Effect of nitrogen deposition on fluxes of green house gases in a forest ecosystem

氮沉降影响森林生态系统绿色温室气体的排放和吸收。氮沉降增加了森林土壤氧化亚氮的排放，抑制了甲烷的排放。氮沉降对森林生长和CO_2固定有促进或抑制作用。然而，大多数研究都集中在氮饱和的森林接受高沉积的氮（DIN &gt; 10 kgN ha^<-1>y^<-1>），我们需要更多的信息，氮沉降对绿色室内气体通量在森林接受低氮沉降（DIN &lt; 10 kgN ha^<-1>y^<-1>）的影响。IPCC提出了“全球变暖潜势”（GWP）的概念，作为衡量生态系统地球化学过程对全球变暖影响的综合指标。以前的研究主要集中在这些绿色室内气体中的一种，例如，二氧化碳一氧化二氮和甲烷很少有研究报告这些气体或森林生态系统全球升温潜能值的总体影响。本研究旨在 关于我们 揭示极低氮沉降对落叶松林GWP的影响。我们研究了在五个地点在落叶松林山。日本北方札幌市白幡。用密闭箱法测定了土壤/积雪表面N_2O排放和CH_4吸收。通过测定树木的高度和呼吸高度处的直径、异速生长方程和室内培养的土壤微生物呼吸来估算CO_2的固定量，无雪季节的氮沉降量为0.8 ~ 1.8 kgN ha^<-1>y^<-1>。CH_4年吸收量为5 ~ 7 kgC ha^<-1>y^<-1>，与氮沉降量无相关性。但是，我们的结果与文献数据的比较表明，高的CH_4吸收在这个研究地点是由非常低的氮沉降，已知抑制CH_4吸收。由于N_2O排放与土壤温度和土壤湿度没有相关性，因此本研究中N_2O排放属于背景型排放。背景型N_2O排放不受氮沉降的影响。年N_2O排放量为0.02 ~ 0.09 kgN ha^<-1>y^<-1>。无雪季节N_2O排放量与现雪季节氮沉降量呈正相关。通过与文献中背景型N_2O排放数据的比较，表明氮沉降对背景型N_2O排放也有影响。净生态系统生产力（NEP）为0.2 - 2.1 tC ha^<-1>y^<-1>。无雪季节NEP与氮沉降呈正相关。计算结果表明，森林植被对CO2的吸收是该研究区GWP的最大组成部分，N2 O排放和CH 4吸收对GWP的贡献可以忽略不计。综上所述，氮沉降对全球变暖具有负效应，氮沉降对树木生长的促进作用远大于氮沉降对N_2O排放的促进作用和对CH_4吸收的减少作用。少

Nitrogen deposition has been known to affect emission and absorption of green house gases in forest ecosystems. Nitrogen deposition enhances nitrous oxide emission from forest soils and inhibits methane emission into forest soils. Nitrogen deposition might enhance or diminish forest growth and CO_2 sequestration. Most researches, however, focus on nitrogen-saturated forests receiving high deposition of nitrogen (DIN > 10 kgN ha^<-1> y^<-1>), and we need more information on the effect of nitrogen deposition on green house gases fluxes in forests receiving low nitrogen deposition (DIN < 10 kgN ha^<-1> y^<-1>). IPCC proposed the concept of 'Global Warming Potential' (GWP) as a comprehensive measure of effect of ecosystem biogeochemical processes on global warming. Previous studies mainly focused on one of these green house gases, e.g., carbon dioxide, nitrous oxide and methane. Very few studies reported total effect of these gases or GWP of forest ecosystems. The purpose of this study is … More to reveal the effect of very low nitrogen deposition on GWP in a larch forest. We studied at five sites in larch forest in Mt. Shirahata, Sapporo city, northern Japan. N_2O emission and CH_4 absorption at the surface of soil/snowpack were measured with closed chamber method. CO_2 sequestration was estimated with measurement of tree heights and diameters at breath height, allometric equation, and microbial respiration measured by incubation of moist soils in laboratory.Nitrogen deposition during no-snow season ranged 0.8 〜 1.8 kgN ha^<-1> y^<-1>. Annual CH_4 absorption ranged 5 〜 7 kgC ha^<-1> y^<-1> and showed no correlation with nitrogen deposition. But comparison of our result with literature data suggested that high CH_4 absorption in this study site was caused by very low nitrogen deposition that is known to inhibit CH_4 absorption. Nitrous oxide emission in this study was classified as background type emission because N_2O emission showed no correlation with soil temperature and soil moisture. Background type N_2O emission has been believed not to affected by nitrogen deposition. Annual N_2O emission ranged 0.02 〜 0.09 kgN ha^<-1> y^<-1>. Accumulated N_2O emission during no-snow season showed positive correlation to nitrogen deposition during now-snow season. Comparison of our results with literature data on background type N_2O emission suggested that even background type N_2O emission is affected by nitrogen deposition. Net ecosystem productivity (NEP) ranged 0.2 〜 2.1 tC ha^<-1> y^<-1>. NEP showed positive correlation to nitrogen deposition during no-snow season. Calculation of GWP revealed that CO_2 sequestration by forest vegetation was largest component in GWP in this study site ; contribution of N_2O emission and CH_4 absorption to GWP was negligible. In summary, nitrogen deposition has a negative effect on global warming and tree growth enhancement by nitrogen deposition has much larger role than enhanced N_2O emission and reduced CH_4 absorption by nitrogen deposition. Less