Total Primary Production Research Articles

Recent Primary Production and Small Phytoplankton Contribution in the Yellow Sea during the Summer in 2016

The high nutrient concentration associated with the mixing dynamics of two warm and cold water masses supports high primary production in the Yellow Sea. Although various environmental changes have been reported, no recent information on small phytoplankton contribution to the total primary production as an important indicator for marine ecosystem changes is currently available in the Yellow Sea. The major objective of this study is to determine the small (< 2 μm) phytoplankton contribution to the total primary production in the Yellow Sea during August, 2016. In this study, we found relatively lower chlorophyll a concentrations in the water column than those previously reported in the central waters of the Yellow Sea. Moreover, the overall contribution of small phytoplankton (53.1%) to the total chlorophyll a concentration was considerably higher in this study than that (10.7%) observed previously. Based on the N/P ratio (67.6 ± 36.6) observed in this study, which is significantly higher than the Redfield ratio (16), we believe that phytoplankton experienced P-limiting conditions during the study period. The average daily carbon uptake rate of total phytoplankton in this study was 291.1 mg C m-2 d-1 (± 165.0 mg C m-2 d-1) and the rate of small phytoplankton was 205.7 mg C m-2 d-1 (± 116.0 mg C m-2 d-1) which is 71.9% (± 8.8%) of the total daily carbon uptake rate. This contribution of small phytoplankton observed in this study appears to be higher than that reported previously. Our recent measured primary production is approximately 50% lower than the previous values decades ago. The higher contributions of small phytoplankton to the total chlorophyll a concentration and primary production might be caused by P-limited conditions and this resulted in lower chlorophyll a concentration and total primary production in this study compared to previous studies.

Accelerated Nutrient Cycling and Increased Light Competition Will Lead to 21st Century Shrub Expansion in North American Arctic Tundra

AbstractRecent changes in species composition, and increases in shrub abundance in particular, have been reported as a result of warming in Arctic tundra. Despite these changes, the driving factors that control shrubification and its future trajectory remain uncertain. Here we used an ecosystem model, ecosys, to mechanistically represent the processes controlling recent and 21st century changes in plant functional type using RCP8.5 climate forcing across North American Arctic tundra. Recent and projected warming was modeled to deepen the active layer (spatially averaged by ~0.35 m by 2100) and thereby increase nutrient availability. Shrub productivity was modeled to increase across much of the tundra, particularly in Alaska and tundra‐boreal ecotones. Deciduous and evergreen shrubs increased from ~45% of total tundra ecosystem net primary productivity (NPP) in recent decades to ~70% by 2100. The increased canopy cover of shrubs reduced incoming shortwave radiation for low‐lying plants, causing declines in graminoids NPP from a current 35% of tundra NPP to 18%, and declines in nonvascular plants from 20% to 12%. The faster‐growing deciduous shrubs modeled with less efficient nutrient conservation dominated much of the low Arctic by 2100 where nutrient cycling became more rapid, while the slower‐growing evergreen shrubs modeled with more efficient nutrient conservation dominated a wider latitudinal range that extended to the high Arctic where nutrient cycling remained slower. We conclude that high‐latitude vegetation dynamics over the 21st century will depend strongly on soil nutrient dynamics, diversity in plant traits controlling nutrient uptake and conservation, and light competition.

Estimation of Annual Kara Sea Primary Production

Primary production of phytoplankton and ice and under-ice flora of the Kara Sea and regions thereof has been assessed using region-specific models and MODIS-Aqua satellite data for 2002–2015. Average annual primary production of phytoplankton calculated for the growing season (April–October) amounted to 165 mg С m–2 day–1. Annual primary production of phytoplankton was 35 g C/m2. Annual primary production of phytoplankton in the entire Kara Sea was 13 × 1012 g C. Annual primary production of ice and underice flora calculated using an integrated biophysical model was 1.7 × 1012 g C, or 12% of total primary production of the Kara Sea; the ice cover dynamics and published data were taken into account for the calculations. The results have been compared to earlier primary production estimates for the Kara Sea. The extent of the increase in sea productivity during warming of the Arctic and the decrease in ice cover area are discussed.

