Aboveground-root biomass allocation in natural field grasses with different photosynthetic syndromes and resource utilization strategies.

Abstract

Natural field forage grasses can be grouped based on their photosynthetic syndrome: C3 and C4 species; and based on their resource use economy: conserving and acquisitive species. However, the relationships between functional groups and their biomass allocation strategies to aboveground and root parts in different seasons are unknown. The objective of this study was to evaluate the patterns of biomass allocation to the aboveground and root fractions of four natural field grasses with distinct photosynthetic syndromes (Bromus auleticus (brau), Stipa setigera (stse), C3; Paspalum dilatatum (padi), and Paspalum quadrifarium (paqu), C4) and resource economy (stse and paqu, “slow”; brau and padi, “fast”), in two seasons (winter and summer). Festuca arundinacea (fear) was used as a “control” given the information available on its functional attributes. Plants were grown in pots under controlled growth conditions, and destructive serial harvests were performed to obtain accumulated aboveground and root dry weight from successive harvests. Linear models were fitted for the relationship between root dry weight (Ln) and shoot dry weight (Ln), determining the slopes of each model by species and in each growing season. In winter, C3 species brau and stse exhibited significant linear relationships (p < 0.05) with slopes less than 1 (greater allocation to roots), while C4 species padi, paqu, and feau exhibited significant linear relationships with slopes greater than 1 (greater allocation to shoots). In summer, C4 species exhibited slopes less than 1, while C3 species exhibited slopes greater than 1. Except for the control species, the photosynthetic syndrome was a determining factor in the seasonal response to biomass allocation among the different fractions.