Nutrient Relationships: Cycling
نویسنده
چکیده
Figure 1. Nutrients may be tied up in bryophytes for decades, or recycle within months, in forests with abundant bryophytes, as in this forest with Isothecium myosuroides. Photo by Michael Lüth. Few quantitative studies have addressed the role of bryophytes in ecosystem nutrient cycling. Nevertheless, bryophytes may play a significant role in N retention and release in the ecosystem (Figure 1). Bowden (1991) found that in primary succession on exposed New Hampshire sands, the rate of N accumulation in Polytrichum was 10.1 kg ha-1 y-1. Even for this endohydric moss, he found that 58% of the annual input of N is from bulk precipitation. As suggested by this study, the bryological component of the ecosystem often plays a significant role in that nutrient When the Polytrichum was removed from the soil, N losses from the ecosystem temporarily exceeded inputs, underlining the importance of the mosses in sequestering and holding N at the site. Lamontagne (1998) found that nitrification increased 13-fold under lichen and moss patches. In this case, the lichens did not fix atmospheric N and thus did not contribute directly to the N supply. Without the mosses (and lichens), the N from precipitation and throughfall can be lost to surface water that ultimately ends up in waterways and is carried from the local system. In addition, the mosses and lichens can contribute organic acids that leach N from the underlying bedrock, thus making it available to plants. In the Alaskan black spruce forest, the bryophyte layer intercepts and accumulates more of every nutrient element but Ca ++ than it receives from throughfall and litter (Oechel & van Cleve 1986), again suggesting that soil nutrients are also contributed. Only in peatlands and the polar latitudes have most ecosystem ecologists traditionally acknowledged the role of the bryophytes in storing or releasing nutrients. Nevertheless, bryophytes play several roles in the nutrient status of their home ecosystems. Whereas tracheophytes
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