Grassland biomass allocation across continents and grazing practices and its response to climate and altitude

Biomass allocation in grasslands is key to understanding plant response to environmental changes and grazing management. Yet, global studies on how this split between above-ground and below-ground biomass varies across continents and grazing practices are notably scarce. We employ a comprehensive field-oriented grassland database to examine differences in total net primary productivity (TNPP), above-ground net primary productivity (ANPP), below-ground net primary productivity (BNPP), and the BNPP to ANPP ratio across continents and between grazed and non-grazed grasslands. Oceania showed the greatest ANPP (916 g·m⁻²·a⁻¹), while Asia had the lowest (192 g·m⁻²·a⁻¹). BNPP values were similar among Oceania, Africa, and Asia (∼600 g·m⁻²·a⁻¹), significantly exceeding those in Europe (289 g·m⁻²·a⁻¹) and North America (408 g·m⁻²·a⁻¹). South America, Africa, and Oceania had the highest TNPP (around 1418 g·m⁻²·a⁻¹ to 1466 g·m⁻²·a⁻¹), while Europe had the lowest TNPP (344 g·m⁻²·a⁻¹). The BNPP to ANPP ratio was highest in South America (4.17) and Asia (3.46). Global differences in TNPP and BNPP between grazed and non-grazed grasslands were minimal, but ANPP (169 g·m⁻²·a⁻¹ and 198 g·m⁻²·a⁻¹, respectively) and the BNPP to ANPP ratio (4.87 and 2.40, respectively) differed significantly. Across continents and grazing practices, climate had a greater role in regulating grassland biomass allocation than altitude, and warming may have a more detrimental impact on grazed grasslands than non-grazed grasslands. Distinct biomass allocation trends under various continental and grazing conditions exert effects on the economic and ecological functions of grasslands. Our study underscores the need for balanced grassland utilization strategies at a global scale. This involves optimizing grazing in high ANPP grasslands and protecting those with significant BNPP, thereby contributing to a sustainable and ecologically sound use of grasslands in the future.