The low utilization efficiency of nitrogen fertilizer in agricultural ecosystem has caused serious economic and environmental issues. Dicyandiamide (DCD) is a widely used nitrification inhibitor, which can inhibit nitrification via affecting ammonia oxidizing microorganisms with minimal influence on other soil microorganisms, thereby reducing the leaching of nitrate and emission of greenhouse gases. The factors influencing the efficiency of DCD in soil include soil temperature, pH, texture, organic matter, moisture, etc. Recently, the application of molecular methods in agricultural systems has shed new light on the microbial mechanism underlying nitrification inhibition by DCD. In this review, the enzymatic inhibition mechanism, the application effects and their influence factors of DCD were summarized, and the prospects of its application were discussed as well.

Effects and influence factors of dicyandiamide (DCD) application in agricultural ecosystem

Summary 1 Mathematical indices, formed by combining several primary measures, can help researchers summarize, interpret and display results from plant competition experiments. This essay compiles and discusses more than 50 indices that have been used in studies of plant competition. 2 Indices allow researchers to quantify and express several attributes of plant competition, including competition intensity and importance, competitive effects and responses, and the outcome of competition. 3 Several qualities should be considered when selecting a competition index for use. These include specificity and clarity of meaning, mathematical and statistical properties, density dependence, versatility and freedom from size bias. 4 Many indices are based on comparisons of plant performance in mixtures compared with pure stands or control plots. Additional measures of competition are also available from yield-density functions, size distributions and neighbourhood analysis. 5 Indices reflect the consequences of competition. In order to appreciate competitive processes, indices have to be used in conjunction with studies of the chronology, circumstances and composition of plant associations.

/pdf/indices-of-plant-competition-snzobtkkdz.pdf

Indices of plant competition

The last 15 years has seen parallel surges of interest in two research areas that have rarely intersected: biodiversity and ecosystem functioning (BEF), and multispecies predator– prey interactions (PPI). Research addressing role of biodiversity in ecosystem functioning has focused primarily on single trophic-level systems, emphasizing additive effects of diversity that manifest through resource partitioning and the sampling effect. Conversely, research addressing predator–prey interactions has focused on two trophiclevel systems, emphasizing indirect and non-additive interactions among species. Here, we use a suite of consumer-resource models to organize and synthesize the ways in which consumer species diversity affects the densities of both resources and consumer species. Specifically, we consider sampling effects, resource partitioning, indirect effects caused by intraguild interactions and non-additive effects. We show that the relationship between consumer diversity and the density of resources and consumer species are broadly similar for systems with one vs. two trophic levels, and that indirect and nonadditive interactions generally do little more than modify the impacts of diversity established by the sampling effect and resource partitioning. The broad similarities between systems with one vs. two trophic levels argue for greater communication between researchers studying BEF, and researchers studying multispecies PPI.

http://snre.umich.edu/cardinale/wp-content/uploads/2012/04/ives_ecol_lett_2005.pdf

A synthesis of subdisciplines: predator–prey interactions, and biodiversity and ecosystem functioning

1 Designs for greenhouse studies of interactions between plants are reviewed and recommendations for their use are provided.

2 Papers published over a 10-year period showed the replacement series design to be the most popular, especially in studying crop–weed interactions. Fifty per cent of the studies involved only two species, although studies testing the interaction between different genotypes of only a few species were also popular.

3 Limitations imposed by the choice of design, the variables measured, and the analysis used on the range of inferences that may be validly drawn from the experiment are frequently not well understood or appropriate for the questions that appear to be addressed. One example is the failure to distinguish the outcome of competition (the long-term outcome of interaction) and the effects of species on each other.

4 Studies in which only final yield is measured are severely limited as to the inferences which may be drawn. Effects due to interspecific interaction during the course of the experiment cannot then be separated from pre-existing differences, and interpretation may be biased towards species whose individuals were initially larger. In addition, measurements at several times are necessary to understand the changing dynamics of species interaction.

5 Simple pair-wise mixtures can assess the effect of treatment factors on the outcome of competition. Replacement series and related diallel designs generally produce results that may be size-biased even when initial interspecific differences are known. Additive designs (including target–neighbour designs), despite confounding density with species proportions, offer considerable scope for addressing mechanistic questions about interspecific interactions. Designs that allow response surface analysis can avoid many of the problems inherent in the other methods, but all need to be adjusted for initial interspecific differences. Designs for multiple species experiments are still largely untested, although several designs have been used. At the level of the individual plant, hexagonal fan designs permit study of the effects of varying the spatial pattern, and the densities and the relative proportions of interacting species, but suffer from lack of independence and lack of randomization.