Study on the ecosystem construction of using ecopath model in inland waterway

In this paper, Ecopath with Ecosim 5.1 software is used to simulate the constructed water ecosystem of inland waterway. According to the characteristics of feeding relationship, the ecopath model of water ecosystem is divided into seven functional groups: phytoplankton, hydrophyte, zooplankton, herbivorous, omnivorous, polychaetes and detritus. By analyzing the important ecological parameters of the ecosystem, such as biomass, biomass / biomass, consumption / biomass, trophic level and ecological nutrient conversion efficiency, the software integrates the energy flow process of the ecosystem, the ratio of the total net primary production and the sum of all respiratory flows is 1.314, it’s indicating that the ecosystem is equilibrium. The research method of this paper can be widely used to evaluate the stability of the ecosystem of the domestic river.

Diatom frustules protect DNA from ultraviolet light

The evolutionary causes for generation of nano and microstructured silica by photosynthetic algae are not yet deciphered. Diatoms are single photosynthetic algal cells populating the oceans and waters around the globe. They generate a considerable fraction (20–30%) of all oxygen from photosynthesis, and 45% of total primary production of organic material in the sea. There are more than 100,000 species of diatoms, classified by the shape of the glass cage in which they live, and which they build during algal growth. These glass structures have accumulated for the last 100 million of years, and left rich deposits of nano/microstructured silicon oxide in the form of diatomaceous earth around the globe. Here we show that reflection of ultraviolet light by nanostructured silica can protect the deoxyribonucleic acid (DNA) in the algal cells, and that this may be an evolutionary cause for the formation of glass cages.

Logging disturbance shifts net primary productivity and its allocation in Bornean tropical forests.

Tropical forests play a major role in the carbon cycle of the terrestrial biosphere. Recent field studies have provided detailed descriptions of the carbon cycle of mature tropical forests, but logged or secondary forests have received much less attention. Here, we report the first measures of total net primary productivity (NPP) and its allocation along a disturbance gradient from old-growth forests to moderately and heavily logged forests in Malaysian Borneo. We measured the main NPP components (woody, fine root and canopy NPP) in old-growth (n=6) and logged (n=5) 1ha forest plots. Overall, the total NPP did not differ between old-growth and logged forest (13.5±0.5 and 15.7±1.5 Mg C ha-1 year-1 respectively). However, logged forests allocated significantly higher fraction into woody NPP at the expense of the canopy NPP (42% and 48% into woody and canopy NPP, respectively, in old-growth forest vs 66% and 23% in logged forest). When controlling for local stand structure, NPP in logged forest stands was 41% higher, and woody NPP was 150% higher than in old-growth stands with similar basal area, but this was offset by structure effects (higher gap frequency and absence of large trees in logged forest). This pattern was not driven by species turnover: the average woody NPP of all species groups within logged forest (pioneers, nonpioneers, species unique to logged plots and species shared with old-growth plots) was similar. Hence, below a threshold of very heavy disturbance, logged forests can exhibit higher NPP and higher allocation to wood; such shifts in carbon cycling persist for decades after the logging event. Given that the majority of tropical forest biome has experienced some degree of logging, our results demonstrate that logging can cause substantial shifts in carbon production and allocation in tropical forests.

Technological change and metal demand over time: What can we learn from the past?

This paper contributes to the understanding of metal demand development over time by illustrating the impacts of different aspects of technological change using historical data. We provide a direct, quantitative comparison of relative change in global primary production for 30 metals over 21 years (1993–2013), capturing the range and variation of demand development for different metals within this period. The aspects of technological change contributing to this variation are investigated in more depth for nine metals. Demand for 15 of the 30 metals increased significantly more than GDP between 1993 and 2013. For five metals, demand in 2013 was about or more than 400% of their demand in 1993. All of these metals had a total primary production of <100 kt in 2013. Concerning the metals under detailed investigation, comparatively high growth (demand2013> 500% demand1993) could be attributed to emerging technologies in the case of indium and cobalt. Comparatively low growth (demand2013 < 200% demand1993) was due to substitution of a technology in case of silver and caused by improvements regarding material efficiency and recycling in case of tin, palladium and platinum.

