Casper Brenda B, Cahill James F, Hyatt Laura A
Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.
To whom correspondence should be addressed. E-mail:
New Phytol. 1998 Oct;140(2):231-238. doi: 10.1046/j.1469-8137.1998.00271.x.
We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root∶shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.
我们测试了植物是否会根据最优分配理论的预测，因地上竞争而按比例减少分配给根系的生物量。通过每盆种植一株苘麻并改变盆间距，实现了两种种群密度，使得两种密度下的植物拥有相同的土壤体积，但冠层重叠程度不同。密度并未影响根冠比、细根与贮藏根之间的生物量分配、细根长度或根比长度。高密度生长的植物对邻体表现出典型的地上响应，其茎生物量与叶生物量的比值以及叶比面积均高于低密度生长的植物。总根生物量与地上生物量高度相关。然而，贮藏根生物量与地上生物量的相关性比细根生物量更强。仅在拥挤种群中的小冠层植物中，细根长度与地上生物量相关。由于叶面积随生物量增加，吸收根表面积与蒸腾叶表面积的比值随植株大小而下降，这种关系可能使较大植株更易受干旱影响。我们得出结论，苘麻不会因地上竞争而将生物量从根系重新分配到地上部分，尽管许多根生物量显然用于贮藏而非资源获取。
