A number of observational, theoretical and experimental studies have indicated that local plant species diversity can have positive effects on ecosystem productivity; however, little is known about the ecological mechanisms that regulate this relationship. To investigate the relationship between plant species diversity and ecosystem productivity and the effect of resource complementarity on productivity, we established experimental communities containing different levels of diversity using nine cultivated annual plant species. To address questions of complementary resource use, we planted each species in monocultures as well as in different polycultures, which allowed us to evaluate complementary effects. Complementarity was assessed by using four analytical methods. The first two methods were tested for an absolute increase in productivity with increasing diversity. The hypothesis was that a polyculture would outperform the most productive monoculture of a component species, defined as overyielding effect 1 (OV₁), and a polyculture would perform better than the average yield of monocultures of the component species, defined as overyielding effect 2 (OV₂). The third method measured the relative yield of the polyculture, Relative Yield Totals (RYTs), and the last method measured the D value, the proportional deviation of the productivity of a polyculture from its expected value. The results indicated that, to a certain extent, species diversity showed a positive effect on community productivity. The relationship between species richness and community productivity could be represented by a quadratic equation y = -98.449x² + 1 039.2x - 42.407 (R² = 0.423). Large differences in productivity were found among treatments with similar levels of diversity indicating that species composition had an important impact on community productivity. Calculation of a complementarity index indicated that about 40% of the polycultures outperformed its most productive component monoculture, more than 95% of the polycultures performed better than the average yield of its component monocultures, and more than 50% of the polycultures had significant RYTs > 1 and D > 0. These results suggest that resource complementarity was partly responsible for the positive effect of species diversity on productivity. Complementarity, however, was not significantly related to species diversity. Four analytic methods were used for estimating the net outcome of complementary effects and the different levels of ecological interaction in a community. Each method had its advantages and disadvantages. Therefore, in assessing how complementarity influences ecosystem productivity, different methods should be integrated.

We determined the δ¹³C values of leaf samples collected from plants belonging to 6 genera in the Rhizophoraceae family grown in four locations in China, including three coastal areas (Dongzhaigang of Hainan Province, Xiamen of Fujian Province, Beihai of Guangxi Zhuang Autonomous Region), and one inland area (Xishuangbanna of Yunan Province) in May and September, 2002. The nine plant species included Carallia brachiata, C. diphopetala, Pellacalyx yunnanensis, Rhizophora apiculata, R. stylosa, Bruguiera sexangula, B. gymnorhiza, Kandelia candel, and Ceriops tagal. The results indicated that leaf δ¹³C values, corresponding to integrated wateruse efficiency (WUE) (ratio of CO₂ assimilation rate to leaf transpiration), ranged from -32‰ to -26‰, but did not vary significantly between May and September in most of those plant species. However, there were significant differences in leafδ¹³C values among growing environments with lower foliar δ¹³C values for the plants grown in the inland than those in the coastal areas on two sampling dates, indicating a higher intercellular CO₂ concentration and thus a lower water use efficiency for the plants grown in the inland. In addition, among those plants living in the coastal areas, the leaves of plants grown in the Beihai had the highest δ¹³C values indicating the lowest intercellular CO₂ concentration and thus highest WUE, which may be caused by the high salt content in the seawater or high water stress in Beihai. Our results suggest that the foliar δ¹³C values of the plants in the Rhizophoraceae family could be highly affected by intermittent environmental factors, although their genetic characteristics may play a significant role in determining their foliar δ¹³C values.

Dwarf bamboo (Fargesia denudata), a staple food of the giant panda, is the dominant synusia of the forest ecosystem in Wanglang National Nature Reserve, which plays an important role in the maintenance of forest ecosystem structure and function. The seasonal changes of nutrients in bamboo litter and nutrient retranslocation is one of the most profound ecological processes in the forest system. The seasonal change of nutrients in bamboo litter and nutrient retranslocation is regulated by the density of the bamboo stand as well as by biotic and abiotic factors. Although there have been a number of studies on nutrient cycling in bamboo forests, the effects of the bamboo density has not been investigated. The influence of bamboo density on the dynamics on litterfall, nutrient concentrations in bamboo litter, the differences in nutrient concentrations between litter and fresh leaves, and potential nutrient retranslocation were studied in three bamboo communities with different densities (D₁ with (220±11) stems·m^-2, D₂ with (140±7) stems·m^-2, and D₃ with (80±4) stems·m^-2) beneath a bamboo-fir (Picea purpurea) forest. Plots were chosen that had similar slope, aspect, soil parent material and texture, tree canopy, etc. Bamboo litter was collected in each stand and fresh leaves collected over a growing period from May to October, 2003, and nutrient concentrations (C, N, P, K, Ca and Mg) analyzed. The results indicated that litterfall production of bamboo increased with stem density during the growing period. The concentrations of C, N, P and K in litter decreased with stem density, but Ca and Mg showed the opposite pattern. It was found that N, P and K concentrations were lower in litter than in fresh leaves, increased from May to July, and decreased after July. Carbon concentrations in both litter and fresh leaves did not vary with the stem densities and month. Calcium concentrations were higher in litter than in fresh leaves over the growing season, but there was no significant monthly variation. Litter had the lowest Mg concentrations in July (during the exponential growth period) whereas fresh leaves showed the opposite pattern. No significant monthly differences in nutrients were found among the three communities. The potential retranslocation capacity of P was strongly regulated by stem density, but N and K retranslocation was not influenced by stem density. The potential retranslocation capacity of N, P and K showed the ranked order as K>N>P. The retranslocation of C in bamboo was not significantly different among the three bamboo communities. The accumulation of Ca in litter increased with stem density. The accumulation of Mg in litter increased with stem density, but the retranslocation capacity decreased with stem density. Density, therefore, greatly influenced the seasonal changes of nutrient concentrations in litter and their potential retranslocation capacity.

