Cyanobacteria are oxygenic photosynthetic Gram-negative bacteria that can form potentially toxic blooms in eutrophic and slow flowing aquatic ecosystems. Bloom toxicity varies spatially and temporally, but understandi...Cyanobacteria are oxygenic photosynthetic Gram-negative bacteria that can form potentially toxic blooms in eutrophic and slow flowing aquatic ecosystems. Bloom toxicity varies spatially and temporally, but understanding the mechanisms that drive these changes remains largely a mystery. Changes in bloom toxicity may result from changes in intracellular toxin pool sizes of cyanotoxins with differing molecular toxicities, and/or from changes in the cell concentrations of toxic and non-toxic cyanobacterial species or strains within bloom populations. We show here how first-order rate kinetics at the cellular level can be used to explain how environmental conditions drive changes in bloom toxicity at the ecological level. First order rate constants can be calculated for changes in cell concentration( μ_c : specific cell division rate) or the volumetric biomass concentration( μ_g : specific growth rate) between short time intervals throughout the cell cycle. Similar first order rate constants can be calculated for changes in nett volumetric cyanotoxin concentration( μ_(tox) : specific cyanotoxin production rate) over similar time intervals. How μ_c(or μ_g) covaries with μ tox over the cell cycle shows conclusively when cyanotoxins are being produced and metabolised, and how the toxicity of cells change in response to environment stressors. When μ_(tox)/μ_c >1, cyanotoxin cell quotas increase and individual cells become more toxic because the nett cyanotoxin production rate is higher than the cell division rate. When μ_(tox)/μ_c =1, cell cyanotoxin quotas remains fixed because the nett cyanotoxin production rate matches the cell division rate. When μ_(tox)/μ_c <1, the cyanotoxin cell quota decreases because either the nett cyanotoxin production rate is lower than the cell division rate, or metabolic breakdown and/or secretion of cyanotoxins is occurring. These fundamental equations describe cyanotoxin metabolism dynamics at the cellular level and provide the necessary physiological background to understand how environmental stressors drive changes in bloom toxicity.展开更多
The responses of photosynthesis and growth of forest trees to rising atmospheric carbon dioxide concentration [CO2] are modified by ecosystem conditions. With the exception of a few, the vast majority of empirical stu...The responses of photosynthesis and growth of forest trees to rising atmospheric carbon dioxide concentration [CO2] are modified by ecosystem conditions. With the exception of a few, the vast majority of empirical studies on the impact of future high CO2 levels on forest trees have focused on [CO2] alone or in combination with an environmental factor. This paper uses the case of CO2 × nutrient and CO2 × nutrient-related interactions to evaluate the relative value of single or multiple ecosystem factors in determining the responses of photosynthesis and growth to elevated [CO2]. A comprehensive literature search was conducted with Google Scholar. The findings show a consensus among studies that CO2 and nutrient availability have synergistic effects on photosynthesis and growth. However, combinations of nutrient availability with temperature or moisture modify the CO2 effect in ways different from nutrient availability alone. To increase the predictive power of empirical studies, it is recommended that conclusions on the responses of forest trees to elevated atmospheric [CO2] be based on interactions with multiple, rather than single, ecosystem conditions.展开更多
Aims Habitat loss and fragmentation are the main threats to biodiversity in tropical forests.Agroecosystems such as shaded cocoa plantations(SCP)provide refuge for tropical forest biota.However,it is poorly known whet...Aims Habitat loss and fragmentation are the main threats to biodiversity in tropical forests.Agroecosystems such as shaded cocoa plantations(SCP)provide refuge for tropical forest biota.However,it is poorly known whether the interspecific ecological interactions are also maintained in these transformed habitats.We evaluated the diversity,reproductive status and photosynthetic metabolism(CAM or C3)of the epiphytic orchid community,and their interactions with host trees(phorophytes)in SCP compared to tropical rainforest(TRF).Methods In southeastern Mexico,three sites each in TRF and SCP were studied,with four 400 m2 plots established at each site to record all orchids and their phorophytes.We determined the reproductive(adult)or non-reproductive(juvenile)status of each orchid individual in relation to the presence or absence,respectively,of flowers/fruits(or remnants),and assigned the photosynthetic pathway of each orchid species based in literature.We used true diversity and ecological networks approaches to analyze orchid diversity and orchid–phorophyte interactions,respectively.Important Findings In total,607 individuals belonging to 47 orchid species were recorded.Orchid diversity was higher in TRF(19 effective species)than in SCP(11 effective species)and only seven species were shared between the two habitats.CAM orchid species were more frequent in SCP(53%)than in TRF(14%).At the community level the proportion of non-reproductive and reproductive orchid species and the nested structure and specialization level of the TRF orchid–phorophyte network were maintained in SCP.However,only a subset of TRF epiphytic orchids remains in SCP,highlighting the importance of protecting TRF.Despite this difference,shaded agroecosystems such as SCP can maintain some of the diversity and functions of natural forests,since the SCP epiphytic orchid community,mainly composed of CAM species,and its phorophytes constitute a nested interaction network,which would confer robustness to disturbances.展开更多
