养分有效性和大气二氧化碳分压调节了养分异质性对草原物种种群大小结构的影响。
Nutrient availability and atmospheric CO2 partial pressure modulate the effects of nutrient heterogeneity on the size structure of populations in grassland species.
作者信息
Maestre Fernando T, Reynolds James F
机构信息
Department of Biology, Duke University, Phytotron Building, Box 90340, Durham, NC 27708, USA.
出版信息
Ann Bot. 2006 Jul;98(1):227-35. doi: 10.1093/aob/mcl093. Epub 2006 May 16.
BACKGROUND AND AIMS
Size-asymmetric competition occurs when larger plants have a disproportionate advantage in competition with smaller plants. It has been hypothesized that nutrient heterogeneity may promote it. Experiments testing this hypothesis are inconclusive, and in most cases have evaluated the effects of nutrient heterogeneity separately from other environmental factors. The aim of this study was to test, using populations of Lolium perenne, Plantago lanceolata and Holcus lanatus, two hypotheses: (a) nutrient heterogeneity promotes size-asymmetric competition; and (b) nutrient heterogeneity interacts with both atmospheric CO2 partial pressure (P(CO2)) and nutrient availability to determine the magnitude of this response.
METHODS
Microcosms consisting of monocultures of the three species were grown for 90 d in a factorial experiment with the following treatments: P(CO2) (37.5 and 70 Pa) and nutrient availability (NA; 40 and 120 mg of N added as organic material) combined with different spatial distribution of the organic material (NH; homogeneous and heterogeneous). Differences in the size of individual plants within populations (size inequality) were quantified using the coefficient of variation of individual above-ground biomass and the combined biomass of the two largest individuals in each microcosm. Increases in size inequality were associated with size-asymmetric competition.
KEY RESULTS
Size inequality increased when the nutrients were heterogeneously supplied in the three species. The effects of NH on this response were more pronounced under high nutrient supply in both Plantago and Holcus (significant NA x NH interactions) and under elevated P(CO2) in Plantago (significant P(CO2) x NA x NH interaction). No significant two- and three-way interactions were found for Lolium.
CONCLUSIONS
Our first hypothesis was supported by our results, as nutrient heterogeneity promoted size-asymmetric competition in the three species evaluated. Nutrient supply and P(CO2) modified the magnitude of this effect in Plantago and Holcus, but not in Lolium. Thus, our second hypothesis was partially supported.
背景与目的
当大型植物在与小型植物竞争中具有不成比例的优势时，就会发生大小不对称竞争。据推测，养分异质性可能会促进这种竞争。检验这一假设的实验尚无定论，而且在大多数情况下，都是将养分异质性的影响与其他环境因素分开评估的。本研究的目的是利用多年生黑麦草、披针叶车前和绒毛草种群来检验两个假设：(a) 养分异质性促进大小不对称竞争；(b) 养分异质性与大气二氧化碳分压（P(CO2)）和养分有效性相互作用，以确定这种响应的程度。
方法
在一项析因实验中，由这三个物种的单一栽培组成的微观世界生长90天，实验处理如下：P(CO2)（37.5和70帕）和养分有效性（NA；以有机物质形式添加40和120毫克氮）与有机物质的不同空间分布（NH；均匀和不均匀）相结合。利用每个微观世界中个体地上生物量的变异系数和两个最大个体的总生物量，对种群内个体大小的差异（大小不平等）进行量化。大小不平等的增加与大小不对称竞争相关。
主要结果
当三种植物的养分供应不均匀时，大小不平等增加。在车前和绒毛草中，高养分供应条件下（显著的NA×NH相互作用）以及车前中二氧化碳浓度升高时（显著的P(CO2)×NA×NH相互作用），NH对这种响应的影响更为明显。黑麦草未发现显著的二元和三元相互作用。
结论
我们的第一个假设得到了结果的支持，因为养分异质性促进了所评估的三种植物中的大小不对称竞争。养分供应和P(CO2)改变了车前和绒毛草中这种效应的程度，但在黑麦草中没有。因此，我们的第二个假设得到了部分支持。
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