Department of Renewable Resources, University of Wyoming, Laramie, WY 82071, USA.
Oecologia. 2010 Oct;164(2):297-310. doi: 10.1007/s00442-010-1643-z. Epub 2010 May 9.
The C isotope composition of leaf dark-respired CO(2) (δ(13)C(l)) integrates short-term metabolic responses to environmental change and is potentially recorded in the isotopic signature of ecosystem-level respiration. Species differences in photosynthetic pathway, resource acquisition and allocation patterns, and associated isotopic fractionations at metabolic branch points can influence δ(13)C(l), and differences are likely to be modified by seasonal variation in drought intensity. We measured δ(13)C(l) in two deep-rooted C(3) trees (Prosopis velutina and Celtis reticulata), and two relatively shallow-rooted perennial herbs (a C(3) dicot Viguiera dentata and a C(4) grass Sporobolus wrightii) in a floodplain savanna ecosystem in southeastern Arizona, USA during the dry pre-monsoon and wet monsoon seasons. δ(13)C(l) decreased during the nighttime and reached minimum values at pre-dawn in all species. The magnitude of nocturnal shift in δ(13)C(l) differed among species and between pre-monsoon and monsoon seasons. During the pre-monsoon season, the magnitude of the nocturnal shift in δ(13)C(l) in the deep-rooted C(3) trees P. velutina (2.8 ± 0.4‰) and C. reticulata (2.9 ± 0.2‰) was greater than in the C(3) herb V. dentata (1.8 ± 0.4‰) and C(4) grass S. wrightii (2.2 ± 0.4‰). The nocturnal shift in δ(13)C(l) in V. dentata and S. wrightii increased to 3.2 ± 0.1‰ and 4.6 ± 0.6‰, respectively, during the monsoon season, but in C(3) trees did not change significantly from pre-monsoon values. Cumulative daytime net CO(2) uptake was positively correlated with the magnitude of the nocturnal decline in δ(13)C(l) across all species, suggesting that nocturnal δ(13)C(l) may be controlled by (13)C/(12)C fractionations associated with C substrate availability and C metabolite partitioning. Nocturnal patterns of δ(13)C(l) in dominant plant species in the semiarid savanna apparently have predictable responses to seasonal changes in water availability, which is important for interpreting and modeling the C isotope signature of ecosystem-respired CO(2).
叶片暗呼吸 CO2 的 C 同位素组成（δ(13)C(l)）综合了短期代谢对环境变化的响应，并且可能记录在生态系统水平呼吸的同位素特征中。光合作用途径、资源获取和分配模式的种间差异，以及代谢分支点处相关的同位素分馏作用，都会影响 δ(13)C(l)，而且这些差异可能会随着干旱强度的季节性变化而改变。我们在美国亚利桑那州东南部的洪泛区草原生态系统中，对两种深根系 C(3)树（银叶相思和朴树）和两种相对浅根系多年生草本植物（C(3)双子叶植物 Viguiera dentata 和 C(4)草 Sporobolus wrightii）进行了 δ(13)C(l)的测量，分别在旱前季风季和湿季风季进行。在所有物种中，δ(13)C(l)在夜间下降，并在黎明前达到最小值。物种之间以及旱前季风季和季风季之间的 δ(13)C(l)夜间变化幅度不同。在旱前季风季，深根系 C(3)树 P. velutina（2.8±0.4‰）和 C. reticulata（2.9±0.2‰）的 δ(13)C(l)夜间变化幅度大于 C(3)草本植物 V. dentata（1.8±0.4‰）和 C(4)草 S. wrightii（2.2±0.4‰）。V. dentata 和 S. wrightii 的 δ(13)C(l)夜间变化幅度在季风季增加到 3.2±0.1‰和 4.6±0.6‰，而 C(3)树则与旱前季风季的值相比没有显著变化。全天净 CO2 吸收量与所有物种 δ(13)C(l)夜间下降幅度呈正相关，表明夜间 δ(13)C(l)可能受到与 C 底物可用性和 C 代谢物分配相关的 (13)C/(12)C 分馏的控制。半干旱草原中主要植物物种的夜间 δ(13)C(l)模式显然对水分可利用性的季节性变化有可预测的响应，这对于解释和模拟生态系统呼吸 CO2 的 C 同位素特征很重要。
