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1.
Crop performance, nitrogen and water use in flooded and aerobic rice 总被引:11,自引:0,他引:11
P. Belder B. A. M. Bouman J. H. J. Spiertz S. Peng A. R. Castañeda R. M. Visperas 《Plant and Soil》2005,273(1-2):167-182
Irrigated aerobic rice is a new system being developed for lowland areas with water shortage and for favorable upland areas with access to supplementary irrigation. It entails the cultivation of nutrient-responsive cultivars in nonsaturated soil with sufficient external inputs to reach yields of 70–80% of high-input flooded rice. To obtain insights into crop performance, water use, and N use of aerobic rice, a field experiment was conducted in the dry seasons of 2002 and 2003 in the Philippines. Cultivar Apo was grown under flooded and aerobic conditions at 0 and at 150 kg fertilizer N ha–1. The aerobic fields were flush irrigated when the soil water potential at 15-cm depth reached –30 kPa. A 15N isotope study was carried out in microplots within the 150-N plots to determine the fate of applied N. The yield under aerobic conditions with 150 kg N ha–1 was 6.3 t ha–1 in 2002 and 4.2 t ha–1 in 2003, and the irrigation water input was 778 mm in 2002 and 826 mm in 2003. Compared with flooded conditions, the yield was 15 and 39% lower, and the irrigation water use 36 and 41% lower in aerobic plots in 2002 and 2003, respectively. N content at 150 kg N ha–1 in leaves and total plant was nearly the same for aerobic and flooded conditions, indicating that crop growth under aerobic conditions was limited by water deficit and not by N deficit. Under aerobic conditions, average fertilizer N recovery was 22% in both the main field and the microplot, whereas under flooded conditions, it was 49% in the main field and 36% in the microplot. Under both flooded and aerobic conditions, the fraction of 15N that was determined in the soil after the growing season was 23%. Since nitrate contents in leachate water were negligible, we hypothesized that the N unaccounted for were gaseous losses. The N unaccounted for was higher under aerobic conditions than under flooded conditions. For aerobic rice, trials are suggested for optimizing dose and timing of N fertilizer. Also further improvements in water regime should be made to reduce crop water stress. 相似文献
2.
P. J. Goodman 《Plant and Soil》1988,112(2):247-254
The stable isotope15N is particularly valuable in the field for measuring N fixation by isotope dilution. At the same time other soil-plant processes can be studied, including15N recovery, and nitrogen transfer between clover and grass. Three contrasting sites and soils were used in the present work: a lowland soil, an upland soil, and an upland peat. Nitrogen fixation varied from 12 gm–2 on lowland soil to 2.7 gm–2 on upland peat. Most N transfer occurred on upland soil (4.2 gm–2) which, added to nitrogen fixed, made a total of 8.7 gm2 input during summer 1985.15N recovery for the whole experiment was small, around 25%.Measurement of dead and dying leaves, stubble and roots, suggests that plant organ death is the first stage in N transfer from white clover to ryegrass, through the decomposer cycle. Decomposition was fastest on lowland soils, slowest on peat. On lowland soil this decomposer nitrogen is apparently subverted before transfer, probably by soil microbes.Variations in natural abundance of15N in plants were found in the two species on the different soils. These might be used to measure nitrogen fixation without adding isotope, but the need for many replicates and repeat samples would limit throughput. 相似文献
3.
