Cortical development in roots of the aquatic plant Pontederia cordata (Pontederiaceae)

Adventitious roots of marsh-grown Pontederia cordata were examined to determine cortical development and structure. The innermost layer of the ground meristem forms the endodermis and aerenchymatous cortex. The outermost layer of the early ground meristem undergoes a precise pattern of oblique and periclinal cell divisions to produce a single or double layer of prohypodermis with an anchor cell for each radial file of aerenchyma cells. At maturity, endodermal cell walls are modified only by narrow Casparian bands. The central regions of the ground meristem become proaerenchyma and exhibit asymmetric cell division and expansion. They produce an aerenchymatous zone with barrel-shaped large cells and irregularly shaped small cells traversing the aerenchyma horizontally along radii; some crystalliferous cells with raphides are present in the aerenchyma. The walls of the hypodermis are modified early by polyphenols. The outermost layer of the hypodermis later matures into an exodermis with Casparian bands that are impermeable to berberine, an apoplastic tracer dye. The nonexodermal layer(s) of the hypodermis has suberin-modified walls. Radial files of aerenchyma are usually connected by narrow protuberances near their midpoints, the aerenchyma lacunae having been produced by expansion of cells along walls lining intercellular spaces. We are terming this type of aerenchyma development, which is neither schizogenous nor lysigenous, "differential expansion."     

Growth of water hyacinth (Eichhornia crassipes (Mart.) Solms) in the middle Paraná River (Argentina)

The productivity of water hyacinth in the middle Paraná River was measured at three initial biomass levels by means of periodic harvesting of plants contained in 2 m² floating baskets. The measuring period extended between August 1981 and July 1982. Initial biomass densities were 2, 5 and 10 kg (fw) m^–2.Compared with inner island ponds, flowing waters connected to the main river showed better conditions for water hyacinth growth. The duration of the growth period was some 30% longer than in island ponds, probably due to the relatively warmer river waters. Productivity ranged between 108 and 164 g (fw) m ^–2 d^–1 (annual average) for the lower and higher initial biomass values, respectively.     

深圳福田红树林植被碳储量和净初级生产力

红树林是滨海湿地“蓝碳”的主要类型之一.准确和定位评估不同植物群落的固碳能力,对于红树林保育管理和恢复造林具有指导作用.本研究对深圳福田红树林4种代表性群落(白骨壤群落、秋茄群落、海桑群落、无瓣海桑群落)的各个植被碳库组分(乔木植物生物量碳库、林下灌丛碳库、呼吸根碳库、枯立木碳库、枯倒木碳库和枯枝落叶层碳库等)进行调查,计算各群落的植被碳储量,并通过生长增量-凋落物产量法计算得到各群落的净初级生产力.结果表明: 白骨壤群落、秋茄群落、海桑群落和无瓣海桑群落的植被碳储量分别为28.7、127.6、100.1、73.6 t C·hm^-2,各群落的净初级生产力分别为8.75、7.67、9.60、11.87 t C·hm^-2·a^-1.位于深圳市中心的福田红树林,每年固定大气CO₂高达4000 t.本研究结果将为红树林“蓝碳”碳汇功能的评估提供理论指导,并为我国红树林碳汇林建设提供依据.     

High rates of net primary production and turnover of floating grasses on the Amazon floodplain: implications for aquatic respiration and regional CO2 flux

