马尾松人工林林窗大小对四种凋落叶质量损失和养分释放的影响

马尾松人工林乔木层植物凋落物的分解对林地养分平衡和系统物质循环具有重要意义,并可能受不同大小林窗下微环境差异的影响。采用凋落物袋分解法,以马尾松(Pinus massoniana)人工林人为砍伐形成的7个不同大小林窗(G1:100 m~2、G2:225 m~2、G3:400 m~2、C4:625 m~2、G5:900 m~2、G6:1225m~2、G7:1600 m~2)为研究对象,林下(G0)为对照,研究林窗大小对红椿(Toona ciliata)、桢楠(Phoebe zhennan)、香樟(Cinnamomum camphora)和马尾松4种乡土树种凋落叶质量损失及养分释放的影响。结果显示:1)林窗大小(G0-G7)显著影响林窗中心放置的红椿和桢楠凋落叶N和P释放率、香樟凋落叶失重率和N、P、K释放率以及马尾松凋落叶P和K释放率。相对于林下,中小型林窗(G1-G4)的凋落叶失重率和N、P释放率明显较大,而大型林窗(G6-G7)的凋落叶K释放率明显较大。2)林窗内放置位置显著影响红椿、桢楠和马尾松凋落叶的K释放率及香樟凋落叶的P释放率。红椿和桢楠的凋落叶K释放率从林窗中心到边缘显著减少,而马尾松凋落叶K释放率及香樟P释放率从林窗中心到边缘显著增加。3)4种凋落叶类型中红椿凋落叶分解最快,其分解50%和95%所需时间分别为5.29和23.14个月。上述结果表明,林窗大小和林窗内位置对凋落物质量损失及其养分释放具有显著影响,但影响大小及趋势随物种初始基质质量的差异具有明显变化,研究结果为亚热带低山丘陵区马尾松人工低效林的科学经营及管理提高了一定的科学依据。

Effects of forest gap size on leaf litter weight loss and nutrient release of four species in Pinus massoniana plantations

Litter decomposition is an essential component of the nutrient balance and material cycling in Pinus massoniana plantations. Forest gap size could play an important role in litter decomposition due to its effects on the microenvironment. To evaluate the effects of forest gap size on leaf litter mass loss and nutrient release of four native species (Toona ciliata, Phoebe zhennan, Cinnamomum camphora, Pinus massoniana), a field experiment consisting of seven gap sizes (i.e., G1:100 m², G2:225 m², G3:400 m², G4:625 m², G5:900 m², G6:1225m², and G7:1600 m²) was established in 2013. The results showed that:1) Forest gap size significantly affected leaf litter mass loss of C. camphora, but not the mass loss of the other three species. The litter nutrient release rate at the gap center for T. ciliata (N, P), P. zhennan (N, P), C. camphora (N, P, K) and P. massoniana (P, K) were significantly influenced by forest gap size. Furthermore, leaf litter mass loss rate, and N and P release rates were significantly higher in small and medium sized gaps (G1-G4) than in large gaps (G5-G7) (P < 0.05). However, litter K release rates were significantly lower in small and medium sized gaps (G1-G4) than in the larger gaps (P < 0.05). 2) The leaf litter collection location in the forest gaps influenced the litter K release rate of T. ciliata, P. zhennan, and P. massoniana. The K release rate of T. ciliata and P. zhennan litter at the gap centers were significantly higher than those at the gap edges (P < 0.05). In contrast, P release rates of C. camphora litter and K release rates of P. massoniana litter at the gap center were significantly lower than rates at the gap edges (P < 0.05). 3) Litter mass loss and nutrient release rates of T. ciliata were the highest among the four species. According to the fitting equation, the 50% and 95% decomposition times for T. ciliata were 5.29 and 23.14 months, respectively. Overall, forest gap size and litter sampling location in the gaps significantly affected litter mass loss and nutrient release. However, the extent of these effects and dynamic changes depended on the initial litter quality. These results can be beneficial for the scientific management of P. Massoniana plantations in low mountainous and hilly areas of subtropical zones.