Biomass production and temporal stability are similar in switchgrass monoculture and diverse grassland

Authors: Polley, Herbert; Collins, Harold; Fay, Philip

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2020
Publication Date: 9/18/2020
Citation: Polley, H.W., Collins, H.P., Fay, P.A. 2020. Biomass production and temporal stability are similar in switchgrass monoculture and diverse grassland. Biomass and Bioenergy. 142. Article 105758. https://doi.org/10.1016/j.biombioe.2020.105758.
DOI: https://doi.org/10.1016/j.biombioe.2020.105758

Interpretive Summary: One goal of bioenergy research is to identify grassland systems in which production is temporally stable, where stability is defined as the ratio of mean biomass production to inter-annual variation in production. Questions remain as to the number and types of plant species that should be included in grassland communities in order to maximize temporal stability. Two schools of thought predominate. One view posits that stability is increased by increasing species number. A second view holds that stability depends primarily on leaf and other properties of species in the community. We measured temporal stability in aboveground biomass production in 104, 7-m patches each of a species-rich mixture of native perennial grass and forb species and monoculture of switchgrass in central Texas, USA. For communities of both vegetation types, we measured the average value of a leaf property previously identified to influence stability (leaf dry matter content; leaf wet weight/leaf dry weight). We found that production varied among years in response inter-annual variation (IAV) in precipitation. The precipitation effect on stability was expressed through IAV in both the community-averaged value of leaf dry matter content and the relationship between production and leaf dry matter content. Temporal stability over 4 years was similar between vegetation types but was regulated by different components of the leaf dry matter content effect on production in species mixture and switchgrass. Our results support the view that stability in biomass production depends more on leaf properties of the species present in a plant community than species number. Similar levels of stability can be achieved among communities despite differences in the primary pathway via which leaf traits influence production.

Technical Abstract: Research into herbaceous bioenergy production has focused on identifying grassland systems that are both productive and temporally stable, where stability equals the ratio of mean biomass production to its temporal standard deviation. The question remains as to effects of community properties, including species richness, on temporal stability. We compared aboveground net primary productivity (ANPP) and the temporal stability in ANPP of unfertilized grassland planted either as a mixture of native perennial grass and forb species or monoculture of Panicum virgatum L. (switchgrass) in Texas, USA. ANPP varied in response inter-annual variation (IAV) in precipitation. The precipitation effect on ANPP stability was mediated through two components of the influence of a single community property, community (species-abundance) weighted values of leaf dry matter content (LDMC), on productivity. These components include community LDMC and ANPP-LDMC regressions. Stability was similar between vegetation types but was regulated by different components of the LDMC effect on ANPP in mixture and switchgrass. Temporal stability in mixture depended mainly on ANPP variation that resulted from change in community LDMC. Stability of switchgrass depended primarily on ANPP variation that resulted from precipitation-caused change in ANPP-LDMC regressions. Stability declined as ANPP increased in mixture because LDMC variation increased when productivity was high. We find that ANPP and ANPP stability can be as great in an unfertilized planting of a switchgrass monoculture as diverse mixture of grassland species. Similar levels of stability can be achieved via different components of the LDMC effect on productivity.