Nutrient characteristics and proline accumulation in relation to Picea abies status on drained peat soils

Monocultures of Norway spruce widely used for afforestation of drained peat soils often have low productivity and decline in vitality. The research aim was to elucidate: (1) imbalances in the nutrient status of soil and plants in relation to Norway spruce crown status and annual increment on drained peat soil in the sub-boreal zone; (2) the suitability of using proline accumulation as a biomarker for Norway spruce vitality and stress in nutrient imbalance conditions. The study was conducted at five forest (Oxalidosa turf. mel.) sites in Latvia, each containing trees with different crown condition status. Chemical analyses of soil and spruce needles, assessment of tree crown vitality and annual increment measurements were done. Our results revealed serious disturbances in the supply of nutrients, which is an important factor in the decline of Norway spruce in monoculture stands on drained peat soils. Deficiency of K, Fe, Cu, B, N and P was found in the current year needles for all trees, but in damaged trees (≥61% defoliation, ≥61% discoloration) Zn deficiency was also found. For 2-year-old needles, deficiency of K, P, S, Zn, and Cu was found in all trees, additionally, deficiency of Fe was found in healthy and medium damaged trees (26–60% defoliation, 21–60% discoloration), and N deficiency was found for medium damaged and damaged trees. Thus, K, Cu, B, Fe concentrations had significant negative correlations with crown status parameters – defoliation, discoloration, and density. K and B deficiency could play the most significant causal role in decreased stem increment. The results revealed that the stress amino-acid proline is a reliable biomarker, having a significant relationship with spruce crown condition parameters, annual increment and nutrient status in needles – low levels of K, Fe, S, Cu, B, N. The increase in proline content in spruce needles was pronounced in moderately damaged trees, indicating the potential for the use of proline accumulation as early stress indicator for spruce. Therefore, further studies on the identification of early stress and factors affecting nutrient uptake and accumulation in needles are particularly valuable for evaluation of stand management options before significant decline of spruce stands.