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1.
2.
Legume N2 fixation is variable, but nonetheless is a valuable process in world agriculture. There is great potential to increase the contribution by the crop legumes to the world's supply of soil.N. This will be achieved by (i) increasing the area of legumes sown by farmers; (ii) improved management of the crops in order that the major determinants of productivity, e.g. land area, water availability, are converted to harvested product with maximum efficiency; and (iii) genetic modification of the commonly-grown species to ensure high dependence of the legume crop on N2 fixation at all levels of productivity. Currently-used methods for measuring N2 fixation and for assessing heritability and repeatability of N2 fixation in breeding and selection programs are reviewed. Results from research programs to define genetic variation in N2 fixation and to enhance N2 fixation through selection and breeding are presented with particular emphasis on common bean (Phaseolus vulgaris) and soybean (Glycine max). 相似文献
3.
CHRISTIAN M. TOBIAS DANIEL M. HAYDEN PAUL TWIGG GAUTAM SARATH 《Molecular ecology resources》2006,6(1):185-187
Switchgrass is a large, North American, perennial grass that is being evaluated as a potential energy crop. There is a need to assess genetic diversity in stored accessions and in remaining native stands to assist breeding and conservation efforts. Marker development will also be necessary for genetic linkage mapping. Toward this end, 32 switchgrass genic di‐, tri‐ and tetranucleotide repeat microsatellites were identified from expressed sequence tags (ESTs). These microsatellites were used to screen individuals from two different named cultivars. The markers displayed a high level of polymorphism consistent with the tetraploid, allogamous behaviour of the cultivars tested. 相似文献
4.
Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality. 相似文献
5.
S. Usha 《Journal of biomolecular structure & dynamics》2013,31(7):1474-1492
We have analyzed the nonbonded interactions of the structurally similar moieties, adenine and guanine forming complexes with proteins. The results comprise (a) the amino acid–ligand atom preferences, (b) solvent accessibility of ligand atoms before and after complex formation with proteins, and (c) preferred amino acid residue atoms involved in the interactions. We have observed that the amino acid preferences involved in the hydrogen bonding interactions vary for adenine and guanine. The structural variation between the purine atoms is clearly reflected by their burial tendency in the solvent environment. Correlation of the mean amino acid preference values show the variation that exists between adenine and guanine preferences of all the amino acid residues. All our observations provide evidence for the discriminating nature of the proteins in recognizing adenine and guanine. 相似文献
6.
Accurate prediction of the leaching requirements (Lr) of crops and striving to attain them is essential for efficient irrigation
water use. Solute modeling was extended to develop four Lr conceptual models that do not neglect solute reactions in the root-zone,
surface evaporation, and the influence of immobile wetted pore space. The models were based on: (i) the water movement equation
which included an exponential water-uptake function (-e) or the 40-30-20-10 water-uptake function (-4); (ii) the solute movement
equation for a reactive salt of a linear reaction term (the Lrchem-e and Lrchem-4 models); or the employment of output (salinity
of soil solution, EC vs concentration factor, CF) of the SAO comprehensive chemical model (the LrSAO-e and LrSAO-4 models);
and (iii) the inclusion of an effective soil solution volume in the transport equations. The root-zone average relative effective
soil solution volume νeff (L | L50, p) was of sigmoidal response to leaching fraction (L) with two adjustable parameters L50
and p; the root-zone average reduced retention coefficient decreased linearly with L; and salt concentration at soil surface
was related to salt concentration of irrigation water (ECi) by the fraction of irrigation water that evaporated (∈). The resulted
concentration profiles indicated the salt behaved as a conservative one down to a threshold depth (xs) below of which salt
was retained and precipitated. The depth of the conservative-salt front, xs increased with L and the 40-30-20-10 water-uptake
pattern overestimated the xs depth relative to the exponential pattern. Concentration profiles were integrated to compute
the root-zone average salinity, which was converted to crop salt-tolerance threshold (AE). The four conceptual models were
successfully calibrated using experimental AE/ECi vs. Lr data with the input parameter values: ς = 0.27, p = 1.44, L50 = 0.16,
ω = 2, and ∈ = 0 or 0.1 for the exponential or the 40-30-20-10 pattern, respectively; where ς is relative root length parameter
and ω is a weighing parameter. No significant difference existed between the four model correlations at the 0.05 level. The
four models require ECi and AE of the crop as input for Lr prediction. Sensitivity analysis revealed predicted Lr was sensitive
the least to error in ∈. For tolerant and moderately tolerant crops Lr was sensitive the most to ς, and for sensitive crops
to L50 and p. Model verification and validation were discussed. In deriving the present Lr models, no osmotic adjustment was
required and both the exponential and the 40-30-20-10 water uptake patterns were, equivalently, applicable.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
How do elevated CO2 and O3 affect the interception and utilization of radiation by a soybean canopy?
