The carbon (C) and nitrogen (N) contents and decomposition rates of the aboveground litter were measured in five peatlands (bog, poor fen, open moderately rich fen, wooded moderately rich fen, and lacustrine sedge fen) in central Alberta, Canada, over a period of 2 years. Decay rates and C and N content of the dominant species were measured at each site. Weight losses after 1 and 2 years were negatively correlated with initial and final C/N ratios. Weight losses were positively correlated with initial and final %N, with the fastest weight losses in the species with the highest N content. Rates of decay within sites differed according to litter types, with Carex > Betula > mosses. Decay rates and C and N content were also determined for a standard litter type (Carex lasiocarpa), to make cross-site comparisons. Standard litter weight losses differed between sites after 1 and 2 years of decay. The sites ranked poor fen > wooded–rich fen > bog > open–rich fen > sedge fen in order of greatest to smallest percent weight loss after 2 years. After 1 year, weight loss of the standard litter was negatively correlated with water level and pH-related parameters and positively correlated with total dissolved P. Decomposition was correlated with both substrate quality and environmental parameters, but the former may be more important than the latter in controlling decomposition in these peatlands. Keywords: decomposition, peatlands, carbon, nitrogen, hydrology, water chemistry.

Intercrops have been associated with greater yields and pest and weed control compared with sole crops. In this field experiment, we investigated agronomic performance and weed suppression by three crops—spring wheat (Triticum aestivum), canola (Brassica napus), and field pea (Pisum sativum)—alone and in all possible combinations at two sites in Manitoba, Canada, from 2001 to 2003. Crop treatments were planted at the same total density (144 seeds m−2). The effects of the different crop combinations on weed recruitment and biomass and crop production were studied in both the presence and absence of in-crop herbicides. The agronomic performance of intercrop and sole crop treatments varied greatly across site-years. Some intercrop treatments (e.g., wheat–canola and wheat–canola–pea) tended to produce greater weed suppression compared with sole component crops, indicating synergism among crops within intercrops with regard to weed suppression. Intercrop treatments resulted in land-equivalent ratios (LER) > 1 (i.e., overyielding) in both the presence and absence of in-crop herbicides. In the presence of herbicides, canola–pea was the most consistent intercrop treatment in terms of overyielding for grain (mean LER = 1.22), whereas in the absence of herbicides, wheat–canola–pea produced the most consistent overyielding frequency for dry matter production (mean LER = 1.28). In the presence of herbicides, overall grain yield stability was greatest for the wheat–canola–pea intercrop treatment. Results indicate that annual intercrops can enhance both weed suppression and crop production compared with sole crops.

The nitrogen (N) supply is limited in many peatlands, and the mineralization of organic matter represents a major source of N to plants. The goal of this paper is to establish the relationship between decomposition rates, mineralization rates, and the N concentration of peat along a peatland gradient in four peatlands in western, boreal Canada. The four peatlands differ physically, chemically, and floristically and include a bog, a poor fen, and two moderate-rich fens, one wooded and the other open. The fens are enriched by ground water inputs, which we hypothesized led to higher concentrations of N in peat, faster decomposition of litter, and higher N mineralization rates. Net N mineralization was virtually identical to net ammonification over a 2-y period, both measured using an in situ incubation technique. Net daily mineralization rates increased from the bog to the open, moderate-rich fen, with intermediate values in the poor fen and moderate-rich wooded fen. This increasing trend along the bog-open, moderate-rich fen peatland gradient was mirrored for mineralization rates on a temporal and spatial basis. Virtually no nitrification was detected in any of the sites. Estimated aboveground integrated ecosystem decomposition rates ranged from 17%·y -1 in the bog to 31%·y -1 in the wooded, moderate-rich fen. Decomposition rates were significantly correlated with the mean daily net N mineralization rate and with total N in the upper 20 cm of peat. The net mineralization rate also was positively correlated with the total N content of the peat in 1991. The total N content of the peat increased from 5.8 mg·g -1 in the bog to 11.5 mg·g -1 in the open, moderate-rich fen, with poor fen and moderate-rich wooded fen values intermediate. The total C content of the peat ranged from 370 to 400 mg·g -1 and was not significantly different among the four peatlands. TC:TN quotients for the peat cores were 68 in the bog and 36-38 in the fens, correlating negatively with net ammonification rates. Based on our data, the processes of mineralization of N and decomposition are tightly linked processes, both of which were higher in the fens than in the bog in our four western continental peatlands. Moreover, both processes are more affected by the quality of the organic matter, as indicated by the TC:TN quotients of the surface peat, than by surface water chemistry variables.Résumé : L'apport en azote est limité dans plusieurs tourbières. La minéralisation de la matière organique représente donc une source importante d'azote pour les plantes. Cet article vise à établir la relation entre le taux de décomposition, le taux de minéralisation et la concentration en azote de la tourbe le long d'un gradient de tourbières dans la zone boréale de l'Ouest du Canada. Quatre tourbières différant par leurs caractéristiques physiques, chimiques et floristiques ont été retenues, soit une tourbière ombrotrophe (bog), une tourbière minérotrophe (fen) pauvre et deux tourbières minérotrophes modérément riches, l'une boisée et l'autre ouverte. Les tourbiè...

