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941.
An understanding of the effects of salinity and sodicity on soil carbon (C) stocks and fluxes is critical in environmental
management, as the areal extents of salinity and sodicity are predicted to increase. The effects of salinity and sodicity
on the soil microbial biomass (SMB) and soil respiration were assessed over 12weeks under controlled conditions by subjecting
disturbed soil samples from a vegetated soil profile to leaching with one of six salt solutions; a combination of low-salinity
(0.5dSm−1), mid-salinity (10dSm−1), or high-salinity (30dSm−1), with either low-sodicity (sodium adsorption ratio, SAR, 1), or high-sodicity (SAR 30) to give six treatments: control (low-salinity
low-sodicity); low-salinity high-sodicity; mid-salinity low-sodicity; mid-salinity high-sodicity; high-salinity low-sodicity;
and high-salinity high-sodicity. Soil respiration rate was highest (56–80mg CO2-C kg−1 soil) in the low-salinity treatments and lowest (1–5mg CO2-C kg−1 soil) in the mid-salinity treatments, while the SMB was highest in the high-salinity treatments (459–565mg kg−1 soil) and lowest in the low-salinity treatments (158–172mg kg−1 soil). This was attributed to increased substrate availability with high salt concentrations through either increased dispersion
of soil aggregates or dissolution or hydrolysis of soil organic matter, which may offset some of the stresses placed on the
microbial population from high salt concentrations. The apparent disparity in trends in respiration and the SMB may be due
to an induced shift in the microbial population, from one dominated by more active microorganisms to one dominated by less
active microorganisms. 相似文献
942.
Experimental snowpack reduction alters organic matter and net N mineralization potential of soil macroaggregates in a northern hardwood forest 总被引:1,自引:0,他引:1
J. Megan Steinweg Melany C. Fisk Benjamin McAlexander Peter M. Groffman Janet P. Hardy 《Biology and Fertility of Soils》2008,45(1):1-10
Climate change is predicted to reduce or delay annual wintertime snow pack formation in the forests of the northeastern US.
Any delay in snowpack formation could increase soil freezing in winter and, thereby, alter soil characteristics and processes.
We examined the hypothesis that delayed snowpack would disrupt soil structure and change organic matter bioavailability in
an experimental snow removal study at the Hubbard Brook Experimental Forest (HBEF), NH, USA. Pairs of reference and snow removal
treatment plots were studied in four different sites at HBEF. Snow was removed from November–January of two winters, inducing
soil freezing throughout both winters. Size class distribution and organic matter concentration and content of aggregates,
and carbon and nitrogen mineralization potential of size fractions were quantified for surface mineral soils in the spring
of both years immediately after snowmelt. In the first year of sampling, the only significant effect of snow removal was an
increase in the smallest (<53 μm) size fraction of mineral soil. In the second year, snow removal increased organic matter
concentrations of macroaggregate (250–2,000 μm) and microaggregate (53–250 μm) size fractions. This change corresponded to
an increase in net N mineralization potential and the ratio of N to C mineralized in the macroaggregate fraction, but there
were no effects of snow removal on C mineralization. We propose that soil freezing increases the movement of organic matter
from organic to mineral soil horizons and increases the N content of mineralizable substrates in mineral soil following years
with delayed snowpack formation. 相似文献
943.
Sarah J. Kemmitt David Wright Daniel V. Murphy David L. Jones 《Biology and Fertility of Soils》2008,44(7):933-941
Dissolved organic nitrogen (DON) and in particular free amino acids represent a key pool in the terrestrial soil C and N cycle.
The factors controlling the rate of turnover of this pool in soil, however, remain poorly understood. We investigated the
factors regulating the rate of amino acid turnover at different depths (up to 1.2 m) in five low-input, acid soil profiles.
