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氮素在森林生态系统的能量流动与物质循环过程中有着非常重要的作用[1-2]。长期氮沉降以及人类活动干扰等,造成全球氮(N)沉降的增加,对自然生态系统产生了一系列影响[2-3]。研究表明:即使在没有物理扰动的情况下,长期氮沉降也会通过降低碳周转率、改变氮的有效性和转化来影响温带森林生态系统的生物地球化学循环[4]。此外,也有研究表明:氮添加会通过改变凋落叶特性(碳、氮、磷变化)对其养分分解速率产生影响[3]。据报道,中国已成为全球第三大氮沉降地区,大气含氮化合物增长迅速[5]。在未来几十年中氮沉降继续增加的背景下,研究氮沉降对森林凋落物养分分解的影响显得尤为重要[6-7]。凋落物在森林生态系统组成中占据重要地位,它的分解也会对森林生态系统的生物地球化学循环产生相当大的影响[8-9]。凋落物分解不仅是林下土壤有机质形成所需碳源以及土壤养分的主要来源,而且对于土壤质地的构建、肥力的维持、微生物代谢的调控都起重大作用,并且通过这一系列作用进而影响微生物的群落结构[10-11]。大果木姜子Cinnamomum migao又名米槁,系樟科Lauraceae樟属Cinnamomum常绿乔木,主要分布于中国广西、云南、贵州三省交界的南北盘江、红水河流域,为中国特有种。其果实常常被苗族作为治疗胃肠道疾病的传统药物,并且疗效卓越。21世纪初,贵州省科学技术厅以及贵州省民族医药研究所确定大果木姜子为贵州省的道地药材[12]。近年来,随着其药用价值的提高,大果木姜子野生资源受到极大破坏,在《中国生物多样性红色名录——高等植物卷》(2013版)已将其列为近危种,野外资源储量极其有限。目前,相关学者对大果木姜子的研究报道还不是很全面,主要集中在果实精油、脂肪油、挥发油化学成分分析[13]、药用成分的药理作用与生物活性[14-15]、栽培技术与病虫害防治[12]、地理分布[15]、生物生理特性[16-17]等方面。大果木姜子凋落叶的分解对氮沉降增加的响应规律还未见报道。本研究通过野外模拟氮沉降的试验,探讨不同施氮处理对大果木姜子凋落叶养分分解的影响,以期探讨大果木姜子凋落叶分解对外源氮添加的响应机制,且为其物质循环机理研究提供理论依据。
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图1显示:1−9月各处理凋落叶质量损失率随着时间的推移表现为迅速递增趋势,其中ck凋落叶质量损失率大于其他处理;9月以后各处理凋落叶分解速率趋于平缓。整个分解试验过程中,N3处理凋落叶质量损失率为0~53.35%,且始终低于其他处理。9月以前,N1、N2处理凋落叶质量损失率显著高于N3处理(P<0.05),即凋落叶质量损失率从大到小依次为N2、N1、N3;分解结束时(11月),各处理凋落叶质量损失率从大到小依次为N2、ck、N1、N3。
图 1 不同处理下大果木姜子凋落叶质量损失率
Figure 1. Change of mass loss rate and residual rate of leaf litter of C. migao under the condition of different treatments
从表1可以看出:4个处理的拟合模型R2均大于0.9000,且达到显著水平(P<0.05),其中N3处理Olson模型的拟合效果最佳。ck处理的凋落叶质量分解系数最大(K=0.085),N3处理最小(K=0.060)。N1、N2、N3处理凋落叶分解95%所需时间分别比ck长0.653、0.312、0.698 a,其中N3处理下凋落叶分解时间所需最长。综合表明:氮添加延缓了大果木姜子凋落叶的分解。
表 1 不同处理大果木姜子凋落叶质量残留率(y)随时间(x)变化的Olson模型
Table 1. Decomposition rate model of litter residue rate (y) with time (x) under different treatments
处理 分解方程 分解系数(K) 决定系数(R2) 相关系数(r) 显著性 凋落叶分解50%所需时间/月 凋落叶分解95%所需时间/a ck y=81.727e−0.085x 0.085 0.970 −0.944 0.005 8.155 2.973 N1 y=81.666e−0.067x 0.067 0.948 −0.940 0.005 10.045 3.626 N2 y=87.461e−0.076x 0.076 0.907 −0.963 0.002 9.120 3.285 N3 y=87.319e−0.068x 0.060 0.977 −0.951 0.004 10.193 3.671 -
由图2可知:各处理凋落叶碳质量数总体均呈下降趋势,且分解前期(1−5月)下降较快,后期(5−11月)下降较慢。各处理凋落叶全氮质量分数变化趋势基本相同,整体上均呈先增加后降低的趋势,其中9月最高。各处理凋落叶全磷与全钾质量分数变化趋势相似,即在分解初期下降,之后整体上升,最后趋于平稳。
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由图3可以看出:由于碳元素主要以有机形式存在于凋落叶中,受淋溶影响,各处理碳残留率呈降低趋势,其中分解各时段3个施氮处理碳残留率整体上显著高于ck(P<0.05)。ck的全氮残留率整体上呈先上升后下降再上升后下降趋势,各施氮处理的全氮残留率整体上呈先上升后下降趋势;1−7月,各处理全磷残留率呈先下降后升高再下降的趋势;7月之后,N1、N2、N3处理全磷的残留率趋于稳定,ck处理全磷残留率呈先上升后下降趋势。1−3月,各处理全钾残留率迅速降低,3月之后各处理全钾残留率总体呈增加趋势,整体表现为淋溶—富集—释放模式。
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从图4可以看出:试验期间各处理C/N为24.60~177.51,整体表现出下降趋势。分解前期(1−7月) C/N下降速度较快,后期(7−11月)变化总体上比较平稳。在分解各时间段,ck的C/N基本高于其他各施氮处理。在试验前期(1−7月) ck处理与各施氮处理间有显著差异(P<0.05);试验后期(7−11月) ck组与N1、N2处理差异显著(P<0.05),与N3差异不显著(P>0.05)。总体来看,添加氮降低了大果木姜子凋落叶的C/N。
Effects of nitrogen addition on decomposition and nutrient release of Cinnamomum migao litter leaves
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摘要:
