EFFECTS OF ACID IRRIGATION AND LIMING ON NITRATE REDUCTION AND NITRATE CONTENT OF PICEA-ABIES (L.) KARST. AND OXALIS-ACETOSELLA L

Nitrate reductase activities (NRA) and nitrate concentration per unit biomass in Picea abies (L.) Karst. roots from four different soil hori zons and in leaves and roots of the frequent field-layer species Oxali s acetosella L. were measured on six different irrigation and liming t reatments within the Hoglwald project, S-Bavaria, Germany. Liming incr eased and acid irrigation reduced soil nitrate availability when compa red to control plots. Nitrate assimilation capacities of the respectiv e plant compartments per unit of soil volume or ground area were calcu lated from the NRA per unit of biomass and from the biomass distributi on on the various treatments. Mean NRA per unit of biomass in Picea ab ies roots ranged between 0.23 and 0.09 mu mol NO2- g(-1) d.w. h(-1) wi thout significant effects of soil horizon or treatment. Limed and non- limed treatments showed for Picea different root distributions within the soil profile, but root biomass per unit of ground area (295 to 220 g d.w. m(-2)) was not affected by the various treatments. Thus, nitra te assimilation capacity of Picea roots per unit of ground area ranged between 19.5 and 11.4 mu mol NO2- m(-2) h(-1) without major treatment effects. In laminae of Oxalis acetosella mean NRA per unit of biomass ranged between 2.91 and 0.27 mu mol NO2- g(-1) d.w. h(-1) and, in con trast to Picea abies, treatment effects were found with NRA on limed p lots increased and on acid irrigated plots reduced when compared to co ntrol plots. Mean leaf biomass of Oxalis per unit of ground area range d between 9.57 and 0.66 g d.w. m(-2) and responded in a similar manner to the various treatments. Thus, for the Oxalis leaf NRA per unit of ground area (27.85 to 0.18 mu mol NO2 m(-2) h(-1)) a cumulative respon se to the variations in nitrate availability was found. The different responses of Picea abies and Oxalis acetosella to changes in soil nitr ate availability are discussed with respect to their suitability to pr event soil nitrate leaching.