韓國(guó)赤楊純林中土壤水分條件和氮素動(dòng)態(tài)的關(guān)系

1、Soil moisture condition and soil nitrogen dynamics in a pure Alnus japonica forest in Korea韓國(guó)赤楊純林中土壤濕度狀況對(duì)土壤氮素動(dòng)態(tài)的影響 LANDSCAPE AND ECOLOGICAL ENGINEERING卷: 7期: 1頁(yè): 93-99 出版年: JAN 2011 赤楊（中國(guó)樹(shù)木分類學(xué)）又名日本榿木，樺木科榿木屬Abstract This study was conducted to examine the influences of soil-moisture conditions on soi

2、l nitrogen (N) dynamics, including in situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using the buried bag incubation method, ion exchange r

3、esin bag method, and acetylene block method, respectively. The annual net N mineralization rate (kg N ha1 year1) and annual N availability (mg N bag1) were 40.26 and 80.65 in the relatively dry site, 5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site, respectively. The annual net N

4、 mineralization rate and annual N availability in the dry site were significantly higher than those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual mean denitrification rate (kg N ha1 year1) in the dry, moist, and wet sites was 2.37

5、, 2.76, and 1.59, respectively. However, there was no significant difference among sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of

6、 proper drainage for poorly drained sites would increase soil N mineralization and N availability and consequently be useful to conserve and manage the A. japonica forest.這項(xiàng)研究是探討位于韓國(guó)首都首爾附近的赤楊純林中土壤水分條件對(duì)土壤氮（N）動(dòng)態(tài)的影響，包括原位土壤中N的礦化，有效性以及反硝化作用。分別采用埋袋培育法，離子交換樹(shù)脂袋法，乙炔阻塞法來(lái)測(cè)定土壤氮的礦化、有效性和反硝化作用。在相對(duì)干燥的地方，每年N凈礦化速率為40

7、.26kg N ha1 year1，有效N含量為80.65mg N bag1 ，在潮濕的地區(qū)，每年N凈礦化速率和有效N含量分別為-5.43kg N ha1 year1和45.39mg N bag1，在濕潤(rùn)地區(qū)，每年N凈礦化速率和有效N含量分別為7.09kg N ha1 year1和39.17mg N bag1。干燥地方，每年的凈氮礦化速率和有效氮含量明顯比潮濕和濕潤(rùn)地區(qū)高，而在潮濕地方和濕潤(rùn)地區(qū)沒(méi)有顯著差異。年平均反硝化速率在干燥，潮濕，濕潤(rùn)地區(qū)分別為2.37kg N ha1 year1，2.76kg N ha1 year1，1.59kg N ha1 year1。然而，在各個(gè)地區(qū)并沒(méi)有因?yàn)闃O度

8、的時(shí)空變化出現(xiàn)顯著性差異。我們的研究結(jié)果表明，赤楊純林中，土壤水分條件影響著原位氮礦化和樹(shù)脂袋中有效性氮的含量，在排水不良的地區(qū)，適當(dāng)排水會(huì)提高土壤氮素礦化速率和增加有效N含量，因此可以用來(lái)保護(hù)和管理赤楊林。Introduction 引言 Alnus spp. play an important role in the soil nitrogen (N)cycle. It can convert gaseous N2 in the atmosphere into ammonia in the soil through N-fixation for symbiosis with Frankia.

9、 Therefore, Alnus spp. can increase not only the soil N content but also the rate of the soil N cycle (Binkleyet al. 1992b). In particular, Alnus spp. accelerates the soil N turnover rate and increases the N availability (Binkley et al. 1992a, b; Hart et al. 1997). Alnus japonica (Thunb.) Steud is d

10、istributed widely in temperate Asia and is native to China, Japan, and Korea. It is known that the typical habitats of A. japonica are swamps and constantly or periodically flooded areas with poorly drained soils (Iwanaga and Yamamoto 2007). In Korea, A. japonica occurs as a single tree in the wetla

