Biodiversity is dwindling in natural and agricultural landscapes. This could have serious consequences not only for food security. Pflanzenforschung.de tries to give an overview.
The International Union for Conservation of Nature and Natural Resources estimates there are around 380,000 plant species in the world. The “Textbook of Botany at Universities” even speaks of half a million described plant species and assumes a large number of species that have not been recorded. More recent estimates speak, for example, of 300,000 seed plants that green our world. Whatever the actual number, it is certain that one fifth of all plant species are on the verge of extinction due to endangered habitats. The main causes of this threat are the deforestation of forests, the draining of wetlands, and expanding agricultural areas and cities.
“What the heck?”, Some will ask, we don’t even know many of the threatened species, how should we miss them? In general, extinction and the emergence of new species are an integral part of the earth’s history. Not least in order to dispel such misleading objections, researchers have endeavored for years to record the extent of biodiversity and to quantify its value.
Biodiversity is worth trillions of dollars
In a huge study, the “The Economics of Ecosystems and Biodiversity” report, around 500 scientists came to the conclusion that the costs of nature destruction and the associated loss of species could soon run into the trillions.
Poor people in particular benefit from nature’s services: while in Brazil, for example, only six percent of the total gross domestic product is attributable to the ecosystem, 89 percent are limited to the low-income part of the local population.
But anyone who determines the economic benefits of biodiversity encounters two problems: On the one hand, the estimates of how many species there are divergent. Half of all plant species live on just 2.3 percent of the global land area. If these so-called hotspots of biodiversity change, the number of species often changes dramatically. On the other hand, there are very many economic areas in which biodiversity plays a role. It has long been known that species introduced from distant regions can disrupt entire ecosystems. The same could happen through the loss of a key species. But most ecosystems are too complex to make reliable forecasts.
Source of cancer cures
More obvious is the importance of biodiversity when one considers the genetic potential that humanity could harness. The pharmaceutical industry has long since discovered plants as a potent source of medicinally effective substances. To put it bluntly, every species that is lost means less chance of a cure for cancer.
However, it is not just the unfathomed diversity in wild nature that humans can benefit from. In agriculture, too, many researchers expect great benefits from the untapped genetic diversity. Resistance to pests and tolerance to harsh environmental conditions – all of this can be found in the wild relatives of today’s agricultural plants; Potential that is just waiting to be identified and incorporated into high-performance varieties.
There has been a new method for finding potentially interesting plants for several years: the ecotilling, which is based on the tilling. Instead of using chemicals to generate mutations in high-performance lines using chemicals and cross attractive mutations, Ecotilling searches the natural diversity of a species for variations.
Food for the world depends on six types of plants
Genetic diversity is also a protection against pests and diseases: Today two thirds of the world’s food depend on only six cultivated plant species. A single emerging disease that is spreading rapidly could destroy large chunks of crops. This has certainly happened in the past. The more diverse the cultivated species – and within the species the varieties – the lower the loss from a single pest.
The assumption that highly bred species have a narrow genetic base is not always true, however. Researchers at Wageningen University were able to show that the opposite is often the case, because in modern breeding exotic material is regularly crossed in order to improve certain properties. Genetic diversity seems to have been lost primarily with the transition from landrace to commercial varieties, but not afterwards.
Mixed cultures increase the yield
The potential of mixed cultures is also far from being fully explored. Different types of crops are grown together in it and benefit from each other. If, for example, grain peas and spring barley are grown in this way, the combined grain yield is up to 20 percent higher than when barley is grown alone. A mixed culture of lupins and spring barley even increases the yield by a good 40 percent.
But it is not only the yield that gains from the mixed culture. When farmers combine lentils with barley or oats, the height of the lentils increases from 30 to 50 centimeters and makes harvesting easier. At the same time, the growing risk is reduced: in dry years the farmer harvests a particularly large number of lentils, in wet years the grain harvest is all the better. However, the often different time of ripening can be difficult with mixed cultures.
The push-pull strategy popular in East Africa also relies on positive interactions: there, maize cultivation suffers from the stem borer, a relative of the European corn borer. However, if farmers plant Desmodium, which is commonly used as a green manure, between the rows of maize, it produces fragrances that repel the stem borer. In addition, Desmodium suppresses certain weeds such as witchweed. The “pull” part of the strategy is done by napier grass, which is planted around the fields and lures the pest with its fragrance. If its larva eats its way into the stem of the Napier grass, it produces a secretion that is fatal for the stem borer.