15N abundance of surface soils,roots and mycorrhizas in profiles of European forest soils 总被引:6,自引:0,他引:6
Peter Högberg Lars Högbom Helga Schinkel Mona Högberg Christian Johannisson Håkan Wallmark 《Oecologia》1996,108(2):207-214
15N natural abundances of soil total N, roots and mycorrhizas were studied in surface soil profiles in coniferous and broadleaved forests along a transect from central to northern Europe. Under conditions of N limitation in Sweden, there was an increase in 15N of soil total N of up to 9% from the uppermost horizon of the organic mor layer down to the upper 0–5 cm of the mineral soil. The 15N of roots was only slightly lower than that of soil total N in the upper organic horizon, but further down roots were up to 5% depleted under such conditions. In experimentally N-enriched forest in Sweden, i.e. in plots which have received an average of c. 100 kg N ha–1 year–1 for 20 years and which retain less than 50% of this added N in the stand and the soil down to 20 cm depth, and in some forests in central Europe, the increase in 15N with depth in soil total N was smaller. An increase in 15N of the surface soil was even observed on experimentally N-enriched plots, although other data suggest that the N fertilizer added was depleted in15N. In such cases roots could be enriched in15N relative to soil total N, suggesting that labelling of the surface soil is via the pathway: — available pools of N-plant N-litter N. Under N-limiting conditions roots of different species sampled from the same soil horizon showed similar 15N. By contrast, in experimentally N-enriched forest 15N of roots increased in the sequence: ericaceous dwarf shrubs15N enriched compounds in fungal material, which could contribute to explain the observed 15N profiles if fungal material is enriched, because it is a precursor of stable organic matter and recalcitrant N. This could act in addition to the previous explanation of the isotopically lighter soil surface in forests: plant uptake of 15N-depleted N and its redeposition onto the soil surface by litter-fall. 相似文献
4.
Crop and tree roots are crucial in the nutrient recycling hypotheses related to alley cropping systems. At the same time, they are the least understood components of these systems. The biomass, total N content and urea-derived N content of the Senna and maize roots in a Senna-maize alley cropping system were followed for a period of 1.5 years (1 maize-cowpea rotation followed by 1 maize season) to a depth of 90 cm, after the application of 15N labeled urea. The highest maize root biomass was found in the 0–10 cm layer and this biomass peaked at 38 and 67 days after planting the 1994 maize (DAP) between the maize rows (112 kg ha–1, on average) and at 38, 67 and 107 DAP under the maize plants (4101 kg ha–1, on average). Almost no maize roots were found below 60 cm at any sampling date. Senna root biomass decreased with time in all soil layers (from 512 to 68 kg ha–1 for the 0–10 cm layer between 0 and 480 DAP). Below 10 cm, at least 62% of the total root biomass consisted of Senna roots and this value increased to 87% between 60 and 90 cm. Although these observations support the existence of a Senna root `safety net' between the alleys which could reduce nutrient leaching losses, the depth of such a net may be limited as the root biomass of the Senna trees in the 60–90 cm layer was below 100 kg ha–1, equivalent to a root length density of only < 0.05 cm cm–3. The proportion of maize root N derived from the applied urea (%Ndfu) decreased significantly with time (from 21% at 21 DAP to 8% at 107 DAP), while %Ndfu of the maize roots at the second harvest (480 DAP) was only 0.6%. The %Ndfu of the Senna roots never exceeded 4% at any depth or sampling time, but decreased less rapidly compared to the %Ndfu of the maize roots. The higher %Ndfu of the maize roots indicates that maize is more efficient in retrieving urea-derived N. The differences in dynamics of the %Ndfu also indicate that the turnover of N through the maize roots is much faster than the turnover of N through the Senna roots. The recovery of applied urea-N by the maize roots was highest in the top 0–10 cm of soil and never exceeded 0.4% (at 38 DAP) between the rows and 7.1% (at 67 DAP) under the rows. Total urea N recovery by the maize roots increased from 1.8 to 3.2% during the 1994 maize season, while the Senna roots never recovered more than 0.8% of the applied urea-N at any time during the experimental period. These values are low and signify that the roots of both plants will only marginally affect the total recovery of the applied urea-N. Measurement of the dynamics of the biomass and N content of the maize and Senna roots helps to explain the observed recovery of applied urea-N in the aboveground compartments of the alley cropping system. 相似文献
5.
