Mahall B E, Schlesinger W H
Department of Biological Sciences, University of California, 93106, Santa Barbara, CA, USA.
Department of Botany, Duke University, 27706, Durham, NC, USA.
Oecologia. 1982 Sep;54(3):291-299. doi: 10.1007/BF00379995.
The effects of irradiance during growth on biomass allocation, growth rates, leaf chlorophyll and protein contents, and on gas exchange responses to irradiance and CO partial pressures of the evergreen, sclerophyllous, chaparral shrub, Ceanothus megacarpus were determined. Plants were grown at 4 irradiances for the growth experiments, 8, 17, 25, 41 nE cm sec, and at 2 irradiances, 9 and 50 nE cm sec, for the other comparisons.At higher irradiances root/shoot ratios were somewhat greater and specific leaf weights were much greater, while leaf area ratios were much lower and leaf weight ratios were slightly lower than at lower irradiances. Relative growth rates increased with increasing irradiance up to 25 nE cm sec and then leveled off, while unit leaf area rates increased steeply and unit leaf weight rates increased more gradually up to the highest growth irradiance.Leaves grown at 9 nE cm sec had less total chlorophyll per unit leaf area and more per unit leaf weight than those grown at 50 nE cm sec. In a reverse of what is commonly found, low irradiance grown leaves had significantly higher chlorophyll a/b than high irradiance grown leaves. High irradiance grown leaves had much more total soluble protein per unit leaf area and per unit dry weight, and they had much higher soluble protein/chlorophyll than low irradiance grown leaves.High irradiance grown leaves had higher rates of respiration in very dim light, required higher irradiances for photosynthetic saturation and had higher irradiance saturated rates of photosynthesis than low irradiance grown leaves. CO compensation irradiances for leaves of both treatments were very low, <5 nE cm sec. Leaves grown under low and those grown under high irradiances reached 95% of their saturated photosynthetic rates at 65 and 85 nE cm sec, respectively. Irradiance saturated rates of photosynthesis were high compared to other chaparral shrubs, 1.3 for low and 1.9 nmol CO cm sec for high irradiance grown leaves. A very unusual finding was that leaf conductances to HO were significantly lower in the high irradiance grown leaves than in the low irradiance grown leaves. This, plus the differences in photosynthetic rates, resulted in higher water use efficiencies by the high irradiance grown leaves. High irradiance grown leaves had higher rates of photosynthesis at any particular intercellular CO partial pressure and also responded more steeply to increasing CO partial pressure than did low irradiance grown leaves. Leaves from both treatments showed reduced photosynthetic capability after being subjected to low CO partial pressures (≃100 μbars) under high irradiances. This treatment was more detrimental to leaves grown under low irradiances.The ecological implications of these findings are discussed in terms of chaparral shrub community structure. We suggest that light availability may be an important determinant of chaparral community structure through its effects on water use efficiencies rather than on net carbon gain.
测定了生长期间光照强度对常绿硬叶丛林灌木大果鼠李的生物量分配、生长速率、叶片叶绿素和蛋白质含量以及对光照强度和二氧化碳分压的气体交换响应的影响。在生长实验中，植株在4种光照强度下生长，分别为8、17、25、41微爱因斯坦·厘米⁻²·秒⁻¹，在其他比较实验中，植株在2种光照强度下生长，分别为9和50微爱因斯坦·厘米⁻²·秒⁻¹。在较高光照强度下，根冠比略大，比叶重更大，而叶面积比更低，叶重比略低于较低光照强度下的情况。相对生长速率随着光照强度增加至25微爱因斯坦·厘米⁻²·秒⁻¹而增加，然后趋于平稳，而单位叶面积速率急剧增加，单位叶重速率在最高生长光照强度之前增加较为缓慢。在9微爱因斯坦·厘米⁻²·秒⁻¹光照强度下生长的叶片，单位叶面积总叶绿素含量比在50微爱因斯坦·厘米⁻²·秒⁻¹光照强度下生长的叶片少，但单位叶重总叶绿素含量更多。与常见情况相反，低光照强度下生长的叶片叶绿素a/b显著高于高光照强度下生长的叶片。高光照强度下生长的叶片单位叶面积和单位干重的总可溶性蛋白质含量更多，其可溶性蛋白质/叶绿素比也高于低光照强度下生长的叶片。高光照强度下生长的叶片在极弱光下呼吸速率更高，光合作用达到饱和所需的光照强度更高，且光照强度饱和光合作用速率高于低光照强度下生长的叶片。两种处理的叶片的二氧化碳补偿光照强度都非常低，<5微爱因斯坦·厘米⁻²·秒⁻¹。低光照强度和高光照强度下生长的叶片分别在65和85微爱因斯坦·厘米⁻²·秒⁻¹时达到其饱和光合速率的95%。与其他丛林灌木相比，光照强度饱和光合作用速率较高，低光照强度下生长的叶片为每秒1.3微摩尔二氧化碳·厘米⁻²，高光照强度下生长的叶片为每秒1.9微摩尔二氧化碳·厘米⁻²。一个非常不寻常的发现是，高光照强度下生长的叶片对水蒸气的叶导度显著低于低光照强度下生长的叶片。这一点，再加上光合速率的差异，导致高光照强度下生长的叶片水分利用效率更高。在任何特定的细胞间二氧化碳分压下，高光照强度下生长的叶片光合速率更高，并且对二氧化碳分压增加的响应也比低光照强度下生长的叶片更强烈。在高光照强度下，两种处理的叶片在受到低二氧化碳分压（≃100微巴）后光合能力都有所下降。这种处理对低光照强度下生长的叶片更有害。从丛林灌木群落结构的角度讨论了这些发现的生态意义。我们认为，光照可用性可能是丛林群落结构的一个重要决定因素，其通过对水分利用效率而非净碳增益的影响来实现。
