[Effects of Different Topdressing Nitrogen Rates on Soil Fungal Community Structure and Ecological Network in Wheat Field Under Crop Residue Retention].

Crop residue retention and fertilizer application are the main sources of soil nutrient input in fields. Crop residue retention combined with appropriate fertilizer application rates could provide necessary nutrients for crop production under the premise of environmentally friendly conditions. The aim of this study was to clarify the influence of different topdressing nitrogen rates on the soil fungal community in a wheat field under crop residue retention and to evaluate the rationality of nitrogen fertilizer management in winter wheat from the perspective of soil ecological function. On the basis of full straw retention and 150 kg·hm-2 basal nitrogen, treatments with five topdressing nitrogen rates (0, 37.5, 75, 112.5, and 150 kg·hm-2) were set up. The abundance, diversity, structure, and ecological network of soil fungal communities were analyzed using real-time fluorescence quantitative PCR and high-throughput sequencing, and the main soil physical and chemical factors driving the change in soil fungal communities were explored. The results showed that, compared with the no topdressing nitrogen and low topdressing nitrogen rate treatments, high topdressing nitrogen rate treatments increased soil total nitrogen and mineral nitrogen and decreased soil pH, total phosphorus, available phosphorus, and available potassium. Compared with the no topdressing nitrogen treatments, the 37.5-150 kg·hm-2 topdressing nitrogen treatments significantly increased soil fungal community abundance (P<0.05), whereas there was no significant difference among different topdressing nitrogen treatments (P>0.05). The Heip index and Shannon index of soil fungal communities decreased gradually with the increase in topdressing nitrogen rate, and the Sobs index, Heip index, and Shannon index of soil fungal communities in the treatment with 150 kg·hm-2 topdressing nitrogen were significantly lower than those of 0-75 kg·hm-2 topdressing nitrogen treatments (P<0.05). Principal component analysis and similarity analysis showed that there were significant differences in soil fungal community structure under different topdressing nitrogen rate treatments (P<0.05). With the increase in topdressing nitrogen rate, the number of network edges and average number of neighbors of soil fungal ecological network increased first and then decreased, and the network complexity of 37.5 kg·hm-2 topdressing nitrogen treatments was the highest. Compared with 0-75 kg·hm-2 topdressing nitrogen treatments, 112.5 kg·hm-2 and 150 kg·hm-2 topdressing nitrogen treatments increased the characteristic path length of the soil fungal ecological network, whereas it decreased the network density. With the increase in topdressing nitrogen rate, the relative abundance of soil saprotrophs gradually increased, and the pathotroph-saprotroph-symbiotroph relative abundance gradually decreased. Redundancy analysis showed that soil pH, total phosphorus, mineral nitrogen, available phosphorus, and available potassium were the main soil physicochemical factors affecting the soil fungal community structure in the wheat field under different topdressing nitrogen rate treatments. In conclusion, on the basis of straw retention and basal nitrogen, topdressing nitrogen at the wheat jointing stage could change the diversity, structure, and species composition of the soil fungal community, in turn affecting the soil fungal ecological network and function, and high topdressing nitrogen rates could reduce soil fungal community diversity, ecological network complexity, and network density.

[Response of Soil Fungal Communities in Diversified Rotations of Wheat and Different Crops].

