Marler Thomas E, Krishnapillai Murukesan V
College of Natural and Applied Sciences, University of Guam, Mangilao, Guam 96923, USA.
Cooperative Research and Extension, College of Micronesia-FSM, Yap Campus, Yap 96943, Federated States of Micronesia.
Plants (Basel). 2020 Feb 11;9(2):230. doi: 10.3390/plants9020230.
Stem respiration is influenced by the vertical location of tree stems, but the influence of vertical location on stem respiration in a representative cycad species has not been determined. We quantified the influence of vertical strata on stem carbon dioxide efflux () for six arborescent L. species to characterize this component of stem respiration and ecosystem carbon cycling. The influence of strata on was remarkably consistent among the species, with a stable baseline flux characterizing the full mid-strata of the pachycaulous stems and an increase in at the lowest and highest strata. The mid-strata flux ranged from 1.8 µmol·m·s for K.D. Hill to 3.5 µmol·m·s for Thunb. For all species, increased about 30% at the lowest stratum and about 80% at the highest stratum. A significant quadratic model adequately described the patterns for all six species. The increase of at the lowest stratum was consistent with the influence of root-respired carbon dioxide entering the stem via sap flow, then contributing to via radial conductance to the stem surface. The substantial increase in at the highest stratum is likely a result of the growth and maintenance respiration of the massive cycad primary thickening meristem that constructs the unique pachycaulous cycad stem.
茎呼吸受树木茎干垂直位置的影响，但垂直位置对一种代表性苏铁物种茎呼吸的影响尚未确定。我们对六种乔木状苏铁属物种的垂直分层对茎二氧化碳通量（）的影响进行了量化，以表征茎呼吸和生态系统碳循环的这一组成部分。各物种之间，分层对的影响非常一致，粗壮茎干的整个中间分层具有稳定的基线通量，最低和最高分层的增加。中间分层通量范围从K.D. Hill的1.8 μmol·m·s到Thunb.的3.5 μmol·m·s。对于所有物种，最低分层增加约30%，最高分层增加约80%。一个显著的二次模型充分描述了所有六个物种的模式。最低分层处的增加与通过液流进入茎干的根系呼吸二氧化碳的影响一致，然后通过径向传导至茎干表面对产生贡献。最高分层处的大幅增加可能是由于构建独特粗壮苏铁茎干的大量苏铁初生加厚分生组织的生长和维持呼吸所致。
