Responses of a C4 Grass and Three C3 Forbs to Variation in Nitrogen and Light in Tallgrass Prairie
Responses of a C4 Grass and Three C3 Forbs to Variation in Nitrogen and Light in Tallgrass Prairie
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DOI：
10.2307/2265779
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发表时间：
1996-09
期刊：
影响因子：
4.8
通讯作者：
C. L. Turner;A. Knapp
中科院分区：
文献类型：
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作者：
C. L. Turner;A. Knapp
在高草草原上，植物物种多样性高的原因不是草本植物种类多，而是杂草(非草、草本)种类多。杂草的形态、生活史和生态生理特征与优势C4草本植物形成鲜明对比。次优杂草的成功与否与地形位置和燃烧制度有很大的不同，丰度的景观尺度模式也有很好的记录。但相对较少的人知道，在持久的高草草原杂交草中决定这些模式的机制。为了阐明这些机制，(1)测量了优势C4草、仙人掌和4种共生C3杂草的叶水平生理特征，以响应自然和人工操纵的N有效性梯度；(2)比较了处于不同地形位置和燃烧模式的杂交草的季节性光环境及其形态和生理响应，以确定资源可用性和利用模式是否有助于杂草的分布和丰度格局。燃烧方式和地形位置对叶片最大光合作用速率(A)和气孔导度(G)的影响与杂草丰度的模式不一致。氮素似乎不会限制植物的生理过程，尽管增加的氮素利用率会导致组织中氮素浓度更高，生物量也更大。对受精的反应，A和g没有一致的增加或减少。然而，与未受精的植株相比，受精的巴氏斑潜蝇和长尾斑潜蝇在弱光下的A高出67%。与低地相比，高地杂草的生物量较低，而与火烧地相比，未焚烧地杂草的生物量较低。杂草在形态上(叶面积和株高)似乎不能适应不同地点的不同光环境。结果表明，火烧低地约90%的杂交叶面积处于弱光下，而旱地中只有30%的杂交叶面积处于弱光下。基于叶面积相对于有效光的分布和A作为光可利用性的函数，对潜在的全株碳吸收的估计与杂草丰度和产量的模式很好地吻合。光可获得性的差异可能是与燃烧制度和地形位置有关的杂草丰度变化的主要原因，因为与其他地点相比，燃烧低地限制了杂草的碳增量。
In tallgrass prairie, high plant species diversity results not from a large number of grass species, but from a large number of forb (nongrass, herbaceous) species. Forbs exhibit morphological, life history, and ecophysiological characteristics that contrast sharply with those of the dominant C4 grasses. Success of the subdominant forbs varies strongly with topographic position and burning regime, and landscape scale patterns of abundance are well documented. But comparatively little is known about the mechanisms determining these patterns in persistent tallgrass prairie forbs. To elucidate these mecha- nisms, (1) leaf-level physiological characteristics of the dominant C4 grass, Andropogon gerardii, and four co-occurring C3 forbs were measured in response to natural and exper- imentally manipulated gradients of N availability, and (2) seasonal light environments of forbs in contrasting topographic positions and burning regimes and their morphological and physiological responses in these environments were compared to determine whether resource availability and utilization patterns contributed to patterns of forb distribution and abundance. The effects of burning regime and topographic position on maximum rate of photosynthesis (A) and stomatal conductance to water vapor (g) measured at the leaf level were not consistent with patterns of forb abundance. Nitrogen did not appear to limit forb physiological processes, even though increased N availability resulted in higher tissue N concentrations and greater biomass. There was no consistent increase in A or decrease in g in response to fertilization. However, A at low light levels was as much as 67% higher in fertilized Vernonia baldwinii and A. gerardii compared to unfertilized plants. Greater light availability to forbs in the canopy was associated with lower grass biomass production in uplands compared to lowlands and in unburned compared to burned sites. Forbs did not appear to adjust morphologically (leaf area and plant height) to different light environments at different sites. As a result, as much as 90% of forb leaf area in the burned lowland was displayed in low light, whereas as little as 30% of forb leaf area was in low light in the uplands at midseason. Estimates of potential whole-plant carbon uptake, based on leaf area distribution relative to available light and A as a function of light availability, agreed well with patterns of forb abundance and production. Differences in light availability may ac- count for much of the variability in forb abundance related to burning regime and topo- graphic position by limiting carbon gain in forbs more in burned lowlands than in other sites.