We investigated whether rates of net primary production (NPP) and biomass turnover of floating grasses in a central Amazon floodplain lake (Lake Calado) are consistent with published evidence that CO₂ emissions from Amazon rivers and floodplains are largely supplied by carbon from C4 plants. Ground‐based measurements of species composition, plant growth rates, plant densities, and areal biomass were combined with low altitude videography to estimate community NPP and compare expected versus observed biomass at monthly intervals during the aquatic growth phase (January–August). Principal species at the site were Oryza perennis (a C3 grass), Echinochloa polystachya, and Paspalum repens (both C4 grasses). Monthly mean daily NPP of the mixed species community varied from 50 to 96 g dry mass m^?2 day^?1, with a seasonal average (±1SD) of 64±12 g dry mass m^?2 day^?1. Mean daily NPP (±1SE) for P. repens and E. polystachya was 77±3 and 34±2 g dry mass m^?2 day^?1, respectively. Monthly loss rates of combined above‐ and below‐water biomass ranged from 31% to 75%, and averaged 49%. Organic carbon losses from aquatic grasses ranged from 30 to 34 g C m^?2 day^?1 from February to August. A regional extrapolation indicated that respiration of this carbon potentially accounts for about half (46%) of annual CO₂ emissions from surface waters in the central Amazon, or about 44% of gaseous carbon emissions, if methane flux is included.     

Responses of aquatic macrophyte cover and productivity to flooding variability on the Amazon floodplain

Macrophyte net primary productivity (NPP) is a significant but understudied component of the carbon budget in large Amazonian floodplains. Annual NPP is determined by the interaction between stem elongation (vertical growth) and plant cover changes (horizontal expansion), each affected differently by flood duration and amplitude. Therefore, hydrological changes as predicted for the Amazon basin could result in significant changes in annual macrophyte NPP. This study investigates the responses of macrophyte horizontal expansion and vertical growth to flooding variability, and its possible effects on the contribution of macrophytes to the carbon budget of Amazonian floodplains. Monthly macrophyte cover was estimated using satellite imagery for the 2003–2004 and 2004–2005 hydrological years, and biomass was measured in situ between 2003 and 2004. Regression models between macrophyte variables and river‐stage data were used to build a semiempirical model of macrophyte NPP as a function of water level. Historical river‐stage records (1970–2011) were used to simulate variations in NPP, as a function of annual flooding. Vertical growth varied by a factor of ca. 2 over the simulated years, whereas minimum and maximum annual cover varied by ca. 3.5 and 1.5, respectively. Results suggest that these processes act in opposite directions to determine macrophyte NPP, with larger sensitivity to changes in vertical growth, and thus maximum flooding levels. Years with uncommonly large flooding amplitude resulted in the highest NPP values, as both horizontal expansion and vertical growth were enhanced under these conditions. Over the simulated period, annual NPP varied by ca. 1.5 (1.06–1.63 TgC yr^?1). A small increasing trend in flooding amplitude, and by extension NPP, was observed for the studied period. Variability in growth rates caused by local biotic and abiotic factors, and the lack of knowledge on macrophyte physiological responses to extreme hydrological conditions remain the major sources of uncertainty.     

Land Use Change in India (1700–2000) as Examined through the Lens of Human Appropriation of Net Primary Productivity

Land use caused by human socioeconomic activities is a driver of change in the global environment. To understand and quantify land‐use change on Earth's natural systems, interdisciplinary approaches linking biophysical and socioeconomic parameters are required. One approach to understand the degree of terrestrial colonization of the biosphere is using the human appropriation of net primary productivity (HANPP). HANPP is defined as the difference between the net primary productivity (NPP) of potential vegetation and the actual NPP for a given area of land. Here, we use HANPP as a lens to examine land‐use change in India from 1700 to 2007 using a spatially explicit data set that extends over this period. We also used the nongridded, Food and Agriculture Organization (FAO) data set to calculate HANPP for India from 1961 to 2012 and compared our results. The average potential NPP for India was estimated to be 664 grams of carbon per square meter per year (g C/m²/year). Between 1700 and 2012, the fraction of pastureland and cropland increased from 20% to almost 60%. HANPP as a fraction of the potential NPP increased from 29% to 73% over this period. Calculations of HANPP using the FAO data set yielded an increase from 600 g C/m² to just over 700 g C/m² between 1961 and 2012. We also calculated the embodied HANPP of India by considering imports and exports, but the difference between the two is negligible in comparison to the HANPP of India. We further examined the variation of HANPP with socioeconomic parameters such as the Human Development Index (HDI) and population density. There was a roughly negative trend of HANPP with HDI. HANPP roughly increases with population density and then plateaus above a population density of roughly 200 persons per square kilometer.     

