写作与实验、统计一样重要        

        研究生的学习往往会遵循这样的过程：实验——数据分析——写作。虽然写作是最后进行的，但写作的学习这应该和实验的学习、数据分析的学习保持同步，因为写作与统计和实验技能一样，是科研工具箱的必备武器。下面我们选取了一篇最近发表在soil biology and biochemistry上的论文“Increasing plant species diversity enhances microbial necromass carbon content but does not alter its contribution to soil organic carbon pool in a subtropical forest”，对其前言部分进行分析，利用实例学习SCI英文论文写作的方法。       

第一段

1.Owing to its huge amount, minor variations in the soil organic carbon (SOC) pool may substantially affect the atmospheric carbon dioxide concentration and in turn global climate, so that SOC sequestration has been proposed as one of the major nature-based climate solutions

第一句话作者强调了土壤有机碳对于大气二氧化碳浓度和全球气候的重要性，是一个大帽子，为后面的研究赋予了意义，并引出了一个词——SOC sequestration。

2. Since SOC sequestration is determined by the balance of plant detritus inputs and SOC decomposition, strategies that stimulate plant productivity and in turn plant detritus inputs have the potential to promote SOC sequestration

接着作者对“SOC sequestration”进行了介绍，这个过渡很流畅，第一句话和第二句都出现了“SOC sequestration”这个词这，第二句话是对第一句话的进一步细化，这一点作者做的很好。随后又引出 “ plant detritus”，在第三句中进行进一步地介绍。

3. Upon plant detritus inputs, microbes continuously transform plant detritus into microbial necromass with parts of organic C lost as carbon dioxide, so that SOC is mostly composed of plant and microbial residues

接着又由 “ plant detritus ”过渡到“ microbial necromass ”，指出SOC包含植物和微生物残体这两部分。然后接着对植物和微生物的残体进行分别的介绍。

4. Plant residues mainly exist as particulate organic carbon, while microbial necromass is mostly associated with minerals by forming the so-called mineral-associated organic C, which is more stable than particulate organic carbon

比较了植物残体和微生物残体的不同之处，微生物残体更加稳定

5. According to a meta-analysis, microbial necromass C (MNC) accounts for 35% on average of the SOC pool in the top 20 cm of mineral soil horizon across the global forests

因此，微生物残体占到了土壤有机质的35%，你说microbial necromass，是不是很值得研究？

 6. Compelling evidence has shown that increasing plant species diversity (PSD) benefits SOC accumulation across terrestrial ecosystems worldwide due to enhanced plant detritus inputs

指出提高植物的物种多样性可以增加植物残体来增加土壤有机碳，便于引出后面的knowledge gap。

7. However, how increasing PSD would impact MNC accumulation and its contribution to the SOC pool remains largely unknown

提出了作者本篇论文期望填补的knowledge gap。

注意每一句的时态，不是现在时就是现在完成时，也是introduction中的基本时态，是对基本事实的一种描述。在论文的第一段，作者成功地从一个大的背景出发，不断深入、延伸、细化，最后提出了自己期望填补的knowledge gap。论文前后句的衔接都很流畅，如果硬要说这一段有什么缺点，就是plant diversity这个词出现的有点晚了。

第二段

1. Multiple variables have been found to regulate MNC accumulation.

段首的第一句话很重要，看了这句话就知道作者接下来要介绍的内容了。

2.  Climatic factors such as temperature and moisture may directly influence substrate availability and microbial growth or activity, and subsequently affect MNC content

对第一句话的细化,介绍了气候因子的影响

3.  Soil nitrogen (N), as an important substrate necessary for microbial growth, may strongly influence the reutilization of microbial necromass by living microorganisms with low soil N availability likely resulting in relatively high reutilization, so that high soil N availability may benefit soil MNC accumulation

