McAllister Christine A, Knapp Alan K, Maragni Laura A
Mojave Desert Ecosystem Program, Fort Irwin, CA 92310-5097, USA, , , , , , US.
Division of Biology, Kansas State University, Manhattan, KS 66506, USA, , , , , , US.
Oecologia. 1998 Nov;117(1-2):40-46. doi: 10.1007/s004420050629.
We addressed the question: "Are short-term, leaf-level measurements of photosynthesis correlated with long-term patterns of plant success?" in a productive grassland where interspecific competitive interactions are important. To answer this question, seasonal patterns of leaf-level photosynthesis were measured in 27 tallgrass prairie species growing in sites that differed in species composition and productivity due to differences in fire history. Our specific goals were to assess the relationship between gas exchange under field conditions and success (defined as aerial plant cover) for a wide range of species, as well as for these species grouped as dominant and sub-dominant grasses, forbs, and woody plants. Because fire increases productivity and dominance by grasses in this system, we hypothesized that any relationship between photosynthesis and success would be strongest in annually burned sites. We also predicted that regardless of fire history, the dominant species (primarily C grasses) would have higher photosynthetic rates than the less successful species (primarily C grasses, forbs and woody plants). Because forbs and woody species are less abundant in annually burned sites, we expected that these species would have lower photosynthetic rates in annually burned than in infrequently burned sites. As expected, the dominant C␣grasses had the highest cover on all sites, relative to␣other growth forms, and they had the highest maximum and seasonally averaged photosynthetic rates (17.6 ± 0.42 μmol m s). Woody species had the lowest average cover as well as the lowest average photosynthetic rates, with subdominant grasses and forbs intermediate in both cover and photosynthesis. Also as predicted, the highest overall photosynthetic rates were found on the most productive annually burned site. Perhaps most importantly, a positive relationship was found between leaf-level photosynthesis and cover for a core group of species when data were combined across all sites. These data support the hypothesis that higher instantaneous rates of leaf-level photosynthesis are indicative of long-term plant success in this grassland. However, in contrast to our predictions, the subdominant grasses, forbs and woody species on the annually burned site had higher photosynthetic rates than in the less frequently burned sites, even though their average cover was lower on annually burned sites, and hence they were less successful. The direct negative effect of fire on plant cover and species-specific differences in the availability of resources may explain why photosynthesis was high but cover was low in some growth forms in annually burned sites.
“短期的叶片水平光合作用测量值与植物长期的成功模式相关吗？” 我们在一个种间竞争相互作用很重要的高产草原上进行了研究。为了回答这个问题，我们测量了27种高草草原物种的叶片水平光合作用的季节模式，这些物种生长在因火灾历史不同而物种组成和生产力各异的地点。我们的具体目标是评估一系列物种在田间条件下的气体交换与成功（定义为地上植物覆盖度）之间的关系，以及将这些物种分为优势和亚优势禾本科植物、草本植物和木本植物后它们之间的关系。因为火灾会提高该系统中禾本科植物的生产力和优势度，所以我们假设光合作用与成功之间的任何关系在每年都被火烧的地点最为明显。我们还预测，无论火灾历史如何，优势物种（主要是C₄禾本科植物）的光合速率会高于不太成功的物种（主要是C₃禾本科植物、草本植物和木本植物）。由于草本植物和木本物种在每年都被火烧的地点数量较少，我们预计这些物种在每年都被火烧的地点的光合速率会低于火烧频率较低的地点。正如预期的那样，相对于其他生长形式，优势C₄禾本科植物在所有地点的覆盖度最高，并且它们具有最高的最大光合速率和季节性平均光合速率（17.6 ± 0.42 μmol m⁻² s⁻¹）。木本物种的平均覆盖度最低，平均光合速率也最低，亚优势禾本科植物和草本植物的覆盖度和光合作用处于中间水平。同样如预测的那样，在生产力最高的每年都被火烧的地点发现了最高的总体光合速率。也许最重要的是，当综合所有地点的数据时，发现一组核心物种的叶片水平光合作用与覆盖度之间存在正相关关系。这些数据支持了这样的假设，即较高的叶片水平瞬时光合速率表明了该草原上植物的长期成功。然而，与我们的预测相反，每年都被火烧的地点的亚优势禾本科植物、草本植物和木本物种的光合速率高于火烧频率较低的地点，尽管它们在每年都被火烧的地点的平均覆盖度较低，因此它们不太成功。火灾对植物覆盖度的直接负面影响以及资源可用性的物种特异性差异可能解释了为什么在每年都被火烧的地点某些生长形式的光合作用很高但覆盖度很低。
