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.

What Is in the Bank? Assessing Persistent Soil Seed Bank Density of Sclerocactus wrightiae (Cactaceae)

“…With seed-rain loss in other members of Cactaceae typically near 98-99% [16][17][18]20,21], and mean seed production per reproductive size individual for this location being 91 seeds [12], we estimated that approximately 1 seed per year would make it into the seed bank for a given individual in this population. The leading cause for the relatively high seed loss has been shown to be granivory [16][17][18]20,21,41].…”

“…Across Cactaceae, the presence of sheltering microhabitats such as nurse plants or soil surface cracks lead to greater seed bank densities and recruitment rates primarily due to their sheltering of seeds from predators [15,17,41,42]. Additionally, the slight shading of cacti seedlings during the early stages of germination in arid environments has been shown to increase recruitment rates [43].…”