不同林龄马尾松与红锥混交对凋落物和土壤碳储量的影响

Effects of mixed plantation of Pinus massoniana and Castanopsis hystrix at different stand ages on litter and soil carbon storage

关键词:  马尾松人工林, 混交改造, 凋落物, 土壤碳储量, 林龄

Key words:  Pinus massoniana plantation, mixed-plantation transformation, litter, soil carbon storage, stand age

摘要:

凋落物是森林生产力的重要组成部分,其产量及化学计量比(高N和低C:N、C:P、N:P有利于凋落物的分解)通过调控分解速率和养分归还效率,直接影响土壤碳动态。虽然营造混交林能够显著改变凋落物和土壤碳储量,但是这些混交效应如何随不同林龄阶段变化仍知之甚少。为探究不同林龄马尾松人工林引入阔叶树种混交改造对凋落物和土壤碳储量的影响,该研究以不同林龄马尾松纯林(25年、36年、46年和63年生)及其对应的马尾松/红锥混交林为对象,测定不同林分类型凋落物产量、凋落物化学计量比及土壤碳储量。结果表明:(1)树种混交显著增加了成熟林(36年生)凋落物产量。凋落物产量正的混交效应主要存在于近熟林(25年生)和成熟林(36年生)中。混交改造后凋落物N含量随林龄的增加逐渐增加,P含量先增加后减少。除成熟林(46年生)以外,其他混交林C:N均低于纯林。在过熟林(63年生)中,凋落物N含量、N:P的混交效应最大,C:N的混交效应最小。(2)多数林龄阶段树种混交促进了土壤碳储量的提升,0～60 cm土层土壤碳储量混交效应受林龄显著影响,各土层最大混交效应值多在过熟林。(3)Spearman相关性分析表明,混交引起的土壤碳储量变化与凋落物C、N、C:N和N:P密切相关。综上认为,马尾松人工林引入阔叶树种混交能有效提升凋落物的产量和质量,从而提高土壤碳储量和促进土壤养分循环。适度延长混交林的经营周期,有利于更大程度地发挥其生态系统功能。

Abstract:

Litter is an important part of forest productivity, and its productivity and stoichiometric ratio(high N and low C:N, C:P and N:P, which facilitate litter decomposition)are vital in regulating soil carbon dynamics through decomposition rate modulation and nutrient release optimization. Although mixed-species plantations are known to significantly alter litter production and soil carbon sequestration compared with monocultures, but how these mixing effects change across different stand age stages remains poorly understood. The objective of this study was four pure Pinus massoniana plantation with different stand ages(25, 36, 46 and 63 years old)and their corresponding mixed plantations with Castanopsis hystrix. We measured litter production, litter stoichiometric ratio, and soil carbon storage to assess how mixing broad-leaved tree species with pure Pinus massoniana affects these factors across different stand ages. The results were as follows:(1)Tree species mixing significantly increased litter production in mature forests(36 years old). The positive mixing effect on litter production mainly existed in near-mature forests(25 years old)and mature forests(36 years old). Consequently, the litter N content gradually increased with increasing stand age, whereas the P content firstly increased and then decreased. Except for the mature forest(46 years old), mixed plantations had lower C:N than pure plantations. In over-mature forests(63 years old), we observed maximal mixing effects on litter N content and N:P but minimal effects on C:N.(2)Mixing also promoted an increase in soil carbon storage for most stand ages, particularly in the 0-60 cm soil layer. We also observed that the over-mature forest exhibited maximal mixing effect values in each soil layer.(3)Spearman's correlation analysis showed strong association between mixing-influenced soil carbon storage variations and litter C, N, C:N and N:P. Thus, introducing Castanopsis hystrix into pure Pinus massoniana plantations can effectively increase litter production and quality, thereby increasing soil carbon storage and promoting nutrient cycling. Moderately extending the management cycle of mixed plantations is beneficial for maximizing their ecosystem functions.