Decline of N and P Uptake in the Inner Protection Zone of a Terminal Reservoir during Inter-Basin Water Transfers

Inter-basin water transfer projects are designed to relieve water scarcity around the world. However, ecological problems relating to reductions in protection zone functions can occur during inter-basin transfers. This paper uses the largest inter-basin water transfer project in the world, namely, the South-to-North Water Transfer Project (SNWTP) in China, as an example to analyze the variation of Miyun Reservoir’s inner protection zone functions when water is transferred. Specifically, a riparian model (RIPAM) coupled with remote sensing data were used to calculate the nitrogen (N) and phosphorus (P) losses due to plant uptake, and these results were validated by in situ survey data. Then, correlations between water levels and N and P removal were analyzed. The results show that water table disturbances resulting from elevated water levels strongly influence the growth of plants and have obvious negative impacts on N and P removal in the inner protection zone. With the implementation of the middle route of the SNWTP, the water level of Miyun will rise to 150 m in 2020, and subsequently, the total net primary productivity (NPP) could decline by more than 40.90% from the level in 2015, while the N and P uptake could decline by more than 53.03% and 43.49%, respectively, from the levels in 2015, according to the modeling results. This will lead to declines in the inner protection zone’s defense effectiveness for N and P interception and increases in risks to the security of water resources. The results of this study provide useful knowledge for managing the defense function of the terminal reservoir’s inner protection zone and for ensuring that water quality is maintained during the diversion process.

Nitrogen Fixation by Trichodesmium and unicellular diazotrophs in the northern South China Sea and the Kuroshio in summer

Distribution of diazotrophs and their nitrogen fixation activity were investigated in the northern South China Sea (nSCS) and the Kuroshio from July 16th to September 1st, 2009. N2 fixation activities in whole seawater and <10 μm fraction at the surface were measured by acetylene reduction assay. Higher activities were observed at the East China Sea (ECS) Kuroshio and the nSCS shelf. The nSCS basin showed a low N2 fixation activity. The <10 μm fractions (unicellular diazotrophs) contributed major portion to the whole-water activity in the survey time, indicating that nanoplanktonic cyanobacterias were the major diazotrophs in the survey area. Daily N2 fixation rates of Trichodesmium ranged from 0.11 to 9.83 pmolNtrichome−1 d−1 with an average of 4.03 pmolNtrichome−1 d−1. The Luzon Strait and the ECS Kuroshio had higher N2 fixation rates of Trichodesmium than the nSCS shelf and basin. Calculated activities of Trichodesmium at most stations were moderately low compared with that of the whole-water. The contribution of N2 fixation by the whole-water to primary production ranged from 1.7% to 18.5%. The estimated amount of new nitrogen introduced by Trichodesmium contributed up to 0.14% of the total primary production and 0.41% of the new production in the Luzon Strait.

Eddy Covariance Measurements of Carbon dioxide (CO2) Exchange in Pichavaram Mangrove Ecosystem, Southeast Coast of India

Net Ecosystem Productivity (NEP) and Net Ecosystem Exchange (NEE) of carbon dioxide (CO2) between the mangrove forest and the atmosphere were assessed during May 2016 to April 2017 in the Pichavaram mangrove ecosystem in India. An eddy covariance (EC) flux tower of about 10 m height was established in the middle portion of the mangrove forests to have a maximum carbon footprint from the mangroves. The EC tower was established to investigate whether the mangrove ecosystem acts as a sink or source of CO2. The monthly mean CO2 concentration varied from 376 ppm in July 2016 (during day time) to 466 ppm in December 2016 at night time. The EC based NEE showed a positive CO2 flux ranging from 4 μmol m-2s-1 in July 2016 to 6 μmol m-2s-1 in February 2017 during the night time. This was mainly due to respiration of the mangrove ecosystem. Negative CO2 flux values ranging from – 8 μmol m-2 s-1 (March 2017) to -18 μmol m-2 s-1 (August 2016) was observed during daytime, due to photosynthesis. The monthly analysis of the NEE during the daytime and night clearly indicate that the NEP of the Pichvaram mangrove was found to be positive throughout the study period suggesting that the Pichvaram mangrove ecosystem acts as a sink for CO2.The measured annual Net Ecosystem Productivity during the study period was 345 g Cm-2year-1, which is higher than the NEP reported for Sundraban mangroves (249 g C m-2 year-1). The total Gross Primary Productivity (GPP) and ecosystem respiration (Re) of the study area for the annual cycle was 2305 g C m-2 year-1and 1072 g C m-2 year-1, respectively. A long term study is needed to draw a logical conclusion on carbon sequestration potentials of this mangrove as well as to find out the role of environmental factors controlling CO2 fluxes.Keywords: Pichavaram Mangrove, Carbon dioxide, Eddy covariance, Net Ecosystem Productivity, Carbon sequestration

