Stream nitrogen concentration, but not plant N-fixing capacity, modulates litter diversity effects on decomposition

1. We are facing major biodiversity loss and there is evidence that such loss can alter ecosystem functioning. However, the effects of plant diversity on decomposition – a key component of the global carbon cycle – are still unclear. A recent study suggested that a plant trait – their nitrogen (N)-fixing capacity – could mediate effects of litter diversity on decomposition by means of a microbial transfer of N from N-fixers to non-fixers.
2. We explored this possibility in a microcosm experiment in which we manipulated litter species richness (1, 2 or 4 species), N-fixing capacity (N-fixer or non-fixer species), the presence of detritivores (Sericostoma pyrenaicum larvae present or absent), and water N concentration [natural stream water (0.366 mgL-1 of NO3-N) or elevated N concentration (5 times the natural concentration: 1.835 mgL-1)].
3. We show that litter diversity accelerated decomposition by microorganisms and detritivores (by 7 and 15%, respectively), mostly through complement...

1. 当前人类正面临严峻的生物多样性丧失问题，且有证据表明这类丧失会改变生态系统功能。然而，植物多样性对分解作用（decomposition）——全球碳循环的关键组成部分——的影响仍未明确。近期一项研究提出，植物的一项功能性状——固氮能力（nitrogen (N)-fixing capacity）——或可通过微生物介导的氮从固氮植物向非固氮植物的转移过程，调控凋落物多样性对分解作用的影响。
2. 我们通过微宇宙实验（microcosm experiment）探究了这一可能性，实验中我们设置了四类调控变量：凋落物物种丰富度（1、2或4个物种）、固氮能力（固氮植物或非固氮植物）、食碎屑动物（detritivores）的存在与否（添加或不添加Pyrenea石蛾（Sericostoma pyrenaicum）幼虫），以及水体氮浓度[天然溪流水体（硝态氮（NO3-N）含量为0.366 mgL⁻¹）或高氮浓度（为天然浓度的5倍：1.835 mgL⁻¹）]。
3. 我们的研究结果表明，凋落物多样性可分别通过微生物和食碎屑动物途径加速分解作用（分别提升7%和15%），主要依赖于互补作用（complement）……