11、nds along rivers and streams (Kimet al. 2005), but the species is rarely found as a forest. 赤楊在土壤的N循環(huán)中起著重要的作用。在土壤中，赤楊在與弗蘭克氏菌共生情況下發(fā)生固氮效應(yīng)，將大氣中的氣態(tài)氮轉(zhuǎn)化成氨態(tài)。因此赤楊不僅增加了土壤氮含量，還提高了土壤氮循環(huán)的速率。特別的是，赤楊增加了氮的周轉(zhuǎn)率和可利用率。赤楊廣泛分布在亞洲溫帶地區(qū)，是中日韓的鄉(xiāng)土種。據(jù)了解，赤楊的典型生境為沼澤和土壤排水性差、時(shí)常遭遇洪水的地區(qū)。在韓國(guó)，赤楊獨(dú)棵地出現(xiàn)在在河畔溪邊的濕地，而罕見(jiàn)以森林形式呈現(xiàn)。 A pure A. jap

12、onica forest in Korea is designated as Ecological Landscape Preservation Area, and a long-term monitoring program is being conducted in the forest.However, studies on ecological characteristics of A.japonica are necessary to prepare forest management plans for protecting the forest. Interestingly, s

13、oil-moisture conditions in the A. japonica forest are different from those of common forests, and it is speculated that soil-moisture influences nutrient distribution and cycling in the forest.Therefore, it is important to examine the relationship between soil-moisture conditions and N dynamics, inc

14、luding N mineralization, N availability, and denitrification in the alder forest and to propose management practices for the forest. 一片赤楊純林在韓國(guó)被定為生態(tài)景觀保護(hù)區(qū)，林區(qū)里會(huì)實(shí)行長(zhǎng)期的觀測(cè)方案。為了給森林保護(hù)的管理計(jì)劃做準(zhǔn)備，對(duì)于赤楊的生態(tài)特征的研究是必須的。有趣的是，赤楊林中的土壤濕度情況同那些常見(jiàn)的森林不同。據(jù)推測(cè)，土壤濕度影響林內(nèi)的養(yǎng)分分配和循環(huán)。因此，找出土壤濕度情況與氮?jiǎng)討B(tài)（包括氮的礦化作用，氮的可利用率和反硝化作用）之間的關(guān)系的是很重要的，可以

15、為森林的水肥管理提供參考。 There are numerous studies on the N cycle of Alnus spp.(Binkley et al. 1992a, b; Hart et al. 1997; Vermes and Myrold 1992). However, information on the seasonal changes in soil N cycles in Alnus spp. is very limited (Struwe and Kjller 1990). Also, only a few studies focus on the relati

16、onship between soil-moisture conditions and soil N dynamics in Alnus spp. (Sexstone et al. 1988; Struwe and Kjller 1990). We hypothesized that there would be significant temporal variations in N mineralization, N availability, and denitrification, and we hypothesized that soil-moisture condition wou

17、ld increase these soil N dynamics in a pure A. japonica forest. The objectives of the study were to: (1) examine the seasonal pattern of N mineralization, N availability, and denitrification, (2) investigate relationships between soil moisture and N dynamics, and (3) suggest management approaches fo

18、r the long-term ecological conservation of a pure A. Japonica forest located in Heonilleung, Seoul, Korea. 關(guān)于赤楊的研究有很多，但關(guān)于赤楊種土壤氮循環(huán)季節(jié)變換的信息卻很有限。而且，很少有著重于赤楊土壤濕度情況和土壤氮?jiǎng)討B(tài)之間關(guān)系的研究。我們假設(shè)在氮的礦化作用、可利用率和反硝化作用有了顯著的時(shí)空變化，也可以假設(shè)在赤楊林中，土壤濕度情況能提高這些土壤氮?jiǎng)討B(tài)。這項(xiàng)研究的目標(biāo)如下：1. 尋找氮的礦化作用、可利用率和反硝化作用的季節(jié)性變化模式。2. 調(diào)查土壤濕度和氮?jiǎng)討B(tài)之間的關(guān)系。3. 為韓國(guó)首爾