Within the root zone (0–60 cm), amino acids constituted 8% of the DON and represented only a small fraction of plant available
N. In all the soil profiles, the rate of amino acid mineralisation decreased progressively with depth. The average half-life
of the exogenously added amino acids in the soil was 5.8 h in topsoils (0–10 cm), falling to 20 h at a depth of 50 cm and
to 33 h at 100 cm. Generally, the rate of amino acid mineralisation correlated positively with total soil C and N, soil microbial
activity (basal soil respiration rate) and soil content. The relatively rapid rates of microbial amino acid assimilation in subsoils below the root zone (>60 cm) indicate
that long-term transport of amino acids (e.g. from soil to freshwaters) will be low. Based upon the C-to-N ratio of the amino
acid substrate and the microbial C assimilation efficiency, we estimate that approximately 40–60% of the amino acid-N will
be excreted as . In conclusion, the rapid rate of free amino acid turnover and their low concentration in soil solution indicate that the
formation of inorganic N ( and ) in soil is limited primarily by the rate of free amino acid appearance in soil and not by the rate of amino acid mineralisation. 相似文献
944.
Moses F. A. Maliro David McNeil Bob Redden James F. Kollmorgen Chris Pittock 《Genetic Resources and Crop Evolution》2008,55(1):53-63
Six hundred accessions of chickpea (Cicer arietinum L.) landraces and its wild relatives from 28 different countries, available at Australian Temperate and Field Crops Collection
(ATFCC) were screened for tolerance to salt under greenhouse conditions using three sampling strategies; (1) random sampling
of 200 accessions from different countries, (2) restricted random sampling of 200 accessions from geographical regions with
salinity problems and high diversity (Middle East and West & South Asia) and (3) as for strategy 1 but with a reduced representation
of accessions from the geographical regions used in strategy 2. Degree of salt tolerance was based on necrosis scores and
shoot biomass reduction relative to unstressed controls at harvest after subjecting stressed plants to salt treatment from
21 to 42 days after sowing. There was a wide variation in salinity tolerance determined by both measures. For sampling strategies
1, 2 and 3 respectively; 24, 28 and 14% of accessions were salt tolerant. Accessions from the middle east and south Asian
(regions with salinity problem, a long history of chickpea cultivation and high diversity) gave a higher probability (P < 0.01) of getting salt tolerant accessions. 相似文献
945.
We established protocols for the analysis of genetic diversity in chayote (Sechium edule) by using isozyme markers, thereby determining the level of genetic diversity present in 42 accessions of chayote from Costa
Rica. We obtained clear and reproducible zymograms for eight enzyme staining systems: PGM, 6-PGD, PGI, IDH, MDH, SOD, SKD,
and EST, and were able to score 14 putative loci. Eight of the 14 loci examined were polymorphic. We found 35 distinct multilocus
genotypes among these accessions. Five of these multilocus genotypes were homozygous for all loci. In addition, our data also
revealed that most of the multilocus genotypes (24) were heterozygous for only one of the eight loci, and the rest were heterozygous
for two or three loci (9 and 4 accessions, respectively). Seven multilocus genotypes were found in two different accessions.
Dice similarity coefficient was used to study the relationship between accessions. This analysis, based on the presence and
absence of alleles, revealed that accessions collected in the same location seldom shared the same multilocus genotype. The
value of isozyme polymorphisms as tools to continue studies on the characterization of chayote is discussed. 相似文献
946.
947.
Evaluation of genetic diversity of bread wheat landraces from Pakistan by AFLP and implications for a future collection strategy 总被引:1,自引:0,他引:1
Ryoko Hirano Akira Kikuchi Makoto Kawase Kazuo N. Watanabe 《Genetic Resources and Crop Evolution》2008,55(7):1007-1015
We used amplified-fragment-length polymorphism (AFLP) markers to evaluate genetic variation in a set of bread wheat (Triticum aestivum L.) landraces and improved materials. Landraces collected from different geographic and agro-ecological zones in Pakistan
in 1987, 1989 and 1991 were separated into two groups based on their geographic origins: northern (Himalaya) and south-western
(Balochistan) Pakistan. Six AFLP primer combinations detected 453 AFLP markers in the 43 landrace accessions and four high-yield
varieties (HYVs). Of these, 225 (49.67%) were rare (shared with < 5% of all accessions). Among these rare alleles, 23 (10.22%)
were common in the Himalaya (shared with > 10% of accessions collected there) but were not found in Balochistan. We conclude
that there is a higher probability of collecting rare alleles at overall, but which are in contrast locally common ones in
the Himalayan region. Gene diversity was 0.17 in the Himalayan group and 0.15 in the Balochistan group. Considerable genetic
variability was found in both groups. Accessions from different agro-ecological zones were indistinguishable by cluster analysis,
indicating intensive seed trading within the country. Cluster analysis indicated that the landraces and the HYVs are genetically
distinct; suggesting that genetic erosion of wheat landraces has been unlikely taken in place. This study provides an example
of how analysis of existing materials and data, can serve as a basis for future collection planning and conservation policies. 相似文献
948.
