Foliar free polyamine and inorganic ion content in relation to soil and soil solution chemistry in two fertilized forest stands at the Harvard Forest, Massachusetts

Polyamines (putrescine, spermidine, and spermine) are low molecular weight, open-chained, organic polycations which are found in all organisms and hav e been linked with stress responses in plants. The objectives of our study were to investigate the effects of chronic N additions to pine and hardwood stands at Harvard Forest, Petersham, MA on foliar polyamine and inorganic ion contents as well as soil and soil solution chemistry. Four treatment pl ots were established within each stand in 1988: control, low N (50 kg N ha( -1) yr(-1) as NH4NO3), low N + sulfur (74 kg S ha(-1) yr(-1) as Na2SO4), an d high N (150 kg N ha(-1) yr(-1) as NH4NO3). All samples were analyzed for inorganic elements; foliage samples were also analyzed for polyamines and t otal N. In the pine stand putrescine and total N levels in the foliage were significantly higher for all N treatments as compared to the control plot. Total N content was positively correlated with polyamines in the needles ( P less than or equal to 0.05). Both putrescine and N contents were also neg atively correlated with most exchangeable cations and total elements in org anic soil horizons and positively correlated with Ca and Mg in the soil sol ution (P less than or equal to 0.05). In the hardwood stand, putrescine and total N levels in the foliage were significantly higher for the high N tre atment only as compared to the control plot. Here also, total foliar N cont ent was positively correlated with polyamines (P less than or equal to 0.05 ). Unlike the case with the pine stand, in the hardwood stand foliar polyam ines and N were significantly and negatively correlated with foliar total C a, Mg, and Mn (P less than or equal to 0.05). Additional significant (P les s than or equal to 0.05) relationships in hardwoods included: negative corr elations between foliar polyamines and N content to exchangeable K and P an d total P in the organic soil horizon; and positive correlations between fo liar polyamines and N content to Mg in soil solution. With few exceptions, low N + S treatment had effects similar to the ones observed with low N alo ne for both stands. The changes observed in the pine stand for polyamine me tabolism, N uptake, and element leaching from the soil into the soil soluti on in all treatment plots provide additional evidence that the pine stand i s more nitrogen saturated than the hardwood stand. These results also indic ate that the long-term addition of N to these stands has species specific a nd/or site specific effects that may in part be explained by the different land use histories of the two stands.