Abstract:Spatial heterogeneous characteristics of aboveground biomass and total soil nitrogen and phosphorus in old-field communities, Artemisia scoparia (early stage), Stipa bungeana (mid stage) and Lespedeza dahurica (later stage), in 0–20 cm and 20–40 cm depths with 3 different successional stages were studied using geostatistical methods. The correlations of aboveground biomass and total nitrogen and phosphorus at different scales were analyzed using partial Mantel correlation analyses on distance matrices. Moreover, the variations of aboveground biomass were partitioned into community space processes and environment components (including soil nitrogen and phosphorus). The results show that: 1) total phosphorus of the 3 communities has relatively larger spatial autocorrelation coefficients than total nitrogen. Total nitrogen of different layers also has different spatial heterogeneous extents. The variability of total nitrogen ranked as L. dahurica > S. bungeana > A. scoparia in 0–20 cm, and S. bungeana > L. dahurica > A. scoparia in 20–40 cm, so we infer that the variability of total nitrogen in the top layer increases as succession occurs, while in subsoil the variability of mid-succession stage is greater than that of earlier and later succession stages. The total phosphorus in both layers also has greater variability in mid-succession stage and smaller values in earlier and later succession stages. 2) Aboveground biomass of the 3 communities has different spatial autocorrelation coefficients, and S. bungeana has the smallest value. The variability ranked as A. scoparia > L. dahurica > S. bungeana. The partial Mantel correlogram of A. scoparia community shows significantly positive partial correlation at small scale (0.71 m) between aboveground biomass and total nitrogen, and relatively significantly negative correlation at small scale (0.71 m) between aboveground biomass and total phosphorus. For L. dahurica community, significantly positive correlation between aboveground biomass and total phosphorus occurred at 7.07–20.51 m scale, while at small scale (0.71 m) there also existed significantly positive correlation. No significant correlation was found for S. bungeana community with either total nitrogen or total phosphorus (only at small scale, the value was relatively great). 3) The environment, i.e., total nitrogen and phosphorus, explained about 19.59% of the spatial heterogeneity of aboveground L. dahurica biomass, 2.75% of A. scoparia and 1.95% of S. bungeana. The space process accounted for about 5.42% of the heterogeneity of A. scoparia, 1.79% of L. dahurica and 1.16% of S. bungeana.

Abstract:Crop nitrogen status is a key indicator for evaluating crop growth, increasing yield and improving grain quality. Non-destructive and rapid assessment of leaf nitrogen is required for improving nitrogen management in wheat production. This study aims at identification of the quantitative relationship between leaf nitrogen accumulation and canopy reflectance spectra in winter wheat (Triticum aestivum L.), and to derive regression equations to monitor N nutrition status in wheat. 3 field experiments were conducted with different N application rates and wheat cultivars across 3 growing seasons, and time-course measurements were taken on canopy spectral reflectance, leaf N content and leaf dry weights under various treatments. In these studies, leaf nitrogen accumulation in wheat increased with increasing nitrogen rates. Canopy reflectance changed with increasing leaf nitrogen accumulation. Sensitivity bands mainly occurred in near infrared and visible light, and strong correlation existed between red light and leaf nitrogen accumulation. The relationships of 8 vegetation indicators and leaf nitrogen accumulation were analyzed using statistical models. Hyper-spectral variables were significantly correlated with leaf nitrogen accumulation, and the relationships between the leaf nitrogen accumulation and SDr/SDb, FD742 and AVHRR-GVI were all highly significant with determination of coefficients (R²) of 0.9163, 0.9097 and 0.9142, respectively, and standard errors (SE) of 1.165, 1.079 and 1.077, respectively. Tests with another independent dataset showed that FD742 and REPIG could be well used to predict leaf nitrogen accumulation in wheat with R² of 0.8449 and 0.8394, and root mean square error (RMSE) of 0.984 and 1.014, respectively. This suggests that FD742 and REPIG can be used to estimate leaf nitrogen accumulation, of which FD742 performed better in modeling and testing.

Abstract:The influence of small hydropower plants (SHPs) on the spatial distribution of macroinvertebrate assemblages was investigated in 5 cascade SHPs along the Xiangxi River in October 2005. 5 sites were sampled at each SHP. A total of 4656 macroinvertebrates belonging to 69 genera were collected. The characteristics of macroinvertebrate community structures were analyzed by using richness, abundance, dominant species and functional feeding groups. The results suggested that construction of SHPs had no significant impact on water chemistry, but on physical variables (such as current velocity and water depth) which varied significantly among the 5 sites. All the characteristics of the macroinvertebrate community were more or less affected by the construction, especially by the abundance, filter-collector percentage, predator percentage, and the stations. The results also suggested that the sites beneath the dam had the most different community structures, indicating that diverting the water current completely is harmful to the protection of macroinvertebrate diversity of the river.

