凋落物分解模型研究进展

森林凋落物分解模型的研究经历了一个由简单到复杂的过程,从最初的对凋落物失重率的简单描述到广为人知的单指数分解模型,随着对凋落物分解研究的深入,双指数模型、三指数模型也应运而生。国外大部分的研究都集中于欧洲温带森林、北方森林。国内的研究也正在经历一个应用、改进和开发的过程,目前还主要处在应用和改进的阶段。为了准确预测森林生态系统尤其是在全球气候变化背景下C等元素的动态,急需建立适合于我国各类森林生态系统凋落物分解模型。本文回顾了各个历史时期出现的重要模型并进行了简单的分类和评述。     

Nutrient dynamics of foliar litter in reciprocal decomposition in tropical and subtropical forests

In order to explore the release of nutrients and the effects of global warming on the decomposition rate of forest litter, an experiment is designed to reciprocally decompose forest foliar litter in two sites across climatic zones: Mt. Jianfengling in Hainan Province in the tropics and Mt. Dinghushan in Guangdong Province in the subtropics. The two sites have similar altitudes, soil types, annual mean rainfall and seasonality of dry and wet. The main difference between these two sites is the annual mean temperature with the difference of 3.7°C. Foliar litters of 10 native dominant tree species have been collected respectively from the two sites and divided into single-species litter and mixed litter. They are decomposed reciprocally in the two sites. The results indicate that litter decomposes in the tropical site 1.36–3.06 times more rapidly than in the subtropical site. Apparent Q ₁₀, calculated on the basis of the temperature difference between the two sites, ranges from 3.7 to 7.5. The return amount of N, P and C will increase by 32.42, 1.033 and 741.1 kg/hm², respectively in Mt. Dinghushan in the first year’s litter decomposition under the prevailing temperature condition. Only in Mt. Dinghushan is the correlation between decomposition rate constant and initial litter quality high and significant in the ratio of lignin to N, lignin, the ratio of lignin to P, HLQ and C. This is not the case at Mt. Jianfengling. __________ Translated from Journal of Beijing Forestry University, 2005, 27(1): 24–32 [译自: 北京林业大学学报, 2005, 27(1): 24–32]     

Nutrient dynamics in decomposing forest leaf litter: A comparison of field and laboratory microcosm approach

The effect of incubation setting (greenhouse: GM and field: FM microcosms) on nutrient element dynamics during decomposition of Japanese Konara Oak (Quercus serrata Murray) and Japanese Red Pine (Pinus densiflora Sieb et. Zucc.) litter was studied. Results show a disparity in relative concentrations and amounts of the same type of litter when incubated in different settings. The nutrient mobility, however, showed similar trend. The order of elemental mobility after 12 months forQuercus in FM was: P>K>Mg>C>Mn>Ca>N>Al>Cu>Zn>Fe; for GM it was: P>K>Mn>Mg>C>Ca>N>Al>Cu>Zn>Fe. ForPinus, elemental mobility in FM was: K>Mg>C>Mn>N>P>Cu>Zn>Al>Fe; while for GM was: K>C>Mn>N>Ca>Mg>Cu>Al>P>Zn>Fe. The elements inQuercus that lost their mass were P, K, Mg, Ca, Mn and C while those that increased were N, Cu, Al, Fe and Zn. ForPinus, K and Mg lost their nutrient mass while the other elements had increased or fluctuated but tended to increase. Three patterns of nutrient mobility were observed: first, the concentration increased while the nutrient mass (absolute amount) decreased; second, both concentration and nutrient mass increased; third, the concentration and nutrient mass decreased. On tracing nutrient mobility over time, the linear regression of nutrient element mass and litter element mass was preferred over the carbon to element ratios because the former gave a clearer picture of the relationship. On the over-all, the pattern of nutrient changes in greenhouse microcosms were different from those observed in the field, hence nutrient cycling studies using greenhouse-microcosm approach alone may give inaccurate results. This study was conducted while the senior author holds a Japanese government scholarship (MONBUSHO Grant No. 920205).     

