氮、磷添加对不同林型土壤磷酸酶活性的影响

Effects of nitrogen and phosphorus addition on soil phosphatase activity in different forest types

研究了鼎湖山3种森林类型(南亚热带季风常绿阔叶林、马尾松人工林和针叶阔叶混交林)的土壤酸性磷酸单酯酶活性(APA)对施肥的响应情况。在3种林型中分别设置对照、加氮(150 kg N hm-2a-1)、加磷(150 kg P hm-2a-1)以及N和P同时添加(150 kg N hm-2a-1+150 kg P hm-2a-1)4种不同处理。结果表明,季风林土壤APA((15.83±2.46)μmol g-1h-1)显著高于混交林((10.71±0.78)μmol g-1h-1)和马尾松林((9.12±0.38)μmol g-1h-1),且3种林型土壤APA与土壤有效磷含量均呈显著负相关。施加N肥显著提高了季风林土壤APA,而对混交林和马尾松林的作用不显著。施加P肥显著降低了混交林和马尾松林土壤APA,但对季风林的影响不明显。N和P同时添加仅显著降低了马尾松林土壤APA,但在季风林中存在交互作用。因此,N沉降会加剧亚热带成熟林土壤P的限制,可以考虑施加P肥作为森林管理的一种方式来缓解这种限制作用。

Phosphorus（ P） as a basic mineral nutrient is considered to constrain primary productivity in many tropical and subtropical forests. Soil phosphatase plays a very important role in P cycling in forest ecosystems because it catalyzes the hydrolysis of soil organic P compounds（ e. g.,nucleic acids and phospholipids） into forms that are available to plants and soil microbes. Soil phosphatase activity is widely considered an effective indicator of the P demand of plants and microbes due to its ability to mediate plant and microbial nutrient acquisition from organic P compounds. In recent decades,increasing nitrogen（ N） deposition due to human activity has been demonstrated to cause soil P deficiency and increase soil acid phosphomonoesterase activity（ APA） in several tropical or subtropical forests. However,little is known about the effects of N deposition on soil APA in other forest types（ e. g.,broadleaf forest and coniferous forest） or whether P addition may relieve soil P limitation in these forests. The present study investigated the responses of soil APA to N and P additions in a monsoon evergreen broadleaf forest（ MEBF）,a Pinus massoniana forest（ PF）,and a mixed broadleaf and pine forest（ MF） in Dinghushan Mountain,Guangdong Province of southern China via a six- year fertilization experiment. The experiment used full factorial design,including four treatments： control（ no fertilization）,N addition（ 150 kg N hm- 2a- 1）,P addition（ 150 kg P hm- 2a- 1）,and combined N and P addition（ 150 kg N hm- 2a- 1plus 150 kg P hm- 2a- 1）.Each 5 m × 5 m plot was established with a surrounding buffer strip（ 5 m wide）. For each N and P application,NH4NO3 and Na H2PO4 solutions were applied below the canopy with a backpack sprayer,every other month from January 2007 to July 2013. In July 2013,soil samples were collected for analysis. Results showed that soil APA was significantly higher in MEBF（（ 15. 83 ± 2. 46） μmol g- 1h- 1） than that in MF（（ 10. 71 ± 0. 78） μmol g- 1h- 1） or PF（（ 9. 12 ± 0. 38） μmol g- 1h- 1） soils,and a significant negative correlation existed between soil APA and soil available P contents in all forest types. N addition significantly increased soil APA in MEBF,while no statistical difference was found in MF or PF. P addition significantly decreased soil APA in MF and PF,but had no significant effect in MEBF. Combined N and P addition notably depressed soil APA in PF,but had no significant influence in MEBF and MF. Importantly,interactions between N and P additions were observed in MEBF. Based on our results,N deposition is expected to aggravate soil P deficiency in mature subtropical forest,while the N-induced P-limited state of these forests might be effectively relieved by P addition. In conclusion,the addition of P fertilizer may serve as an effective method for the sustainable future development of tropical and subtropical forests.