CAJ | 학술논문

【目的】退耕还林还草引起地表植被盖度变化不仅能有效控制坡耕地的土壤侵蚀，而且会显著增加土壤有机碳储量。但目前关于退耕坡地人工恢复植被后土壤CO2排放的空间变化及其控制机理却较少研究，增大了定量估算退耕还林工程土壤碳循环效应的不确定性。本文以黄土丘陵典型退耕还林坡地为对象，研究了土壤CO2排放的空间变化及其控制机理，为进一步认识黄土高原有机碳库周转和估算陆地生态系统碳收支提供科学依据。【方法】为了确定人工林山坡土壤CO2排放空间变异及其影响因素，将人工林全山坡划分为峁顶、峁坡、坡上部、坡中部和坡下部5个坡位，并按照从峁顶到坡下部沿顺坡断面每间隔10 m确定一个研究小区，利用点测法测定不同植被类型盖度，利用原状根钻采集土壤剖面样品用于测定根系密度、土壤有机碳( SOC)含量和137 Cs面积含量，并利用LI-8100碳通量自动测量仪原位测定土壤CO2排放速率的季节变化，同时测定土壤水分和表层土壤5cm深度的温度，利用相关回归分析法确定影响土壤CO2排放空间变化的主要因素。【结果】试验期间，不同坡位土壤CO2排放速率均表现为夏季>秋季>春季。与春季相比，人工林全山坡土壤CO2排放速率的平均值在夏、秋季分别增加了48%和9%。研究期内人工林坡地土壤CO2排放速率在春、夏、秋三个季节具有相同的空间分异特征，其平均值的大小为峁顶(参考点)[2．51±0．07μmol/(m2·s)]>峁坡[2．19±0．17μmol/(m2·s)]>坡下部[1．88±0．12μmol/(m2·s)]>坡中部[1．71±0．09μmol/(m2·s)]>坡上部[1．62±0．12μmol/(m2·s)]。与峁顶参考点相比，坡上部和坡中部的137 Cs面积含量分别减少了46%和29%；峁坡和坡下部的137 Cs面积含量分别增加了88%和52%，这说明研究区人工林山坡的坡上部发生了严重土壤侵蚀，坡中部发生了轻度土壤侵蚀，而峁坡和坡下部则发生了土壤堆积，尤以峁坡的土壤堆积最为显著。人工林坡地土壤CO2排放的空间变化与地形坡度、137 Cs面积含量(土壤侵蚀指标)均呈显著相关关系(P<0．01)，与土壤水分、土壤温度和SOC储量只在夏季有显著相关(P<0．01)，在其它季节无显著相关性；人工林坡地土壤CO2排放的空间变化与植被根系密度无明显相关性。【结论】地形坡度变化驱动的土壤侵蚀和堆积过程是控制黄土丘陵区人工林坡地土壤CO2排放空间分异的主要因子，应在定量评价退耕还林工程的土壤固碳效应时予以考虑。【目的】退耕還林還草引起地錶植被蓋度變化不僅能有效控製坡耕地的土壤侵蝕，而且會顯著增加土壤有機碳儲量。但目前關于退耕坡地人工恢複植被後土壤CO2排放的空間變化及其控製機理卻較少研究，增大瞭定量估算退耕還林工程土壤碳循環效應的不確定性。本文以黃土丘陵典型退耕還林坡地為對象，研究瞭土壤CO2排放的空間變化及其控製機理，為進一步認識黃土高原有機碳庫週轉和估算陸地生態繫統碳收支提供科學依據。【方法】為瞭確定人工林山坡土壤CO2排放空間變異及其影響因素，將人工林全山坡劃分為峁頂、峁坡、坡上部、坡中部和坡下部5箇坡位，併按照從峁頂到坡下部沿順坡斷麵每間隔10 m確定一箇研究小區，利用點測法測定不同植被類型蓋度，利用原狀根鑽採集土壤剖麵樣品用于測定根繫密度、土壤有機碳( SOC)含量和137 Cs麵積含量，併利用LI-8100碳通量自動測量儀原位測定土壤CO2排放速率的季節變化，同時測定土壤水分和錶層土壤5cm深度的溫度，利用相關迴歸分析法確定影響土壤CO2排放空間變化的主要因素。【結果】試驗期間，不同坡位土壤CO2排放速率均錶現為夏季>鞦季>春季。與春季相比，人工林全山坡土壤CO2排放速率的平均值在夏、鞦季分彆增加瞭48%和9%。研究期內人工林坡地土壤CO2排放速率在春、夏、鞦三箇季節具有相同的空間分異特徵，其平均值的大小為峁頂(參攷點)[2．51±0．07μmol/(m2·s)]>峁坡[2．19±0．17μmol/(m2·s)]>坡下部[1．88±0．12μmol/(m2·s)]>坡中部[1．71±0．09μmol/(m2·s)]>坡上部[1．62±0．12μmol/(m2·s)]。與峁頂參攷點相比，坡上部和坡中部的137 Cs麵積含量分彆減少瞭46%和29%；峁坡和坡下部的137 Cs麵積含量分彆增加瞭88%和52%，這說明研究區人工林山坡的坡上部髮生瞭嚴重土壤侵蝕，坡中部髮生瞭輕度土壤侵蝕，而峁坡和坡下部則髮生瞭土壤堆積，尤以峁坡的土壤堆積最為顯著。人工林坡地土壤CO2排放的空間變化與地形坡度、137 Cs麵積含量(土壤侵蝕指標)均呈顯著相關關繫(P<0．01)，與土壤水分、土壤溫度和SOC儲量隻在夏季有顯著相關(P<0．01)，在其它季節無顯著相關性；人工林坡地土壤CO2排放的空間變化與植被根繫密度無明顯相關性。【結論】地形坡度變化驅動的土壤侵蝕和堆積過程是控製黃土丘陵區人工林坡地土壤CO2排放空間分異的主要因子，應在定量評價退耕還林工程的土壤固碳效應時予以攷慮。
