沙地疏林草地和樟子松人工林土壤中不同形态磷素含量和磷酸单酯酶活性的比较

为评价我国北方大规模人工造林对土壤磷素转化及磷素有效性的影响,对半干旱沙地樟子松人工林和天然植被(疏林草地)不同层次(0～5 cm, 5～20 cm)土壤中不同形态磷组分和磷酸单酯酶活性进行了比较.结果表明:除人工林土壤中活性有机磷不受土壤深度影响外,各样地表层土壤中各种磷素含量和酶活性均显著高于低层土壤,但分层效应在人工林中低于疏林草地;与疏林草地土壤相比,除Al-P外,人工林土壤中各种磷素绝对含量和酶活性均显著降低,总有机磷和Ca-P在全磷中的比例显著下降,而活性磷,Al-P和Fe-P占全磷的比例增加.可见表层土壤是磷素转化最活跃的区域,凋落物分解是土壤磷的主要来源;用樟子松进行人工造林促进了有机磷的矿化和Ca-P的溶解,提高了土壤磷素的有效性,同时导致土壤总磷库逐渐耗竭.要维持该人工防护林功能和稳定性,必须对地被物予以保护,并进行适当施肥.表3参38.     

Carbon storage in biomass,litter, and soil of different plantations in a semiarid temperate region of northwest China

? Context

A large area of abandoned land in the semiarid temperate region of China has been converted into plantations over the past decades. However, little information is available about the ecosystem C storage in different plantations.

? Aim and methods

Our objective was to estimate the C storage in biomass, litter, and soil of four different plantations (monospecific stands of Larix gmelinii, Pinus tabuliformis, Picea crassifolia, and Populus simonii). Tree component biomass was estimated using allometric equations. The biomasses of understory vegetation and litter were determined by harvesting all the components. C fractions of plant, litter, and soil were measured.

? Results

The ecosystem C storage were as follows: Picea crassifolia (469 t C/ha)?>?Larix gmelinii (375 t C/ha), Populus simonii (330 t C/ha)?>?Pinus tabuliformis (281 t C/ha) (P?<?0.05), 59.5–91.1 % of which was in the soil. The highest tree and understory C storage were found in the plantation of Pinus tabuliformis (247 t/ha) and Larix gmelinii (1.2 t/ha) respectively. The difference in tree C fraction was significant among tree components (P?<?0.05), following the order: leaf?>?branch?>?trunk?>?root. The highest soil C (SC) was stored in Picea crassifolia plantation (411 t C/ha), while Populus simonii plantation had a higher SC sequestration rate than others.

? Conclusion

C storage and distribution varied among different plantation ecosystems. Coniferous forests had a higher live biomass and litter C storage. Broadleaf forests had considerable SC sequestration potential after 40 years establishment.     

Establishment and early growth of introduced indigenous tree species in typical plantations and shrubland in South China

Unsuccessful colonization by indigenous tree species into established plantations has retarded the succession of artificial plantations to more natural, secondary forests in South China. To understand how to improve colonization by seedlings of indigenous species, we determined how performance of indigenous seedlings is affected by seedling species (the shade-intolerant Castanopsis chinensis, the moderately shade-intolerant Michelia chapensis, and the shade-tolerant Psychotria rubra), the site into which the seedlings were transplanted (a mixed-legume plantation, a eucalyptus plantation, a mixed-native plantation, a mixed-conifer plantation, and a shrubland), and site preparation (removal or retention of understory vegetation and litter). Seedling survival and growth were generally increased by removal of understory vegetation and litter. C. chinensis and M. chapensis grew better in the mixed-legume and mixed-conifer plantations, while P. rubra grew better in mixed-native and mixed-conifer plantations. Responses of the transplanted seedlings to environmental factors were species specific. The effects of light on seedling survival and growth were correlated with the shade tolerance of the species. Soil moisture was important; it was positively correlated with survival but negatively correlated with growth of C. chinensis seedlings. Growth of C. chinensis and M. chapensis was positively correlated with soil potassium, while growth of P. rubra was positively correlated with soil organic matter but negatively correlated with soil hydrolyzed nitrogen. These findings suggest that we should select suitable native species under the different plantations before improvement of plantations. Light and soil moisture are most important environmental factors for the selection of species specific. Site preparation and fertilizer are needed during the improvement of those plantations.     

