Declining growth and changes in biomass allocation with warming in rainforest trees from temperate to tropical climates

Australian rainforests occur from temperate to tropical latitudes, but how climate warming will affect tree growth along this climate gradient remains poorly understood. We examined how changes in biomass allocation, leaf area, and photosynthetic capacity were linked to the capacity to maintain growth rates with +3.5, +7 and +10.5 °C warming in seedlings of 12 tropical, subtropical, and temperate rainforest tree species. Temperate species maintained or increased final biomass (+14%), leaf area, and leaf area ratio (the ratio of leaf area to plant dry mass) with warming, along with similar or increased leaf mass fraction (+14%). Subtropical species increased biomass with +3.5 °C (+28%) and +7 °C (+17%) warming but were negatively impacted with >10 °C warming (−31%). Tropical species reduced leaf area, leaf area ratio, photosynthetic capacity, and leaf nitrogen, along with 14% increased root allocation in response to warming, resulting in large biomass reductions with +3.5 °C (−20%) and +7 °C (−53%). Tropical species were more susceptible to climate warming with reduced photosynthetic capacity and reduced biomass, which can lead to a reduced carbon sink in the future, especially in late-successional tree species, which are the most abundant with a large role in carbon assimilation of tropical rainforests.