Spatial and temporal dynamics of two cacti seed banks in a xerophytic shrubland in Mexico City

Abstract

Background: Soil and aerial seed banks directly affect recruitment in plant populations. Soil banks result as the balance between seed inputs and outputs. Seed bank dynamics vary by species and environmental conditions. Few records on cacti seed banks are available. Questions: What types of seed banks do two cacti genera form in a lava-field reserve? Does seasonality influence the seed bank dynamics? Are inputs and outputs associated to the microenvironment? Studied species: Opuntia tomentosa, O. lassiacantha, Mammillaria haageana subsp. san-angelensis, M. magnimamma. Study site and dates: Xerophytic shrubland in the “Reserva Ecológica del Pedregal de San Ángel” in Mexico City. 2016 to 2018. Methods: We collected soil samples from four microenvironments during the rainy and the dry seasons, searched for seeds and tested their viability. We compared the number of inputs, outputs and viable seed by microenvironment and season. For M. magnimamma, each month we registered fruit maturation and searched for seeds remaining between tubercles. Results: Opuntia seed bank inputs occurred in all microenvironments and in both seasons. Rain favored inputs in hollows by secondary seed dispersal. We registered a large number of outputs caused by germination, granivory and loss of viability. Opuntia seed bank was developed in headland, plain and slope. No Mammillaria seed inputs were found, neither an aerial bank in M. magnimamma. Conclusion: Opuntia seed banks were restricted to microenvironments that provided “safe sites” which stored viable seeds. Mammillaria seed dynamics may hinders recruitment for their populations.