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961.
962.
Above-ground biomass production in seedling and semi-mature individual plants of Sesbania sesban varieties were compared to non-destructive measurements of stem allometrics. The results indicate that measurements of stem characteristics (diameter and total height) are suitable for estimating biomass of S. sesban varieties and therefore useful in the selection of particular varieties for inclusion in short-rotation agroforestry systems in arid- and semi-arid regions. Less labour-intensive methods for accurately assessing the productivity of agroforestry species, such as the use of allometric regressions, could significantly increase the number of individual plants that could be screened in any particular trial. A multiple polynomial regression accurately estimated above-ground biomass in all plants ranging in age from six weeks to eighteen months (r
2=0.99;p<0.001). 相似文献
963.
Vyn TJ Yin X Bruulsema TW Jackson CJ Rajcan I Brouder SM 《Journal of agricultural and food chemistry》2002,50(12):3501-3506
Soybean isoflavone concentrations vary widely, but the contribution of soil fertility and nutrient management to this variability is unknown. Field experiments from 1998 to 2000 on soils with low to high exchangeable potassium (K) concentrations evaluated K application and placement effects on isoflavone concentrations and composition of soybean in various tillage and row-width systems. Soybean seed yield and concentrations of daidzein, genistein, glycitein, leaf K, and seed K were measured. Significant increases in daidzein, genistein, and total isoflavone were observed with direct deep-banded K or residual surface-applied K on low-K soils. Positive effects of K fertilization on isoflavones were less frequent on medium- to high-testing K soils. Both individual and total isoflavones were often positively correlated with seed yield, leaf K, and seed K on low-K soils. Appropriate K management could be an effective approach to increase isoflavone concentrations for soybeans produced on low- to medium-K soils. 相似文献
964.
Orlando Salvador-Neto Simone Azevedo Gomes Angélica Ribeiro Soares Fernanda Lacerda da Silva Machado Richard Ian Samuels Rodrigo Nunes da Fonseca Jackson Souza-Menezes Jorge Luiz da Cunha Moraes Eldo Campos Flávia Borges Mury José Roberto Silva 《Marine drugs》2016,14(2)
Dengue is considered a serious public health problem in many tropical regions of the world including Brazil. At the moment, there is no viable alternative to reduce dengue infections other than controlling the insect vector, Aedes aegypti Linnaeus. In the continuing search for new sources of chemicals targeted at vector control, natural products are a promising alternative to synthetic pesticides. In our work, we investigated the toxicity of a bioactive compound extracted from the red alga Laurencia dendroidea J. Agardh. The initial results demonstrated that crude extracts, at a concentration of 5 ppm, caused pronounced mortality of second instar A. aegypti larvae. Two molecules, identified as (−)-elatol and (+)-obtusol were subsequently isolated from crude extract and further evaluated. Assays with (−)-elatol showed moderate larvicidal activity, whereas (+)-obtusol presented higher toxic activity than (−)-elatol, with a LC50 value of 3.5 ppm. Histological analysis of the larvae exposed to (+)-obtusol revealed damage to the intestinal epithelium. Moreover, (+)-obtusol-treated larvae incubated with 2 µM CM-H2DCFDA showed the presence of reactive oxygen species, leading us to suggest that epithelial damage might be related to redox imbalance. These results demonstrate the potential of (+)-obtusol as a larvicide for use against A. aegypti and the possible mode of action of this compound. 相似文献
965.
966.
He Y Tang RH Hao Y Stevens RD Cook CW Ahn SM Jing L Yang Z Chen L Guo F Fiorani F Jackson RB Crawford NM Pei ZM 《Science (New York, N.Y.)》2004,305(5692):1968-1971
The correct timing of flowering is essential for plants to maximize reproductive success and is controlled by environmental and endogenous signals. We report that nitric oxide (NO) repressed the floral transition in Arabidopsis thaliana. Plants treated with NO, as well as a mutant overproducing NO (nox1), flowered late, whereas a mutant producing less NO (nos1) flowered early. NO suppressed CONSTANS and GIGANTEA gene expression and enhanced FLOWERING LOCUS C expression, which indicated that NO regulates the photoperiod and autonomous pathways. Because NO is induced by environmental stimuli and constitutively produced, it may integrate both external and internal cues into the floral decision. 相似文献
967.
Pasture yield, quality and species distributions were compared between zones around live and killed eucalypt trees at two
woodland sites in northeast Queensland which differed markedly in soil fertility. Trees affected pasture quality and yield
on an individual tree basis: N concentration and dry matter digestibility tended to be higher under trees than in inter-tree
areas at both sites and pasture yields declined with distance from killed trees at the lower fertility site. However, the
distribution of individual species did not vary markedly with distance from trees. Trees also affected pasture yield on a
woodland basis: yields were greater where the trees were killed than under intact woodland. Soil under trees had higher levels
of organic carbon and greater litter cover than soil in inter-tree areas. However, pasture yields did not generally reflect
this fertility gradient since growth was limited by moisture availability due to drought conditions during the study period.
Pasture N concentration was higher under trees that in inter-tree areas since plants under trees produced a similar amount
of biomass as plants in inter-tree areas, but had access to higher nutrient levels. Trees appeared to have a greater effect
on soil nutrient availability at the low fertility site. Live trees depressed pasture yields to a lesser degree at the low
fertility site, demonstrating that the effects of trees on soil water availability (on a woodland scale) are less important
when soil nutrients are more limiting to growth. These results indicate that, while removing trees may enhance pasture productivity,
this benefit may be offset by a reduction in pasture quality. Given the beneficial effect of trees on soil nutrients, tree
removal may also have longer term implications for soil nutrient dynamics.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
968.
969.
970.