Copper and zinc dynamics in foliar litter during decomposition from gap center to closed canopy in an alpine forest

Forest gap in alpine forests may redistribute the hydrothermal conditions in winter and growing season, which may affect the releases of copper and zinc in foliar litter during decomposition. However, the details of this process are largely unknown. Foliar litters of willow (Salix paraplesia), larch (Larix mastersiana), fir (Abies faxoniana), azalea (Rhododendron lapponicum), birch (Betula albosinensis) and cypress (Sabina saltuaria) were selected in an alpine forest of eastern Tibetan Plateau. The litterbags were placed on the forest floor from gap center, canopy gap edge and expanded gap edge to closed canopy. Zinc and copper contents were studied as litter decomposition proceeded. After one year of decomposition, zinc accumulated in all foliar litters regardless of gap positions, but copper accumulated in the litters of fir, azalea and cypress. Separately, copper was released from all foliar litters in winter, whereas zinc in litters of larch, azalea, birch and cypress was released in winter. Moreover, both copper and zinc accumulated during the growing season regardless of litter species. Nevertheless, higher accumulation rates were observed under closed canopy compared with other gap positions. These results suggest that forest gap slows the releases of copper and zinc in foliar litter during forest regeneration in these cold biomes.     

Insights into seasonal variation of litter decomposition and related soil degradative enzyme activities in subtropical forest in China

We used a litterbag method to investigate litter decomposition and related soil degradative enzyme activities across four seasons in a broad-leaved forest and a coniferous forest on Zijin Mountain in s...     

Leaf-litter decomposition of 15 tree species in a lowland tropical rain forest in Sarawak: decomposition rates and initial litter chemistry

In a lowland tropical rain forest in Sarawak, leaf-litter decomposition and the initial litter chemistry of 15 tree species were studied. During 13 months of field experiment, weight loss of litter samples was between 44% and 91%, and calculated decomposition rate constants (k) ranged from 0.38 to 2.36 year⁻¹. The initial litter chemistry also varied widely (coefficients of variation: 19%–74%) and showed low N and P concentrations and high acid-insoluble residue (AIS) concentration. For nutrient-related litter chemistry, correlations with the decomposition rate were significant only for P concentration, C/P ratio, and AIS/P ratio (r _s = 0.59, −0.62, and −0.68, n = 15, P < 0.05, respectively). For organic constituents, correlations were significant for concentrations of AIS and total carbohydrates, and AIS/acid-soluble carbohydrate ratio (r _s = −0.81, 0.51, and −0.76, n = 15, P < 0.05, respectively). These results suggested that the relatively slow mean rate of decomposition (k = 1.10) was presumably due to the low litter quality (low P concentration and high AIS concentration), and that P might influence the decomposition rate; but organic constituents, especially the concentration of AIS, were more important components of initial litter chemistry than nutrient concentrations.     

气候和枯落物质量对印度东部亚热带森林凋落叶分解和营养回归的影响(英文)

为了评价印度东部曼尼普尔亚热带橡树混交林中的土壤养分收支平衡情况,研究了全年不同月份的3个主要树种,枹栎(Quercus serrata)、木荷(Schima wallichi)和滇石栎(Lithocarpus dealbata)的枯落物分解和营养回归情况。印度东部橡树林是生产柞蚕丝的重要经济树种。林下2-7月月枯落物为25.6 g·m-2(7月)和198.0 g·m-2(2月),年枯落物为1093 8g·m-2。在初始月(11月3),滇石栎森林壤土的氮和碳浓度最高,其次是在枹栎林。最低的是木荷林。但就木质素和纤维素含而言,木荷林中的最高,其次是袍栎林和滇石栎林。滇石栎林(k=0.54)具有较高的枯落物分解率,这与月初枯落物中含有较高的氮和碳浓度以及低含量的纤维素相符合。然而,在木荷森林中枯落物分解率低,是与月初时森林土中具有低浓度氮和碳及高浓度木质素和纤维素相符合。在不同月份,剩余的生物量与木质素、碳、碳氮比和纤维素含量呈正相关,但与氮含量呈负相关。由于环境条件的影响,在寒冷和冬季枯落物分解率最低,而在雨季枯落物分解率最高。图3表5参52。     

