2023-05-10 14:45:44
Climate change and consequent global warming threaten to affect the distribution of plant species. Specifically in the Mediterranean region, where high temperatures coincide with a dry period, climate models predict a reduction in rainfall, which could alter the growth, reproductive capacity and survival of many plant species and, in the medium term, the composition of the plant community.
With the aim of evaluating the impact of climate change on the Mediterranean pastures, a study, in which a researcher from the Higher Technical School of Forestry, Forestry and Natural Environment Engineering of the Polytechnic University of Madrid (UPM) participates in Spain, has focused on analyzing an abundant herbaceous plant in Spain, Geranium dissectum L., verifying the effect of three years of increased temperature and reduced rainfall.
The results after this period show that the physiological alterations experienced by these plants, although notable, allowed them to adapt to climatic changes and maintain their importance in the community. However, the researchers warn that the synergistic effect of increased heat and drought brings with it uncertainty about the future impact on ecosystems.
The methodology used, through the simulation of climatic changes in situ for several years, is useful to anticipate the effects of climate changes on natural ecosystems and to be able to mitigate them through appropriate management measures, such as the planting of species, provenances or progenies better adapted to the new climate, soil modifications or the regulation of the stocking rate and the uses of the pasture.
Agricultural field of the Mediterranean area. (Photo: Amazings/NCYT)
A recreation to scale
The study in which UPM professor Jesús Rodríguez Calcerrada has participated, together with researchers from the University of Seville in Spain, the University of Göttingen in Germany and the Seville Institute of Natural Resources and Agrobiology of the Higher Council for Scientific Research ( CSIC) in Spain, is based on a clear premise: studying the effect of climate change on emblematic species of natural ecosystems is a priority line of research at a European level, in order to assess and understand the effects of climate change.
“In this sense, plant ecophysiology provides analysis tools that make it possible to detect effects that are not visible at other observation scales, or explain the effects that are visible,” says Jesús Rodríguez, from the Forest Systems in a Changing Environment research group. (Forest) of the ETSI of Forestry, Forestry and the Natural Environment.
To carry out the study, the researchers recreated climatic changes in situ in a pasture in the Valle de los Pedroches (Córdoba), which simulated conditions similar to those that these systems could face in the future. The increase in temperature was achieved by placing six transparent methacrylate panels that formed a truncated pyramid open at the top, which created a greenhouse effect. Rainfall reduction was achieved by placing transparent gutters over 33% of the plot’s surface, which intercepted rain and conducted it outside the facility.
Two experimental heating subplots, two precipitation reduction subplots, two heating and precipitation reduction subplots, and two normal subplots (control group, no weather modification).
Adaptation to disturbances
The experimental heating device increased the temperature by 1.4 degrees Celsius and the reduction in precipitation decreased soil moisture by 4% in the three years of study. Based on these small mean climate variations, a remarkable impact on plant physiology was recorded. “The warming alone and the reduction in precipitation alone hardly affected the water status of the plants, or their levels of photosynthesis, respiration, or stomatal opening rates (stomata are cells specialized in regulating the entry of carbon dioxide ). However, the combination of both factors significantly altered the values of these variables”, explains Rodríguez.
“Thus, after three years of continuous warming and reduced precipitation, stomatal opening decreased by 92%, photosynthesis by 79%, and respiration by 37% with respect to the control group plants (not exposed to any climatic treatment). ). In addition, the plants flowered on average 15 days earlier with the simulated combination of more heat and less rain”, he adds.
Despite this, the alterations produced did not affect the relative abundance of Geranium dissectum L. in the community. After three years of study, the grass Hordeum murinum subsp. leporinum L. replaced Geranium dissectum as the most abundant species, but the reduction of the analyzed herbaceous cover in these three years was similar in the three experimental treatments and in the plots of the control group.
Interpretation of these results is not straightforward, as the researchers claim. One might think that the physiological changes experienced by Geranium dissectum plants allow it to acclimatize to climate change and maintain its importance in the community. The plant increased the efficiency in the use of water: with more heat and less rain, it assimilated a certain volume of carbon dioxide (CO2) with less water use. Furthermore, earlier flowering would allow this herbaceous annual to complete its life cycle before temperatures become too high or the soil dries up completely on its surface horizons.
On the contrary, it could be interpreted that an increase in the imbalance between respiration and photosynthesis would reduce the availability of carbohydrates to produce flowers and fruits. In fact, the number of fruits was lower in the plants exposed to more heat and less rain, although not significantly, which could compromise the abundance of the species if the climatic treatments were prolonged.
This research suggests among its conclusions that the increase in aridity accelerates the flowering and aging of the leaves to provide the fruits with the nutrients that are recycled from them. But these changes do not seem to affect the composition of the herbaceous plants, since they reflect the adaptation of the Mediterranean vegetation to the high interannual climatic variability. However, the researchers warn that there is still much uncertainty about the impact of climate change on ecosystems. The results, for now, can be applied to improve predictive models of vegetation behavior under changing conditions.
The study is titled “Three years of warming and rainfall reduction alter leaf physiology but not relative abundance of an annual species in a Mediterranean savanna.” And it has been published in the academic journal Journal of Plant Physiology. (Source: UPM)
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