather than from individual seed mass. Elevated CO₂ concentrations have little effect on seed [N] of legumes, but significantly reduce seed [N] of most nonlegumes. Contents of proteins, amino acids, and some mineral ions usually decrease in seeds of most nonlegumes. Different functional groups of plants are often found to differ markedly in their reproductive responses to elevated CO₂: 1) crops allocate more mass to reproduction and produce more fruits and seeds than do undomesticated species; 2) indeterminate plants have stronger responses to elevated CO₂ in comparison with determinate species; 3) legumes are most responsive to elevated CO₂, followed by nonlegume C₃ species, then C₄ species. Based on the data available, it seems rational to believe that changes in plant reproductive traits resulting from elevated CO₂ may alter the competitive hierarchy, the species composition, and hence the functioning of plant community. Finally, some issues noteworthy for future researches in this field are also put forward with reference to the existing unsolved questions.