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1.
The purpose of this study was to characterize leaf photosynthetic and stomatal responses of wheat ( Triticum aestivum L.) plants grown under two N-nutritional regimes. High- and low-N regimes were imposed on growth-chamber-grown plants by fertilizing with nutrient solutions containing 12 or 1 millimolar nitrogen, respectively. Gas-exchange measurements indicated not only greater photosynthetic capacity of high-N plants under well-watered conditions, but also a greater sensitivity of CO 2 exchange rate and leaf conductance to CO 2 and leaf water potential compared to low-N plants. Increased sensitivity of high-N plants was associated with greater tissue elasticity, lower values of leaf osmotic pressure and greater aboveground biomass. These N-nutritional-related changes resulted in greater desiccation (lowered relative water content) of high-N plants as leaf water potential fell, and were implicated as being important in causing greater sensitivity of high-N leaf gas exchange to reductions in water potential. Water use efficiency of leaves, calculated as CO 2 exchange rate/transpiration, increased from 9.1 to 13 millimoles per mole and 7.9 to 9.1 millimoles per mole for high- and low-N plants as water became limiting. Stomatal oscillations were commonly observed in the low-N treatment at low leaf water potentials and ambient CO 2 concentrations, but disappeared as CO 2 was lowered and stomata opened. 相似文献
2.
Below-ground carbon (C) production and nitrogen (N) flows in the root-zone of barley supplied with high or low amounts of N-fertilizer were investigated. Interest was focused on the effect of the level of N-fertilizer on the production of root-derived C and on gross immobilization ( i) and gross mineralization ( m) rates. The plants were grown for 46 days in a sandy loam soil. Principles of pool dilution and changes in 15N pool abundances were used in conjunction with mathematical modelling to calculate the flows of N. N was applied at a high or a low rate, as ( 15NH 4) 2SO 4 solution (17.11 atom% 15N excess), before sowing. Nitrification was inhibited by using nitrapyrin (N-Serve). Pots were sampled four or five times during the experimental period, i.e. 0, 22, 30, 38 and 46 days after germination. On the three last sampling occasions, samples were also collected from pots in a growth chamber with 14C-labelled atmosphere.The release of 14C, measured as the proportion of the total 14C translocated below ground, was higher in the high-N treatment, but the differences between treatments were small. Our results were not conclusive in demonstrating that high-N levels stimulate the decomposition and microbial utilization of root-released materials. However, the internal circulation of soil-N, calculated N fluxes ( m), which were in accordance with C mineralization rates and amounts of unlabelled N found in the plants (PU), suggested that the decomposition of native soil organic matter was hampered in the high-N treatment. Apparently, towards the end of the experimental period, microorganisms in the low-N treatment used C from soil organic matter to a greater extent than C they used from root released material, presumably because lower amounts of mineral N were available to microorganisms in the low-N treatment. Immobilization of N appeared to be soil driven (organisms decomposing soil organic matter account for the N demand) at low-N and root-driven (organisms decomposing roots and root-derived C account for the N demand) at high-N.Abbreviations AU
Ammonium N-unlabelled
- AL
Ammonium N-labelled
- AT
Ammonium N-labelled and unlabelled (total)
- NU
Nitrate N-unlabelled
- OU
Organic N-unlabelled
- OL
Organic N-labelled
- OT
Organic N-total
- PU
Plant N-unlabelled (shoots and roots)
- PL
Plant N-labelled (shoots and roots)
- PT
Plant N-total (shoots and roots)
- SL
Sink or source of N-labelled
- S
Source or sink of N, mainly to and from the outer part of the cylinder
- SU
Sink or source of N-unlabelled
-
m
Mineralization rate
-
i
Immobilization rate
-
ua
Uptake of ammonium
-
un
Uptake of nitrate
-
la
Loss of ammonium. 相似文献
3.
The rate of photosynthesis and its relation to tissue nitrogen content was studied in leaves and siliques of winter oilseed
rape ( Brassica napus L.) growing under field conditions including three rates of nitrogen application (0, 100 or 200 kg N ha -1) and two levels of irrigation (rainfed or irrigated at a deficit of 20 mm).