【목적】퇴경환림환초인기지표식피개도변화불부능유효공제파경지적토양침식，이차회현저증가토양유궤탄저량。단목전관우퇴경파지인공회복식피후토양CO2배방적공간변화급기공제궤리각교소연구，증대료정량고산퇴경환림공정토양탄순배효응적불학정성。본문이황토구릉전형퇴경환림파지위대상，연구료토양CO2배방적공간변화급기공제궤리，위진일보인식황토고원유궤탄고주전화고산륙지생태계통탄수지제공과학의거。【방법】위료학정인공림산파토양CO2배방공간변이급기영향인소，장인공림전산파화분위묘정、묘파、파상부、파중부화파하부5개파위，병안조종묘정도파하부연순파단면매간격10 m학정일개연구소구，이용점측법측정불동식피류형개도，이용원상근찬채집토양부면양품용우측정근계밀도、토양유궤탄( SOC)함량화137 Cs면적함량，병이용LI-8100탄통량자동측량의원위측정토양CO2배방속솔적계절변화，동시측정토양수분화표층토양5cm심도적온도，이용상관회귀분석법학정영향토양CO2배방공간변화적주요인소。【결과】시험기간，불동파위토양CO2배방속솔균표현위하계>추계>춘계。여춘계상비，인공림전산파토양CO2배방속솔적평균치재하、추계분별증가료48%화9%。연구기내인공림파지토양CO2배방속솔재춘、하、추삼개계절구유상동적공간분이특정，기평균치적대소위묘정(삼고점)[2．51±0．07μmol/(m2·s)]>묘파[2．19±0．17μmol/(m2·s)]>파하부[1．88±0．12μmol/(m2·s)]>파중부[1．71±0．09μmol/(m2·s)]>파상부[1．62±0．12μmol/(m2·s)]。여묘정삼고점상비，파상부화파중부적137 Cs면적함량분별감소료46%화29%；묘파화파하부적137 Cs면적함량분별증가료88%화52%，저설명연구구인공림산파적파상부발생료엄중토양침식，파중부발생료경도토양침식，이묘파화파하부칙발생료토양퇴적，우이묘파적토양퇴적최위현저。인공림파지토양CO2배방적공간변화여지형파도、137 Cs면적함량(토양침식지표)균정현저상관관계(P<0．01)，여토양수분、토양온도화SOC저량지재하계유현저상관(P<0．01)，재기타계절무현저상관성；인공림파지토양CO2배방적공간변화여식피근계밀도무명현상관성。【결론】지형파도변화구동적토양침식화퇴적과정시공제황토구릉구인공림파지토양CO2배방공간분이적주요인자，응재정량평개퇴경환림공정적토양고탄효응시여이고필。
[Objectives]Changes in vegetation as a result of converting cultivated land into forested areas are known to effectively prevent the soil erosion as well as significantly increase the soil organic carbon storage in these regions. However, the spatial change of soil CO2 emission and its control mechanism are poorly understood and can thus lead to further uncertainties in the quantitative estimations of soil carbon sequestration in these reforestedareas. A typical re-forested hillslope was selected in order to investigate the spatial variation of soil CO2 emissions and its control mechanism in the Loess Plateau. This study aims to provide a scientific basis for further understanding the Loess Plateau organic carbon turnover and improve methods for estimating the carbon balance of terrestrial ecosystems. [Methods]In order to determine tempo-spatial dynamics of soil CO2 emission of sloping cultivated land and its influencing factors, the re-forested hillslope(250 m total length) was divided into 5 sections-hilltop, shoulder, upper, middle and lower slope-and each section analyzed. The point method was used to estimate the vegetation coverage of all study plots selected at intervals of 10 meters along the entire slope. Soil samples were collected by drill and root density, soil organic carbon ( SOC ) content and 137 Cs inventory were analyzed. In situ soil CO2 emission was monitored by LI-8100 carbon flux automatic systems on a monthly basis, and soil water content and soil temperature ( at a depth of 5cm) were also measured. Correlation and regression analysis was applied to determine the main factors that affect spatial soil CO2 emissions.