Recruitment preferences of blue mussel spat (Mytilus edulis) for different substrata and microhabitats in the White Sea (Russia) 总被引:3,自引:0,他引:3
We adapted the chloroform fumigation method to determine microbial nitrogen (N) and microbial incorporation of 15N on three common substrates [leaves, wood and fine benthic organic matter (FBOM)] in three forest streams. We compared microbial N and 15N content of samples collected during a 6-week 15N–NH4 tracer addition in each stream. The 15N was added during late autumn to Upper Ball Creek, a second-order stream at the Coweeta Hydrologic Lab, North Carolina, U.S.A.; during spring to Walker Branch, a first-order stream on DOE's Oak Ridge National Environmental Research Park, Tennessee; and during summer to Bear Brook, a first-order stream in the Hubbard Brook Experimental Forest, New Hampshire. FBOM was the largest component of organic matter and N standing stock in all streams. Microbial N represented the highest proportion of total N in leaves and least in FBOM in Walker Branch and Bear Brook. In Upper Ball Creek, the proportion of microbial N was higher in FBOM than in used biofilm or on leaves. Standing stock of microbial N on leaves and in FBOM ranged from 37 mg N m–2 in Bear Brook to 301 mg N m–2 in Walker Branch. Percent of detrital N in living microbial cells was directly related to total microbial biomass (fungal and bacterial biomass) determined from microscopic counts. 15N values for microbes were generally higher than for bulk detritus, which would result in higher 15N values for animals preferentially consuming or assimilating microbial cells. The proportion of 15N taken up by detritus during the 15N experiments that remained in microbial cells by the end of the experiments was highest for wood biofilm in Upper Ball Creek (69%), leaves in Walker Branch (65%) and FBOM in Upper Ball Creek (31%). Lower retention proportions (<1–25%) were observed for other substrates. Our results suggest that microbial cells associated with leaves and wood biofilm were most active in 15N–NH4 immobilization, whereas microbial cells associated with FBOM immobilized little 15N from stream water. 相似文献
6.
Microplot field experiments with 15N-labeled (NH4)2SO4 were conducted to investigate the changes in the percentage of fertilizer 15N recovery (%FNR) of transplanted rice (Oryza sativa L.) with basal (4 g m–2) and topdress (3 g m–2) applications for two years. In 1999, %FNR from the basal 15N application decreased by 6% (0.23 g N m–2)from heading + 2 d to maturity, and %FNR from the topdress 15N application decreased by 11% (0.32 g N m–2)from heading – 4 d to maturity. In 2000, %FNR from the topdress 15N application decreased by 9% (0.26 g N m–2) from heading – 1 d to maturity, whereas there was no significant decline in %FNR from the basal 15N application after heading. A decrease in %FNR occurred even when total N of rice plants showed no decrease after heading. Nitrogen harvest index of fertilizer 15N with the topdress 15N application was not significantly different from that with the basal 15N application in 1999, whereas N harvest index of fertilizer 15N with the topdress 15N application was higher than that with the basal 15N application in 2000. N harvest index of fertilizer 15N, that indicated the proportion of the 15N remobilized to panicles after heading, was substantially responsible for changes in %FNR from the basal and topdress 15N applications after heading. 相似文献
7.
S. Nussbaum P. von Ballmoos H. Gfeller U. P. Schlunegger J. Fuhrer D. Rhodes C. Brunold 《Oecologia》1993,94(3):408-414
During spring and autumn 1991, potted 6-yearold spruce trees (Picea abies (L.) Karst.) were fumigated with 60 nl·1–1
15NO2 for 4 days under controlled conditions in constant light. Current and previous flush needles, the bark and the fine roots were analysed for total 15N content and incorporation of 15N into the -amino nitrogen of free amino acids. In addition, in vitro nitrate reductase activity and stomatal conductance of the needles were measured. Nitrate reductase activity was significantly higher in the needles of fumigated trees compared to control trees exposed to filtered air. With an average of 9.1% 15N, free glutamate was the pool with the most label. Taking into account the time-course of the labelling of this pool, this figure can be taken as an estimate of the minimum contribution of NO2 to the N nutrition of the needles. 15N-labelled amino acids were also detected in the bark and the roots, indicating export from the needles. 相似文献
8.