杉木纯林、混交林土壤微生物特性和土壤养分的比较研究

本文于2005年5月份,在中国科学院会同森林生态实验站选择了一块15年生的杉木纯林和两块15年生杉阔混交林作为研究对象,调查了林地土壤有机碳、全氮、全磷、硝态氮、有效磷和土壤微生物碳、氮、磷、基础呼吸以及呼吸熵,比较了纯林和混交林土壤微生物特性和土壤养分.结果表明,杉阔混交林的土壤有机碳、全氮、全磷硝态氮和有效磷含量高于杉木纯林;在混交林中,土壤微生物学特性得到改善.在0(10 cm和10(20 cm两层土壤中,杉阔混交林土壤微生物氮含量分别比杉木纯林高69%和61%.在0(10 cm土层,杉阔混交林土壤微生物碳、磷和基础呼吸分别比杉木纯林高11%、14%和4%;在10(20 cm土层,分别高6%、3%和3%.但是,杉阔混交林土壤微生物碳:氮比和呼吸熵较杉木纯林低34%和4%.另外,土壤微生物与土壤养分的相关性高于土壤呼吸、微生物碳:氮比和呼吸熵与土壤养分的相关性.由此可知,在针叶纯林中引入阔叶树后,土壤肥力得以改善,并有利于退化森林土壤的恢复.     

Change in soil macrofauna and vegetation when fast-growing trees are planted on savanna soils

Many forest species can be found in understory vegetation of old plantation plots, despite the fact that the native vegetation was a poor savanna growing on highly nonfertile sandy soils. The aim of the present paper is to describe the changes that occur in the environmental conditions when savanna is planted with fast-growing trees, and is particularly concerned with vegetation and soil macrofauna. The study was carried out in industrial eucalyptus plantations, and in experimental Acacia and pine plantations. Most plots were located on sandy soil, but some measurements were also carried out on clay soil planted with the same species in order to assess the influence of soil type.

A strong correlation was shown between the age of the eucalyptus trees and the percentage of forest species in undergrowth, emphasizing the progressive change from savanna vegetation towards forest vegetation.

Biomass and density of macrofauna were very low in both sandy and clayey savanna soils, total biomass being 3.3 and 5.8 g/m² respectively. Soil macrofauna became more important as the age of plantations increased, and biomass reached 29 g/m² in the 20-year-old eucalyptus plot on sandy soil, and 74 g/m² in 26-year-old eucalyptus plantation on clay soil, compared to 33 g/m² in the natural forest plot on sandy soil; however, frequency of occurrence and number of taxa were lower in old eucalyptus plot as compared to forest. Large differences in the abundance of macrofauna were observed in relation to planted species. Acacia was most favourable to soil macrofauna, with a total biomass of 60 g/m² on sandy soil and many taxa present. Pine plantations had a poor macrofauna and several taxa were lacking, particularly in the sandy soil.

Total macrofauna frequency was significantly correlated with the percentage of forest species in understory vegetation. Both were correlated with soil pH and soil organic-matter content. The results suggest that soil organic matter and litter quality are of main importance in changing the above- and below-ground habitat in plantations.     