[Results] The results show that the temporal dynamics of soil CO2 emission rates at different slope positions during the data collection period was highest in the summer, followed by autumn, with spring having the lowest observed soil CO2 emission rates. When calculating the average value of soil CO2 emission rates across the whole hillslope, emission rates for summer and autumn were found to be higher by 48% and 9%, respectively, when compared to spring. The spatial patterns of soil CO2 emission rates were found to be similar across spring, summer and autumn and the average emission rate of the three seasons was found to decrease as follows across the slope: hilltop ( reference ) [ 2. 51 ± 0. 07μmol/(m2·s)]> shoulder[2. 19±0. 17 μmol/(m2·s)]> lower[1. 88±0. 12 μmol/(m2·s)]> middle[1. 71± 0. 09 μmol/(m2·s)]>upper[1. 62±0. 12 μmol/(m2·s)]. Using the hilltop as a reference, the 137Cs inventory in the upper and middle hillslope was lower by 46% and 29%, respectively;however 137 Cs inventory calculated at the shoulder and lower region of the hillslope was 88% and 52% higher than the reference. These results indicate that there was serious soil erosion at the upper section of the hillslope with lighter soil erosion at the middle section. Furthermore, soil accumulation occurred at both the shoulder and lower sections, with more significant accumulation occurring at the shoulder. We found that soil CO2 emission rates significantly correlated with the slope gradient(P<0. 01)and 137Cs inventory(P<0. 01)during the data collection period. Interestingly, only in summer did the soil CO2 emission rates have significant correlation with soil moisture, soil temperature and SOC stock( P<0. 01). No significant relationship was found between soil CO2 emission and root density. [Conclusions]These results suggested that soil erosion and deposition processes induced by the change of topographic slope are the main factors controlling the spatial variation of soil CO2 emission rate on the Loess plateau ecological forest slopes. These factors should thus be taken into consideration in the quantitative evaluation of the effectiveness of soil carbon sequestration by the Grain to Green Project.