The fate of 15N-labelled ammonium fertilizer applied once to six-year-old field-grown kiwifruit (Actinidia deliciosa Hayward) vines was measured over three years. The three main treatments were nitrogen (N) applied singularly at 100 or 200 kg N ha–1 in early spring (two weeks before bud burst) or split with 100 kg N ha–1 (unlabelled) in early spring and 100 kg N ha–1 (15N-labelled) ten weeks later. All N treatments were applied to vines with a history of either 50 or 200 kg N ha–1 yr–1. For three years after 15n application, components of the vines and soil (0–600 mm depth) were sampled at harvest in late autumn and the N and 15N contents determined.By the first harvest, all plant uptake of 15N had occurred and this represented 48–53% of the 15N applied. There was no significant effect of current N fertilizer treatment or of N history on 15N recovery by vines. Removal of 15N in harvested fruit was small at 5–6% in the first year and 8% over 3 years. After 2–3 years, most plant 15N occurred in the roots and this component declined only slowly over time. In contrast, there was a large temporal decline in 15N in above-ground plant components due to the annual removal in leaf fall and pruning. An associated experiment showed that when 15N-labelled prunings and leaves were mulched and returned to the soil, only about 9% was recovered by plants within 2 years. Almost all remaining mulched material had been immobilised into the soil organic N.In all treatments, about 20% of the added 15N remained in soil at the first harvest. This was almost entirely in organic fractions (<0.4% in inorganic N) and mostly in the surface 150-mm layer. The 15N content in soil changed little over time (from 20 to 17% between the first and third harvests respectively) and indicated that most of the N had been immobilised into stable humus forms. 相似文献
9.
The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus 总被引:9,自引:0,他引:9
In short-term water culture experiments with different 15N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH4
+ at a higher rate than NO3
–. Maximum NO3
– uptake by the whole plant occurred at 120 mg L–1 NO3
–-N, whereas NH4
+ absorption was saturated at 240 mg L–1 NH4
+-N. 15NH4
+ accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO3
– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH4
+ (15–60 mg L–1 N) to nutrient solutions containing 120 mg L–1 N as 15N labeled nitrate reduced 15NO3
– uptake. Maximum inhibition of 15NO3
– uptake was about 55% at 2.14 mM NH4
+ (30 mg L–1 NH4
+-N) and it did not increase any further at higher NH4
+ proportions.In a long-term experiment, the effects of concentration and source of added N (NO3
– or NH4
+) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH4
+ versus NO3
– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO3
–-N:NH4
+-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO3
– or NH4
+ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO3
–-N/NH4
+-N ratio. With increasing proportions of NH4
+ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH4
+, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO3
–-N:NH4
+-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH4
+ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO3
–:NH4
+ ratio. 相似文献
10.
We compared symbiotic N2 fixation by winter forage legumes (clovers, medics and vetches) using the 15N natural abundance technique in three experiments. Vetches (Vicia spp.) were the most productive legumes, and woollypod vetch fixed (shoot+root) up to 265 kg N ha–1 (mean 227 kg N ha–1) during a 4–5 months period over winter and early spring. Balansa and Berseem clovers, and Gama medic were highly productive in the first experiment, but fixed significantly less N than woollypod vetch in the second experiment. A 6-year study (1997–2003) compared cotton (Gossypium hirsutum L.) systems with and without vetch, or with faba beans (Vicia faba L.) to assess the effects of these crops on cotton production. Woollypod vetch was grown either between annual cotton crops, or between wheat (Triticum aestivumL.) and cotton crops. Vetch added 230 kg N ha–1 (174 kg fixed N ha–1) to the soil when incorporated as a green manure. Faba bean shoot residues and nodulated roots contributed 108 kg fixed N ha–1 to the soil, following the removal of 80 kg N ha–1 in the harvested seed (meaned over three crops). Lablab (Lablab purpureus L. – summer-growing and irrigated) added 277 kg N ha–1 (244 kg fixed N ha–1) before incorporation as a green manure in the first year of the experiment. The economic optimum N fertiliser rate for each cropping system was determined every second year when all systems were sown to cotton. Cotton following cotton required 105 kg fertiliser N ha–1, but only 40 kg N ha–1 when vetch was grown between each cotton crop. Cotton following wheat required 83 kg fertiliser N ha–1 but no N fertiliser was needed when vetch was grown after wheat (the highest yielding system). Cotton following faba beans also required no N fertiliser. The vetch-based systems became more N fertile over the course of the experiment and produced greater lint yields than the comparative non-legume systems, and required less N fertiliser. While no cash flow was derived from growing vetch, economic benefits accrued from enhanced cotton yields, reduced N fertiliser requirements and improved soil fertility. These findings help explain the rotational benefits of vetches observed in other regions of the world. 相似文献
11.
