Individual study: Seedling growth of bog plants in relation to the recolonization of milled peatlands: a growth chamber experiment, Québec, Canada
Campbell D.R. & Rochefort L. (2003) Germination and seedling growth of bog plants in relation to the recolonization of milled peatlands. Plant Ecology, 169, 71-84
After commercial peat extraction, restoration of vegetation is a desired objective, preferably using those native species occurring in peatlands prior to peat extraction. In this study conducted in Québec, Canada, two experiments were conducted to evaluate the potential of vascular plants (both those species occurring in undisturbed bogs and those, sometimes undesirable species, colonising milled bogs) to germinate and establish in abandoned milled peatlands and to assess whether easily measured plant traits can be used to predict their probable success. Study species included 20 frequently occurring perennial herbs, graminoids, shrubs and trees of undisturbed bogs or abandoned milled bogs. A glasshouse experiment was performed to test the effect of different burial depths under peat on germination and seedling emergence (for a summary see: www.conservationevidence.com/ViewEntry.asp?ID=1168), and a growth chamber experiment was conducted to measure growth parameters of seedlings (summarised here).
Study species: Study species were chosen as the most frequent vascular plants occurring in either natural bogs or abandoned milled bogs in Québec, Canada. Desirable species for restoration are those of natural bogs, while some species which recolonize milled bogs may include undesirable species not usually found in undisturbed bogs (e.g. birch Betula spp.). In total, 21 species were chosen, including perennial herbs, graminoids, shrubs and trees (Table 1, attached). Seeds of all species were collected from milled and natural peatlands at three sites in Québec.
Seedling growth experiment: Pots (6 x 6 cm) were filled with sieved Sphagnum peat and wetted with a nutrient solution ((20% Rorison solution, nutrient concentrations similar to maxima found in natural and milled bogs in eastern Canada). Between 10 and > 100 seeds were sown per pot on the peat surface. Pots were refrigerated at 4ºC until the start of the experiment, when placed in two growth chambers following a random block design (eight blocks, one pot for each harvest/species per block). Pots received 14 hours of daylight and were watered every 2 to 3 days with 50 mL of the nutrient solution.
Once germinated, seedlings were thinned to one per pot. Seedlings were harvested at 7 and 21 days after germination and scanned digitally using an image scanner. Leaf area and maximum rooting depth (i.e. the length of the longest root) were measured. Seedlings were weighed whole during the first harvest due to the small size of many species, but were separated into component parts (roots, shoot, leaves) at the second harvest and weighed.
Numerous growth parameters were calculated (based on harvests of seedling dry weight, leaf dry weight and leaf area) including: absolute growth rate (mg/day); relative growth rate; (mg/mg/day), leaf area ratio (mmÂ²/mg) and specific leaf area (mmÂ²/mg). (See original paper for additional parameters measured).
Growth parameters could not be determined for Carex stricta due to poor germination and for Kalmia angustifolia as seedlings were often too light to be weighed even at 21 days. The remaining species showed wide variation in growth parameters; relative growth rate was not correlated with seed mass, as might have been expected during the earlier stages of growth.
Birches Betula papyrifera and B. populifolia had the highest absolute and relative growth rates (both species frequently colonise milled bogs) with Aronia melanocarpa also having high values, whilst the three Carex species tested (C.limosa, C.oligosperma, C.stricta) had the lowest.
Relative growth rate was strongly correlated with leaf area ratio and especially specific leaf area of seedlings, except for species with a seed mass of less than about 0.01 mg (see Table 1 for study species and their average seed masses).
Conclusions: The authors conclude that screening of plant species for seed mass and specific leaf area should help predict their germination and establishment success in milled peatlands and allow more directed interventions to favour the establishment of desirable native species during vegetation restoration attempts.
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