Photosynthetic depression in relation to plant architecture in two alpine herbaceous species

The Qinghai-Tibet Plateau is characterized by extremely high radiation, which may induce down-regulation of photosynthesis in plants living in this alpine ecosystem. To clarify whether photoinhibition occurs in the alpine environment and to discern its underlying mechanisms, we examined photosynthetic gas exchange and fluorescence emission in response to the changes in photosynthetic photon flux density (PPFD) and leaf temperature under natural regimes for two herbaceous species: prostrate Saussurea superba and erect-leaved Saussurea katochaete from altitude 3250 m on the Qinghai-Tibet Plateau. S. superba intercepted a higher maximum PPFD and experienced much higher leaf temperature than the erect-leaved S. katochaete. S. superba exhibited a much higher light saturation point for photosynthesis than S. katochaete. Under controlled conditions, the former species had higher CO2 uptake rates and neither species showed obvious photosynthetic down-regulation at high PPFD. Under natural environmental conditions, however, apparent photoinhibition, indicated by reduced electron transport rate (ETR), was evident at high PPFD for both species. After a night frost, the photochemistry of S. katochaete was depressed markedly in the early morning and recovered by mid-day. After a frost-free night, it was high in the morning and low at noon due to high radiation. S. superba did not respond to the night frost in terms of daytime photochemical pattern. In both species, photochemical depression was aggravated by high leaf temperature and the erect species was more sensitive to high temperature. This study suggests that the high radiation on the Qinghai-Tibet Plateau is likely to induce rapidly reversible photoinhibition, which is related closely to plant architecture. Photochemistry in the prostrate species seems able to tolerate higher PPFD, without obvious suppression, than the erect species. (C) 2003 Elsevier Science B.V. All rights reserved.

Chemical constituents from the whole plant of Euphorbia altotibetic

Four new jatrophane diterpenoids, altotibetin A (1), altotibetin B (2), altotibetin C (3), altotibetin D (4), and nine known compounds, beta-sitosterol, cycloart-23-ene-3beta,25-diol, cycloart-25-ene-3beta,24-diol, lupeol acetate, scopoletin, kaempferol, uracil, uridine, astragalin, and daucosterol have been isolated from the whole plant of Euphorbia altotibetic PAULS. Their structures were established by spectral methods, and the configurations of 1 and 2 were confirmed by X-ray analysis.

Effects of plateau zokors (Myospalax Fontanierii) on plant community and soil in an alpine meadow

Effects of plateau zokors (Myospalax fontanierii) on seasonal above- and belowground plant biomass, plant species diversity, and soil moisture and organic matter were examined at an alpine meadow site in Qinghai Province, People's Republic of China. Above- and belowground biomass increased significantly in areas where zokors were removed or burrow systems were abandoned for 5 years compared with areas that zokors had occupied for >10 years. Biomass of monocotyledons was reduced greatly, but biomass of nonpalatable dicotyledons increased significantly, in occupied areas. Diversity of dicotyledons, monocotyledons, and total plants in unoccupied areas was significantly greater than in occupied or abandoned areas. Vegetation cover and height in occupied areas were significantly less than in unoccupied and abandoned areas. No consistent effect by zokors on soil moisture and organic matter was observed.

湛江湖光岩玛珥湖55ka以来植硅体化石记录及古环境变迁

The study of biogenic proxy of tropical and subtropical regions provides important evidence about the process and history of vegetation and environmental changes, and is of globally importance for understanding the dynamic mechanism of paleoclimatic and paleoenvironmental changes. The sediments from the Huguangyan Maar lake in Guangdong Province offer a continuous high-resolution record of the past 55 ka about environmental and vegetational changes. The studies of chronology, and physical, chemical environmental proxies have provided much important information about the paleoenvironmental and paleoclimatic histories. The phytolith, a new biogenicl proxy, has been used to determine the nature and types of plants in this area since the last 55 ka. This study presents a preliminary result about the characteristics of phytolith shapes, the variations of the fossils assemblages, and their significance for environmental changes. Moreover, the author probes the process of special specie evolution and their relationship to climatic parameters. The history of fire has been reconstructed based on the variations in charcoals. The main results and conclusions include: 28 types of phytoliths from 233 samples have been identified. Their environmental meanings are investigated in detail. Based on the variations in phytolith associations, the history and process of climatic and environmental changes in the last 55 kaBP have been established for this region. Climatic changes experienced eight intervals during this period, showing the variations of hot-humid to cool-try climate in the ten thousands years scale, and a shorter dry-hot climate condition in millennial scale. The history of palm plant has been established in this region. Two peaks appeared from 55-39 ka and since the Holocene. Plants in Bambusoideae have been growing in this area all the period, representing the impact of the East Asian summer monsoon. Bamboo plants have similar tendency in their abundance to palm plants, but with a lag of 1-2 ka BP. Panicoideae plants, the representative of C4 plants, have 6 flourishing periods occurred at 54.5, 44, 41.5, 32.5, 14, and 10 kaBP, respectively, reflecting 6 times short-term arid events. Charcoal record from the Huguang Marr lake reveals the history of nature fire, that mostly happened in dry period of last glacial from 55-10 kaBP, centered at 50-45, 40-35, 30-25, and 20-15kaBP, showing about a cycle of 10,000 years.