19、獻(xiàn)仁陵地區(qū)的赤楊純林的長(zhǎng)期生態(tài)保護(hù)提出管理方法。Materials and methodsStudy siteThe study was conducted in a pure A. japonica forest at Heonilleung in Seoul, central Korea (37N, 127E). The Heonilleung is the royal tomb of the Joseon Dynasty located within the administrative district of Seoul City. The alder forest has been

20、designated and protected as the Ecological Landscape Preservation Area by laws since 2005. The pure A. japonica forest was naturally established, and the total area of the forest is about 2 ha. A small natural creek runs through the forest. The 40-year old forest has approximately 600 A. japonica tr

21、ees per hectare, and the mean DBH and height of A. japonica was 25.5 cm and 15 m, respectively. The mean annual temperature and precipitation in the area was 12.2C (25.4C in August and -2.5C in January) and 1344.3 mm, respectively (data available online at http:/www.kma.go.kr). 這項(xiàng)研究是在韓國(guó)中部，首爾Heonille

22、ung地區(qū)的一片赤楊林中進(jìn)行的，獻(xiàn)仁陵屬于首爾的管轄區(qū)域，是朝鮮王朝的皇家陵墓。從2005年開(kāi)始，在法律上，榿木林被選為生態(tài)景觀保護(hù)區(qū)進(jìn)行保護(hù)。這片野生榿木純林，面積大約為2公頃，一條小溪橫穿森林。這片樹(shù)齡40年的森林，密度約為每公頃600棵赤楊，平均胸徑（DBH）和平均樹(shù)高分別為25.5cm和15m。年均溫和年降雨量分別為12.2 0C（八月25.4度，一月-2.5度）和1344.3mm。 In accordance with the soil-moisture regimes, the pure A. japonica forest was divided into three sites

23、: relatively low soil-moisture condition (LMC), medium soil-moisture condition (MMC), and high soil-moisture condition (HMC). Whereas the LMC site was well drained, the MMC and HMC sites were poorly drained. The water table of the MMC and HMC sites was near the land surface and several ponds had for

24、med naturally. The understory vegetation at the LMC site was Viola verecunda, Oplismenus undulatifolius, and Parthenocissus tricuspidata. The surface of the MMC and HMC sites was covered with a high portion of hydrophytes: Persicaria thunbergii, Carex dispalata, Impatiens noli-tangere, and Impatiens

25、 textori. Three 10 m x 10 m plots were established in each site. 依據(jù)土壤濕度狀況，赤楊純林可被分為3種生境：相對(duì)低的土壤濕度情況（LMC），中等土壤濕度情況（MMC），高土壤濕度情況（HMC）。LMC地區(qū)排水良好，而MMC和HMC地區(qū)排水不暢，MMC和HMC地區(qū)的土壤水分情況接近自然土壤和一些天然池塘的土壤。土壤濕度低的區(qū)域林下植被為堇菜、求米草和爬山虎。在土壤濕度中等和濕度高的地區(qū)表面大部分是水生植物，如戟葉蓼、皺果薹草、水金鳳和野鳳仙花。在每個(gè)區(qū)域選擇三個(gè)10m x 10m的樣地。Soil sampling and anal

26、ysis 土壤采樣和分析Five soil samples were collected from each plot in the three sites on 5 May 2007 using soil cores (5 cm inner diameter by 15 cm deep). Soil temperature was measured using a copper constant thermometer (Digi-Sense, Type K thermocouple thermometer, Cole-Parmer, USA). The volumetric water c

27、ontent was determined using a portable measurement system with 12-cm probes (HydroSense, Campbell Scientific Inc., Australia). Soil texture was determined using the hydrometer. The water-filled (%, WFPS) and air-filled (%, AFPS) pore space was calculated. 2007年5月5號(hào)，在3種生境的每一塊地上取5份土樣，內(nèi)徑5cm、15cm深的土柱。測(cè)量