To better understand the effects of elevated nitrogen deposition on biomass production and allocation in seedlings of Schima superba and Cryptocarya concinna, the dominant species in subtropical monsoon evergreen broadleaved forests in China, a simulated nitrogen deposition field experiment was conducted. S. superba and C. concinna seedlings were exposed to five nitrogen treatments using NH₄NO₃ solutions of 0, 0.12, 0.24, 0.36 and 0.72 mol N·L^-1. Solutions were applied twice a month from January through November, 2003, equivalent to nitrogen deposition rates of 0, 5, 10, 15 and 30 g N·m^-2·a^-1. Each treatment was divided into three subplots and 40 seedlings of each of the two species were transplanted into each subplot. The two species responded differently to the different rates of nitrogen deposition. The stem base diameter, height, whole-plant biomass and relative growth rate of C. concinna seedlings grown in 5, 10, 15 g N·m^-2·a^-1 treatments were all higher than those in the control plot; however, the stem base diameter, height, whole-plant biomass and relative growth rate of treated S. superba seedlings were lower than those in the control plot with the exception of the 10.0 treatment. The leaf-weight ratio of seedlings of the two species was the lowest in the highest treatment, implying that the high N deposition was harmful to the foliage. The branch-and-stem weight ratio of seedlings of both species was the highest in the highest treatment indicating that the biomass allocated to branches and stems increased under high N deposition. The root-weight ratio and the root to shoot ratio of seedlings in the control plots were the highest, demonstrating that the ratio of biomass allocated to roots decreased under the conditions of elevated nitrogen deposition. Overall, except for the highest N treatment, nitrogen additions enhanced the growth of C. concinna but had the opposite effect on S. superba individuals, indicating that C. concinna seedlings were more resistant to high nitrogen loads.

Larch (Larix gmelinii) is the most important industrial timber species in northeastern China, and is ecological significant in boreal forest ecosystems. However, the growth of larch is often limited by nitrogen (N) availability because of slow litter decomposition rates due to low temperatures and the long winter in these northern forests. To explore the relationship between growth and soil N availability in larch, we treated one-year old larch seedlings to four different N supply levels (1, 4, 8 and 16 mmol·L^-1, respectively) and measured acquisition and allocation of carbon and N. The results showed that the biomass, whole plant N concentration, whole plant N content and special N absorption rate of larch seedlings were enhanced with N supply levels. With the increase in N supply, needle and stem weight ratios and needle and stem N weight ratios increased, whereas the root weight ratio and root N weight ratio decreased. As N supply levels increased from 1 mmol·L^-1 to 8 mmol·L^-1, whole plant relative growth rate (RGR) increased linearly, whereas whole plant N productivity (NP_P) remained constant. At the highest N treatment (16 mmol·L^-1), whole plant RGR was the same as in the 8 mmol·L^-1 N treatment, but NP_P decreased significantly compared with the 8 mmol·L^-1 treatment. In contrast, needle N productivity of larch seedlings exhibited a negative relationship with N supply level.

Coarse woody debris (CWD) in forest ecosystems provides critical habitat for many organisms, maintains a healthy forest structure, and is important in the biogeochemical cycling of carbon and nutrients. However, the characteristics and ecological functions of CWD are poorly documented and understood in the subtropical forests of southern China. In this study, the amount and characteristics of CWD in three typical forest ecosystem types in southern China were investigated at the Dinghushan Nature Reserve. These forests were selected to form a successional sequence with a Pinus massoniana forest, a mixed coniferous broad-leaved forest, and a monsoon evergreen broad-leaved forest representing early-, mid-, and advanced-successional stages, respectively. Both the Pinus massoniana and the mixed coniferous broad-leaved forests developed on artificial Pinus massoniana plantations planted in the 1930s. Nevertheless, these two forests were at different successional stages. The Pinus massoniana forest was harvested for leaf/needle litterfall, CWD, and undergrowth until 1990 whereas human interventions were excluded in the mixed coniferous broad-leaved forest. Results indicated that human disturbance dramatically altered the successional process of the Pinus massoniana forest and its ecological functions. Total aboveground biomass was just 35% of that of the mixed coniferous broad-leaved forest. The number of tree species that contributed to CWD increased along the successional sequence with 7, 18, and 29 species in the Pinus massoniana, mixed coniferous broad-leaved, and monsoon evergreen broad-leaved forest sites, respectively. There was almost no CWD (0.1 Mg C·hm^-2) in the Pinus massoniana forest, while CWD amounted to 8.7 Mg C·hm^-2 in the mixed coniferous broad-leaved forest and 13.2 Mg C·hm^-2 in the monsoon evergreen broad-leaved forest, representing 9.1% and 11.3% of the total aboveground biomass, respectively. Only about 10% of the CWD was standing in the mixed coniferous broad-leaved and the monsoon evergreen broad-leaved forests, suggesting that sudden forest canopy gaps created by falling or snapping of trees might be more important than gradual gaps formed by standing dead trees in the succession of these forests in this region. Although the decomposition rate of CWD was relatively fast, it was still comparable to that of the soil organic carbon in the region, suggesting that CWD can play an important role in the global carbon cycle. Keeping CWD on the forest floor is a critical strategy for maintaining forest productivity and implementing sustainable forest management in southern China.

