Sustainable use of the biological wealth of Sri Lanka: under-explored plant resources

Presidential Address by Pradeepika Shaminie Saputhanthri

“The most wonderful mystery of life may well be the means by which it created so much diversity from so little physical matter. The biosphere, all organisms combined, makes up only about one part in ten billion of the earth’s mass. It is sparsely distributed through a kilometre-thick layer of soil, water and air stretched over a half billion square kilometres of surface. If the world were the size of an ordinary desktop globe and its surface were viewed edgewise an arm’s length away, no trace of the biosphere could be seen with the naked eye. Yet life has divided into millions of species, the fundamental units, each playing a unique role in relation to the whole.” Edward O Wilson, (1992)

Our biological wealth:

Biological wealth in simple terms is the natural species of living things that are responsible for the structure and maintenance of all ecosystems. Human life and economic activity, in turn, are sustained by the ecosystem capital with goods and services. Sri Lanka is a nation blessed with an immense biological wealth, reflected in its rich biological diversity. It is well known that Sri Lanka, along with the Western Ghats, has been identified as one of 34 ‘biodiversity hotspots’ of the world. A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened with destruction. To qualify as a biodiversity hotspot, “a region must contain at least 1,500 species of vascular plants (>0.5% of the world’s total) as endemics, and it has to have lost at least 70% of its original habitat.”

In economic terms, as per the country classifications by the World Bank, we are a “developing- or a lower middle-income country of 21.4 million people with per capita GDP in 2017 of $4,065. The economy is transitioning from a predominantly rural-based economy towards a more urbanized economy oriented around manufacturing and services”. For a developing country like Sri Lanka, it is a great challenge to balance both ecological and economic development targets. Thus biodiversity in Sri Lanka is under several threats, the major ones being habitat loss, human population growth, pollution, invasive alien species, and overharvesting of natural resources. Poor land use planning, weak legislation, lack of proper management policies etc have aggravated the threats.

We depend on biodiversity for all aspects of life and value natural species for agriculture, medicines they provide, recreational, aesthetic, scientific and cultural purposes, and thus utilization of our biological wealth is essential. However, it has to be done in a manner that will ‘not deprive the quality of life of future generations’ (use sustainably).

Considering the biological wealth of the island in terms of plants, 3771 flowering plant species, 314 ferns & fern allies, 561 mosses and 227 liverworts have been recorded. It has been documented that endemic plant species diversity of Sri Lanka comprises 927 or 28 % of flowering plants, of which 60 % are found in the lowland wet zone and 34% in the montane zone ecosystems of the island. Among the ferns, 59 species are endemic to Sri Lanka. Of the island’s moss flora, 11% are endemic. Recent revisions on the island’s liverworts have not been made and its endemic component is yet to be compiled. Similarly, there is little information on the endemic species among fungi, algae and lichens.

For biologists in the country there are still many underexplored areas related to the Sri Lankan flora, which warrant further investigations for better awareness on potential benefits, for conservation and for sustainable utilization. This address focuses on two such under-explored plant resources in the country: ‘lower plants’ and ‘plants in the extreme’.

Lower plants:

Although being essential components of our natural ecosystems, ‘lower plants’ (algae, bryophytes, ferns and fern allies), particularly, the bryophytes, have received only a little attention other than for taxonomic purposes. Biological sources including plants, microbes, lichens etc. produce a range of structurally diverse compounds known as secondary metabolites (=natural products, phytochemicals). Some of these natural products have beneficial uses for the mankind and can serve as the basis for the production of pharmaceuticals, agrochemicals, cosmetics, food flavours, colouring agents etc. Currently, biological compounds from lower plants are being explored in the world for their bioactive potency, particularly as pharmaceutically important chemicals. Although only a few have been developed for medicinal use, many compounds with antibiotic, antitumor, antioxidant, phyto- or cytotoxic and other bioactive properties have been isolated from bryophytes. Bryophytes have gained attention in recent times as having anticancer properties. Anti-leukemic activity has been shown by several compounds from some liverworts. Reports on bioactive properties or any sort of biochemical analyses on bryophytes are scarce in Sri Lanka. This gap in scientific evidence supporting significance of these non-vascular lower plants, which are at present apparently overlooked by the research community of the country. Two reasons for this may be the lack of many bryologists in the country, and difficulty in identification of bryophyte species without proper training or expertise.

