In many lowland streams, macrophytes are highly abundant and play a key role in ecosystem structure and function. However, no studies on annual stream metabolism have been conducted in streams with significant macrophyte abundance, despite the well-known effect on both gross primary production (GPP) and ecosystem respiration (ER). Macrophyte abundance in temperate streams is strongly seasonal, with highest biomass during summer and lowest during winter. We expected that this phenological pattern would drive annual fluctuations in GPP and ER. We measured daily metabolism for one year in two stream reaches, one with and one without macrophytes. Our results demonstrated that annual, aggregated GPP and ER were 2.2 and 1.3 times higher in the macrophyte reach. Furthermore, while daily GPP was the same between the two reaches during winter where biomass was negligible, GPP was higher during spring, summer and fall for the macrophyte reach. The range in daily ER was more constrained during summer, but more variable during fall and winter in the macrophyte reach relative to the non-macrophyte reach. Macrophyte abundance and chlorophyll-a controlled 80% of the variation in annual GPP for the macrophyte reach. Similarly, 63% of the variation in annual ER was controlled by macrophyte abundance together with discharge in the macrophyte reach. Although macrophytes enhanced GPP on an annual and seasonal time scale in agricultural lowland streams, both reaches were heterotrophic (i.e., GPP < ER) reflecting high organic matter supply from the landscape and in-stream retention and decomposition of organic matter within the macrophyte beds.

中文翻译：

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在农业低地溪流中，大型植物每天、季节性和每年都能增强河段范围的新陈代谢

在许多低地河流中，大型植物非常丰富，在生态系统结构和功能中起着关键作用。然而，尽管对总初级生产 (GPP) 和生态系统呼吸 (ER) 的影响众所周知，但尚未对具有显着大型植物丰度的河流进行年度河流代谢研究。温带河流中的大型植物丰度具有很强的季节性，夏季生物量最高，冬季最低。我们预计这种物候模式将推动 GPP 和 ER 的年度波动。我们测量了两个河流河段一年的每日新陈代谢，一个有大型植物，一个没有大型植物。我们的结果表明，在大型植物范围内，年度综合 GPP 和 ER 分别高出 2.2 和 1.3 倍。此外，虽然冬季两个河段之间的每日 GPP 相同，但生物量可以忽略不计，但大型植物河段在春季、夏季和秋季的 GPP 较高。在夏季，每日 ER 的范围受到更多限制，但在秋季和冬季，大型植物河段相对于非大型植物河段的变化更大。大型植物丰度和叶绿素-a 控制了大型植物河段年度 GPP 变化的 80%。同样，63% 的年度 ER 变化受大型植物丰度和大型植物河段的排放控制。尽管大型植物在农业低地河流中在年度和季节性时间尺度上提高了 GPP，但两个河段都是异养的（即 GPP <