Effects of Terrestrial Organic Matter on Aquatic Primary Production as Mediated by Pelagic\u2013Benthic Resource Fluxes

Flows of energy and matter across habitat boundaries can be major determinants of the functioning of recipient ecosystems. It is currently debated whether terrestrial dissolved organic matter (tDOM) is a resource subsidy or a resource subtraction in recipient lakes. We present data from a long-term field experiment in which pelagic phosphorus concentration and whole-ecosystem primary production increased with increasing tDOM input, suggesting that tDOM acted primarily as a direct nutrient subsidy. Piecewise structural equation modeling supports, however, a substantial contribution of a second mechanism: colored tDOM acted also as a resource subtraction by shading benthic algae, preventing them from intercepting nutrients released across the sediment–water interface. Inhibition of benthic algae by colored tDOM thus indirectly promoted pelagic algae and whole-ecosystem primary production. We conclude that cross-ecosystem terrestrial DOM inputs can modify light and nutrient flows between aquatic habitats and alter the relative contributions of benthic and pelagic habitats to total primary production. These results are particularly relevant for shallow northern lakes, which are projected to receive increased tDOM runoff.

Spatio-temporal variability of the size-fractionated primary production and chlorophyll in the Levantine Basin (northeastern Mediterranean)

Summary Spatial and temporal variations in size-fractionated primary production (PP) and chl a, in relation to ambient physicochemical parameters, were studied in the three distinct ecosystems of northeastern Levantine Basin namely eutrophic Mersin Bay, mesotrophic Rhodes Gyre, and oligotrophic offshore waters. These ecosystems were visited in July and September 2012 and March and May 2013. Total primary production (TPP) rates ranged between 0.22 and 17.8 mg C m−3 h−1 within the euphotic zone, whereas depth-integrated TPP rates were in the range 21.5–348.8 mg C m−2 h−1 (mean: 105.5 ± 88 mg C m−2 h−1), with the lowest rates recorded for offshore waters. Similar spatio-temporal variations were observed in chl a concentrations, ranging from 2.3 to 117.9 mg m−2 (mean: 28.9 ± 24.9 mg m−2) in the study area. The Mersin Bay TPP rates have exceeded almost 8–12 times those measured in the offshore waters and the Rhodes Gyre; however, the chl a concentrations measured in coastal waters (0.343 mg m−3) and the Rhodes Gyre (0.308 mg m−3) were only threefold larger than the offshore values. PP and chl a were dominated by picoplankton in the study area whereas small nanoplankton, being the most active, displayed the highest assimilation ratio in offshore waters (6.8) and the Rhodes Gyre (2.8). In the upper-layer waters depleted of P (0.02–0.03 μM) of the northeastern Mediterranean, a positive correlation was observed between NO3 + NO2 and PP (and thus, chl a), which strongly suggests that reactive P and inorganic nitrogen are co-limiting factors in the production and biomass distribution of the phytoplankton community in both shelf and offshore waters.