影响C4草本植物C／N比值变化的因素与土壤有机C积累的关系

文章对采自贵州从低海拔的东部到高海拔的西部且大致平行的石灰岩和砂岩两地带均生长的3种C4草本植物，即巴茅(Miscanthus floridulus)、白茅(Imperata cylindrica)和类芦(Neyraudia reynaudiana)，以及相对应的土壤表层样品，进行了营养元素和C同位素组成分析；研究营养元素含量随着海拔的不同而出现的变化趋势，以及这些元素之间的相互协变作用，尤其是Ca和N之间的相互协变作用对植物的N含量、C／N比值和δ^13C值的影响，以了解植物的C／N比值(指示植物残留物质量的一种标志)与土壤有机C积累的关系。研究结果表明，植物的N含量和δ^13C值具有随海拔的上升而显著增大趋势，而植物的C／N比值在砂岩地区虽有减小的趋势，在石灰岩地带则没有。对所研究的C4草本植物来说，在土壤pH值为5．8的中性条件下显示出Ca的最大吸收，因此，Ca与其他营养元素之间的协变模式在两种土壤类型中表现出相反的倾向，并存在土壤交换性Ca的边界浓度：当土壤可交换性Ca的含量为2．24mg／g，相应土壤的pH值在5．8以下时，随着土壤可交换性Ca浓度的增大，植物的N含量上升，而植物的C／N比值会显著降低；当Ca在边界浓度以上时，随着土壤可交换性Ca浓度的增大，植物的N含量下降，而植物的C／N比值有增加的趋势。由此可见，植物残留物的N含量和C／N比值受Ca元素含量的相互协变作用的影响。在砂岩地区，随着植物C／N比值的增高，土壤有机质的含量却随之下降，而在石灰岩地区则没有这种倾向。因此得出结论：植物的C／N比值的增大对土壤有机碳积累的影响主要取决于土壤的性质，尤其是取决于土壤可交换性Ca的含量。

贵州石灰岩和砂岩地区C4和C3植物营养元素的化学计量对N／P比值波动的影响

陆地生态系统植物的生长受到营养元素氮（N）和磷（P）的可利用性的限制。已有的证据表明营养元素的相对丰度将控制生态系统的营养元素循环和能量流动的速度。文章提出如下假设：为了适应环境的变化，植物具有可伸缩性地调整营养元素含量的能力，也就是营养元素化学计量比值变化的能力，植物N／P比值波动的影响不仅来源于N对P的相对可利用性的变化，也来源于其他营养元素化学计量的变化，尤其是与Ca的化学计量的变化。为了验证上述假设，本研究利用3种C4植物和11种C3植物，研究了植物N／P化学计量比值的波动随N与Ca和P与Ca化学计量的变化模式：对C4植物来说，N／P比值的波动主要受生物量P与Ca化学计量变化的影响；而对C3植物来说，则同时受N与Ca和P与Ca化学计量变化的控制，它们之间的相对控制能力的大小将决定植物N／P比值波动的变化梯度，C4植物和C3植物的N／P比值的波动都要受土壤pH值的影响。本研究对了解物种丰度和N对P的相对可利用性、N与Ca，以及P与Ca的化学计量之间关系具有重要意义.

C4.5: um recurso para geração de árvores de decisão.

O Sistema de Indução C4.5. Requerimentos-chave para a utilização do software. Um exemplo ilustrativo. Algumas dicas de uso.