In memoriam

James Lovelock 

(1919-2022)

https://en.wikipedia.org/wiki/James_Lovelock

 

Aprendizaje automático para ciencias ecológicas y gestión de ecosistemas 

Thomas G. Dietterich 

Agricultural management and pesticide use reduce the functioning of beneficial plant symbionts  

Edlinger et al., 2022

Phosphorus (P) acquisition is key for plant growth. Arbuscular mycorrhizal fungi (AMF) help plants acquire P from soil. Understanding which factors drive AMF-supported nutrient uptake is essential to develop more sustainable agroecosystems. Here we collected soils from 150 cereal fields and 60 non-cropped grassland sites across a 3,000 km trans-European gradient. In a greenhouse experiment, we tested the ability of AMF in these soils to forage for the radioisotope 33P from a hyphal compartment. AMF communities in grassland soils were much more efficient in acquiring 33P and transferred 64% more 33P to plants compared with AMF in cropland soils. Fungicide application best explained hyphal 33P transfer in cropland soils. The use of fungicides and subsequent decline in AMF richness in croplands reduced 33P uptake by 43%. Our results suggest that land-use intensity and fungicide use are major deterrents to the functioning and natural nutrient uptake capacity of AMF in agroecosystems.

@vandeHeijdenLab: 

Unseen and hidden effects of pesticides: pesticide suppress natural soil fertilizers.  Our new study  demonstrates that pesticides suppress the natural nutrient uptake capacity of beneficial mycorrhizal fungi with 42%.

This result is important because 70% of all land plants and many crops form a beneficial symbiosis with mycorrhizal fungi. The fungi supply nutrients to the plant in return for sugars and fatty acids. They do this through highly sophisticated arbuscules in plant cells.

This study confirms our previous study showing that the abundance of beneficial mycorrhizal fungi is strongly and negatively linked to the number of pesticides in arable soils. 

Pesticide effects worked in two ways: the diversity and richness of mycorrhizal fungi was 50% lower in plots where fungicides had been applied and fungicides reduced the natural nutrient uptake capacity. 

We already found out that synthetic pesticides are widespread in soil and we found up to 16 different pesticides after 20 years of organic management – and we only analysed 46 pesticides far less as the number being applied.

A large study across Germany even demonstrated that all air samples analysed contained pesticides. Up to 36 different pesticide compounds were detected in the air, including pesticides not approved for use anymore.

In Switzerland pesticides are also found in drinking water, especially in areas with intensive agricultural production. Many people are concerned about potential health effects.

These findings are not surprising. Large amounts of pesticides are used worldwide and in some countries, over 20 kg per hectare and year are applied. With a 50% increase in pesticides use since the 90ies.

Pesticide use varies strongly among crops. For some crops (fruit-trees, vinyards) >25 kg of pesticides are applied per hectare and year, which is a lot. For others (grassland) hardly any pesticide are applied.

Farmers apply pesticides because they often work very well against pests and diseases. It is logical that farmers apply pesticides because they help to secure yield and food security. However, many crops can be grown without pesticides.

For many crops there are cultivars that are (largely) resistant to disease and with appropriate farming practices (e.g. crop rotation, mixed cropping) and weed control measures it is possible to drastically reduce pesticide use without yield or income loss.

Also organic farmers apply pesticides, but only those that are not synthetic and produced in nature. Still, some of these organically certified pesticides are harmful. However, negative effects are usually (not always) much lower compared to synthetic pesticides.

Interestingly >150 different synthetic pesticides have been banned in Switzerland between 2005 & 2020 (source BLW).

Society is more and more critical about the use of pesticides and this is reflecting in increased consumption of organic and pesticide free produced products (a growth of >50% in 5 years). In Switzerland 17% of agricultural land is under organic management (source Biosuisse).

I assume that (big) companies selling synthetic #pesticides are getting nervous because their business model is under pressure when more and more farmers move to organic or pesticide free production.

It is logical that companies sell synthetic pesticides because there is still a big market and a large demand. What is very questionable is that several companies sell and produce pesticides that have been banned in many countries (e.g. CH, EU) because they are very harmful.

As long as such companies do sell banned pesticides, simply to make profit, there are no arguments to trust such companies, even if they focus more on sustainability, soil health or biodiversity.

This tweet thread is written by Marcel van der Heijden (Professor for Agroecology) and these comments reflect my personal opinion, not necessarily those of Agroscope, University of Zurich or Utrecht University.

https://www.nature.com/articles/s41559-022-01799-8

 Chaos in ecology is more common than you think

We find evidence for chaos in over 30% of time series in an ecological database using updated, flexible, and rigorously tested algorithms. Lack of evidence for chaos in prior meta-analyses is likely the result of methodological and data limitations, rather than inherent stability.

Systems that are 'chaotic' are sensitive to small changes in initial conditions, and are predictable in the short term, but not in the long term. The weather is an example of a chaotic system - it is completely governed by the rules of physics, but difficult to predict accurately beyond several days. This is in contrast to 'stable' dynamics, which are predictable over long periods, or 'random' fluctuations, which are not predictable over any time horizon. Populations in nature fluctuate a great deal, and knowing whether these fluctuations are regular, chaotic, or random has major implications for how well (and how far into the future) we can predict population sizes, and how they will respond to management interventions.  

Chaos was first introduced to ecology in the 1970s, and there was great interest in whether the seemingly erratic population fluctuations we see in nature could be explained by relatively simple (single species) chaotic population models. However, by the late 1990s, it had become increasingly clear that this wasn’t the case. Chaos detection studies based on these simple models found little evidence for chaos in field data, and the idea that chaos is rare in ecology became increasingly widespread. 

Source: https://go.nature.com/3bwHoGe

Research paper:

Chaos is not rare in natural ecosystems  

Chaotic dynamics are thought to be rare in natural populations but this may be due to methodological and data limitations, rather than the inherent stability of ecosystems. Following extensive simulation testing, we applied multiple chaos detection methods to a global database of 172 population time series and found evidence for chaos in >30%. In contrast, fitting traditional one-dimensional models identified <10% as chaotic. Chaos was most prevalent among plankton and insects and least among birds and mammals. Lyapunov exponents declined with generation time and scaled as the −1/6 power of body mass among chaotic populations. These results demonstrate that chaos is not rare in natural populations, indicating that there may be intrinsic limits to ecological forecasting and cautioning against the use of steady-state approaches to conservation and management.

Rogers et al., 2022. https://www.nature.com/articles/s41559-022-01787-y

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