Estimation of Net Primary Productivity of Terrestrial Vegetation in China by Remote Sensing (in English)

Among the many approaches for studying the net primary productivity ( NPP ), a new method by using remote sensing was introduced in this paper. With spectral information source (the visible band, near infrared band and thermal infrared band) of NOAA-AVHRR, we can get the relative index and parameters, which can be used for estimating NPP of terrestrial vegetation. By means of remote sensing, the estimation of biomass and NPP is mainly based on the models of light energy utilization. In other words, the biomass and NPP can be calculated from the relation among NPP , absorbed photosynthetical active radiation (APAR) and the rate (ε) of transformation of APAR to organic matter, thus：NPP=(FPAR×PAR)×［ε*×σT×σE×σS×(1-Ym)×（1-Yg）］ . Based upon remote sensing (RS) and geographic information system (GIS), the NPP of terrestrial vegetation in China in every ten days was calculated, and the annual NPP was integrated. The result showed that the total NPP of terrestrial vegetation in China was 6.13×109 t C·a-1in 1990 and the maximum NPP was 1 812.9 g C/m. According to this result, the spatio-temporal distribution of NPP was analyzed. Comparing to the statistical models, the RS model, using area object other than point one, can better reflect the distribution of NPP , and match the geographic distribution of vegetation in China.     

Ultrastructure of Myxobolus brycon n. sp. (Phylum Myxozoa), parasite of the piraputanga fish Brycon hilarii (Teleostei) from Pantanal (Brazil)

Light and electron microscopy studies of a myxosporean, parasitizing the gill filaments of the freshwater fish Brycon hilarii (Valenciennes, 1850) (Characidae) collected in the Paraguay River (18°49'S, 57°39'W) (Pantanal), Brazil, is described. This parasite produces spherical to ellipsoidal polysporic histozoic plasmodia (Pmd) (up to ～180 μm in diameter) delimited by a double membrane and with several pinocytic channels. The plasmodial cyst contained the youngest developmental stages at the cortical periphery and immature and mature spores more internally. The Pmd developed near the cartilaginous structure of the gill filament, forming a prominent deformation where the gill lamellae disappear. Pyriform spores measured 6.9±0.6 (range 6.5-7.2) μm long, 4.2±0.5 (range 3.9-4.8) μm wide, and 2.5±0.7 (range 1.9-2.8) μm thick. The spores composed of two equal shell valves (～70 nm thick), adhering together along the straight suture line, surrounded two equal symmetric and elongated to pyriform polar capsules (PC) 4.2±0.6 (range 3.8-4.7) × 1.9±0.6 (1.7-2.5) μm; each PC contained a coiled polar filament with eight or nine (rarely 10) turns and a binucleated sporoplasm cell. Dense irregular masses were observed among the polar filaments coils. An intercapsular appendix was not observed. The sporoplasm contained several globular sporoplasmosomes randomly distributed among an extensive rough endoplasmic reticulum system with numerous vesicles and cisternae. Based on the morphological and ultrastructural differences and specificity of the host, we establish the new species, Myxobolus brycon n. sp.     

Seed banks on Attalea phalerata (Arecaceae) stems in the Pantanal wetland, Brazil

Background and Aims

Seeds can accumulate in the soil or elsewhere, such as on the stems of palms when these are covered by persistent sheaths. These sheaths could act as a safe site for some species. Here, we studied whether persistent sheaths of the palm Attalea phalerata (Arecaceae) are available sites for seed accumulation in the Pantanal wetland of Brazil. We also investigated whether the composition, richness and diversity of species of seeds in the persistent sheaths are determined by habitat (riparian forest and forest patches) and/or season (wet and dry).

Methods

All accumulated material was collected from ten persistent sheaths along the stems of 64 A. phalerata individuals (16 per habitat and 16 per season). The material was then individually inspected under a stereomicroscope to record seed species and number.

