Callaway R M, DeLucia E H, Thomas E M, Schlesinger W H
Plant Biology, University of Illinois, 61801, Urbana, IL, USA.
Department of Botany and Geology, Duke University, 27708, Durham, NC, USA.
Oecologia. 1994 Jul;98(2):159-166. doi: 10.1007/BF00341468.
Increases in the concentration of atmospheric carbon dioxide may have a fertilizing effect on plant growth by increasing photosynthetic rates and therefore may offset potential growth decreases caused by the stress associated with higher temperatures and lower precipitation. However, plant growth is determined both by rates of net photosynthesis and by proportional allocation of fixed carbon to autotrophic tissue and heterotrophic tissue. Although CO fertilization may enhance growth by increasing leaf-level assimilation rates, reallocation of biomass from leaves to stems and roots in response to higher concentrations of CO and higher temperatures may reduce whole-plant assimilation and offset photosynthetic gains. We measured growth parameters, photosynthesis, respiration, and biomass allocation of Pinus ponderosa seedlings grown for 2 months in 2×2 factorial treatments of 350 or 650μ bar CO and 10/25° C or 15/30° C night/day temperatures. After 1 month in treatment conditions, total seedling biomass was higher in elevated CO, and temperature significantly enhanced the positive CO effect. However, after 2 months the effect of CO on total biomass decreased and relative growth rates did not differ among CO and temperature treatments over the 2-month growth period even though photosynthetic rates increased ≈7% in high CO treatments and decreased ≈10% in high temperature treatments. Additionally, CO enhancement decreased root respiration and high temperatures increased shoot respiration. Based on CO exchange rates, CO fertilization should have increased relative growth rates (RGR) and high temperatures should have decreased RGR. Higher photosynthetic rates caused by CO fertilization appear to have been mitigated during the second month of exposure to treatment conditions by a ≈3% decrease in allocation of biomass to leaves and a ≈9% increase in root:shoot ratio. It was not clear why diminished photosynthetic rates and increased respiration rates at high temperatures did not result in lower RGR. Significant diametrical and potentially compensatory responses of CO exchange and biomass allocation and the lack of differences in RGR of ponderosa pine after 2 months of exposure of high CO indicate that the effects of CO fertilization and temperature on whole-plant growth are determined by complex shifts in biomass allocation and gas exchange that may, for some species, maintain constant growth rates as climate and atmospheric CO concentrations change. These complex responses must be considered together to predict plant growth reactions to global atmospheric change, and the potential of forest ecosystems to sequester larger amounts of carbon in the future.
大气中二氧化碳浓度的增加可能通过提高光合速率对植物生长产生施肥效应，因此可能抵消由较高温度和较低降水量相关的胁迫所导致的潜在生长下降。然而，植物生长既由净光合速率决定，也由固定碳在自养组织和异养组织中的比例分配决定。尽管二氧化碳施肥可能通过提高叶片水平的同化速率来促进生长，但响应于较高的二氧化碳浓度和较高温度，生物量从叶片重新分配到茎和根可能会降低整株植物的同化作用并抵消光合增益。我们测量了在350或650微巴二氧化碳以及10/25°C或15/30°C昼夜温度的2×2析因处理中生长2个月的黄松幼苗的生长参数、光合作用、呼吸作用和生物量分配。在处理条件下培养1个月后，高二氧化碳处理中幼苗总生物量更高，并且温度显著增强了二氧化碳的正向效应。然而，2个月后，二氧化碳对总生物量的影响下降，并且在2个月的生长期间，二氧化碳和温度处理之间的相对生长速率没有差异，尽管在高二氧化碳处理中光合速率增加了约7%，在高温处理中光合速率下降了约10%。此外，二氧化碳增强降低了根系呼吸作用，高温增加了地上部分呼吸作用。基于二氧化碳交换速率，二氧化碳施肥应该增加相对生长速率（RGR），高温应该降低RGR。在暴露于处理条件的第二个月期间，由二氧化碳施肥引起的较高光合速率似乎因生物量向叶片的分配减少约3%和根冠比增加约9%而得到缓解。目前尚不清楚为什么高温下光合速率降低和呼吸速率增加没有导致较低的RGR。二氧化碳交换和生物量分配的显著径向和潜在补偿响应以及高二氧化碳暴露2个月后黄松RGR缺乏差异表明，二氧化碳施肥和温度对整株植物生长的影响由生物量分配和气体交换的复杂变化决定，对于某些物种而言，这些变化可能在气候和大气二氧化碳浓度变化时维持恒定的生长速率。必须综合考虑这些复杂响应，以预测植物对全球大气变化的生长反应以及森林生态系统未来固存大量碳的潜力。
