氮沉降增加将影响草原生态系统固碳,但如何影响草原生态系统CO_2交换目前为止还没有定论。同时,不同类型和剂量氮素对生态系统CO_2交换影响的差异也不明确。选取内蒙古额尔古纳草甸草原,开展了不同类型氮肥和不同剂量氮素添加条件下生...氮沉降增加将影响草原生态系统固碳,但如何影响草原生态系统CO_2交换目前为止还没有定论。同时,不同类型和剂量氮素对生态系统CO_2交换影响的差异也不明确。选取内蒙古额尔古纳草甸草原,开展了不同类型氮肥和不同剂量氮素添加条件下生态系统CO_2交换的野外测定。实验设置尿素和缓释尿素2种类型氮肥各5个剂量水平(0、5.0、10.0、20.0和50.0g N·m^(–2)·a^(–1))。结果显示,生长季初期及中期降雨量低时,氮素添加抑制生态系统CO_2交换;而生长季末期降雨量较高时促进生态系统CO_2交换。随着氮素添加水平的提高,NEE和GEP均显著增加,当氮素添加量达到10 g N·m^(–2)·a^(–1)时,NEE和GEP的响应趋于饱和。2种氮肥(尿素和缓释尿素)仅在施氮量为5 g N·m^(–2)·a^(–1)时,缓释尿素对生态系统CO_2交换的促进作用显著大于尿素,在其它添加剂量时差异不显著。研究结果表明:氮素是该草甸草原生态系统的重要限制因子,但氮沉降增加对生态系统CO_2交换的影响强烈地受降雨量与降雨季节分配的限制,不同氮肥(尿素和缓释尿素)对生态系统CO_2交换作用存在差异。展开更多
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
文摘氮沉降增加将影响草原生态系统固碳,但如何影响草原生态系统CO_2交换目前为止还没有定论。同时,不同类型和剂量氮素对生态系统CO_2交换影响的差异也不明确。选取内蒙古额尔古纳草甸草原,开展了不同类型氮肥和不同剂量氮素添加条件下生态系统CO_2交换的野外测定。实验设置尿素和缓释尿素2种类型氮肥各5个剂量水平(0、5.0、10.0、20.0和50.0g N·m^(–2)·a^(–1))。结果显示,生长季初期及中期降雨量低时,氮素添加抑制生态系统CO_2交换;而生长季末期降雨量较高时促进生态系统CO_2交换。随着氮素添加水平的提高,NEE和GEP均显著增加,当氮素添加量达到10 g N·m^(–2)·a^(–1)时,NEE和GEP的响应趋于饱和。2种氮肥(尿素和缓释尿素)仅在施氮量为5 g N·m^(–2)·a^(–1)时,缓释尿素对生态系统CO_2交换的促进作用显著大于尿素,在其它添加剂量时差异不显著。研究结果表明:氮素是该草甸草原生态系统的重要限制因子,但氮沉降增加对生态系统CO_2交换的影响强烈地受降雨量与降雨季节分配的限制,不同氮肥(尿素和缓释尿素)对生态系统CO_2交换作用存在差异。
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.
