Physiological ecology of seed respiration in some tropical species

We examine the relationship of seed oxygen consumption rate (V̇_o2 ) to seed moisture content, seed mass, and seed age in 22 ecologically diverse tropical species. These seeds vary greatly in moisture content, age, mass, mechanism of dormancy and length of viability. We quantify each relationship with a power equation, V̇_o2 =aX^b , where X is the independent variable. Seed moisture content (MC) explains 80% of the variation in mass-specific V̇_O2 (ml O₂ g^-1 h^-1 ) among seeds of all species, whereas seed mass explains < 1%. However, when seeds are reclassified as moist (> 28% MC) or dry (≤ 28% MC), seed mass explains 54% of the variation in mass-specific V̇_o2 (ml O₂ g^-1 h^-1 ) within dry seeds, but no significant variation within moist seeds. In dry seeds, seed age explains only 27% of the variance in mass-specific V_o2 , although seed age and moisture content are negatively correlated. On a per seed basis, seed mass explains 54% of the variation in mass-specific V̇_o2 (ml O₂ h^-1 per seed) in dry seeds and 83 % of the variation in moist seeds: the exponents of the power function, 0.54 in dry seeds and 0.78 in moist seeds, are within the range reported for the allometric relationship of oxygen consumption and body size in animals and prokaryotes. We present a framework for future studies that recognizes seed respiration as an important, yet unstudied, component of tropical seed ecophysiology. We discuss the ecological significance of seed respiration in three groups of tropical species which differ in seed moisture content, mass, viability, and post-dispersal moisture regimes: (1) shade-intolerant pioneer species with small, dry, orthodox seeds; (2) seasonally dormant species; and (3) shade-tolerant primary forest species with large, moist recalcitrant seeds.