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Tree-rings of在祁连山东部西营河流域不同海拔采集年轮样品,利用树木年代学方法建立高海拔(3000 m)、中海拔(2750 m)、低海拔(2500 m)青海云杉标准化年表,将年轮宽度指数与不同时段气温和降水分别进行相关分析,研究祁连山东部不同海拔青海云杉径向生长对气候变暖的响应。结果表明: 水热是祁连山东部青海云杉径向生长的主要限制因子,不同海拔树木的生长限制因子基本一致。在显著升温之前(1961—1986年),低、中、高海拔3个样点的青海云杉径向生长均与上一年7—8月和当年8月平均最高温呈显著负相关,与当年6月相对湿度呈显著正相关。显著升温之后(1986—2014年),高、中、低海拔树木生长与气温仍呈显著负相关,而与当年2月的相对湿度由升温前的不显著负相关转为显著正相关,与6月降水和相对湿度由升温前的显著正相关转为不显著的负相关。升温导致祁连山东部各海拔青海云杉树轮生长变慢,其中高海拔所受影响最大。气候变暖导致的干旱胁迫可能是青海云杉径向生长发生变化的主要原因。.

The radial growth of eight individuals of利用树木径向生长监测仪(Dendrometer)和自动气象站在祁连山西部对8棵青海云杉的径向生长及环境因子进行了连续监测研究。结果表明: Gompertz函数拟合结果显示,2018—2020年青海云杉的径向生长分别开始于4月19日、4月17日和4月10日,在日平均气温超过5.5 ℃时径向生长开始;青海云杉生长结束时间分别为8月17日、8月21日和7月19日,生长结束时间与生长季末期降水量有关。研究区青海云杉径向生长量受干旱抑制强烈,其中与7月的日均温(负相关)和日降水量(正相关)相关性最高,与生长季初期(5月)的日降水量的相关关系存在年际间差异。.

Tree growth is the main way of carbon sequestration in forest ecosystems, which is influenced by climatic and non-climatic factors. The long-term location monitoring of cambial phenology and wood formation dynamics (xylogenesis) is an important method to clarify the responses of radial growth to climate change. Here, we reviewed studies on cambial phenology and xylogenesis by microcoring method. Firstly, we reviewed the effects of climatic factors on cambial phenology. The onset and cessation of xylogenesis were determined by temperature in cold and humid conditions. Temperature and water availability collectively modulated the onset of xylogenesis under dry conditions, and the later determined the end of xylogenesis. The radial increment was regulated by rate and duration of cell production, with the maximum of growth rate occurring around the summer solstice. Short-term N addition did not affect wood formation dynamics. Secondly, we reviewed the roles of biological factors in regulating xylogenesis. The onset of xylogenesis differred among species, ages, and inter-specific competition. Seasonal dynamics of non-structural carbohydrates were coupled with wood formation. Finally, we reviewed the response mechanisms of xylogenesis to the interaction of climatic and biological factors. In conclusion, we put forward problems in current studies and prospected future development to provide reference for further scientific research.树木生长是森林生态系统固碳的主要方式,树木生长过程受到气候与非气候因素的共同作用。树木径向生长长期定位监测是明确树木生长对气候变化响应的重要研究手段。本文对运用微树芯法的树木形成层活动及径向生长过程研究进行了总结。首先,综述了气候因素对树木形成层活动的影响: 寒冷湿润区温度决定树木生长开始和停止,干旱半干旱区水分和温度共同决定生长开始,水分决定生长停止;生长速率和持续时间共同决定生长量,最大生长速率出现在夏至前后;短期施氮并不能影响树木径向生长动态。其次,探讨了生物因素对树木径向生长过程的调控: 形成层活动开始时间因树种、树龄、竞争关系而有所差异;非结构性碳水化合物的季节动态与径向生长过程相耦合。最后,阐述了气候因素和生物因素交互作用下树木次生生长的响应机制。针对以上进展,本文提出了目前研究尚存在的问题并展望了未来的发展前景,以期为进一步的科学研究提供参考。.

Different stomatal behaviors among species under drought conditions may affect species-specific seasonal variations in photosynthesis and water use efficiency (WUE), and could enable species to follow differing growth strategies. Here we monitored leaf gas exchange, intra-annual radial growth, leaf stoichiometry, and microclimate of three conifers with contrasting stomatal behaviors (isohydric Picea wilsonii and Pinus tabuliformis vs. anisohydric Juniperus przewalskii) over three growing seasons, and collected tree-ring records of the monitored species, on the cold and arid northeastern Tibet Plateau. We used these data to assess the species-specific seasonal variations in net photosynthetic rate (An), transpiration efficiency (TE) and intrinsic water use efficiency (WUEi), and their impacts on growth. Our observations show that the An of all three conifers was greatest in autumn. This peak was closely related to increasing stomatal conductance following alleviation of drought stress, rather than to variations in leaf nitrogen concentrations. WUEi of the three conifers did not exhibit a regular seasonal pattern, but TE was significantly lower in summer than in spring and autumn, due to the regulation by vapor pressure deficit (VPD). Increasing summer VPD reduced TE mainly by increasing transpiration rate for J. przewalskii and by decreasing An for the isohydric conifers. The increases of An from summer to autumn were much greater for the two isohydric Pinaceae plants than for J. przewalskii. This was consistent with the growth-climate relationships, in which the autumn drought in the previous year limited radial growth of the isohydric conifers more strongly than in the anisohydric conifer. Therefore, we suggest that the growth of isohydric species may profit more from the photosynthates accumulated during the previous post-growing season in the cold and arid Tibetan Plateau.

Studies of xylogenesis can provide mechanistic understandings of the influence of climate on wood production and carbon sequestration at the cellular level. It is not yet clear how trees will respond to increasing temperature and precipitation variability and other extreme meteorological events that are expected to occur as climate continues to change. Here, we analyzed cambial phenology and xylogenesis of Juniperus przewalskii Kom. weekly (2011–2014) or biweekly (2015–2016) over six years on the northeastern Tibetan Plateau. We found that temperature plays a decisive role in the onset of xylogenesis and a daily mean temperature of 6.1 °C appears to be the threshold that determines growth onset. Additionally, we observed the end of xylogenesis is related to summer drought conditions. During the course of our observations, the onset of xylogenesis advanced nearly twice as much as the end of xylogenesis (3.1 vs 1.8 days decade−1, respectively), indicating a slight lengthening of the growing season. However, an increase in the duration of the growing season did not necessarily result in a greater level of wood production. In fact, we found that water availability affects the growth rate and early summer precipitation appears to be a key factor of wood production over the northeastern Tibetan Plateau. Our study provides new evidence of the malleable nature of tree growth and reveals potential mechanisms of how tree growth adjusts to climatic variations in cold and arid region.