The predominant effect of increasing N application under conditions without water deficiency was enhanced expansion of photosynthetically
active leaf and silique surfaces, while the rate of photosynthesis per unit leaf or silique surface area was similar in the
different N treatments. Thus, oilseed rape did not increase N investment in leaf area expansion before a decline in photosynthetic
rate per unit leaf area due to N deficiency could be avoided. Much less photosynthetically active radiation penetrated into
high-N canopies than into low-N canopies. The specific leaf area increased markedly in low light conditions, causing leaves
in shade to be less dense than leaves exposed to ample light.
In both leaves and siliques the photosynthetic rate per unit surface area responded linearly to increasing N content up to
about 2 g m -2, thus showing a constant rate of net CO 2 assimilation per unit increment in N (constant photosynthetic N use efficiency). At higher tissue N contents, photosynthetic
rate responded less to changes in N status. Expressed per unit N, light saturated photosynthetic rate was three times higher
in leaves than in silique valves, indicating a more efficient photosynthetic N utilization in leaves than in siliques. Nevertheless,
from about two weeks after completion of flowering and onwards total net CO 2 fixation in silique valves exceeded that in leaves because siliques received much higher radiation intensities than leaves
and because the leaf area declined rapidly during the reproductive phase of growth.
Water deficiency in late vegetative and early reproductive growth stages reduced the photosynthetic rate in leaves and, in
particular, siliques of medium- and high-N plants, but not of low-N plants. 相似文献
4.
Hydrogen (H 2) is a by-product of the symbiotic nitrogen fixation (N 2 fixation) between legumes and root-nodule bacteria (rhizobia). Some rhizobial strains have an uptake hydrogenase enzyme (commonly referred to as Hup +) that recycles H 2 within the nodules. Other rhizobia, described as Hup ?, do not have the enzyme and the H 2 produced diffuses from the nodules into the soil where it is consumed by microorganisms. The effect of this phenomenon on the soil biota and on the soil itself, and consequent stimulation of plant growth, has been demonstrated previously. Soybeans [ Glycine max (L.) Merr.] cv. Leichhardt, inoculated with either a Hup + strain (CB1809) or one of two Hup ? strains (USDA442 or USDA16) of Bradyrhizobium japonicum and uninoculated soybeans, plus a non-legume control [capsicum ( Capsicum annuum L.)] were grown in the field at Ayr, North Queensland, Australia. The objectives were to examine (1) relationships between N 2 fixation and H 2 emission, and (2) the influence H 2-induced changes in soil might have during the legume phase and/or on the performance of a following crop. Strains CB1809 and USDA442 were highly effective in N 2 fixation (“good” fixers); USDA16 was partly effective (“poor” fixer). The soil had a large but non-uniformly distributed naturalised population of B. japonicum and most uninoculated control plants formed nodules that fixed some N 2. These naturalised strains were classified as “poor fixers” of N 2 and were Hup +. H 2 emissions from nodules were assessed for all treatments when the soybean crop was 62 days old. Other parameters of symbiotic N 2 fixation and plant productivity were measured when the crop was 62 and 96 days old and at crop maturity. Immediately after final harvest, the land was sown to a crop of maize ( Zea mays L.) in order to determine the consequences of H 2 emission from the soybean crop on maize growth. It was estimated that soybeans inoculated with USDA442, the highly effective Hup – strain of B. japonicum, fixed 117 kg shoot N/ha (or about 195 kg total N/ha if the fixed N associated with roots and nodules was taken into account), and contributed about 215,000 l H 2 gas per hectare to the ecosystem over the life of the crop. The volume of H 2 evolved from soybeans nodulated by the Hup + strain CB1809 was only 6% of that emitted by the USDA442 treatment, but there was no indication that soybean inoculated with USDA442 benefited from the additional H 2 input. The shoot biomass, grain yield, and amounts of N fixed (105 kg shoot N/ha, 175 kg total N/ha) by the CB1809 treatment were little less than for USDA442 plants. Three days after the soybean crop was harvested, the plots were over-sown with maize along the same row lines in which the soybeans had grown. This procedure exposed the maize roots to whatever influence soybean H 2 emission might have had on the soil and/or the soil microflora immediately surrounding soybean nodules. The evidence for a positive effect of soybean H 2 emission on maize production was equivocal. While the consistent differences between those pre-treatments that emitted H 2 and those that did not indicated a trend, only one difference (out of the 12 parameters of maize productivity that were measured) was statistically significant at P?<?0.05. The findings need substantiation by further investigation. 相似文献
5.
