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Why are Nitrogen Concentrations in Plant Tissues Lower under Elevated CO_2? A Critical Examination of the Hypotheses

查看全文 作　　者：Daniel R. [1]Taub;Xianzhong [2]Wang 高影响力作者 机构地区：[1]Biology Department and Environmental Studies Program, Southwestern University, Georgetown, Texas 78626, USA;[2]Department of Biology, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202, USA高影响力机构 出　　处：《Journal of Integrative Plant Biology》索引2008年第50卷第11期,共10页高影响力期刊 基　　金：Supported by the Cullen Fund of Southwestern University to D. R. Taub. 摘　　要：Plants grown under elevated atmospheric CO2 typically have decreased tissue concentrations of N compared with plants grown under current ambient CO2.The physiological mechanisms responsible for this phenomenon have not been definitely established,although a considerable number of hypotheses have been advanced to account for it.In this review we discuss and critically evaluate these hypotheses.One contributing factor to the decreases in tissue N concentrations clearly is dilution of N by increased photosynthetic assimilation of C.In addition,studies on intact plants show strong evidence for a general decrease in the specific uptake rates (uptake per unit mass or length of root) of N by roots under elevated CO2.This decreased root uptake appears likely to be the result both of decreased N demand by shoots and of decreased ability of the soil-root system to supply N.The best-supported mechanism for decreased N supply is a decrease in transpiration-driven mass flow of N in soils due to decreased stomatal conductance at elevated CO2,although some evidence suggests that altered root system architecture may also play a role.There is also limited evidence suggesting that under elevated CO2,plants may exhibit increased rates of N loss through volatilization and/or root exudation,further contributing to lowering tissue N concentrations. 关 键 词：二氧化碳 氮 植物 根 组织浓度
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