兴安落叶松对环境变化的物候驯化和光合能力适应

Acclimation of leaf phenology and adaptation of photosynthetic capacity of Larix gmelinii to environmental changes

兴安落叶松(Larix gmelinii Rupr.)作为欧亚北方森林的优势树种,在全球变化和区域碳平衡研究中具有重要作用,但其物候和光合能力在环境变化下的响应是一种表型驯化还是基因调控下的适应还不清楚。于2009—2011年生长季内在帽儿山森林生态系统研究站(45°24'N,127°40'E)测定了6个来自不同气候条件(纬度:48—52°N,年均温:-2.3—2.6℃)下的兴安落叶松种源在同质园内的32年生树木的叶片物候(4—10月)和光合能力季节动态(5—9月)。结果表明:6个种源的树木叶片的展叶和落叶起始日期均无显著差异,均在4月下旬展叶、在9月下旬开始落叶,2009年、2010年和2011年的生长季天数分别波动在150—153 d、145—147 d和148—151 d之间。6个种源树木叶片展叶起始日期和春季展叶前>0℃积温均显著负相关,而落叶起始日期和秋季均温均显著正相关(P<0.05)。这表现出物候对环境变化的表型驯化效应。最大净光合速率(Pmax)的季节动态具有明显的种源差异。来自于较高纬度的塔河、根河、中央站种源的Pmax仅在生长季初期(5—6月)明显低于其各自的年均值,而在其他生长阶段则在年均值以上;来自较低纬度的鹤北和乌伊岭种源的Pmax仅在生长盛期(8月)明显高于其各自年均值,而在其他阶段则处于年均值以下。6个种源树木Pmax和生长季均温均显著正相关(P<0.01),且来自较高纬度的中央站、根河、三站种源树木Pmax随温度升高的增幅程度明显高于其他种源树木。在每个生长阶段Pmax均存在显著的种源差异(P<0.05),并且差异趋势随生长季进程而有所不同:中央站种源在每个生长阶段都具有最高的Pmax,而根河、塔河、乌伊岭分别在生长季初期(5—6月)、中期(7月)和盛期(8月)、后期(9月)具有最小Pmax。这些光合能力的差异是基因调控下的树木对种源原地气候条件长期适应的结果。兴安落叶松的物候可塑性和光合能力遗传适应性对其能够在广阔多样的生境中生存和繁衍具有重要意义。

Dahurian larch （Larix gmelinii Rupr.）, the dominant tree species in Eurasian boreal forests, is important for studies on global change and regional carbon balance. However, few studies have focused on changes in the seasonal dynamics of its leaf phenology and photosynthetic capacity in response to environmental changes. It is unclear whether these responses are driven by genetic adaptation or by phenotypic acclimation. We examined the seasonal dynamics of leaf phenology （April to October） and photosynthetic capacity （May to September） of 32-year-old Dahurian larch trees for three years （2009-2011）. The larch trees were from six provenances and were growing at the Maoershan Forest Ecosystem Research Station （45°24＇N, 127°40＇E）. The six provenances originated from areas spanning approximately 4° in latitude （48-52°N） and an approximately 5 ℃ gradient of mean annual temperature （-2.3-2.6 ℃）, arranged from north to south as follows： Tahe （TH）, Genhe （GH）, Sanzhan （SZ）, Zhongyangzhan （ZYZ）, Wuyiling （WYL）, and Hebei （HB）. To access the top canopy of the sampled trees, we constructed 15-m-high wooden scaffolds at the site. We selected three representative trees from each provenance for analyses. We examined 5-10 representative branches per tree twice a week from early April to mid-May to evaluate bud development and leaf unfolding, and from early September to mid-October to evaluate leaf shedding. To measure gas exchange for phenology observations, we analyzed three fully expanded sunlit fascicles on young short shoots at the top of the canopy of each tree in situ. There were no significant differences in leaf unfolding and shedding dates among the provenances. For trees from all provenances, leaf unfolding began in late April and leaf shedding began in late September, resulting in a mean growing season length of 150-153 days, 145-147 days, and 148-151 days in 2009, 2010, and 2011, respectively. The starting date of leaf unfolding was significantly and negatively correlated with the accumulated temperature above 0 SymbolpB@C before leaf unfolding in spring （from 1 March to 4 May）. The starting date of leaf shedding was significantly and positively correlated with the mean temperature in the fall （from 1 August to 30 September） （P 〈 0.05）. These results suggested that there is phenotypic acclimation of leaf phenology to environmental changes. The seasonal dynamics of the light-saturated net photosynthetic rate （Pmax） differed among the provenances. Compared with the annual mean Pmax value, the Pmax values of trees from the higher-latitude provenances （i.e., TH, GH, and ZYZ） were lower in the early growing season and higher in the other growing seasons. In contrast, the Pmax values of trees from the lower-latitude provenances （i.e., HB and WYL） were higher than the annual mean value only in the middle of the growing season. Across the whole growing season, the Pmax values for all six provenances were positively correlated with the mean seasonal temperature （P 〈 0.01）. In terms of Pmax values, trees from the higher-latitude provenances were more temperature-sensitive than were trees from the lower-latitude provenances, except for those from the TH provenance. In any given growing season, Pmax differed significantly among the six provenances （P 〈 0.05）. Among all the provenances, the trees from the ZYZ provenance had the highest Pmax across the whole growing season. The lowest Pmax values in the early, mid, and late growing season were in trees from the GH, TH, and WYL provenances, respectively. These variations in the seasonal dynamics of Pmax among the six provenances provide evidence for the genetic adaptation of larch trees to the climatic conditions in their region of origin. These findings suggest that the phenological plasticity and photosynthetic adaptability of L. gmelinii play crucial roles in its survival and reproduction in extensive and diverse habitats