小麦冠层不同光质透光率与叶面积指数的定量关系研究

为探究小麦叶面积指数（LAI）的空间分布及与不同光质透光率间的关系，通过三年田间试验，设置不同品种、氮肥水平和灌水次数，测定分析了小麦拔节期至灌浆后期冠层不同空间层次的透射光及叶面积指数（LAI），并对不同光质透光率与LAI间进行回归分析。结果表明，小麦LAI随生育时期的推进呈单峰动态变化，最高值出现在抽穗-开花期，且随灌水和施氮水平的增加而增大；光合有效辐射（PAR）透光率随生育时期呈先降后升趋势，且随灌水和施氮水平的增加而减小。LAI与PAR透光率均存在时空异质性，叶面积的垂直分布直接影响冠层内光分布。水氮处理对植株上层LAI影响较小，而对下层影响较大；40 cm处透光率递变明显，低水高氮以及高水低氮处理对透光率递减的影响较大。不同光质透光率均随冠层高度的下降均出现不同程度消减，透光率与向下累积LAI间均呈显著指数相关，相关性由强到弱依次为红边、蓝光、光合有效辐射（PAR）、绿光、近红外和红光。经回归分析，红边和蓝光透光率与LAI的定量关系表现较好，拟合性均优于PAR，尤其是红边透光率（R=0.749），因此可以利用红边透光率建立模型，以监测小麦冠层 LAI。

Quantitative Relationship between Light Transmittance of Different Light Quality and Leaf Area Index in Wheat Canopy

In order to explore the spatial distribution of wheat leaf area index(LAI) and its relationship with different light quality transmittance, the light transmittance and LAI of different spatial layers of canopy from jointing stage to late filling stage were measured and analyzed through a three-year field experiment with different varieties, nitrogen fertilizer levels, and irrigation times.The regression analysis between different light quality transmittance and LAI was carried out. The results showed that wheat LAI showed a single peak dynamic change with the advance of growth period, with the highest value at heading-flowering period, and it increased with the increase of irrigation and nitrogen application level. The light transmittance of photosynthetically active radiation (PAR) decreased first and then increased with the growth period, and decreased with the increase of irrigation and nitrogen application level. Both LAI and PAR transmittance had spatiotemporal heterogeneity, and the vertical distribution of leaf area directly affected the light distribution in the canopy. Water and nitrogen treatment had little effect on LAI in the upper layer of the plant, but had a greater effect on LAI in the lower layer. The light transmittance changed obviously at 40 cm, and the treatment of low water and high nitrogen, and high water and low nitrogen had a great influence on the decline of light transmittance. The light transmittance of different light quality decreased in varying degrees with the decline of canopy height. There was an exponential significant correlation between the light transmittance and the downward cumulative LAI. The correlation from strong to weak was red edge, blue light, PAR, green light, near-infrared and red light. Through regression analysis, the quantitative relationship between red edge and blue light transmittance and LAI is better, compared withPAR, especially the red edge transmittance (R=0.749). Therefore, the red edge transmittance can be used to establish a model to monitor wheat canopy LAI.