A study was designed to (a) identify sources and sinks of N in the maize ( Zea mays L.) shoot, by estimating net N fluxes for each of seven parts of the shoot, (b) determine effects of N entering the plant upon fluxes of N absorbed before reproductive growth, and (c) determine the effects of the opaque-2 gene on N fluxes in the maize shoot during early reproductive growth. Plants of a maize hybrid (Pioneer 3369A) and its opaque-2 counterpart (Pioneer L3369) were grown in a greenhouse using nutrient solution/sand culture, with NO 3− as the N source during the vegetative growth phase. Beginning at the time of pollination, the same nutrient regime was continued, except that some plants received no N, and others received 3.75 millimolar 15N as NO 3−-N. Stalk and leaves were found to be primary N sources for the grain, while shank, husk, and cob acted first as N sinks, then as N sources during reproductive growth. Net fluxes of N for each plant part were estimated by calculating the first derivatives of regression equations used to fit data for N contents of each plant part as functions of time. All parts of the shoot were sinks for exogenous N (absorbed after pollination). Thirty-six days after pollination, the grain contained 60% endogenous N (absorbed before pollination) when 3.75 millimolar NO3−-N was supplied after pollination. Rates of total N influx to the grain were identical whether or not N was supplied in the nutrient solution during reproductive growth. At 36 days after pollination, less N had accumulated in the grain of the opaque-2 genotype, but otherwise there were no differences in N contents or dry weights of the shoots due to the opaque-2 gene. Absence of N from the rooting medium significantly affected N fluxes throughout the shoot during reproductive growth, but there were no detectable effects of the opaque-2 gene on N fluxes in parts of the plant other than the grain. 相似文献
6.
Theoretical plant growth models postulate that the relative rates of shoot and root growth are largely modulated by signals related to carbon and nitrogen status of the plant. To test this experimentally, 6-week-old vegetative cuttings of grapevine ( Vitis vinifera L. cv Merlot) were grown aeroponically in different controlled conditions of irradiance (13.8, 8.4 and 5.3 mol PAR m −2 day −1) and/or nitrogen nutrition (0.15, 1.20 and 7.11 mM N). Total non-structural carbohydrates (TNC) and amino acids (FAA) in leaves and roots were analysed 0, 6 and 28 days after treatment initiation. Both whole-plant biomass accumulation as well as C and N contents were highly responsive to light and N availability. At day 28, plant dry weight was significantly reduced in shaded vines (−35% of that of the control plants) and stimulated under the high irradiance environment (+30%). Deprivation of N enhanced root growth (+51%) at the expense of above-ground growth, whereas leaf dry weight was significantly greater in the high-N treatment than in the control. Vines grown under low-N and high irradiance conditions had the highest root-to-shoot ratios and those grown under low light and high N the lowest. Finally, redistribution of biomass among vegetative vine parts was significantly related to different indicators of the vine C:N status measured either at the whole-plant (N concentration) or at the organ level (TNC:FAA ratio), suggesting that root-to-shoot biomass partitioning was controlled by some aspect of plant C:N balance. Such relationships will be useful to improve allocation rules in a process-based growth model of grapevine. 相似文献
7.
Lotus pedunculatus L., Medicago sativa L., Macroptilium atropurpureum, Glycine max, and Trifolium repens L. were grown in a N-free medium and inoculated with one of ten Rhizobium strains. Dry matter, N content, and δ 15N values were determined for various plant parts. Nodules, with the exception of those from lucerne, were enriched in 15N relative to atmospheric N. Considerable variation was found in δ15N values of plant herbage (−4.5 to +0.8). The extent of isotopic discrimination was dependent on both the host plant and the infecting rhizobial strain. This further complicates, but does not invalidate, the use of small variations in the natural abundance of 15N to estimate the contribution of symbiotically fixed N2 to the N in legume herbage. Some other implications of the observed differences are also discussed. 相似文献
8.
