The Role of Fine Roots in the Organic Matter and Nitrogen Budgets of Two Forested Ecosystems

Abstract

Standing crop, rates of production, mortality, decomposition, and nitrogen dynamics of two size classes of fine roots (0—05 mm and 0.5—3.0 mm diameter) were estimated for 1 yr in a 53—yr—old red pine (Pinus resinosa Ait.) plantation and in an adjacent 80—yr—old mixed hardwood stand in north—central Massachusetts. Dry matter of live fine roots was higher in the hardwoods (mean = 6.1 Mg/ha; annual range 3.6—8.6 Mg/ha) than in the plantation (mean = 5.1 Mg/ha; annual range 2.5—7.8 Mg/ha.) Dead root mass was similar in the hardwoods (mean = 4.4 Mg/ha) and the plantation (mean = 4.0 Mg/ha). Nitrogen standing crop of live roots in the hardwoods was higher than in the plantation (mean = 65 kg/ha and 42 kg/ha, respectively). Net fine root production was estimated from changes in standing crop. Production estimates ranged from 4.1 to 11.4 Mg°ha—1°yr—1 in the hardwoods and from 3.2 to 10.9 Mg°ha—1°yr—1 in the plantation, depending on the assumptions made in the calculations. Concurrent estimates of total nitrogen requirement for this production ranged from 73 to 184 kg°ha—1°yr—1 in the hardwoods and from 44 to 122 kg°ha—1°yr—1 in the plantation. Decomposition, measured as mass loss from buried cloth bags, was °20% in 0.4—mm mesh bags and as high as 47% in 3—mm mesh bags after 1 yr. Integrating production and nitrogen requirements with estimates of decomposition rates and nitrogen mineralization for these ecosystems suggested that the lower estimates of production are more accurate.

Responses of tree fine roots to temperature

“…This seasonal pattern seems to correspond roughly to leaf duration. In temperate forests, the most significant period of root growth corresponds to canopy development in the spring and the most significant period of root mortality corresponds to canopy senescence in the fall (McClaugherty et al, 1982 ;Kurtz & Kimmins, 1987 ;Hendrick & Pregitzer, 1992, 1993a, 1996. Root-shoot phenological observations of temperate trees presented by Lyr & Hoffmann (1967) suggest that most of the flush of fine-root growth in the spring might occur after canopy development.…”

Conversion of a natural broad-leafed evergreen forest into pure plantation forests in a subtropical area: Effects on carbon storage

“…Studies have indicated that litter input belowground could account for 6.2-88.7% (average 50%) those aboveground and constitute 14-86.6% (most above 40%) of total soil organic input (e.g., [27,44]). In the present study, C inputs belowground in the NF almost equaled those aboveground, and amounted to about half of aboveground C input respectively in the plantations.…”

Root biomass and biomass increment in a beech (Fagus sylvatica L.) stand in North-East France

“…However, an estimation of fine root production could be calculated at the stand level by using an annual turnover ratio of 0.6 and using the method devised by MacClaugherty et al [26] to estimate annual fine root production. The turnover ratio, defined here as the ratio between the production of fine roots during the growing season and the biomass of living fine roots at the end of the growing season, was derived from data obtained by Farque on the same site (unpublished data).…”