Judging by the fact that mixed cultures were already known among the Maja – especially the combination of pumpkin, corn and beans – it is astonishing how little the principle could establish itself in modern agriculture. Certainly there are still numerous, previously unknown combination possibilities for better food production slumbering in the diversity of plants.
New uses need new types
A combination of several plant species is by no means always required. The history of maize already shows how versatile a species can be: Since it was developed from the tea ink, the goal of farmers has been to maximize the grain yield and limit the height of the plant so that the plant does not invest an unnecessary amount of energy in growth. Today, when maize is also used as an energy crop, it is all about pure biomass again, for example in the GABI-ENERGY project. The higher the growth, the better, is the new motto. Six meters are possible, report researchers from the University of Hohenheim.
Or you remember that grain ripening is not necessary if you are only looking for biomass. The cultivation period could be better utilized and would result in a higher productivity per unit area. At the Leibniz Center for Agricultural Landscape Research in Müncheberg, scientists working with Hubert Wiggering are investigating this strategy.
Scientists at the US University of Berkeley headed by Chris Somerville are pursuing yet another approach. They indicate that today’s agricultural plants have been optimized for food production over decades. However, if one pursues other goals, for example the generation of bioenergy, one should search the biodiversity for new species that have particularly good facilities for this. For example, prairie grasses are more reliable than maize. After a few generations of breeding, they could be superior to today’s species, so the researchers hope.
Gene banks conserve diversity
Against this background, seed banks and gene banks are of particular value. The frozen seeds and genes of varieties and species are stored there, some of which have not been cultivated for a long time – or in the case of wild species may have already died out. The countries of the world maintain around 1400 such institutions. The largest gene bank, the Svalbard Global Seed Vault, is currently being built in the permafrost of the island of Spitsbergen and is said to be able to survive epidemics, natural disasters and even nuclear war.
Almost always when plant researchers want to improve the properties of a species, they also search stocks in the gene banks. If, for example, wheat is to become more heat-resistant, attention should be paid to varieties that should have this property due to their origin. Once the corresponding gene has been identified, it can be incorporated into established varieties that have already been optimized for other important properties.
Emergence of new species
Species don’t just die out, however. New species are also continuously developing, which is ultimately what the concept of evolution is based on – even if this process is much slower than disappearance. Since Charles Darwin first put forward theories in the mid-19th century, it has been assumed that species arise primarily when a population is spatially split up, be it because part of it migrates or because geological changes lead to separation. In any case, both parts of the group now find different living conditions, so that different mutations mean the greatest fitness advantage.
We now know about a second mechanism that can create new species: direct changes within the genetic material through so-called transposons. These are short sections of DNA that, due to their edge sequences, can easily change their position in the entire genome. In addition, many transposons code for an enzyme that supports their mobility.
Transposons presumably go back to DNA that was originally introduced into the host organism by retroviruses. Due to their high mobility, they can interrupt the sequence of genes, making the genes mostly unusable. If the transposon disappears again, the gene reactivates. If the transposon contains one or more genes, it can happen that these are regulated differently elsewhere in the genome and thus produce a different protein. In rare cases, moving a transposon creates a completely new, functional section in the genome.
Understanding how new species arise is also important for researchers because it enables them to accelerate this process. So far, the active use of biodiversity has mainly been limited to identifying genes in model plants that are important for a desired property, then tracking down these genes in land races and crossing them in high-performance lines.
Interaction of species
The field of interactions is more recent: The aim here is to examine how plants and beneficial insects or pests interact with one another on a protein basis. For example, if a certain scent molecule in the plant attracts a pest’s predator, one could try to get the plant to produce more of this scent – or transfer the ability to other species. If a pest needs a certain protein from the plant to start its attack, researchers could modify this protein so that the attack would not work. One of the projects that is working on it is GABI PROTECT.
With a little imagination, the potential of biodiversity seems almost infinite. This is perhaps the greatest difficulty when research is looking for ways to use diversity: even if you know which trait you want to influence, the search for a species or variety with suitable genetic traits can be the proverbial search for the needle in the Like a haystack. This work would only be accelerated if as many plants as possible were genetically engineered and the meaning of their genes deciphered. As long as we are not yet in a position to fully unearth the treasure of biodiversity, the task of our generation is to guard and preserve it. Nor can we know today which properties and combinations will be required in the future.