Ozone and carbon dioxide tests in Wisconsin (courtesy UWM)

Previous research had already revealed that hyphae of ectomycorrhizal fungi in tree roots release organic acids that disolve mineral particles, releasing nutrients such as calcium. However, this is the first study to show that the trees are able to use this harvested calcium.

“Instead of drinking their calcium, they mine it,” said Blum.

By analysing calcium in the leaves of trees, the researchers were able to establish that spruce and fir trees are able to make use of the fungi, whereas sugar maples and ash lacked the fungi, and so were only able to take up calcium from that available in the soil. However, if maples and ash trees are close enough to trees with the symbiotic fungi, they could gain some benefit from them.

Sugar maples are disappearing across New England in the United States, which some researchers believe is due to loss of calcium brought about by acid rain.

However, there is no reason to become complacent and presume that acid rain is no longer a problem, Blum is keen to emphasise. “Our research shows that some trees have other strategies for getting their calcium, which may be important when the plant-available pool starts running out, but trees that don’t have the ability to go deeper are still in the same dilemma they’ve always been in,” said Blum.

Co-author of the paper, Timothy J Fahey, Professor of Natural Resources at Cornell University, agrees. “And although our findings suggest that trees with the right fungal associations may be able to short-circuit the loss of calcium in the soil, that may not get them around other problems with acidification of soil,” he said. This includes the increased availability of naturally occurring aluminium, which hinders plant growth.

Another new study into the effects of pollution on trees – conducted by researchers at the University of Wisconsin-Madison - has also revealed the long-term effects of carbon dioxide and ozone. The study has confirmed that elevated carbon dioxide concentrations increase the growth of young aspen and birch in Wisconsin, USA, and high levels of ozone decrease their growth. However, when the two occur together, as is expected in the coming decades in Wisconsin, the study found that the two gases cancel each other out.

Elevated levels of carbon dioxide were found to increase tree growth by 20% to 28%, with elevated ozone levels decreasing growth by around the same amount. With both gases at high levels, tree growth was normal. However, the researchers believe that as the trees mature, the growth-promoting effects of carbon dioxide will decrease and the negative effects of ozone will increase.

The scientists note that further research also needs to be carried out into the effects of both gases on the insects in the ecosystem. They have already noticed that forest tent caterpillars grow larger under high ozone treatment, although other species do not appear to be affected in the same way. Leaf decay rates for some species also appear to be slower with higher levels of carbon dioxide. The results suggest that high levels of both gases could change the makeup and biological diversity of forests.

“We hope to continue the experiment for a least 15 years to determine the impact the gases have in the long term on the trees themselves and the larger ecological community,” said Richard Lindroth, an insect ecologist at the University of Wisconsin-Madison.

 

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