Designs for greenhouse studies of interactions between plants

Based on the investigation data of 133 samples from 30 grid stations in the Fujian-Guangdong coastal upwelling region (21.6 degrees - 24.3 degrees N,115.7 degrees -118.7 degrees E) in 11-16 June 2009, this paper studied the phytoplankton species composition and cell abundance in the region in three dimensions (vertical, horizontal, and sectional), and approached their relations with major environmental factors. A total of 159 taxa belonging to 85 genera of 4 phyla were identified, among which, diatom was predominant, followed by dinoflagellate. Cyanophyceae mainly composed of Trichodesmium also occupied a greater proportion, but Chrysophyceae was only checked out in the upper 10 m water layer at coastal stations. The dominant species were Rhizosolenia alata f. gracillma, Thalassionema nitzschioides, Pseudonitzschia pungens, Skeletonema costatum, Thalassionema frauenfeldii, Paralia sulcata, Guinadia striata, Trichodesmium thiebautii, Ceratium fusus, and Gyrodinium spirale. Most of the phytoplankton taxa were cosmopolitan species, followed by warm-water species, while tropic high-salinity or oceanic eurythermal species were lesser. The cell abundance of the phytoplankton was average of 67.59 x10(2) ind x L(-1). In vertical profile, the cell abundance of the phytoplankton was the highest in surface water, and decreased with water depth. In horizontal and sectional profiles, the cell abundance had no definite patterns, but the high abundance region was in Nanao Island water area, being anastomosed with the center of upwelling region, which indicated that the weak and small intensity of deep-sea water upwelling caused lesser phytoplankton cell abundance and superposition. The comparatively high phytoplankton cell abundance in the four sections (B, C, D, E) along Nanao-Zhangpu was resulted from the upwelling from Taiwan Bank. The phytoplankton cell abundance had a significant positive correlation with the PO4(3-) concentration in the upper 10 m water layer, but no correlation with the dissolved inorganic nitrogen (DIN) concentration. Thereby, to study the eco-physiological responses of phytoplankton species to nutrient stress would be helpful to reveal the formation mechanism of algal bloom in upwelling region.

Community composition of phytoplankton in Fujian-Guangdong coastal upwelling region in summer and related affecting factors

This paper studied the effects of different storage medium (coelomic fluid, Hepes solution, and modified Ringer's solution), temperature (4 degrees C and 16 degrees C), and duration (4 h, 8 h, 16 h, and 24 h) on the short-term storage of Siberian sturgeon (Acipenser baerii) eggs. The results showed that storage medium, temperature, and duration all had significant effects on the fertilization rate, hatching success, and malformation of newly hatched larvae (P < 0.05). With the increase of storage duration, the fertilization and hatching rates decreased, while the malformation rate of hatched larvae increased. The A. baerii eggs stored at 16 degrees C had higher fertilization, hatching, and malformation rates but shorter holding time than those stored at 4 degrees C. The optimal conditions for the short-term storage of A. baerii eggs were Hepes solution prepared according to the biochemical composition of A. baerii coelomic fluid, 16 degrees C, and 4 h, under which, 86.36% fertilization rate, 94.74% hatching rate, and zero malformation would be obtained.

[Effects of storage medium and temperature on short-term storage of Acipenser baerii eggs].

This paper dealt with the diet composition and monthly variation in feeding habits of juvenile Acipenser sinensis accidentally caught along with other fish in Yangtze River estuary from May to September, 2004. The results showed that the juvenile A. sinensis mainly fed on demersal fish, polychaeta and amphipoda, as well as some small-sized benthic invertebrates including shrimp, crab and bivalve. The feeding rate and intensity were higher, and the feeding intensity varied monthly. The main food items also varied monthly, and changed from small-sized to relative large-sized species. The main diet composition included polychaeta and crab in May, fish and amphipoda in June, fish and polychaeta in July, empty stomach in August, and fish and shrimp in September. In the diet, the proportion of Platycephalidae, an important prey of juvenile A. sinensis in the past, was very low, only accounting for 1.81% of the total food by mass, while that of Gobiidae and Isopoda, which had not been recorded in the diet, was higher, accounting for 50.54% and 10:07% of the total, respectively.

