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气候变化和放牧对青藏高原高寒草甸生态系统温室气体通量影响的研究
胡宜刚
Subtype博士
Thesis Advisor汪诗平
2010-06-01
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline生态学
Keyword气候变化 高寒草甸 移栽 放牧 温室气体 净氮矿化 活性碳 惰性碳 微生物量碳
Abstract青藏高原正在经历着以增温为主要特征的气候变化过程。气候变化必然会对
高寒草甸生态系统带来各种各样的影响。当地最重要的人类活动—自由放牧可能
加速或削弱高寒草甸生态系统对气候变化的响应和反馈。本研究的目的是为了了
解不同增温幅度下高寒草甸生态系统温室气体通量的变化及其主要影响因子,评
价自由放牧方式对高寒草甸生态系统温室气体通量的影响。同时,本研究中不同
增温幅度下土壤氮循环关键过程和不同土壤碳库容量变化的研究有助于提高对高
寒草甸生态系统对气候变化响应的认识。
本研究利用温度随海拔高度增加而降低的原理以及空间代替时间的方法,选
择4 个不同样点的高寒草甸,在3200、3400、3600 和3800 m 4 个海拔高度梯度上采用双向移栽方法模拟气候变化,对2 个生长季(2008-2009)气候变化和自由放牧条件下高寒草甸生态系统温室气体通量的变化进行了观测。同时,在此山体垂直带上开展了气候变化条件下土壤氮矿化和不同土壤碳库容量变化的研究。研究结果表明:
1、环境变化。山体垂直带双向移栽试验可以很好的模拟气候变化。3200、
3400、3600 和3800 m 两个生长季内20 cm 土壤平均温度分别为9.8、7.5、6.2 和5.8℃。3200-3800m 的温差范围在0.3~4.2℃之间,海拔每升高200 m,20 cm 土壤温度平均降低1.2℃。3200、3400、3600 和3800 m 4 个海拔高度两个生长季内土壤20 cm 平均湿度分别为35.3、27.9、38.7 和14.3%,3600 m 处土壤湿度较高的原因是因为地处山体与滩地交界处,以及地形雨较多的缘故。
2、甲烷(CHB4B)通量。青藏高原高寒草甸生态系统是CHB4B的汇,生长季内平均吸收88.9 mg mP-2P。总体而言,CHB4B的吸收随着土壤温度的增加有增加的趋势,但不同试验样点之间增加的程度有一定的变化。CHB4B吸收通量与土壤温度显著正相关,与土壤湿度相关性不显著。但在各试验样点表现不一致。土壤温度和土壤湿度结合起来只解释了2-11%的CHB4B通量变异,说明CHB4B通量更大程度上受到其它因子的影响。降雨增加抑制了高寒草甸对CHB4B的吸收。放牧对高寒草甸CHB4B吸收能力的影响依据试验样点、取样日期和取样年份的不同而发生变化。总体上放牧对高寒草甸CHB4B通量没有显著影响。低海拔(3200 m)高强度冬季放牧的高寒草甸CHB4B吸收能力可能通过土壤温度的快速升高而增加。而其他情况下放牧降低了该地区高寒草甸CHB4B平均通量和累积通量,但差异不显著。
3、氧化亚氮(NB2BO)通量。青藏高原高寒草甸生态系统是NB2BO的排放源,生长季内平均排放30.2 mg mP-2P。总体上,NB2BO通量与土壤温度相关性不显著,与土壤湿度显著正相关(P<0.001)。土壤温度和土壤湿度二者结合能解释11-13%的NB2BO通量变异,说明NB2BO通量更大程度上受到其它因子的影响。气候变化对NB2BO通量的影响不同的试验样点依增温幅度和降雨量的变化而变化。放牧对高寒草甸NB2BO通量的影响依据试验样点、取样日期和取样年份的不同而发生变化。总体上放牧没有显著改变该地区生长季NB2BO的累积排放量。冬季高强度放牧增加的NB2BO来源于放牧家畜的排泄物;夏季长期放牧减少了海拔3600 和3800 m高寒草甸NB2BO的排放。
4、生态系统呼吸(COB2B)。各类高寒草甸生态系统呼吸均随着温度的增加而
增加。20 cm土壤温度每升高1℃,生态系统呼吸增加32.0%(13.7-49.4%)。土壤温度能解释该地区高寒草甸生态系统60~68%的生态系统呼吸变异。在0.3~4.2℃的增温幅度上,高寒草甸生态系统呼吸温度敏感性随着海拔高度的升高而增加,即地处高海拔的高寒草甸生态系统呼吸对温度更敏感。但在10℃的增温幅度上,金露梅灌丛高寒草甸的生态系统呼吸温度敏感性(QB10B)高于3800 m以下的矮嵩草高寒草甸,但低于3800 m的矮嵩草高寒草甸。高寒草甸生态系统呼吸与土壤湿度的相关性很弱(r = 0.05),且不同试验样点之间表现不一致。自由放牧对高寒草甸生态系统呼吸的影响依据不同的试验样点有增加或降低的趋势,但放牧和不放牧处理之间差异并不显著,说明该地区目前的自由放牧方式对高寒草甸生态系统呼吸没有显著影响。依据不同温室气体的增温潜值,综合三种温室气体通量,发现温度每升高1℃,该地区整个生长季内高寒草甸生态系统将平均累积多释放341.7 g COB2B当量。放牧降低了该地区4.4%的全球增温潜能(GWP),生长季内平均减少124.2 g COB2B当量mP-2P,但差异不显著。因而,自由放牧对气候变暖的响应在温室气体方面表现为较弱的负反馈。
5、土壤净氮矿化。海拔高度和试验样点显著影响各层次(0-30 cm)土壤