Comparative study of Jiaozhou Bay ecosystem based on an Ecopath model

PDF HTML阅读 XML下载 导出引用 引用提醒 基于Ecopath模型的胶州湾生态系统比较研究 DOI: 作者: 作者单位: 1. 中国水产科学研究院 南海水产研究所, 农业部南海外海渔业开发重点实验室, 广东 广州 510300;2. 上海海洋大学 海洋科学学院, 上海 201306;3. 中国水产科学研究院 黄海水产研究所, 山东 青岛 266071 作者简介: 马孟磊(1992-),男,硕士研究生,从事渔业资源和海洋生态研究.E-mail:nysymml@163.com 通讯作者: 中图分类号: S931 基金项目: 国家重点基础研究发展计划项目（2015CB452904）；广东省自然科学基金项目（2015A030313785）；广州市科技计划项目珠江科技新星专项（2014J2200020）. Comparative study of Jiaozhou Bay ecosystem based on an Ecopath model Author: Affiliation: 1. Key Laboratory of Open-Sea Fishery Development, Ministry of Agriculture;South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China;2. College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;3. Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:文章根据2015-2016年胶州湾渔业资源与生态环境调查数据，并收集20世纪80年代胶州湾渔业资源数据，利用Ecopath with Ecosim 6.5（EwE）软件构建了由21个功能组组成的胶州湾1980-1982年和2015-2016年两个时期的Ecopath模型，比较分析了不同时期胶州湾生态系统结构和功能变化以及系统发育特征。研究结果显示，与1980-1982年生态系统相比，胶州湾2015-2016年生态系统中大型底层鱼类生物量减少，菲律宾蛤仔（）生物量提高，渔获物产出以菲律宾蛤仔为主，渔获平均营养级降低，系统能量转化效率从1980-1982年的15.83%提高到2015-2016年的16.35%，能量流动始终以牧食食物链为主。关键种分析表明，胶州湾生态系统两个时期的关键种均为菲律宾蛤仔。此外，与1980-1982年生态系统相比，2015-2016年胶州湾生态系统整体规模增大，净生产量提高5倍，系统总初级生产量与总呼吸量的比值由1980-1982年的1.267提高到2015-2016年的2.518，系统连接指数、杂食指数与Finn's循环指数和平均路径长度均减小，说明在过去30多年胶州湾生态系统成熟度和稳定性不断降低，发育过程出现由成熟向幼态的逆行演替现象，目前处于不稳定的幼态阶段。 Abstract:Based on survey data from fishery resources and on the ecological environment in the Jiaozhou Bay during 2015-2016 and 1980-1982, we constructed ecosystem models of Jiaozhou Bay for these two periods using Ecopath with Ecosim 6.5 software. The models of the Jiaozhou Bay consisted of 21 functional groups. Based on the two models, we compared and analyzed the differences in ecosystem structure, function, and attributes. The trophic structure of the Jiaozhou Bay ecosystem in 2015-2016 had changed, with a decrease in the proportion of top predator biomass and an increase in the proportion of R. philippinarum, and the mean trophic level of fishery catch had reduced. The energy flow of the Jiaozhou Bay ecosystem was mainly dominated by a grazing food chain, and the system-energy-transfer efficiencies increased from 15.83% in 1980-1982 to 16.35% in 2015-2016. Analysis of the keystones species for Jiaozhou bay ecosystem indicated that is a keystones species in both the 1980-1982 and 2015-2016 periods. Compared with the 1980s ecosystem, the scale of the Jiaozhou Bay system had increased and the net system production increased by 5 times by 2015. The parameters of the ratio of total primary production to total respiration increased from 1.267 in 1980-1982 to 2.518 in 2015-2016. In addition, the connectance index, system omnivory index, and Finn's cycling index decreased from the 1980s to 2015-2016. In conclusion, the maturity and stability of the Jiaozhou Bay ecosystem has been reduced over the past 30 years, and the system has shown a trend moving from a mature stage to an immature stage. In short, the Jiaozhou Bay ecosystem is currently in an unstable, young stage. 参考文献 相似文献 引证文献

Large Plankton Enhance Heterotrophy Under Experimental Warming in a Temperate Coastal Ecosystem

