How prevalent is crassulacean acid metabolism among vascular epiphytes?

The occurrence of crassulacean acid metabolism (CAM) in the epiphyte community of a lowland forest of the Atlantic slope of Panama was investigated. I hypothesized that CAM is mostly found in orchids, of which many species are relatively small and/or rare. Thus, the relative proportion of species with CAM should not be a good indicator for the prevalence of this photosynthetic pathway in a community when expressed on an individual or a biomass basis. In 0.4 ha of forest, 103 species of vascular epiphytes with 13,099 individuals were found. As judged from the C isotope ratios and the absence of Kranz anatomy, CAM was detected in 20 species (19.4% of the total), which were members of the families Orchidaceae, Bromeliaceae, and Cactaceae. As predicted, the contribution of CAM epiphytes to the total number of individuals and to total biomass (69.6 kg ha^-1) was considerably lower (3.6% or 466 individuals and, respectively, 3.0% or 2.1 kg ha^-1).     

雷州半岛桉树生物质能源林生长的密度效应研究

以雷州半岛2年生桉树无性系DH201(Eucalyptus grandis  E. tereticornis)能源林为研究对象,对6种不同密度配置下的林分生长量、生物量以及热值等进行了分析,探讨密度对桉树生物质能源林生长的影响。结果表明,密度对桉树胸径和树高生长量影响极显著,在林分不同发育阶段对林分蓄积量的影响不同;单株生物量随密度增大而减小。1年生的林分蓄积量和生物量均以密度为10000 ind. hm-2的最大,分别为52.57 m3 hm-2和32.02 t hm-2;2年生的林分蓄积量和生物量均以密度为2500 ind. hm-2的最大,分别为75.85 m3 hm-2和45.66 t hm-2;密度对热值及灰分含量的影响不显著。因此,1年生和2年生的桉树能源林的最优密度分别为10000 ind. hm-2和2500 ind. hm-2。     

四种挺水植物生理生态特性和污水净化效果研究

采用人工气候室水培系统以人工污水培养慈姑(Sagittaria trifolia)、花皇冠(Echinodorus berteroi)、菖蒲(Acorus calamus)和芦苇(Phragmites australis) 4种挺水植物,比较它们的根和地上部分生物量、根长、根寿命、根孔隙度、根径向泌氧量(ROL)、光合作用等生理生态特性及对总氮(TN)、总磷(TP)、化学需氧量(COD)的去除效果。结果表明,ROL与根孔隙度、光合速率、地上生物量呈显著正相关(P<0.05),与根长极显著正相关(P<0.01);TP的去除与光合速率、COD的去除与ROL显著正相关; TN的去除与生物量极显著正相关(P<0.01),但与根生物量和地上部分生物量的比值(根茎比)显著负相关(P<0.05)。慈姑和花皇冠拥有庞大生物量和发达的根系,根孔隙度、ROL和光合作用等生理指标较高,在水培系统中的污水净化效果接近甚至优于菖蒲和芦苇,是构建人工湿地的优良植物。     

钻形紫菀开花期种群构件的生物量分配

在野外用样方法,选取60株钻形紫菀(Aster subulatus Michx.)开花植株,进行根、茎、叶及花等构件的生物量及其物质分配关系的研究.结果表明:钻形紫菀开花期构件生物量为茎>花>根>叶,其变异系数分别为57.15%、64.66%、57.65%和55.2%,具有较大表型可塑性;在各构件物质分配变异系数中,花生物量分配的变异系数相对较大,说明其调节生殖分配的能力较强;植株高度与各构件生物量呈显著的正相关性,随着各构件生物量的增加均呈幂函数形式增加;花生物量分配与总生物量呈显著的正相关性,其余构件生物量分配均与总生物量及花生物量分配呈负相关性,物质分配由营养构件、支持构件、光合构件向生殖构件转移.反映出钻形紫菀具有自我调节生长力的分配策略,对异质环境具有较强适应能力.     