28、土壤溫度的儀器為美國(guó)Cole-Parmer出品的銅制恒定溫度計(jì)（數(shù)碼傳感，熱電偶）。體積含水量的測(cè)量是用帶有12cm探針的便攜測(cè)量系統(tǒng)（澳大利亞Campbell科技公司，水傳感）。土壤結(jié)構(gòu)由液體比重計(jì)測(cè)量，孔隙含水量和孔隙含氣量通過(guò)計(jì)算得到。 The following chemical analyses were made on soil samples: soil pH by a pH meter (model 420A, Orion, USA); total carbon (TC) and total nitrogen (TN) concentrations by an elementa

29、l analyzer (vario Macro CN analyzer, Elementar Analysestmeme GmbH, Germany); available phosphorous (P) concentration by a spectrophotometer (U-1100, Hitachi, Japan); cation exchange capacity (CEC) by ammonium acetate. 土壤樣品還有下列的化學(xué)分析：pH用pH計(jì)測(cè)；全碳（TC）和全氮（TN）濃聚物由元素分析器測(cè)；有效磷（P）由分光光度計(jì)（日本日立U-1100）測(cè)；陽(yáng)離子交換量（CEC

30、）通過(guò)醋酸銨測(cè)。Soil N mineralization and nitrification土壤氮礦化作用和硝化作用In situ soil N mineralization was measured using the buried bag incubation method. This method is widely used in field studies due to its sensitivity to the soil microclimate (Binkley and Hart 1989). Two soil cores were taken from five locat

31、ions of each plot to a depth of 15 cm. One core was placed in a gas permeable polyethylene bag, and replaced into its original hole and incubated. The other soil core was used for analysis; 15 g soil of each sample was dried to measure the gravimetric moisture content, and another 15 g soil was extr

32、acted with a 2 M KCl solution.The extract was analyzed for the inorganic N using a Lachat flow-injection autoanalyzer (QuikChem AE, Lachat Instrument, USA). 原位土壤氮礦化作用通過(guò)埋袋培育法測(cè)定。這種方法因?yàn)閷?duì)土壤微氣候的靈敏度高在田間研究被廣泛應(yīng)用。在每塊地的五個(gè)位置的15cm深處取兩個(gè)土柱。一個(gè)土柱放置在一個(gè)透氣的聚乙烯塑料袋內(nèi)，再移到它原先的坑中并培育。另一個(gè)土柱分析用，每份樣土的15g被弄干來(lái)測(cè)重含水量，另外15g土壤由2mol/L

33、 的KCl溶液浸提。浸提液通過(guò) Lachat流動(dòng)注射分析儀測(cè)定無(wú)機(jī)氮。 The soil samples were incubated for 45 days during the growing season, and for 60 days in autumn due to flooding. The winter soil samples were incubated for 115 days because soils were frozen. The net N mineralization rate was calculated as the difference in ammon

34、ium plus nitrate between the initial and incubated samples. The net nitrification rate was also calculated as the difference between the nitrate concentrations during the incubation period. 一般來(lái)說(shuō)，在生長(zhǎng)季節(jié)，土壤樣品培養(yǎng)45天，秋季，由于洪水的影響，需要培養(yǎng)60天。冬季，因?yàn)橥寥辣粌鼋Y(jié)，土壤樣品需要培養(yǎng)115天。用銨加硝酸鹽作為初始狀態(tài)和培養(yǎng)樣本之間的差異來(lái)計(jì)算凈氮礦化率。凈硝化率也能計(jì)算出在潛伏期的硝

35、酸鹽濃度之間的差異。N availability 有效NThe N availability was evaluated using the ion exchange resin bag method, which is widely used due to its sensitivity to changing field conditions and usefulness for examining spatial and temporal patterns of N availability (Binkley and Matson 1983). Five resin bags were

36、placed in each plot, and an individual resin bag was buried 5 cm below the surface of the mineral soil. The resin bags included 14 ml of anion resins (Sybron IONAC ASB-1P OH-, Sybron International, USA) and 14 ml of cation resins (Sybron IONAC C-251 H?) in separate compartments of a nylon stocking.