Crop-soil microorganism interactions and feedback are critical to soil health and crop production. The aim of this study was to clarify the difference in soil fungal communities under diversified rotations of wheat and different crops in the North China Plain and to provide a theoretical basis for the construction and optimization of ecological sustainable planting systems. The soil fungal community abundance, composition, and diversity of continuous winter wheat-summer maize M, winter wheat-summer peanut (summer maize) PM, and winter wheat-summer soybean (summer maize) SM treatments were studied using real-time quantitative PCR and high-throughput sequencing technology. The results showed that, compared with those of the continuous winter wheat-summer maize treatment, the peanut rotation treatment PM2 and soybean rotation treatment SM2 significantly reduced soil fungal ITS sequence copy numbers (P<0.05); there was no significant difference in soil fungal ITS sequence copy numbers between other rotation treatments and those of the control (P>0.05). Rotation treatments with peanut or soybean increased soil fungal community richness (Chao1 and ACE indices) and diversity (Shannon and InvSimson indices), in which the community richness of all rotation treatments and the community diversity of SM1/SM2 treatments varied significantly (P<0.05). The result of non-metric multidimensional scaling (NMDS) analysis showed that the soil fungal community among different rotation crops were obviously separated. The rotation crops significantly affected soil fungal community structure (PERMANOVA:r2=0.350, P=0.001; ANOSIM:r=0.478, P=0.001). Ascomycota (73.67%-85.48%) was the dominant phylum, whereas Sordariomycetes (30.53%-48.19%) and Eurotiomycetes (11.12%-31.19%) were the dominant classes of the fungal communities of sandy-loam fluvo-aquic soil in the North China Plain. There were significantly different taxa of soil fungal communities in different rotations. Potential pathogens such as Neocosmospora, Plectosphaerella, and Gibellulopsis were significantly enriched in the rotations of winter wheat-summer peanut (summer maize), whereas potential beneficial fungi such as Penicillium and Zopfiella were significantly enriched in the rotations of winter wheat-summer soybean (summer maize). Compared with that under the continuous winter wheat-summer maize treatment, rotations with peanut or soybean increased the relative abundance of pathotroph, pathotroph-symbiotroph, and saprotroph-symbiotroph fungi and decreased the relative abundance of saprotroph fungi. The soil fungal community richness and structure were significantly related to soil organic carbon and available nutrients, and the Shannon diversity index was significantly related to soil mineral nitrogen and available phosphorus. In summary, on the basis of continuous winter wheat-summer maize rotation in the North China Plain, adding summer peanut or summer soybean instead of summer maize for rotations with different interval years could increase the richness and diversity of soil fungal communities and significantly change soil fungal community structure. In particular, summer soybean as the preceding crop had a positive effect on the enrichment of potential beneficial fungi.

[Method for estimating relative chlorophyll content in wheat leaves based on chlorophyll fluorescence parameters]. / åŸºäºŽå¶ç»¿ç´ è§å ‰å‚æ•°çš„å°éº¦å¶ç‰‡å¶ç»¿ç´ ç›¸å¯¹å«é‡ä¼°ç®—æ–¹æ³•.

Chlorophyll content is a physiological index widely used in the research of botany and agriculture. It is closely associated with leaf photosynthetic function. The current methods cannot simultaneously determine chlorophyll content and photosynthetic function and analyze their correlation. To solve this problem, we measured the SPAD value and chlorophyll fluorescence induction kinetic curve with 35 wheat varieties. We established a linear regression model using the fluorescence values of the fast chlorophyll fluorescence kinetic curve at different times, 33 common fluorescence parameters, and the correlation between the parameters and the SPAD values. We further verified the model using laboratory and field data. Our results showed that the linear model based on chlorophyll fluorescence parameter RC/CSm could reliably predict the SPAD value of the leaves, which could be used to estimate the relative content of chlorophyll in wheat leaves under non-severe stress. The linear model enriched the method of nondestructive measurement of chlorophyll relative content in wheat, simplified the experimental flow, and achieved the simultaneous determination and analysis of wheat photosynthesis function and chlorophyll content.

[Effects of irrigation regimes on photosynthesis, water use efficiency and grain yield in winter wheat]. / çŒæ°´æ¨¡å¼å¯¹å†¬å°éº¦å ‰åˆç‰¹æ€§ã€æ°´åˆ†åˆ©ç”¨æ•ˆçŽ‡å’Œäº§é‡çš„å½±å“.

