Bazzaz F A, Garbutt K, Reekie E G, Williams W E
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambrige, MA, USA.
Oecologia. 1989 May;79(2):223-235. doi: 10.1007/BF00388482.
Detailed growth analysis in conjunction with information on leaf display and nitrogen uptake was used to interpret competition between Abutilon theophrasti, a C annual, and Amaranthus retroflexus, a C annual, under ambient (350 μl l) and two levels of elevated (500 and 700 μl l) CO. Plants were grown both individually and in competition with each other. Competition caused a reduction in growth in both species, but for different reasons. In Abutilon, decreases in leaf area ratio (LAR) were responsible, whereas decreased unit leaf rate (ULR) was involved in the case of Amaranthus. Mean canopy height was lower in Amaranthus than Abutilon which may explain the low ULR of Amaranthus in competition. The decrease in LAR of Abutilon was associated with an increase in root/shoot ratio implying that Abutilon was limited by competition for below ground resources. The root/shoot ratio of Amaranthus actually decreased with competition, and Amaranthus had a much higher rate of nitrogen uptake per unit of root than did Abutilon. These latter results suggest that Amaranthus was better able to compete for below ground resources than Abutilon. Although the growth of both species was reduced by competition, generally speaking, the growth of Amaranthus was reduced to a greater extent than that of Abutilon. Regression analysis suggests that the success of Abutilon in competition was due to its larger starting capital (seed size) which gave it an early advantage over Amaranthus. Elevated CO had a positive effect upon biomass in Amaranthus, and to a lesser extent, Abutilon. These effects were limited to the early part of the experiment in the case of the individually grown plants, however. Only Amaranthus exhibited a significant increase in relative growth rate (RGR). In spite of the transitory effect of CO upon size in individually grown plants, level of CO did effect final biomass of competitively grown plants. Abutilon grown in competition with Amaranthus had a greater final biomass than Amaranthus at ambient CO levels, but this difference disappeared to a large extent at elevated CO. The high RGR of Amaranthus at elevated CO levels allowed it to overcome the difference in initial size between the two species.
结合叶片展示和氮吸收信息进行详细的生长分析，以解释一年生C4植物苘麻和一年生C4植物反枝苋在环境CO₂浓度（350 μl l⁻¹）以及两种升高浓度（500和700 μl l⁻¹）下的竞争情况。植物分别单独种植以及相互竞争种植。竞争导致两个物种的生长均减少，但原因不同。在苘麻中，叶面积比（LAR）降低是原因所在，而在反枝苋中则是单位叶速率（ULR）降低。反枝苋的平均冠层高度低于苘麻，这可能解释了反枝苋在竞争中ULR较低的原因。苘麻LAR的降低与根冠比的增加相关，这意味着苘麻受到地下资源竞争的限制。反枝苋的根冠比实际上随着竞争而降低，并且反枝苋单位根的氮吸收速率比苘麻高得多。后一结果表明，反枝苋比苘麻更能竞争地下资源。虽然两个物种的生长都因竞争而减少，但总体而言，反枝苋的生长减少幅度大于苘麻。回归分析表明，苘麻在竞争中的成功归因于其更大的起始资本（种子大小），这使其比反枝苋具有早期优势。升高的CO₂对反枝苋的生物量有积极影响，对苘麻的影响较小。然而，对于单独种植的植物，这些影响仅限于实验的早期阶段。只有反枝苋的相对生长速率（RGR）有显著增加。尽管CO₂对单独种植植物的大小有短暂影响，但CO₂水平确实影响了竞争种植植物的最终生物量。在环境CO₂水平下，与反枝苋竞争种植的苘麻具有比反枝苋更大的最终生物量，但在升高的CO₂水平下，这种差异在很大程度上消失了。在升高的CO₂水平下，反枝苋的高RGR使其能够克服两个物种之间初始大小的差异。