Inner Mongolia grasslands are an important ecosystem of the Euro-Asia plateau. However, in recent decades, it has been severely degraded due to overgrazing, and, at the same time, soil carbon storage has changed. Because of the high background variation and diversity of natural soils, it is difficult to detect changes in soil carbon pools, especially over short time periods. Some experiments have attempted to detect changes in different fractions of soil carbon pools. In Inner Mongolia grasslands, experiments have showed there was no evident decrease of soil organic carbon for grazing. In this study, we examined the effects of grazing on soil carbon fractions: soil microbial carbon (MB-C) and soil labile carbon (Lab-C) in the grasslands of the Xilin River Basin of Inner Mongolia. MB-C was determined using the chloroform fumigation method and Lab-C was determined using the potassium permanganate oxidation method. The results indicated that after 22 years of grazing in Leymus chinensis dominated grasslands. Soil microbial biomass decreased by 27.9% and 12.8% in the 0-10 cm and 10-20 cm layers, respectively, and Lab-C decreased by 22.0% and 12.6% in the two soil layers. After 22 years of grazing in a Stipa grandis grassland, MB-C decreased by 38.2% and 12.2% in the 0-5 cm and 5-15 cm soil layers, respectively. The time at which soil microbial biomass reached a peak in S. grandis was delayed (August) as compared to L. chinensis, and MB-C was significantly correlated with aboveground grass biomass (p<0.000 1). Soil microbial carbon and Lab-C were more sensitive than SOC to the impacts of grazing on changes in soil carbon storage. There were no significant decreases in any of the soil carbon fractions in theArtemisia frigida+short bunchgrasses grassland with increases in the stocking rates, but the ratios of MB-C/total C and Lab-C/total C decreased gradually with increases in stocking rates. These results indicate that the ratios of MB-C/total C and Lab-C/total C are more sensitive indicators than MB-C and Lab-C in reflecting soil carbon changes under grazing pressure in the Artemisia frigida+short bunchgrasses grassland.

The services provided by croplands have been underestimated. Besides providing food and fiber, croplands provide many other functions and services, such as nutrient transformation, pollination, biological control, beautiful scenery, recreation, and so on. In this study, gas regulation services provided by fertilized and unfertilized rice (Oryza sativa) paddy ecosystems and their values were investigated based on field experiments conducted on the Wusi Farm in Fengxian County, Shanghai in 2002. Paddy fields regulated two types of gases: O₂ emissions and greenhouse gases (GHGs), including CO₂ uptake and CH₄ and N₂O emissions.
At elongation stage, booting stage, panicle initiation stage and maturation stage, the biomass of fertilized and unfertilized paddy fields were determined and O₂ emissions calculated using the photosynthesis formula based on plant biomass. The maximum O₂ emissions from fertilized and unfertilized paddy fields were 770.15 and 506.62 kg·hm^-2·d^-1, respectively. Compared to the price of industrial O₂ and the cost of afforestation in China, their values were calculated as 190.72 and 289.93 yuan·hm^-2·d^-1.
On August 15, 18, 21 and 25, and September 2, 8, 14 and 22, the gases from paddy fields were sampled and their fluxes determined. The results showed that the fluxes of CH₄ from fertilized and unfertilized paddy fields ranged from 4.86 mg·m^-2·h^-1 to 14.96 mg·m^-2·h^-1 and from 3.34 mg·m^-2·h^-1 to 50.67 mg·m^-2·h^-1, respectively. For N₂O, they ranged from 0.008 6 mg·m^-2·h^-1 to 0.056 6 mg·m^-2·h^-1 and from 0.000 6 mg·m^-2·h^-1 to 0.014 9 mg·m^-2·h^-1, and for CO₂ from 347.63 mg·m^-2·h^-1 to 730.20 mg·m^-2·h^-1 and from 205.06 mg·m^-2·h^-1 to 679.51 mg·m^-2·h^-1, in fertilized and unfertilized paddy fields, respectively. Using a CO₂ equivalent, the integrated GHGs fluxes were computed as -1.42-39.71 kg·hm^-2·d^-1 CO₂-C (fertilized) and -50.56-25.60 kg·hm^-2·d^-1 CO₂-C (unfertilized). Based on the average cost of the Sweden carbon tax and afforestation in China, the economic value of GHGs regulation was calculated. The results indicated that the valuation of CO₂ absorption by fertilized paddy fields was not much more than that by unfertilized ones. Second, urea amendment aggravated the negative values of N₂O emissions from paddy fields. Third, the negative values of CH₄ emission from paddy fields were mitigated by urea amendment. And fourth, the valuation of GHGs regulation by fertilized fields was promoted by urea amendments. In this study, we were trying to provide a fair method to evaluate the values of croplands to support an effective way to recognize the benefits derived from croplands, especially by paddy fields, and to promote the sustainability of cropland ecosystems.

