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Climate Change risks to pastoral production systems

Authors: Anthony Clark, Andrew Tait

Download the full report in PDF format [PDF 162KB]

Executive summary

Goal

To determine whether additional evidence supports the initial observation that New Zealand’s pastoral production systems may have a substantially reduced ability to cope with environmental stress under elevated CO2 conditions likely to be encountered with global change.

Context of the project

An initial study at New Zealand’s only long-term elevated CO2 site, in collaboration with AgResearch, has shown that ryegrass suffers substantially increased levels of stress compared with non-elevated CO2 conditions, in the mature phase of the growth cycle under slower-growing autumn conditions (Guo et al. 2006). That is, higher stress levels exist when demand for photosynthetic products is low. This has raised a question about how New Zealand’s future pastoral production systems may behave when already under additional environmental stress from other factors associated with climate change – particularly drought and temperature extremes.

Approach

To help better understand the issue of elevated CO2-induced stress, we analysed data available from an initial study on three grass species under two nutrient treatments at an elevated CO2 site in the USA. It was thought the lower nutrient availability in one treatment might lead to a smaller total demand for photosynthetic products, and thus to initiation of CO2-induced stress even when plants were actively growing.

Outcomes

We found that:

• Long-term exposure to elevated CO2 appears to confer no net long-term advantage to overall photosynthetic performance at the US site under low nutrient conditions. This is consistent with other results from the site, and also with New Zealand studies under elevated CO2 but with considerably higher nutrient availability.
• Grasses adapted to lower nutrient environments under elevated CO2 do not suffer stress levels beyond those under either non-elevated CO2 conditions or higher nutrient conditions, when actively growing with the demand for photosynthetic products being relatively high (the conditions in the US study).
• Overall, taking also the previous New Zealand study (Guo et al. 2006) into account, it appears enhanced stress due to elevated CO2 is likely to be present only towards the end of a growth cycle, in the mature growth phase. It is thus not expected to be a factor significantly limiting future pastoral production, because New Zealand pastures are not expected to spend much time in the mature growth phase (i.e. they generally will be grazed at or before that point).

Recommendations

Future work, which could be completed as part of a PhD or postdoctoral project, should concentrate on determining:

• At what stage in the growth cycle does elevated CO2-induced stress become apparent – in particular, could it affect production of silage or hay crops that develop further into the mature phase than encountered in a normal grazing situation?
• Is the capacity of grasses to tolerate normal environmental stress during the active phase of the growth cycle affected by the presence of elevated CO2? Could reduced demand for photosynthetic products during environmental stress initiate additional elevated CO2-induced stress, and result in damage to the plant’s photosynthetic system?

Contact for Enquiries

Sustainable Land Management and Climate Change
MAF
Pastoral House
25 The Terrace
PO Box 2526, Wellington
Tel: 0800 CLIMATE (254 628)
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