Belowground productivity of roots and rhizomes in a giant cordgrass marsh

Belowground production of roots and rhizomes in the top 20 cm of soil was 2.2 kg m^?2 yr^?1 based on a maximum minus minimum estimation procedure in a giant cordgrass (Spartina cynosuroides (L.) Roth) marsh in Mississippi. Approximately 1.9 kg m^?2 (86%) of this production occurred in late spring-summer and 0.3 kg m^?2 in late fall. This estimate ignores any production below 20 cm depth and is thus an underestimate. Production values increased to 4.0 kg m^?2 yr^?1 using Smalley’s technique and accounting for decomposition. Aboveground tissues (leaves and stems) were depleted in nitrogen in July which corresponded to peaks in both above- and belowground biomass. The low root/shoot ratio (2.6) on this marsh does not suggest that growth is nutrient limited. Indeed, total productivity (above- and belowground) for this marsh was high (between 4.4 and 6.2 kg m^?2 yr^?1).