根状茎型植物扁秆荆三棱对土壤养分异质性尺度和对比度的生长响应

Growth responses of a rhizomatous herb Bolboschoenus planiculmis to scale and contrast of soil nutrient heterogeneity

土壤养分的空间异质性在自然界普遍存在,而克隆植物被认为能很好地适应和利用土壤养分异质性。尽管尺度和对比度是异质性的两个重要属性,但有关土壤养分异质性的尺度和对比度及其交互作用对克隆植物生长和分株分布格局影响的研究仍比较缺乏。在一个温室实验中,根状茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)(异名扁秆藨草(Scirpus planiculumis))被种植在由高养分斑块和低养分斑块组成的异质性环境中。实验为两种尺度处理(大斑块和小斑块)和两种对比度处理(高对比度和低对比度)交叉组成的4种处理组合。在每个处理中,高养分和低养分斑块的总面积相同;在所有4种处理中,土壤养分的总量也完全相同。无论在整个克隆(植株)水平,还是在斑块水平,尺度、对比度及其交互作用对扁秆荆三棱的生物量、分株数、根状茎长和块茎数的影响均不显著。然而,在斑块水平,扁秆荆三棱在高养分斑块中的生物量、分株数、根状茎长和块茎数均显著高于低养分斑块,而在高养分斑块中相邻分株间的距离(间隔物长)小于低养分斑块,并且这种效应均不依赖于斑块尺度的大小和对比度的高低。因此,在土壤养分异质性环境中,扁秆荆三棱可以通过缩短间隔物长,并可能通过提高根状茎的分枝强度,把较多的分株和潜在分株放置在养分条件好的斑块中。这种响应格局体现出克隆植物的觅食行为,有利于整个克隆对异质性资源的吸收和利用。然而,该实验中的尺度和对比度对扁秆荆三棱分株的放置格局均没有显著效应。作者推测,在一个更大的斑块尺度和(或)对比度范围内,扁秆荆三棱对土壤养分异质性的响应可能不同。因此,下一步的研究应涉及更广泛的尺度和对比度。

Aims Spatial heterogeneity in soil nutrients is common in nature, and clonal plants are supposed to be able to better use spatially heterogeneously distributed soil nutrients. Although scale and contrast are two of the most important elements of spatial heterogeneity, few studies have tested effects of scale and contrast of soil nutrient het- erogeneity on the growth of clonal plants. Methods We conducted a greenhouse experiment in which we grew individual ramets of a rhizomatous clonal plant, Bolboschoenus planiculmis, in heterogeneous conditions consisting of nutrient-rich and nutrient-poor patches. The experiment had two levels of patch scale （large vs. small patch） crossed with two levels of patch contrast （high vs. low contrast）, thereby consisting of four treatments. In each treatment, the total area of the nu- trient-rich patches and that of the nutrient-poor patches were the same, and the total amount of soil nutrients was also the same in all the four treatments. Important findings At both clone （whole plant） level and patch level, patch scale, contrast or their interaction did not significantly affect biomass, number of ramets, total rhizome length or number of tubers ofB. planiculmis. At the patch level, however, biomass, number of ramets, total rhizome length and number of tubers of B. plani- culmis were significantly greater in the nutrient-rich patches than in the nutrient-poor ones, whereas spacer length （i.e., distance between adjacent ramets） was smaller. Such effects depended on neither patch scale nor patch contrast. Therefore, when growing in environments with heterogeneous soil nutrients, B. planiculmis was able to shorten its spacer length and likely also increased branching intensity of the rhizomes, such that more ramets and tubers （i.e., potential ramets） were placed in nutrient-rich patches. These responses are generally considered one aspect of the foraging behavior of clonal plants and are thought to be adaptive. However, the patch scale or contrast designed in the present experiment could not affect the placement of the ramets in the heterogeneous environments. We presume that the responses of S. planiculmis are likely different if a wider range of scale and contrast is used and thus future studies to test effects of scale and contrast of resource heterogeneity should consider a wider range of scale and/or contrast.