基于林龄的滨海盐碱地刺槐人工林生产力衰退机制

Robinia pseudoacacia forest is the largest man-made forest in the Yellow River Delta in the 1980s and has been playing a significant role in the improving of environment. It started to show the declining at the beginning of the century and has been associated with obvious aging characteristics, but the recession mechanism is not clear. This project applicant has thoroughly studied R. pseudoacacia seedling salt tolerance and the dynamics of forest soil water and salt movements, but the aging response mechanism on R pseudoacacia plantation.productivity is still not studied, which we believe, is the core element of R. pseudoacacia forest declining. Using the existing forest in the Yellow River Delta as well as the experimental forests the applicants planted, which are at different ages and saline-alkali gradient, the researchers will discover the mechanism of individual differentiation through studying the root architecture and genetic diversity at the individual levels and salt tolerance ability of individuals in different R. pseudoacacia plantations. And further on to discuss the correlation.between the aboveground and underground parts of the individuals under salt stress. In addition, the researcher will also clearly illustrate the mechanism of soil deterioration in R. pseudoacacia plantation through studying soil properties and the abilities of absorb and utilization of roots in different R. pseudoacacia plantations. At the stand level, track the space-time dynamic features of forest productivity, distribution patterns, diameter class structure and forest eco-physiological response in different age levels. Clarify the age effect of.stand productivity declination, find out the dominant factors, and illustrate the age response mechanism of productivity decline R. pseudoacacia plantation. All the above discoveries will provide a solid theoretical basis for vegetation restoration and reconstruction of coastal saline alkali land.

上世纪八十年代营造的刺槐林是黄河三角洲最大的乔木林，本世纪初出现生长衰退且年龄特征明显，但机理并不明确。项目申请者在刺槐耐盐性、林地水盐动态等方面进行了深入研究，对于盐碱逆境下刺槐林生产力的年龄动态响应机制尚没人研究，而这正是阐明刺槐林衰退的核心内容。本研究利用已有和申请者营造的不同年度、盐碱梯度的试验林，在个体水平上，研究不同年龄刺槐个体根系构型、遗传和耐盐能力差异，探讨逆境下其地上与地下部分相关性，找出个体分化机制；研究各类林分林地土壤特性、树木对土壤养分吸收利用能力，阐明林地土壤劣变规律。在林分水平上，追踪研究随年龄增加林分生产力动态格局，分析林分叶面积、生物量分配、衰退程度与生产力的关系，明确林分生产力衰退的关键因素；找出主导因子，阐明刺槐林生产力与年龄相关的衰退机制，为滨海盐碱地植被恢复与重建提供理论依据。

本研究在个体水平上探讨了不同年龄刺槐个体根系构型、耐盐能力差异及生理生态适应机制，弄清了刺槐个体分化的生理生态和年龄特征及不同衰退程度个体的生长规律，发现快速高生长是刺槐前期较好适应盐碱地的原因，盐分在体内逐步积累是个体分化和衰退重要促进因素。从林龄角度弄清了黄河三角洲刺槐人工林细根动态及与林土互作机制，得出了细根生物量降低是林分地上部分生产力降低的主要原因；水盐和pH值是滨海盐碱地刺槐衰退林分细根生物量、生产量和周转速率降低成因等重要结论。阐明了林地土壤劣变规律，表明潜水埋深和地下水矿化度通过影响土壤水盐分布进而间接影响刺槐生长且潜水埋深影响更大。刺槐衰退主要原因是水涝和盐胁迫，刺槐适应逆境的机制是增加根系生物量分配。.在林分水平上，追踪研究了随年龄增加林分生产力动态格局，认为盐碱程度和林龄显著影响黄河三角洲刺槐林林分生产力。高盐林地健康木比例下降，中等木和濒死木比例增大，导致林分生产力降低；随着林龄增加，材积生长和地上生物量表现出先升高后降低的趋势。林分生产力特征是盐胁迫、林龄、光合能力、衰退进程、径级分布、林土互作以及外界环境综合作用的结果。该研究丰富了黄河三角洲滨海盐碱地区人工林的经营理论，为我国北方相似滨海盐碱地的生态环境建设提供了理论依据。