中国森林生态系统氮循环特征与生产力间的相互关系

为了更好地了解森林生态系统净初级生产力(NPP)与氮循环之间的关系，本文对中国主要森林生态系统类型中净初级生产力（NPP）、枯落物氮、植被年氮积累量和土壤氮矿化速率之间的关系进行了研究分析.结果表明，我国森林生态系统净初级生产力与枯落物氮、植被年氮积累量和土壤氮矿化速率之间均存在比较显著的相关关系.其中相关性最显著的是净初级生产力与氮矿化速率之间的相关关系(R²=0.74，n=37)，其次是净初级生产力与植被年氮积累量之间的相关关系(R²=0.60，n=37).  

Manipulation of quality and mineralization of tropical legume tree prunings by varying nitrogen supply

The effect of N supply on the quality of Calliandra calothyrsus and Gliricidia sepium prunings was studied in a glasshouse over a 7-month growing period. Increasing the concentration of N supplied from 0.625 to 10.0 mM NO₃-N resulted in increased N concentration but decreased polyphenol concentration, protein-binding capacity and C:N ratio of prunings from both species. Lignin concentration was not consistently altered by the N treatment. Mineralization of N from the prunings was measured over a 14-week period under controlled leaching and non-leaching conditions. The results indicated a strong interaction between legume species and concentration of N supply in their influence on N mineralization of the prunings applied to the soil. Differences in the %N mineralized were dictated by the quality of the prunings. The (lignin + polyphenol):N ratio was the pruning quality factor which could be used most consistently and accurately to predict N mineralization of the legume prunings incubated under leaching conditions, and the relationship was best described by a linear regression. Under non-leaching conditions, however, the protein-binding capacity appeared to be the most important parameter in determining the patterns of N release from the prunings studied. The relationship between the N mineralization rate constant and the protein-binding capacity was best described by a negative exponential function, y=0.078 exp(–0.0083x). The present study also indicated that the release of N from legume prunings containing a relatively high amount of polyphenol could be enhanced by governing the N availability conditions under which the plant is grown, for example whether or not it is actively fixing nitrogen. Estimates of pruning N mineralization after 14 weeks with the difference method averaged 6% (leaching conditions) and 22% (nonleaching conditions) more than with the ¹⁵N method for all legume prunings studied. The recovery of pruning by maize (4–38%) was well correlated with the % pruning N mineralized suggesting that incubation data closely reflect the pruning N value for a given catch crop under non-leaching conditions.  

湖南省4种森林群落土壤氮的矿化作用

2007年7月,用树脂芯原位测定土壤无机氮含量的方法,对湖南杉木、马尾松、樟树和枫香4种森林群落的土壤氮矿化进行了研究.研究结果表明,经过28d培养,4种森林群落土壤中NH+4-N含量分别下降了31.4%～50.5%,NO-3-N含量增加了8.2～17.3倍,氮矿化主要表现为硝化作用;氮矿化速率由大到小依次为樟树(0.05mg·kg-1·d-1)>马尾松(0.04 mg·kg-1·d-1)>枫香(-0.12 mg·kg-1·d-1)>杉木(-0.15 mg·kg-1·d-1).在4个森林群落的土壤中,NH+4-N是无机氮的主要存在形式,表现为在杉木群落中占78.42%、在马尾松中占79.17%、在樟树中占71.14%和枫香中占79.22%,而且NH+4-N的变化可以解释氮矿化量变化的96.1%～98.8%.土壤氮矿化速率与0～15 cm土壤的C/N、pH值呈显著性正相关,但与凋落物量和0～30 cm 土壤中细根生物量相关性不显著.  

A simple model for estimating the contribution of nitrogen mineralization to the nitrogen supply of crops from a stabilized pool of soil organic matter and recent organic input

A simple model was developed to estimate the contribution of nitrogen (N) mineralization to the N supply of crops. In this model the soil organic matter is divided into active and passive pools. Annual soil mineralization of N is derived from the active pool. The active pool comprises stabilized and labile soil organic N. The stabilized N is built up from accumulated inputs of fresh organic N during a crop rotation but the labile N is a fraction of total N added, which mineralizes faster than the stabilized N. The passive pool is considered to have no participation in the mineralization process. Mineralization rates of labile and stabilized soil organic N from different crop residues decomposing in soil were derived from the literature and were described by the first-order rate equation dN/dt =-K*N, where N is the mineralizable organic N from crop residues andK is a constant. The data were groupedK ₁ by short-term (0–1 year) andK ₂ by long-term (0–10 years) incubation. Because the range of variation inK ₂ was smaller than inK ₁ we felt justified in using an average value to derive N mineralization from the stabilized pool. The use of a constant rate ofK ₁ was avoided so net N mineralization during the first year after addition is derived directly from the labile N in the crop residues. The model was applied to four Chilean agro-ecosystems, using daily averages of soil temperature and moisture. The N losses by leaching were also calculated. The N mineralization varied between 30 and 130 kg N ha^–1 yr^–1 depending on organic N inputs. Nitrogen losses by leaching in a poorly structured soil were estimated to be about 10% of total N mineralized. The model could explain the large differences in N- mineralization as measured by the potential N mineralization at the four sites studied. However, when grassland was present in the crop rotation, the model underestimated the results obtained from potential mineralization.  

