Root Dynamics in Restored and Naturally Regenerated Atlantic White Cedar Wetlands

Abstract

This work addressed the seasonal and successional factors of root dynamics in natural and restoration Atlantic white cedar (AWC) wetlands. Using minirhizotrons and soil root cores, fine root dynamics were measured in a chronosequence of reference and restoration AWC wetlands to compare trends in ecosystem development after canopy harvest. Seasonal fine root abundance, production, and mortality were sampled during a 439-day period in one restoration and three reference AWC wetlands. Soil cores were collected to measure fine root biomass and to determine allometric relationships between root length and biomass. Significant seasonal variation of root dynamics was observed in the young reference and restoration sites. The mature and intermediate-aged sites exhibited little seasonal variability in root abundance and mortality. Root production was variable but not seasonally consistent. Results suggest that root dynamics become less seasonal as AWC communities shift from herbaceous to woody vegetation dominance. No trend in fine root abundance along the chronosequence was observed, suggesting that roots rapidly reestablish following tree harvest. Measurements of annual root length production suggest increasing annual production with decreasing stand age. However, a reversal of this trend was observed when using production estimates calculated from minirhizotron measurements and root lengthmass relationships. These findings underscore the importance of supplementing minirhizotron data with root allometric relationships when analyzing vegetation gradients. Overall, results indicate substantial differences in the form and quantity of root contributions to soil organic matter in the restoration site compared to that in the reference chronosequence. Higher initial planting densities of AWC are recommended to achieve similar contributions of roots to soil organic matter accumulation in the restoration site.

Advancing the use of minirhizotrons in wetlands

“…Previous minirhizotron studies in wetlands have used anchors consisting of wood (Sloan 2010), metal conduit (Baker et al 2001;O'Connell et al 2003;Rodgers et al 2003;Rodgers et al 2004), or steel rebar (Dickinson 2007) installed to a depth between 1 and 3 m, and attached to the minirhizotron using hose clamps, plastic cable ties, or duct tape. However, in contrast to upland ecosystems, it may be important to consider redox dynamics in these often highly acidic and water-logged environments (i.e., Mitsch and Gosselink 1986); a fiberglass or Teflon-coated stainless steel rod could be used in place of metal conduit in order to avoid metal contamination of the surrounding soil.…”

“…Timing of image capture in wetlands has ranged from intervals of 1-2 weeks (Sullivan and Welker 2005;Sullivan et al 2008) to 1 month or more (Aerts et al 1989;Steinke et al 1996;Steele et al 1997;Baker et al 2001;O'Connell et al 2003;Rodgers et al 2003;Rodgers et al 2004;Sullivan et al 2007). However, 3 days to 1 week have been previously recommended as the longest sampling intervals to avoid underestimating root production and mortality in upland ecosystems (Stewart and Frank 2008;Kitajima et al 2010), and there is little evidence to indicate that environmental conditions in wetlands result in substantially slower root turnover when compared with uplands (e.g., Gill and Jackson 2000).…”

“…For example, a 3 mm value was chosen in sedgedominated arctic tundra (Sullivan and Welker 2005;Sullivan et al 2007;Sloan 2010) based on comparison of minirhizotron data with values in the literature (Sullivan and Welker 2005) and estimates of annual production made using in-growth cores (Sullivan et al 2008), whereas a 2-mm depth of field was used in poorly-drained boreal black spruce forests (Steele et al 1997;Ruess et al 2003). Loosely consolidated peat in wetland ecosystems may make it difficult to estimate an average field depth, especially at shallow soil depths in where bulk density is least (Rodgers et al 2004;Fig. 3, this paper).…”

“…Only a handful of studies have employed minirhizotron technology in wetlands (Aerts et al 1989;Steinke et al 1996;Steele et al 1997;Baker et al 2001;O'Connell et al 2003;Rodgers et al 2003;Ruess et al 2003;Rodgers et al 2004;Sullivan and Welker 2005;Kalyn and Van Rees 2006;Dickinson 2007;Sullivan et al 2007;Sullivan et al 2008;Sloan 2010). While these studies provide evidence that minirhizotron technology can be used effectively to examine fine-root dynamics in these systems, there remains a need for review and standardization of approaches to mange outstanding problems associated with unique wetland characteristics.…”

Stress-Tolerant Feedstocks for Sustainable Bioenergy Production on Marginal Land

“…In contrast, Pennisetum purpureum showed major reductions in shoot biomass in saline conditions [146], and M. × giganteus was only moderately salt tolerant [160]. Upland ecotypes of Panicum virgatum (e.g., "Blackwell," "Trailblazer," and "PV-1777") were among the more salt-tolerant cultivars [151,164,166,184], although the upland ecotype, "Cave-in-Rock," was not tolerant at the seedling stage [167].…”