生态学报  2015, Vol. 35 Issue (20): 6703-6710

文章信息

郑棉海, 黄娟, 陈浩, 王晖, 莫江明
ZHENG Mianhai, HUANG Juan, CHEN Hao, WANG Hui, MO Jiangming
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
生态学报, 2015, 35(20): 6703-6710
Acta Ecologica Sinica, 2015, 35(20): 6703-6710
http://dx.doi.org/10.5846/stxb201405120970

文章历史

收稿日期:2014-05-12
网络出版日期:2014-12-18
氮、磷添加对不同林型土壤磷酸酶活性的影响
郑棉海1, 3, 黄娟1, 陈浩1, 3, 王晖2, 莫江明1     
1. 中国科学院华南植物园, 中国科学院退化生态系统植被恢复与管理重点实验室, 广州 510650;
2. 中国林业科学研究院森林生态环境与保护研究所, 国家林业局森林生态环境重点实验室, 北京 100091;
3. 中国科学院大学, 北京 100039
摘要: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-2 a-1)、加磷(150 kg P hm-2 a-1)以及N和P同时添加(150 kg N hm-2 a-1+150 kg P hm-2 a-1)4种不同处理。结果表明,季风林土壤APA((15.83±2.46) μmol g-1 h-1)显著高于混交林((10.71±0.78) μmol g-1 h-1)和马尾松林((9.12±0.38) μmol g-1 h-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。
关键词酸性磷酸酶活性    氮沉降    氮添加    磷添加    磷限制    鼎湖山    
Effects of nitrogen and phosphorus addition on soil phosphatase activity in different forest types
ZHENG Mianhai1, 3, HUANG Juan1, CHEN Hao1, 3, WANG Hui2, MO Jiangming1     
1. Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China;
2. Key Laboratory of Forest Ecology and Environment, China's State Forestry Administration, Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing 100091, China;
3. University of Chinese Academy of Sciences, Beijing 100039, China
Abstract: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-2 a-1), P addition (150 kg P hm-2 a-1), and combined N and P addition (150 kg N hm-2 a-1 plus 150 kg P hm-2 a-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 NaH2PO4 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-1 h-1) than that in MF ((10.71±0.78) μmol g-1 h-1) or PF ((9.12±0.38) μmol g-1 h-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.
Key words: acid phosphatase activity    nitrogen deposition    nitrogen addition    phosphorus addition    phosphorus limitation    Dinghushan Mountain    

磷(P)是自然界中的基本矿质元素,它不仅参与生物细胞膜的合成、酶的活化以及信号的转导[1],同时也是构成绝大多数生物能源物质(ATP)的重要成分[2]。然而,P的缺乏导致许多森林植物和土壤生物的生长受到限制。尤其在热带森林中,长期的风化淋溶和生物吸收使土壤P的含量逐渐减少,所以热带成熟林生产力普遍受到P的限制[3, 4]。土壤磷酸酶在土壤P的循环中起重要的作用,即它可以将土壤中的复杂有机P水解成可被生物直接吸收的无机P,从而缓解了土壤P的限制[5]。因此,土壤磷酸酶活性的高低直接反映了土壤P的基本状况。

有研究认为,人类活动引起大气氮(N)沉降的增加将会加剧土壤P的限制,进而改变土壤磷酸酶的活性[6, 7, 8]。据统计,目前全球多数地区的N沉降速率已经超过10 kg N hm-2 a-1[9],而我国N沉降以每年0.41 kg/hm2的速率增加,仅在2000年的记录就达到了21.1 kg N hm-2 a-1[10]。长期N沉降对森林植物和土壤生物的生长造成危害[11],尤其是N沉降引起的土壤P限制将会进一步抑制森林生物的生长。多数研究表明,长期N沉降或施加N肥提高了温带森林土壤的磷酸酶活性[12, 13, 14],但目前关于N沉降影响热带或亚热带森林土壤磷酸酶活性的报道很少。前期,在亚热带森林(鼎湖山)的研究已经发现,长期N沉降可能引起土壤P的限制并提高了土壤的磷酸酶活性[15],然而这种限制作用是否可以通过施加P肥得到缓解需要进一步的研究。