哀牢山木果柯林及退化植被下土壤氮素矿化和硝化作用(英文)

采用封顶埋管法,我们于11月对21至次年4月15日,分3个培养期共165天(包括干季初期、中期和末期),对哀牢山原生本果柯林(Lithocarpus xylocarpus forest)、栎类次生林(sccondary oak forest)和人工茶叶地(tea planation)三种群落类型的土壤氮素矿化和硝化作用进行了研究。结果表明:在3个培养期中,不同群落下土壤的氮素矿化和硝化作用都具有明显差异;而且它们均具有明显的干季动态,但变化趋势不尽相同。净氨化速率远高于净硝化速率,后者约为前者的0.5％～10％。结果表明,培养期、群落类型和样方诸因子对净氮矿化速率和净硝化速率的影响均存在不同程度的交互作用。人为干扰能导致氮素矿化和硝化速率等生态系统过程的变化,我们的研究结果为此提供了证据支持。与木果柯原始林相比,茶地和次生林的氮素转化过程更多地受物理因素的控制(如温度和水分)。这意味着哀牢山地区的木果柯原始林的保护应该受到重视。  

不同土地利用类型对丹江口库区土壤氮矿化的影响

 氮(N)素是陆地生态系统净初级生产力的重要限制因子, 土地利用类型的变化对生态系统氮循环过程有着重要的影响。采用PVC顶盖埋管原位培养的方法, 对丹江口库区清塘河流域相邻的侧柏(Platycladus orientalis)人工林、人工种植灌木林地和农田3种土地利用类型的氮素矿化和硝化作用进行了研究。结果表明, 侧柏人工林、灌木林地和农田的NH₄⁺-N浓度(mg·kg^–1)依次为1.33 ± 0.20、1.67 ± 0.17和1.62 ± 0.13, 不同土地利用类型间的NH₄⁺-N浓度无显著性差异; 而3种土地利用类型下土壤NO₃^–-N浓度(mg·kg^–1)差异显著, 农田NO₃^–-N浓度(9.00 ± 0.73)显著高于侧柏人工林(1.27 ± 0.18)和灌木林地(3.51 ±0.11)。NO₃^–-N在灌木林地和农田中分别占土壤无机氮库的67.8%和84.8%, 是土壤无机氮库的主要存在形式; 而侧柏人工林中NO₃^–-N和NH₄⁺-N浓度则基本相等。土壤硝化速率(mg·kg^–1·30 d^–1)从农田(7.13 ± 2.19)、灌木林地(2.56 ± 1.07)到侧柏人工林(0.85± 0.10)显著性降低。侧柏人工林、灌木林地和农田的矿化速率(mg·kg^–1·30 d^–1)依次为0.98 ± 0.12、2.52 ± 1.25和6.58 ± 2.29。矿化速率和硝化速率显著正相关, 但是矿化速率在不同的土地利用类型间差异不显著。培养过程中灌木林地和农田NH₄⁺-N的消耗大于积累, 氨化速率为负值, 导致灌木林地和农田矿化速率小于硝化速率。氮素的矿化和硝化作用受土壤含水量和土壤温度的影响, 并对土壤含水量更为敏感。土壤C:N与土壤矿化和硝化速率显著负相关。研究结果表明: 土地利用类型的变化会改变土壤微环境和土壤C:N, 进而会影响到土壤氮循环过程。  

土壤水分和氮添加对华北平原高产农田有机碳矿化的影响

通过105 d的恒温(25℃)控湿室内培养方法,探讨了华北平原高产粮田土壤有机碳矿化特征以及水分和有机、无机氮输入对其影响。试验设4个肥料添加水平和4个水分梯度,分别为对照(S0)、仅添加无机氮(尿素)(S1)、无机氮和有机氮(鸡粪)配施(S2)以及仅添加有机氮(S3)和25%(田间持水量;M0)、50%(M1)、75%(M2)和100%(M3)共16个处理,每处理3次重复。结果表明,各处理有机碳矿化速率均在培养后1 d达第1高峰,之后直线下降,培养7 d时下降幅度达57.2%—75.0%,培养20—30 d时出现第2高峰。有机碳累积矿化量有208.8—1161 mg/kg,主要集中在前30 d,可占整个培养期的59.1%—69.9%,105 d的净矿化率为0.07%—2.01%。根据双指数方程模拟结果,研究了土壤潜在矿化碳库(C1+C2),其中活性碳库(C1)和惰性碳库(C2)分别为53.0—135.1 mg/kg和156.9—1069 mg/kg,潜在矿化率为1.75%—9.66%。土壤含水量显著影响有机碳矿化,且与潜在矿化碳库呈二次函数关系(P0.05)。田间持水量25%—100%范围内,随着土壤含水量的升高,有机碳矿化速率呈增加趋势,但增幅降低,其中M2(田间持水量75%)的有机碳净矿化率最高。有机碳矿化量与土壤微生物碳和矿质氮含量呈线性正相关(P0.05),保持氮水平(200 kg N/hm2)相同,有机氮(鸡粪)和无机氮(尿素)均显著促进土壤有机碳矿化,但两者间差异不显著(P0.05),且有机氮和无机氮对有机碳矿化的影响均与土壤含水量有显著交互作用(P0.05)。  

