Environmental and Ontogenetic Influences on Growth, Photosynthesis, and Survival for Young Pitayo (Stenocereus queretaroensis) Seedlings

Abstract

The columnar cactus Stenocereus queretaroensis is cultivated for its fruits in southern Jalisco, Mexico. Plantations are established by clonal propagation of individuals that produce fruits with desirable characteristics. Because recruitment of wild individuals originated from sexual reproduction is paramount for the maintenance of genetic diversity for this species (for example, plantations are established near wild populations where gene flow may occur) and because young seedlings are most vulnerable to mortality, their performance was studied in the greenhouse for young S. queretaroensis seedlings of different ages (3, 5, 9, or 14 weeks after germination). Initially, seedling height and fresh weight were similar among cohorts, averaging 0.92 cm and 0.03 g. The volume-to-area ratio was higher and the nocturnal acid accumulation was lower for older seedlings. Seedlings were exposed to two watering treatments (Irrigated and Droughted) and to three photosynthetic photon flux (PPF) treatments (2.83, 9.53, or 18.49 mol m–2 day–1) in a factorial experimental design, and harvested after one month. In general, irrigated seedlings had greater height and fresh weight than droughted seedlings. Volume to area ratio decreased during the experiment for the younger seedlings under the highest PPF treatment and for the oldest seedlings under the lowest PPF. Nocturnal acid accumulation decreased for younger seedlings under the two higher PPF treatments, but it increased for 5-week-old seedlings under the lowest PPF treatment. Seedling survival was also assessed during the experiment. The greatest contrast was observed between the seedlings under the lowest and the highest PPF treatments, for which survival amounted to 67% or 97%, respectively.