1. 4820 Old Main Hill, Dep. of Plants, Soils & Climate, Utah State Univ. Logan UT 84322
2. now at Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences; Beijing China
3. Shantz Bldg. 38, Room 526, Dep. of Soil, Water, and Environmental Science, The Univ. of Arizona Tucson AZ 85721