Can conservation kill?

Normally when someone asks a dramatic question in a headline the answer is no. This time though it’s different. A paper in the new open-access journal Conservation Physiology shows that some plants in a biodiversity hotspot are under threat from a common conservation practice, as well as development of surrounding regions.

‘Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot‘ by Lambers et al. highlights an odd problem. Plants need phosphorus for growth. It’s a big component of many fertilisers. So for somewhere like phosphorus-poor soils in southwest Australia, you’d expect an increase in phosphorus to be good news. In fact it’s not.

There are a couple of problems.

One is that to survive in phosphorus-poor soils you need special skills. Utricularia menziesii, for example is one of the fastest plants on the planet. The speed isn’t in growth or seed dispersal. It is a bladderwort. It has bladders that act as traps for insects. The speed these traps work at is astonishing. An insect can be swept from outside to inside faster than a human could blink an eye. There are plenty of adaptations you can make to live in low phosphorus soils, but these have costs. You wouldn’t be able to compete against other plants in soils with more phosphorus, which is just one reason why many plants found in these soils are rare.

Another is that some plants have no self control. If you live in place where phosphorus is limited, you’ll want to grab all that you can. If there’s a boom in phosphorus, that ability to grab it becomes a glut and you’re in deep trouble.

Lambers et al. show that one of the most interesting feature of the southwest Australian plants isn’t simply that they live in low-phosphorus soils. It’s also that they do it alone. Plants often work with fungi to build what is called mycorrhizal symbiosis. This is where a fungus provides nutrients in exchange for carbohydrates from the plant. It makes plant-fungus interactions part of much wider ecosystem, so it’s noteworthy that many of the plants in this region do not have mycorrhizal partners. It seems that a variety of phosphorus gathering strategies can be used by neighbouring plants.

In this situation then it’s clear that run-off of phosophorus-rich fertilizer is a problem. What Lambers et. al. also highlight as a potential problem is the fight against Phytophthora cinnamomi.

P. cinnamomi is a mould responsible for root rot. It’s one of the most invasive pathogens in the world, so it’s no surprise that humans have developed a counter-measure. Unfortunately the best way to fight P. cinnamomi is with phosphite. As the name suggests, it’s a phosphorus salt. It acts to slow the spread of P. cinnamomi but a strong application of phosphite to an area will also increase the phosphorus levels of local soils. In southwest Australia where many native plants are susceptible to P. cinnamomi, the cure is as fatal as the disease.

It’s a knotty problem and Lambers et al. point out that while the plants in southwest Australia are unique, the problem itself is not. They point to a similar problem in the fynbos of South Africa and the cerrado of Brazil.

Image

Utricularia menziesii by Jean and Fred Hort/Flickr. [cc]by-nc[/cc]