NOB3PB¯P-N、NHB4PB+P-N和总无机氮(NOB3PB¯P-N和NHB4PB+PN的含量。试验样点和海拔高度之间没有互作效应。土壤无机氮含量没有明显而统一的增加或降低的趋势。取样时间、试验样点、海拔高度以及试验样点和海拔高度的互作显著影响0-20 cm土壤净氮矿化速率和净氨化速率。温度对同一试验样点高寒草甸生长季内净氮矿化率的影响主要是通过影响净硝化率而实现的,温度对土壤净氨化率没有明显的影响。自由放牧对该地区高寒草甸中土壤表层(0-10 cm)无机氮含量没有显著影响。6、土壤可溶性碳(DOC)。温度是影响高寒草甸土壤可溶性有机碳(DOC)的主要因子,可以解释75.8%的土壤DOC 变异。增温(0.6-4.2℃)增加高寒草甸生长季4.4~32.9%的土壤DOC 含量。处于高海拔的高寒草甸土壤DOC 含量对温度更敏感,可能导致地处高海拔的高寒甸生态系统呼吸对温度更敏感。温度能解释21.9%的该地区土壤活性碳库的变异。高寒草甸土壤微生物量碳库、土壤活性碳库容量都随着温度的增加而增加。短期内增温可能通过提高微生物的活性,加快有机物质的分解速率,增加土壤活性碳库而增加高寒草甸生态系统呼吸。
Other AbstractThe Qinghai-Tibet plateau is experiencing climate change especially for global warming which is thought to cause various problems for alpine meandow. Grazing, as a main human activity in the region, may accelerate or weaken the responses and feedbacks of alpine meadow ecosystem to climate change. In this study, according to
the principle that temperature varies with elevation and method that space substitude for time, we conducted an experiment to study the effects of climate change on GHGs fluxes on the Qinghai-Tibetan plateau using reciprocal translocation experiment with four different alpine meadow sites along the elevation gradient from 3200 to 3800 m. During the growing seasons in 2008 and 2009, the dynamics of the GHGs fluxes were investigated under different elevations and free-grazing. Meanwhile, soil nitrogen net mineralization and size of various soil carbon pools were also studied. The objectives of this study are to: 1)determine varations of greenhouse gases (GHGs) fluxes in alpine meadow ecosystem and their main controlling factors under different climate conditions; 2)access effects of free-grazing on GHGs fluxes of alpine medow ecosystem; 3) investigate the effects of climate change on soil nitrogen net mineralization and carbon stock. The results showed as bellows:
1. Variation of environmental factors. Reciprocal translocation experiment could finely imitate climate change along the elevation gradient. During the growing seasons in 2008 and 2009, average soil temperature at 20cm depth was 9.8,7.5,6.2 and 5.8℃
for 3200, 3400, 3600 and 3800 m, respectively. Difference of soil temperature at the depth of 20 cm ranged from 0.3 to 4.2℃ which averagely increased 1.2℃ for each 200 m elvation rise. The mean soil moisture at 20 cm depth for 3200, 3400, 3600 and 3800m was 35.3, 27.9, 38.7 and 14.3%, respectively. The soil moisture at the site of 3600m was greater because of more runoff from anow melting with more topographic rainfall during growing seasons.
