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91.
Rates of apparent photosynthesis (AP), dark respiration, photorespiration, mesophyll resistance, and concentrations of soluble starch, sugars, chlorophyll and nitrogen were measured in alfalfa leaves ( Medicago sativa L.) grown under high or low light levels in an attempt to evaluate the effect of nonstructural carbohydrate concentration on net CO2 assimilation.
Leaf N and chlorophyll levels of high light plants exceeded those of low-light plants. Constant light increased both starch and sugar levels in low-light plants, but had little effect on high-light plants. Rates of AP declined in low-light plants upon transfer to constant light conditions, apparently due to increases in stomatal and mesophyll resistance. Leaf starch levels were negatively correlated (P > 0.05) with rates of AP and positively correlated with mesophyll resistance in both groups of plants but leaf sugar content was not correlated with either AP or mesophyll resistance.
Starch and sugar levels of high-light plants declined substantially upon transfer to constant darkness, while low-light plants were less affected. Rates of AP declined in both groups of plants due to increases in both mesophyll and stomatal resistances. Neither sugar nor starch levels were correlated with AP or mesophyll conductance in this treatment.
The data support the hypothesis of feedback inhibition of photosynthesis, mediated through an increase in mesophyll resistance, which is associated with high levels of starch in the leaves. 相似文献
Leaf N and chlorophyll levels of high light plants exceeded those of low-light plants. Constant light increased both starch and sugar levels in low-light plants, but had little effect on high-light plants. Rates of AP declined in low-light plants upon transfer to constant light conditions, apparently due to increases in stomatal and mesophyll resistance. Leaf starch levels were negatively correlated (P > 0.05) with rates of AP and positively correlated with mesophyll resistance in both groups of plants but leaf sugar content was not correlated with either AP or mesophyll resistance.
Starch and sugar levels of high-light plants declined substantially upon transfer to constant darkness, while low-light plants were less affected. Rates of AP declined in both groups of plants due to increases in both mesophyll and stomatal resistances. Neither sugar nor starch levels were correlated with AP or mesophyll conductance in this treatment.
The data support the hypothesis of feedback inhibition of photosynthesis, mediated through an increase in mesophyll resistance, which is associated with high levels of starch in the leaves. 相似文献
92.
93.
Richard D. Scheffe Jason A. Lynch Adam Reff James T. Kelly Bryan Hubbell Tara L. Greaver J. Travis Smith 《Water, air, and soil pollution》2014,225(2):1-15
This study compares a traditional agricultural approach to minimise N pollution of groundwater (incorporation of crop residues) with applications of small amounts of biodiesel co-product (BCP) to arable soils. Loss of N from soil to the aqueous phase was shown to be greatly reduced in the laboratory, mainly by decreasing concentrations of dissolved nitrate-N. Increases in soil microbial biomass occurred within 4 days of BCP application—indicating rapid adaptation of the soil microbial community. Increases in biomass-N suggest that microbes were partly mechanistic in the immobilisation of N in soil. Straw, meadow-grass and BCP were subsequently incorporated into experimental soil mesocosms of depth equal to plough layer (23 cm), and placed in an exposed netted tunnel to simulate field conditions. Leachate was collected after rainfall between the autumn of 2009 and spring of 2010. Treatment with BCP resulted in less total-N transferred from soil to water over the entire period, with 32.1, 18.9, 13.2 and 4.2 mg N kg?1 soil leached cumulatively from the control, grass, straw and BCP treatments, respectively. More than 99 % of nitrate leaching was prevented using BCP. Accordingly, soils provided with crop residues or BCP showed statistically significant increases in soil N and C compared to the control (no incorporation). Microbial biomass, indicated by soil ATP concentration, was also highest for soils given BCP (p?<?0.05). These results indicate that field-scale incorporation of BCP may be an effective method to reduce nitrogen loss from agricultural soils, prevent nitrate pollution of groundwater and augment the soil microbial biomass. 相似文献
94.
Travis J 《Science (New York, N.Y.)》1992,257(5071):750
In San Francisco 2 weeks ago, AAAS and Science sponsored a new meeting, Science Innovation '92. The unusual gathering focused not on research results but on new techniques and instruments, particularly for biomedical science. As seen in the stories below, some of the most eye-catching innovations emerged at the intersection of physics and biology. 相似文献
95.
