Liu Xiaohong, Wang Wenzhi, Xu Guobao, Zeng Xiaomin, Wu Guoju, Zhang Xuanwen, Qin Dahe
State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, No. 320 Donggang West Road, Lanzhou 730000, China
State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, No. 320 Donggang West Road, Lanzhou 730000, China University of the Chinese Academy of Sciences, Beijing 100049, China.
Tree Physiol. 2014 Sep;34(9):966-80. doi: 10.1093/treephys/tpu067. Epub 2014 Aug 21.
The rising atmospheric CO2 concentration (Ca) has increased tree growth and intrinsic water-use efficiency (iWUE). However, the magnitude of this effect on long-term iWUE and whether this increase could stimulate the growth of riparian forests in extremely arid regions remain poorly understood. We investigated the relationship between growth [ring width; basal area increment (BAI)] and iWUE in a riparian Populus euphratica Oliv. forest to test whether growth was enhanced by increasing CO2 and whether this compensated for environmental stresses in the lower reaches of the inland Heihe River, northwestern China. We accomplished this using dendrochronological methods and carbon (δ(13)C) and oxygen (δ(18)O) isotopic analysis. We found an increase in BAI before 1958, followed by a decrease from 1958 to 1977 and an increase to a peak around 2000. Tree-ring carbon discrimination (Δ) and δ(18)O indicated significant negative overall trends from 1920 to 2012. However, the relationship shifted in strength and direction around 1977 from significantly negative to a weak connection. The seasonal minimum temperature in April to July showed strong influence on Δ, and δ(18)O was controlled by relative humidity (negatively correlated) and temperature (positively correlated) in June and July. The patterns of internal to atmospheric CO2 (Ci/Ca) suggest a specific adaptation of tree physiology to increasing CO2. Intrinsic water-use efficiency increased significantly (by 36.4%) during the study period. The increased iWUE explained 19.8 and 39.1% of the observed yearly and high-frequency (first-order difference) variations in BAI, respectively, after 1977. Our results suggest significant CO2 stimulation of riparian tree growth, which compensated for the negative influences of reductions in river streamflow and a drying climate during the study period.
大气中二氧化碳浓度（Ca）的上升促进了树木生长和内在水分利用效率（iWUE）。然而，这种效应在长期iWUE上的程度以及这种增加是否能刺激极端干旱地区河岸森林的生长，目前仍知之甚少。我们研究了中国西北内陆黑河下游河岸胡杨林中生长[年轮宽度；断面积生长量（BAI）]与iWUE之间的关系，以检验生长是否因二氧化碳增加而增强，以及这是否补偿了环境压力。我们使用树木年代学方法以及碳（δ(13)C）和氧（δ(18)O）同位素分析来完成此项研究。我们发现，1958年之前BAI有所增加，随后在1958年至1977年下降，到2000年左右又增加至峰值。树木年轮碳同位素分馏（Δ）和δ(18)O表明，1920年至2012年总体呈显著负趋势。然而，这种关系在1977年左右在强度和方向上发生了变化，从显著负相关变为弱相关。4月至7月的季节性最低温度对Δ有强烈影响，而δ(18)O在6月和7月受相对湿度（负相关）和温度（正相关）控制。内部与大气二氧化碳（Ci/Ca）的模式表明树木生理对二氧化碳增加有特定适应性。在研究期间，内在水分利用效率显著提高（36.4%）。1977年之后，iWUE的增加分别解释了观察到的BAI年度变化和高频（一阶差分）变化的19.8%和39.1%。我们的结果表明，二氧化碳对河岸树木生长有显著刺激作用，这补偿了研究期间河流流量减少和气候干燥的负面影响。