Abstract:With colorimetric methods, the concentrations of total phenolics, flavonoids and condensed tannins were analyzed in 9 categories of organs in Populus euphratica, including lanceolate leaves, ovate leaves, green branches, branches (D < 5 mm in diameter), branches (5–10 mm in diameter), barks, roots (D < 2 mm in diameter), roots (2–5 mm in diameter) and roots (5–10 mm in diameter). The results showed that phenolic compounds were present throughout the collected organs with the higher total phenolics concentrations in barks (27.93 mg/g), and the mean total phenolics concentrations in two categories of leaves, three classes of roots and three classes of branches were 17.64, 16.72 and 12.19 mg/g, respectively. The higher flavonoids were present in barks (51.30 mg/g), and the mean flavonoid contents in two categories of leaves, three classes of roots and three classes of branches were 28.45, 39.99 and 23.67 mg/g, respectively. The higher condensed tannin contents were found in roots (mean = 22.10 mg/g for three categories of roots), and the average condensed tannin contents in barks, leaves in two categories and branches in three classes were 8.41, 4.03 and 4.47 mg/g, respectively. There was no significant difference between the phenolic compounds of lanceolate leaves and ovate leaves (P > 0.05). Phenolic compounds in branches decreased with the branches maturing, resulting in the following orders: green branches > branches (D < 5 mm) > branches (5–10 mm). Condensed tannins in roots increased with the root diameter decreasing, and the highest condensed tannin contents were found in small roots (D < 2 mm) (25.95 mg/g). By analyzing correlation between phenolic compounds in all collected organs and soil water contents, it was indicated that the phenolic compounds in ovate leaves had negative relation with soil water contents (P < 0.05), and the r values for total phenolics, flavonoids and condensed tannins were –0.949, –0.923 and –0.944, respectively. Data reported here revealed the variation of phenolic compounds in different organs of P. euphratica, and their relationships with the environmental factors in extremely arid areas were discussed.

Abstract:Analysis on the numerical dynamics of populations has been widely used to study endangered species, and yet its application to China orchid is rare. By investigating biological characteristics and reproductive behavior of Cypripedium lentiginosum, an orchid endemic to Yunnan of China, the number of survivals in each age-class, the frequency and number of filial generations, and the reproductive behavior and mechanism were explored. The internal distribution pattern was figured out based on genet frequency. On the basis of the number of survivals in each age-class and the number of filial generations, the static life table and fecundity table of the populations were made, the survival curve and age pyramid were drawn, and the Leslie matrix model and the density-dependent growth model N_t=658e^0.211t were structured to predict numerical dynamics. Reproductive behavior and breeding strategy were analyzed by observing phenological characteristics and pollination biology. Based on these, we analyzed the relationship between the numerical dynamics and the reproductive behavior, as well as its internal distribution pattern and age pyramid. We found that C. lentiginosum showed a clumped dispersion distribution pattern, its age pyramid was pyramid-bell shaped, and its population survival exhibited a Deevey I shape. The net reproductive rate and the intrinsic and finite rates of increase for C. lentiginosum were comparatively high, indicating that the population was expanding. The population growth is affected by self-density, and the prediction model based on this factor is Nt=6000/(1+ e^2.094-0.211t), which is suitable for predicting the numerical dynamics of C. lentiginosum. The species are endowed with both asexual and sexual reproductions. The former, i.e., asexual reproduction, does not increase individual quantity, but sustains the current genetics of the populations and accumulates energy for sexual reproduction, while the latter, i.e., sexual reproduction, involves pollinating flowers by mimicking brood-sites to lure the hoverfly into the labellum, whose fruit set rate is 54.37% ± 6.08%. The fruits grow into sufficient young plants and most of them could live through the sexual reproduction stage. Sexual reproduction generates progeny many times over a long period, suggesting that this kind of reproductive mode is the main factor affecting the numerical dynamics of a population. The species' successful reproductive strategies and their impacts on the numerical dynamics in spatial and age distributions indicate that the population development of C. lentiginosum corresponds to its biological characteristics. Discontinuity and narrowness of growing space in the habitat are the main factors restricting population development. However, at present, the species does not need or will not prosper from ex-situ conservation.

Abstract:Abies georgei is one of the endemic trees at timberline on Qinghai-Tibetan Plateau, but little research has been done about its timberline population. One plot was set up at timberline above 4400 m on the north-facing slope of Baima Snow Mountain in Southwest China, covering an area of 0.8 hm2. Height, DBH (diameter at breast high) or root-collar diameter of seedlings and saplings, and position were recorded for each individual. The population showed a growing trend and the number of individuals decreased with increase of DBH. The survival curve can be described by Deevy-III. The population had 2 distinct peaks of mortality: age I (seedlings, DBH = 0–5 cm) and age V-VI (DBH = 20–30 cm). The highest mortality of seedlings was due to severe climate at timberline. As the saplings grew up, the interspecific and intraspecific competition resulted in another mortality peak. Through SPPA (spatial point pattern analysis), individuals of all age-classes showed uniform, random or clumped distribution with the change of scales; however, they had mainly clumped distribution. Moreover, the relationships between individuals in different age-classes were all significantly correlated with each other. Seedlings showed the highest clumping intensity and scale.

Abstract:Soil microbial community structure and function are commonly used as indicators for soil quality and fertility. In this paper, the bacterial community structure and function in a black soil of Dehui region influenced by fertilization were investigated by Biolog and PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) methods. Biolog examination showed that substrate richness and catabolic diversities of bacterial communities were the highest in the treatment of farm yard manure, and the lowest in the chemical fertilizer treatment. DGGE fingerprint showed that the majority of bands were similar among all treatments, suggesting that microbial communities with those bands were stable, and not influenced by fertilization. In general, chemical fertilizer decreased the diversity of soil bacterial communities. The PCA (principal component analysis) plots of Biolog and DGGE revealed that the structure and function of bacterial communities were similar in the non-fertilized control and the treatment of farm yard manure alone, which inferred that the application of farm yard manure increased the quantity of soil microbes but had less effect on the changes of community structure. The catabolic function was similar, but the composition structure differed between the treatments of chemical fertilizer alone and combined application of farm yard manure with chemical fertilizer. These results suggest that the use of chemical fertilizer mainly decreased the catabolic activity of the fast growth bacteria or eutrophic bacteria.