Belowground Carbon Allocation in Forest Ecosystems: Global Trends

Abstract

Carbon allocation to roots in forest ecosystems is estimated from published data on soil respiration and litterfall. On a global scale, rates of in situ soil respiration and aboveground litter production are highly and positively correlated, suggesting that above— and belowground production are controlled by the same factors. This relationship also allows us to predict rates of total soil respiration and total carbon allocation to roots in forest ecosystems from litterfall measurements. Over a gradient of litterfall carbon ranging from 70 to 500 g°m^—2°yr^—1, total belowground carbon allocation increases from 260 to 1100 g°m^—2°yr^—1. The ratio of belowground carbon allocation to litterfall decreases from 3.8 to 2.5 as litterfall carbon increases from 70 to 200 g°m^—2°yr^—1, but changes little (2.5 to 2.2) as litterfall carbon increases from 200 to 500 g°m^—2°yr^—1. Use of this relationship permits the construction of simple carbon budgets that can be used to place upper limits on estimates of fine root production in forest ecosystems. Determining live—root respiration rates in forest ecosystems will further constrain the range of possible root production rates.