Bryophytes and bryology have many other potential applications. In some parts of the world they have been used in traditional medicines. They are now increasingly being used in horticulture, pollution monitoring etc. Bryophytes (and lichens), being poikilohydric (maintain a moisture equilibrium with their environment, and have no control over dehydration), are often used as bioindicators of air quality.

Bryophytes perform a significant function in ecological balance on earth. Habitat destruction and degradation, air pollution, over exploitation etc. are enhancing the rate of extinction of bryophytes due to their fragile nature. Ex situ conservation is one approach in conservation of bryophytes which are under threatened status. In vitro culture techniques are used for ex situ conservation of lower plants in some countries. This would be a novel approach to Sri Lanka.

Plants in the extreme:

Tectonic and climatic factors over the Earth’s history have generated territories that exhibit harsh environmental conditions that are hostile for many living organisms. However, some have adapted to survive under extreme environmental conditions, for example high salt concentrations (halophytes) and water deficit (xerophytes). Yet, we know very little about how those survival traits have evolved and function in such ‘extremophytes’- plants in the extreme.

In Sri Lanka, there is a group of unique geological sites named as ‘Serpentines’ which have soils naturally rich in heavy metals. When ultramafic (high-iron and magnesium) rocks and minerals formed from olivine and pyroxene rich magma in the Earth’s mantle and oceanic crust are exposed at the surface of the earth due to tectonic movement, these may become ‘serpentinized’ – altered in contact with water, and weather to give a variety of soils known collectively as ultramafic soils or ‘serpentine’ and such soils are often enriched in Mg, Fe and sometimes with Ni, Cr and Co. Serpentine outcrops have long been subjected to mining for the extraction of heavy metals Ni and Cr as well as minerals such as asbestos. The serpentine soils are deficient in plant-essential nutrients, and often also in organic matter, cation exchange capacity, and water availability. These characteristic features of provide a harsh edaphic environment against which only a few species of plants have adapted morphologically and physiologically to colonize and for survival. Due to the harsh conditions ruling serpentine habitats, plants growing on serpentine and their associated biota (rhizosphere bacteria, mycorrhizae, pollinators, seed dispersers, pathogens, herbivores etc.) show unique adaptations or biotic associations. Some serpentine plants bear the unique physiological uptake mechanism of hyperaccumulation, in which they may accumulate to concentrations >1000 μg metal per g dry plant tissue. Recent breakthroughs at the global level have given first insights into the molecular basis underlying the complex extreme model trait of metal hyperaccumulation and associated metal hypertolerance. Heavy metal contamination of soils is an increasing environmental problem worldwide. Hyperaccumulator plants can be used to remove heavy metals by sequestrating, stabilizing or biochemically transforming them. This technology, phytoremediation, is relatively cost-effective and environment-friendly.

Geological studies in Sri Lanka have shown at least five serpentine outcrops at Ussangoda, Uda-Walawe (Indikolapelessa and Ginigalpelessa), Yodhagannawa (in the Wasgomuwa National Park) and Rupaha. Recent studies have reported identification of nickel hyperaccumulator plants, especially from the Ussangoda serpentinite. Also, there are reports on bioactivities of some serpentine flora. World-wide, serpentine flora has been treated as a model system for understanding mechanisms of adaptation, ecotypic differentiation, and the linkage between natural selection and speciation. They also provide a model for botanical studies on plant physiology and ecology, and for applications for habitat conservation and restoration. Many serpentine plants in the world are used as indicator plants in geo-botanical exploration of mineral deposits. Hyperaccumulators have been successfully used to re-vegetate degraded (due to mining etc.) serpentine substrates, but their most common and effective application is in heavy metal phytoremediation of polluted non-serpentine soils. In Sri Lanka too we have the unique ‘biological wealth’ of serpentine flora (also fauna, and microbes). However, awareness on the significance of these sites along with the species they harbor has to be enhanced in order to conserve and sustainably use these natural resources.

In 1798, the English cleric and scholar Thomas Malthus wrote in his book An Essay on the Principle of Population:

“Famine seems to be the last, the most dreadful resource of nature. The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction, and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague advance in terrific array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world”.

Due to the advances in science and dedicated scientists, the world, however, did not encounter a Malthusian Catastrophe as predicted.

Likewise, it is our responsibility to find means to prevent further damage to our biological wealth and to move in the direction of sustainability.