区域尺度农田最大光能利用率参数估算及时空变化分析

基于遥感数据的光能利用率模型被广泛应用于计算农田生态系统的生产力，其结果对最大光能利用率（εmax）参数非常敏感。利用农业产量统计数据、MODIS遥感数据、气象观测数据和植被光合模型（VPM）推算2001~2011年黄淮海3省（冀、鲁、豫）和长江中下游5省（苏、皖、鄂、湘、赣）各市逐年的农田平均εmax，并分析其时空变化特征及其影响因素。研究表明:黄淮海3省（冀、鲁、豫）和长江中下游5省（苏、皖、鄂、湘、赣）各市农田εmax的11a平均值为0.6~2.8 g C·MJ-1，表现出西北和南部较高、东北和中部较低的分布特征；大部分市农田εmax呈现出上升趋势，但上升的幅度存在着明显的年际波动和空间差异；各市农田εmax的年际波动总体呈现北高南低、中间高四周低的空间分布特征。大部分市农田εmax的年际变化与单位耕地面积农用化肥施用量存在显著的正相关性（P < 0.05）；C4作物面积比例变化也是导致εmax变化的原因之一。在利用光能利用率模型计算农田生产力时，需要发展考虑εmax时空变化的参数化方案。

Estimation and analysis on the Temporal-spatial Variations of Cropland Maximum Light Use Efficiency at Regional Scale

Remote sensing driven light use efficiency models have been widely utilized to calculate the productivity of terrestrial ecosystems, and the outputs of these models are very sensitive to the values of maximum light use efficiency (εmax). In this study, city-level yield census data, MODIS reflectance data, locally observed meteorological data, and the vegetation photosynthesis model (VPM) were employed to derive annual mean city-level cropland εmax in Huang-huai-hai area (including Hebei, Shandong, and Henan) and the middle-lower Yangtze area (including Jiangsu, Anhui, Hubei, Hunan, and Jiangxi) for the period from 2001 to 2011. Then, the spatial and temporal variations of εmax and possible driving factors were analyzed. The results showed that the average annual value of the city-level means of cropland εmax in Huang-huai-hai area (including Hebei, Shandong, and Henan) and the middle-lower Yangtze area (including Jiangsu, Anhui, Hubei, Hunan, and Jiangxi) varied between 1.8-2.8 g C·MJ-1 during the period from 2001 to 2011. It was higher in the northwest and south parts and lower in the northeast and central parts. Annual mean cropland εmax increased during the period from 2001 to 2011 in most cities, but showed obvious interannual fluctuations and spatial difference in the rising amplitude. The interannual fluctuations of city-level cropland εmax were normally higher in the north than in the south and higher in the central than in the around. The annual means of cropland εmax had strong positive correlation with the amount of fertilizer used in per unit area of cultivated cropland in most cities, and it reached significant level (P<0.05), so the increase of the consumption of chemical fertilizer in these regions was one of the main causes of the increase of cropland εmax. The increase of the yield fraction of C4 crops could also induce the increase of cropland εmax. This study proves that it is of importance to develop a parameterization scheme accounting for the temporal and spatial variations of εmax for improving the calculation of productivity in croplands using light use efficiency models and remote sensing data.