Long-term dynamics of leaf and root decomposition and nitrogen release in a grey alder (Alnus incana (L.) Moench) and silver birch (Betula pendula Roth.) stands

The decomposition of the leaf litter, fine roots (d?<?2?mm) and coarser roots (2?≤?d?<?5?mm) of grey alder and silver birch, as well as of α-cellulose sheets using the litterbag method was studied in two experimental stands on Podzoluvisol soils in Southern Estonia. For both tree species, the coarser roots decomposed faster than the fine roots, (p?<?.05), tree species did not affect the decomposition rate of the roots (p?>?.5). The nitrogen (N) input to soil from aboveground litter was multiple times higher than the N flux from roots. The remaining relative ash-free mass of the leaves of grey alder and silver birch after three and a half years was similar. After 11 years the remaining relative ash-free mass of the fine and coarser roots of grey alder still accounted for around 10% of the initial value. For silver birch the remaining value was around 20% after 9 years. The litterbag method to underestimates in fertile soils the decomposition of organic matter and thus did not reflect the actual dynamics of decomposition.     

Mixed litter decomposition in a managed Missouri Ozark forest ecosystem

We monitored the decomposition of mixed leaf litter (Quercus spp., Carya spp., and Pinusechinata) in a Missouri Ozark forest eight years after experimental harvest. Leaf litter mass losses and changes in carbon chemistry (extractive, acid soluble, and acid insoluble fractions) were measured over 32 months in field incubations to determine the effects of litter composition and stand manipulation on decomposition and nitrogen (N) concentration in the remaining litter. The decay (k) rate over this period ranged between 0.39 (±0.010) and 0.51 (±0.002) year⁻¹ for oak, oak–hickory, and oak–pine litter. There were significant main effects of stand manipulation (p = 0.03) and litter type (p < 0.01) on decay. Mass losses of oak and oak–hickory litter were 7% (p = 0.02) and 4% (p = 0.04) higher on harvested stands than controls, respectively. Mass loss of oak–hickory litter was 3% faster than oak–pine (p = 0.03) and 6% faster than oak (p = 0.02) litter on control stands, whereas the oak–hickory litter mass loss was 5% higher than oak litter on harvested stands (p = 0.01). The decay (k) rate had a linear relationship with initial leaf litter nitrogen content and lignin-to-N ratio. The nitrogen concentration in remaining litter had a nonlinear relationship to cumulative mass loss suggesting an exogenous source of N. In summary, this study demonstrated significant effects of timber harvest and litter mixtures on decomposition and N dynamics in a managed Missouri Ozark forest.     

Effects of clear-cutting on decomposition processes in leaf litter and the nitrogen and lignin dynamics in a temperate secondary forest

The effects of clear-cutting on the decomposition rate of leaf litter and on nitrogen (N) and lignin dynamics were investigated in a temperate secondary forest. Decomposition processes were examined over an 18-month period by the litterbag method and compared between a clear-cut site and an adjacent uncut control site using leaf litter from five dominant tree species (Clethra barvinervis, Quercus serrata, Camellia japonica, Ilex pedunculosa and Pinus densiflora). The decomposition rate for litter from C. barvinervis, Q. serrata and I. pedunculosa was significantly greater in the clear-cut plot than in the control plot, and there was no significant difference between plots for C. japonica and P. densiflora. Water content of litter was consistently lower in the clear-cut plot than in the control plot. Nitrogen mass increased after 6 months in the control plot, whereas no net increase of N was observed in the clear-cut plot. Nitrogen concentration increased with respect to accumulated mass loss of litter and was consistently lower in the clear-cut plot for all five species. The mass of lignin remaining in decomposing litter was generally lower in the clear-cut plot, but lignin concentration in decomposing litter was not significantly different between the clear-cut and control plots.     

