西南高山地区生态系统类型丰富、地形复杂,是响应全球气候变化的重点区域,对全球气候变化具有重要的指示作用。研究应用生态系统模型CEVSA(Carbon Exchange between Vegetation,Soil,and the Atmosphere)估算了1954—2010年西南高山地区土壤有机碳(Soil Organic Carbon,SOC)的时空变化,分析了其对气候变化的响应。结果表明:1西南高山地区1954—2010年平均土壤有机碳密度为14.16 kg C·m-2,在空间分布上,SOC密度自东南向西北递增,与温度显著负相关(r=-0.447,P<0.01),而与降水量相关性不显著;2西南高山地区1954—2010年SOC总量变动范围为6.95~7.64 Pg C,增加趋势显著(P<0.05),平均每年增加0.013 Pg C,土壤有机碳密度平均增加26.94 g C·m-2;3常绿针叶林、常绿阔叶林和草地SOC密度增加趋势均显著,除常绿阔叶林SOC密度与温度相关性不显著外,其他两种植被类型SOC都与年平均温度显著正相关(草地:r=0.527,P<0.01;常绿针叶林:r=0.501,P<0.01),且3种植被类型SOC与年降水量均相关性不显著;4由于作为土壤有机碳输入的凋落物产生量对温度不如异养呼吸敏感,所以未来升温条件下,土壤有机碳储量的增速减缓或者呈下降趋势。
以内蒙古锡林浩特市南部中国科学院草原生态系统定位研究站周围的草场为研究对象,分析比较了统计模型和亚像元分解模型进行草地植被覆盖度(vegetation coverage,VC)遥感估算的适用性。结果表明,根据Landsat-5TM影像数据计算的比值植被指数(simple ratio vegetation index,SR)与观测的VC的相关性最高(R2=0.761);统计模型和亚像元分解模型生成的VC空间分布特征相似,但亚像元分解模型得到的VC平均值比统计模型的结果高0.091;在VC的低值和高值区,两种方法得到的VC结果相似;但在VC的中值区,亚像元模型得到的结果较统计模型的结果偏高。
Canopy foliar Nitrogen Concentration （CNC） is one of the most important parameters influencing vegetation productivity in forest ecosystems. In this study, we explored the potential of imaging spectrometry （hyperspectral） remote sensing of CNC in conifer plantations in China’s subtropical red soil hilly region. Our analysis included data from 57 field plots scattered across two transects covered by Hyperion images. Single regression and partial least squares regression （PLSR） were used to explore the relationships between CNC and hyperspectral data. The correlations between CNC and nearinfrared relfectance （NIR） were consistent in three data subsets （subsets A-C）. For all subsets, CNC was signiifcantly positively correlated with NIR in the two transects （R2=0.29, 0.33 and 0.36, P＆lt;0.05 or P＆lt;0.01, respectively）. It suggested that the NIR-CNC relationship exist despite a weak one, and the relationship may be weakened by the single canopy structure. Besides, we also applied a shortwave infrared （SWIR） index - Normalized Difference Nitrogen Index （NDNI） to estimate CNC variation. NDNI presented a signiifcant positive correlation with CNC in different subsets, but like NIR, it was also with low coefifcient of determination （R2=0.38, 0.20 and 0.17, P＆lt;0.01, respectively）. Also, the correlations between CNC and the entire spectrum reflectance （or its derivative and logarithmic transformation） by PLSR owned different signiifcance in various subsets. We did not ifnd the very robust relationship like previous literatures, so the data we used were checked again. The paired T-test was applied to estimate the inlfuence of inter-annual variability of FNC on the relationships between CNC and Hyperion data. The inter-annual mismatch between period of ifeldwork and Hyperion acquisition had no inlfuence on the correlations of CNC-Hyperion data. Meanwhile, we pointed out that the lack of the canopy structure variation in conifer plantation area may lead to these weak relationsh
Soil dissolved organic carbon （DOC） is an active fraction of the soil organic carbon （SOC） pool and links terrestrial and aquatic systems. The degradation of DOC can affect carbon cycling, nutrient dynamics and energy supply to microorganism, and consequently change biogeochemical processes. This study investigated the vertical and seasonal variability of soil DOC concentrations and its controls in a 23-year-old planted slash pine （Pinus elliottii） forest at Qianyanzhou Forest Experimental Station （QFES） in Southern China. Soil solutions were collected at bimonthly intervals at depths of 10, 20 and 30 cm by a mechanical-vacuum extractor from November 2007 to March 2009, and at monthly intervals at depths of 10, 30 and 50cm from April 2009 to October 2010. The DOC concentrations were determined with a total organic carbon （TOC） analyzer. Mean （±standard deviation） DOC concentrations at depths of 10cm, 20cm, 30cm and 50cm were 12.4±4.4, 10.6±6.3, 8.7±2.6, and 8.0±5.9 mg L^-1, respectively. Both seasonal and spring means of DOC concentration showed a decreasing trend with increasing depth, while there was no clear trend for the summer, autumn, or winter seasons. DOC concentrations during spring, summer, autumn and winter ranged from 4.8 to 21.5, 4.9 to 26.2, 5.4 to 17.1, 4.9 to 14.6 mg L-1, respectively, their mean DOC concentrations were 10.2, 10.5, 10.8 and 8.3 mg L 1, respectively. No consistent pattern of seasonal variability of DOC concentrations at different depths was observed. No obvious relationship between organic carbon content of forest litter and DOC concentration was found. There was a positive linear relationship between SOC and DOC concentration （R2=0.19, p〈0.01）, which showed that SOC was one of the main controls of DOC. A positive exponential relationship existed between soil temperature at 5 cm and DOC concentrations at 10 cm depth in slash pine, masson pine （Pinus massoniana） and Chinese fir （Cunninghamia lanceolata） planted forests （R2=0.12, p〈0.01�
