Comparative drought tolerance of four Mexican pine species

Graduation date: 1990Forest tree nurseries in Mexico produce millions of seedlings per year. This is accomplished with high financial investment and unsatisfactory quality control of\ud seedlings. Drought is a major stress factor in Mexico. Thus, planting drought tolerant pine seedlings on dry sites will result in better survival and growth of seedlings. The main objective of this research was to gain\ud information on drought tolerance developed in\ud containerized Mexican pine seedlings. Specific objectives were to compare 1. growth of four species subjected to\ud different watering regimes in the greenhouse; 2. survival and growth of the same pre-conditioned seedlings at two\ud outplanting locations; and 3. survival, growth, and transpiration rates of the pre-conditioned seedlings under three controlled levels of drought stress. Seedlings were grown for one season under three distinct watering treatments arbitrarily called wet, intermediate, and dry regimes. Some of the seedlings were\ud later subjected to three levels of drought stress called low, moderate, and high. Others were outplanted in the Oregon Coast Range and in Central Mexico. Differences among seedling response to the watering\ud regimes varied by species in the greenhouse. Pinus patula was the species whose growth was most affected by the dry treatment.\ud Seedling performance of the two outplantings did not show interaction between watering regimes and species in any of the variables. The watering treatments previously carried out in the greenhouse did not have any effect on seedling field performance. Excellent survival in the Oregon Coast Range contrasted with poor survival in Mexico.\ud Seedlings in the various drought levels reacted differently depending on their previous watering regimes. Seedlings under high stress previously subjected to the\ud dry treatment survived better than those of the other watering regimes. The differences among the drought levels varied by species. The survival, as well as morphological and\ud physiological characteristics of Pinus qregqii were the least affected by the levels of stress. Pinus patula was the species most affected in terms of survival and diameter growth. Its transpiration rate was intermediate. Pinus pseudostrobus var. apulcensis transpired more than the other species. However, it was intermediate for\ud most growth measurements. Pinus montezumae transpired less than the other species and survival was intermediate