Evaluation of native tree species for the rehabilitation of deforested areas in a Mexican cloud forest

Four native tree species (Liquidambar styraciflua, Juglans pyriformis, Podocarpus matudae, and Carpinus caroliniana) were evaluated for their suitability in rehabilitating degraded areas of Mexican cloud forest. Plant survival and growth in height and diameter were determined in three mixed-experimental plantations with different land use histories; their performance was compared with two on-farm plantations started by landowners for forest restoration. Nearby forest fragments were controls for soil compaction. An experimental plantation with remnant trees had the highest plant survival (82%), height, basal diameter and relative growth rate. The plantation with the steepest slope had high plant survival (63%) and growth. The plantation characterized by dominance of grasses and compacted soils had the lowest survival (22%) and growth. On-farm plantations had good establishment of planted trees (5–10 species planted), and facilitated the recruitment of 9–11 woody species. Carpinus and Liquidambar appear to be suitable species for reforestation in all these areas. Podocarpus grew relatively slowly, although it performed well in two experimental sites. Juglans had high survival (76%) under the stressful conditions of the most adverse site, and therefore may be useful for rehabilitation of degraded sites. Differences among species and sites strongly suggest that species success depends on plantation site quality.     

Changes in soil P chemistry as affected by conversion of natural secondary forests to larch plantations

To assess the impact of conversion of native forests to monocultural larch plantations on soil chemical properties, we compared the total and various fractions of soil phosphorus (P) and acid phosphatase activity (APA) between natural secondary forests (NSF) and Larix olgensis plantations (LOP) on a montane forest site in eastern Liaoning Province, Northeast China. We found that the concentrations of total P (TP), inorganic P, and iron-bound P (Fe-P) were significantly higher, and the concentrations of microbial biomass P (MBP), sodium bicarbonate-extractable organic P (NaHCO₃-Po), and APA were significantly lower, in the LOP stands than in the NSF stands; whilst organic P, sodium bicarbonate-extractable inorganic P (NaHCO₃-Pi), aluminum-bound P (Al-P) and calcium-bound P (Ca-P) were comparable between the two forest types. Our study also showed that the ratios of MBP/TP, NaHCO₃-Pi/TP, NaHCO₃-Po/TP, and APA significantly varied with time during the growing season. Moreover, the concentrations of NaHCO₃-Pi, NaHCO₃-Po, and MBP had significant (P < 0.01) and positive linear relationships with APA. Overall, results from this study suggest that conversion of native forests to larch plantations in the region is more likely to cause compositional change in soil P than to result in reduction in overall P availability.     

孟加拉吉大港地区丘陵森林有机物积累

在孟加拉吉大港丘陵地区,调查了热带季风气候条件下的3种人工林(7年生大叶相思(Acacia auriculiformis)林、15年生大叶相思林和18年生混交林)和1种天然林的森林凋落物及其对土壤性质的作用.结果表明,总的有机质积累随人工林树龄增加而增加,但是年积累量随之降低.在同一植被类型内,不同坡位新鲜或部分分解的凋落物有机质累计量变化较大,坡底部有机质积累量最高,沿着山坡向上逐渐减少.在15年生大叶相思人工林内,土壤整合有机物积累量变化趋势与新鲜或部分分解有机质积累量变化趋势相反.在7年生和15年生的大叶相思林以及18年龄的阔叶混交人工林内,新鲜、部分分解和完全分解(含土壤整合有机质)有机质总生产速率分别是2554.31、705.79和1028.01kg.ha-1·a-1,新鲜凋落物有机质在3种林分中的生产速率分别是38.23,19.40和30.48 kg·ha-1·a-1.3种人工林和自然林内,平均新鲜凋落物的有机质积累占有机质产出总量的32.45%,部分分解凋落物占13.50%,而全分解整合土壤有机质占54.56%.森林土壤酸度随凋落物分解阶段的深入而增加.     