R. Ortiz José Crossa Jorge Franco Ricardo Sevilla Juan Burgueño 《Genetic Resources and Crop Evolution》2008,55(1):151-162
The maize of Latin America, with its enormous diversity, has played an important role in the development of modern maize cultivars of the American continent. Peruvian highland maize shows a high degree of variation stemming from its history of cultivation by Andean farmers. Multivariate statistical methods for classifying accessions have become powerful tools for classifying genetic resources conservation and the formation of core subsets. This study has two objectives: (1) to use a numerical classification strategy for classifying eight Peruvian highland races of maize based on six vegetative traits evaluated in two years and (2) to compare this classification with the existing racial classification. The numerical classification maintained the main structure of the eight races, but reclassified parts of the races into new groups (Gi). The new groups are more separated and well defined with a decreasing accession within group × environment interaction. Most of the accessions from G1 are from Cusco Gigante, all of the accessions from G3 (except one) are from Confite Morocho, and all of the accessions from G7 are from Chullpi. Group G2 has four accessions from Huayleño and four accessions from Paro, whereas G4 has four accessions from Huayleño and five accessions from San Geronimo. Group G5 has accessions from four races, and G6 and G8 formed small groups with two and one accession each, respectively. These groups can be used for forming core subsets for the purpose of germplasm enhancement and assembling gene pools for further breeding. 相似文献
949.
For the selection of donors with valuable characteristics for breeding, 39 thyme accessions were evaluated in three years
according to a staggered schedule. The criteria investigated were: winter hardiness, beginning of flowering, growth height,
yield of the dry herb, content of essential oil, composition of the essential oil, DNA content of cell nuclei and number of
chromosomes. The most strongly varying traits between the populations were the yield of dry herb, the content of essential
oil and the content of volatile phenols with coefficients of variation (CV) between CV 40% and 50%. The largest variation
within a population was detected for the yield of dry herb (CV 25–46%) and the content of essential oil (CV 17–48%). The homogeneity
of the populations was different. The minimal average coefficient of variation of all traits (CV 19%) was determined in the
population of the cultivar ‘Varico II’ and in a population from Lithuania. The ploidy level of T. vulgaris was diploid (2n = 30). 相似文献
950.
Ashutosh Mukherjee Satyesh Chandra Roy S. De Bera Hong-En Jiang Xiao Li Cheng-Sen Li Subir Bera 《Genetic Resources and Crop Evolution》2008,55(4):481-485
Hemp (Cannabis sativa L.) cultivation and utilization is an ancient practice to human civilization. There are some controversies on the origin
and subsequent spread of this species. Ancient plant DNA has proven to be a powerful tool to solve phylogenetic problems.
In this study, ancient DNA was extracted from an archaeological specimen of Cannabis sativa associated with archaeological human remains from China. Ribosomal and Cannabis specific chloroplast DNA regions were PCR amplified. Sequencing of a species-specific region and subsequent comparison with
published sequences were performed. Successful amplification, sequencing and sequence comparison with published data suggested
the presence of hemp specific DNA in the archeological specimen. The role of Humulus japonicus Sieb. et Zucc. in the evolution of Cannabis is also indicated. The identification of ancient DNA of 2500 years old C. sativa sample showed that C. sativa races might have been introduced into China from the European–Siberian center of diversity. 相似文献