模拟CO2升高及降水变化对红砂碳氮特征的影响

摘要

为探讨荒漠植物红砂根、茎、叶在CO2升高与降水变化条件下的碳氮含量及分配特征,以当年生民勤红砂为试验材料,利用开顶式CO2控制气室,研究了350、550及700 μmol·mol-1 3种CO2浓度和降水减少30％(-W2)、减少15％(-W1)、自然降水(W0)、增加15％(+W1)和增加30％(+W2)5个降水变化下红砂根、茎、叶的有机碳、全氮含量、C/N及有机碳和全氮积累(吸收)量.结果表明:1)相同降水条件下,CO2浓度升高使根、茎、叶有机碳含量显著增加,全氮含量显著减少;在-W2降水量和700 μmol·mol-1 CO2浓度时根有机碳含量增幅最大(13.33％),在+W1降水量和700 μmol·mol-1 CO2浓度时叶全氮含量降幅最大(56.31％);CO2浓度升高使红砂根、茎、叶C/N显著升高,对有机碳、全氮积累(吸收)量影响显著.2)相同CO2浓度条件下,降水增加对根、茎、叶有机碳含量及全氮含量影响显著;550 μmol·mol-1 CO2浓度和+W2降水量时叶有机碳含量增幅最大(11.56％),700 μmol·mol-1 CO2浓度和+W2降水量时叶全氮含量降幅最大(35.31％);降水量对红砂根、茎、叶的C/N及有机碳、全氮积累量影响显著.3)在CO2浓度升高与降水变化下,红砂有机碳含量在根中最高,全氮含量在叶中最高,C/N在根中最大,红砂有机碳、全氮积累(吸收)量在叶中最高.综上所述,未来CO2浓度升高及降水改变的情况下,红砂生长情况取决于CO2浓度与降水量的协同作用对有机碳、全氮含量的影响,CO2浓度升高会在一定程度上减缓干旱对红砂碳氮吸收及利用的抑制作用,在湿润条件下能有效地增强红砂对碳氮的吸收及利用能力.%Atmospheric CO2 concentrations are predicted to increase from approximately 350 μmol · mol-1 today to over 700 μmol · mol-1 in the late 21st century.In the future,elevated CO2 levels are likely to have profound effects on precipitation.This change would seriously affect the desert ecosystem,altering the carbon and nitrogen allocations of desert plants and so leading to changes in ecosystem structure and function.Although many studies have examined the effects of precipitation and CO2,the interactions between precipitation changes and CO2 in desert plants have attracted little attention to date.In order to assess the possible effect of global climate change on desert ecosystems,a pot experiment was conducted to study the interaction of elevated CO2 concentrations and changing precipitation with organic carbon,total nitrogen,C/N,organic carbon accumulation (absorption),and total nitrogen accumulation (absorption) in the roots,stems and leaves of Reaumuria soongorica,a dominant species on desert steppe in the arid regions of China.The main experiment included three CO2 concentrations (350,550 and 700 μmol · mol-1) and five precipitation conditions (natural precipitation as control [W0],precipitation minus 30％ [-W2],precipitation minus 15％ [-W1],precipitation plus 15％ [+W1],and precipitation plus 30％ [+W2]).The main results are as follows:1) At the same precipitation treatment,organic carbon in root,stem and leaf were significantly increased and total nitrogen decreased by elevated CO2.The rise of organic carbon contents in roots was highest at 13.33％ under 700 μmol · mol-1 CO2 concentration and-W2 precipitation.Total nitrogen contents in leaves were lowest at 56.31％ under 700 μmol · mol-1 CO2 concentration and +W1 precipitation.C/N,organic carbon and total nitrogen accumulation (absorption) in root,stem and leaf were significantly increased by elevated CO2.2) At the same CO2 concentrations,organic carbon and total nitrogen in roots and stems significantly increased with raised precipitation levels.The largest increase in organic carbon in leaves was 11.56％ under +W2 precipitation and 550 μtmol ·mol-1 CO2 concentration.The largest decrease in total nitrogen in leaves was 40.16％ under precipitation +W2 and 700 μmol · mol-1 CO2 concentration.C/N,organic carbon and total nitrogen accumulation (absorption) in root,stem and leaf were affected significantly by precipitation.3) Under the interactive effects of elevated CO2 and changing precipitation conditions,organic carbon contents and C/N were allocated mostly to roots,total nitrogen,organic carbon accumulation and total nitrogen accumulation (absorption) mostly to leaves.These results suggest that in the future,with CO2 concentration and precipitation changes,the growth states of R.soongorica will be decided by the interactive effects of CO2 concentration and precipitation changes on carbon and nitrogen.Elevated CO2 concentration can relieve the inhibition of drought on the carbon and nitrogen absorbed and used of R.soongorica,and moist conditions can reinforce the impact of these elements.