Abstract: In order to determine and reveal temperature properties in areas adapted for American ginseng (Panax quinquefolium) growth, the authors measured both air temperatures at 15cm height aboveground, where canopies of two-year-old seedlings were distributed, and soil temperatures at 10cm depth underground, where roots of the plant extended, within 4 plastic greenhouses of the plant located in Zaomulan (alt. 1236m) and Zhakoushi (alt. 1722m) villages, Liuhou Township, Liuba County, Shaanxi Province, China, both from May to October 2012 and from March 2013 to April 2014. The valid observational dates were categorized into a data set, and all the valid daily temperatures into 8 data sets such as air mean (AMT), air minimum (AMIN), air maximum (AMAX), range of air temperature (RAT), soil mean (SMT), soil minimum (SMIN), soil maximum (SMAX), and range of soil temperature(RST), which were each designated as a dependent variable (Y). Ordinal dates were coded from observational ones and then calculated into sine and cosine values of their 1- to 4-fold radian angles by Fourier’s transform, with each of the 8 sets designated as an independent variable (X). Each Y was regressed against the 8 sets of X through stepwise regression analysis, and a total of 16 polynomial regression equations were established. The simulation effect of AMT, AMIN, SMT, SMIN and SMAX against Xs retained was excellent, with their compound correlation coefficients high, R= 0.933 - 0.985 (P＜0.001); and valleys and peaks of the periodic temperature curves obtained appeared mostly in January and July. Estimated by AMT equations, values of annual mean temperature (℃), valley (℃), peak (℃), accumulated temperatures above 10 and 6℃ (℃?d) in the greenhouses were respectively: Zaomulan, 11.2, -0.9, 21.1, 1475, 2403; Zhakoushi, 8.3, -3.5, 18.7, 957, 1736. Corresponding values estimated by SMT equations were: Zaomulan, 11.2, 0.1, 20.3, 1338, 2292; Zhakoushi, 8.8, -1.7, 17.8, 872, 1710. Average low of daily air temperature and the lower limit of daily minimum in winter were: Zaomulan, -5.6, -10.3; Zhakoushi, -8.8, -14.5. Average high of daily air temperature and the upper limit of daily maximum in summer were: Zaomulan, 27.6, 37.8; Zhakoushi, 25.3, 34.3. Average low of daily soil temperature and the lower limit of daily minimum in winter were: Zaomulan, 0.1, -2.1; Zhakoushi, -2.2, -4.4. Average high of daily soil temperature and the upper limit of daily maximum in summer were: Zaomulan, 21.3, 24.8; Zhakoushi, 18.9, 22.1. The study establishes regression models that match periodically changing trends of annual temperatures inside local plastic greenhouses for the plant, and reveals many temperature eigenvalues, which will benefit practices directing plantations of American ginseng, and provide other scientific studies and applications dealing with field temperatures with parameters.

Key words: Panax quinquefolium, Periodic temperature curve, Fourier’s transform, Regression model, Eigenvalue