Primary and secondary stem growth in arctic shrubs: implications for community response to environmental change
Primary and secondary stem growth in arctic shrubs: implications for community response to environmental change
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DOI：
10.1046/j.1365-2745.2001.00657.x
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发表时间：
2002-04-01
影响因子：
5.5
通讯作者：
Chapin, FS
中科院分区：
文献类型：
--
作者：
Bret-Harte, MS;Shaver, GR;Chapin, FS
1灌木是对环境变化最敏感的苔原植物之一。我们测量了初级和次级茎生长的三个共显性灌木（矮桦，柳pulchra，杜香palustre ssp。在阿拉斯加州的图里克湖，暴露于温室和N + P肥料的长期田间处理。2在对照条件下，柳的分株具有最大的主茎生长，因为它们相对较高的分枝率。然而，在施肥下，桦产生了比其他物种更多的主茎生长，因为在对照分株中会生长为短枝的腋芽被刺激而产生长枝（结构枝）。对桦属和Ledum属来说，在分配给每一茎段的长度和某一年产生的茎段数量之间似乎存在着一种权衡。我们推导出了灌木次生生长的表达式，该表达式基于茎质量和长度随年龄的分布，并考虑到实验诱导的次生生长速率的变化。4所有三个物种的分株茎质量测量值和计算值之间具有良好的一致性，验证了我们对次生生长的数学分析。与观察到的积累其干质量在生态系统级样方收获一致。白桦的次生生长是施肥地块生态系统净初级生产力的主要组成部分，可能对生态系统碳储量有重大贡献。6次生生长的增加使白桦在施肥下成为主导，而Leduna的老茎无法以这种方式做出反应，使其无法生长到树冠中。
1 Shrubs are among the tundra plants most responsive to environmental change. We measured primary and secondary stem growth in a retrospective analysis of ramets of three codominant shrubs (Betula nana, Salix pulchra, and Ledum palustre ssp. decumbens) exposed to long-term field treatment with greenhouses and N + P fertilizers at Toolik Lake, Alaska.2 Ramets of Salix had the greatest primary stem growth under control conditions, because of their relatively high branching rate. Under fertilization, however, Betula produced much more primary stem growth than the other species, because axillary buds that would have grown as short shoots in control ramets were instead stimulated to produce long shoots (structural branches). There appeared to be a trade-off between allocation to length per stem segment and number of stem segments produced in a given year, for both Betula and Ledum.3 Although secondary growth in stems is the largest component of above-ground net primary production in forests, it is often ignored in shrub-dominated ecosystems. We derived an expression for secondary growth in shrubs based on distributions of stem mass and length with age, and allowing for experimentally induced changes in secondary growth rate.4 There was good agreement between measured ramet stem mass and calculated values for all three species, validating our mathematical analysis of secondary growth.5 Fertilization greatly increased the relative rate of secondary growth only in Betula, consistent with observed accumulations of its stem mass in ecosystem-level quadrat harvests. Secondary growth of Betula was a major component of ecosystem NPP in fertilized plots and probably contributes significantly to ecosystem carbon storage.6 The increase in its secondary growth enabled Betula to become dominant under fertilization, whereas the inability of older stems of Leduna to respond in this way prevented it from growing into the canopy.