We studied the fate of 15N-labelled fertilizer nitrogen in a sandy loam soil after harvest of winter oilseed rape (Brassica napus L. cv. Ceres) given 100 or 200 kg N ha-1 in spring, with or without irrigation. Our main objective was to quantify the temporal variations of the soil mineral N, the extractable soil organic N and soil microbial biomass N, and fertilizer derived N in these pools during autumn and winter. Nitrogen use efficiency of the oilseed rape crop varied from 47% of applied N in the 100N, irrigated treatment to 34% in the 200N, non-irrigated treatment. However, only in the latter treatment did we find significantly higher fertilizer derived soil mineral N than in the three other treatments which all had low soil mineral N contents at the first sampling after harvest (8 days after stubble tillage). Between 31% and 42% of the applied N could not be accounted for in the harvested plants or 0-15 cm soil layer at this first sampling. Over the following autumn and winter none of the remaining fertilizer derived soil N was lost from the 0–5 cm depth, but from the 5–15 cm depth a marked proportion of N derived from fertilizer was lost, probably by leaching. Negligible amounts of fertilizer derived extractable soil organic and mineral N (<1 kg N ha-1, 0-15 cm) were found in all treatments after the first sampling.Soil microbial biomass N was not significantly affected by treatments and showed only small temporal variability (±11% of the mean 76 kg N ha-1, 0- 15 cm depth). Surprisingly, the average amount of soil microbial biomass N derived from fertilizer was significantly affected by the treatments, with the extremes being 5.5 and 3.1 kg N ha-1 in the 200N, non-irrigated and 100N, irrigated treatments, respectively. Also, the estimated exponential decay rate of microbial biomass N derived from fertilizer, differed greatly (2 fold) between these two treatments, indicating highly different microbial turnover rates in spite of the similar total microbial biomass N values. In studies utilising 15N labelling to estimate turnover rates of different soil organic matter pools this finding is of great importance, because it may question the assumption that turnover rates are not affected by the insertion of the label. 相似文献
12.
The effects of planted fallows of Sesbania sesban (L.) Merr. and Calliandra calothyrsus (Meissner) on soil inorganic nitrogen dynamics and two subsequent maize crops were evaluated under field conditions in the highlands of eastern Kenya. Continuous unfertilised maize, maize/bean rotation and natural regrowth of vegetation (weed fallow) were used as control treatments. The proportion of symbiotic N2-fixation was estimated by measuring both leaf 15N enrichment and whole-plant 15N enrichment by the 15N dilution technique for Sesbania and Calliandra, using Eucalyptus saligna (Sm.) and Grevillea robusta (A. Cunn) as reference species. Above- and below-ground biomass and N contents were examined in Sesbania, Calliandra, Eucalyptus and Grevillea 22 months after planting. Both the content of inorganic N in the topsoil and the quantity of N mineralised during rainy seasons were higher after the Sesbania fallows than after the other treatments. Compared to the continuous unfertilised maize treatment, both residual crop yields were significantly higher when mineral N (one application of 60 kg N ha–1) was added. Furthermore, the second crop following the Sesbania fallow was significantly higher than the continuous maize crop. The above-ground biomass of the trees at final harvest were 31.5, 24.5, 32.5 and 43.5 Mg ha–1 for the Sesbania, Calliandra, Grevillea and Eucalyptus, respectively. For the total below-ground biomass the values for these same tree species were 11.1, 15.5, 17.7, and 19.1 Mg ha–1, respectively, of which coarse roots (>2 mm), including tap roots, amounted to 70–90%. About 70–90% of the N in Sesbania, and 50–70% in Calliandra, was derived from N2-fixation. Estimates based on leaf 15N enrichment and whole-plant 15N enrichment were strongly correlated. The N added by N2-fixation amounted to 280–360 kg N ha–1 for Sesbania and 120–170 kg N ha–1 for Calliandra, resulting in a positive N balance after two maize cropping seasons of 170–250 kg N ha–1 and 90–140 kg N ha–1, for Sesbania and Calliandra, respectively. All the other treatments gave negative N balances after two cropping seasons. We conclude that Sesbania sesban is a tree species well suited for short duration fallows due to its fast growth, high nutrient content, high litter quality and its ability to fix large amounts of N2 from the atmosphere. 相似文献
13.