鼎湖山处于南亚热带地区,并且长期受到大气N沉降的影响。据估计,2004—2005年该地区大气中的无机氮和有机氮输入分别达到32—34 kg N hm-2 a-1和18 kg N hm-2 a-1[16]。此外,鼎湖山土壤呈酸性,因此通过测定土壤酸性磷酸单酯酶活性(Acid Phosphomonoesterase Activity,APA)可以直接了解土壤P的状况。本研究的目的是通过原位的N、P添加试验,研究N沉降对亚热带森林土壤APA的影响,同时探索P素输入是否可以缓解N沉降对森林土壤P的限制,进而为N沉降不断增加背景下的亚热带森林管理提供理论依据。

1 材料和方法 1.1 样地基本概况

鼎湖山自然保护区位于广东省中部(112°30′—112°33′E,23°09′—23°11′N),占地面积约1200 hm2。该地属亚热带季风湿润型气候,年降水量为1927 mm,其中75% 分布在3月至8月,而12月至2月仅占6%;年平均气温为21 ℃,最冷月(1月)和最热月(7月)气温分别为12.6 ℃和 28.0 ℃[17]

该保护区主要包括3种典型的森林类型,即马尾松人工林(Pinus massoniana Forest,简称马尾松林(PF))、针叶阔叶混交林(Mixed Pine and Broadleaf Forest,简称混交林(MF))和季风常绿阔叶林(Monsoon Evergreen Broadleaf Forest,简称季风林(MEBF))。马尾松林由人工种植于1930年,覆盖面积占保护区面积约20%,其主要植被为马尾松(Pinus massoniana)[18]。混交林是由人工种植的马尾松林被一些阔叶树种入侵而形成的针叶、阔叶混交树林,其占地面积约50%,主要植被为马尾松、荷木(Schima superba)和中华锥(Castanopsis chinensis)等[18]。季风林占保护区面积20%,其主要树种为中华锥、荷木、黄果厚壳桂(Cryptocarya concinna)和中华楠(Machilus chinensis)等[19]。马尾松林和混交林分别在1930—1998年和1930—1956年受到人类活动的干扰(如收割地表植被和凋落物等),而季风林则受到长期的保护[18, 20]。3种森林类型的土壤基本概况见表1

表 1 2013年鼎湖山3种森林类型的土壤基本概况 Table 1 Soil characteristics of three forest types at Dinghushan Mountain in 2013
土壤基本指标Soil characteristics 森林类型 Forest types
季风林 MEBF 混交林 MF 马尾松林 PF
土壤类型Soil type 赤红壤 赤红壤 赤红壤
土壤有机碳SOC/%) 3.96 (0.74) a 2.00 (0.53) b 2.39 (0.41) b
铵态氮NH + 4/(mg/kg) 19.43 (2.07) a 17.63 (1.74) ab 13.88 (1.00) b
硝态氮NO - 3/(mg/kg) 13.28 (0.60) a 3.15 (0.43) c 7.05 (1.24) b
全氮 TN/(g/kg) 2.48 (0.22) a 1.01 (0.06) b 1.24 (0.10) b
全磷 TP/(g/kg) 0.20 (0.01) 0.21 (0.01) 0.17 (0.02)
有效磷 AP/(mg/kg) 3.77 (0.33) a 1.63 (0.52) b 1.98 (0.25) b
全磷/全氮TP/ TN 0.10 (0.01) a 0.15 (0.10) b 0.14 (0.11) b
pH(H 2O) 3.92 (0.05) a 4.21 (0.02) c 4.05 (0.03) b
酸性磷酸酶活性APA 15.83 (2.46) a 10.71 (0.78) b 9.12 (0.38) b
APA:酸性磷酸酶活性acid phosphatase activity; MEBF:季风林monsoon evergreen broadleaf forest; MF:混交林mixed pine and broadleaf forest; PF:马尾松林 Pinus massoniana forest; SOC:土壤有机碳soil organic carbon; TN:全氮total nitrogen; TP:全磷total phosphorus; AP:有效磷available phosphorus; 结果表示为平均值(标准误); 不同字母表示林型之间的差异显著( P < 0.05)
1.2 样地设计

