不同林龄短枝木麻黄小枝单宁含量及养分再吸收动态

Dynamics of tannin concentration and nutrient resorption for branchlets of Casuarina equisetifolia plantations at different ages

通过对福建省惠安县不同林龄短枝木麻黄人工林不同发育阶段小枝单宁含量及氮磷再吸收率的研究,探讨了短枝木麻黄林分发育过程中的营养保存策略。结果表明,幼龄林(5年生)成熟小枝中的总酚(TP)、可溶性缩合单宁(ECT)总缩合单宁(TCT)含量及蛋白质结合能力(PPC)显著高于成熟林(21年生)和衰老林(38年生)。随着林分发育,成熟小枝中N含量显著升高,而P含量呈降低趋势。不同发育阶段林分成熟小枝中N∶P比均大于20,且随着林龄的增加而升高。磷再吸收率(PRE)显著高于氮再吸收率(NRE),均以成熟林分最高。这表明短枝木麻黄小枝单宁含量与养分再吸收受林龄影响,其养分保存机制会随着林分生长发育的变化而进行调节。

Casuarina equisetifolia is characterised by high primary productivity in coastal sandy soils, which are generally low in nutrient contents. High tannin production and nutrient resorption may be important strategies for C. equisetifolia in coastal environments. Despite the widespread planting and known ecological and physiological properties of C. equisetifolia, there is scant information about the nutrient resorption patterns and tannin concentrations for branchlets of C. equisetifolia plantations during stand development. Since plant ecophysological traits are associated with ageing, tannin content and nutrient resorption efficiency could change with stand development. Therefore, tannin level and nutrient resorption of C. equisetifolia at different developmental phases （juvenile, mature and senescent） were examined to evaluate possible nutrient conservation strategies under nutrient limitation in Huian County,Fujian Province. The results showed that total phenolics （TP） contents, which were in the order juvenile stand 〉 senescent stand 〉 mature stand for senescent branchlets and decreased from 218.52 to 180.49 mg/g during stand development for mature branchlets, decreased during branchlet senescence in all stands. The extractable condensed tannin contents （ECT） in mature and senescent branchlets of C. equisetifolia were juvenile stand 〉 senescent stand 〉 mature stand. The ECT contents of C. equisetifolia increased during branchlet senescence both in the mature and senescent stands but decreased in the juvenile stand. The protein-bound condensed tannin （PBCT） contents of branchlets increased during senescence in juvenile and mature stands and remained the same in senescent stand. The fibre-bound condensed tannins （FBCT） of branchlets increased during senescence in mature stand and did not change in juvenile and senescent stands. Total condensed tannin （TCT） followed similar pattern as ECT during stand development. Protein precipitation capacity （PPC） in mature and senescent branchlets were significantly higher in juvenile stand than in mature and senescent stands. PPC decreased during branchlet senescence in the three stands. Significant positive linear correlations were found between PPC and TP or TCT. Nitrogen （N） concentrations both in mature and senescent branchlets obviously increased during stand development. Phosphorus （P） concentrations in mature branchlets were similar in juvenile and mature stands but lower in senescent stand. Phosphorus concentrations in senescent branchlets of juvenile stand were significantly higher than those of mature and senescent stands. Nitrogen：phosphorus ratios （N：P ratios） of mature branchlets, were all above 20, also increased during stand development. Nitrogen resorption efficiencies （NRE） in three stands were basically below 50%, the lowest in senescent stand. Phosphorus resorption efficiencies （PRE） were above 70% with the highest in mature stand （78.08%）. There were significant negative correlations between N and P concentrations in mature and senescent branchlets. Nitrogen resorption efficiency had a particular strong relationship with the N：P ratios of branchlets. On the other hand, PRE was not significantly related to N：P ratios of branchlets. There were significant correlations between TP or TCT and N or P concentrations in branchlets except for the relationship between TCT and P concentrations in senescent branchlets. The above results indicated that the tannin level, nutrient concentration and resorption were affected by stand age. C. equisetifolia could adjust their nutrient conservation with stand development at intraspecific level.