| 摘要: |
| 【目的】探究氮添加对秦岭华山松抚育间伐剩余物分解的影响，为秦岭地区华山松林的保护和可持续经营提供科学依据。【方法】2019年5月至2020年5月在陕西观音山国家自然保护区内，采用分解袋法开展不同形态及水平氮对华山松抚育间伐剩余物分解的影响试验,氮形态分别为铵态氮（NH4Cl）、硝态氮（NaNO3）和混合态氮（NH4NO3），每种氮形态设置N1（0.5 g/(m2·a)）、N2（1.25 g/(m2·a)）、N3（2.5 g/(m2·a)）、N4（5.0 g/(m2·a)）和N5（10.0 g/(m2·a)）5个水平，以N0（0 g/(m2·a)）为对照，共16个处理。在试验区设置3块20 m×20 m的样地，每个样地内设置16个1 m×1 m的小样方，将上述16个处理对应布置在16个小样方内。在试验开始1个月后定期取样，测定华山松抚育间伐剩余物残留量及碳（C）、氮（N）、纤维素和木质素含量，并计算间伐剩余物年平均质量残留率、分解50%和95%所需时间、分解系数和C/N值。【结果】（1）添加铵态氮、混合态氮和硝态氮的处理，华山松抚育间伐剩余物年平均质量残留率分别为82.47%，81.83%和84.96%，均低于对照的年平均质量残留率84.99%。（2）与对照相比，不同形态氮处理使抚育间伐剩余物分解50%所需时间最多可减少0.41～1.65年，分解95%所需时间最多可减少4.16～7.15年。（3）当氮添加水平低于5.0 g/(m2·a)时,可促进华山松抚育间伐剩余物纤维素的降解，当氮添加水平高于5.0 g/(m2·a)时，可抑制纤维素的降解；不同形态不同水平的氮均促进了华山松抚育间伐剩余物木质素的降解。（4）随着时间的延长，华山松抚育间伐剩余物C含量和C/N值在分解过程中呈减少的趋势，而N元素含量呈增加趋势；抚育间伐剩余物分解系数与 C/N值呈负相关关系，即C/N值越低分解速率越快。【结论】经过1年的分解，3种形态的氮均表现为低水平促进分解，高水平抑制分解，其中铵态氮、混合态氮和硝态氮的氮添加水平分别低于或等于2.5，5.0和1.25 g/(m2·a)时，对华山松抚育间伐剩余物的分解起促进作用，高于上述添加量则有抑制作用。 |
| 关键词: 氮添加 秦岭华山松 抚育间伐剩余物 |
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| 基金项目:国家“十三五”重点研发计划项目（2017YFD0600504-2） |
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| Effects of nitrogen addition on decomposition of tending and thinning residues of Pinus armandi in the Qinling Mountains |
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ZHAO Chuanting,ZHANG Shuoxin,PANG Junzhu,et al
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| Abstract: |
| 【Objective】This study clarified the effects of nitrogen addition on decomposition of tending and thinning residues of Pinus armandi to provide scientific basis for protection and sustainable management of P. armandi forest in the Qinling Mountains.【Method】From May 2019 to May 2020,the litterbag method was applied for the study of decomposition of tending and thinning residues of Pinus armandi with nitrogen addition at different forms and levels in the Guanyinshan National Nature Reserve of Shaanxi Province.Nitrogen forms included ammonium nitrogen (NH4Cl),nitrate nitrogen (NaNO3) and mixed nitrogen (NH4NO3) and five nitrogen addition levels were N1(0.5 g/(m2·a)),N2(1.25 g/(m2·a)),N3(2.5 g/(m2·a)),N4(5.0 g/(m2·a)）and N5(10.0 g/(m2·a)) with the control without nitrogen addition N0 (0 g/(m2·a)). Three 20 m×20 m plots were set with 16 subplots in each plot.Each treatment was arranged in one subplot.Samples were taken regularly to determine dry matter,carbon (C),nitrogen (N),cellulose and lignin contents of tending and thinning residues of P. armandi one month after the beginning.Then,annual average mass remaining rates, decomposition times of 50% and 95%,decomposition coefficients and C/N values were calculated. 【Result】(1) The annual average mass remaining rates of tending and thinning residues of P. armandi with ammonium,mixed nitrogen and nitrate were 82.47%,81.83% and 84.96%,respectively,which were lower than the control of 84.99%.(2) Compared with the control,the times required for decomposing tending and thinning residues to 50% were reduced by 0.41 to 1.65 years,and that for 95% were reduced by 4.16 to 7.15 years.(3) When nitrogen addition level was lower than 5.0 g/(m2·a),the decomposition of tending and thinning residues was promoted,while it was inhibited when higher than 5.0 g/(m2·a).Different forms and levels of nitrogen addition promoted the degradation of lignin.(4) With the increase of decomposition time,C content and C/N ratio of tending and thinning residues of P. armandi decreased,while N content increased.The decomposition coefficients were negatively correlated with the C/N ratio,indicating that lower C/N ratio resulted in more rapid decomposition.【Conclusion】After one year of decomposition,the decomposition of tending and thinning residues was promoted with low levels of nitrogen addition while inhibited with high levels of nitrogen addition.The decomposition was promoted when amounts of ammonium,mixed nitrogen and nitrate were no higher than 2.5,5.0 and 1.25 g/(m2·a),respectively. |
| Key words: nitrogen addition Pinus armandi in the Qinling Mountains tending and thinning residues |