2007年,在鼎湖山季风林、混交林和马尾松林分别建立了20个5 m×5 m的N、P添加样方。每个样方之间留有5m宽的缓冲带,以防样方之间的相互干扰。按照析因设计的原则,在3个林子中分别设置对照、加N(150 kg N hm-2a-1)、加P(150 kg P hm-2a-1)、N和P同时添加(150 kg N hm-2a-1 +150 kg P hm-2a-1)4个处理,每个处理各5个重复,且所有的样方均随机分布。本研究所用的样方大小及施肥量均参考国际上同类研究的处理方法[21]。2007年1月至2013年7月(6a),每两个月对3个林子的林下层进行一次施肥处理。方法是将每个样方所施加的N(NH4NO3)、P(NaH2PO4)或者N+P(NH4NO3+NaH2PO4)溶解于5 L水中,用背式喷雾器人工来回进行喷洒。对照样方喷洒等量的水,以减少因外加的水对森林生物地球化学循环造成影响。

1.3 采样和处理

2013年7月,在季风林、混交林和马尾松林土壤分别进行随机布点采样。在每个样方中用内径为2.5 cm的土钻随机钻取3钻土,取土深度为0—10 cm(前期研究认为鼎湖山森林10—20 cm土层APA对施肥的响应规律与0—10 cm基本一致[22])。将每个样方所钻的土混合均匀并挑出细根和石粒等杂物,通过2mm的土筛后分成两部分:一部分保存在4 ℃的冰箱,并于14d内完成对土壤APA的分析[23];另一部分风干后用于测定土壤的理化性质。

1.4 测定方法

土壤APA的测定参照Schneider 等的方法[24],并进行适当的改进。具体操作即称取1 g鲜土样品置于50 mL 锥形瓶中,加入4 mL 缓冲液(MUB)和1 mL 质量浓度为100 mmol/L 的对硝基酚底物(p-NPP)。盖上瓶盖后充分摇匀,并在37 ℃下培养1 h。待培养结束后,立即加入1 mL CaCl2(0.5 mol/L)和 4 mL NaOH(0.5 mol/L)以终止反应。反应结束后,所有样品均用90 mL蒸馏水进行稀释,并用滤膜(Whatman-42 filter)过滤去除杂质。滤液在400 nm波长下进行比色以测定吸光值。磷酸酶活性的单位用μmol g-1 h-1表示。

土壤理化性质的分析均采用中国生态系统研究网络观测与分析标准方法进行[25]。其中,土壤含水率(Moisture)的测定采用烘干法;土壤pH的测定采用土水比1:2.5的电位法;土壤有机碳(SOC)的测定采用重铬酸钾氧化-外加热法;土壤全氮(TN)采用半微量开氏法;土壤铵态氮(NH+4)、硝态氮(NO3-)的测定分别采用氯化钾浸提-靛酚蓝比色法和镀铜镉还原-重氮化偶合比色法;土壤有效氮(AN)以NH+4和NO3-的总和表示;土壤全磷(TP)的测定采用硫酸-高氯酸消煮-钼锑抗比色法;土壤有效磷(AP)的测定采用盐酸-氯化铵浸提-钼锑抗比色法。