The contribution of nitrogen by promiscuous soybeans to maize based cropping the moist savanna of Nigeria 总被引:1,自引:0,他引:1
Agronomic results indicate that maize grain yields generally are higher when the crop is planted following soybean than in continuous maize cultivation in the moist savanna agroecological zones of West Africa. Many factors have been hypothesized to explain this phenomenon, including enhanced N availability and the so-called `rotational effect'. There is, however, hardly any quantitative information on the residual N benefits of promiscuous soybeans to subsequent cereal crops grown in rotation with soybean. Three IITA promiscuous soybean breeding lines and two Brazilian soybean lines were grown in 1994 and 1995 at Mokwa in the southern Guinea savanna, Nigeria, to quantify the nitrogen contribution by soybeans to a succeeding crop of maize grown in rotation with soybean for two consecutive years, 1996 and 1997 using two methods of introducing 15N into soil (fresh 15N labelling and its residual 15N) and three maize cultivars (including one cultivar with high N use efficiency) used as reference plants. The nodulating soybeans fixed between 44 and 103 kg N ha–1 of their total N and had an estimated net N balance input from fixation following grain harvest ranging from –8 to 43 kg N ha–1. Results in 1996 and in 1997 showed that maize growing after soybean had significantly higher grain yield (1.2 – 2.3-fold increase compared to maize control) except for maize cultivar Oba super 2 (8644-27) (a N-efficient hybrid). The 15N isotope dilution method was able to estimate N contribution by promiscuous soybeans to maize only in the first succeeding maize crop grown in 1996 but not in the second maize crop in 1997. The first crop of maize grown after soybean accumulated an average between 10 and 22 kg N ha–1 from soybean residue, representing 17–33% of the soybean total N ha–1. The percentage 15N derived from residue recovery in maize grown after maize was influenced by the maize cultivars. Maize crop grown after the N-efficient hybrid cultivar Oba Super 2 (844-27) had similar 15N values similar to maize grown after soybeans, confirming the ability of this cultivar to use N efficiently in low N soil due to an efficient N translocation ability. The maize crop in 1997 grown after maize had lower 15N enrichment than that grown in soybean plots, suggesting that soybean residues contributed a little to soil available N and to crop N uptake by the second maize crop. The differential mineralization and immobilization turnover of maize and soybean residues in these soils may be important and N contribution estimates in longer term rotation involving legumes and cereals may be difficult to quantify using the 15N labelling approaches. Therefore alternative methods are required to measure N release from organic residues in these cropping systems. 相似文献
14.
A pot experiment was conducted in a greenhouse using the 15N isotope dilution method and two reference plants, Parkia biglobosa and Tamarindus indica to estimate nitrogen fixed in four Acacia species: A raddiana, A. senegal, A. seyal and Faidherbia albida (synonym Acacia albida). For the reference plants, the 15N enrichments in leaves, stems and roots were similar. With the fixing plants, leaves and stems had similar 15N enrichments; they were higher than the 15N enrichment of roots. The amounts of nitrogen fixed at 5 months after planting were similar using either reference plant. Estimates of the percentage of N derived from fixation (%Ndfa) for the above ground parts, in contrast to %Ndfa in roots, were similar to those for the whole plant. However, none of the individual plant parts estimated accurately total N fixed in the whole plant, and excluding the roots resulted in at least 30% underestimation of the amounts of N fixed. Between species, differences in N2 fixation were observed, both for %Ndfa and total N fixed. For %Ndfa, the best were A. seyal (average, 63%) and A. raddiana (average, 62%), being at least twice the %Ndfa in A. senegal and F. albida. Because of its very high N content, A. seyal was clearly the best in total N fixed, fixing 1.62 g N plant–1 compared to an average of 0.48 g N plant–1 for the other Acacia species. Our results show the wide variability existing between Acacia species in terms of both %Ndfa and total N fixed: A. seyal was classified as having a high N2 fixing potential (NFP) while the other Acacia species had a low NFP. 相似文献
15.