Moisture extraction and crop yield as a function of distance from a row of Eucalyptus tereticornis

A study was made on the effect of an east-west tree line of years old Eucalyptus tereticornis on soil physical parameters and adjoining mustard and wheat crops as a function of distance from the tree-crop interface in north- and south-facing sides. Maximum soil temperature, pan evaporation, moisture extraction, number of plants/m², and yields of mustard and wheat did not differ significantly on the two sides of plantation. Plant growth parameters decreased linearly with distance from the plantation. Mustard yield, Y (kg/ha) was linearly related to moisture extraction, ME (mm) as Y = 1914–120.3 ME. Eucalyptus tereticornis was found to extract 5 times more water than mustard from 0–150cm soil profile. Mustard and wheat yield reductions in adjoining 10 meter strips on both sides of the plantation were 47 and 34 per cent, respectively. Eucalyptus tereticornis is, therefore, not a suitable species for row plantations in agro-forestry systems in deep water table conditions of semi-arid regions.     

Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China

The distribution in tree biomass and understorey vegetation and annual biological and geochemical cycling of total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured in young, middle-aged and mature plantations (8-, 14- and 24-years old) of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in southern China. Although >98% of nutrients occurred in the soil, soil nutrient content decreased with plantation age. Nutrient outputs from the soil exceeded inputs in stands of all ages but the net soil nutrient loss increased significantly for N, P and Ca with plantation age. Comparison of nutrient fluxes showed that the smallest (and hence limiting for nutrient cycling) fluxes were litter decomposition in the young plantation in contrast to canopy fluxes (apart from for Mg) in the middle-aged and mature plantations. Nutrient use efficiency, release of nutrients from litter decomposition and nutrient return, particularly in litterfall, increased significantly with plantation age. These results suggest that, as stand age increases, nutrient cycling in Chinese fir plantations is increasingly dominated by biological processes and becomes less dependent on external nutrient sources in rainfall and the soil. It therefore appears that prolonging the rotation length of Chinese fir plantations by approximately 5 years could be beneficial for maintaining the soil nutrient status for successive plantings.     

Assessing the effects of vegetation types on carbon storage fifteen years after reforestation on a Chinese fir site

Forest ecosystems play a significant role in sequestering carbon (C) in biomass and soils. Plantations established in subtropical China since the 1980s, mainly of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) in monocultures, have proved to be major C sinks. However, information is lacking about whether mixing Chinese fir with broadleaved tree species will increase stand growth and C sequestration. We address this question by comparing a pure Chinese fir plantation and two mixed plantations established in 1990 at Huitong Experimental Station of Forest Ecology, Hunan Province, China. The mixed plantations include Chinese fir and either Kalopanax septemlobus (Thunb.) Koidz or Alnus cremastogyne Burk., planted at 4:1 ratios. We found that total C storage was 123, 131 and 142 Mg ha⁻¹ in the pure plantation, mixed plantation with K. septemlobus, and mixed plantation with A. cremastogyne, respectively. The mixed plantation with A. cremastogyne increased C storage in biomass relative to the pure Chinese fir plantation (P < 0.05). No significant difference was detected between mixed plantations. Soil C storage did not differ among these plantations, ranging from 67.9 ± 7.1 to 73.3 ± 9.1 Mg ha⁻¹, which accounted for about 55% of the total C pools. Our results indicated that as the mixture of Chinese fir and broadleaved species will increase both biomass C and soil C storage over pure Chinese fir, and will do it, within 15 years of planting.     

Estimation of drought-related limitations to mid-rotation aged plantation grown Eucalyptus globulus by phloem sap analysis

Previous research has shown that carbon isotope signatures (Δ¹³C) may correlate well with water status in 1–2 years old, plantation grown Eucalyptus globulus. Here we investigate this relationship for mid-rotation aged (5 years) trees and whether a simple field determination of phloem sugar concentrations is a reliable surrogate for Δ¹³C. We sampled six plantations covering much of the climatic range of E. globulus plantations in Australia (average annual rainfall 618–1094 mm). We found significant correlations between phloem Δ¹³C and phloem sugar concentrations across and within plantations. Both parameters were also correlated with a climate wetness index. We thus conclude that phloem sugar concentration is a useful surrogate for Δ¹³C and hence water status of mid-rotation E. globulus. We also observed strong correlations of phloem Δ¹³C and phloem sugar concentrations with growth across all plantations, providing some confirmation that water limits growth of E. globulus at a larger scale. This relationship was much weaker or absent within plantations, suggesting that factors other than water supply contribute significantly to growth limitations at smaller (within-plantation) scales.     

