lovesouthernsocial.com

Study assesses the possibility of CO2 interfering with the growth of tropical trees

Some statistical models that represent the dynamics of global vegetation have previously been used to predict the environmental responses of forest environments to climate change. These models argue that the role of carbon dioxide in tree growth may be more important than we thought, in that the increase in the concentration of CO 2 in the atmosphere will cause the biomass of tropical forests to increase, that is, that the CO 2 will have a fertilizing effect of tropical climate trees.

Like

With the increase in the concentration of CO 2 in the atmosphere, more raw material is then available to be used in photosynthesis reactions. Thus, this increase would accelerate the photosynthetic rates of plants. In addition, CO 2 fertilization would increase the efficiency of water use, making the plants better use this resource, with less water loss through transpiration.

Despite predictions, there is no concrete evidence that this process would actually influence the growth of trees in tropical forests.

The magazine nature published a study that investigated whether or not there is a relationship between the increase in atmospheric CO 2 and the growth of trees by measuring the rings of their trunks. The study also investigated whether there is a relationship between the increase in the concentration of CO 2 and changes in the rate of use of water by trees.

An increase in water use efficiency would be particularly interesting for trees that are subject to periods of water scarcity or seasonal droughts, so that less water loss would reduce the water stress suffered by them and extend their growing seasons.

The first step of the study was to verify whether there was an increase in carbon uptake by trees that could be related to the increase in atmospheric CO 2 concentration, and whether this changed the rates of photosynthesis and water use. The other step was to verify whether there was growth of rings and trunk width in this period of time, so that a relationship could be established between the increase in CO 2 and the increase in biomass in tropical forests.

The study

More than a thousand trees of 12 different species were selected, and, for a greater representation of the tropical environment, they were distributed in three different locations in the tropics. The study aimed to analyze the relationship between the increase in CO2 and changes in tree growth rates over the last 150 years, and to obtain long-term data, the carbon isotopes (element carbon variants) present were analyzed. in the cellulose of the trunks. From these isotopes it was possible to estimate the intracellular carbon present in the leaves and the efficiency of water use in previous years.

From this, a significant increase in intracellular carbon present in the leaves of trees in the three locations over the last 150 years was identified. However, this increase was smaller than those of atmospheric CO 2 . In other words, the identified increase occurred on a much smaller time scale than the rise in carbon dioxide concentrations in the atmosphere, which began to occur at the beginning of the Industrial Revolution, around 1850.

Anyway, it was identified that, simultaneously, there was an increase in the efficiency of water use. Previous studies with enrichment of CO2 in the air have identified this improvement in the use of water in some tropical tree species, as well as in temperate trees, and this effect seems to have occurred on a pan-tropical scale.

The long-term increase in water use efficiency indicates two likely explanations: the first would be the increase in photosynthesis, which may thus be related to the increase in CO 2 concentration. The second is the decrease in sweating.

Results

The study concluded that the increase in atmospheric CO 2 concentration over the past 150 years has resulted in increases in the levels of carbon present in the leaves, as well as improvements in the use of water for the three study sites. However, no detectable increases in trunk diameter were identified for the period analyzed.

Despite this, a low capacity to detect changes in trunk growth was proven by the methodology used in the study, which is one of the possible reasons for not having identified tree growth.

Justifications

These divergences between the study carried out and the statistical models with regard to the growth of trees can be attributed to technical reasons of the methodology used by each researcher, which may vary in the period analyzed, in the units of analysis, and sizes of the lots from which the trees were sampled, for example. The results obtained from the study presented by the nature indicate that, contrary to common assumptions, the increase in atmospheric CO 2 concentration did not stimulate the growth of trees of the studied species on a centenary time scale.

Another possible reason why an increase in tree growth has not been verified is the existence of external stressors, such as increases or decreases in the average daily temperature, as identified in the period studied, or the scarcity of other resources fundamental to growth besides CO 2 or of water, such as limiting nutrients or reducing light levels.

Furthermore, additional assimilations generated by increased photosynthesis may have been applied in the development of fruits and root biomass, not being identified by measuring tree rings or trunk diameters.

Changes in water use rates, on the other hand, can be explained by a reduction in the conduction of water by the stomata, which reduced transpiration rates. One concern to be taken into account is that a reduction in plant transpiration would lead to lower air humidity and higher temperatures (read more about global warming by clicking here). It is not possible to say that this would cause changes in the hydrological cycle, because deforestation, while increasing the concentrations of CO 2 in the atmosphere (thus occurring simultaneously with changes in the use of water by plants), also has a large share of responsibility in the interference in the cycle.

Considering the important role of tropical forests in the global carbon cycle, it is important to know what their responses to climate change will be. As mentioned, it is predicted that they will increase their biomass as a result of CO 2 fertilization. However, if these effects do not exist (as identified in the study presented by the magazine), it is possible to affirm that current models overestimate the capacity of tropical forests to act as carbon sinks, indicating that they will absorb more atmospheric carbon than they actually do. , actually playing a smaller role in reducing the effects of global warming than predicted by current models.