Innovative experiments using temperature-controlled plots of field have helped explain the link between early winter temperatures and yield in some of our most marketable arable crops.
Laboratory and field technology enabled the John Innes Center team of researchers to simulate full growing seasons and demonstrate that cooling is important in late November/early December because it enhances growth during the early flower development of the crop.
They showed that rapeseed oil plants can go through a growth phase known as flower bud dormancy if the winter temperature is too warm. This physiological process occurs when newly formed microscopic buds are inactive waiting for low temperatures to signal growth and is well understood in perennials that grow year after year.
This stage of development was not present in annual crops; Those that complete their life cycle in one growing season.
Rapeseed plants that were cooled at this key developmental stage developed faster and had higher yields, producing more seeds per pod. On the contrary, plants grown in warmer conditions grew slowly and had lower yields.
Professor Steve Benfield, group leader at the John Innes Center, said: “It was surprising to find that winter annuals have this flower bud hibernating – no one has ever indicated that this mechanism is important for controlling flowering time in annual plants. Our experiments also showed that if If flower buds are warmer than average temperatures, growth slows down and plants produce errant flowers and a low yield. Conversely, we know that if plants are cooled at this point, this promotes faster growth and higher yields.”
Previous studies have shown a strong relationship between temperatures in late November and early December and yield in crops such as oilseed rape, a winter annual, planted in the fall and harvested the following summer.
Cooler temperatures during this weather period are associated with higher productivity, while warmer temperatures result in lower productivity. Variations in conditions during this significant weather window are responsible for a variance of up to 25% of the total return.
Understanding the reasons behind the statistical correlations between climate and yield is important for predicting the impact of climate change on crop production and can be used to develop strategies for crop adaptation to produce higher yields with warmer winters.
First author of the paper Dr Carmel O’Neill said: “We want to understand the impact of climate change on crop yield in the UK. To predict and respond to these impacts, we must understand all the processes by which changing weather affects the crop. And that’s what we did here in this study – Experimental proof of what we’ve seen previously in correlative studies.”
In what is believed to be a unique set of experiments, the researchers used internally controlled environment chambers programmed to simulate the annual winter growing season based on weather data collected from a farm.
After the indoor and laboratory experiment, the team transferred the experiment to a field trial, using an outdoor heated field plot system at the John Innes Center Field and Experiment Site, Church Farm.
The results of laboratory and field trials were similar, and warmer conditions resulted in slower growth and lower yields.
Using molecular techniques, the team analyzed genes expressed in the bud tissues of rapeseed oil plants that were affected by changes in temperature. This showed that a previously known cryogenic response gene called FLC was mediating the dormant response of plant buds to winter temperatures.
Professor Penfield added: “We have seen this relationship between cooling and yield in the data, but so far we cannot say that cooling is related to the physiology of the crop – it is not for example that cooling only kills certain diseases or pests – although it may also do so. But we now know why cooling affects the yield and it is due to the physical effect on the growth rate of plants.”
Previous research identified the importance of temperature in a plant’s biological evolution process called vernalisation, which occurs in oilseed rape in October.
By determining that there is a second temperature-sensitive process, bud dormancy, that occurs later in the growing season, researchers and breeders can help us better respond to the challenge of climate change. One of the strategies under consideration is to identify taxa that are less sensitive to temperature.
Winter warming controls flowering time by activating bud dormancy and affects yield in emergence of annual winter crop. PNAS (Proceedings of the National Academy of Sciences).