Jackson R B, Reynolds H L
Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
Department of Integrative Biology, University of California, 94720, Berkeley, CA, USA.
Oecologia. 1996 Jan;105(1):74-80. doi: 10.1007/BF00328793.
Sustained increases in plant production in elevated CO depend on adequate belowground resources. Mechanisms for acquiring additional soil resources include increased root allocation and changes in root morphology or physiology. CO research to date has focused almost exclusively on changes in biomass and allocation. We examined physiological changes in nitrate and ammonium uptake in elevated CO, hypothesizing that uptake rates would increase with the amount of available CO. We combined our physiological estimates of nitrogen uptake with measurements of root biomass to assess whole root-system rates of nitrogen uptake. Surprisingly, physiological rates of ammonium uptake were unchanged with CO, and rates of nitrate uptake actually decreased significantly (P<0.005). Root boomass increased 23% in elevated CO (P<0.005), but almost all of this increase came in fertilized replicates. Rates of root-system nitrogen uptake in elevated CO increased for ammonium in nutrient-rich soil (P<0.05) and were unchanged for nitrate (P>0.80). Root-system rates of nitrogen uptake were more strongly correlated with physiological uptake rates than with root biomass in unamended soil, but the reverse was true in fertilized replicates. We discuss nitrogen uptake and changes in root biomass in the context of root nutrient concentrations (which were generally unchanged with CO) and standing pools of belowground plant nitrogen. In research to date, there appears to be a fairly general increase in root biomass with elevated CO, and little evidence of up-regulation in root physiology.
在二氧化碳浓度升高的情况下，植物产量的持续增加依赖于充足的地下资源。获取额外土壤资源的机制包括增加根系分配以及根系形态或生理的变化。迄今为止，关于二氧化碳的研究几乎完全集中在生物量和分配的变化上。我们研究了在二氧化碳浓度升高时硝酸盐和铵盐吸收的生理变化，假设吸收速率会随着可利用二氧化碳量的增加而提高。我们将氮吸收的生理估计值与根系生物量的测量值相结合，以评估整个根系的氮吸收速率。令人惊讶的是，铵盐吸收的生理速率在二氧化碳浓度升高时没有变化，而硝酸盐吸收速率实际上显著下降（P<0.005）。在二氧化碳浓度升高时，根系生物量增加了23%（P<0.005），但几乎所有这种增加都出现在施肥的重复样本中。在二氧化碳浓度升高时，富营养土壤中铵盐的根系氮吸收速率增加（P<0.05），而硝酸盐的吸收速率没有变化（P>0.80）。在未改良土壤中，根系氮吸收速率与生理吸收速率的相关性比与根系生物量的相关性更强，但在施肥的重复样本中情况则相反。我们在根系养分浓度（一般随二氧化碳浓度升高无变化）和地下植物氮的现存库的背景下讨论氮吸收和根系生物量的变化。在迄今为止的研究中，随着二氧化碳浓度升高，根系生物量似乎普遍有相当程度的增加，而几乎没有证据表明根系生理有上调现象。