Production-to-decomposition quotients and asymptotic limits of peat accumulation were determined to estimate peat and carbon accumulation potentials along a bog-fen-marsh wetland gradient in southern boreal Alberta, The wetlands were a bog. a poor fen (PF). a wooded modcrate-rich fen (WRF), a lacustrine sedge fen (LSF), a riverine sedge fen (RSF), a riverine marsh (RM), and a lacustrine marsh (LM). First year mass losses increased along this gradient (bog 14%, fens 25-61%, marshes 57-62%), with second year total mass losses increasing from 18 to 38% from the bog to the moderate-rich fens. Ratios of aboveground net primary production to decomposition and asymptotic limits of peat accumulation showed decreasing trends from the bog to the fens to the marshes as decay rates increased along the same gradient.The Sphagnum-dominated sites (bog, PF) showed greater peat accumulation potentials than the brown mossdominated sites (WRF, LSF) and those sites with an insignificant-to-no moss stratum (RSE RM, LM), which is paralleled by their decreasing peat thicknesses. Rates of litter accumulation in the first year averaged 170 g m-: yr -~ in Sphagnum-dominated sites, 130 g m -2 yr ~ in brown moss-dominated sites, and 103 g m ' yr ' in sites with an insignificant-to-no moss stratmn. All three wetland types showed similar carbon accumulation potentials (83, 67, and 50 g m -" yr-~, respectively) after the first year of decomposition. Peat depth, asymptotic limits of peat accumulation, and production-to-decomposition ratios correlated negatively with waler levels, pH, and Ca -'+, and they con'elated positively with moss and woody plant production (shrubs, trees). Peatlands with strong moss and shrub/tree strata (bog, PE WRF) accumulate more peat than those wetlands dominated by graminoids (LSF, RSE RM, LM). In the bog, high peat accumulation potentials may be related to low rates of decomposition. The peat accumulation potentials of some fens (PE WRF) are similar to the bog and may be maintained by higher decomposition rates, which are offset by higher litter inputs. In the graminoid-dominated fens and marshes, peat accumulation potentials are lowest and may be related to higher litter quality, resulting in higher decomposition rates.

Abstract:The above-ground net primary production (NPP) and litter fall of five peatlands (bog, poor fen, wooded moderate-rich ten, lacustrine sedge fen, and extreme-rich fen) representing the bog-rich fen gradient in central Alberta, Canada were measured during two growing seasons. Total above-ground NPP increased along the gradient from the bog to moderate-rich fen and then decreased in the sedge and extreme-rich fens. Above-ground NPP in the bog (264-297 g.m-:.yr -]) was low compared to other North American bogs, while the Alberta fens had intermediate values of NPP (214-360 g-m Z-yr-L) compared to other North American fens. Moss NPP was lowest in the sedge fen but did not differ significantly between the other peatlands. Vascular plant NPP was highest in the poor fen, moderate-rich fen, and sedge fen and lowest in the bog and extreme-rich fen. Herb NPP tended to increase along the bog-rich fen gradient, while shrub NPP tended to decrease along the gradient. Litter fall was greatest in the poor and moderate-rich fens and lowest in the sedge and extreme-rich fens.