同样是对第一句话的细化,介绍了土壤氮含量的影响

4. Additionally, MNC (microbial necromass carbon)  is prone to forming organic carbon-mineral associations with soil minerals including exchangeable calcium (Ca) and magnesium (Mg), or iron (Fe) and aluminium (Al) oxides

Additionally是英文论文中的常用词，很好地连接两个句子。

5. Therefore, a higher contribution of MNC to the SOC pool may be attributed to relatively higher mineral protection

从第4句推理而来

这一段作者介绍了影响microbial necromass carbon的因素有哪些。为下面介绍植物多样性如何影响微生物残体碳提供基础。

第三段

1. Increasing PSD may impact MNC accumulation via its effects on soil biotic and abiotic variables.

第一句话统领全段。

2. Increasing PSD has been found to promote both above- and belowground biomass and subsequent detritus inputs to soils, leading to increased levels of SOC, dissolved organic C and living microbial biomass 

介绍植物多样性增加对微生物量的影响，和第一句话也是共用一个主语“Increasing PSD”

3. As microbial biomass is the precursor of MNC, higher microbial biomass would have a greater potential of forming more soil MNC under similar environmental conditions

从微生物量过渡到微生物残体碳

 4. Plant N use efficiency would increase attributed to the complementarity of plant N acquisition strategies under higher PSD, subsequently resulting in decreased soil N loss, which would benefit soil N accumulation and increase soil N availability, and may contribute to MNC accumulation as aforementioned.

这句话和上句话的衔接没有之前的流畅，主要是说植物多样性对氮的利用效率的影响，进而影响微生物残体碳。

5-6.  Increasing PSD would elevate soil exchangeable Ca and Mg contents via root mining of nutrients including Ca and Mg from deeper soil horizons with these nutrients returning to the surface soil horizon through stimulated detritus inputs.  PSD exerts a positive effect on soil water holding capacity, so that soil water content would be higher under higher PSD

植物多样性对理化性质的影响，而这些理化性质会影响微生物残体碳

7. As these biotic and abiotic variables are closely linked with MNC accumulation, PSD would theoretically benefit soil MNC accumulation. Nevertheless, only one study has explored the effects of PSD on soil MNC accumulation in a subtropical forest with acidic soil, so that more investigations under various soil or climate conditions are urgently needed.

这句对整段进行总结，并强调该研究的必要性。这里作者通过指出相关的研究较少来强调研究的必要性虽然无可厚非，但过于平淡了些。我觉得有更好的选择：作者之前对植物多样性如何影响理化性质，进而影响微生物残体碳做了很多介绍，这里作者可以进一步提出自己的研究假设，把前言部分推向高潮，会更加精彩。

第四段

1-2. In the current study, the effects of PSD on soil MNC content and its contribution to the SOC pool were explored on 45 plots covering a natural gradient of PSD.The scientific questions we aimed to address include: (i) how do soil MNC content and its contribution to the SOC pool change with PSD, (ii) what are the mechanisms underlying the variation of MNC in response to PSD?

简单介绍下自己的实验，然后引出后面希望回答的问题或者假设，前言最后一段一般都这么写，做了很好地结尾。

总体而言，100分满分的话，这篇前言可以给90分，写的很好，但依然有可以强化的空间。

• 第一段写得最好，但plant diversity出现得太晚，重要性被弱化了，错失了进一步提升论文重要性的机会。
• 第二段和第三段可以合为一段，介绍植物多样性如何影响理化性质，进而影响微生物残体碳。而不用将这两者分开，作者先介绍土壤理化性质对微生物残体碳的影响，再介绍植物多样性对微生物残体碳的影响。
• 作者可以进一步提出自己的研究假设，而不是强调相关的研究很少（尽管这也是事实）。

  写前言既简单也复杂。简单之处在于前言的目的很简单，就是从一个大的背景出发，逐渐细化、延伸到一个小的、特别的问题，也就是论文希望填补的知识空白。难的地方在于如何最大化研究的意义，同样的议题不同的写作会体现出不同的科研价值（图1a, b）。