Photosynthetic rate is a function of not only the CO₂ concentration gradient between the outside and inside of the leaf, but also the CO₂ diffusional resistance. It is accepted that stomatal resistance is the greatest factor that controls CO₂ diffusional resistance and is thus a crucial factor influencing photosynthesis. Hence, adequate analysis of CO₂ diffusional resistance is necessary for understanding photosynthesis. Intercellular CO₂ concentrations (C_i) are often utilized to calculate stomatal limitation (L_s). This traditional analysis is unreliable when plants are under stress, because C_i cannot be accurately measured under such conditions. Here we introduced the concept of diffusional limitation and introduced a new method to calculate the diffusional limitation value (L_d) without using C_i. In addition, C_i, estimated indirectly through chlorophyll fluorescence parameters (C_i'), was used to calculate a new stomatal limitation value (L_s') for plants grown under 40% relative soil moisture (RSM). We compared the L_s', L_s and L_d for Amomum villosum grown under both 100% and 40% RSM. Photosynthetic rates (P_n) and stomatal conductance (G_s) decreased after noon in both RSM treatments, and P_n and G_s were both higher in 100% RSM than in 40% RSM. Under 100% RSM, L_s did not increase after noontime in A. villosum, indicating stomatal limitation of photosynthesis did not increase, whereas L_d increased indicating the diffusional limitation of photosynthesis increased due to the relatively high mesophyll resistance. Under 40% RSM, L_s' increased sooner than L_d after noon, indicating stomatal resistance was the dominant factor controlling diffusional resistance. In contrast, L_s, calculated using the traditional stomatal limitation method, did not increase under 40% RSM, which might lead us to the wrong conclusion that stomatal limitation was not a factor. The estimated value, C_i', was lower than C_i, indicating that gas exchange system was overestimated using C_i under conditions of water stress. Our results suggest that the traditional method is unreliable under soil water stress conditions, and the two new methods presented are more reliable. Furthermore, mesophyll resistance can be estimated indirectly through the joint analysis of diffusional and stomatal limitation.

Ammopiptanthus mongolicus, which is an endemic and endangered species in China listed in the Red Data book, is a type of evergreen broad-leaved shrub in dry deserts of Asia. A. mongolicus is distributed mainly in the Alashan region of Inner Mongolia, but, for unknown reasons, the range of the population has been declining. We studied the distribution patterns and characteristics of A. mongolicus as a preliminary step in understanding the dynamic changes of the population and community and the factors causing the population decline. In Alashan Zuoqi, 36 quadrats (20 m×20 m) and 150 grids (5 m×5 m) were set up at 3 sites (Dongqingliang, Sumutu and Luanjingtan). There were at least 12 quadrats and 50 grids in every plot. The distribution patterns, stand density characteristics, morphological characteristics, and dynamic changes of theA. mongolicus populations at the 3 sites were compared. The results showed that A. mongolicus populations formed different distribution patterns under environmental conditions. The population was distributed evenly on flowing-sand or semi-fixed windy sand but was distributed contagiously on ancient riverbeds or stone slopes caused by seasonal floods. Individuals of A. mongolicus had different morphologies based on the population density and environment characteristics. On flowing-sand, individuals had shorter heights and smaller diameters but the relationship between height and width was not significant (R₁=0.096). There was a negative relationship between population density and the height and diameter of individuals in the population on flowing-sand (R₂=-0.214, R₃=-0.339). Individuals growing on semi-fixed windy sand and stone slopes had significantly greater heights and diameters, but there was no significant relationship between population density, and the diameter and the height. On stone slopes, the relationships between individual diameters and the heights were not significant (R₁ = 0.886), and there were no significant relationships between population density and height and width (R₂ = 0.089, R₃= 0.055). The densities of A. mongolicus populations were the highest at the flowing-sand site and the lowest at the stone slope population where seasonal floods occurred. Populations of A. mongolicus had different age structures at the different sites. At the flowing-sand site, there were even numbers of mid- to old-aged individuals but few young individuals, indicating that the population was senescing. At the semi-fixed windy sand and stone slope sites, there were also very few young individuals, and the number of individuals in the different age classes was distributed very unevenly. All three populations had limited the regeneration questioning the long-term viability of these populations.

