Epipactis tremolsii Seed Diversity in Two Close but Extremely Different Populations: Just a Case of Intraspecific Variability?

Abstract

Analysis of the seed morphology is a widely used approach in ecological and taxonomic studies. In this context, intraspecific variability with respect to seed morphology (size, weight, and density) was assessed in two close Epipactis tremolsii Pau. populations sharing the same ecological conditions, except for the soil pollution distinguishing one of them. Larger and heavier seeds were found in plants growing on the heavy metal polluted site, while no differences in seed density were detected between seeds produced by plants growing on the contaminated and the control site. Moreover, seed coats and embryos varying together in their dimensions were described in the control population, while coats varying in their size independently from embryos were described in plants growing on the polluted site. Seeds from the two studied populations significantly differed in several parameters suggesting that intraspecific seed variability occurred in the case study.

Seed Bank Conservation and Incipient Seed Development in Orchids Colonizing Mining Wastes: Results of a Field Pilot Experiment

“…Thus, we proceeded to evaluated seed development by morphometry. Seed morphometry may be affected by the availability of nutrients, light and peculiar growth conditions affecting mother plants [ 15 , 29 ] as well as by the position and number of capsules in the inflorescence and by differences in the timing of flower pollination [ 34 , 35 ]. In the specific study case, seeds produced in the tailing dump are characterized by larger coats and fixed-sized embryos when compared with seeds produced by non-metallicolous populations [ 15 ].…”

“…Seed morphometry may be affected by the availability of nutrients, light and peculiar growth conditions affecting mother plants [ 15 , 29 ] as well as by the position and number of capsules in the inflorescence and by differences in the timing of flower pollination [ 34 , 35 ]. In the specific study case, seeds produced in the tailing dump are characterized by larger coats and fixed-sized embryos when compared with seeds produced by non-metallicolous populations [ 15 ]. Nevertheless, the significant variations in seed morphometry that were observed in the present study should be attributed to the sowing treatment, since seed material was sampled to avoid the factors listed above to confound experimental results.…”

“…As a result, high contents of Pb (up to 5 mg g −1 ), Zn (up to 13 mg g −1 ) and Fe (up to 56 mg g −1 ) were measured in the dump (more extensive data on soil pollution are reported as supplementary data in Table S8 ). The mining by-products in the dump are formed by fine particles and the plant coverage is almost absent there [ 14 , 15 ]. NP is located near (around 1 Km as crow flies) the Barraxiutta tailing dump, and the growth conditions between the two populations are comparable except for soil features ( Figure 5 ).…”

“…The Barraxiutta tailing dump (Sardinia, Italy) makes no exception in this sense since it hosts a population of Epipactis tremolsii Pau (Orchidaceae) counting approximately 500 individuals. The Barraxiutta tailing dump is contaminated by Pb, Zn and Fe (among the others) and is formed by fine particles [ 14 , 15 ]. Given the features of the area, its reclamation appears urgent and more and more imminent (2020–2024 according to the Sardinian Industrial Plan guidelines).…”

“…Previous studies on the metallicolous orchid population described the orchids settling there bioaccumulating and translocating soil pollutants in their organs. As a result, plants have reduced photosynthetic efficiency and, despite being smaller, produce bigger and heavier seeds [ 14 , 15 ]. Despite the extreme ecological growing context, orchids complete their biological cycle, reaching the flowering stage, and producing fruits and thousands of viable seeds per plant each year [ 14 ].…”