Phosphorus and ammonia excretion by planktonic protists
Phosphorus and ammonia excretion by planktonic protists
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DOI：
10.1016/s0025-3227(96)00106-5
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发表时间：
1997-06-01
期刊：
影响因子：
2.9
通讯作者：
Dolan, JR
中科院分区：
文献类型：
--
作者：
Dolan, JR
食草动物的排泄物是有机颗粒(浮游植物和细菌)生产者的营养物质正磷酸盐和氨的重要来源。排泄物可能由最小的颗粒消耗者浮游原生动物控制，因为单位重量的代谢率通常与大小成反比。然而，原生生物是一个异质的组合，大小超过3个数量级，包括混合营养的形式，同时受益于光合作用和颗粒物质的摄取。分析了原生生物、纤毛虫和鞭毛虫的排泄率，包括异养和混合营养，以确定与细胞大小和生长速度的关系。较小的原生动物，如鞭毛虫，表现出比纤毛虫等较大的原生动物更高的特定重量排泄率。以干重(DW)表示的最大排泄率(EXCR)与大小之间的关系式为：对于正磷酸盐，对数EXCR(µg P单元(-1)h(-1))=-2.101+0.570对数大小(mg DW单元(-1))，r=0.847，n=12；对于氨，LOG EXCR(µg N单元(-1)h(-1))=-1.388+0.622 mg DW单元(-1)，r=0.899，混合营养原生生物的最大排泄率与同等大小的异养原生生物相似。对于磷，原生动物的最大重量比排泄率高于通过对后生浮游动物建立的大多数大小-排泄率关系的外推而预测的。氨的最大排泄率接近后生动物方程中报道的关系式的平均值。快速生长的原生动物相对于氨的排泄量似乎远远超过红场原子比16：1，即排泄量N：P的2：1-8：1。对于正磷酸盐，排泄率可以根据细胞大小和生长速度进行预测。相反，在10个物种中，有5个物种的氨排泄与生长速率的相关性很弱，而在其余的物种中，氨的排泄与生长速率无关，这可能是由于氮素排泄形式的多样性所致。因此，浮游原生生物在正磷酸盐的再生中可能比氨更重要。然而，磷排泄的明显规模和简单性可能是将主要排泄化合物--可溶性活性磷--完全视为正磷酸盐的产物。(C)Elsevier Science B.V.保留所有权利。
Excretion by grazers is an important source of the nutrients orthophosphate and ammonia to producers of organic particles (phytoplankton and bacteria). Excretion may be dominated by the smallest of particle consumers, planktonic protists, because metabolic rates per unit weight are usually inversely related to size. However, protist taxa are a heterogenous assemblage, ranging over 3 orders of magnitude in size, and include forms which are mixotrophic, profiting simultaneously from photosynthesis and ingestion of particulate matter. Excretion rates from laboratory studies of protists, ciliates and flagellates, both heterotrophic and mixotrophic, were analysed to determine relationships with both cell size and growth rate. Smaller protists, such as flagellates, showed higher weight-specific excretion rates than larger protists like ciliates. Equations relating maximal excretion rate (excr) to size in terms of dry weight (DW) were, for orthophosphate, log excr (mu g P cell(-1) h(-1)) = -2.101 + 0.570 log size (mg DW cell(-1)), r = 0.847, n = 12 and for ammonia, log excr (mu g N cell(-1) h(-1)) = -1.388 + 0.622 log mg DW cell(-1), r = 0.899, n = 15. Mixotrophic protists showed maximum excretion rates similar to like-sized heterotrophic protists. For phosphorus, the maximum weight-specific excretion rates of protists were higher than predicted by extrapolation of most size-excretion rate relationships established for metazoan zooplankton. Maximum excretion rates for ammonia approached the average of reported relationships for metazoan-based equations.Rapidly growing protozoa appear to excrete orthophosphate (measured as soluble reactive phosphorus) relative to ammonia well in excess of the Redfield atom ratio of 16:1, i.e., excretory N:P ratios of 2:1-8:1. For orthophosphate, excretion rate may be predictable based on cell size and growth rate. In contrast, ammonia excretion appeared weakly related to growth rate in five out of ten species, and independent of growth rate in the remaining species, probably due to variability of the form of nitrogenous excretion. Consequently, planktonic protists may be much more important in the regeneration of orthophosphate than ammonia. However, the apparent magnitude and simplicity of phosphorous excretion may be an artefact of considering the dominant excretory compound, soluble reactive phosphorus, as entirely orthophosphate. (C) Elsevier Science B.V. All rights reserved.