A new behavioral outbreeding mechanism, “flexistyly”, was found in some species of the genus Amomum and Alpinia (Zingiberaceae). In this paper, the floral and pollination biology of Alpinia oxyphylla were studied in two populations at the South China Botanical Garden in Guangzhou during the 2002-2003 flowering seasons. The objectives of this study were to determine whether A. oxyphylla showed the same flexistyly pollination mechanism as that in other species of Alpinia previously reported and to examine the breeding system. According to our observation, flowering of A. oxyphylla took place from late February to late April. The flowering period of inflorescence lasted on average about 16-26 d, with most individuals at 23-26 d, and anthesis of a single flower lasted 1 d. Generally, populations of A. oxyphylla had two floral morphs that differed in flowering behavior: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther in the afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther in the morning and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon. The stylar movements in the two floral morphs were synchronous, and they had similar traits to those found in other Alpinia species previously reported. However, our observations indicated that if the maximal air temperature was under 18 ℃, the anthesis of a single flower was prolonged to 2 d, and the populations of A. oxyphylla showed only a single floral morph, viz., the cataflexistylous morph, in which the stigma was held erect above the dehiscent anther when the flower starts to open in the morning and begins to curve under the anther until the second day at 6:30-11:00 a.m. During the flowering period, both the stigma acceptability (H₂O₂ test) and pollen viability (MTT test) held high levels (>96%) and even retained levels above 75% until 9:00 a.m. on the second day when the flower withered. The P/O ratios of the two floral morphs were different: the cataflexistylous morph had lower pollen grains and P/O ratio than that of the anaflexistylous morph, but approximately equal ovules. Field experiments indicated thatA. oxyphylla was self-compatible. The seed sets were significantly high in both out-crossed and artificial self-pollinated flowers, while no seed set occurred in bagged emasculated flowers and bagged flowers indicating that there is no apomixes. There were significant differences in the seed set between the self-pollination and cross-pollination treatment on anaflexistylous morph. However, no significant differences were found in the seed set between the self-pollination and cross-pollination treatment on the cataflexistylous morph. Our results showed that the breeding system of A. oxyphylla is xenogamy and dependent upon insects for fertilization. The effective pollinators were solitary bees and the honeybee, which visited the flowers mostly for nectar. Uhe pollen is starchy and the flower produced ample nectar, 8.37-15.79 μl, with a sugar concentration of 30.12%-32.83%, which was the main reward for pollinators. During the day, the nectar volume augmented with time and attained a peak (15.79±5.7) μl at about 14:00 p.m., after which it descended to (11.22±8.11) at about 18:00 p.m.; however, the nectar sugar and amino acid (0.031±0) mg·ml^-1 concentrations were steady. Our observations also showed that the labellum with red stripes, which act as a “honey guide”, may be an indirect advertisement, and nectar may be a direct advertisement in attracting pollinators.

The ability to forecast the timing of florescence in trees is valuable for fruit trees, beekeeping, gardens and tourism. In this paper, measurements of bud morphometry (length and width) of Prunus sargentii were taken when its buds were beginning to expand at Yuyuantan Park in Beijing from 1998 to 2000.
Our results showed that linear and exponential equations could adequately forecast the timing of bud florescence. A three-day running mean method measured on three trees was used in the forecast model. The forecast accuracy within 3 days in 2002 was more than 80% of florescence, and the forecast in 2003 was more precise, from 1.6 to 2.1 days.
It was found that this new method is a convenient and precise method for forecasting florescence of plants having bigger buds in winter. A primary forecasting model could be developed by amending and perfecting this method by, for example, measuring several trees in a year. Additionally, the method can be applied to forecasting the first day of leaf out.

Using principal component analysis (PCA) and cluster analysis method, the community structure and species diversity characteristics of corticolous lichen communities in a western Tianshan forest ecosystem were studied in this paper. The results showed that corticolous lichen communities differed with altitude and on different tree types. Based on the results of a multivariate analysis and universal characteristics of habitat, the corticolous lichens communities in the forest ecosystem in western Tianshan can be generalized into four major types: 1) Chaenotheca stemonea + Candellaria aurella Association; 2) Bryoria furcellata + Evernia esorediosa + Physcia tribacoides Association; 3) Parmelia fertilis + Parmelia sulcata + Parmeliopsis ambigua Association; 4) Phaeophyscia ciliata + Phaeophyscia nigricans Association. Community 3 had the highest species diversity (1.920) and community 2 had the lowest (1.562). At the same time, we found that altitude and forest canopy density were the two most important environmental factors influencing the structural patterns of corticolous lichen communities in these forest ecosystems.

Fatty acids, being energy-rich compounds, are useful for understanding the transfer of energy from primary production to secondary production. One of the factors affecting the energy value of phytoplankton as a food source in aquatic food chains is a species of polyunsaturated fatty acid (PUFA) content. Polyunsaturated fatty acids, especially eicosapentaesnoic acid (EPA), play a key role in the transfer of energy in aquatic ecosystems. A low EPA content results in a low efficiency of energy transfer between phytoplankton and zooplankton which can contribute to the formation of algal blooms. Phaeocystis globosa and Microcystis aeruginosa are two common species that cause blooms in marine and freshwater systems. The fatty acid composition of cultured P. globosa HK and two strains of M. aeruginosa WN1 and WN2, were measured during their logarithmic and stationary growth phases by gas chromatography-mass spectrophotometry. These three strains of algae have simple fatty acid compositions, and their carbon chain lengths of fatty acids varied from 14 to 20. Saturated fatty acids are the dominant class, but the two essential fatty acids, EPA and docosahexaenoic acid (DHA), were not detected in the three strains. The total fatty acid content varied from 247.294 μg·g^-1 DW to 735.44 μg·g^-1 DW in P. globosa, C14:0 and C16:0 were dominant in the logarithmic and stationary phases, respectively. The total fatty acid content was much higher inM. aeruginosa WN1 and WN2, ranging from 1 405.095 μg·g^-1 DW to 6 087.617 μg·g^-1 DW weight, and C16:0 dominated both growth phases for the two strains. There was a significant difference in the content of fatty acid on a dry weight basis between the two growth phases for both strains ofM. aeruginosa. This indicated that the composition of algal fatty acid changed with growth phase. However, this difference did not occur in P. globosa. Due to the absence of EPA and DHA in these two species, both P. globosa and M. aeruginosa cannot provide the essential fatty acids to grazers at higher tropic levels, such as Daphnia. Because of the poor food quality, these two species are not grazed by zooplankton, which most likely contributes to their noxious quality of forming algal blooms.