Anthropogenic N deposition and the fate of 15NO
3
−
in a northern hardwood ecosystem 总被引:5,自引:1,他引:4
Donald R. Zak Kurt S. Pregitzer William E. Holmes Andrew J. Burton Gregory P. Zogg 《Biogeochemistry》2004,69(2):143-157
Human activity has substantially increased atmospheric NO
3
–
deposition in many regions of the Earth, which could lead to the N saturation of terrestrial ecosystems. Sugar maple (Acer saccharum Marsh.) dominated northern hardwood forests in the Upper Great Lakes region may be particularly sensitive to chronic NO
3
–
deposition, because relatively moderate experimental increases (three times ambient) have resulted in substantial N leaching over a relatively short duration (5–7 years). Although microbial immobilization is an initial sink (i.e., within 1–2 days) for anthropogenic NO
3
–
in this ecosystem, we have an incomplete understanding of the processes controlling the longer-term (i.e., after 1 year) retention and flow of anthropogenic N. Our objectives were to determine: (i) whether chronic NO
3
–
additions have altered the N content of major ecosystem pools, and (ii) the longer-term fate of 15NO
3
–
in plots receiving chronic NO
3
–
addition. We addressed these objectives using a field experiment in which three northern hardwood plots receive ambient atmospheric N deposition (ca. 0.9 g N m–2 year–1) and three plots which receive ambient plus experimental N deposition (3.0 g NO3
–-N m–2 year–1). Chronic NO
3
–
deposition significantly increased the N concentration and content (g N/m2) of canopy leaves, which contained 72% more N than the control treatment. However, chronic NO
3
–
deposition did not significantly alter the biomass, N concentration or N content of any other ecosystem pool. The largest portion of 15N recovered after 1 year occurred in overstory leaves and branches (10%). In contrast, we recovered virtually none of the isotope in soil organic matter (SOM), indicating that SOM was not a sink for anthropogenic NO
3
–
over a 1 year duration. Our results indicate that anthropogenic NO
3
–
initially assimilated by the microbial community is released into soil solution where it is subsequently taken up by overstory trees and allocated to the canopy. Anthropogenic N appears to be incorporated into SOM only after it is returned to the forest floor and soil via leaf litter fall. Short- and long-term isotope tracing studies provided very different results and illustrate the need to understand the physiological processes controlling the flow of anthropogenic N in terrestrial ecosystems and the specific time steps over which they operate. 相似文献
16.
Summary In a split root experiment translocation of N from shoot to root was studied using15NO
3
–
. The three plant species selected for this experiment differed significantly with respect to root NRA. For lupin, maize and cocklebur about 80, 50 and 6% of all absorbed NO
3
–
was assmilated in the roots, respectively.Although NO
3
–
was reduced in the roots of lupin and maize plants to a greater extent than required for the roots' demand for organic N, a significant phloem flow of N from shoot to roots was found in these plants. Unexpectedly, for cocklebur, the plant with the very low root NRA, the fraction of total N present in the root that has been imported from the shoot was only half that as found for lupin and maize. 相似文献
17.
A glasshouse study was made of the distribution of 15N among vegetative organs of sunflower and its later remobilization and redistribution to seeds, as influenced by the developmental
stage at which 15N was provided, and by the N status of the plants. Plants of Hysun 30 sunflower were grown in sand culture and provided with
K15NO3 for a 3-day period at: (a) 3 days before the end of floret initiation; (b) 3 days before anthesis; (c) the start of anthesis;
(d) full anthesis; and (e) 8 days after full anthesis. The plants were grown on a range of N supply rates, from severely deficient
to more than adequate for maximum growth.
Nitrogen-15 was distributed to all parts of the plant at the end of the 15N uptake periods. With the exception of the most N-stressed plants, subsequent remobilization of 15N from roots, stems and leaves occurred irrespective of the time the 15N was taken up. However, the percentage redistribution to seeds of 15N taken up at the end of floret initiation was less than for 15N taken up at anthesis. Remobilization of 15N from leaves and roots was higher (70%) for 15N taken up during and after anthesis than for 15N taken up at the end of floret initiation (45%), except for plants grown on the lowest N supply. By contrast, remobilization
of 15N from the stem was lower for 15N taken up after full anthesis (40%) than before or during anthesis (>70%). The proportion of 15N remobilized from the top third of the stem was less than that from the bottom third, and decreased with increasing plant
N status. Nitrogen-15 taken up over the 3-day supply periods during anthesis contributed from 2 to 11% of the total seed N
at maturity; the contribution to seeds was greatest for plants grown on the highest N supply. Nitrogen taken up just before
and during anthesis contributed most of the N accumulated in mature seeds of plants grown on an adequate N supply, but N taken
up between the end of floret initiation and just before anthesis, or after full anthesis seemed to make an equally important
contribution to mature seeds as N taken up during anthesis for plants grown on a very low N supply.