滇中高原森林凋落物不同分解阶段C、N、P的化学计量特征及种间差异

【目的】为了解滇中高原磨盘山典型森林凋落物在不同分解阶段的化学计量特征,揭示滇中高原森林不同分解阶段凋落物的质量特征,为更好地促进滇中高原森林生态系统的凋落物分解进程和养分循环提供理论依据。【方法】以滇中高原的华山松Pinus armandii林、云南松Pinus yunnanensis林、高山栎Quercus semecarpifolia林、滇油杉Keteleeria evelyniana林、常绿阔叶林5种林地为试验区,人为地将自然状态下的森林凋落物分为未分解层、半分解层、已分解层,用以模拟凋落物的不同分解阶段,对不同分解层凋落物的碳氮磷(C、N、P)含量、化学计量比及元素释放率进行分析。【结果】1)随着凋落物分解程度的加剧,5种森林凋落物的C含量不断减少,P、N含量大体呈增加趋势,其中云南松林及华山松林的N含量呈先增加后减少的趋势,常绿阔叶林P含量为先减少后增加,且C、N、P含量在同一分解层中不同森林之间差异显著;2)5种森林凋落物的C∶N、C∶P随着凋落物分解程度的不断降低,云南松林的二者比值最高,N∶P在云南松林、华山松林和常绿阔叶林中先升高后降低,在高山栎林中先降低后升高,在滇油杉林中逐渐降低,且滇中高原森林凋落物C∶P和N∶P均显著小于全球平均水平;3)森林凋落物中C、N、P的总释放率均为滇油杉林>华山松林>高山栎林>云南松林>常绿阔叶林,常绿阔叶林前期元素释放效率快,后期减弱,华山松林和云南松林则相反,滇中磨盘山5种森林凋落物的化学元素易富集难释放。【结论】根据碳、氮、磷的化学计量特征表明,森林种间差异及不同的分解阶段会显著影响凋落物分解过程中的碳氮磷含量、化学计量比及其释放效率。     

Biomass,decomposition and nutrient release of Vaccinium myrtillus leaf litter in four forest stands

Biomass and nutrient transfer (N, P, K, Ca, Mg) of bilberry (Vaccinium myrtillus L.) leaf litter fall, as well as decomposition and nutrient release, were studied in four mature forest stands situated in Central and South Sweden. Bilberry leaf litter fall amounted to between 33 and 55 kg ha^‐1 yr^‐1 in the four stands. Only minor differences between sites were noted for litter concentrations of N, P and Ca, whereas K and Mg showed somewhat larger variability. Relative amounts of the five nutrient elements in the litter fall were generally in the order N > Ca > K > Mg > P. The amounts of nutrients returned to the forest floor by the annual leaf litter fall in the stands ranged from 0.4 to 0.8 kg ha^‐1 for N, 0.4 to 0.6 kg ha^‐1 for Ca, 0.2 to 0.7 kg ha^‐1 for K, 0.1 to 0.2 kg ha^‐1 for Mg and 0.04 to 0.08 kg ha^‐1 for P.

The decomposition of the local bilberry leaf litter was followed by means of litterbags during three years. At all sites there was an extremely rapid mass loss from the litter (between 45% and 54%) during the first four to five months of decomposition. After this initial phase, the decomposition rates decreased markedly and after three years the accumulated mass losses of the litters varied between 64% and 78% at the studied sites. After two and three years of decomposition, three of the sites exhibited almost similar litter mass losses whereas at the fourth site the litter was decomposed to a significantly lower degree. The pattern of nutrient release from the decomposing bilberry leaf litter differed somewhat from site to site. Minor differences were, however, noted for P, Ca and Mg while N and K were more strongly retained in the litter at one of the sites.     