The effect of understory removal on microclimate and soil properties in two subtropical lumber plantations

Understory vegetation is an important component in forest ecosystems. However, the effects of understory on soil properties in subtropical forests are not fully understood. We thus conducted an experimental manipulative study in two young fast-growing plantations—Eucalyptus urophylla and Acacia crassicarpa—in southern China, by removing understory vegetation in both plantations, to estimate the effects of understory vegetation on microclimate, soil properties and N mineralization. Our data showed that, after 6 months, understory removal (UR) in both plantations had greatly increased soil surface luminous intensity (90–500 cd) and temperature (0.5–0.8 °C); soil moisture was reduced in the Eucalyptus plantation but not in the Acacia plantation. Understory removal also reduced soil organic matter (SOM), but had little impact on other soil chemical properties, including total phosphorus, C/N, pH, exchangeable cations (K, Ca, Mg), available P, ande extractable NH₄–N and NO₃–N. We found a significant decline of soil N mineralization and nitrification rates in the 0–5 cm soils of UR in both plantations. The decline of SOM in UR may contribute to the lower N transformations rates. This study indicates that a better understanding of understory vegetation effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing management practices.     

退耕还林不同人工林类型对土壤养分的影响

对内蒙古敖汉旗2006年退耕还林的樟子松纯林、山杏纯林、山杏沙棘混交林和荒草地（对照）不同深度的土壤养分状况进行研究,结果表明：3种人工林的土壤有机质和碱解氮含量明显增加,山杏沙棘混交林中沙棘林带表层的速效磷含量明显增加,山杏纯林浅层的速效钾含量明显增加;3种人工林和荒草地的土壤养分随着土壤深度的增加而降低,表层土壤养分条件较好,说明土壤养分具有很强的表聚性;3种人工林与荒草地相比都不同程度地提高了土壤养分水平,樟子松纯林和山杏沙棘混交林中沙棘林带的土壤养分条件较好.     

我国樟子松人工林天然更新研究进展

樟子松人工林天然更新问题的研究一直在进行,但人工林内幼苗数量过少及难以发育为幼树的问题一直难以彻底解决。文中综述了影响我国沙地樟子松人工林天然更新能力的因素,如光照、温度、水分、土壤环境、生物因子及人工营林技术等的研究概况。在研究过程中发现,樟子松人工林的遗传多样性与土壤微生物对樟子松人工林天然更新影响方面的研究尚少有报道,或可以为解决樟子松人工林天然更新问题提供更深入的思路。     

Ecosystem carbon stocks and distribution under different land-uses in north central Alberta,Canada

