Accurate estimation of non-photosynthetic biomass is critical for modeling carbon dynamics within grassland ecosystems.We evaluated the cellulose absorption index(CAI),widely used for monitoring non-photosynthetic vegetation coverage,for non-photosynthetic biomass estimation.Our analysis was based on in situ hyperspectral measurements,during the growing seasons of 2009 and 2010,in the desert steppe of Inner Mongolia.ASD(Analytical Spectral Device)-derived and Hyperion-derived CAI were found to be effective for non-photosynthetic biomass estimation,yielding relative error(RE) values of 26.4% and 26.6%,respectively.The combination of MODIS(Moderate Resolution Imaging Spectroradiometer)-derived(MODIS2 MODIS5)/(MODIS2 +MODIS5) and(MODIS6 MODIS7)/(MODIS6 +MODIS7) showed a high multiple correlation(multiple correlation coefficient,r=0.884) with ASD-derived CAI.A predictive model involving the two MODIS indices gave greater accuracy(RE=28.9%) than the TM(Landsat Thematic Mapper)-derived indices.The latter were the normalized difference index(NDI),the soil adjusted corn residue index(SACRI),and the modified soil adjusted crop residue index(MSACRI).These indices yielded RE values of more than 42%.Our conclusions have great significance for the estimation of regional non-photosynthetic biomass in grasslands,based on remotely sensed data.
植物光合产物分配受环境因子和生物因子的共同影响。为增进对植物对全球变化响应的理解,从植物个体水平与群落/生态系统水平综述了植物光合产物分配的影响因子与影响机理的最新研究进展。植物个体在光照增强及受水分和养分胁迫时,会将光合产物更多地分配到根系;CO2浓度升高对植物光合产物分配的影响受土壤氮素的制约,植物受氮素胁迫时,CO2浓度升高会促进光合产物更多地分配到根系;反之,对植物光合产物分配没有影响。植物群落/生态系统的光合产物分配对环境因子的响应不敏感;光合产物向根系的分配比例随其生长阶段逐渐降低。功能平衡假说、源汇关系假说和相关生长关系假说分别从环境因子、个体发育和环境因子与个体发育协同作用方面阐述了植物光合产物分配的影响机理。在此基础上,指出了未来拟重点加强的研究方向:1)生态系统尺度的光合产物向呼吸部分的分配研究;2)地下净初级生产力(belowground net primary productivity,BNPP)研究;3)温室和野外条件下及幼苗和成熟林光合产物分配对环境因子响应的比较研究;4)生态系统尺度的多因子控制试验;5)整合环境因子和个体发育对植物光合产物分配格局的影响研究。
