Ma Xiangqing

Aboveground litterfall in Eurasian forests

With a data set of Eurasian forest litter fall based on 471 stands, annual litterfall was estimated to be 6.53 Pg dm·a−1 (1 Pg=1015 g;dm, dry matter) in Eurasian forests, of which more than half occurred in tropical and subtropical forests, and a third in the boreal area. With litterfall, around 2.94 Pg C per year is transferred from the forest vegetation to the soil on this continent.

Strategies of organic acid production and exudation in response to low-phosphorus stress in Chinese fir genotypes differing in phosphorus-use efficiencies

Key messagePlants with high P-use efficiency adapted more effectively via increased organic acid content in roots and root exudates than those with low P-use efficiency. Plants with high P-use efficiency also redistributed P in their tissues as an adaptive response, when organic acid exudation did not improve P-use efficiency.AbstractIncreased organic acid exudation enables plants to cope with low-phosphorus (P) stress conditions. We aimed to clarify the variation in organic acid exudation strategies among different breeding genotypes presenting high-phosphorous (P) use efficiency. In this study, Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] seedlings differing in P-use efficiency were compared regarding low-molecular weight organic acid content in roots and root exudates under low-P stress conditions, and dry weight and P-use efficiency also were examined. Compared to the genotype characterized by low P-use efficiency (M24), passive low-P tolerance (M1) or active capture of soil P (M4) genotypes effectively increased organic acid content in roots and root exudates. Although M1 was more sensitive to low P than M4, the former exhibited a specific tolerance to low P. Accordingly, the production of organic acids was slower, and the resultant stress response was less effective in M1 than in M4. Organic acid exudation did not improve P-use efficiency, given the absence of insoluble P in the rhizosphere, but M1 and M4 redistributed P in the tissues as an adaptive response. M4 also increased the root/shoot ratio and allocated more assimilation to root system to enhance P acquisition under low-P condition. In conclusion, the studied genotypes revealed different organic acid exudation strategies. Plants with high P-use efficiency adapted more effectively than those with low P-use efficiency. Metabolic and energy-use adjustments by plant organs, which facilitate plants’ passive adaptation under P-stress, are important survival strategies that allow adaptation to low-P environments.

杉木磷转运蛋白基因 ClPht1;1 的克隆及表达分析

目的 PHT1基因家族是影响植物吸收磷营养的重要磷转运子之一。从杉木32号磷高效家系cDNA中克隆得到PHT1基因家族的1个杉木磷转运蛋白基因ClPht1；1，并对不同程度磷胁迫下ClPht1；1的时空表达进行研究，为杉木PHT1基因序列特征和功能结构的研究以及磷高效利用杉木基因型的选育奠定基础。n 方法 根据PHT1基因家族序列保守性设计简并引物，以32号磷高效杉木基因型根系cDNA为模板进行扩增获得目的基因ClPht1；1的cDNA序列，使用RACE技术对目的基因进行全长克隆，并对其序列特征、同源性和编码磷转运蛋白结构进行分析。实时荧光定量PCR检测ClPht1；1在32号磷高效杉木家系根、茎、叶中的表达，检测中度缺磷胁迫下ClPht1；1在不同磷利用效率杉木4号、15号、25号、27号、28号、32号家系根系中的表达差异，以及在中度、重度缺磷胁迫下ClPht1；1在32号磷高效杉木家系根系中随时间序列的表达量变化。n 结果 克隆得到1个杉木磷转运蛋白PHT1基因，命名为ClPht1；1（GenBank登录号：KX302006），基因序列编码区长1 638 bp，编码545 aa的蛋白质。ClPht1；1所编码蛋白质由12个疏水的跨膜区域组成，1个疑似跨膜域。每个跨膜结构域基本由17~25个氨基酸残基组成螺旋，同时跨膜蛋白的N端和C端均位于细胞质内，保守序列位于第4个跨膜域。构成蛋白质的主要骨架是α-螺旋，无信号肽序列。ClPht1；1基因编码蛋白与日本柳杉PHT基因编码蛋白的氨基酸序列相似性达到87.0%，与胡杨、油茶、马尾松等PHT家族基因编码蛋白的氨基酸序列相似性均在75%以上。ClPht1；1基因在杉木的根、茎、叶组织中均有表达，其中在根中的表达量最高，在叶中的表达量最低。在中度缺磷胁迫下，ClPht1；1基因在杉木不同家系根部的表达量为25号> 27号> 4号> 15号> 32号> 28号。在中度和重度缺磷胁迫下，ClPht1；1基因在32号杉木家系根部的表达量随胁迫时间的延长而逐渐上升；恢复供磷后，ClPht1；1基因表达量逐渐下降至正常水平；重度缺磷胁迫下，ClPht1；1基因表达量要高于其在中度缺磷胁迫下的表达量。n 结论 ClPht1；1基因具有PHT1基因家族的典型结构，其编码蛋白的氨基酸序列与日本柳杉等磷转运蛋白氨基酸序列具有高度相似性，为杉木高亲和磷转运蛋白PHT1基因家族成员。ClPht1；1基因主要在杉木的根部表达，在叶片中的表达量较低；杉木磷利用效率越强，ClPht1；1基因在其根部的表达量越高。在不同磷利用效率的杉木家系中ClPht1；1基因表达量存在较大差异。ClPht1；1基因的表达受低磷胁迫的诱导，缺磷胁迫下ClPht1；1基因表达量明显升高，恢复供磷后ClPht1；1基因表达量明显降低。