Yellowing leaves on a young lemon threaten that potential and signal deeper problems. Nitrogen is a nutrient used in almost every process of life for citrus and fruit trees, from growth to the production of fruit. While yellowing of the leaves is not always a problem, investigate the source of the yellowing if you suspect the leaves should not be yellowing at this time. Meyer lemon trees (Citrus x Meyeri) typically have waxy, dark-green leaves all year round. A lack of nitrogen in the soil will affect the tree's health, beginning with the leaves. However, there are some problems in citrus tress, specifically citrus leaves curling, yellow leaves and brown spots on the leaves. When it exhibits yellow leaves, too much water or a mineral deficiency may be the culprit. Lemon trees (Citrus limonia) are thorny evergreen citrus trees with narrowly ovate light green leaves and purplish-tinted white flowers. Curled leaves disease on lemon plants like limes, lemon and orange trees are a matter of concern as it may indicate significant problems. Several related difficulties cause young lemon leaves to turn yellow in between their dark green veins. Nitrogen deficiency is one of the main causes of yellow leaves on a citrus tree.