2. Fluxes of methane (CHB4B). Alpine meadow was a sink for methane with average absorption of 88.88 mg mP-2P during growing season from May to September. In general, the absorption of methane increased with temperature rise, but increase extent varied
among different alpine sites. The absorption of methane was positive correlated to soil temperature but not to soil moisture. However, both of soil temperature and moisture could only explain 2-11% of the variation of methane, suggesting other factors controls the fluxes of methane in large scale. Higher precipitation could restrain the absorption of methane. Effects of free-grazing on methane absorption of alpine meadow depended on site, sampling date and year. Heavily winter grazing at low elevation of 3200 m stimulated
methane absorption which probably attributes to quickly soil temperature rise. Free-grazing reduced average and cumulative methane fluxes in other cases, but the difference was not significant.
3. Fluxes of nitrous oxide (NB2BO). Alpine meadow was a weak source for nitrous oxide with average release of 30.22 mg mP-2P during the growing seasons. Generally, nitrous oxide was not related to soil temperature but positively related to soil moisture(P<0.001). However, both of soil temperature and moisture could only explain 11-13% of the variation of nitrous oxide, indicating that other factors mainly controls the fluxes of NB2BO in large scale. Effects of climate change on NB2BO fluxes among different sites varied with extent of temperature rise and precipitation. Effects of free-grazing on NB2BO flux of alpine meadow depended on site, sampling date and year. In general, there was no significant effect of free-grazing on accumulative NB2BO fluxes during the growing seasons. Heavily winter grazing at low elevation of 3200 m stimulated emission of NB2BO which probably result from animal excrement. Long-term summer grazing reduced the emission of NB2BO of the alpine
meadow at the elevations of 3600 and 3800 m, but the difference was not significant.
4. Ecosystem respiration (COB2B). Ecosystem respiration increased with temperature rise for all alpine meadow sites. Ecosystem respiration averagely increased by 32.0%(13.74~49.44%) for every 1℃ soil temperature increase at the depth of 20 cm. Soil temperature could explaine 60-68% of the variations of alpine meadow ecosystem resipiration in the region. The sensitivity of ecosystem respiration increased with elevation rise for temperature rise ranged 0.3-4.2℃, indicating that respiration of alpine meadow at higher elevation was more sensitive to temperature. However, at 10
℃ temperature rise level, the sensitivity of ecosystem respiration (ie.QB10B) for alpine shrub meadow at 3400 m was higher than alpine meadow situated at 3200 and 3600 m, but lower than the alpine meadow at 3800 m. The ecosystem respiration was weakly
related to soil moisture (r = 0.05) and varied among various Sites.
Free-grazing increased or decreased ecosystem respirations which depended on sites at different elevations, even though the differences were not significant. Based on global warming potential (GWP) for each greenhouse gas, alpine meadow in this area accumulately emitted 341.7 g COB2 BmP-2P equivalent. Free-grazing
averagely reduced 4.4% of GWP which was comparative to 124.2 g COB2B mP-2Pduring thegrowing season, but the difference between grazing and no-grazing was not significant.5. Soil nitrogen net mineralization. Elevation and site significantly affectedcontents of nitrate, ammonia and inorganic nitrogen within 30 cm soil. There was nointeraction between site and elevation. Sampling date, site, elevation and interaction between site and elevation significantly affected rate of net nitrogen mineralization and ammonization within 20 cm soil. Effects of temperatue on net nitrogen mineralization
mainly came from effects of net nitrification. There was no significant effect of temperature on soil net ammonization. Free-grazing did not significantly affect content of inorganic nitrogen within 10 cm soil in the alpine meadows.
6. Soil dissolved organic carbon (DOC). Temperature significantly influenced soil DOC in alpine meadows which could explain 75.8% of the variation of soil DOC. Soil DOC increased by 4.4-32.9% during the growing seasons. Content of soil DOC in alpine meadow at higher elevation was more sensitive to temperature. Sizes of soil microbial biomass carbon and labile carbon pool increased with temperature rise. Temperature could explain 21.9% of the variation of soil labile carbon pool. Sizes of soil microbial biomass carbon and soil labile carbon also increased with temperature rise. Short-term temperature rising increased ecosystem respiration of alpine meadow could be attributed to improvement of microbial activity, acceleration of soil organic matter decomposition as well as increase in size of soil labile carbon pool.
Subject Area生物科学
Language中文
Document Type学位论文
Identifierhttp://210.75.249.4/handle/363003/3399
Collection中国科学院西北高原生物研究所
Recommended Citation
GB/T 7714
胡宜刚. 气候变化和放牧对青藏高原高寒草甸生态系统温室气体通量影响的研究[D]. 北京. 中国科学院研究生院,2010.
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