A really interesting story appeared recently in the world’s top science journal, and it comes from a group out of Western Sydney University. Putting it simply, the level of CO2 around various trees in an old growth forest was increased. These plants have been there for centuries undisturbed by farming or other practices. They wanted to show that increasing CO2 leads to increases in plant growth – the idea being that this is a way of offsetting CO2 emissions.
These types of experiments had previously been done in glasshouses, where plant growth increased significantly, however, when these experiments were done in a more realistic setting, there were no increases in plant growth, which indicated that CO2 emissions can’t be readily offset by increased plant growth – at least not in Australian forests.
Interestingly, the increase in CO2 increased the efficiency of photosynthesis, which increased the ability of the trees to produce sugar, but it didn’t increase the growth of the plants. I suppose it would be like us eating sugar and expecting to grow muscles – you need the right nutrients. The trees simply did not have the necessary nutrients to grow more biomass. So this extra sugar produced by the trees was simply pumped down to the roots and released into the soil, where soil microbes used it and converted it back into CO2. The conclusion from this is that native trees are not lacking CO2 as a nutrient, but they are lacking other nutrients, and this has obvious implications on fertilising natives.
This is why we should be applying fertiliser to our natives in the garden. We know Australian soils are generally impoverished, and if old growth forest soils are lacking nutrients, think about what your garden soil may be like for growing natives. It may have been used as farmland or an industrial site, so nutrients are going to be low even for natives, which people seem to think can get by without any help.
Without fertiliser, natives tend to look spindly and dry, so giving them something like Bush Tucker – which has been specifically formulated for natives with reduced phosphate availability – gives your natives a gentle feed which they love. This study has shown two things – firstly, we can’t easily offset CO2 emissions by expecting additional plant growth, and even natives need some fertiliser to grow and perform at their best.
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