Two plant species, Medicago truncatula (legume) and Avena sativa (non-legume), were grown in low-or high-N soils under two CO 2 concentrations to test the hypothesis whether C allocation within plant-soil system is interactively or additively controlled
by soil N and atmospheric CO 2 is dependent upon plant species. The results showed the interaction between plant species and soil N had a significant impact
on microbial activity and plant growth. The interaction between CO 2 and soil N had a significant impact on soil soluble C and soil microbial biomass C under Madicago but not under Avena. Although both CO 2 and soil N affected plant growth significantly, there was no interaction between CO 2 and soil N on plant growth. In other words, the effects of CO 2 and soil N on plant growth were additive. We considered that the interaction between N 2 fixation trait of legume plant and elevated CO 2 might have obscured the interaction between soil N and elevated CO 2 on the growth of legume plant. In low-N soil, the shoot-to-root ratio of Avena dropped from 2.63±0.20 in the early growth stage to 1.47±0.03 in the late growth stage, indicating that Avena plant allocated more energy to roots to optimize nutrient uptake (i.e. N) when soil N was limiting. In high-N soil, the shoot-to-root
ratio of Medicago increased significantly over time (from 2.45±0.30 to 5.43±0.10), suggesting that Medicago plants allocated more energy to shoots to optimize photosynthesis when N was not limiting. The shoot-to-root ratios were
not significantly different between two CO 2 levels. 相似文献
9.
Two plant species, Medicago truncatula (legume) and Avena sativa (non-legume), were grown in low-or high-N soils under two CO 2 concentrations to test the hypothesis whether C allocation within plant-soil system is interactively or additively controlled
by soil N and atmospheric CO 2 is dependent upon plant species. The results showed the interaction between plant species and soil N had a significant impact
on microbial activity and plant growth. The interaction between CO 2 and soil N had a significant impact on soil soluble C and soil microbial biomass C under Madicago but not under Avena. Although both CO 2 and soil N affected plant growth significantly, there was no interaction between CO 2 and soil N on plant growth. In other words, the effects of CO 2 and soil N on plant growth were additive. We considered that the interaction between N 2 fixation trait of legume plant and elevated CO 2 might have obscured the interaction between soil N and elevated CO 2 on the growth of legume plant. In low-N soil, the shoot-to-root ratio of Avena dropped from 2.63±0.20 in the early growth stage to 1.47±0.03 in the late growth stage, indicating that Avena plant allocated more energy to roots to optimize nutrient uptake (i.e. N) when soil N was limiting. In high-N soil, the shoot-to-root
ratio of Medicago increased significantly over time (from 2.45±0.30 to 5.43±0.10), suggesting that Medicago plants allocated more energy to shoots to optimize photosynthesis when N was not limiting. The shoot-to-root ratios were
not significantly different between two CO 2 levels. 相似文献
10.
E3 ubiquitin ligases determine the substrate specificity of ubiquitination. Plant U-box (PUB) E3 ligases, with a typical 70-amino acid U-box domain, participate in plant developmental processes and environmental responses. Thus far, 64 PUB proteins have been identified in Arabidopsis and 77 PUB proteins have been identified in Oryza. However, detailed studies on U-box genes in the model microalgae Chlamydomonas reinhardtii are lacking. Here, we present a comprehensive analysis of the genes encoding U-box family proteins in C. reinhardtii. Following BLASTP analysis, 30 full-length U-box genes were identified in the C. reinhardtii genome sequence. Bioinformatics analyses of CrPUB genes were performed to characterize the phylogenetic relationships, chromosomal locations and gene structures of each member. The 30 identified CrPUB proteins are clustered into 3 distinct subfamilies, and the genes for these proteins are unevenly distributed among 14 chromosomes. Furthermore, the quantitative real-time RT-PCR or semi-quantitative RT-PCR analysis of 30 CrPUB mRNA abundances under nitrogen starvation showed that 18 CrPUB genes were induced by N starvation and that 7 genes were repressed in the N-poor environment. We selected five CrPUB genes exhibiting marked changes in expression under N-free conditions for further analysis in RNAi experiments and examined the oil content of these gene-silenced transgenic strains. The silencing of CrPUB5 and CrPUB14, which are typically down-regulated under N starvation, induced 9.8%-45.0% and 14.4%-61.8% lipid accumulation, respectively. In contrast, the silencing of CrPUB11, CrPUB23 and CrPUB28, which are markedly up-regulated under N-free conditions, decreased the lipid content by 5.5%-27.8%, 8.1%-27.3% and 6.6%-27.9%, respectively. These results provide a useful reference for the identification and functional analysis of this gene family and fundamental information for microalgae lipid metabolism research. 相似文献
11.