Microbes are key players in oceanic carbon fluxes. Temperate ecosystems are seasonally variable and thus suitable for testing the effect of warming on microbial carbon fluxes at contrasting oceanographic conditions. In four experiments conducted in February, April, August and October 2013 in coastal NE Atlantic waters, we monitored microbial plankton stocks and daily rates of primary production, bacterial heterotrophic production and respiration at in situ temperature and at 2 and 4°C over ambient values during 4-day incubations. Ambient total primary production (TPP) exceeded total community respiration (< 200 µm, TR) in winter and fall but not in spring and summer. The bacterial contribution to ecosystem carbon fluxes was low, with bacterial production representing on average 6.9 ± 3.2% of TPP and bacterial respiration (between 0.8 and 0.2 µm) contributing on average 35 ± 7% to TR. Warming did not result in a uniform increase in the variables considered, and most significant effects were found only for the 4°C increase. In the summer and fall experiments, under warm and nutrient-deficient conditions, the net TPP/TR ratio decreased by 39 and 34% in the 4°C treatment, mainly due to the increase in respiration of large organisms rather than bacteria. Our results indicate that the interaction of temperature and substrate availability in determining microbial carbon fluxes has a strong seasonal component in temperate planktonic ecosystems, with temperature having a more pronounced effect and generating a shift toward net heterotrophy under more oligotrophic conditions as found in summer and early fall.

Food web structure and ecosystem properties of the largest impounded lake along the eastern route of China's South-to-North Water Diversion Project

Hongze Lake (HZL) is the largest impounded lake along the eastern route of China's South-to-North Water Diversion Project. However, there is surprisingly little ecological understanding on this important ecosystem, especially under the potential water diversion threats. Here, a mass-balance model was constructed to characterize trophic structure and ecosystem properties of HZL. The model outputs indicated that small sized fishes have dominated the food web, and fishery resources were suffered from high pressures of overfishing. Mandarin fish, Northern snakehead, Other piscivores and Large culters occupied the top trophic niche, while macrophytes, phytoplankton and detritus consisted of the main energy sources. HZL food web was fairly based on two main food chains: primary production (49.9%) and detritus pool (50.1%), but transfer efficiencies in both chains were relatively low as 6.37% and 6.49%, respectively. Predator-prey interactions, trophic cascading effects and competition of different components were also exhibited in the mixed trophic impacts map. Results from the network analysis suggested that the HZL ecosystem was a relatively mature ecosystem since the total primary production to respiration (TPP/TR) and to biomass (TPP/TB) were 1.138 and 6.922, and the Finn Cycling Index was 6.77%. Nevertheless, the relatively low values of Connectance Index (0.195) and System Omnivory Index (0.089), together with Finn's Mean path Length (2.849) also indicated that the food web structure was vulnerable, characterized by linear, rather than web-like features. Our results suggested that the HZL ecosystem would be potentially affected by the future inter-basin water diversion, and thus ecosystem-based strategies were also presented accordingly.

On the relationship between sub-daily instantaneous and daily total gross primary production: Implications for interpreting satellite-based SIF retrievals

Spatially and temporally continuous estimation of plant photosynthetic carbon fixation (or gross primary production, GPP) is crucial to our understanding of the global carbon cycle and the impact of climate change. Besides spatial, seasonal and interannual variations, GPP also exhibits strong diurnal variations. Satellite retrieved solar-induced chlorophyll fluorescence (SIF) provides a spatially continuous, but temporally discrete measurement of plant photosynthesis, and has the potential to be used to estimate GPP at global scale. However, it remains unclear whether the seasonal time series of SIF snapshots taken at a fixed time of the day can be used to infer daily total GPP variation at spatial and seasonal scales. In this study, we first used GPP estimates from 135 eddy covariance flux sites, covering a wide range of geographic locations and biome types, to investigate the relationship between the instantaneous GPP (GPPinst) and daily GPP (GPPdaily) on the seasonal course for different times of the day. Latitudinal and diurnal patterns were found to correspond to variations in photosynthetically active radiation (PAR) and light use efficiency (LUE), respectively. We then used the Soil-Canopy Observation Photosynthesis and Energy Balance (SCOPE) model and the FluxCom GPP product to investigate the instantaneous and daily SIF-GPP relationships at five flux tower sites along a latitudinal gradient and at a global scale for different biome types. The results showed that daily SIF had a stronger linear correlation with daily GPP than instantaneous SIF at the seasonal scale, with an instantaneous to daily SIF conversion factor following the latitudinal and seasonal pattern driven by PAR. Our study highlights the necessity to take the latitudinal and diurnal factors into consideration for SIF-GPP relationship analyses or for physiological phenology analyses based on SIF.