ORLA DERMODY STEPHEN P. LONG†§ KELLY McCONNAUGHAY‡ EVAN H. DeLUCIA †§ 《Global Change Biology》2008,14(3):556-564
Net productivity of vegetation is determined by the product of the efficiencies with which it intercepts light (?i) and converts that intercepted energy into biomass (?c). Elevated carbon dioxide (CO2) increases photosynthesis and leaf area index (LAI) of soybeans and thus may increase ?i and ?c; elevated O3 may have the opposite effect. Knowing if elevated CO2 and O3 differentially affect physiological more than structural components of the ecosystem may reveal how these elements of global change will ultimately alter productivity. The effects of elevated CO2 and O3 on an intact soybean ecosystem were examined with Soybean Free Air Concentration Enrichment (SoyFACE) technology where large field plots (20‐m diameter) were exposed to elevated CO2 (~550 μmol mol?1) and elevated O3 (1.2 × ambient) in a factorial design. Aboveground biomass, LAI and light interception were measured during the growing seasons of 2002, 2003 and 2004 to calculate ?i and ?c. A 15% increase in yield (averaged over 3 years) under elevated CO2 was caused primarily by a 12% stimulation in ?c , as ?i increased by only 3%. Though accelerated canopy senescence under elevated O3 caused a 3% decrease in ?i, the primary effect of O3 on biomass was through an 11% reduction in ?c. When CO2 and O3 were elevated in combination, CO2 partially reduced the negative effects of elevated O3. Knowing that changes in productivity in elevated CO2 and O3 were influenced strongly by the efficiency of conversion of light energy into energy in plant biomass will aid in optimizing soybean yields in the future. Future modeling efforts that rely on ?c for calculating regional and global plant productivity will need to accommodate the effects of global change on this important ecosystem attribute. 相似文献
8.
9.
G. A. Bykova E. B. Belykh V. A. Anuchin 《Archives Of Phytopathology And Plant Protection》2013,46(1):87-90
Studies of glasshouse tomato bacterial diseases agents complex have been conducted in some regions of Russia in 1987–1996. Microbiological analysis of seeds and plants of local and foreign selection made it possible to assess quality of the seed material and phytosanitary condition of tomato plants. It's very important to obtain and to cultivate healthy seed material of high quality. This is one of the main conditions of preventing epiphytoty and obtaining ecologically pure agricultiral products. 相似文献
10.
Summary Amylase, dehydrogenase, arylsulphatase and phosphatases activities were measured in a clay-loam soil amended with seven different
crop residues. All enzyme activities, except phosphomonoesterase, were generally higher in the derived soil samples than in
the original soil. Addition of tobacco and sunflower residues caused an increase on most of the enzyme activities while tomato
residues increased only the amylase and phosphodiesterase activities.
As the enzyme activities were positively correlated to each other, a common source of the enzymes is suggested even though
the coefficients of correlation demonstrate that only a low percentage of the variability can be ascribed to the interactions
among enzyme activities. 相似文献