The Release of Endogenous Nitrogen and Phosphorus in the Danjiangkou Reservoir: A Double-Membrane Diffusion Model Analysis

Endogenous contamination from the newly submerged sediment may have an impact on the water quality of the Danjiangkou Reservoir, the water source of the middle route of the South-to-North Water Diversion Project. In this study, in situ sediment samples were collected at different locations (Guojiashan (DJK1), Kongqueyuan (DJK2), Shijiagou (DJK3), Shiqiao Wharf (DJK4), and Songgang Wharf (DJK5) from the north to the south) of the Danjiangkou Reservoir and the upstream tributary using a columnar sediment sampler and statically cultured in laboratory, and the distribution and release of endogenous N and P from the sediment were investigated based on a double-membrane diffusion model. The results showed that the P contents in the main reservoir and the upstream tributary followed the order of inorganic phosphorus IP > organic phosphorus OP > calcium − phosphorus Ca − P > iron − phosphorus Fe − P > labile phosphorus LP . IP accounted for the largest proportion (47.10-59.70%) of total phosphorus (TP), while LP accounted for only a small proportion (0.10-0.90%) of TP. There is a significant difference in the spatial distribution of P at different sampling points, especially for the OP content (226.90 mg·kg-1) with a coefficient of variation of 26.90%. The contents of different forms of P and NH4+-N decreased from the upstream tributary to the main reservoir, which was mainly attributed to the land use type. In the vertical distribution, the contents of different forms of P in DJK4 and DJK5 decreased with the increase of sediment depth. The contents of NH4+-N and PO43--P in the sediment interstitial water of DJK4 and DJK5 were higher than those in the overlying water. In addition, the contents of NH4+-N and PO43--P were higher in DJK5 than that in DJK4. The static culture experiments showed that N and P were mainly released from the sediment-overlying water interface to the overlying water. The release rate of NH4+-N and PO43--P ranged from 13.08 mg·(m2·d)-1 to 21.39 mg·(m2·d)-1 and from 3.06 mg·(m2·d)-1 to 6.02 mg·(m2·d)-1, and the release amount calculated based on the double-membrane diffusion model was 1.17 × 10 3 t·a-1 and 0.53 × 10 3 t·a-1, respectively. Thus, endogenous contamination from the newly submerged land is an important factor affecting the water quality of the Danjiangkou Reservoir.

Phytoregulators and Explant Size in the in vitro Culture of Malva sylvestris

In vitro propagation of plants makes it possible to accelerate the process of plant multiplication, the study of secondary metabolite production and the cultivation of biotrophic fungi. The objective of this work was to study the combination of indoleacetic acid (IAA) and benzylaminopurine (BAP) and explant sizes in in vitro multiplication of M. sylvestris. Five concentrations of BAP (0, 0.5, 1.0, 1.5 and 2.0 mg L-1) and two of IAA (0 and 0.5 mg L-1) were used in explants of 4 to 9 mm and of 14 to 23 mm. Contaminated explants, oxidation, establishment, relative growth rate (RGR), sprouting, rooting and callus formation were evaluated. There was no interaction effect between BAP and IAA concentrations. At 28 days, explants were established at 32.76% and callus formation was 62.5% for explants associated with 0.0 mg L-1 of IAA. There was 32.14% establishment and 63.79% callus formation at 0.5 mg L-1 of IAA. Bacterial contamination at 28 days was 60.53%, twice as much the amount found at 14 days, suggesting that the explants presented endogenous contamination. It was found that explant size influences the subsequent meristematic development. The use of smaller explants (4 to 9 mm) allowed greater formation of calli and larger explants (14 to 23 mm) allowed greater formation of shoots. In conclusion, larger explants are preferable for production of M. sylvestris in vitro by organogenesis while smaller ones are preferable for embryogenesis.

Validation of use of purine bases as a microbial marker by15N labelling in growing lambs given high-concentrate diets: effects of grain processing, animal age and digesta sampling site

The origin of post-ruminal purine bases (PB) was studied in 24 growing lambs that were given a pelleted concentrate plus barley straw (C) or whole barley grain plus protein supplement (WB). Six lambs from each treatment were slaughtered at 10 and 30 days post weaning after15N labelling of microbial nitrogen (N) and PB. Microbial contribution to digesta non-ammonia N (NAN) and PB was lower (P< 0·01) when estimated from duodenal rather than abomasal samples (0·36 v. 0·52 (s.e.d. 0·021) for NAN and 0·47 v. 0·77 (s.e.d. 0·029) for PB) as a result of endogenous contamination. In comparison with15N, total PB/N led to higher estimates (P< 0·01) of microbial contribution to abomasal NAN in WB treatment (0·62 v. 0·46 s.e.d. 0·049). The difference was removed after correcting for microbial PB, while this effect was not observed with < the C diet, resulting in a marker by diet interaction (P< 0·05). Abomasal PB flow increased (P< 0·1) from 10 to 30 days after weaning mainly due to the higher proportion of microbial PB (0·70 v. 0·81 (s.e.d. 0·047)). Rumen apparent PB degradation did not differ between diets in older lambs, but it was proportionally 0·39 lower for WB treatment (P< 0·05) in younger lambs. When the microbial PB flow was estimated indirectly from labelled microbial N and the PB/N ratio of bacterial extracts the estimates were in agreement with those derived from PB-15N in the WB treatment but resulted in unrealistic values in lambs on diet C. Results suggest that significant proportions of dietary PB can escape rumen degradation which may lead to overestimation of microbial contribution to abomasal NAN when the PB/N ratio is used as marker. The extent of the overestimation is affected by the lamb age and grain processing.