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REVERSAL OF NITROGEN SATURATION AFTER LONG‐TERM DEPOSITION REDUCTION: IMPACT ON SOIL NITROGEN CYCLING
Author(s) -
Corre Marife D.,
Lamersdorf Norbert P.
Publication year - 2004
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/03-0423
Subject(s) - cycling , mineralization (soil science) , nitrogen cycle , throughfall , abiotic component , nitrification , leaching (pedology) , nitrogen , environmental chemistry , environmental science , biogeochemical cycle , ammonium , chemistry , ecology , soil water , soil science , biology , history , archaeology , organic chemistry
An ongoing roof experiment, where N and acid inputs were reduced to the recommended critical load levels, has been conducted since 1991 in an N‐saturated spruce stand in Solling, Germany. Our study was aimed at (1) quantifying the changes in gross rates of microbial N cycling under ambient and reduced N conditions, and (2) relating the soil N dynamics to the changes in N leaching and N status of trees. Two roofs were used, one to achieve “ambient” and the other reduced (“clean rain”) inputs, with a roofless plot as a control for possible roof effects. In 2001, the ambient roof and ambient no‐roof plots showed an apparent decrease in gross N mineralization rates and significantly lower microbial NH 4 + immobilization rates and turnover rates of NH 4 + and microbial N pools. The microbial NO 3 − immobilization rates and NO 3 − pool turnover rates were lower than the microbial NH 4 + immobilization rates and NH 4 + pool turnover rates, showing that less NO 3 − cycled through microorganisms than NH 4 + . There was also low abiotic NO 3 − immobilization. High NO 3 − input from throughfall and low microbial turnover rates of the NO 3 − pool, combined with low abiotic NO 3 − retention, may have contributed to the high NO 3 − leaching losses in these ambient plots. The clean rain plot showed a slight increase in gross N mineralization rates and significantly higher microbial NH 4 + immobilization rates and turnover rates of NH 4 + and microbial N pools. Neither nitrification nor soil NO 3 − was detectable. There was an increase in abiotic NO 3 − immobilization. Foliar N concentration had decreased but was still adequate. An efficient cycling of NH 4 + through microorganisms, combined with the high abiotic NO 3 − immobilization, indicated efficient mineral N retention in the clean rain plot. These results indicated that long‐term reduction of throughfall N and acid inputs had induced high but tightly coupled microbial NH 4 + cycling and an increase in abiotic NO 3 − retention, which contributed to the reversal of N saturation.