Plant Diversity and Decomposition

Submitted by editor on 24 January 2017.Get the paper!

CO2 becomes plant biomass through photosynthesis and then returns to the atmosphere through respiration, including the decomposition of this biomass, forming the basis of the terrestrial carbon cycle. Research has shown that higher biodiversity of plants can increase the total rate of photosynthesis of a plant community. However, the link between plant biodiversity and CO2 re-emission is less clear. Understanding this link is important for both accurately predicting changes in CO2 emissions with biodiversity loss and managing ecosystems for carbon sequestration.

Our work explores the link between plant diversity, the speed of decomposition rates and below ground respiration. We studied this link in an experimental tree plantation of ~10,000 trees, planted to explicitly manipulate functional diversity independently from species diversity: two plots with the same number of tree species can have different functional diversity, where plots with more similar species have lower functional diversity. Partitioning plant diversity into a number of components, we found each to have different effects on components of the CO2 emission process (decomposition and total below-ground respiration).

 

Measuring litter decompostion with litterbags

Firstly, we compared the effects of two measures of diversity (functional and species diversity) of the decomposing litter on litter decomposition rates and found that while increasing the number of species in the litter mix can idiosyncratically influence decomposition rates, sometimes decomposing faster and sometimes decomposing slower than expected, increasing certain aspects of functional diversity, namely litter chemical diversity, had a systematic effect of accelerating litter decomposition.

 

 

Measuring soil respiration with soil CO2 flux

Secondly, we further broke plant diversity into two components: the diversity of the litter decomposing on the ground, and the diversity of the living plant host community, which provides the decomposition environment. We found that litter diversity had a largely unpredictable effect on decomposition rates, while increasing the diversity of the host plant community tended to accelerate decomposition.

Finally we measured two different related but independent processes. The first, litter decomposition, was measured as mass loss over a 6-month month period from litterbags and comprised early stages of the mostly mechanical breakdown of surface litter. The second, soil respiration, was measured as the CO2 flux from the soil, was comprised of later stages of litter decomposition, decomposition of dead roots and other soil organic matter decomposition, as well as non-decomposition related processes like root respiration. Measuring these two different but closely related processes, we found two very different results. Mass loss from litterbags was best predicted by functional identity (primarily the average chemical properties of the litter) as opposed to functional diversity. On the other hand, soil respiration was best predicted by functional diversity (the variation in these traits), and not functional identity suggesting that diversity may be more important in increasing later stages of decomposition.

Our results show that increasing tree functional (and species) diversity resulted in higher rates of below ground respiration, potentially reducing the net CO2 uptake associated with increasing plant productivity with increasing biodiversity.

The authors through Mark Davidson Jewell

Measuring litter decompostion with litterbags

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