Competition Between Grasses and Khaya ivorensis A. Chev. During Initial Growth: Physiological and Nutritional Aspects

This study aimed to evaluate the competitive effects of invasive grasses on the growth, physiology, and nutrient utilization of Khaya ivorensis . The treatments consisted of one K. ivorensis plant positioned at the center of each pot and one grass individual, in addition to a control treatment containing only one K. ivorensis seedling. The study compared the cultivation of K. ivorensis without competition and in coexistence with Urochloa decumbens , Megathyrsus maximus , Sorghum arundinaceum , Digitaria insularis , and Cynodon dactylon . Plants of K. ivorensis grown in association with U. decumbens , M. maximus , and S. arundinaceum showed lower increases in height and stem diameter. Evaluations included height and diameter increments, specific leaf area, shoot and root dry mass, chlorophyll a and b indices, photosynthetic rate, water use efficiency, transpiration, stomatal conductance, nutrient content, biological utilization coefficient (BUC), and nutrient absorption efficiency. The presence of the competitors M. maximus and S. arundinaceum reduced the leaf area of K. ivorensis . Plants grown in coexistence with U. decumbens , M. maximus , and S. arundinaceum also exhibited lower chlorophyll a and b indices, reduced photosynthetic rate, lower water use efficiency, and decreased relative content and concentration of macronutrients. Coexistence with grasses altered the BUC by weed species, notably increasing the nitrogen BUC under competition with M. maximus , while generally decreasing the macronutrient absorption efficiency of K. ivorensis. Invasive grasses negatively affect the growth, physiological performance, and macronutrient utilization of K. ivorensis , with Megathyrsus maximus being the most detrimental weed species to the growth and physiology of the tree species.