Epron Daniel, Cabral Osvaldo Machado Rodrigues, Laclau Jean-Paul, Dannoura Masako, Packer Ana Paula, Plain Caroline, Battie-Laclau Patricia, Moreira Marcelo Zacharias, Trivelin Paulo Cesar Ocheuze, Bouillet Jean-Pierre, Gérant Dominique, Nouvellon Yann
UMR 1137, Ecologie et Ecophysiologie Forestières, Faculté des Sciences, Université de Lorraine, F-54500 Vandoeuvre-les-Nancy, France INRA, UMR 1137, Ecologie et Ecophysiologie Forestières, Centre de Nancy, F-54280 Champenoux, France CIRAD, UMR Eco&sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agro-écosystèmes, F-34060 Montpellier, France
Embrapa Meio Ambiente, CEP 13820-000, Jaguariúna, São Paulo, Brazil.
Tree Physiol. 2016 Jan;36(1):6-21. doi: 10.1093/treephys/tpv090. Epub 2015 Sep 30.
Potassium (K) is an important limiting factor of tree growth, but little is known of the effects of K supply on the long-distance transport of photosynthetic carbon (C) in the phloem and of the interaction between K fertilization and drought. We pulse-labelled 2-year-old Eucalyptus grandis L. trees grown in a field trial combining K fertilization (+K and -K) and throughfall exclusion (+W and -W), and we estimated the velocity of C transfer by comparing time lags between the uptake of (13)CO2 and its recovery in trunk CO2 efflux recorded at different heights. We also analysed the dynamics of the labelled photosynthates recovered in the foliage and in the phloem sap (inner bark extract). The mean residence time of labelled C in the foliage was short (21-31 h). The time series of (13)C in excess in the foliage was affected by the level of fertilization, whereas the effect of throughfall exclusion was not significant. The velocity of C transfer in the trunk (0.20-0.82 m h(-1)) was twice as high in +K trees than in -K trees, with no significant effect of throughfall exclusion except for one +K -W tree labelled in the middle of the drought season that was exposed to a more pronounced water stress (midday leaf water potential of -2.2 MPa). Our results suggest that besides reductions in photosynthetic C supply and in C demand by sink organs, the lower velocity under K deficiency is due to a lower cross-sectional area of the sieve tubes, whereas an increase in phloem sap viscosity is more likely limiting phloem transport under drought. In all treatments, 10 times less (13)C was recovered in inner bark extracts at the bottom of the trunk when compared with the base of the crown, suggesting that a large part of the labelled assimilates has been exported out of the phloem and replaced by unlabelled C. This supports the 'leakage-retrieval mechanism' that may play a role in maintaining the pressure gradient between source and sink organs required to sustain high velocity of phloem transport in tall trees.
钾（K）是树木生长的一个重要限制因素，但关于钾供应对韧皮部光合碳（C）长距离运输的影响以及钾肥施用与干旱之间的相互作用，我们所知甚少。我们对田间试验中生长的2年生巨桉（Eucalyptus grandis L.）树进行脉冲标记，该试验结合了钾肥施用（+K和-K）和穿透雨排除（+W和-W），并通过比较（13）CO2吸收与在不同高度记录的树干CO2流出中其恢复之间的时间滞后，估算了碳转移速度。我们还分析了在叶片和韧皮部汁液（内皮提取物）中回收的标记光合产物的动态。标记碳在叶片中的平均停留时间较短（21 - 31小时）。叶片中过量（13）C的时间序列受施肥水平影响，而穿透雨排除的影响不显著。树干中碳转移速度（0.20 - 0.82 m h(-1)）在+K树中是-K树中的两倍，穿透雨排除除了在干旱季节中期标记的一棵+K -W树受到更明显的水分胁迫（中午叶片水势为-2.2 MPa）外，没有显著影响。我们的结果表明，除了光合碳供应减少和库器官对碳需求降低外，钾缺乏时速度较低是由于筛管横截面积较小，而韧皮部汁液粘度增加更可能在干旱时限制韧皮部运输。在所有处理中，与树冠基部相比，树干底部内皮提取物中回收的（13）C少10倍，这表明大部分标记同化物已从韧皮部输出并被未标记的碳取代。这支持了“渗漏-回收机制”，该机制可能在维持高大树木中韧皮部运输高速所需的源器官和库器官之间的压力梯度方面发挥作用。