Grain protein content in rice (Oryza sativa) is an important indication of rice nutritional quality and is determined by both genotype and environmental factors. Much attention has been paid to the relationships between protein accumulation in rice grains and environmental factors. Modeling changes of protein content in rice under different environmental conditions is of great help for predicting rice quality and ecological zoning. In this study, Indica and Japonica rice varieties grown under different ecological environments in China (Jiangsu), Japan (Iwate, Shimane, Kyoto) and Thailand (Changmai) were grown for two years, and the relationships between grain protein content and environmental factors, including latitude (x₁), altitude (x₂), ecological height, latitude, altitude, (x₃), and average temperature (x₄), lowest temperature (x₅), highest temperature (x₆) and solar radiation during the grain filling period were analyzed. Environmental factor-driven equations were established for Indica rice: f (x₁) =8.4E-$04x_1^2$ +0.049 05x₁+0.282 1, f(x₂) =2.82E-$07x_2^2$-3.8E-04x₂+1.128 6, f (x₃) = 9.2E-$10x_3^2$-3.1E-05x₃+1.255 6, f (x₄) =-0.007 $02x_4^2$+0.303 7x₄-2.285, f (x₅)=-0.009 $18x_5^2$+0.313 9x₅-1.684 6, f (x₆)= -0.006 $99x_6^2$+0.372 8x₆-3.971 7; and for Japonica rice: f (x₁)=-0.000 $695x_1^2$+0.038 51x₁+0.466 1, f (x₃)= 4.02E-$10x_3^2$-1.2E-05x₃+1.090 4, f (x₄)= -0.004 $16x_4^2$++0.185 9x₄-1.077 4, f (x₅)=-0.006 $54x_5^2$+0.228 6x₅-0.996 8, f (x₆)=-0.004 $12x_6^2$+0.226x₆-2.099 1. By using a weighted method to modify the impacts of environmental factors on grain protein accumulation, an ecological model was developed for predicting grain protein content in Indica rice: PC=PC₀×[0.138 9×f(x₁)+0.152 6×f(x₂)+0.187 4×f(x₃)+0.180 2×f(x₄)+0.168 5×f(x₅)+0.173 4×f(x₆)]; and PC=PC₀×[0.262 3×f(x₁)+0.09×f(x₃)+0.202 3×f(x₄) +0.246 1×f(x₅)+0.198 4×f(x₆)] for Japonica rice, where PC₀ is the specific protein content of cultivar. The model was validated using the data sets for different years, eco-sites and varieties. The root mean square error (RMSE) was 0.27% and 0.24% for Indica rice and Japonica rice, respectively, and the RMSE was 0.25% and 0.22% for the growing areas of Indica and Japonica rice types, respectively. The results indicated that the model was accurate and applicable for predicting protein content in rice under different conditions. Yet, more experimental data in different eco-environments are required for wider testing of the present model.

Starch, one of the main products metabolized in the grain of maize, directly affects the yield and quality of maize. The synthesis of starch in maize grain is affected by the activities of several enzymes. We studied the effects of different water treatments on the grain starch content and components and related enzyme activity during the grain-filling period of two cultivars—the common corn, Yedan22, and the high oil corn, Gaoyou115. Three water treatments were chosen: W0 (no water irrigation after anthesis), W1 (irrigation one time after anthesis), W2 (irrigation two times after anthesis). The results showed that the patterns of starch accumulation and related enzyme activity were the same in the two cultivars, but their response to water treatments were different. Water duress significantly increased starch and amylopectin content and decreased amylose content in Yedan22, but increased the starch, amylopectin and amylose content in Gaoyou115. When sufficient levels of water were supplied, starch yield and its components significantly increased, as did the SS and SPS activities in ear leaves and ADPG-PPase, UDPG-PPase, SSS and GBSS activities in the grain, especially 10 to 30 days after anthesis. Increased enzyme activity in grain increased the amylopectin and amylose content in Gaoyou115. The activities of these enzymes in grain under water duress decreased early and quickly, and the activities of SPS, ADPG-PPase, and SSS were more sensitive to water duress than other enzymes.

The aim of this study was to determine the effects of Al stress on the physiological responses of four herbaceous plants and to analyze the differences in their physiological responses. Four southern herbaceous plants, Pharbitis nil, Cassia occidentlis, Echinochloa colonum and Aeschynomene indica, which are distributed in the red soils of South China, were used to study the seed germination, chlorophyll content, levels of proline, malondialdehyde (MDA), membrane permeability (MP) and soluble sugar (SS), and activities of peroxides (POD) and catalase (CAT) in their leaves under five Al treatments (0, 80, 400, 2 000, 10 000 mg·L^-1) with the sand culture method.
The results showed significant effects of Al on the physiological characteristics of these four herbaceous plant species. The seeds of all four species could not germinate at the 10 000 mg·L^-1 Al³⁺ treatment and were disadvantageous to growth under the 2 000 mg·L^-1 Al³⁺ treatment. When compared to the control, the 2 000 mg·L^-1 Al³⁺ treatment significantly (p<0.05) reduced the contents of chlorophyll a and chlorophyll a+b (p<0.05), promoted levels of MDA and MP (p<0.05), very significantly increased the content of proline (p<0.01) and depressed activities of POD and CAT (p<0.01). In the 80 mg·L^-1 and 400 mg·L^-1 Al³⁺ treatments, levels of MDA and MP in P. nil and A. indica leaves decreased, and the activities of POD and CAT increased compared to the control, but variations in C. occidentlis leaves showed an opposite response. Changes in E. colonum leaves were similar to P. nil and A. indica under 80 mg·L^-1 but opposite to those under the 400 mg·L^-1. These species maintained higher activities of POD and CAT, higher contents of chlorophyll and proline, and lower contents of MDA and MP, thus improving their tolerance to Al stress under low and medium Al treatments.

