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141.
Decomposition patterns of leaf litter of seven common canopy species in a subtropical forest: N and P dynamics 总被引:12,自引:1,他引:11
Litter decomposition, governing nutrient and C cycling, is strongly influenced by the chemical litter quality. In order to determine the interspecific variation in leaf decomposition rates and to understand the chemical basis for such variation, decomposition dynamics of seven common canopy species was investigated over 2year using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. The species studied are representatives of the vegetation in the study area and differed significantly in their chemical litter quality. Dry mass loss at the end of study varied in the order: Distylium racemosum< Quercus miyagii< Rapanea neriifolia< Symplocos confusa< Castanopsis sieboldii< Schima wallichii< Daphniphyllum glaucescens. All species showed a pattern characterized by a rapid initial decomposition followed by lower rates except for D. glaucescenswhich decomposition rate appeared to be rather constant. In the late phase, decomposition rates were correlated positively to initial N and ash contents and negatively to lignin content, lignin:N, C:N, and C:P ratios. The effects of N and lignin content or lignin:N ratio were stronger than other quality parameters. There was a wide range in patterns of N and P concentrations, from a net accumulation to a rapid loss in decomposition. The correlation between N and P release suggests that N and P dynamics may have influenced each other during litter decomposition. Analysis of initial quality for species showed that the C:P ratios were extremely high (range 1639–3811) but the N:P ratios were from 28 to 56, indicating a likely P-limitation for this forest. Our results suggest that P is an important control of litter decomposition and N and P dynamics. 相似文献
142.
Selfing and inbreeding depression in seeds and seedlings of Neobalanocarpus heimii (Dipterocarpaceae) 总被引:1,自引:0,他引:1
Naito Y Konuma A Iwata H Suyama Y Seiwa K Okuda T Lee SL Muhammad N Tsumura Y 《Journal of plant research》2005,118(6):423-430
We evaluated the degree of selfing and inbreeding depression at the seed and seedling stages of a threatened tropical canopy tree, Neobalanocarpus heimii, using microsatellite markers. Selection resulted in an overall decrease in the level of surviving selfed progeny from seeds to established seedlings, indicating inbreeding depression during seedling establishment. Mean seed mass of selfed progeny was lower than that of outcrossed progeny. Since the smaller seeds suffered a fitness disadvantage at germination in N. heimii, the reduced seed mass of selfed progeny would be one of the determinants of the observed inbreeding depression during seedling establishment. High selfing rates in some mother trees could be attributed to low local densities of reproductive individuals, thus maintenance of a sufficiently high density of mature N. heimii should facilitate regeneration and conservation of the species. 相似文献
143.
Exchange of Proton and Major Elements in Two-Layer Canopies Under Acid Rain in a Subtropical Evergreen Forest in Central-South China 总被引:1,自引:0,他引:1
Gong Zhang Guang-Ming Zeng Yi-Min Jiang Chun-Yan DU Guo-He Huang Mei Zeng Xiao-Kang Su Ren-Jun Xiang 《植物学报(英文版)》2006,48(10):1154-1162
Canopy exchanges of H^+ and N (NH4^+-N, NO3^--N) and other major ions were evaluated and quantified In twolayer canopies based on throughfall measurements in Shaoshan Forest during the period 2000-2002, central-south China, The collected annual rainfall, throughfall, and sub-throughfall were 1 401, 1 191, and 1 084 mm/year, respectively. Fifteen percent and 8% of rainfall (or 9% of throughfall) were intercepted by the top canopy and sub-canopy layers, respectively, The foliar leaching of base cations from the top canopy was significantly higher than that from the sub-canopy, and the latter accounted for 25% of the former. The uptake of H^+ and NH4^+ was significantly higher in the top canopy than in the sub-canopy, indicating that the canopy buffering capacity in the top canopy was stronger than the sub-canopy; Mg^2+ can be absorbed from water flux on the sub-canopy foliar surfaces to compensate for the Mg deficit in the forest soil during the growing season, 相似文献
144.
林窗几何特征的测定方法 总被引:1,自引:0,他引:1
林窗面积、形状及边界木高是决定林窗环境异质性的3个林窗几何特征,影响林窗内植物更新。林窗几何特征的快速测量方法是林窗研究的基础,测量方法可分为2类:基于地面实际测量的地面法和基于林窗林冠照片的相片法。地面法费时费力,受人为因素影响大,可测量林冠林窗和扩展林窗的面积,但不能测量林窗形状和边界木高。相片法具有简单、客观、可重复的优点,但仅适用于林冠林窗。相片法共有5种:"平面相片法"、"航片法"、"半球面影像法"、"双半球面影像法"和"改进的半球面影像法"。前3种测量方法只能测量林冠林窗面积;"改进的半球面影像法"可测量林冠林窗面积和形状,且精度高于前3种相片法,但所需参数最多;"双半球面影像法"可测量林窗面积、形状及边界木高这3个林窗几何特征,且精度较高,但拍摄要求较高。 相似文献
145.
146.