The effects of different irrigation regimes on photosynthesis, plant growth, water use efficiency (WUE), and grain yield in winter wheat were examined in a common garden with rainout shelter during 2013-2014 and 2014-2015 growing seasons. The experiment consisted of two irrigation timings, jointing stage (J) and anthesis (F), and three irrigation levels, 0, 37.5 and 75 mm, which generated nine irrigation combinations, i.e. J0F0, J0F1, J0F2, J1F0, J1F1, J1F2, J2F0, J2F1 and J2F2. All plots received 75 mm irrigation at grain filling stage. The results showed that water stress at jointing stage significantly reduced leaf area after jointing stage and the net photosynthetic rate (Pn) at anthesis. Post-anthesis flag leaf Pn was significantly affected by irrigation at anthesis. Water stress at jointing stage followed irrigation at anthesis or that at anthesis followed irrigation at grain filling stage increased dry matter accumulation of wheat plants. Higher amount of irrigation at jointing stage led to higher water consumption in the entire growing period. High amount of irrigation during the entire growing period resulted in high water consumption and grain yield with an exception of J1F2 treatment. Among all the treatments, the J1F2 treatment had superior grain yield and WUE. Sufficient water supply at anthesis resulted in high flag leaf Pn after flowering in J1F2. Irrigation at anthesis for J1F2 enhanced wheat dry matter accumulation and kernel numbers per spike, and consequently high yield. Small amount of irrigation at jointing stage reduced wheat water consumption at middle and late growth stages. The wheat WUE in treatments with small amount of irrigation at jointing stage (J1F2) was higher than in other treatments. In this study, J1F2 was the best irrigation regime for winter wheat.

[Impact of temperature increment before the over-wintering period on growth and development and grain yield of winter wheat].

The effect of temperature increment before the over-wintering period on winter wheat development and grain yield was evaluated in an artificial climate chamber (TPG 1260, Australia) from 2010 to 2011. Winter wheat cultivar 'Zhengmai 7698' was used in this study. Three temperature increment treatments were involved in this study, i.e., temperature increment last 40, 50 and 60 days, respectively, before the over-wintering period. Control was not treated by temperature increment. The results showed that temperature increment before the over-wintering period had no significant effect on earlier phase spike differentiation. But an apparent effect on later phase spike differentiation was observed. High temperature effect on spike differentiation disappeared when the difference of effective accumulated temperature between the temperature increment treatment and the control was lower than 25 °C. However, the foliar age at the jointing stage was enhanced more than 0.8, heading and physiological ripening were advanced 1 day each, when the effective accumulated temperature before the over-wintering period increased 60 °C. Higher effective accumulated temperature before the over-wintering period accelerated winter wheat growth and development, which resulted in a short spike differentiation period. Winter wheat was easy to suffer freeze damage, which lead to floret abortion and spikelet death in spring under this situation. Meanwhile, higher effective accumulated temperature before the over-wintering period also reduced, photosynthetic capacity of flag leaf, shortened the grain filling period, and led to wheat grain yield reduction.

[Research on Cultivation and Stability of Nitritation Granular Sludge in Integrated ABR-CSTR Reactor].

Abstract: The last two compartments of the Anaerobic Baffled Readtor ( ABR) were altered into aeration tank and sedimentation tank respectively to get an integrated anaerobic-aerobic reactor, using anaerobic granular sludge in anaerobic zone and aerobic granular sludge in aerobic zone as seed sludge. The research explored the condition to cultivate nitritation granular sludge, under the condition of continuous flow. The C/N rate was decreased from 1 to 0.4 and the ammonia nitrogen volumetric loading rate was increased from 0.89 kg x ( m3 x d)(-1) to 2.23 kg x (m3 x d)(-1) while the setting time of 1 h was controlled in the aerobic zone. After the system was operated for 45 days, the mature nitritation granular sludge in aerobic zone showed a compact structure and yellow color while the nitrite accumulation rate was about 80% in the effluent. The associated inhibition of free ammonia (FA) and free nitrous acid (FNA) dominated the nitritation. Part of granules lost stability during the initial period of operation and flocs appeared in the aerobic zone. However, the flocs were transformed into newly generated small particles in the following reactor operation, demonstrating that organic carbon was benefit to granulation and the enrichment of slow-growing nitrifying played an important role in the stability of granules.