State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
PLoS One. 2012;7(8):e43614. doi: 10.1371/journal.pone.0043614. Epub 2012 Aug 20.
Vegetation light use efficiency (LUE) is a key parameter of Production Efficiency Models (PEMs) for simulating gross primary production (GPP) of vegetation, from regional to global scales. Previous studies suggest that grasslands have the largest inter-site variation of LUE and controlling factors of grassland LUE differ from those of other biomes, since grasslands are usually water-limited ecosystems. Combining eddy covariance flux data with the fraction of photosynthetically active radiation absorbed by the plant canopy from MODIS, we report LUE on a typical steppe and a desert steppe in Inner Mongolia, northern China. Results show that both annual average LUE and maximum LUE were higher on the desert steppe (0.51 and 1.13 g C MJ(-1)) than on the typical steppe (0.34 and 0.88 g C MJ(-1)), despite the higher GPP of the latter. Water availability was the primary limiting factor of LUE at both sites. Evaporative fraction (EF) or the ratio of actual evapotranspiration to potential evapotranspiration (AET/PET) can explain 50-70% of seasonal LUE variations at both sites. However, the slope of linear regression between LUE and EF (or AET/PET) differed significantly between the two sites. LUE increased with the diffuse radiation ratio on the typical steppe; however, such a trend was not found for the desert steppe. Our results suggest that a biome-dependent LUE(max) is inappropriate, because of the large inter-site difference of LUE(max) within the biome. EF could be a promising down-regulator on grassland LUE for PEMs, but there may be a site-specific relationship between LUE and EF.
植被的光能利用率（LUE）是模拟植被总初级生产力（GPP）的生产力效率模型（PEM）的关键参数，从区域到全球尺度都有涉及。先前的研究表明，草原的 LUE 具有最大的站点间变异性，且草原 LUE 的控制因素与其他生态系统不同，因为草原通常是受水分限制的生态系统。本研究结合涡度相关通量数据和 MODIS 测量的冠层吸收的光合有效辐射，报告了中国内蒙古典型草原和荒漠草原的 LUE。结果表明，尽管后者的 GPP 较高，但荒漠草原的年平均 LUE 和最大 LUE 均高于典型草原（分别为 0.51 和 1.13 g C MJ(-1)）。水分可用性是两个地点 LUE 的主要限制因素。蒸散分数（EF）或实际蒸散与潜在蒸散的比值（AET/PET）可以解释两个地点 50-70%的季节 LUE 变化。然而，LUE 与 EF（或 AET/PET）之间线性回归的斜率在两个地点之间有显著差异。LUE 随典型草原漫射辐射比例的增加而增加；然而，荒漠草原没有发现这种趋势。我们的结果表明，由于生物群落内 LUE(max)的站点间差异较大，基于生物群落的 LUE(max)并不合适。EF 可能是 PEM 中草原 LUE 的一个有前途的下调因子，但 LUE 与 EF 之间可能存在特定于地点的关系。