Calcium has been found to be a second-messenger in plants involved in the perception and regulation of responses and adaptations of plants to the environment. During this period, polyamines (PAs) accumulation, the activities of diamine oxidase (DAO) and polyamine oxidase (PAO) play an important role in increasing stress-resistance of plants. However, little is known about the effect of Ca²⁺ on polyamines metabolism of seedlings under hypoxia stress. In this experiment, muskmelon cultivar `Xiyu 1' (Cucumis melo var. raticulalus) seedlings with less hypoxia-resistance under hydroponic cultivation were used to study the relationship between Ca²⁺ and PAs metabolism under hypoxia stress. When seedlings grew to 3 euphylla, the seedlings were transferred from quartz sand to Hoagland nutrient solutions for preculture. After 2 days, the seedlings were divided into four sets. The first and second sets of seedlings were all cultured in normal Hoagland nutrient solutions containing 4 mmol·L^-1 Ca²⁺. The third set of seedlings was cultured in a calcium sufficient Hoagland nutrient solution which contained 10 mmol·L^-1 Ca²⁺, and the fourth set of seedlings was cultured in a calcium deficient Hoagland nutrient solution with no Ca²⁺ (0 mmol·L^-1 Ca²⁺). The first set of seedlings was exposed to normal dissolved oxygen (DO) level by using vigorous aeration (30 min·h^-1) to keep DO level at 8-8.5 mg·L^-1, and seedlings in the other treatments were exposed to hypoxia stress by using DO analyzer (QUANTUM-25) to maintain DO level at (2±0.2) mg·L^-1. Hence, the four treatments were control, hypoxia stress, Ca²⁺ sufficient-hypoxia stress treatment, and Ca²⁺ deficient-hypoxia stress treatment. After 4 d of hypoxia stress, the growth of seedlings, PAs content, DAO and PAO activities, and H₂O₂ content were all assayed. The results showed that the fresh weight and dry weight of seedlings declined significantly after 4 d of hypoxia stress, the content of three polyamines (Put, Spd, Spm) of different forms (free, conjugated, bound), DAO and PAO activities, and H₂O₂ content in roots and leaves of seedlings all increased significantly with hypoxia stress treatment compared to the control. In the calcium sufficient-hypoxia stress treatments, seedling growth under hypoxia stress was not inhibited, PAs (Put, Spd, Spm) and their three different forms in roots and leaves were significantly higher in the Ca²⁺ sufficient-hypoxia stress than in the hypoxia stress treatment, but DAO and PAO activity and H₂O₂ contents were lower. In the Ca²⁺ deficient treatment, seedlings incurred the greatest damage due to hypoxia stress, and PAs metabolism indices under Ca²⁺ deficiency showed opposite trends as compared to seedlings in the Ca²⁺ sufficient treatment. We suggest that Ca²⁺ might be involved in the regulation of polyamines metabolism and play an important role in enhancing hypoxia tolerance in muskmelon seedlings.

Remediation of soils contaminated by heavy metals is one of the most pressing environmental problems facing the biosphere. Phytoremediation is a new biotechnique to clean environmental pollutants by plants, including heavy metals. In the long term, major improvements in phytoremediation will rely on the isolation and application of the genes from various plant, bacteria, and animal sources that can enhance metal accumulation. Phytochelatin is a type of polypeptide that combines heavy metals in plants, and its synthesis is regulated by phytochelatin synthesase (PC synthase). In this study, we determined that the roots of garlic (Allium sativum) can accumulate up to 3 000 mg·kg^-1 cadmium. A yeast-expressed plasmid with PC synthesase from garlic (AsPCS) was constructed and transferred into heavy metal sensitive yeast mutant cells. The results showed that the expression of AsPCS was improved by 4 folds in yeast cells with cadmium tolerance and a 2 folds increase was observed in arsenate tolerant cells as compared to the control cells. Further study about the growth patterns of AsPCS-expressed yeast indicated that the expression of AsPCS was critical for yeast heavy metal tolerance. As an important role in the garlic's response to heavy metal, AsPCS can work as a significant gene tool in the phytoremediation of heavy metal pollution.

This paper provides a review of some biological control or mitigation strategies for HABs, a problem worldwide in coastal waters. Bacteria, viruses and parasites are abundant in marine ecosystems and their abilities for rapid replication and host-specificity make them attractive HAB controlling agents; however, potential ecological impacts need to be taken into account. Species interactions between bloom microalgae and other algae play essential roles in affecting the phytoplankton sequence either by competing for the available nutrient supply or by secreting extracellular organic substances (allelopathy) into the environmental medium. This control strategy is not well understood due to a lack of experimental data, especially under natural conditions. Grazing of phytoplankton by zooplankton and suspension-feeding benthos is also considered a promising control agent, but this approach has many logistical problems and is a long way from the application stage. Collectively, some of the biological strategies discussed are decades from possible implementation, but others are further developed and thus worth considering in the immediate future.