放牧对若尔盖高寒草甸土壤氮矿化及其温度敏感性的影响

过度放牧和气候暖干化是若尔盖高寒草甸面临的严峻生态问题,它对土壤氮矿化过程的影响将在某种程度上决定高寒草甸生态系统的氮素利用状况。基于野外放牧实验,(禁牧(CK)、轻度放牧(L)、中度放牧(M)、重度放牧(H)),通过室内培养方法(5、10、15、20、25℃),探讨了不同放牧强度对若尔盖高寒草甸土壤氮矿化及其温度敏感性的影响。实验结果表明:放牧增加了土壤硝化速率和净氮矿化速率,其整体趋势为LMHCK。培养温度较低时(5—10℃),温度升高对硝化和净氮矿化速率无显著影响,而培养温度较高时(15—25℃),温度升高显著增加了硝化和净氮矿化速率。土壤硝态氮和无机氮积累量随培养时间增长显著增加,而铵态氮无显著增长。此外,放牧显著提高了土壤氮矿化的温度敏感性,重度放牧样地的土壤具有最高的氮矿化温度敏感性(Q10=2.72)。上述结果预示着在未来温度升高情景下,重度放牧将使土壤氮矿化速率的增速更快,短期内将通过提高氮的可利用性促进植物生长,但长远而言可能加速土壤氮素流失,从而对植物生长和高寒草甸生态系统结构与功能造成负反馈效应。  

硝化抑制剂DCD、 DMPP对褐土氮总矿化速率和硝化速率的影响

采用15N库稀释-原位培养法研究了硝化抑制剂DCD、DMPP对华北盐碱性褐土氮总矿化速率和硝化速率的影响.试验在山西省运城市种植玉米的盐碱性土壤上进行,设单施尿素、尿素+DCD、尿素+DMPP 3个处理.结果表明:施肥后2周,DCD、DMPP分别使氮总矿化速率和氮总硝化速率减少了25.5％、7.3％和60.3％、59.1％,DCD对氮总矿化速率的影响显著高于DMPP,两者对氮总硝化速率的影响无显著差异;而在施肥后7周,不同硝化抑制剂对氮总硝化速率的影响存在差异.施肥后2周,3个处理的土壤氮总矿化速率和硝化速率分别是施肥前的7.2 ～10.0倍和5.5 ～21.5倍;NH4+和NO3-消耗速率分别是施肥前的9.1 ～12.2倍和5.1 ～8.4倍,这是由氮肥对土壤的激发效应所致.硝化抑制剂使氮肥更多地以NH4+形式保持在土壤中,减少了NO3-的积累.土壤氮总矿化速率和总硝化速率受硝化抑制剂的抑制是N2O减排的主要原因.  

Annual nitrogen budget of a temperate coastal barrier salt-marsh system along a productivity gradient at low and high marsh elevation

An annual nitrogen budget was established for a temperate back barrier salt-marsh system along a productivity gradient at low and high marsh elevation. We measured plant biomass and nitrogen content in three plant compartments to deduce plant N-allocation patterns. Measurements were done along a successional sequence in a salt-marsh system. In addition, N-mineralization, wet and dry atmospheric N-deposition and sediment N-deposition were measured.

Plant-species dominance changed along the successional sequence. In early stages, Elymus farctus and Spergularia media formed a large part of total plant biomass. Festuca rubra and Puccinellia maritima were dominant at intermediate stages, whereas Elymus pycnanthus and Limonium vulgare were dominant at late stages of succession. Shoot biomass was highest in June, whereas litter biomass was highest in September and December. Root biomass formed by far the largest fraction of total plant biomass, especially at a low-marsh elevation.

Wet deposition of nitrate and ammonium was 1.7 g N m⁻² yr⁻¹, whereas throughfall deposition (dry and wet deposition) amounted to 2.1–3.6 g N m⁻² yr⁻¹, and was positively related to the height of an artificial plant canopy. Sediment organic nitrogen deposition rate was 0.3–5.4 g N m⁻² yr⁻¹, and negatively related to marsh elevation. Nitrogen mineralization rate increased from 2.5–2.8 g N m⁻² yr⁻¹ in young marshes towards 8.0–12.7 g N m⁻² yr⁻¹ at older marshes, depending on marsh elevation.

At a low-marsh elevation, plant N-availability depended equally on tidal N, atmospheric N and mineralized N, especially in young marshes, whereas the decomposition pathway became more important in older marshes. Tidal N contributed most to ecoystem N-accumulation rate at early successional stages, whereas atmospheric N was more important at later stages. Tidal influence was low at high-marsh elevation sites. Here, atmospheric deposition was the dominant exogenous nitrogen source both in young and old marshes.