The shade avoidance syndrome: A non-Markovian stochastic growth model

Plants at high population density compete for light, showing a series of physiological responses known as the shade avoidance syndrome. These responses are controlled by the synthesis of the hormone auxin, which is regulated by two signals, an environmental one and an internal one. Considering that the auxin signal induces plant growth after a time lag, this work shows that plant growth can be modelled in terms of an energy-like function extremization, provided that the Markov property is not applied. The simulated height distributions are bimodal and right skewed, as in real community of plants. In the case of isolated plants, theoretical growth dynamics and speed correctly fit Arabidopsis thaliana experimental data reported in literature. Moreover, the growth dynamics of this model is shown to be consistent with the biomass production function of an independent model. These results suggest that memory effects play a non-negligible role in plant growth processes.     

Potential respiration is a better respiratory predictor than biomass in young Artemia salina

These experiments test whether respiration can be predicted better from biomass or from potential respiration, a measurement of the mitochondrial and microsomal respiratory electron transport systems. For nearly a century Kleiber's law or a similar precursor have argued the importance of biomass in predicting respiration. In the last decade, a version of the Metabolic Theory of Ecology has elaborated on Kleiber's Law adding emphasis to the importance of biomass in predicting respiration. We argue that Kleiber's law works because biomass packages mitochondria and microsomal electron transport complexes. On a scale of five orders of magnitude we have shown previously that potential respiration predicts respiration as well as biomass in marine zooplankton. Here, using cultures of the branchiopod, Artemia salina and on a scale of less than 2 orders of magnitude, we investigated the power of biomass and potential respiration in predicting respiration. We measured biomass, respiration and potential respiration in Artemia grown in different ways and found that potential respiration (Ф) could predict respiration (R), both in µlO₂ h⁻¹ (R = 0.924Φ + 0.062, r² = 0.976), but biomass (as mg dry mass) could not (R = 27.02DM + 8.857, r² = 0.128). Furthermore the R/Ф ratio appeared independent of age and differences in the food source.     

Importance of assemblage‐level thinning: A field experiment in an alpine meadow on the Tibet plateau

Question: Which fraction of the decrease in species richness under fertilization can be explained by assemblage‐level thinning? Location: An alpine meadow on the eastern Tibet plateau. Methods: 60‐m² plots were randomly assigned to a control or one of four levels of ammonium phosphate fertilizer. Treatments were repeated for three years. The effect of as semblage‐level thinning was decided based on similarity in quadrats within and between fertilizing levels, bootstrap simulation based on random thinning of the high density (low production, low fertility) quadrats and correlation of species’ biomass in low fertility and high fertility. Results: Fertilization increased production, reduced species richness and reduced density of individuals. Heavily fertilized quadrats are more similar in species composition in 2000 but less similar in 2001 and 2002. Rarefaction showed that a decrease in density can account for 32.3‐42.9% decrease of species richness, but the simulated species richness is always significantly higher than the observed one. When production and species richness are similar at two levels of fertilization, species biomass in the higher fertility treatment is positively correlated with biomass at lower fertility. When the two fertilizer levels differed in production and species richness, there was no evidence of correlation in species biomass, suggesting that assemblage level thinning cannot explain all the loss of species. Conclusion: Although a decrease in density could explain much of the decrease (up to 42.9%) in species richness when this alpine meadow was fertilized, other important mechanisms such as interspecific competition cannot be ignored. Future studies should investigate the effect of assemblage level thinning on species diversity, and search for mechanisms responsible for a decrease in diversity.     

Effects of vapour pressure deficit on growth of temperate and tropical evergreen rainforest trees of Australia

Little is known about the effect of vapour pressure deficit (VPD) on the growth of trees. Rainforest trees of eastern Australia provide an opportunity to investigate responses to VPD in species that occur in high precipitation areas but have contrasting dry seasons—summer in the temperate south and winter in the tropical north. Growth responses to VPD were measured in eight species of Australian rainforest trees from different latitudes to investigate possible differences in their response to atmospheric drought. Previous work on these species found that the tropical species have large reductions in gas exchange with increasing VPD whereas the temperate species were mainly unresponsive to increasing VPD. Plants were grown in glasshouses for a year under either low VPD or ambient conditions of a temperate climate. All species had non-significant increases in growth rates (1–9%) of plants grown under low VPD compared with plants grown under ambient VPD. In addition, growing the species under low VPD had no effect on allocation of biomass (leaf area ratio, leaf weight ratio and root/shoot ratio). Therefore, the high sensitivity of gas exchange to increasing VPD found in the tropical rainforest trees did not have a significant, long-term effect on growth under high VPD.     

