题目：Defence strategies in African savanna trees 生活在非洲萨王纳的树的防御策略
Southern African savannas are commonly polarised into two broad types based on plant functional types and defences; 非洲南部萨王纳根据功能类型和防御策略大致可以分为两种： infertile savannas dominated by broad-leaved trees typically defended by nitrogen-free secondary compounds 土壤贫瘠的萨王纳上面主要长的是宽叶子的树，他们通过不含氮的次级代谢产物来防御， and fertile savannas dominated by fine-leaved trees defended by structural defences. 土壤肥沃的萨王纳主要由小叶子的树组成，它们通过物理结构进行防御。 In this study, we use trait and other data from 15 wooded savanna sites in Southern Africa and ask if broad-leaved and fine-leaved species dominate on nutrient-poor and nutrient-rich soils, respectively. 为了进一步验证这个pattern，本研究在南非15个长树的萨王纳样地采集了一些树的性状以及其他数据，想看看是不是真的宽叶子长在贫瘠的，细叶子长在肥沃的土壤上。 We then test if there is there any evidence for trade-offs in chemical (i.e., condensed tannins and total polyphenols) vs. structural defences on different soil types. 然后我们检测了在不同的土壤类型中，化学防御（浓缩单宁和总酚）跟结构防御之间有没有trade-off. We did not find strong evidence for a general divide in fine- vs. broad-leaved savannas according to soil fertility, 并没有很强的证据表明细叶和宽叶萨王纳可根据土壤肥沃程度来分开， nor for a simple trade-off between chemical and structural defences. 也没有发现化学和结构防御之间的trade-off. Instead, we found savanna species to cluster into three broad defence strategies: species were high in leaf N and either (A) highly defended by spines and chemicals or (B) only structurally defended, or (C) low in leaf N and chemically defended. 但是我们也不是什么都没发现。我们发现，萨王纳植物分为三大类更为合适：（A）高叶片氮含量+有刺+化学防御（B）高叶片氮含量+结构防御（C) 低叶片氮含量+化学防御。也就是说高氮不一定没有化学防御（即leaf N跟CT不一定成反比），但低氮肯定有化学防御。有刺也不一定就没有化学防御，但有刺肯定高leaf N。 Finally, we tested for differences in browser utilisation between soil types and among plant defence strategies and found that browsing by meso-herbivores was higher on nutrient-rich soils and targeted species from groups A and B and avoided C, 最后我们发现，中兽类喜欢肥沃萨王纳和高叶片氮的植物（A&B） while browsing by elephants was mostly not affected by soil type or defence strategy. 大象就没那么讲究了，哪儿都去，什么都吃。
We propose a framework that can be used as a basis for asking strategic questions that will help improve our understanding of plant defences in savannas. 最后，我们觉得我们提出了一个框架，作为我们理解萨王纳植物防御策略的基础。（作为读者我觉得这个框架可能讲的是（1）三类植物的分法（2）植食动物的preference.
另： Eight defence-related traits were measured for a total of 66 woody species from 15 sites.
Leaf N, SLA(specific leaf area), ADF(acid detergent fibre), TP(total polyphenols), CT(condensed tannins), Branch density or BI(Branching index), BSI(bite size index), Spine density or ASD(average spine density)
The thing about catena:
On nutrient-poor substrates, sites were chosen to avoid the bottom of catenal sequences (if present) to avoid the locally enriched soils typically found at the bottom of a catena.
In the context of this study, a catena refers to the distinctive sequential pattern found on soils derived from granitic parent material in southern Africa. Sandy soils are found on crests and clayey soils along footslopes, and these are separated by a thin band of grey hydromorphic soils called the seepline (Scholes et al. 2002; Venter et al. 2003
crest: the top of a mountain or hill. At a smaller scale, across catena,