Spenders versus savers: climate-induced carbon allocation tradeoffs in a recently introduced woody plant

Non-structural carbohydrate(NSC) storage may be under strong selection in woody plant species that occur across strong environmental gradients. We therefore investigated carbon allocation strategies in a widely distributed, introduced woody plant. We predicted genotypes from cold climates with exposure to episodic freeze events, would have elevated NSC concentrations with the tradeoff of reduced growth and reproduction relative to warm-adapted genotypes. We established an experimental common garden using genotypes of Tamarix spp., sourced across a large thermal gradient within their introduced range. We measured seasonal NSC storage in coarse roots and stems, above-ground growth and flower production. Autumn NSC concentrations were 50% higher in genotypes from sites with spring freeze events compared to genotypes from warmer sites. Cold-adapted genotypes also had a 2.3-fold higher starch to soluble sugar ratio than warm-adapted genotypes. Across all genotypes and seasons, NSC storage was inversely correlated with growth and reproduction. Results suggest that Tamarix from colder locations cope with freeze events by maintaining large storage pools to support tissue regrowth, but with the tradeoff of reduced growth and reproduction. Our results provide evidence of rapid selection in carbon allocation strategies in response to climate in introduced woody species.非结构性碳水化合物（Non-structural carbohydrate, NSC）的储存，在跨越强烈环境梯度分布的木本植物类群中可能处于强选择压力之下。为此，我们针对一种广泛分布的引入型木本植物开展了碳分配策略的研究。我们预测：相较于适应温暖环境的基因型，来自寒冷气候、经历间歇性冻害事件的基因型，其非结构性碳水化合物浓度会升高，但会以生长和繁殖能力下降作为权衡代价。我们利用柽柳属（Tamarix spp.）的多个基因型构建了同质园（common garden）实验，这些基因型采自其引入范围内的大范围温度梯度区域。我们测定了粗根与茎秆中的季节性非结构性碳水化合物储存量、地上生长量以及开花量。与来自温暖区域的基因型相比，经历春季冻害事件的采样位点对应的基因型，其秋季非结构性碳水化合物浓度高出50%。适应寒冷环境的基因型，其淀粉与可溶性糖的比值也较适应温暖环境的基因型高2.3倍。在所有基因型与季节中，非结构性碳水化合物储存量与生长、繁殖均呈负相关关系。结果表明，来自寒冷区域的柽柳属植物通过维持大量储存池以支持组织再生来应对冻害事件，但代价是生长与繁殖能力受到抑制。本研究为引入型木本植物的碳分配策略响应气候而发生快速选择提供了实证支持。