High-light stress does not impair biomass accumulation of sun-acclimated tropical tree seedlings (Calophyllum longifolium Willd. and Tectona grandis L. f.)

Studies with seedlings of tropical rainforest trees ( Calophyllum longifolium Willd.; Tectona grandis L. f.) were designed to test whether high-light stress affects photosynthetic performance and growth. Seedlings were cultivated in pots at a field site in Central Panama (9 degrees N) and separated into two groups: (1) plants exposed to full solar radiation; (2) plants subjected to automatic neutral shading (48 %) whenever visible irradiance surpassed 1000, 1200, or 1600 micromol photons m-2 s-1. After 2-4 months, chlorophyll fluorescence (Fv/Fm ratio), photosynthetic net CO2 uptake, pigment composition, alpha-tocopherol content of leaves, and plant biomass accumulation were measured. Fully sun-exposed, compared to periodically shaded plants, experienced substantial high-light stress around midday, indicated by photoinhibition of photosystem II and depressed net CO2 uptake. Higher contents of xanthophyll cycle pigments, lutein, and alpha-tocopherol showed an enhancement of photoprotection in fully sun-exposed plants. However, in all experiments, the maximum capacity of net CO2 uptake and plant dry mass did not differ significantly between the two treatments. Thus, in these experiments, high-light stress did not impair productivity of the seedlings studied. Obviously, the continuously sun-exposed plants were capable of fully compensating for any potential costs associated with photoinhibition and repair of photosystem II, reduced CO2 assimilation, and processes of high-light acclimation.     

Biomass and primary production of a 8–11 m depth meadow versus <3 m depth meadows of the seagrass Cymodocea nodosa (Ucria) Ascherson

Current knowledge about the abundance, growth, and primary production of the seagrass Cymodocea nodosa (Ucria) Ascherson is biased towards shallow (depth <3 m) meadows although this species also forms extensive meadows at larger depths along the coastlines. The biomass and primary production of a C. nodosa meadow located at a depth of 8–11 m was estimated at the time of maximum annual vegetative development (summer) using reconstruction techniques, and compared with those available from shallow meadows of this species. A depth-referenced data base of values at the time of maximum annual development was compiled to that end. The vegetative development of C. nodosa at 8–11 m depth was not different from that achieved by shallow (depth <3 m) meadows of this species. Only shoot density, which decreased from 1637 to 605 shoots m⁻², and the annual rate of elongation of the horizontal rhizome, which increased from 23 to 71 cm apex⁻¹ year⁻¹, were different as depth increased from <3 to 8–11 m. Depth was a poor predictor of the vegetative development and primary production of C. nodosa. The biomass of rhizomes and roots decreased with depth (g DW m⁻² = 480 (±53, S.E.) − 32 (±15, S.E.) depth (in m); R² = 0.12, F = 4.65, d.f. = 35, P = 0.0381) which made total biomass of the meadow to show a trend of decrease with depth but the variance of biomass data explained by depth was low. The annual rate of elongation of the horizontal rhizome showed a significant positive relationship with depth (cm apex⁻¹ year⁻¹ = 18 (±5.1, S.E.) + 5.0 (±1.33, S.E.) depth (in m); R² = 0.50, F = 14.07, d.f. = 14, P = 0.0021). As shoot size and growth did not change significantly with depth, the reduction of shoot density should drive any changes of biomass and productivity of C. nodosa as depth increases. The processes by which this reduction of C. nodosa abundance with depth occur remain to be elucidated.