Key message

Differences in temporal dynamics of radial growth and use of stem water reserves in co-occurring saplings and mature conifers are caused by soil water availability and canopy structure.

Abstract

High-resolution time series of stem radius variations (SRVs) record fluctuations in tree water status and temporal dynamics of radial growth. The focus of this study was to evaluate the influence of tree size (i.e., saplings vs. mature trees) and soil water availability on SRVs. Dendrometers were installed on Pinus sylvestris at an open xeric site and on Picea abies at a dry-mesic site, and the SRVs of co-occurring saplings and mature trees were analyzed during two consecutive years. The results revealed that irrespective of tree size, radial growth in P. sylvestris occurred in April–May, whereas the main growing period of P. abies was April–June (saplings) and May–June (mature trees). Linear relationships between growth-detrended SRVs (SSRVs) of mature trees vs. saplings and climate-SSRV relationships revealed greater use of water reserves by mature P. abies compared with saplings. This suggests that the strikingly depressed growth of saplings compared with mature P. abies was caused by source limitation, i.e., restricted photosynthesis beneath the dense canopy. In contrast, a tree size effect on the annual increment, SSRV, and climate–SSRV relationships was less obvious in P. sylvestris, indicating comparable water status in mature trees and saplings under an open canopy. The results of this study provided evidence that water availability and a canopy atmosphere can explain differences in temporal dynamics of radial growth and use of stem water reserves among mature trees and saplings.

中文翻译：

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土壤水分的可用性和蒸发需求会影响季节性生长动态以及干旱条件下共生树苗和成熟针叶树对储存水的使用。

关键信息

同生树苗和成熟针叶树径向生长和茎水储备利用的时间动态差异是由土壤水分可用性和冠层结构引起的。

抽象的

高分辨率时间序列的茎半径变化 (SRV) 记录了树木水分状况的波动和径向生长的时间动态。本研究的重点是评估树木大小（即树苗与成熟树木）和土壤水分对 SRV 的影响。在开放旱地地点的樟子松和干燥的旱地地点的云杉上安装了树木测量仪，并连续两年分析了共生树苗和成熟树的 SRV。结果表明，无论树木大小，樟子松的径向生长发生在4-5月，而冷杉的主要生长期是 4 月至 6 月（树苗）和 5 月至 6 月（成熟的树木）。成熟树木与树苗的生长抑制 SRV (SSRV) 与气候-SSRV 关系之间的线性关系表明，与树苗相比，成熟的冷杉对水储备的利用更多。这表明，与成熟的冷杉相比，幼树的生长显着降低是由来源限制引起的，即在茂密的树冠下光合作用受到限制。相比之下，在P. sylvestris中，树木大小对年增量、SSRV 和气候-SSRV 关系的影响不太明显，表明开放树冠下成熟树木和树苗的水状况相当。这项研究的结果提供了证据，表明水的可用性和树冠大气可以解释成熟树木和树苗之间径向生长和茎水储备利用的时间动态差异。