96.
Travis J 《Science (New York, N.Y.)》1994,265(5180):1915-1916
97.
Travis LD Coffeen DL Hansen JE Kawabata K Lacis AA Lane WA Limaye SS Stone PH 《Science (New York, N.Y.)》1979,203(4382):781-785
The first polarization measurements of the orbiter cloud photopolarimeter have detected a planet-wide layer of submicrometer aerosols of substantial visible optical thickness, of the order of 0.05 to 0.1, in the lower stratosphere well above the main visible sulfuric acid cloud layer. Early images show a number of features observed by Mariner 10 in 1974, including planetary scale markings that propagate around the planet in the retrograde sense at roughly 100 meters per second and bright- and dark-rimmed cells suggesting convective activity at low latitudes. The polar regions are covered by bright clouds down to latitudes aproximately 50 degrees, with both caps significantly brighter (relative to low latitudes) than the south polar cloud observed by Mariner 10. The cellular features, often organized into clusters with large horizontal scale, exist also at mid-latitudes, and include at least one case in which a cell cuts across the edge of the bright polar cloud of the northern hemisphere. 相似文献
98.
Jennifer M. Giles Conner L. Tordsen Travis R. Rebstock Bruna Bucciarelli Deborah A. Samac Andrew E. Sathoff 《Plant pathology》2022,71(6):1231-1240
Alfalfa (Medicago sativa) is one of several legumes that is affected by Aphanomyces root rot (ARR) caused by Aphanomyces euteiches. Symptoms of ARR on alfalfa seedlings include a yellow-grey discolouration of roots, rotting and loss of lateral roots, stunted growth, chlorotic foliage and reduction of nitrogen-producing nodules on roots. Infection can also occur on adult plants leading to loss of lateral roots and nodules. At the seedling stage, ARR decreases alfalfa stand establishment, and field longevity is reduced when adult plants are infected. A. euteiches is an oomycete pathogen that has motile zoospores and thick-walled oospores that can survive for many years in soil. Two races are currently recognized by pathogenicity on differential alfalfa check cultivars. Most alfalfa cultivars contain race 1 resistance, but there is an increasing development of cultivars with resistance to race 2. Management strategies include planting resistant cultivars, avoiding planting in fields with poor drainage and rotating crops with nonhost plants. 相似文献
99.
100.
Elizabeth Throckmorton Travis Brenden Amber K. Peters Tammy J. Newcomb Gary E. Whelan Mohamed Faisal 《Journal of aquatic animal health》2013,25(1):31-42
AbstractViral hemorrhagic septicemia virus genotype IVb (VHSV IVb) has caused major, sporadic fish die-offs in the Laurentian Great Lakes region of North America since 2005. Presently, factors affecting VHSV IVb persistence in enzootic systems are not well understood. Even with annual surveillance, the virus can go undetected for several years after an outbreak before again re-emerging, which suggests that the virus is maintained in the system either below detectable levels or in untested reservoirs. The aim of this study was to identify potential reservoirs of VHSV IVb in Budd Lake, Michigan; VHSV IVb was first detected in Budd Lake in 2007 but remained undetected until 2011. Additionally, we explored the susceptibility of naive fish introduced into a water body enzootic for VHSV IVb by stocking age-0 Largemouth Bass Micropterus salmoides at varying densities into enclosures in the lake. The virus was not detected among samples of the fishes Notropis spp. and Lepomis spp., cylindrical papershell mussels Anodontoides ferussacianus, leeches (subclass Hirudinea), sediment, or water. However, the virus was successfully isolated from amphipods (family Hyalellidae) and Largemouth Bass held in the enclosures. Our finding of VHSV IVb in Hyalellidae amphipods in combination with other research that has detected the virus in Diporeia spp., a large benthic amphipod important as a food resource to Great Lake fishes, suggests that benthic macroinvertebrates are a reservoir for VHSV IVb in infected systems. If there are environmental reservoirs for VHSV IVb in infected systems, they are likely unevenly distributed. Findings of this study add to our understanding of the seemingly complex ecology of this deadly and economically detrimental virus.Received February 22, 2016; accepted October 16, 2016 Published online February 6, 2017 相似文献