1.5 统计分析

所有数据均用SPSS 21.0统计软件进行分析。采用单因素方差分析(one-way ANOVA)和最小显著极差法(LSR)比较不同森林类型土壤理化指标和APA的差异显著性。用两因素方差分析(two-way ANOVA)比较N、P及NP处理对土壤APA的影响。用Pearson相关系数评价土壤APA与土壤理化性质之间的相关性。如无特别说明,显著性水平均设为P < 0.05。

2 结果与分析 2.1 3种林型土壤APA与土壤理化性质的关系

3种森林类型(季风林、混交林和马尾松林)土壤APA分别为(15.83±2.46)、(10.71±0.78)、(9.12±0.38) μmol g-1 h-1。不同森林类型土壤APA之间的差异达到显著水平(P=0.021),季风林土壤APA显著高于混交林和马尾松林,但混交林与马尾松林土壤APA之间没有显著差异(表1)。

表2得知,季风林土壤APA与AP和pH之间均存在显著相关性,相关系数R分别为-0.451和-0.459。混交林土壤APA与AP、TP、AP/TP、TP/TN、AP/AN均有极显著相关性(P < 0.005),相关系数分别达到-0.756、-0.614、-0.767、-0.701和-0.745。马尾松林土壤APA与土壤理化性质之间的相关性与混交林相似,即与AP、TP、AP/TP、TP/TN、AP/AN均存在显著相关性,相关系数分别为:-0.524、-0.485、-0.537、-0.523和-0.523。

表 2 不同森林类型土壤APA与土壤理化性质的相关性 (n=20) Table 2 Correlations between soil APA and soil physiochemical properties in different forest types
含水率Moisture 有效磷AP 全磷TP 有机碳SOC 有效磷/全磷AP/TP 全磷/全氮TP/TN 有效磷/有效氮AP/AN pH
不同林型土壤酸性磷酸酶活性 季风林MEBF 0.170 -0.451 * -0.432 0.110 -0.294 -0.309 -0.428 -0.459 *
Soil APA in different forest types 混交林MF 0.140 -0.756 ** -0.614 ** 0.260 -0.767 ** -0.701 ** -0.745 ** 0.167
马尾松林PF 0.198 -0.524 * -0.485 * 0.127 -0.537 * -0.523 * -0.523 * 0.015
APA:酸性磷酸酶活性acid phosphatase activity; MEBF:季风林monsoon evergreen broadleaf forest; MF:混交林mixed pine and broadleaf forest; PF:马尾松林 Pinus massoniana forest; SOC:土壤有机碳soil organic carbon; TN:全氮total nitrogen; TP:全磷total phosphorus; AN:有效氮available nitrogen; AP:有效磷available phosphorus; * P < 0.05, ** P < 0.01
2.2 N、P添加对3种林型土壤APA的影响

图1可以看出,(1)N添加处理使季风林土壤APA显著提高了131.96% ;在混交林和马尾松林中,施加N肥分别使土壤APA降低了10.55% 和17.76%,但差异均不显著;(2)P添加处理分别使季风林、混交林和马尾松林土壤APA降低了32.41% 、56.12% 和41.67%,但只在混交林和马尾松林中的作用达到显著水平;(3)N和P同时添加使季风林土壤APA轻微增加了1.64%,使混交林和马尾松林土壤APA分别降低28.94% 和30.15%,其中对马尾松林的作用达到显著水平。两因素方差分析表明,N和P同时添加在季风林中存在交互作用(P=0.008),而在混交林和马尾松林中的作用均不显著。

图 1 氮、磷添加对不同森林类型土壤酸性磷酸酶活性的影响 Fig.1 Effect of N and P addition on soil APA in different forest types MEBF:季风林monsoon evergreen broadleaf forest;MF:混交林mixed pine and broadleaf forest;PF:马尾松林Pinus massoniana forest;APA:酸性磷酸酶活性acid phosphatase activity;C:对照control;N:施加N肥N addition;P:施加P肥P addition;NP:同时施加N肥和P肥combined N and P addition;同一林型中不同字母表示差异达到显著水平(P < 0.05); Different letters indicated significant differences (P < 0.05) among treatments in the same forest type;**表示交互作用达到极显著水平(P < 0.01); Significant level of interactive effect (P < 0.01);ns表示不存在交互作用(P > 0.05);no significant level of interactive effect (P > 0.05)
3 讨论 3.1 3种林型土壤APA的差异