目的 研究不同施氮水平对大果木姜子Cinnamomum migao凋落叶养分分解的影响。 方法 于2017年1月,以药用植物大果木姜子人工林凋落叶为研究对象,将凋落叶清洗风干后装入分解袋中,每袋10.00 g。试验期间放置在不同施氮处理[对照(ck,0 g·m−2·a−1)、N1(5 g·m−2·a−1)、N2(15 g·m−2·a−1)、N3(30 g·m−2·a−1)]样地中,每处理3个重复,分别于试验的3、5、7、9、11月采集凋落叶样品,测定凋落叶质量及养分质量分数的变化,分析氮沉降对大果木姜子凋落叶养分释放动态影响。 结果 凋落叶分解试验结束时,各施氮组凋落叶质量损失率整体小于ck,凋落叶残留率整体大于ck,且N2与ck差异不显著,N2、N3差异显著(P<0.05),ck、N1、N2、N3凋落叶分解95%时所需的时间分别为2.973、3.626、3.285、3.671 a;各处理凋落叶碳质量分数总体均呈下降趋势,全氮质量分数整体上均呈先增加后降低的趋势,全磷与全钾质量分数变化趋势相似,为分解初期下降,之后整体上升,最后趋于平稳;各处理凋落叶碳、全磷、全钾残留率总体呈降低趋势,全氮残留率整体上呈先上升后下降趋势。其中分解各时段各施氮处理碳残留率均显著高于ck (P<0.05);随着时间推移,ck处理氮的残留率呈先上升后下降趋势,各施氮处理的氮残留率整体上呈先上升后下降趋势;整个分解过程中各施氮组碳氮比均小于ck,且分解前期与ck表现出显著差异(P<0.05)。 结论 添加氮不利于大果木姜子凋落叶的分解及养分的释放,且施氮越多抑制分解作用更显著。图4表1参33 Abstract:Objective This research aims to examine the effects of different nitrogen application levels on nutrient decomposition of Cinnamomum migao litter leaves. Method In January 2017, the litter leaves of the medicinal plant C. migao were taken as the research object. The leaves were washed, air dried and put into decomposition bags, 10.00 g each. Nitrogen treatments were designed as ck(0 g·m−2·a−1), N1(5 g·m−2·a−1), N2(15 g·m−2·a−1), and N3(30 g·m−2·a−1), and there were three repetitions for each treatment. The samples of litter leaves were collected in March, May, July, September and November, respectively. The quality and nutrient contents of the leaves were measured, and the dynamic effects of nitrogen deposition on nutrient release from the leaves were analyzed. Result At the end of litter decomposition experiment, the mass loss rate of litter leaves in all nitrogen application groups was lower than that of ck, the residue rate of litter was higher than that of ck. The difference between N2 and ck was not significant, but the difference between N2 and N3 was significant (P<0.05). The time needed for 95% decomposition of ck, N1, N2 and N3 was 2.973, 3.626, 3.285 and 3.671 a, respectively. In the leaves of all treatments, the content of C decreased and the content of total N increased first and then decreased, while the content of total P and total K was similar, which decreased at the initial stage of decomposition, then increased as a whole, and finally stabilized. The residual rates of C, total P, total K in the leaves decreased, while the residue rates of total N increased first and then decreased. The residual rate of C in each nitrogen treatment was significantly higher than that of ck (P<0.05). With the passage of time, the residue rate of N, which increased first and then decreased in ck treatment, showed an overall upward and then downward trend in each nitrogen application treatment. C/N ratio of each nitrogen application group was lower than that of ck in the whole decomposition process, and there was a significant difference between the early decomposition stage and ck (P<0.05). Conclusion Nitrogen addition is not conducive to the decomposition and nutrient release of litter leaves. The more nitrogen is applied, the more obvious the inhibition of decomposition is.[Ch, 4 fig. 1 tab. 33 ref.] -
Key words:
- forest ecology /
- nitrogen deposition /
- Cinnamomum migao /
- litter decomposition /
- nutrient release
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表 1 不同处理大果木姜子凋落叶质量残留率(y)随时间(x)变化的Olson模型
Table 1. Decomposition rate model of litter residue rate (y) with time (x) under different treatments
处理 分解方程 分解系数(K) 决定系数(R2) 相关系数(r) 显著性 凋落叶分解50%所需时间/月 凋落叶分解95%所需时间/a ck y=81.727e−0.085x 0.085 0.970 −0.944 0.005 8.155 2.973 N1 y=81.666e−0.067x 0.067 0.948 −0.940 0.005 10.045 3.626 N2 y=87.461e−0.076x 0.076 0.907 −0.963 0.002 9.120 3.285 N3 y=87.319e−0.068x 0.060 0.977 −0.951 0.004 10.193 3.671 -
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