37、The resin bags were retrieved and replaced at the end of the incubation period. After incubation, the retrieved resin bags were air-dried and brushed to remove the adhering soil. The ammonium and nitrate attached to the resin were extracted in 100 ml of a 2 M potassium chloride (KCl) solution. The i

38、norganic N concentrations were determined using a Lachat flow-injection auto-analyzer. N有效性使用的離子交換樹(shù)脂袋法進(jìn)行評(píng)估，由于其隨環(huán)境變化的靈敏度高，以及有利于利用時(shí)空格局研究N的可利用率（賓克利與馬特森的1983），而被廣泛應(yīng)用。在每個(gè)小區(qū)放置五個(gè)樹(shù)脂袋，每個(gè)樹(shù)脂袋被埋在礦質(zhì)土壤表面5厘米以下的。樹(shù)脂袋包括14毫升陰離子樹(shù)脂和14毫升的陽(yáng)離子樹(shù)脂，用尼龍襪隔開(kāi)。在培養(yǎng)末期對(duì)樹(shù)脂袋進(jìn)行取回和替換。培養(yǎng)后，把取回的樹(shù)脂袋風(fēng)干和刷去除粘附在表面的土壤。用100毫升2 Mol/L氯化鉀（KCl）溶液提取樹(shù)脂袋

39、中得銨和硝酸鹽。用 Lachat流動(dòng)注射自動(dòng)分析儀測(cè)定無(wú)機(jī)氮的濃度。Denitrification 反硝化作用The denitrification rate was estimated using the acetylene block method with intact soil cores in the field (Moiser and Klemedtsson 1994). Soil samples were carefully taken using an improved soil core sampler that does not disturb the soil horiz

40、on (Hwang et al. 2001). Each soil core in the perforated polyvinyl chloride (PVC) was placed in an incubation chamber, and purified acetylene was injected to a final concentration of 10%. The headspace atmosphere in the incubation chamber was sampled after 24 h (Vermes and Myrold 1992). Gas samples

41、were stored in vacutainer tubes (Vacuette, Greiner Bio-One GmbH, Austria) for later analysis. Nitrogen dioxide (NO) was analyzed by gas chromatography (Model 5890, Hewlett Packard, USA) equipped with a 63Ni electron capture detector. The column and detector temperatures were 70 and 300C, respectivel

42、y. The denitrification rate was calculated from the N2O concentration in the headspace, corrected using the appropriate Bunsen coefficient according to temperature (Tiedje 1982). 使用乙炔阻塞法，在該領(lǐng)域內(nèi)用完整的（1994年Moiser和Klemedtsson提出）土樣來(lái)估計(jì)土壤脫氮率。土壤樣品使用改良土樣取樣器仔細(xì)地進(jìn)行取樣，確保不破壞土層結(jié)構(gòu)（2001年黃禹錫等人提出）。將每個(gè)土樣放入穿孔的聚氯乙烯化合物管中，每

43、個(gè)PVC管被放置在一個(gè)培養(yǎng)室，將純化的乙炔注入孔中，至濃度達(dá)到10%為止。24 h后，在培養(yǎng)室頂部的大氣中采樣，（1992年Vermes和Myrold 提出）。氣體樣品被存放在真空管，供以后進(jìn)行分析時(shí)使用。用63Ni電子捕獲檢測(cè)器（型號(hào)5890，惠普，美國(guó)），通過(guò)氣相色譜法分析二氧化氮（NO）。色譜柱和檢測(cè)器溫度分別為70和300C。從頂部收集的NO來(lái)計(jì)算反硝化速率，根據(jù)溫度使用適當(dāng)?shù)腂unsen 系數(shù)來(lái)進(jìn)行修正（Tiedje1982年）。Statistical analysis 統(tǒng)計(jì)分析The experimental design was a completely randomized p

