The transfer mechanisms. calculating methods and ecological significance of nitrogen transfer between legumes and non-legumes are briefly reviewed. There are three pathways 0f nitrogen transf6r from legumes to neighbo...The transfer mechanisms. calculating methods and ecological significance of nitrogen transfer between legumes and non-legumes are briefly reviewed. There are three pathways 0f nitrogen transf6r from legumes to neighboring non-legumes: (1) the nitrogen pass in soluble form from the donor legume root into the soil solution, move by diffusion or/and mass flow to the receiver root and be taken up by the latter, (2) nitrogen pass into the soil solution as before, be taken up and transported by mycorrhizal hyphae attached to the receiver roots,(3) if mycorrhizal hyphae form connections (bridges) between the two root systems, the nitrogen could pass into the fungus within the donor root and be transported into the receiver root without ever being in the soil solution. The mechanisms of nitrogen transfer between N2-fixing plants and non-N2-fixing plants are reviewed in terms of indirect and direct pathways. The indirect N-transfer process is related to the release of nitrogen from legumes(donor plants), the possible interaction of this nitrogen with soil, the decomposition and mineralization of legumes and tumover of nitrogen, the nitrogen absorbing and competing abilities of the legume and the non-legume (receiver plant). The direCt nitrogen transfer process is generally considered to be related to the nitrogen gradient and physiological imbalance between legumes and non-legumes, and when the donor legume lies in stressful stage (i.e. removal of shoots or attacked by insects), the nitrogen transfer can be improved significantly. Themethods of deterrnining nitrogen transfer (lndirect 15N-isotope. dilution method and direct 15N determination method) are evaluated, and their advantages and shortcomings are shown in this review.展开更多
A study was conducted to determine the effects of elevated CO2 on soil N process at Changbai Mountain in Jilin Province, northeastern China （42°24＂N, 128°06＂E, and 738 m elevation）. A randomized complete...A study was conducted to determine the effects of elevated CO2 on soil N process at Changbai Mountain in Jilin Province, northeastern China （42°24＂N, 128°06＂E, and 738 m elevation）. A randomized complete block design of ambient and elevated CO2 was established in an open-top chamber facility in the spring of 1999. Changpai Scotch pine （Pinus sylvestris var. sylvestriformis seeds were sowed in May, 1999 and CO2 fumigation treatments began after seeds germination. In each year, the exposure started at the end of April and stopped at the end of October. Soil samples were collected in June and August 2006 and in June 2007, and soil nitrifying, denitrifying and N2-fixing enzyme activities were measured. Results show that soil nitrifying enzyme activities （NEA） in the 5-10 cm soil layer were significantly increased at elevated CO2 by 30.3% in June 2006, by 30.9% in August 2006 and by 11.3% in June 2007. Soil denitrifying enzyme activities （DEA） were significantly decreased by elevated CO2 treatment in June 2006 （P 〈 0.012） and August 2006 （P 〈 0.005） samplings in our study; no significant difference was detected in June 2007, and no significant changes in N2-fixing enzyme activity were found. This study suggests that elevated CO2 can alter soil nitrifying enzyme and denitrifying enzyme activities.展开更多
The effects of chromium and tin on survival, growth, carbon fixation, nitrate reduction, ammonia assimilation, and nitrogenase activity of a N_2-fixing cyanobacterium, Anabaena doliolum, and their amelioration by synt...The effects of chromium and tin on survival, growth, carbon fixation, nitrate reduction, ammonia assimilation, and nitrogenase activity of a N_2-fixing cyanobacterium, Anabaena doliolum, and their amelioration by synthetic and natural complexans, viz., EDTA, nitrilotriacetic acid (NTA), pyridine dicarboxylic acid (PDA), and citrate, have been studied. Chromium proved to be much more toxic than tin, as it inhibited growth yield (49%), carbon fixation (53%), and nitrate reductase (79%), glutamine synthetase (30%), and nitrogenase activities (77%) at its sublethal concentration, whereas tin induced less inhibition of growth yield (42%), carbon fixation (50%). and nitrate reductase (66%), glutamine synthetase (32.4%), and nitrogenase activities (70%). Despite its inhibitory effects at 10μml^(-1), EDTA supplementation in metal-spiked medium counteracted the toxicity of chromium and tin more significantly than NTA, PDA, and citrate. When supplemented with LD_(50) of Cr, EDTA protected growth, carbon fixation, NR, GS. and Noase, respectively, by 32.6, 50.0, 33.3. 17.7. and 65.4%. However, EDTA-induced restoration of the above parameters at a sublethal concentration of tin was only 30.2, 50.0,28.1, 27.7, and 61.5%, respectively. Although NTA and citrate at 10/μgml^(-1) each were stimulatory to various processes of test cyanobacterium, they were comparatively less effective than EDTA in the amelioration of metal toxicity. On the basis of these observations, a generalized hierarchical sequence of protective efficiency of synthetic and natural cornplexing ligands may be given as EDTA > NTA > citrate > PDA. It seems plausible that the toxicity of various heavy metals may be regulated by a large array of organic complexing agents of the aquatic environment because they possess various metal binding sites. (c) 1989 Academic Press,lnc.展开更多