Five salinity tolerant Azotobacter strains i.e., ST3, ST6, ST9, ST17 and ST24 were obtained from saline soils. These Azotobacter strains were used as inoculant for wheat variety WH157 in earthen pots containing saline soil under pot house conditions, using three fertilizer treatment doses i.e., control (no fertilizer, no inoculation), 90 Kg N ha −1 and 120 Kg N ha −1. Inoculation with salinity tolerant Azotobacter strains caused significant increase in total nitrogen, biomass and grain yield of wheat. Maximum increase in plant growth parameters were obtained after inoculation with Azotobacter strain ST24 at fertilization dose of 120 kg N ha −1 and its inoculation resulted in attaining 89.9 cms plant height, 6.1 g seed yield, 12.0 g shoot dry weight and 0.7 % total nitrogen. The survival of Azotobacter strain ST24 in the soil was also highest in all the treatments at 30, 60 and 90 days after sowing (DAS). However, the population of Azotobacter decreased on 90 DAS as compared to counts observed at 60 DAS at all the fertilization treatments. 相似文献
12.
Controlled environment and field studies were conducted to determine relationships between various measurements of N 2 fixation using soybeans and to use these measures to evaluate a number of Bradyrhizobium japonicum strains for effectiveness in N 2 fixation in Thai soils. 15N dilution measurements of N 2 fixation showed levels of fixation ranging from 32 to 161 kg N ha −1 depending on bacterial strain, host cultivar and location. Midseason measures of N 2 fixation were correlated with each other, but not related measures taken at maturity. Ranking of B. japonicum strains based on performance under controlled conditions in N-free media were highly correlated with rankings based on soybean
seed yields and N 2 fixation under field conditions. This study showed that inoculation of soybeans with effective B. japonicum strains can result in significant increases in yield and uptake of N through fixation. The most effective strains tested
for use in Thai conditions were those isolated from Thai soils; however, effective strains from other locations were also
of benefit. 相似文献
13.
Translocation of carbon and nitrogen within a single source-sink unit, comprising a trifoliated leaf, the axillary pod and the subtending internode, and from this unit to the rest of the plant was examined in soybean ( Glycine max L. cv. Akishirome) plant by feeding 13CO 2 and 15NO 3. The plants were grown at two levels of nitrogen in the basal medium, i.e. low-N (2 g N m –2) and high-N (35 g N m –2) and a treatment of depodding was imposed by removing all the pods from the plant, except the pod of the source sink unit, 13 days after flowering. The plants at high-N accumulated more biomass in its organs compared to low-N and pod removal increased the weight of the vegetative organs. When the terminal leaflet of the source-sink unit was fed with 13CO 2, almost all of the radioactive materials were retained inside the source-sink unit and translocation to rest of the plants was insignificant under any of the treatments imposed. Out of the 13C exported by the terminal leaflet, less than half went into the axillary pod, as the lateral leaflets claimed equal share and very little material was deposited in the petiole. Pod removal decreased 13C export at high-N , but not at low-N. Similar to 13C, the source-sink unit retained all the 15N fed to the terminal leaflet at high-N. At low-N, the major part of 15N partitioning occurred in favour of the rest of the plant outside the source-sink unit, but removal of the competitve sinks from the rest of the plants nullified any partitioning outside the unit. Unlike the situation in 13C, no partitioning of 15N occurred in favour of the lateral leaflets from the terminal leaflet inside the unit. It is concluded that sink demand influences partitioning of both C and N and the translocation of carbon is different from that of nitrogen within a source-sink unit. The translocation of the N is more adjustive to a demand from other sink units compared to the C. 相似文献
14.
