Terrestrial plant productivity and carbon allocation in a changing climate

Carbon dioxide from the atmosphere is assimilated into organic compounds via photosynthesis and subsequently allocated to different processes or pools within the plant. The contribution of plant material to the long-term storage of carbon in terrestrial ecosystems has important implications for our future climate. Plant production and allocation are expected to change in response to four prominent global change factors: elevated [CO₂], warming, precipitation change, and nitrogen deposition. Our main focus in this chapter is on the responses and feedbacks among anthropogenic climate change and plant production and allocation in terrestrial ecosystems that span the globe. Many types of experimental manipulations have been used to examine plant responses to single and interacting environmental factors across a number of biomes. While plant growth often increased in response to elevated [CO₂], warming, increased precipitation, and nitrogen deposition, limitation by nutrients (in the case of elevated [CO₂]) or interaction among factors (e.g., between warming and drought) can preclude or limit increases in plant growth. Also, allocation often changes in response to changing environmental conditions (e.g., increased root production under elevated [CO₂]), with implications for long-term ecosystem carbon storage. Furthermore, plant responses to atmospheric and climatic change occur against a complex background of biotic interactions, including changing plant community composition, competition, and interactions with insect herbivores. Unfortunately, dynamic plant community composition and other complex interactions are not well represented in large-scale land surface models projecting future climatic conditions. Large-scale and long-term experiments, in combination with technological improvements and model development, are needed to quantify plant production and allocation in response to single and interacting environmental factors in ecosystems that are critical to the global carbon budget and climate system.