44、lot with repeated measurements where the treatment was fixed. We examined differences in the soil physical and chemical properties and all N parameters among three sites by analysis of variance with PROC GLM of SAS 9.1 (SASInstitute Inc., USA). Correlation analysis (PROC CORR) was also used to estim

45、ate the linear relationships between N mineralization, N availability, denitrification, and soil-water content using the Pearson correlation coefficient. A p value0.05 was considered significant. 實(shí)驗(yàn)設(shè)計(jì)是在處理方法一致的地方完全隨機(jī)抽樣，進(jìn)行反復(fù)測(cè)量。我們用PROC SAS 9.1版的GLM（SASInstitut Inc., USA）的方差分析，研究了三個(gè)地點(diǎn)之間土壤物理和化學(xué)性質(zhì)以及所有N的參數(shù)

46、的差異。相關(guān)性分析使用Pearson相關(guān)系數(shù) （PROC CORR）來(lái)評(píng)估氮礦化、氮可用性、反硝化作用與土壤水含量之間的線性關(guān)系，當(dāng)P0.05被認(rèn)為差異顯著。ResultsSoil properties and microclimate 土壤成分和小氣候 Table 1 shows the soil physical and chemical properties of the three study sites. The soil bulk density was low at the HMC site because of high organic matter contents. The

47、 soil-moisture condition can be expressed as the WFPS using the bulk density and volumetric soil-water content (Melling et al. 2007). The AFPS was calculated from the difference between the total pore space and WFPS. There was a significant difference in WFPS and AFPS between sites. The WFPS was hig

48、hest at the HMC site and lowest at the LMC site, whereas the AFPS was the opposite. Total C and N concentrations, available P and CEC were highest at the HMC site, possibly because of high organic matter contents. 從表一可以看出三個(gè)研究區(qū)域土壤的物理結(jié)構(gòu)和化學(xué)成分。在土壤濕度高的地方，因?yàn)橛袡C(jī)物含量高，所以土壤密度較低。土壤水分狀況可以用孔隙水含量來(lái)表示，通過(guò)土壤的密度和體積水含量來(lái)

49、計(jì)算。土壤空隙含氣率通過(guò)總的微孔數(shù)量和孔隙含水量來(lái)計(jì)算。在不同區(qū)域間孔隙含水量和含氣量有顯著差異，孔隙含水量在濕度高的地區(qū)最高，在濕度低的地區(qū)最低，而孔隙含氣量正好相反。在濕度高的區(qū)域，總碳量、含氮化合物、有效P和陽(yáng)離子交換量最高大，這可能和高濕度地區(qū)有機(jī)物含量高有關(guān)。 Figure 1 shows the seasonal changes in soil temperature and moisture. The mean soil temperature (0C) for the LMC, MMC, and HMC sites was 14.51, 13.38, and 12.78, re

50、spectively. There was a significant difference in the mean soil temperature among sites; it was highest at the LMC site and lowest at the HMC site. The mean soil temperature showed a seasonal pattern; it was highest in August and lowest in March. The mean volumetric soil-water content (%) for the LM

51、C, MMC, and HMC sites was 20.99, 55.93, and 74.65, respectively. There was a significant difference among the sites. The mean volumetric soil-water content was lowest at the LMC site and highest at the HMC site. The mean volumetric soil-water content also showed a seasonal pattern; it was highest in

52、 November and lowest in June. 圖一表示的是土壤溫度和水分的季節(jié)性變化。低濕度地區(qū)、中等濕度地區(qū)和高濕度地區(qū)的土壤平均溫度（0C）分別為14.51、13.38和12.78。濕度不同的地區(qū)間土壤平均溫度存在顯著差異，其中低濕度地區(qū)土壤平均溫度最高，而高濕度地區(qū)的土壤平均溫度最低。土壤平均溫度呈現(xiàn)季節(jié)性變化趨勢(shì)，最高溫出現(xiàn)在八月，最低溫出現(xiàn)在三月。低濕度地區(qū)、中等濕度地區(qū)和高濕度地區(qū)的土壤體積含水量平均值分別為20.99、55.93和74.65。不同濕度下的土壤體積含水量之間也存在著顯著差異，平均體積含水量最低的是低濕度地區(qū)，最高的是高濕度地區(qū)。平均體積含水量也存在季節(jié)

