Institute of Oceanography, Minjiang University, Fuzhou 350108, China; Chinese Fir Engineering Technology Research Center of the State Forestry and Grassland Administration, Fuzhou 350002, China.
Forestry College, Fujian Agriculture and Forestry University, Fuzhou 350002, China; Chinese Fir Engineering Technology Research Center of the State Forestry and Grassland Administration, Fuzhou 350002, China.
Sci Total Environ. 2021 Mar 25;762:143153. doi: 10.1016/j.scitotenv.2020.143153. Epub 2020 Oct 21.
Canopy litter is an important component of coarse woody debris (CWD), which affects nutrient and carbon cycling in forest ecosystems. For marcescent plant species (characterized by dead branches and leaves remaining in the canopy for several years before abscission), nutrient resorption from senescing leaves is an important nutrient conservation strategy. However, investigating the ecological function of canopy litter is challenging due to its limited accessibility and also the heterogeneous canopy microclimate in terms of light transmission, temperature and moisture. We studied the spatiotemporal distribution of canopy litter mass and seasonal dynamics of leaf nutrients and nutrient resorption during senescence in the canopy along a chronosequence of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantations in southeast China. The dry mass weight of dead branches and dead leaves in the canopy significantly increased with stand stage (14.6, 14.2, and 17.4 t ha for young, middle-aged, and mature stands respectively), accounting for high proportions of total aboveground litter of 85.7%, 79.1% and 80.0%, respectively, along with annual litterfall production (2.44, 3.75, and 4.34 t ha, respectively). The canopy height distribution of dead branches and leaves also increased with stand age, ranging from 0 to 4 m in young stands, 3-8 m in middle-aged stands, to 4-10 m in mature stands. The seasonal pattern of canopy litter mass was the inverse of litterfall production: canopy litter mass peaked, while litterfall production was lowest in winter. Mean N, P, K, and Mg nutrient resorption efficiencies across stands at each stage were 53.8-58.9%, 64.0-68.9%, 85.0-90.2%, and 46.5-56.6%, respectively, while Ca was not retranslocated from senescing leaves. In summary, Chinese fir plantations retain large amounts of dead branches and leaves in the canopy from which at least ~50% of the nutrients N, P, K and Mg are recycled, representing an important nutrient conservation strategy that has evolved to adapt to nutrient-limited habitats. Canopy litter therefore plays an important role in these forest plantation ecosystems and should be protected instead of being removed from the canopy to the forest floor.
林冠凋落物是粗木质残体 (CWD) 的重要组成部分，它会影响森林生态系统中的养分和碳循环。对于枯梢植物物种（以枯枝落叶在脱落前在林冠中保留数年为特征），衰老叶片中的养分再吸收是一种重要的养分保护策略。然而，由于其有限的可及性以及透光性、温度和湿度方面的异质林冠微气候，调查林冠凋落物的生态功能具有挑战性。我们研究了中国东南地区杉木 [Cunninghamia lanceolata (Lamb.) Hook] 人工林林冠凋落物质量的时空分布以及林冠中叶片养分和养分再吸收的季节性动态，这些人工林处于幼龄、中龄和成熟林阶段的时间序列中。林冠中枯梢和枯叶的干重质量随林龄显著增加（幼龄、中龄和成熟林分别为 14.6、14.2 和 17.4 t/ha），占总地上凋落物的比例分别高达 85.7%、79.1%和 80.0%，以及每年的凋落物产量（分别为 2.44、3.75 和 4.34 t/ha）。枯梢和枯叶的林冠高度分布也随林龄而增加，从幼龄林的 0 到 4 m，从中龄林的 3-8 m，到成熟林的 4-10 m。林冠凋落物质量的季节性模式与凋落物产量相反：林冠凋落物质量在冬季达到峰值，而凋落物产量最低。在每个阶段，各林分的平均 N、P、K 和 Mg 养分再吸收效率分别为 53.8-58.9%、64.0-68.9%、85.0-90.2%和 46.5-56.6%，而 Ca 没有从衰老叶片中再转移。总之，杉木人工林保留了大量的枯枝落叶在林冠中，其中至少有~50%的 N、P、K 和 Mg 养分被回收，这是一种重要的养分保护策略，是为了适应养分限制的生境而进化而来的。因此，林冠凋落物在中国东南地区的这些森林人工林生态系统中发挥着重要作用，应该加以保护，而不是从林冠中移除到林地上。
