Understanding the relationship between the timing of N fertilizer applications and crop primary production is crucial for achieving high yield and N use efficiency in agriculture. This study investigated the effects of starting-N plus topdressing N applications (as compared to the common practice of all basal application) on soybean photosynthetic capacity under different planting densities. A field experiment was conducted in two growing seasons (2011 and 2012), and the soybean (Glycine max L. Merrill) cultivar was Dongnong 52, three planting densities (20, 25 and 30 plants m-2), and four N fertilizer application patterns (all N fertilizer of 6 g N m-2 as basal fertilizer, all N fertilizer as topdressing at beginning pod stage (R3), 1.8 g N m-2 as basal fertilizer and 4.2 g N m-2 as topdressing at stage R3 and full pod stage (R4), respectively). The results indicated that under the same planting density, compared to applying all N as basal fertilizer, the application of starter-N plus topdressing N substantially reduced the rate of pod abscission, and enhanced leaf area index (LAI) significantly at beginning seed stage (R5) (P<0.05), net assimilation rate (NAR) during stages R4-full seed stage (R6) (P<0.05), contribution rate of post-seed filling assimilate to seed (CPA) (P<0.05), and yield (P<0.05). Applying topdressing N at stage R4 resulted in higher net primary production and yield than applying topdressing N at stage R3. When applying starter-N plus topdressing N at planting density of 25 plants m-2, LAI after stage R5 and NAR after stage R4 were increased by 5.92-16.3% (P<0.05) and 13.7-26.6% (P<0.05) with the planting density of 20 plants m-2, respectively, and yield was 8.46-14.0% (P<0.05) higher than that under 20 plants m-2. When planting density increased to 30 plants m-2, only LAI during stages R4-R5 and NAR during stages R4-R5 increased by applying starter-N plus topdressing N, while the other indexes declined. Overall, results of this study demonstrated that applying starter-N plus topdressing N could significantly enhance soybean photosynthetic capacity after stage R5 at planting density of 25 plants m-2.

indica and japonica are the two most important subspecies of Asian cultivated rice. Identifying mechanisms responsible for population differentiation in these subspecies is important for indica-japonica hybridization breeding. In this study, subspecies and economic trait differentiation patterns were analyzed using morphological and molecular (InDel and Intron Length Polymorphism) data in F2 and F3 populations derived from indica-japonica hybridization. Populations were grown in Liaoning and Guangdong provinces, China, with F3 populations generated from F2 populations using bulk harvesting (BM) and single-seed descent methods (SSD). Segregation distortion was detected in F3-BM populations, but not in F3- SSD or in F2 populations. Superior performance was observed with respect to economic traits in Liaoning compared with that in Guangdong and 1 000-grain weight (KW), seed setting rate (SSR) and grain yield per plant (GYP) were significantly correlated with indica and japonica subspecies types. Analysis of molecular and morphological data demonstrated that the environment is the main factor giving rise to population differentiation in indica-japonica hybridization. In addition, we also found that KW, SSR and GYP are related to subspecies characteristics and kinship, which is possibly a significant factor resulting in economic trait differentiation and determining environmental adaptability. Our study has provided new insights into the process of population differentiation in these subspecies to inform indica-japonica hybridization breeding.

Naked oat (Avena nuda L.) was originated from China, where soil nitrogen (N) is low availability. The responses of chlorophyll (Chl.) fluorescence parameters and leaf gas exchange to N application were analysed in this study. After the N application rate ranged from 60 to 120 kg ha-1, variable fluorescence (Fv), the maximal fluorescence (Fm), the maximal photochemical efficiency (Fv/Fm), quantum yield (ΦPS II) of the photosynthetic system II (PS II), electron transport rate (ETR), and photochemical quenching coefficient (qP) increased with N application level, however, non-photochemical quenching coefficient (qN) decreased. Moreover, there was no difference in initial fluorescence (Fo) with further more N enhancement. The maximum net photosynthetic rate (Pmax), apparent dark respiration rate (Rd) and light saturation point (LSP) were improved with 40-56 kg N ha-1 as basal fertilizer and 24-40 kg N ha-1 as top dressing fertilizer applied at jointing stage. Initial quantum yield (α) was decreased with 24 kg N ha-1 as basal fertilizer and 56 kg N ha-1 as top dressing fertilizer. Flag-leaf net photosynthetic rate (Pn) was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1 as basal fertilizer; in addition, increased at grain filling stage of naked oat with 40-56 kg N ha-1 as top dressing fertilizer. 90 kg N ha-1 (50-70% as basal fertilizer and 30-50% as top dressing fertilizer) application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.

Since May 2006, a highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) variant characterizedby 30 amino acids deletion within its NSP2-coding region emerged and caused extensive economic losses to China’s pigindustry. To investigate the in vivo pathogenicity and immune responses of the newly emerging PRRSV, 3 groups of 60-d-old conventional piglets were inoculated intranasally with a representative strain of the HP-PRRSV variant HuN4 with3 different infection doses (3×103-3×105 TCID50). The results revealed that the virus variant caused severe disease inpiglets and the significant clinical characteristics consisted of persistently high fever (41.0-41.9ºC) and high morbidity andmortality (60-100%), the marked clinical signs of PRRS and severe histopathogenic damages in multiple organs. It inducedrapid and intense humoral immune responses and seroconversion was detected in most infected pigs at 7 d post-infection(DPI). The virus vigorously replicated in vivo and the highest virus average titer was 9.7 log copies mL-1 serum at 7 DPI.Elevated levels of IFN-γ and IL-10 cytokine production in serum in this study were also observed. Taken together, ourresults demonstrated that the HP-PRRSV variant HuN4 strain is highly pathogenic for piglets and suitable to be a referencestrain of highly virulent PRRSV for evaluating the efficacy of the new vaccines.