US Long-Term Ecological Research Network
Carbon Allocation and Accumulation in Conifers
Forests cover approximately 33\% of the land surface of the earth, yet they are responsible for 65\% of the annual carbon (C) accumulated by all terrestrial biomes (Schlesinger, 1991). In general, total C content and net primary production rates are greater for forests than for other biomes, but C budgets differ greatly among forests. Despite several decades of research on forest C budgets, there is still an incomplete understanding of the factors controlling C allocation. Yet, if we are to understand how changing global events such as land use, climate change, atmospheric N deposition, ozone, and elevated atmospheric C02 affect the global C budget, a mechanistic understanding of C assimilation, partitioning, and allocation is necessary. Numerous abiotic and biotic factors influence C allocation patterns, which in turn affect the capacity of plants to obtain resources from the atmosphere and soil. Although reviews on various components of conifer forest C budgets, such as photosynthesis (see Chapter 4, this volume) and detritus production (Vogt et al., 1986), are available, a synthesis of the influence of abiotic and biotic factors on leaf, canopy, and stand-level C budgets of conifer forests is lacking. The objective of this chapter is to review the major factors that influence C allocation and accumulation in conifer trees and forests. In keeping with the theme of this book, we will focus primarily on evergreen conifers. However, even among evergreen conifers, leaf, canopy, and stand-level C and nutrient allocation patterns differ, often as a function of leaf development and longevity (Gower and Richards, 1990; Gower et al., 1993a; Reich et al., 1994). The terminology related to C allocation literature is often inconsistent, confusing and inadequate for understanding and integrating past and current research. For example, terms often used synonymously to describe C flow or movement include translocation, transport, distribution, allocation, partitioning, apportionment, and biomass allocation. A common terminology is needed because different terms have different meanings to readers. In this paper we use C allocation, partitioning, and accumulation according to the definitions of Dickson and Isebrands (1993). Partitioning is the process of C flow into and among different chemical, storage, and transport pools. Allocation is the distribution of C to different plant parts within the plant (i.e., source to sink). Accumulation is the end product of the process of C allocation.
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Academic Press
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San Diego
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