Key Results

Of the 640 sheaths sampled, 65 % contained seeds (n = 3468). This seed bank included 75 species belonging to 12 families, and was primarily composed of small, endozoochoric seeds, with a few abundant species (Cecropia pachystachya and Ficus pertusa). Moraceae was the richest family (four species) and Urticaceae the most abundant (1594 seeds). Stems of A. phalerata in the riparian forest had 1·8 times more seeds and 1·3 times more species than those in forest patches. In the wet season we sampled 4·1 times more seeds and 2·2 more species on palm stems than in the dry season. Richness did not differ between habitats, but was higher in the wet season. Abundance was higher in forest patches and in the wet season.

Conclusions

Attalea phalerata stems contain a rich seed bank, comparable to soil seed banks of tropical forests. As most of these seeds are not adapted to grow in flooding conditions, palm stems might be regarded as safe sites for seeds (and seedlings) to escape from the seasonal flooding of the Pantanal.     

Physical variables driving epiphytic algal biomass in a dense macrophyte bed of the St. Lawrence River (Quebec, Canada)

The variables affecting epiphyton biomass were examined in a sheltered, multispecies macrophyte bed in the St. Lawrence River. Alteration of light penetration, resulting from the presence of dense macrophytes forming a thick subsurface canopy, primarily determined epiphyton biomass. Seasonal decrease of water levels also coincided with major increases in biomass. Plant morphology was the next important variable influencing epiphytic biomass, whereas the contribution of other variables (sampling depth, macrophyte species, relative abundance of macrophytes, and temperature) was low. Groups of lowest epiphyte biomass (0.1–0.6 mg Chla g^–1 DW) were defined by the combination of a low percentage of incident light (<13% surface light) and simple macrophyte stem types found below the macrophyte canopy. Highest epiphyte biomass (0.7–1.8 mg Chla g^–1 DW) corresponded to samples collected in mid-July and August, under high irradiance (>20% surface light) and supported by ramified stems. Our results suggest that epiphyton sampling should be stratified according to the fraction of surface light intensity, macrophyte architecture, and seasonal water level variations, in decreasing order of influence.     

Nitrogen and phosphorus concentration of different structures of the aquatic macrophytes Eichhornia azurea Kunth and Scirpus cubensis Poepp & Kunth in relation to water level variation in Lagoa Infernão (São Paulo, Brazil)

We evaluated the nitrogen and phosphorus concentration of floating meadows of Eichhornia azurea and Scirpus cubensis in Lagoa do Infernao (State of Sao Paulo, Brazil). The chemical composition of these plants and of the water (littoral and limnetic zones) was determined during the period March 1987 to march 1988. During high water, the water becomes enriched by soluble nutrients and particulates washed from the flooded areas adjacent to the lake, especially from areas situated between the river and Lagoa do Infernão. The soluble allochthonous material is rapidly assimilated and stocked in the plant tissues, which results in an increase in its concentration. Besides this, it was established that the aquatic macrophytes studied utilize the nutrients dissolved in the water of the floating meadow itself, these nutrients being derived principally from their own decomposition.Since these are floating stands, the sediment does not function as a direct source of nutrients, and since concentrations in the water are low, the nutrients excreted by the aquatic macrophytes during growth and liberated during decomposition do not remain available in the water, but are rapidly absorbed by the young plants.This closed nutrient system makes possible the maintenance of the high biomass of the stands during the entire hydrological cycle.     

Soil Temperature, Not Aboveground Plant Productivity, Best Predicts Intra-Annual Variations of Soil Respiration in Central Iowa Grasslands