文摘The transfer mechanisms. calculating methods and ecological significance of nitrogen transfer between legumes and non-legumes are briefly reviewed. There are three pathways 0f nitrogen transf6r from legumes to neighboring non-legumes: (1) the nitrogen pass in soluble form from the donor legume root into the soil solution, move by diffusion or/and mass flow to the receiver root and be taken up by the latter, (2) nitrogen pass into the soil solution as before, be taken up and transported by mycorrhizal hyphae attached to the receiver roots,(3) if mycorrhizal hyphae form connections (bridges) between the two root systems, the nitrogen could pass into the fungus within the donor root and be transported into the receiver root without ever being in the soil solution. The mechanisms of nitrogen transfer between N2-fixing plants and non-N2-fixing plants are reviewed in terms of indirect and direct pathways. The indirect N-transfer process is related to the release of nitrogen from legumes(donor plants), the possible interaction of this nitrogen with soil, the decomposition and mineralization of legumes and tumover of nitrogen, the nitrogen absorbing and competing abilities of the legume and the non-legume (receiver plant). The direCt nitrogen transfer process is generally considered to be related to the nitrogen gradient and physiological imbalance between legumes and non-legumes, and when the donor legume lies in stressful stage (i.e. removal of shoots or attacked by insects), the nitrogen transfer can be improved significantly. Themethods of deterrnining nitrogen transfer (lndirect 15N-isotope. dilution method and direct 15N determination method) are evaluated, and their advantages and shortcomings are shown in this review.
基金supported by the National Natural Science Foundation of China (No.90411020)Major State Basic Research Development Program of China (973 Program)(2002CB412502).
文摘A study was conducted to determine the effects of elevated CO2 on soil N process at Changbai Mountain in Jilin Province, northeastern China （42°24＂N, 128°06＂E, and 738 m elevation）. A randomized complete block design of ambient and elevated CO2 was established in an open-top chamber facility in the spring of 1999. Changpai Scotch pine （Pinus sylvestris var. sylvestriformis seeds were sowed in May, 1999 and CO2 fumigation treatments began after seeds germination. In each year, the exposure started at the end of April and stopped at the end of October. Soil samples were collected in June and August 2006 and in June 2007, and soil nitrifying, denitrifying and N2-fixing enzyme activities were measured. Results show that soil nitrifying enzyme activities （NEA） in the 5-10 cm soil layer were significantly increased at elevated CO2 by 30.3% in June 2006, by 30.9% in August 2006 and by 11.3% in June 2007. Soil denitrifying enzyme activities （DEA） were significantly decreased by elevated CO2 treatment in June 2006 （P 〈 0.012） and August 2006 （P 〈 0.005） samplings in our study; no significant difference was detected in June 2007, and no significant changes in N2-fixing enzyme activity were found. This study suggests that elevated CO2 can alter soil nitrifying enzyme and denitrifying enzyme activities.
文摘The effects of chromium and tin on survival, growth, carbon fixation, nitrate reduction, ammonia assimilation, and nitrogenase activity of a N_2-fixing cyanobacterium, Anabaena doliolum, and their amelioration by synthetic and natural complexans, viz., EDTA, nitrilotriacetic acid (NTA), pyridine dicarboxylic acid (PDA), and citrate, have been studied. Chromium proved to be much more toxic than tin, as it inhibited growth yield (49%), carbon fixation (53%), and nitrate reductase (79%), glutamine synthetase (30%), and nitrogenase activities (77%) at its sublethal concentration, whereas tin induced less inhibition of growth yield (42%), carbon fixation (50%). and nitrate reductase (66%), glutamine synthetase (32.4%), and nitrogenase activities (70%). Despite its inhibitory effects at 10μml^(-1), EDTA supplementation in metal-spiked medium counteracted the toxicity of chromium and tin more significantly than NTA, PDA, and citrate. When supplemented with LD_(50) of Cr, EDTA protected growth, carbon fixation, NR, GS. and Noase, respectively, by 32.6, 50.0, 33.3. 17.7. and 65.4%. However, EDTA-induced restoration of the above parameters at a sublethal concentration of tin was only 30.2, 50.0,28.1, 27.7, and 61.5%, respectively. Although NTA and citrate at 10/μgml^(-1) each were stimulatory to various processes of test cyanobacterium, they were comparatively less effective than EDTA in the amelioration of metal toxicity. On the basis of these observations, a generalized hierarchical sequence of protective efficiency of synthetic and natural cornplexing ligands may be given as EDTA > NTA > citrate > PDA. It seems plausible that the toxicity of various heavy metals may be regulated by a large array of organic complexing agents of the aquatic environment because they possess various metal binding sites. (c) 1989 Academic Press,lnc.