It was concluded that the development of florets and seeds of sunflower is supported by N taken up by the plant between the
end of floret initiation and anthesis, and by N redistributed from vegetative organs. Unless soil N is so low as to impair
early growth, split applications of N fertilizer would be best made just before the end of floret initiation (‘star stage’)
and just before anthesis. 相似文献
18.
Summary The technique of15N isotope dilution was used to verify that nitrogen was fixed and transferred to the plant byKlebsiella pneumoniae strain Pp in association withPoa pratensis orTriticum aestivum. Surface sterilized, sprouting seeds were inoculated withK. pneumoniae and grown in sand in modified Leonard jars. Potassium nitrate enriched with15N was used to provide N concentrations ranging from 10–40 mg Nl–1 nutrient solution. After 10–18 weeks the shoots and roots were analyzed separately for dry matter, N content, total N, and atom %15N excess. The acetylene reduction technique was used to test for the presence of N2-fixing organisms on the roots. The data from15N isotope dilution demonstrated that up to 33.8% of N in the shoots ofP. pratensis and 15.9% in those ofT. aestivum were derived from associative N2 fixation byK. pneumoniae. In most experiments the dry matter yield, N content, and total N yield of the shoots ofP. pratensis were increased byK. pneumoniae inoculation, whereas inoculation had no significant effect on the dry matter yield, N content or total N of the shoots ofT. aestivum. 相似文献
19.
Solid-state 15N NMR spectroscopy was used to determine the chemical nature of nitrogen in 15N-enriched material from the roots and stems of wheat (Triticum aesitivum), field pea (Pisum sativum) and kikuyu grass (Pennisetum clandestinum) and from the roots, stems and leaves of a eucalyptus species (Eucalyptus globulus). Nitrogen-15 cross polarization (CP) spectra of the materials were all very similar, with 64–75% of total signal assigned
to amide N. Spin counting analysis indicated that 37–80% of potential signal was accounted for in the CP spectra, and that
NMR observability using the CP technique (N
obs
-CP) was higher for stems and leaves than for roots, and higher for wheat and eucalyptus than for peas and kikuyu. The 15N direct polarization (DP) spectra contained higher proportions of signal assigned to amine (up to 22%) and nitrate (up to
17%), and less assigned to amide N (50–72%) than the corresponding CP spectra. Spin counting analysis indicated that 68–93%
of potential signal was accounted for in the DP spectra, confirming the DP technique to be more quantitatively reliable than
CP. 相似文献
20.
Common bean (Phaseolus vulgaris L.) is able to fix 20–60 kg N ha–1 under tropical environments in Brazil, but these amounts are inadequate to meet the N requirement for economically attractive seed yields. When the plant is supplemented with N fertilizer, N2 fixation by Rhizobium can be suppressed even at low rates of N. Using the 15N enriched method, two field experiments were conducted to compare the effect of foliar and soil applications of N-urea on N2 fixation traits and seed yield. All treatments received a similar fertilization including 10 kg N ha–1 at sowing. Increasing rates of N (10, 30 and 50 kg N ha–1) were applied for both methods. Foliar application significantly enhanced nodulation, N2 fixation (acetylene reduction activity) and yield at low N level (10 kg N ha–1). Foliar nitrogen was less suppressive to nodulation, even at higher N levels, than soil N treatments. In the site where established Rhizobium was in low numbers, inoculation contributed substantially to increased N2 fixation traits and yield. Both foliar and soil methods inhibited nodulation at high N rates and did not significantly increase bean yield, when comparing low (10 kg N ha–1) and high (50 kg N ha–1) rates applied after emergence. In both experiments, up to 30 kg N ha–1 of biologically fixed N2 were obtained when low rates of N were applied onto the leaves. 相似文献