Abdala-Roberts Luis, Rasmann Sergio, Berny-Mier Y Terán Jorge C, Covelo Felisa, Glauser Gaétan, Moreira Xoaquín
Departamento de Ecología Tropical, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán, Apartado Postal 4-116, Itzimná. 97000. Mérida, Yucatán, México.
Institute of Biology, Laboratory of Functional Ecology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland.
Am J Bot. 2016 Dec;103(12):2070-2078. doi: 10.3732/ajb.1600310. Epub 2016 Dec 13.
It is generally thought that herbivore pressure is higher at lower elevations where climate is warmer and less seasonal, and that this has led to higher levels of plant defense investment at low elevations. However, the generality of this expectation has been called into question by recent studies.
We tested for altitudinal gradients in insect leaf damage, plant defenses (phenolic compounds), and nutritional traits (phosphorus and nitrogen) in leaves of the long-lived tree Quercus robur, and further investigated the abiotic factors associated with such gradients. We sampled 20 populations of Q. robur distributed along an altitudinal gradient spanning 35-869 m above sea level, which covered most of the altitudinal range of this species and varied substantially in abiotic conditions, plant traits, and herbivory.
Univariate regressions showed that leaf herbivory, phenolics, and phosphorus increased toward higher elevations, whereas leaf nitrogen did not vary with altitude. Multiple regression analyses indicated that temperature was the single most important factor associated with herbivory and appears to be strongly associated with altitudinal variation in damage. Leaf phenolics were also correlated with herbivory, but in a manner that suggests these chemical defenses do not underlie altitudinal variation in damage. In addition, we found that variation in leaf traits (phenolics and nutrients) was in turn associated with both climatic and soil variables.
Overall, these findings suggest that altitudinal gradients in herbivory and defenses in Q. robur are uncoupled and that elevational variation in herbivory and plant traits responds mainly to abiotic factors.
一般认为，在气候温暖且季节性较弱的低海拔地区，食草动物的压力更大，这导致低海拔地区植物的防御投资水平更高。然而，最近的研究对这一预期的普遍性提出了质疑。
我们测试了长寿树种欧洲栎叶片的昆虫取食损伤、植物防御（酚类化合物）和营养特性（磷和氮）的海拔梯度，并进一步研究了与此类梯度相关的非生物因素。我们对沿着海拔梯度分布的20个欧洲栎种群进行了采样，该海拔梯度跨度为海拔35 - 869米，涵盖了该物种的大部分海拔范围，且在非生物条件、植物特性和食草作用方面差异很大。
单变量回归显示，叶片食草损伤、酚类物质和磷随海拔升高而增加，而叶片氮含量不随海拔变化。多元回归分析表明，温度是与食草作用相关的唯一最重要因素，并且似乎与损伤的海拔变化密切相关。叶片酚类物质也与食草作用相关，但其方式表明这些化学防御并非损伤海拔变化的基础。此外，我们发现叶片特性（酚类物质和养分）的变化又与气候和土壤变量相关。
总体而言，这些发现表明欧洲栎的食草作用和防御的海拔梯度是不相关的，并且食草作用和植物特性的海拔变化主要响应非生物因素。
