Department of Agriculture, Food, Environmental and Animal Sciences, Plant Biology Unit, University of Udine, via delle Scienze 91, 33100, Udine, Italy.
Am J Bot. 2020 Apr;107(4):639-649. doi: 10.1002/ajb2.1458. Epub 2020 Apr 1.
Despite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant-plant interaction, and elevation.
We studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs.
Glucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue.
We found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands.
尽管人们高度关注高山树种的生长与碳平衡之间的关系，但对林线处灌木的了解甚少。我们假设，主要非结构性碳水化合物（NSC）在各海拔高度的分布模式取决于表型特征可塑性、植物-植物相互作用和海拔之间的相互作用。
我们研究了高山越橘（林线以上）在海拔梯度上的 NSC（即葡萄糖、果糖、蔗糖和淀粉）分布模式。在相同的样地中，我们测量了关键的生长特征（即解剖学茎特征）和灌木覆盖率，并评估了它们与 NSC 之间的潜在关系。
葡萄糖含量与海拔呈正相关，但与灌木覆盖率呈负相关。蔗糖在高海拔和老年种群中减少，而在血管组织比例较高的情况下增加。淀粉含量在中高海拔和高灌木覆盖率的样地中增加。此外，淀粉含量与木质部环数和韧皮部组织比例呈负相关，而与木质部组织比例呈正相关。
我们发现，碳储量的增加与植物生长脱钩，支持了生长限制假说，该假说认为，由于低温，高海拔处的 NSC 会积累。此外，植物特征的表型可塑性缓冲了 NSC 含量对海拔引起的环境胁迫的响应，这表明，在气候变暖的条件下，由于植物生长增强，老而稀疏的林分中灌木的扩张将更为明显。
