沙蒿(Artemisia ordosica)叶面积指数的测定及模拟

Measuring and modeling leaf area index for Artemisia ordosica

对宁夏盐池典型沙生灌木沙蒿(Artemisia ordosica)生长季内叶面积指数(leaf area index,LAI)的动态进行了直接法(异速生长方程法)与间接法(Li-2000冠层分析仪法)相结合的定期观测,探索了利用直接法对间接法测得的有效叶面积指数(effective leaf area index,LAI e)进行校准的方法;并揭示了沙蒿真实叶面积指数(actual leaf area index,LAI a)与积温、光合有效辐射反射率(ρp)与短波辐射反射率(ρs)比值(ρp/ρs)的关系。结果表明:双变量(株高、冠幅)异速生长方程对单株叶面积的拟合优度高于单变量(冠幅)方程,且7、8月拟合优度最高;LAI e与LAI a随时间均呈单峰型变化,7月初到9月中旬为冠层生长的稳定期,LAI e和LAI a稳定期均值分别为1.15和0.31 m2·m-2;整个生长季内,LAI e>LAI a,以8月底为分隔点,LAI e与LAI a呈现不同的线性关系;LAI e与LAI a的季节动态不受当年土壤含水量和降水量变化的影响;LAI a处于上升期和稳定期时,随积温呈明显的先上升后稳定的变化;LAI a随ρp/ρs的增大呈指数下降变化。研究结果将增进对沙蒿群落LAI动态及其机制的了解,为快速、准确地获取LAI提供方法参考,为遥感反演和生态系统建模提供数据支持。

Leaf area index （LAI） of a semiarid Artemisia ordosica community at Yanchi, Ningxia was measured with both direct （allometric equations） and indirect （Li-2000 canopy analyzer） methods throughout the growing season of 2012. Our objectives were to compare the direct and indirect measurements, to explore how actual leaf area index （ LAIa ） values obtained from allo- metric equations can be used to calibrate effective leaf area index （ LAIe） measured by Li-2000, and to model seasonal LAIa variations using climatic variables. Results showed that bivariate functions of height and canopy area generally predicted individual total leaf area better than did the functions of canopy area alone, and the fitting achieved highest coefficient of determination （R2） in July and August. Both LAIe and LAIo showed hump-shaped seasonal patterns. A mid- season stable period started from early July and ended in mid-September. LAI, was always greater than LAI. Over the growing season, with the mean values of LAIe and LAIa in the stable period being 1.15 and 0.31 m2 · m-2, respectively. LAIo and LAIa showed a two-phase linear relation- ship over the growing season, separated by late August. LAIe and LAI, showed a weak relation- ship with rainfall or soil water content in the growing season. LAI varied with accumulated tem- perature above 5 ℃ （D） , first increasing with ∑D, and then being stable during the mid-sea- son. LAIa showed a negative exponential relationship with the ratio of photosynthetically active radiation reflectance （ρp） to shortwave radiation reflectance （ρs） （ρp/ρs）. Our results the understanding of LAI patterns in semiarid A. ordosica communities, could aid in ment of efficient and accurate methods for measuring LAI, and provide ground-based ibrating remotely-sensed information and for parameterizing process-based ecosystem models. Contribute to the develop- data for cal- carbon cycle