International research on cassava photosynthesis, productivity, eco-physiology, and responses to environmental stresses in the tropics 总被引:1,自引:0,他引:1
M.A. El-Sharkawy 《Photosynthetica》2006,44(4):481-512
The review sums up research conducted at CIAT within a multidiscipline effort revolving around a strategy for developing improved
technologies to increase and sustain cassava productivity, as well as conserving natural resources in the various eco-edaphic
zones where the crop is grown, with emphasis on stressful environments. Field research has elucidated several physiological
plant mechanisms underlying potentially high productivity under favourable hot-humid environments in the tropics. Most notable
is cassava inherent high capacity to assimilate carbon in near optimum environments that correlates with both biological productivity
and root yield across a wide range of germplasm grown in diverse environments. Cassava leaves possess elevated activities
of the C4 phosphoenolpyruvate carboxylase (PEPC) that also correlate with leaf net photosynthetic rate (P
N) in field-grown plants, indicating the importance of selection for high P
N. Under certain conditions such leaves exhibit an interesting photosynthetic C3-C4 intermediate behaviour which may have important implications in future selection efforts. In addition to leaf P
N, yield is correlated with seasonal mean leaf area index (i.e. leaf area duration, LAD). Under prolonged water shortages in seasonally dry and semiarid zones, the crop, once established,
tolerates stress and produces reasonably well compared to other food crops (e.g. in semiarid environments with less than 700 mm of annual rain, improved cultivars can yield over 3 t ha−1 oven-dried storage roots). The underlying mechanisms for such tolerance include stomatal sensitivity to atmospheric and edaphic
water deficits, coupled with deep rooting capacities that prevent severe leaf dehydration, i.e. stress avoidance mechanisms, and reduced leaf canopy with reasonable photosynthesis over the leaf life span. Another stress-mitigating
plant trait is the capacity to recover from stress, once water is available, by forming new leaves with even higher P
N, compared to those in nonstressed crops. Under extended stress, reductions are larger in shoot biomass than in storage root,
resulting in higher harvest indices. Cassava conserves water by slowly depleting available water from deep soil layers, leading
to higher seasonal crop water-use and nutrient-use efficiencies. In dry environments LAD and resistance to pests and diseases
are critical for sustainable yields. In semiarid zones the crop survives but requires a second wet cycle to achieve high yields
and high dry matter contents in storage roots. Selection and breeding for early bulking and for medium/short-stemmed cultivars
is advantageous under semiarid conditions. When grown in cooler zones such as in tropical high altitudes and in low-land sub-tropics,
leaf P
N is greatly reduced and growth is slower. Thus, the crop requires longer period for a reasonable productivity. There is a
need to select and breed for more cold-tolerant genotypes. Selection of parental materials for tolerance to water stress and
infertile soils has resulted in breeding improved germplasm adapted to both favourable and stressful environments.
An erratum to this article is available at . 相似文献
147.
1 The ability to quantify whitefly migration provides a tool that can contribute to an improved understanding of the epidemic development of whitefly‐transmitted viruses. 2 In an attempt to develop a protocol for estimating whitefly immigration and emigration rates in an annual crop, new traps and sampling devices were tested in the field and models for population dynamics were developed. 3 An estimate of immigration rate was derived from the growth of a natural population of Trialeurodes vaporariorum (Westwood) in the beginning of a crop cycle before offspring of immigrants contributed to population growth. 4 A model for changes in whitefly density during an entire bean (Phaseolus vulgaris L.) crop cycle, including an immigration parameter, was also developed. 5 Non‐attractant window traps surrounding an annual field crop were assumed to intercept whiteflies immigrating into and emigrating away from the crop. Captures on these traps could not categorically be identified as immigrants or emigrants, but the cumulated captures nevertheless explained 66% of the variation in population density found within the field. Hence, window traps may be used as an efficient and reliable alternative to yellow sticky traps, aspirator methods and leaf‐turn methods, etc., for estimating whitefly densities in field crops. 相似文献
148.
甘肃、新疆、内蒙苹果蠹蛾成虫消长规律 总被引:2,自引:0,他引:2
苹果蠹蛾Cydia pomonella(L.)是我国重要的果树害虫和检疫对象。2005年至2010年,本研究在甘肃、新疆及内蒙古的不同区县选取了16个果园,使用性信息素诱捕器对其中的苹果蠹蛾成虫发生规律进行长期监测。结果表明,苹果蠹蛾在西北地区每年发生2.5个世代;在正常气候条件下,3个成虫发生高峰分别出现在5月上旬、7月中下旬和8月中下旬,但不同地区及同一地区不同果园之间存在较大差异;化学防治、迷向防治等防治措施对苹果蠹蛾成虫捕获量的影响较大,因此生活史研究为主的监测并不适合在上述果园中开展。综合上述研究结果,未对苹果蠹蛾的季节动态进行准确的预测,需要对苹果蠹蛾除成虫外的其他虫态的季节性变化进行详细研究,并建议选择3个以上的果园进行监测,综合各个果园的监测结果并得出结论。 相似文献
149.
Male ornaments can evolve through the exploitation of female perceptual biases such as those involved in responding to cues from food. This type of sensory exploitation may lead to confusion between the male signals and the cues that females use to find/recognize food. Such interference would be costly to females and may be one reason why females evolve resistance to the male ornaments. Using a group of species of viviparous fish where resistance to a sensory trap has evolved, we demonstrate that females exposed to an ornament that resembles food have a diminished foraging efficiency, that this effect is apparent when foraging on a food item with which the ornament shares visual attributes, and that not all species are equally affected by such confusion. Our results lend support to the model of ornamental evolution through chase-away sexual conflict. 相似文献
150.
Here we describe and illustrate a new parasitoid wasp species, Lathrolestes gauldi
sp. n. from the lowland rainforest of eastern Ecuador and provide a key to the Neotropical species of the genus. This is the first record of the subfamily Ctenopelmatinae from Ecuador. 相似文献