Hydrological characteristics of litter in different forest succession stages at Liuxihe Watershed, southern China

The hydrological characteristics of litter in four different forest succession stages, i.e., a Pinus massoniana forest, a mixed conifer and broad-leaved forest with conifer being the dominant species, a mixed conifer and broad-leaved forest with deciduous trees as dominant species, and an evergreen broad-leaved forest, have been studied by means of substituting space for time. The results show that while a community is developing to a zonal climax, the amount of litter becomes larger and its decomposition intensity becomes stronger; there is a positive relation between its water-holding capacity and velocity and its community maturity for the half-decomposed litter layer. __________ Translated from Journal of Central South University of Forestry and Technology, 2007, 27(6): 38–43 [译自: 中南林业科技大学学报]     

Litterfall, litter decomposition and nutrient dynamics in a subtropical natural oak forest and managed plantation in northeastern India

In northeastern India, subtropical forests are over-exploited for timber, fuel wood and common agricultural practice like shifting cultivation, which are responsible for the degradation of natural forest. In degraded areas, large-scale plantations of different species of Quercus have been raised since 1980 for the production of economic Tasar silk. Conversion of natural forest into plantation affects the process of nutrient cycling due to management practices. Thus, it would be of importance to study the litterfall, litter decomposition process and the factors regulating the rate of litter decay in these ecosystems to improve recommendations for their management and conservation. We recorded litterfall by using litter traps and decomposition of leaf litter by nylon net bag technique to understand the amount of organic matter and nutrient return and their release in soils of forest and plantation in Manipur, northeast India. Total litterfall was 419.9 g m⁻² year⁻¹ in plantation and 547.7 g m⁻² year⁻¹ in forest. Litter decomposition rate was faster at plantation site than the forest in the early stage of litter decomposition whereas the reverse was observed at later stages of decomposition. Stepwise regression analysis showed the significant role of relative humidity and mean temperature on mass loss rates in the forest. Relative humidity, maximum temperature, population of fungi and actinomycetes were the best predictor variables for mass loss rates in plantation. Nutrient retranslocation efficiency and the immobilization of N and P in forest litter were higher than plantation. This suggests that Q. serrata growing in natural ecosystem in oligotrophic condition adapted strong nutrient conservation mechanisms to compete with the other plant species for the meager soil nutrients. The same species in plantation loses these adaptive capabilities because of exogenous supply of nutrients and in the absence of intense competition with other plant species. Thus, the optimization of organic and chemical fertilizer input in plantation is recommended for maintaining the soil fertility level to produce quality leaf for silkworm by conserving essential nutrients in the system.     

凋落物和铵态氮添加对亚热带罗浮栲和杉木林土壤碳氮淋溶的影响

目的 凋落物是森林土壤碳氮的主要来源,通过分析凋落物或土壤淋溶碳氮的变化,揭示凋落物分解通过淋溶对土壤碳氮的影响及氮添加情况下这种影响的变化,进而探究凋落物分解与土壤碳氮的关系。 方法 以亚热带天然阔叶林和人工针叶林土壤和凋落物为对象,设置6种处理：凋落物、土壤、凋落物 + 土壤、凋落物 + 氮、土壤 + 氮和凋落物 + 土壤 + 氮,每个处理3重复。氮添加量（NH4 + -N/土壤）为120 mg·kg−1 ,针、阔叶林凋落物添加量分别为12.1、19.7 g·kg−1,凋落物放置在土壤或石英石表面,土壤湿度控制在60%饱和持水量,于25 ℃暗培养箱中,采用氮淋溶模拟氮沉降的方法,进行室内培养试验。培养期间,氮溶液分5次不等氮量淋溶,每次110 mL溶液（按照淋溶次数分配依次为80、10、10、10、10 mg NH4 + -N）,收集淋溶液,测定其溶解性有机碳（DOC）、氮（DON）和无机氮。 结果 凋落物淋溶液有较低的无机氮和DON,较高的DOC;凋落物添加分别降低针阔叶土壤淋溶液中NO3−-N 22.6%和29.9%、提高针叶林土壤淋溶液中DOC 181.4%,但是降低阔叶林土壤淋溶液中DON 39.2%和阔叶林土壤MBN 53.2%。氮添加后,凋落物对添加氮的截留较少,且阔叶林凋落物截留高于针叶林;凋落物通过淋溶输入土壤的DOC减少,而DON增加。氮添加增加土壤可淋溶的无机氮量和针叶林土壤淋溶液DON,但凋落物降低土壤氮淋溶的作用在氮添加情况下没有减弱。 结论 凋落物具有减缓土壤NO3−-N输出对水环境的负面影响,氮添加可通过改变针阔叶林凋落物DOC和DON 的输出影响土壤氮变化。     