鼎湖山森林土壤APA为9.23—15.83 μmol g-1 h-1,在热带森林的研究范围3.89—23.26 μmol g-1 h-1[26, 27, 28]。3种不同林型的土壤APA与土壤AP之间均存在显著负相关(表2),这与Allison等[29]的研究结果一致。原因可能是在土壤处于缺P的情况下,土壤微生物或植物根系可能通过生物固持和吸收等多种方式继续消耗土壤AP[30],而土壤AP的缺乏也将促进微生物或者植物释放出更多的磷酸酶来获取P[31, 32]。这表明鼎湖山森林土壤AP的缺乏间接提高了土壤APA。

本研究发现季风林土壤APA和AP均显著高于混交林和马尾松林(表1),该结果并不支持多数研究得出的结论,即土壤AP的缺乏可能会激发植物或者微生物分泌磷酸酶来获取P[30, 31, 32, 33]。先前的研究认为季风林较高的生物多样性是导致土壤有较高APA的主要原因[15]。此外,养分失衡和较高的年凋落物量也是导致季风林土壤有较高APA的可能原因。鼎湖山森林位于高N沉降的南亚热带地区,长期N素输入已使季风林土壤达到N饱和[16],进而增加了植物对P元素的需求[34]。本研究发现,季风林土壤TP/TN显著低于混交林和马尾松林(表1),这暗示了季风林土壤P已处于相对缺乏的状态。另外,相比混交林和马尾松林,季风林具有较高的年凋落物量[35]。大量的凋落物输入提供给土壤丰富的有机质和分解底物,进而增加了微生物对土壤胞外酶的分泌[36]

此外,混交林和马尾松林土壤APA还与土壤TP、AP/TP、TP/TN、AP/AN均呈显著负相关(表2)。这表明混交林和马尾松林土壤APA对土壤P含量变化的响应可能比季风林敏感。

3.2 N、P添加对3种林型土壤APA的影响 3.2.1 N添加对3种林型土壤APA的影响

在温带森林,Keeler等[14]通过长期的N肥添加试验,发现施加N肥(100 kg N hm-2 a-1)提高了松林、枫叶林和杨树林等林地的土壤APA,平均增量为13%;Saiya-Cork等[13]也发现,长期N肥添加(30 kg N hm-2 a-1)使温带阔叶林土壤APA增加了约17%。本研究同样发现,N添加显著提高了南亚热带季风林土壤APA,且增量高达131.96%。其原因可能是磷酸酶蛋白由C、N等基本元素构成,施加N肥在一定程度上促进了磷酸酶的合成[7];或者是因为长期施加N肥提高了土壤微生物对其他养分的需求(尤其是P元素),所以微生物通过分泌更多的磷酸酶来获取有效P[33]。但本研究季风林样地的土壤APA对施加N肥的响应(Δ=131.96%)远比其他多数研究样地(Δ=17%—26%)[6, 13, 14, 33]强烈,这可能与本样地施加了较高的N肥量(150 kg N hm-2a-1)有关。该结果表明,长期高N沉降可能会加剧季风林土壤P的限制[34]

然而,施加N肥没有显著提高混交林和马尾松林的土壤APA,这与Cusack等[37]和Weand等[38]的研究结果相似。有研究认为当土壤达到N饱和时,植物和微生物才开始分泌磷酸酶获取P素,所以土壤N的饱和度也会影响土壤APA[38]。Huang等[22]通过对鼎湖山森林进行长期的N沉降试验研究,认为由于混交林和马尾松林土壤长期处于N限制的状态,所以长期施加N肥(7a)没有使土壤从N限制向P限制转变。因此,本研究施加N肥没有引起混交林和马尾松林土壤APA的变化,很可能是因为这两个林分土壤仍处于N限制状态[39],以至于无法刺激植物和土壤微生物分泌更多的磷酸酶。

