An assessment of factors leading to the decline of Beclardia macrostachya (orchidaceae) population in Mauritius

Abstract

Clearing of forest land for agriculture and urbanization following colonization have reduced the forest cover in Mauritius to 3% of total land cover. Today exotic species such as Psidium cattleianum (wild guava), Araucaria columnaris, and Ravenala madagascarensis dominate at Pigeon Wood, the only site in Mauritius where Beclardia can be found, leaving little space for very few indigenous tree species like Labourdonnaisia glauca, Apholoia theiformis and Foetida mauritiana. Beclardia macrostachya is an orchid endemic to Mauritius, Madagascar and Reunion. Though it is abundant in the latter countries, it is one of the rarest orchids in Mauritius. An assessment of the factors associated with the stability of this orchid was carried out in forests of these three countries to understand the drastic decline of this orchid in Mauritius. Morphometric and fertility counts carried out at different forests revealed differences in fitness and fertility rates among forests of the same countries and between different countries. Stability of the different Beclardia populations was carried out based on counts of juveniles and adults. Higher fertility rates and most stable populations were observed in the forests of Reunion Island (Bebours) and Madagascar (Ambohitanteley), whereas very low fruit set were observed in Mauritius, unless manual pollination was carried out. Microscopic analysis revealed the presence of pelotons of endomycorrhiza during the early development of the seedlings, in vivo. Based on comparative studies among the different sites, pollinator limitation and absence of suitable hosts were the primary factors that led to the present decline in Mauritius. The high density of wild guava, Psidium cattleianum, which has slowly taken up most of the forest areas in Mauritius has affected the regenerating capacity of Beclardia macrostachya and the density of putative hosts of this orchid. GC-MS/MS analysis of nectar revealed α-Dglucopyranose to be the primary reward of the pollinators and benzyl alcohol, methoxybenzyl alcohol and methoxy methyl phenol to be components floral fragrance.

Fruits of wild and semi‐domesticated Diospyros tree species have contrasting phenological, metabolic, and antioxidant activity profiles

“…Lysophospholipids were the predominant discriminant metabolites in D. digyna fruits, in addition to 8‐diazacyclotetradecane‐2,9‐dione, a volatile compound also identified in finger and barnyard millet and in certain orchids . Lysophospholipids hydrolyzed from the plasma membrane tend to accumulate in response to heat and water stresses in leaves of citrus plants in order to act as signaling molecules .…”

“…2,17,53 Lysophospholipids were the predominant discriminant metabolites in D. digyna fruits, in addition to 8-diazacyclotetradecane-2,9-dione, a volatile compound also identified in finger and barnyard millet and in certain orchids. 64,65 Lysophospholipids hydrolyzed from the plasma membrane tend to accumulate in response to heat and water stresses in leaves of citrus plants in order to act as signaling molecules. 66 Their abundance in D. digyna fruits could, therefore, have occurred as a response to higher temperatures and low humidity registered at the sampling site during this study.…”