53、性變化，含水量最高值出現(xiàn)在十二月，最低值出現(xiàn)在六月。Soil N mineralization and nitrification 土壤N的礦化作用和硝化作用 Figures 2 and 3 show the seasonal patterns of in situ soil N mineralization and nitrification. The net N mineralization rate (mg N kg-1 day-1) for the LMC, MMC, and HMC sites was 0.0912, -0.0050 and -0.0026, respectively

54、. It was significantly higher at the LMC site than at the MMC and HMC sites. However, there was no significant difference between the MMC and HMC sites. The annual net N mineralization rate (kg N ha-1 year-1) was 40.26 for LMC, -5.43 for MMC, and 7.09 for HMC, respectively, and was significantly hig

55、her at the LMC site than at the MMC and HMC sites. The net N mineralization rate was highest in the late summer and early autumn (from 3 August through 29 September 2007) and lowest in the spring (from 20 March through 5 May 2008). The net nitrification rate (mg N kg-1 day-1) for the LMC, MMC, and H

56、MC sites was 0.1060, 0.0146, and 0.0058, respectively. It was also significantly higher at the LMC site than at the MMC and HMC sites. There was no significant difference in net nitrification between the MMC and HMC sites. The net nitrification rate also showed a similar seasonal pattern of net N mi

57、neralization. 圖二和圖三表述了原位土壤氮素的礦化作用和硝化作用的季節(jié)性變化模式。低濕度地區(qū)、中等濕度地區(qū)和高濕度地區(qū)的凈氮素礦化率(mg N kg-1 day-1) 分別為0.0912, -0.0050 和 -0.0026。低濕度地區(qū)的礦化率明顯高于中等濕度地區(qū)和高濕度地區(qū)，但是在中等濕度地區(qū)和高濕度地區(qū)之間，礦化率不存在顯著差異。年均氮素凈礦化率(kg N ha-1 year-1) 在低濕度地區(qū)、中等濕度地區(qū)和高濕度地區(qū)分別為 40.26 、-5.43和7.09。很明顯地看出低濕度地區(qū)的年均氮素凈礦化率高于高濕地地區(qū)。年均氮素凈礦化率最高值出現(xiàn)在夏末秋初（2007年8月3日到9

58、月29日），最低值出現(xiàn)在春季（2008年3月20日到5月5日）。 低濕度地區(qū)、中等濕度地區(qū)和高濕地地區(qū)的凈硝化率(mg N kg-1 day-1) 分別為 0.1060、 0.0146和0.0058，不難發(fā)現(xiàn)，低濕度地區(qū)的凈硝化率顯著高于中等濕度地區(qū)和高濕度地區(qū)。在中等濕度地區(qū)和高濕度地區(qū)沒(méi)有顯著差異，凈硝化率的季節(jié)變化模式與凈氮素礦化率相似。 We found a significantly positive linear correlation between the annual net N mineralization rate and annual net nitrification

59、 rate (R2 = 0.78, p0.01) (Fig. 4a). There was a negative correlation between WFPS and the annual net N mineralization rate (R2 = 0.56, p0.01) and net nitrification rate (R2 = 0.83, p0.01) (figures not shown). 我們發(fā)現(xiàn)年均凈氮素礦化率和年均凈硝化率之間存在確定的線性正相關(guān)（(R2 = 0.78, p0.01) ），如圖四所示。在土壤孔隙含水量和年均凈氮素礦化率之間存在負(fù)相關(guān)（R2 = 0.56, p0.01），土壤孔隙率和凈硝化率之間也存在負(fù)相關(guān)(R2 = 0.83, p0.01)，沒(méi)有在圖中表示出來(lái)。N availab