3.2.2 P添加对3种林型土壤APA的影响

Wang等[40]通过短期( <1a)单次P肥添加试验,发现施加P肥抑制了桉林土壤APA,其中高P处理(150 kg N hm-2)比低P处理(75 kg N hm-2)更加明显。Olander和Vitousek[27]通过对夏威夷群岛不同时间序列的土壤进行长期施肥研究(4—11a),结果表明施加P肥(100 kg N hm-2 a-1)均显著降低了各年龄段的土壤APA。本研究也发现P肥添加显著降低了混交林和马尾松林土壤APA。这可能是因为施加P肥直接抑制了土壤微生物或植物根系对磷酸酶的分泌[41],或者通过降低土壤微生物对P的需求,从而使微生物减少了用于合成磷酸酶的能量投入[27]。此外,长期施加P肥还可能导致土壤可利用性C和N的供应量不足,进而减少了用于合成磷酸酶蛋白的原材料[42]

但是,本研究发现施加P肥没有显著降低季风林土壤APA,这与许多研究的结论[7, 27, 42]不一致。已有多数研究认为长期外源P素的输入会降低微生物对P的需求,进而减少了微生物对磷酸酶的分泌并抑制土壤APA[27, 38]。然而在鼎湖山季风林样地中,长期施加P肥同时也显著提高了季风林土壤的微生物总量[35]。土壤微生物量的增加在一定程度上提高了微生物对P的总需求[43]。因此,施加P肥没有显著抑制季风林土壤APA,可能与季风林土壤微生物对P的总需求增加有关。

3.2.3 N和P同时添加对3种林型土壤APA的影响

N和P同时添加均降低了混交林和马尾松林土壤APA,其中在马尾松林中的抑制作用达到显著水平(图1),这与Olander和Vitousek[27]的研究结果一致。产生该现象的原因可能是本试验的NP处理无法满足这两种林型的植物和土壤微生物对N素的需求。本研究所采用的N、P施肥比例为1:1,远低于植物(28:1)[44]和土壤微生物(7:1)[43]的平均需求水平。因此,长期的NP处理可能导致植物或微生物的生长受到N的限制,从而降低了它们对土壤P的需求并抑制了磷酸酶的分泌。

然而,NP处理却轻微提高了季风林土壤APA,但不显著。这可能是因为季风林土壤长期处于N饱和状态[16],本研究进行为期6a的NP处理还不足以使该样地植物或土壤微生物出现N限制的情况。随着施肥时间的延长,NP处理是否将会抑制季风林土壤APA还有待于进一步研究。

此外,本研究还发现N和P同时添加对季风林土壤APA的影响存在交互作用(P=0.008)。这表明长期N沉降引起亚热带成熟林土壤P的限制可以通过施加P肥得到缓解。该结论为管理森林生态系统并维持其可持续发展提供了理论支持。

4 主要结论

(1)3种林型土壤APA与土壤AP之间均存在显著负相关,表明鼎湖山森林土壤AP的缺乏间接提高了土壤APA。

(2)施加N肥显著提高了季风林土壤APA,但对混交林和马尾松林的作用不显著,说明长期N沉降更容易加剧季风林土壤P的限制。

(3)施加P肥显著抑制了混交林和马尾松林土壤APA,但对季风林的影响不明显,说明施加P肥更容易降低这两个林型土壤生物对P的需求。

(4)N和P同时添加对季风林土壤APA的影响存在交互作用,这表明N沉降引起南亚热带成熟林土壤P的限制可以通过施加P肥得到缓解。

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