Quick Dips

Life in a Fishbowl

An upside-down fishbowl is helping vital research about how plants behave in a changing climate.

Landcare Research scientists have found a unique solution to the problem of developing the specialised equipment they need to measure carbon dioxide use by plants, an important factor in the formation of greenhouse gases. An ordinary fishbowl, upended and sealed onto a base, makes the perfect test tube to isolate plants so researchers can follow the radioactive isotopes which attach to carbon dioxide as they move through growing plants. It still looks like a fishbowl, but it does the job.

Surinder Saggar, an expert in nutrient cycling and soil fertility, developed the "sophisticated" equipment to simplify field work. The plants under the fishbowl canopy are given doses of radioactive carbon dioxide, and air samples are taken until the level of radioactive substance drops to minimum levels, indicating that the carbon dioxide has been almost completely taken up by the plants. Saggar then takes samples over several days to see how the carbon dioxide flows within the plant roots and soil.

The technique can also be used to see what happens to the plants' use of carbon dioxide in different soils varying in fertility. The proportion of plant-fixed carbon transferred below ground via the root system is vital for soil organic matter turnover and nutrient supply. The aim is to establish the values to be used with a carbon turnover model so it can be used for New Zealand pastoral systems.

"The more we know about the process of carbon use the better. In pastures it will show under what situations organic matter will be built up and can also be used to determine carbon flows. We need to know, if there is more carbon dioxide now present in the environment, will soils be used as a carbon sink or a source. This way we get quick answers to those questions."