Phosphorus is one of several factors which affect N 2 fixation and along with N, is a principal yield-limiting nutrient in many regions of the world. Since the legume plant is an essential partner in symbiotic N 2 fixation, knowledge of host genotype variability for this process at different levels of P availability will be useful when breeding bean cultivars for enhanced N 2 fixation. The objective of this study was to obtain common bean ( Phaseolus vulgaris L.) lines able with enhanced ability to support biological N 2 fixation under different levels of available phosphorus.Experiments were conducted in a growth room using a sand-alumina system to provide different levels of available P and in the field on a low-N soil. In the growth room studies, P availability strongly affected plant growth and traits related to N 2 fixation. No significant interaction was detected for P levels × bean lines, indicating that bean lines performed similarly at both high and low P levels.Total shoot N was used as a direct and indirect measure of N 2-fixation potential under growth room (N-free media) and field (low-N soil) conditions, respectively. Based on this criterion, two of the 41 and 54 inbred backcross lines of a segregating population evaluated in the growth room and the field, respectively, contained greater shoot N content than the recurrent parent and N shoot contents similar to the donor parent. Variability of N 2 fixation under low available P was observed, and high N 2 fixing and high yielding progeny lines were detected. 相似文献
15.
Effects of nitrogen (N)-deficiency on midday photoinhibition in flag leaves were compared between two contrastive Japanese
rice cultivars, a traditional japonica cultivar with low yield, cv. Shirobeniya (SRB), and a japonica-indica intermediate type with high yield, cv. Akenohoshi (AKN). Both cultivars were grown under high-N and low-N conditions. At
midday, low-N supply resulted in more intensive reductions in net photosynthetic rate, stomatal conductance, maximal quantum
yield of photosystem II (PSII) and quantum yield of PSII electron transport in SRB than in AKN, indicating that SRB was more
strongly photoinhibited than AKN under low-N condition. At midday, the low-N plants of two cultivars showed higher superoxide
dismutase (SOD) activities than the high-N plants. However, ascorbate peroxidase (APX) activity was maintained in AKN but
significantly decreased in SRB under low-N condition (N-deficiency). In contrast, hydrogen peroxide (H 2O 2) content in SRB significantly increased under low-N condition, indicating that the susceptibility to midday photoinhibition
in the low-N plants of SRB is related to the increased H 2O 2 accumulation. It is suggested that the midday depression in photosynthesis may be a result of oxidative stress occurring
in the low-N plants in which antioxidant capacity is not enough to cope with the generation of H 2O 2. Therefore, H 2O 2-scavenging capacity could be an important factor in determining the cultivar difference of midday photoinhibition in flag
leaves of rice under low-N condition. 相似文献
16.
Background and AimsThe major objective was to identify plant traits functionally important for optimization of shoot growth and nitrogen (N) economy under drought. Although increased leaf N content (area basis) has been observed in dry environments and theory predicts increased leaf N to be an acclimation to drought, experimental evidence for the prediction is rare. MethodsA pedigree of 200 full-sibling hybrid willows was pot-grown in a glasshouse in three replicate blocks and exposed to two water regimes for 3 weeks. Drought conditions were simulated as repeated periods of water shortage. The total leaf mass and area, leaf area efficiency (shoot growth per unit leaf area, EA), area-based leaf N content ( NA), total leaf N pool ( NL) and leaf N efficiency (shoot growth per unit leaf N, EN) were assessed. Key ResultsIn the water-stress treatment, shoot biomass growth was N limited in the genotypes with low NL, but increasingly limited by other factors in the genotypes with greatest NL. The NA was increased by drought, and drought-induced shift in NA varied between genotypes (significant G × E). Judged from the EA– NA relationship, optimal NA was 16 % higher in the water-stress compared with the well-watered treatment. Biomass allocation to leaves and shoots varied between treatments, but the treatment response of the leaf : shoot ratio was similar across all genotypes. ConclusionsIt is concluded that N-uptake efficiency and leaf N efficiency are important traits to improve growth under drought. Increased leaf N content (area basis) is an acclimation to optimize N economy under drought. The leaf N content is an interesting trait for breeding of willow bioenergy crops in a climate change future. In contrast, leaf biomass allocation is a less interesting breeding target to improve yield under drought. 相似文献
17.
