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Abstract Ultrastructural and physiological characteristics of the C3-C4 intermediate Neurachne minor S. T. Blake (Poaceae) are compared with those of C3 and C4 relatives, and C3-C4Panicum milioides Nees ex Trin. N. minor consistently exhibits very low CO2 compensation points (τ: 1.0, usually 0.3–0.6 Pa) yet has C3-like δ13C values. CO2 assimilation rates (A) respond like those of C3 plants to a decrease in O2 partial pressure (2 × 104–1.9 × 103 Pa) at ambient CO2 levels, but this response is progressively attenuated until negligible at very low CO2. By contrast, other species of the Neurachneae are clearly either C4 (two spp.) or C3 (seven spp.). For plants grown and measured at different photon flux densities (PFDs), τ for N. minor and P. milioides increases from 0.5 to 1.0, and from 1.0 to 2.1 Pa, respectively, as PFD is decreased from 1860 to 460 μmol m?2s?1. In N. minor, the O2 response of τ is either biphasic as in P. milioides, but much diminished and with a higher transition point, or is very C4-like. As in C4 relatives, inner sheath cells contain numerous chloroplasts. Their walls possess a suberized lamella, which may make them more CO2-tight than bundle sheath cells of P. milioides, contributing to the almost C4-like τ characteristics of N. minor. The biochemical basis of C3-C4 intermediacy is considered. 相似文献
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1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g−1 snail DW d−1. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m−2, forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae. 相似文献
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Growth, pigmentation and antibacterial activity of Monascus purpureus Went (starch fungus) were affected by zinc. Zinc at concentrations of 2 × 10-3M and 3 × 10-3M nearly stopped the growth, pigmentation and antibiotic production of both wild type and strain NI IS in liquid medium. Relatively vigorous growth, high pigment production, and strong antibacterial activity of NIIS still occurred on solid medium with the same zinc concentrations. Wild type was hardly affected by zinc concentrations lower than 2 × 10-3M. The growth of strain NI IS was significantly inhibited even by 5 × 10-5M zinc, but pigment production and antibacterial activity were highly promoted by 5 × 10-5M zinc. Increase of glucose concentration also promoted pigment and antibiotic productions of strain NI IS. Glucose effects were intensified as 1 × 10-3M zinc was added. Zinc may act as a growth inhibitor and concomitantly as a stimulant for glucose uptake and for the synthesis of metabolites such as pigments and antibiotics. 相似文献
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Control of Ophiobolus patch in Agrostis turf using avirulent fungi and take-all suppressive soils in pot experiments 总被引:2,自引:0,他引:2
The incorporation of avirulent fungi such as Gaeumannomyces graminis var. graminis, an avirulent isolate of G. graminis var. tritici, a Phialophora sp. with lobed hyphopodia synonymous with Phialophora radiciola var. radicicola sensu Deacon and P. radicicola var. graminicola at the time of seeding Agrostis turf in pots of sterilised soil completely controlled Ophiobolus patch disease. The addition of a 5 mm layer of take-all suppressive (TAS) soils, artifically developed by the repeated addition of live mycelium of the varieties avenae, tritici and graminis of G. graminis to soil, controlled the disease to a lesser extent. However, a 20 mm layer of a TAS soil developed from live mycelium of G. g. avenae almost completely suppressed the disease. A survey of 66 golf and bowling greens in four states of Australia showed that P. r. graminicola was the most prevalent avirulent fungus. 相似文献
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