Soil respiration (R_SOIL) is the second largest carbon flux between terrestrial systems and the atmosphere, with a magnitude 10 times greater than anthropogenic carbon dioxide production. Therefore, it is important that we understand, and be able to predict, how R_SOIL responds to climate change. Although a positive, significant temperature effect on R_SOIL has long been recognized, recent studies emphasize the overriding importance of current photosynthesis in controlling R_SOIL. We tested the hypothesis that model inclusion of intra-annual variations in aboveground net primary productivity (ANPP) significantly improves R_SOIL estimates over predictions based on soil temperature alone. We also evaluated the possibility that canopy production is less directly linked to R_SOIL, by testing the hypothesis that intersite differences in R_SOIL correlate more strongly with root biomass than with ANPP. We tested these hypotheses by measuring R_SOIL, ANPP, and root biomass at four Iowa grasslands that differed in aboveground growth phenology and productivity. Among all sites, intra-annual variations in R_SOIL were most strongly related to soil temperature (R ² = 0.89), not ANPP (R ² = 0.53). All sites responded identically to changes in soil temperature (site-by-temperature P = 0.53), but inconsistently to variation in aboveground dynamics (site-by-canopy P < 0.0001). Incorporating canopy dynamics into temperature-based predictive models improved model R ² by a maximum of 0.01. Among-site differences in R_SOIL were related to root biomass (P < 0.001) but not ANPP (P = 0.34). We found no useful linkage between canopy characteristics and intra-annual or site-specific R_SOIL predictions, perhaps because shoot and root dynamics were not consistently linked through time or among sites.     

First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d⁻¹) and erosion (0.01 g dw d⁻¹) than L. nigrescens (production 0.01 g dw d⁻¹ and loss 0.002 g dw d⁻¹). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m⁻²) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m⁻²). Spring net productivities of 42 g dw m⁻²d⁻¹ (254 g ww m⁻²d⁻¹; 11.46 gC m⁻²d⁻¹) for L. nigrescens and 11 g dw m⁻² d⁻¹ (64 g ww m⁻² d⁻¹; 2.46 gC m⁻²d⁻¹) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.     

Effect of reservoir drawdown on biomass of three species of aquatic macrophytes in a large sub-tropical reservoir (Itaipu, Brazil)

The biomass and maximum depth of colonization (Z _max) of Egeria najas Planchon (submerged), and the biomass and area covered by a stand of Eichhornia crassipes (Mart.) Solms and Salvinia herzogii Raddi (floating species) were assessed to measure the effects of a 5 m drawdown in water level of the Itaipu Reservoir (Brazil–Paraguay), which lasted about 3 months. The frequency of occurrence of the two first species, and of Salvinia spp was also assessed in the main arms of the reservoir. A conspicuous decrease of E. najas biomass was observed and this attribute did not reach the previous values even 10 months after the water level had returned to normal. Rapid growth of free-floating species (surface t _doub = 2.9 and 3.2 days for total biomass of S. herzogii and E. crassipes, respectively, and 2.3 days for surface area covered by both species) was recorded immediately after the water level returned to normal. This fast growth was related to phosphorus increases in water. A clear succession was observed over a period of 103 days, during which S. herzogii was slowly substituted by E. crassipes. The effects of water level drawdown were also observed on E. najas frequency, given that this species occurred in 38% of the stands investigated before the water drawdown, but in only 9 and 6% of stands following 1 and 10 months of water level recovery, respectively. Water drawdown did not affect the frequency of occurrence of the floating species, which remained approximately constant, and lower than 15% in several of the reservoir arms investigated.     

Elevation effects on the carbon budget of tropical mountain forests (S Ecuador): the role of the belowground compartment

Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above‐ and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060 m, while stem wood production decreased 20‐fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above‐ and belowground) decreased from about 320 to 175 Mg dry mass ha^?1, total NPP from ca. 13.0 to 8.2 Mg ha^?1 yr^?1. The belowground/aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature‐induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.     

