Untangling germination requirements of Katangan metallophytes for improving seed-based restoration of depleted populations (Democratic Republic of Congo)

Sandrine Godefroid, Ann Van de Vyver, Thierry Vanderborght

Botanic Garden Meise

Contact: sandrine.godefroid@botanicgardenmeise.be

Metal-rich substrates have driven the evolution of some of the world’s most remarkable and rare plants. This is the case in Upper-Katanga, including some of the largest ore bodies of copper and cobalt in the world. These metalliferous sites are represented by hills isolated in the woodland, where the total copper concentration in the soil is 200 times higher than in standard soils. These extreme conditions have led to the formation of a unique type of vegetation: “the copper flora”. Katangan copper hills are recognized as a hotspot with more than 600 species from which 32 are strict endemics. These plants represent a valuable phytogenetic resource for revegetation and restoration programs, for the phytostabilisation and for the remediation of heavy metal pollutions.

Conservation actions are imperative to prevent the extinction of the copper flora which is highly threatened by ongoing mining activities.

The Botanic Garden Meise is involved in a unique conservation and restoration project led by the University of Liège (Belgium) and funded by the company Tenke Fungurume Mining. In-situ and ex-situ conservation strategies are combined, involving ecosystem reconstruction (e.g. topsoil transfer), species translocations, and the development of ex situ collections in Belgium and in DR Congo (University of Lubumbashi).

The seed bank of the Botanic Garden Meise is the only in the world conserving 65 species (883 accessions) of the Katangan copper flora according to international standards (5% moisture content and -20°C). As translocations involving these species at risk are particularly difficult, amongst others because of narrow ecological requirements, the scarcity of seed source populations, low seed quality and/or unknown propagation method, it was of utmost importance to understand the germination requirements of the 65 species conserved in the seed bank. A total of 174 germination trials were conducted under controlled environmental conditions. Considering all species together, germination and viability of fresh seeds reached on average 71 % and 82 %, respectively. Their storage behavior (desiccation tolerance) was also determined through repeated tests after 6, 12 and 24 months in seed bank conditions.

Successful germination of Haumaniastrum robertii, a strict endemic of Cu-rich soils in Katanga.

Successful germination of Haumaniastrum robertii, a strict endemic of Cu-rich soils in Katanga.

A subset of the germinated plants has been transferred to the nursery in order to develop a propagation protocol. After a few years testing in the nursery, we can now confirm that most of these plants do not need the presence of heavy metals in the growing medium, even those that are hyperaccumulators. Their propagation can therefore be done without the addition of copper or cobalt in the substrate, which makes things easier. This research output is used by the mining company in the rehabilitation plans of the areas impacted by the mining activities.

Successful propagation of Aeollanthus saxatilis (left) and Batopedina pulvinellata (right) at the Botanic Garden Meise. Both species are endemic to the Katangan Copperbelt where they are characteristics of the chasmophytic vegetation on rocky outcrops and known in only 4 and 10 different locations, respectively.

Successful propagation of Aeollanthus saxatilis (left) and Batopedina pulvinellata (right) at the Botanic Garden Meise. Both species are endemic to the Katangan Copperbelt where they are characteristics of the chasmophytic vegetation on rocky outcrops and known in only 4 and 10 different locations, respectively.