Carbon and nitrogen dynamics under windrowed residues during the establishment phase of a second-rotation hoop pine plantation in subtropical Australia

The dynamics of carbon (C) and nitrogen (N), derived from the decomposition of windrowed harvest residues, was examined in the establishment phase of a second rotation (2R) hoop pine (Araucaria cunninghamii Aiton ex A. Cunn) plantation in subtropical Queensland, Australia. Following harvesting and site preparation, when residues were formed into windrows, in situ N mineralisation was measured in positions along the three tree-planting rows formed between the windrows. The position above the windrow had a higher nitrification rate than the other positions, averaging about 18 kg N ha⁻¹/month compared with 12 and 9 Kg N ha⁻¹ for the positions between and below the windrow positions, respectively. This position also had consistently greater soil moisture.

Macroplots were formed extending 5 m above and 10 m below a windrow. Windrowed residues within the macroplots were replaced by ¹⁵N-labelled material comprising hoop pine foliage, branch and stem. Hoop pine trees were planted within each macroplot with foliar samples taken at 12 and 24 months. Differences in foliar ¹⁵N enrichment between positions within macroplots were <1‰. Soil samples were taken from positions along the macroplots at 6-monthly intervals. Samples revealed an initial release of labile C and N but soil δ¹⁵N showed that residue-derived N was largely immobilised within the windrows for the 30-month sampling period. Whilst the use of windrows may act as a barrier to the down-slope movement of water, the residue N within the windrows may not be available to the trees of the following rotation for a considerable period following planting. Trees closest to the windrows may be able to introduce roots under the windrows thereby gaining access to the available N, but trees in the central tree planting row are unlikely to derive any significant benefit from the decomposition of windrowed residues.     

北亚热带6种森林类型凋落物分解过程中有机碳动态变化

运用凋落物野外分解模拟实验的方法,对北亚热带地区6种主要森林类型凋落物分解过程中有机碳的变化进行了研究,结果表明:(1)6种土地利用类型森林凋落物分解过程中,有机碳相对含量在分解初始阶段都呈现增加的趋势,表现为凋落物有机碳相对含量的积累过程;分解开始的第3～4个月后,凋落物有机碳相对含量下降;经过1 a的分解周期以后,粗放经营毛竹林凋落物有机碳相对含量变化最大,下降11.7%;(2)集约经营毛竹林凋落物有机碳数量从分解开始就减少,而其它几种类型分解初期有机碳数量都表现一个净积累的过程,然后才逐步释放;经过1 a分解周期以后,粗放经营毛竹林凋落物53.8%的有机碳净释放;凋落物有机碳释放速率由高到低的顺序为:粗放经营毛竹林、早竹林、杉木林、天然次生林、集约经营毛竹林、马尾松林;(3)6种土地利用类型森林凋落物在分解过程中,有机碳剩余率随时间变化的模型都极其显著地符合分解指数模型,因此都可以用指数方程表达;(4)影响凋落物分解的环境因子所发挥的作用不尽相同,凋落物的分解速率和温度之间呈现显著的正相关关系.     

Seasonal and spatial variation of nitrogen dynamics in the litter and surface soil layers on a tropical dry evergreen forest slope

