Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton-bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes
Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton-bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes
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DOI：
10.5194/bg-12-697-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
Helbling, E. W.
中科院分区：
文献类型：
--
作者：
Carrillo, P.;Medina-Sanchez, J. M.;Helbling, E. W.
全球变暖的一个间接影响是上层混合层(UML)深度的减少，导致生物体暴露在更高水平的紫外线(UVR，280-400 nm)和光合作用有效辐射(PAR，400-700 nm)下。这会影响初级和细菌的生产，以及浮游植物-细菌的共生关系。在对来自西班牙南部两个低营养湖泊(高紫外线与低紫外线水域)的天然微微型浮游生物和纳米浮游生物群落进行的现场实验中，对与浮游植物和细菌新陈代谢相关的变量进行了UVR和降低UVR深度的综合影响评估。低UVR对表层初级生产力(PP)和异养细菌产量(HBP)的负效应在低UVR湖大于高UVR湖，对浮游植物的负效应强于异养细菌群落。在UVR和层积增加的情况下，有机碳(EOC)排泄率超过细菌碳需求(BCD；即BCD：EOC(%))的高UVR湖泊浮游植物与细菌的共生关系得到加强。这不发生在低UVR湖(即BCD：EOC(%)比率>；100)。在低紫外线辐射湖泊中发现的对浮游植物和细菌的更大的紫外线辐射破坏以及它们的共生相互作用的减弱表明，作为与全球气候变化相关的压力因素，这些生态系统将特别容易受到紫外线辐射和层化增加的影响。因此，我们的发现可能对地中海地区富营养化湖泊的碳循环具有重要意义。
An indirect effect of global warming is a reduction in the depth of the upper mixed layer (UML) causing organisms to be exposed to higher levels of ultraviolet (UVR, 280-400 nm) and photosynthetically active radiation (PAR, 400-700 nm). This can affect primary and bacterial production as well as the commensalistic phytoplankton-bacteria relationship. The combined effects of UVR and reduction in the depth of the UML were assessed on variables related to the metabolism of phytoplankton and bacteria, during in situ experiments performed with natural pico- and nanoplankton communities from two oligotrophic lakes with contrasting UVR transparency (high-UVR versus low-UVR waters) of southern Spain. The negative UVR effects on epilimnetic primary production (PP) and on heterotrophic bacterial production (HBP), intensified under increased stratification, were higher in the low-UVR than in the high-UVR lake, and stronger on the phytoplanktonic than on the heterotrophic bacterial communities. Under UVR and increased stratification, the commensalistic phytoplankton-bacteria relationship was strengthened in the high-UVR lake where excretion of organic carbon (EOC) rates exceeded the bacterial carbon demand (BCD; i.e., BCD: EOC(%) ratio < 100). This did not occur in the low-UVR lake (i.e., BCD: EOC(%) ratio > 100). The greater UVR damage to phytoplankton and bacteria and the weakening of their commensalistic interaction found in the low-UVR lake indicates that these ecosystems would be especially vulnerable to UVR and increased stratification as stressors related to global climate change. Thus, our findings may have important implications for the carbon cycle in oligotrophic lakes of the Mediterranean region.