The fundamental sexual condition of the vast majority of flowering plant species is hermaphroditism. Hermaphroditic individuals both receive and disperse pollen and may ultimately function as both maternal and paternal parents to the next generation of individuals. Such dual sex roles can result in conflicts and compromise the parental roles of plants during pollination and mating. Our aim in this review is to introduce the key concepts and various forms of sexual interference in flowering plants. Sexual interference can potentially take several distinct forms with contrasting reproductive consequences and has been recognized as occurring within flowers and between flowers. Intra-floral interference includes physical interference between sex functions, pollen clogging, and ovule discounting, while inter-floral interference refers to geitonogamous pollen discounting. The adaptive significance of floral diversity such as dichogamy, herkogamy, unisexuality, and self-incompatibility has largely been regarded in the literature as resulting only from selection to avoid selfing and the harmful effects of inbreeding, but without regard to the possibly important role that sexual interference has played. We review the limited experimental evidence for interference between sex functions and evaluate the hypothesis that some floral adaptations may serve an alternative function in reducing mating costs. In a broader sense, selfing also may be regarded as a form of sexual interference, or more specifically, male function (pollen dispersal) interfering with female function (seed production). Through imaginative experiments involving floral manipulations, it is possible to evaluate various forms of sexual interference in plants and their potential ecological and evolutionary significance.

The temperature coefficient, Q₁₀ (Fractional change in rate with a 10 ℃ increase in temperature), can describe the response of organisms to temperature increases as a result of global warming. It is also a necessary parameter for estimating CO₂ efflux. Although many studies have focused on Q₁₀ values, reported values are highly variable. To better understand the sensitivity of forests to global warming, we reviewed and summarized reported Q₁₀ values in the literature. Our specific objectives were the following: 1) to calculate the frequency distribution of Q₁₀ values for soil, tree root and tree stem respiration and compare the temperature sensitivity of these different forest ecosystem compartments; 2) to determine the Q₁₀ values of evergreen and deciduous tree species and examine the methodological influences on their calculation; and 3) to discuss future Q₁₀-related studies. We found that most Q₁₀ values reported for soil, root and stem respiration fell within a relatively narrow range although there were some outliers. For soil respiration, the median Q₁₀ value was 2.74 with 23% of the values falling between 2.0 - 2.5 and 80% falling between 1.0 to 4.0. The median Q₁₀ value for root respiration was 2.40 with 33% of the values falling between 2.5 - 3.0 and 80% between 1.0 - 3.0. The median Q₁₀ value for stem respiration was 1.91 with 90% of the values falling between 1.0 - 3.0. The stem respiration Q₁₀ value was significantly less than both the root and soil respiration Q₁₀ values. There were no significant differences between the Q₁₀ values for root and stem respiration of evergreen and deciduous trees (p>0.10). Methods for CO₂ analysis (Soda lime absorption, IRGA and chromatograph analysis) and root separation methods (Excised root and trenched box) did not have a significant effect on Q₁₀ values of soil and root respiration (p>0.10), butin vitro measurements of stem respiration yielded a significantly higher Q₁₀ value than in vivo methods (p<0.05). In general, although theQ₁₀ values of stem and root respiration fell within a relatively narrow range, there still was considerable variation between and within reported values for stems and roots. More attention should be paid to the quantitative estimation of total CO₂ efflux by Q₁₀ related models. Future research should focus on the biochemical, environmental and biological factors that control respiration for more precise estimation of total CO₂ efflux. The greatest challenge is to better understand the underlying mechanisms that result in the variation in Q₁₀ values between habitats and tree components to make Q₁₀ values more universal for representation of temperature sensitivity to global warming.

Charcoal, the product of the incomplete combustion of plant organisms, remains embedded in the soil and other kinds of sediments and can be used to construct a chronosequence of fire frequency over thousands to tens of thousands of years. The higher the charcoal concentration was, the more intense and frequent the wildfires were. Wildfire activity is related to both climatic changes and human activities, and this study was undertaken to document changes in the frequency of fire during the Holocene and related these to climatic changes and human activities. This research was carried out on the alluvial plain of the Yuncheng Basin in Xiaxian County, northwest of Zhongtiao Mountain. We analyzed charcoal content in soil samples in three different particle fractions obtained from a DXF-S profile.
During the early Holocene (11500-8500 a B.P.), the climate was dry although it was becoming warmer and wetter. Large amounts of charcoal found in the soil during this period indicated that wildfires were frequent. The dry climate apparently creating favorable conditions for natural fires to occur, suggested the fire frequency was climatically controlled.
The Holocene Megathermal (8500-3100 a B.P.) was the warmest and wettest period during the Holocene, and we found very little charcoal in the soil with the exception of the Xia and Shang dynasties (3800-3500 a B.P.), when a peak in the charcoal content was showed. The high precipitation during this period apparently suppressed natural fires, but human activities increased the fire frequency during the Xia and Shang dynasties.
During the late Holocene (3100-0 a B.P.), the climate became drier and conditions were once again favorable for fires to occur naturally. The amount of charcoal in the soil greatly increased during this period that showed the greatest levels of fire activity of the entire Holocene. The high fire frequency was related to both the arid climate and increased human activities.
In conclusion, climatic conditions and human activities are two important factors that influence fire frequency. Under drier climatic conditions, natural fires are more prevalent and human activities increase both the frequency and intensity of fires.