Hultine Kevin R, Williams David G, Dettman David L, Butterfield Bradley J, Puente-Martinez Raul
Department of Research, Conservation and Collections, Desert Botanical Garden, Phoenix, AZ, USA.
Department of Botany, University of Wyoming, Laramie, WY, USA.
Oecologia. 2016 Nov;182(3):679-90. doi: 10.1007/s00442-016-3690-6. Epub 2016 Jul 6.
Volume-to-surface area ratio (V:S) across stem succulent taxa varies by almost two orders of magnitude. The broad range in V:S of cacti and other succulent species likely has considerable importance for adaptation since stem volume determines the storage capacity of water, carbon and nutrients and stem surface area is directly related to whole-stem photosynthetic capacity. We examined the intrinsic physiological tradeoffs across diverse stem morphologies in three divergent evolutionary groups where stem succulence is common: Cactoideae, Opuntioideae (Cactaceae) and Euphorbiaceae. We predicted that variation in physiological response to environmental conditions would be (1) constrained by stem V:S, and (2) detectable in the stable isotope ratios of plant tissues. Stable isotope ratios were measured in the spines/prickles of 62 stem-succulent species occurring in a common garden setting in Phoenix, AZ, USA. Biomass δ(13)C, δ(2)H and δ(18)O increased with V:S in Cactoideae only, possibly reflecting various levels of Crassulacean acid metabolism (CAM) strength in the other lineages. Within Cactoideae-group with the highest CAM strength and largest range in V:S-δ(13)C and δ(18)O increased 2.2 and 11.5 ‰, respectively, with a 22-fold increase in V:S. Both δ(13)C and V:S decreased with species climate-niche estimates of precipitation, indicating that stem morphology and physiology in Cactoideae may be constrained by available moisture. Taken together, these data suggest that physiological tradeoffs associated with stem V:S are detectable across broad evolutionary groups despite differences in CAM strength.
茎肉质类群的体积与表面积比（V:S）相差近两个数量级。仙人掌和其他肉质物种的V:S范围很广，这可能对适应具有相当重要的意义，因为茎的体积决定了水、碳和养分的储存能力，而茎的表面积与全茎光合能力直接相关。我们研究了三个不同进化类群中不同茎形态之间的内在生理权衡，这些类群中茎肉质化很常见：仙人掌亚科、仙人掌科仙人球亚科和大戟科。我们预测，对环境条件的生理反应变化将：（1）受茎V:S的限制，（2）在植物组织的稳定同位素比率中可检测到。在美国亚利桑那州凤凰城一个共同花园环境中生长的62种茎肉质物种的刺中测量了稳定同位素比率。仅在仙人掌亚科中，生物量δ(13)C、δ(2)H和δ(18)O随V:S增加，这可能反映了其他谱系中不同水平的景天酸代谢（CAM）强度。在CAM强度最高且V:S范围最大的仙人掌亚科组中，δ(13)C和δ(18)O分别随V:S增加2.2‰和11.5‰，V:S增加了22倍。δ(13)C和V:S均随物种气候生态位的降水量估计值降低，这表明仙人掌亚科的茎形态和生理可能受可用水分的限制。综上所述，这些数据表明，尽管CAM强度存在差异，但与茎V:S相关的生理权衡在广泛的进化类群中是可检测到的。