Food Composition for Blue Mussels (Mytilus edulis) in the Menai Strait, UK, Based on Physical and Biochemical Analyses

To clarify the composition of food ingested by blue mussels (Mytilus edulis) in the Menai Strait, where the largest mussel bed in the United Kingdom lies, hydrodynamic observations with organic carbon and nitrogen biochemical analysis were conducted. This strait is characterized by a narrow channel and wide tidal flats with large tidal mixing that influences the distribution of particulate organic matter (POM), which is food formussels. The maximum velocities of the tidal currents were estimated to be 0.5–1.0 m s-1 during northeastward flow and 0.6–1.3 m s-1 during southwestward flow. The residual current was southwestward and the water flux was estimated to be 510 m3 s-1. Field observations indicate that the inflow of pelagic phytoplankton into the strait mainly occurred in the northern region of the strait. Resuspended benthic primary production, however, also causes higher chlorophyll-a concentration in the central region of the strait near the mussel bed and its contribution to mussel growth was estimated to be 22%–50%. The concentrations of chlorophyll-a and particulate organic carbon indicated that the POM in the strait mainly originated from detritus. Benthic microalgae is, however, an important factor to understand the total primary production in the strait. The consumption of the primary producers was estimated to be approximately 6.3 t C day-1. In the phytoplankton community, pelagic and thycopelagic (living in both pelagic and benthic environments) species comprised 59.3%–77.2% and 12.8%–40.7% of the cells, respectively. The primary production by resuspended benthic species in the Liverpool Bay region was considerably larger than that in the Menai Strait region. As a conclusion, theMenai Strait is an area with complex hydrodynamic conditions causing horizontal advection and resuspension of both pelagic and benthic phytoplankton, and this complex would cause the most suitable condition for mussel production.

Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer

Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650L) were filled with 200μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mgCmgchl a−1h−1) decreased with elevated CO2, clearly reducing rates of total gross primary production (mgCL−1h−1). Rates of cell-specific bacterial productivity (μgCcell−1h−1) also decreased under elevated CO2, yet total bacterial production (μgCL−1h−1) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations >2× present day (>780ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate+nitrite (NOx) availability. At NOx concentrations <1.5μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may suppress this OA response but cause a similar decline.

Long‐term nutrient addition alters arthropod community composition but does not increase total biomass or abundance

A simple bottom–up hypothesis predicts that plant responses to nutrient addition should determine the response of consumers: more productive and less diverse plant communities, the usual result of long‐term nutrient addition, should support greater consumer abundances and biomass and less consumer diversity. We tested this hypothesis for the response of an aboveground arthropod community to an uncommonly long‐term (24‐year) nutrient addition experiment in moist acidic tundra in arctic Alaska. This experiment altered plant community composition, decreased plant diversity and increased plant production and biomass as a deciduous shrub, Betula nana, became dominant. Consistent with strong effects on the plant community, nutrient addition altered arthropod community composition, primarily through changes to herbivore taxa in the canopy‐dwelling arthropod assemblage and detritivore taxa in the ground assemblage. Surprisingly, however, the loss of more than half of plant species was accompanied by negligible changes to diversity (rarefied richness) of arthropod taxa (which were primarily identified to family). Similarly, although long‐term nutrient addition in this system roughly doubles plant production and biomass, arthropod abundance was either unchanged or decreased by nutrient addition, and total arthropod biomass was unaffected. Our findings differ markedly from the handful of terrestrial studies that have found bottom‐up diversity cascades and productivity responses by consumers to nutrient addition. This is probably because unlike grasslands and salt marshes (where such studies have historically been conducted), this arctic tundra community becomes less palatable, rather than more so, after many years of nutrient addition due to increased dominance of B. nana. Additionally, by displacing insulating mosses and increasing the cover of shrubs that cool and shade the canopy microenvironment, fertilization may displace arthropods keenly attuned to microclimate. These results indicate that terrestrial arthropod assemblages may be more constrained by producer traits (i.e. palatability, structure) than they are by total primary production or producer diversity.

What controls variation in carbon use efficiency among Amazonian tropical forests?

AbstractWhy do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPPwood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (Ra; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times &lt;40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times &gt;40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times &gt;40 yrs and in stands with lower fertility, but changes to long‐term mean annual temperatures do not impact CUE.