Effects of plant domestication on litter decomposition rates

Background/Question/Methods

Humans have modified crop species for centuries through artificial selection. This process has changed several plant traits in order to get resistance to herbivores, pathogens, drought or increasing productivity. During domestication and further improvement, wild plants have moved from living in nutrient poor and unpredictable environments to more predictable and nutrient richer habitats. This is analogous to the variation that occurs in natural systems between stressful and poorly productive ecosystems to fertile habitats. Plants from the later sites tend to produce litter of higher quality that decomposes readily and promotes fast recycling of nutrients in the soil, whereas the opposite is true for sites where mineral resources are scarce. The ecological significance of domestication for processes such as litter decomposition is poorly known. Here we explored whether patterns described for natural systems extrapolate to the process of domestication, under the hypothesis that domesticated plants should promote faster leaf litter decomposition rates, and thus faster soil nutrient cycling, than their wild ancestors. We conducted a common garden plus microcosm laboratory experiment to assess the decomposition rate of 24 crop-wild relative species pairs. Two soils of contrasted microbial functional diversity and fungal:bacterial ratio were tested.

 Results/Conclusions

The total CO₂ production, our surrogate of decomposition, in microcosms containing litter of wild species was lower than that produced in crop microcosms for most of the species evaluated. This pattern was also found when a subset of the species was evaluated in the two different soils, and was independent of their contrasted microbial functional diversity and fungal:bacterial ratio (soil type × domestication interaction, P > 0.05). Most of the CO₂ produced was due to the addition of litter instead that to the soil respiration measured in the control microcosms. These results suggest that the domestication of plant species has deeply changed their litter quality, with direct consequences for ecosystem processes such as decomposition. We conclude that, given sufficient evolutionary time, a change from wild (i.e. more stressful) to artificial (i.e. less stressful) environments gave rise to plant species with litter that enhances decomposition and probably accelerates rates of nutrient cycling. This is analogous to patterns observed on a regular basis in natural systems and implies a transfer of knowledge originated in the realm of Ecological Theory to the Agro sciences. Future plant breeding programs may take into consideration the fact that artificial selection has promoted, indirectly, faster and perhaps efficient soil nutrient cycling mechanisms.