Orians Colin M, Ardón Marcelo, Mohammad Basma A
Department of Biology, Tufts University, Medford, Massachusetts 02155 USA.
Am J Bot. 2002 Feb;89(2):270-8. doi: 10.3732/ajb.89.2.270.
Within-plant heterogeneity in growth, morphology, and chemistry is ubiquitous, and is commonly attributed to differences in tissue age, light availability, or previous damage by herbivores. Although these factors are important, we argue that plant vascular architecture is an underappreciated determinant of heterogeneity. Vascular architecture can restrict the transport of resources (nutrients, photosynthate, hormones, etc.) to within specific sectors of the plant: this is referred to as sectoriality. Although studies have documented sectoriality in the transport of isotopes and dyes from roots to shoots, the ecological consequences of this sectoriality remain poorly understood. We tested the hypothesis that spatial variation in belowground nutrient availability combined with sectorial transport results in localized "fertilization" of aboveground plant parts and generates heterogeneity in traits important to herbivores. Our split-root experiments with tomato (Lycopersicon esculentum Mill) clearly demonstrate that fertilization to isolated lateral roots generates heterogeneity in leaf morphology, phenolic chemistry, and side-shoot growth. Specifically, leaflets with direct connections to these lateral roots were larger and had lower levels of rutin and chlorogenic acid than did leaflets in other sectors lacking direct vascular connections. Moreover, side-shoot production was greater in the connected sectors. We discuss the implications of this heterogeneity for plant-herbivore interactions.
植物内部在生长、形态和化学性质方面的异质性普遍存在，通常归因于组织年龄、光照条件或先前食草动物造成的损伤差异。尽管这些因素很重要，但我们认为植物维管结构是一个未得到充分重视的异质性决定因素。维管结构会将资源（营养物质、光合产物、激素等）的运输限制在植物的特定区域内：这被称为区域性。尽管已有研究记录了从根到茎的同位素和染料运输中的区域性，但这种区域性的生态后果仍知之甚少。我们检验了这样一个假设，即地下养分有效性的空间变化与区域性运输相结合，会导致地上植物部分出现局部“施肥”现象，并在对食草动物重要的性状上产生异质性。我们用番茄（Lycopersicon esculentum Mill）进行的分根实验清楚地表明，对孤立侧根施肥会在叶片形态、酚类化学性质和侧枝生长方面产生异质性。具体而言，与这些侧根有直接连接的小叶比其他缺乏直接维管连接的区域的小叶更大，芦丁和绿原酸含量更低。此外，在有连接的区域侧枝产量更高。我们讨论了这种异质性对植物 - 食草动物相互作用的影响。