Regeneration capacity of submerged rice ( Oryza sativa) seedlings in terms of CO 2 photosynthetic rate, chlorophyll a fluorescence and chlorophyll and carbohydrate content were investigated in three Indica rice cultivars namely FR 13A, Kalaputia and IR 42 that differed in submergence tolerance. Twenty-one day old plants were completely submerged under water for 8 days. Subsequently, plants were kept under normal conditions with 5–10 cm of stagnant water above soil surface for a further period of 15 days. After complete submergence, all genotypes showed inhibition of CO 2 photosynthetic rate. Submergence treatment resulted in a significant reduction of Rubisco activity. Maximal photochemical efficiency ( Fv/ Fm) of PS II and area above the fluorescence curve between Fo and Fm decreased more under submergence especially in susceptible cultivar IR 42. When re-aerated, the plants recovered to various degrees. The carbohydrate content of plants was found to be significantly and positively associated with submergence tolerance and regeneration growth. The tolerant cultivar (FR 13A) could survive submergence apparently because it possessed 1.9–2.0 and 3.2–3.7-fold more non-structural carbohydrate content before and after submergence compared to the susceptible cultivar (IR 42) and it had a better capability to restore its photosynthetic capacity during post-submergence periods. 相似文献
18.
Three newly selected strains of Cyclopia rhizobia together with an inoculant strain, which has never been tested in the field with adequate experimental design, was assessed under both nursery and field conditions for symbiotic performance. The three new test strains were initially selected for their superior N 2-fbcing abilities under glasshouse conditions, and then evaluated in this study for field performance. Cyclopia subternata Vogel and Cyclopia genistoides (L.) R. Br., which have the potential for producing high quality honeybushtea, were used as host plants in both the nursery and field studies. The effect of seedling inoculation at the nursery level was also examined for the four test strains under nursery conditions. The inoculation of cuttings under nursery conditions produced.significant increases in shoot biomass, shoot %N and shoot N content. More specifically, inoculating C. subternata with strains UCT44b and UCT61a significantly increased shoot biomass and N content relative to strain PPRICI3. Strains UCT44b and UCT61a also showed better nodulation with C. subternata cuttings compared to strains UCT40a and PPRICI3. Field inoculation of Cyclopia increased all growth parameters relative to the uninoculated control, except for leaf %N. Cyclopia subternata inoculated with strains UCT44b, UCT40a and UCT61a produced significantly lower δ 15N values than the uninoculated C. subtemata reference plant. Using the 15N natural abundance method, C. subternata was estimated to be gaining about half of its N from N 2 fixation, while C. genistoides obtained less than half of its N from symbiotic nutrition. 相似文献
19.
Summary Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO 2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO 2 partial pressures of 350 and 650 bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO 2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO 2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO 2 enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO 2. In seedlings supplied with soil N, elevated CO 2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf 15N). While CO 2 enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO 2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO 2 will depend greatly on plant and soil nutrient status. 相似文献
20.
Background and aims Extensive worldwide dryland degradation calls for identification of functional traits critical to dryland plant performance and restoration outcomes. Most trait examination has focused on drought tolerance, although most dryland systems are water and nutrient co-limited. We studied how drought impacts both plant water relations and nitrogen (N) nutrition. Methods We grew a suite of grasses common to the Intermountain West under both well-watered and drought conditions in the greenhouse. These grasses represented three congener pairs ( Agropyron, Elymus, Festuca) differing in their habitat of origin (“wetter” or “drier”). We measured growth, water relations, N resorption efficiency and proficiency and photosynthetic N use efficiency in response to drought. Results Drought decreased growth and physiological function in the suite of grasses studied, including a negative impact on plant N resorption efficiency and proficiency. This effect on resorption increased over the course of the growing season. Evolutionary history constrained species responses to treatment, with genera varying in the magnitude of their response to drought conditions. Surprisingly, habitat of origin influenced few trait responses. Conclusions Drought impacted plant N conservation, although these responses also were constrained by evolutionary history. Future plant development programs should consider drought tolerance not only from the perspective of water relations but also plant mineral nutrition, taking into account the role of phylogeny. 相似文献
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