文摘Cyanobacteria are oxygenic photosynthetic Gram-negative bacteria that can form potentially toxic blooms in eutrophic and slow flowing aquatic ecosystems. Bloom toxicity varies spatially and temporally, but understanding the mechanisms that drive these changes remains largely a mystery. Changes in bloom toxicity may result from changes in intracellular toxin pool sizes of cyanotoxins with differing molecular toxicities, and/or from changes in the cell concentrations of toxic and non-toxic cyanobacterial species or strains within bloom populations. We show here how first-order rate kinetics at the cellular level can be used to explain how environmental conditions drive changes in bloom toxicity at the ecological level. First order rate constants can be calculated for changes in cell concentration( μ_c : specific cell division rate) or the volumetric biomass concentration( μ_g : specific growth rate) between short time intervals throughout the cell cycle. Similar first order rate constants can be calculated for changes in nett volumetric cyanotoxin concentration( μ_(tox) : specific cyanotoxin production rate) over similar time intervals. How μ_c(or μ_g) covaries with μ tox over the cell cycle shows conclusively when cyanotoxins are being produced and metabolised, and how the toxicity of cells change in response to environment stressors. When μ_(tox)/μ_c >1, cyanotoxin cell quotas increase and individual cells become more toxic because the nett cyanotoxin production rate is higher than the cell division rate. When μ_(tox)/μ_c =1, cell cyanotoxin quotas remains fixed because the nett cyanotoxin production rate matches the cell division rate. When μ_(tox)/μ_c <1, the cyanotoxin cell quota decreases because either the nett cyanotoxin production rate is lower than the cell division rate, or metabolic breakdown and/or secretion of cyanotoxins is occurring. These fundamental equations describe cyanotoxin metabolism dynamics at the cellular level and provide the necessary physiological background to understand how environmental stressors drive changes in bloom toxicity.
文摘The responses of photosynthesis and growth of forest trees to rising atmospheric carbon dioxide concentration [CO2] are modified by ecosystem conditions. With the exception of a few, the vast majority of empirical studies on the impact of future high CO2 levels on forest trees have focused on [CO2] alone or in combination with an environmental factor. This paper uses the case of CO2 × nutrient and CO2 × nutrient-related interactions to evaluate the relative value of single or multiple ecosystem factors in determining the responses of photosynthesis and growth to elevated [CO2]. A comprehensive literature search was conducted with Google Scholar. The findings show a consensus among studies that CO2 and nutrient availability have synergistic effects on photosynthesis and growth. However, combinations of nutrient availability with temperature or moisture modify the CO2 effect in ways different from nutrient availability alone. To increase the predictive power of empirical studies, it is recommended that conclusions on the responses of forest trees to elevated atmospheric [CO2] be based on interactions with multiple, rather than single, ecosystem conditions.
基金supported by Consejo Nacional de Ciencia y Tecnología[fellowship 250340 to J.M.L]Instituto de Ecología,A.C.[20030-10144]This manuscript was written during the postdoctoral research of J.M.L.,supported by the Secretaría de Educación Pública-Programa para el Desarrollo Profesional Docente[grant 511-6/17-8702].
文摘Aims Habitat loss and fragmentation are the main threats to biodiversity in tropical forests.Agroecosystems such as shaded cocoa plantations(SCP)provide refuge for tropical forest biota.However,it is poorly known whether the interspecific ecological interactions are also maintained in these transformed habitats.We evaluated the diversity,reproductive status and photosynthetic metabolism(CAM or C3)of the epiphytic orchid community,and their interactions with host trees(phorophytes)in SCP compared to tropical rainforest(TRF).Methods In southeastern Mexico,three sites each in TRF and SCP were studied,with four 400 m2 plots established at each site to record all orchids and their phorophytes.We determined the reproductive(adult)or non-reproductive(juvenile)status of each orchid individual in relation to the presence or absence,respectively,of flowers/fruits(or remnants),and assigned the photosynthetic pathway of each orchid species based in literature.We used true diversity and ecological networks approaches to analyze orchid diversity and orchid–phorophyte interactions,respectively.Important Findings In total,607 individuals belonging to 47 orchid species were recorded.Orchid diversity was higher in TRF(19 effective species)than in SCP(11 effective species)and only seven species were shared between the two habitats.CAM orchid species were more frequent in SCP(53%)than in TRF(14%).At the community level the proportion of non-reproductive and reproductive orchid species and the nested structure and specialization level of the TRF orchid–phorophyte network were maintained in SCP.However,only a subset of TRF epiphytic orchids remains in SCP,highlighting the importance of protecting TRF.Despite this difference,shaded agroecosystems such as SCP can maintain some of the diversity and functions of natural forests,since the SCP epiphytic orchid community,mainly composed of CAM species,and its phorophytes constitute a nested interaction network,which would confer robustness to disturbances.
