Search

Using 13 C pulsed labeling technique, we examined the biomass and carbon accumulation of different organs as well as the distribution characteristics of 13 C assimilate of 6-year-old Korla fragrant pear trees under three nitrogen application levels, i.e ., 150, 300, and 450 kg N·hm -2 (marked as N 1 , N 2 , and N 3 , respectively). Results showed that the biomass, carbon accumulation, 13 C fixation and leaf assimilation capacity of the whole pear tree increased while root to shoot ratio decreased with increasing nitrogen application. Both biomass and carbon accumulation amount of reproductive organs ( i.e ., fruits) were the highest under N 2 treatment. The 13 C content and distribution rate of each organ changed dynamically along with increasing nitrogen application. At the new shoot growing stage, leaves and roots had stronger competitive abilities for photosynthate, with 13 C distribution rates being the highest under N 1 treatment. During fruit swelling and mature stages, leaves and fruits were more competitive, with 13 C content and distribution rate in leaves being the highest under N 3 treatment and those in fruits being the highest under N 2 treatment. According to the absorption and distribution characteristics of carbon assimilate across organs under the three nitrogen application levels, the optimal nitrogen application level for achieving high fruit yield in the 6-year-old Korla fragrant pear tree orchard is recommended as 300 kg·hm -2 .

Six-year-old Korla fragrant pear trees were fertilized with 15 N-labelled urea before early bud stage to examine the absorption, distribution, and utilization of urea. Results showed that there was a significant difference of 15 N distribution rate in organs at different growth stages. 15 N was pre-ferentially distributed in the roots , with Ndff ( 15 N amount absorbed from the fertilizer contribution rate of the total nitrogen organ) being the highest in roots following by new shoots at full-bloom stage. During new shoot growing and fruit expanding stages, 15 N absorbed in roots preferentially moved to new organs (leaves and new shoots), with 15 N distribution rate to roots being continuously decreased. Fruits became the new distribution center with highest Ndff at harvest stage. The amounts of absorbed 15 N in fruits accounted for 19.8% of total absorbed 15 N in the tree. The utilization rate of 15 N-labelled urea at current season increased gradually with the growth stages. The maximum value of utilization rate was 18.5%, which was observed at harvest stage.

Background: Portasystemic shunts, especially total shunts, are effective tools for reducing portal pressure and controlling variceal bleeding but lead to high risk of encephalopathy and accelerating liver failure. The purpose of this study is to evaluate the clinical effects of small-diameter expanded polytetrafluoroethylene (ePTFE) H-graft portacaval shunts in the treatment of portal hypertension., Methods: Thirty-one patients with portal hypertension were treated with ePTFE small-diameter H-graft portacaval shunts from December 1995 to April 2002. Twenty-one had externally ringed grafts and 10 had non-ringed grafts; 20 had 10 mm diameter grafts and 11 had 8 mm grafts. The left gastric artery and coronary vein were ligated in 22 patients. Additionally, 6 patients underwent pericardial devascularization, and splenectomies were performed on 30 patients., Results: An average decrease of free portal pressure (FPP) from (32.13 +/- 4.86) cmH2O before shunting to (12.55 +/- 5.57) cmH2O after shunting was observed. Portal blood flow was reduced by 1/3 compared with the levels measured before shunting. Twenty-eight patients survived after the operation, and no upper gastrointestinal rebleeding occurred in the follow-up period (40.2 months on average). We lost contact with one patient. Color Doppler ultrasonography and/or portography revealed the shunts to be patent in 28 cases and occluded in 2 (6.4%) cases. Encephalopathy developed in 4 patients (12.9%)., Conclusion: Small-diameter ePTFE H-graft portacaval shunts can effectively reduce portal pressure. Moreover, the majority of the hepatopetal flow from the portal vein can be adequately maintained. The reinforced shunts may achieve a higher rate of patency. Morbidity from encephalopathy was less frequent than in patients receiving total shunts. Small-diameter H-graft portacaval shunts are also effective in preventing recurrent variceal bleeding.