Station House, Leadmill, Hathersage, Hope Valley S32 1BA, UK.
Ann Bot. 2011 Nov;108(7):1337-45. doi: 10.1093/aob/mcr225. Epub 2011 Sep 21.
Specific leaf area (SLA), a key element of the 'worldwide leaf economics spectrum', is the preferred 'soft' plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?
SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.
Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.
Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.
比叶面积（SLA）是“全球叶片经济谱”的关键要素，是评估土壤肥力的首选“软”植物特性。SLA 是叶干物质含量（LDMC）和叶厚度（LT）的函数。前者 LDMC 定义了叶片的构建成本，可以替代 SLA。然而，LT 确定了叶片在最暗和最多汁时的状态，与土壤肥力无关。那么，为什么 SLA 比 LDMC 更常被用作土壤肥力的预测指标呢？
对近 2000 种植物进行了 SLA、LDMC 和 LT 的测量和叶密度（LD）的估算，并检验了 LD 预测 LDMC 的能力，以及 LDMC 和 LT 对 SLA 表达的相对贡献。随后，描述了 SLA、LDMC 和 LT 与土壤肥力和遮荫的关系。
尽管 LD 与 LDMC 密切相关，LDMC 和 LT 各自对 SLA 的表达都有同等贡献，但在不同的生态分组中，这种关系是不同的。LDMC 预测叶片氮含量和土壤肥力，但由于 LT 主要随光照强度而变化，因此 SLA 会随着遮荫和肥力的增加而增加。
土壤肥力的梯度通常也是生物量积累的梯度，随着树冠下部光照强度的降低而降低。因此，SLA 包含了肥力和遮荫两个成分，可能比 LDMC 更能区分群落或处理。然而，LDMC 应该始终是评估与遮荫无关的土壤肥力梯度的首选特性。然而，由于叶片具有多种功能，单个叶片特性在物种之间不一定具有完全相同的功能等价性。因此，建议使用几个叶片特性进行多元分析，而不是使用单一的独立预测因子。
