对于任何一个自然生态系统，其成长几乎很难用“一帆风顺”来描述，因为它总是处于各种胁迫因子的影响，其中养分限制尤甚。生态学家在早期也“归纳”出一些规律，如热带森林更可能受到磷限制，而温带森林主要受到氮限制，但这样的规律到底有什么指导意义呢？我们基本上可以断定的是，几乎任何一片森林几乎都会受到氮、磷、铁、镁、钾、钙、硼、锌、铜等等等等等等等的限制，我们几乎可以这么肯定的说 — 它们的生长受到很多因素的限制！同样地，任何一片海洋也会受到这样或那样的养分限制。

据说，海洋浮游植物（phytoplankton）的生长一般情况主要受到氮、铁、钴和磷等养分限制，那么它们的生长更多地受到一种，抑或几种养分的限制呢？近期，德国科学家Browning等人在一次航海旅途中，通过试验证明海洋浮游植物一般主要受到氮和铁的双重养分限制（nitrogen–iron co-limitation），在有氮和铁存在的前提，加入钴元素（或维生素B12替代）在一些试验中能够观察到更大的促进作用。相关研究论文“Nutrient co-limitation at the boundary of an oceanic gyre”已经以快报形式(Letter)发表在Nature上，链接：https://www.nature.com/articles/nature24063

直观的看看题目有可能并不觉得这是多么了不起的科学发现，但就像作者在文中声称的那样，想获得可靠的试验数据是十分艰难的，这个试验看似简单，但做起来不是那么容易。科学往往就是这样，拍拍脑袋好点子一下子就能蹦出好几十个，最终能否通过试验去证明则是另外一回事了。

Abstract

Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre. We find extensive regions in which the addition of nitrogen or iron individually resulted in no significant phytoplankton growth over 48 hours. However, the addition of both nitrogen and iron increased concentrations of chlorophyll a by up to approximately 40-fold, led to diatom proliferation, and reduced community diversity. Once nitrogen–iron co-limitation had been alleviated, the addition of cobalt or cobalt-containing vitamin B₁₂ could further enhance chlorophyll a yields by up to three fold. Our results suggest that nitrogen–iron co-limitation is pervasive in the ocean, with other micronutrients also approaching co-deficiency. Such multi-nutrient limitations potentially increase phytoplankton community diversity.