Diet composition and feeding habits of juvenile Acipenser sinensis in Yangtze River estuary

In order to assess the resource status of Collichthys lucidus in coastal waters of Yangtze estuary, the growth and population parameters were studied by the length frequency distribution method based on the bottom trawl investigation data from 2012 to 2013. Von Bertalanffy growth parameters were calculated by using the ELEFAN module in FiSAT II software while the natural mortality rate (M) was estimated via Pauly's empirical equation. Besides, the Beverton-Holt dynamic model was developed to predict the variation trend of C. lucidus resource in coastal waters of Yangtze estuary. The results showed that in 2012-2013, a total of 4201 samples of C. lucidus with body lengths ranging from 18 to 155 mm were collected from the coastal waters of Yangtze estuary. The growth parameter (K) and limit length (L.) were 1.1 and 162.75 mm while the total mortality rate (Z), the natural mortality rate (M) and the fishing mortality rate (F) were 4.040, 1.683 and 2.357, respectively. Moreover, the current exploitation (E) of C. lucidus in coastal waters of Yangtze estuary was 0.583 per year, which was larger than Fopt (0.5). Corresponding to the average stock of 576.02 t, the resource amount of C. lucidus reached up to 1.33 x 10(8) individuals. These indicated that C. lucidus has been overfished in Yangtze estuary area.

Assessment of resource situation of Collichthys lucidus in coastal waters of the Yangtze estuary

Siberian sturgeon (Acipenser baerii) larvae were raised with Limnodrilus sp., Artemia nauplii, Moina sp., and artificial commercial diet for 30 days to investigate the effects of different initial feeding diets on the growth, survival, and body biochemical composition of the larvae. The results showed that A. nauplii was the best initial feeding diet, with the survival rate of A. baerii larvae being significant higher (96.67%) than the others. Feeding with Limnodrilus sp. gave the highest growth rate of A. baerii larvae, while feeding with artificial commercial diet gave the lowest efficiency on the growth rate and survival rate of the larvae. The larvae raised with different diets had significantly different body biochemical composition. After fed with artificial commercial diet, the larvae had the highest moisture content but the lowest crude protein and crude ash contents. Taking A. nauplii as the initial feeding diet and then feeding with Limnodrilus sp. could gave the ideal growth and survival rates of A. baerii larvae.

[Effects of initial feeding on the growth, survival, and body biochemical composition of Siberian sturgeon (Acipenser baerii) larvae].

To evaluate the choice preference of fish habitat in the Yangtze estuary, juvenile Collichthys lucidus which is the dominant species in spring was selected. The 4 indicator factors, including abundance of Pseudograpsus albus, salinity, substrate type and water depth, were selected from 19 environmental factors. Then, the indices of the habitat suitability curves of the 4 indicator factors were established, and the HSI of juvenile C. lucidus at each site was calculated. The results indicated that HSI was almost more than 0.5 in North Branch, and less than 0.2 in South Branch. It showed that the North Branch of Yangtze estuary was the main nursery area of C. lucidus. The most suitable growth sector was the area with salinity more than 14, mean grain size of substrate less than 29 μm and water depth 2 to 5 m, which was consistent with the distribution of HSI. The study demonstrated that biological factors could be characterized by the response of juvenile C. lucidus to the environment. Chemical oxygen demand, ammonium nitrogen, total phosphorus and volatile phenol did not have significant correlation with the fish abundance, with which nitrite nitrogen, nitrate nitrogen and total nitrogen had significant positive correlation. It suggested that the eutrophication of the survey area had not damaged the habitat of C. lucidus. However, copper ion and cadmium ion had significant negative correlation with the fish abundance, which indicated that the heavy metal pollution had harmed the growth and distribution of juvenile C. lucidus. It was inferred that the heavy metal pollution was the restrictive factor influencing the fish habitat in Yangtze estuary.

Ping Zhuang

Papers

[Effects of storage medium and temperature on short-term storage of Acipenser baerii eggs].

Diet composition and feeding habits of juvenile Acipenser sinensis in Yangtze River estuary

Assessment of resource situation of Collichthys lucidus in coastal waters of the Yangtze estuary

[Effects of initial feeding on the growth, survival, and body biochemical composition of Siberian sturgeon (Acipenser baerii) larvae].

Preliminary assessment of habitat of juvenile Collichthys lucidus in the Yangtze estuary