Biomass production and CO2 uptake in a functionally diverse cover crop mixture

Background/Question/Methods

Increasing the functional biodiversity of plants grown on agricultural fields is one strategy to increase productivity while reducing carbon dioxide (CO₂) emissions. Cover crops are plants grown in the off-season that allow for the manipulation of biodiversity directed at specific outcomes. Intercropping functionally diverse cover crops that occupy different ecological niches may demonstrate complementarity leading to increased ecosystem service provision. Therefore, a greenhouse experiment was conducted to determine if increasing functional diversity lead to greater productivity (i.e., biomass production and Net Ecosystem Exchange (NEE)). Mixtures and monocultures were grown of a C₃ grass, rye (Secale cereale cv. common), a legume, Lana vetch (Vicia villosa ssp. dasycarpa cv. Lana) and a perennial forb, chicory (Cichorium intybus cv. Puna). Treatments consisted of three densities: rye- 0, 29, 59 kg/ha; Lana vetch- 0, 13, 26 kg/ha; and chicory- 0, 1.8, 3.6 kg/ha. These densities were combined in a complete factorial design and harvested at three dates. 

Results/Conclusions

Rye and chicory were significant factors for modeling biomass indicating that these species contributed the most to biomass production. Furthermore, most bicultures of rye and chicory produced equivalent biomass to rye monocultures (p>0.05), but more than chicory monocultures (p<0.001). Chicory and rye were significant factors for modeling leaf area indicating that these species contributed the most to total leaf area. However, these results differed from biomass in that bicultures of rye and chicory produced equivalent leaf area to chicory monocultures (p>0.05), but more than rye monocultures (p<0.001).  Only rye was significant in modeling NEE, whereas chicory was also significant in modeling Ecosystem Respiration (R_e). The highest density bicultures of rye and chicory produced greater R_e compared to either rye or chicory monocultures (p<0.001).

Limited complementarity was observed between chicory and rye. At a high density of rye and low density of chicory, there was no interaction suggesting that chicory captured additional light without limiting rye growth. The contrast between higher leaf area from the perennial forb and greater biomass and photosynthesis from the C₃ grass is an important consideration for designing mixtures. Furthermore, the perennial forb’s greater contribution to R_e warrants further inquiry into root-based ecosystem services. In general, increasing functional diversity did not increase overall productivity. Rye dominated the mixtures driving biomass production and NEE with chicory adding a marginal benefit.