Alpine plants: earlier green – earlier brown

The experimental results also seem to be reflected in nature: early snowmelt (2022, right) leads to earlier browning in alpine grasslands compared to later snowmelt years (2021, left). Webcam photos © research area Bidmer, Alpfor

One might think that climate change can also be good for plants: The shorter cold phases in the year give them more time to grow. However, as far as the European alpine meadows are concerned, this calculation does not seem to work, as a study shows: the grass species dominating there has a fixed growth period. Early budding leads to earlier aging in autumn. Plants with more flexibility in their growth activity could therefore spread and change the alpine flora, say the scientists.

As is well known, climate change is also making itself felt intensively in the Alpine region. The average values ​​are rising, there are more weather extremes and the change of seasons is also changing: In spring it gets warmer earlier and the life-friendly conditions extend further into autumn. Theoretically, this offers the plants of the Alpine region extended growth opportunities. Researchers at the University of Basel have now investigated the extent to which they can use this.

Extended growing season?

For their study, they took blocks of alpine meadows from 2,500-meter-high areas in the Swiss Alps. The pieces were then artificially overwintered in climatic chambers under typical natural conditions. The scientists then "woke up" part of the meadow blocks with mild values ​​as early as February. On the other hand, they kept a control group in “hibernation conditions” until April, before the growth period began for these patches of meadow in the chambers. The researchers were then able to compare the development of the test units with each other and with that of their naturally growing stocks, which only began to sprout at the end of June.

The results of the investigation showed that, regardless of when they were "awakened", most of the alpine plants in the blocks stopped growing after about five to seven weeks and the senescence process began. The researchers explain that this indicates a growth period that is fixed for a certain period of time. Above all, this applied to a particularly important plant in the Alpine region - the crooked sedge (Carex curvula): "We were amazed at how stubbornly this plant species, which is dominant in grasslands, switches to aging after a few weeks," says senior author Erika Hiltbrunner from the University of Basel. First author Patrick Möhl adds: "By the time the natural vegetation was in full growth, the plants with the earliest start of the season were already quite brown".

Temporary growth program

In addition to leaf development, the researchers also studied the root growth of the plants. To do this, they pushed a digital camera into transparent soil tubes to scan the root system at regular intervals. A form of artificial intelligence then automatically recorded the root growth in the images. This glimpse of what was hidden confirmed: Even the early roots hardly grew any more after the first two months, despite the still livable temperatures in the soil.

But why do plants behave this way? As the scientists explain, a fixed period of growth and aging has evolved in some species because this can be advantageous for them in the alpine environment. Because this control mechanism, which is independent of the current temperature, can prevent the onset of winter from catching them in full swing and thereby damaging them. However, there are also individual plant species whose inner clock is less strictly fixed to a certain length of the growth period and which remain active for longer under favorable conditions, the researchers report.

This meant that these crops have an advantage in times of climate change. As a result, they could become more common in the future and displace the species that are dominant today, the scientists explain. According to them, such a vegetation change will probably take a long time. This means that as long as the more flexible species have not yet established themselves, alpine grassland could increasingly look brown in summer.

Source: University of Basel, specialist article: Nature Communications, doi: 10.1038/s41467-022-35194-5

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