Seasonal and spatial variability of litterfall and NO₃⁻ and NH₄⁺ leaching from the litter layer and 5-cm soil depth were investigated along a slope in a tropical dry evergreen forest in northeastern Thailand. Using ion exchange resin and buried bag methods, the vertical flux and transformation of inorganic nitrogen (N) were observed during four periods (dry, early wet, middle wet, and late wet seasons) at 15 subplots in a 180-m × 40-m rectangular plot on the slope. Annual N input via litterfall and inorganic N leached from the litter layer and from 5-cm depth soil were 12.5, 6.9, and 3.7 g N m⁻² year⁻¹, respectively, whereas net mineralization and the inorganic N pool in 0–5-cm soil were 7.1 g N m⁻² year⁻¹ and 1.4 g N m⁻², respectively. During the early wet season (90 days), we observed 82% and 74% of annual NO₃⁻ leaching from the litter layer and 5-cm soil depth, respectively. Higher N input via leaf litterfall in the dry season and via precipitation in the early wet season may have led to higher NO₃⁻ leaching rate from litter and surface soil layers during the early wet season. Large spatial variability in both NO₃⁻ vertical flux and litterfall was also observed within stands. Small-scale spatial patterns of total N input via litterfall were significantly correlated with NO₃⁻ leaching rate from the surface soil layer. In tropical dry evergreen forests, litterfall variability may be crucial to the remarkable seasonal changes and spatial variation in annual NO₃⁻ vertical flux in surface soil layers.     

Microbial activity,nutrient dynamics and litter decomposition in a Canadian Rocky Mountain pine forest as affected by N and P fertilizers

To study the specific effects of N and P fertilizers on soil microbial processes under field conditions, a pine forest in southern Alberta was fertilized with ammonium nitrate and urea (0 and 188 kg N ha⁻¹, respectively) singly and in combination with triple super phosphate (0 and 94 kg P ha⁻¹, respectively). Microbial respiration (BR), substrate induced respiration (SIR), metabolic quotient (qCO₂) and rates of microbially mediated key processes were monitored in the forest floor FH material during the growing periods of spring 1990 to fall 1992. A transient increase in soil NH₄⁺ availability was detected following N addition but significant increases in PO₄³⁻ availability were detected throughout the study as a result of P enhancement. Microbial variables were unaffected by N addition, whereas soil organic matter and SIR was increased with P fertilization. Microbial BR and qCO₂ were reduced with P fertilization suggesting more efficient utilization of C. Increased net mineralization of P in the P-fertilized plots was found during the second and third summers after fertilization, following immobilization of P during the first year. In contrast, NH₄⁺-N mineralization in the N-fertilized plots was significantly increased only during the first year. Rates of nitrification were unaffected by either N or P addition. Decomposition of pine litter was enhanced with N addition only during the first year and P had no effect on decomposition. Addition of N and P at these rates does not appear to impose a major ecological stress to the soil ecosystem.     

Ecological process of leaf litter decomposition in tropical rainforest in Xishuangbanna, southwest China. III. Enzyme dynamics

We tested the dynamics of nine enzymes during leaf litter decomposition in Xishuangbanna tropical rain-forest both in the field and laboratory to explore the response of enzyme dynamics to decomposition under different food-web structures. We used coarse and fine (1 mm and 100 μm mesh size, respectively) litterbags in the field to create different food-web structures during litter decomposition. Most soil macrofauna such as nematodes could access only the coarse mesh litterbags, leaving only microbiota, such as mites, in the fine mesh litterbags. In the laboratory, sterilization and inoculation were adopted to investigate different enzyme dynamics with nematodes or only microbiota participating in litter decomposition. Invertase and amylase increased more for shorter food webs at the early stages of decomposition, while activities of endocellulase, β-glucosidase, xylanase and polyphenoloxydase increased to their maxima at the later stages, but greater increase occurred with extended food webs. Invertase and amylase had negative relationships and endocellulase, β-glucosidase, xylanase and polyphenoloxydase had positive relationships with litter decomposition (mass loss). The activities of enzymes responded to the process of litter decomposition. Invertase and amylase played key roles for microbiota utilizing the substrates at early stages of decomposition, while endocellulase, β-glucosidase, xylanase and polyphenoloxydase worked on the further decay of recalcitrant compounds at later stages. All enzymes related to carbon decay acted as effective indicators of litter decomposition. The decomposition of plant organic matter was essentially an enzymatic process. __________ Translated from Journal of Plant Ecology (Chinese Version), 2008, 32(3): 622–631 [译自: 植物生态学报]