Primary Productivity and Activity Coefficients of the Phytoplankton of a Mesotrophic Soft-Water Lake (Piburger See,Tirol, Austria)

Phytoplankton primary production was measured using the ¹⁴C method once per month from 1973 through 1976 as part of an intensive ecosystem study of a small eutrophic soft-water lake, under restoration since 1970. Relationships among phytoplankton production, species composition, chlorophyll a content, bacteria, zooplankton and a variety of abiotic environmental factors have been studied. Productivity normally showed one peak in spring and another in summer, whereas a minimum was reached under the ice cover in February or March. Maximum production rates in the depth profile ranged from 3 to 144 mg C · m⁻³ · d⁻¹, integral production from 6 to 510 mg C · m̄⁻² · d⁻¹. Species of Cyanophyceae, Dinophyceae, Chlorophyceae and Chrysophyceae dominated alternately and showed significant differences in the level and variation of photosynthetic activity. Maximum activity was observed in summer. A high biomass increase during late winter and spring despite low primary productivity resulted from the immigration of the dominant blue-green alga, Oscillatoria limosa, from the sediment. Energy efficiency increased not only with depth in the light-limited parts of the euphotic zone but at all depths during bad weather conditions and during the decrease of irradiance in autumn.     

Seasonality and relative abundance of Tabanidae (Diptera) captured on horses in the Pantanal, Brazil.

Once a month, from June 1992 to May 1993, collections of tabanids on horse were conducted in the Nhecolandia, Pantanal State of Mato Grosso do Sul, Brazil. Tabanid catches using hand nets were conducted from sunrise to sunset at grassland and cerrad?o (dense savanna) habitats. A total of 3,442 tabanids from 21 species,12 genera, and 3 subfamilies were collected. Although species abundance varied seasonally depending on habitat, no habitat specificity was observed for the most abundant species. In the grassland, 1,625 (47.2%) tabanids belonging to 19 species were collected, while 1,817 (52.8%) tabanids from 17 species were caught in the cerrad?o. The number of tabanid species varied from 7 during winter (July/August) to 15 in the spring (October). Tabanus importunus (56%) was the most abundant species, followed by T. occidentalis (8.2%), and T. claripennis (8.1%). The tabanid peak, in October, coincided with the beginning of the rainy season. The population peak of most species, including those with higher vector potential, suggests that the rainy season can be considered as the period of potentially higher risk of mechanical transmission of pathogens by tabanids to horses in the region.     

气候变化对阔叶红松林不同演替阶段红松种群生产力的影响

本文以长白山地区阔叶红松林不同演替阶段(次生杨桦林、次生针阔混交林、原始红松林)内红松种群作为研究对象,采用树轮学与相对生长式相结合,获取红松种群净初级生产力(NPP)连年生长(1921—2006年)数据以及相对增长率的年际变化数据,建立红松种群NPP与年际和季节性气候因子的关系,分析不同气候时期长白山阔叶红松林不同演替阶段内红松种群NPP年际变化特征及其对气候变化的响应差异.结果表明： 研究期间,不同演替阶段红松种群NPP与气候因子响应关系存在差异.随着温度上升,次生杨桦林红松种群NPP与上年生长季和当年生长季低温由显著负相关关系转变为显著正相关关系;次生针阔混交林红松种群NPP由与当年春季最低温度的正相关关系转变为与上年和当年生长季温度的显著正相关关系,气候因素对次生针阔混交林红松种群NPP影响的滞后效应增强;原始红松林红松种群NPP与温度的相关性减弱,与上年生长季降水量的正相关关系增强.研究区气候变化表现为低温和平均温度显著上升,而最高温度和降水没有明显变化.气候变化有利于提高演替初级阶段次生杨桦林和演替中级阶段次生针阔混交林内红松种群生产力,尤其是次生针阔混交林,而对演替顶极阶段红松种群NPP影响不明显.     

The Epipelic Algal Flora of the River Wye System,Wales, U.K. 1. Productivity and Total Biomass Dynamics

The spatial and temporal fluctuations of the phytopigment content, “potential” primary productivity and total biomass of the epipelic algae of the River Wye System were studied during June 1979 to May 1981. Chlorophyll-a and productivity values showed a downstream increase, much less obvious for the total biomass. Phaeophytin-a values followed almost similar spatial and temporal fluctuations to those of chlorophyll-a. High chlorophyll-a productivity and total biomass values were recorded during warmer months due to favourable environmental conditions for algal growth, but lower values during unfavourable winter and flood periods.