Land-use and land cover strongly influence carbon (C) storage and distribution within ecosystems. We studied the effects of land-use on: (i) above- and belowground biomass C, (ii) soil organic C (SOC) in bulk soil, coarse- (250–2000 μm), medium- (53–250 μm) and fine-size fractions (<53 μm), and (iii) ¹³C and ¹⁵N abundance in plant litter, bulk soil, coarse-, and medium- and fine-size fractions in the 0–50 cm soil layer in Linaria AB, Canada between May and October of 2006. Five adjacent land-uses were sampled: (i) agriculture since 1930s, (ii) 2-year-old hybrid poplar (Populusdeltoides × Populus × petrowskyana var. Walker) plantation, (iii) 9-year-old Walker hybrid poplar plantation, (iv) grassland since 1997, and (v) an 80-year-old native aspen (Populus tremuloides Michx.) stand. Total ecosystem C stock in the native aspen stand (223 Mg C ha⁻¹) was similar to that of the 9-year-old hybrid poplar plantation (174 Mg C ha⁻¹) but was significantly greater than in the agriculture (132 Mg C ha⁻¹), 2-year-old hybrid poplar plantation (110 Mg C ha⁻¹), and grassland (121 Mg C ha⁻¹). Differences in ecosystem C stocks between the land-uses were primarily the result of different plant biomass as SOC in the 0–50 cm soil layer was unaffected by land-use change. The general trend for C stocks in soil particle-size fractions decreased in the order of: fine > medium > coarse for all land-uses, except in the native aspen stand where C was uniformly distributed among soil particle-size fractions. The C stock in the coarse-size fraction was most affected by land-use change whilst the fine fractions the least. Enrichment of the natural abundances of ¹³C and ¹⁵N across the land-uses since time of disturbance, i.e., from agriculture to 2- and then 9-year-old hybrid poplar plantations or to grassland, suggests shifts from more labile forms of C to more humified forms of C following those land-use changes.     

不同种植年限尾巨桉人工林叶片-凋落物-土壤碳氮磷化学计量特征

[目的]为了解雷州半岛尾巨桉速生人工林生态系统的C、N、P分配格局及化学计量特征。[方法]采用空间换时间的方法,选取雷州半岛4种不同林龄(1、3、5、7 a)的尾巨桉人工林为研究对象,对尾巨桉叶片、凋落物及土壤的C、N、P含量及化学计量特征进行测定分析。[结果]表明:C、N含量表现为叶片凋落物土壤,P含量表现为叶片土壤凋落物,且3个库间差异显著;土壤的C含量随林龄增加而增加,N、P含量差异不显著,土壤C∶N随林龄的增加而增加,说明土壤有机质分解速率逐渐下降;凋落物的C∶N为54. 07 92. 18 ( 25),表明尾巨桉林下凋落物分解速率较慢,N元素成为主要限制凋落物分解的元素,凋落物的C∶N随林龄的增加先增加后下降,凋落物分解速度先降低后升高;叶片的N∶P为10. 80 12. 98,说明中幼林龄尾巨桉受N限制较明显。相关性分析表明:凋落物养分元素含量受叶片限制,土壤养分含量受凋落物限制,表明生态系统内部C、N、P元素在植物、凋落物与土壤之间实现了运输和转换。[结论]雷州半岛尾巨桉中、幼林龄时期土壤有机质及凋落物分解速率较慢;随林龄的增加,土壤有机质、凋落物分解速率下降,N元素成为其主要分解限制性元素,林分生长受N限制明显。     

Faunal use of bluegum ( Eucalyptus globulus ) plantations in southwestern Australia

We examined the faunal use of Eucalyptus globulus plantations in southern Western Australia, and compared use of remnant vegetation, agricultural land and plantations in different positions relative to large tracts of remnant vegetation. In general, faunal use of plantations is less than in comparison with adjacent remnant vegetation, but more than in open pasture. For all faunal groups there were almost twice as many species recorded in the native vegetation than in any site in the plantations or on agricultural land and they were in greater abundance. Faunal use of plantation edges and interiors did not show consistent patterns. Generally, edges next to remnants were most frequently used, but individual species showed a wide range of patterns of use across the various habitat types studied. More species of bird identified as being “at risk” were found in plantation edges than in interiors. Adjacency to remnant vegetation increased plantation use by some species, but the overall differences between isolated plantations and those adjacent to remnant vegetation were relatively small. We conclude that plantations provide some value in terms of habitat for some species, including some of conservation concern, but that this value is limited by the lack of habitat complexity in the intensively-managed plantations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Native woody species regeneration in exotic tree plantations at Munessa-Shashemene Forest,southern Ethiopia

Regeneration of native woody species was studied in the plantations and the adjacent natural forest at Munessa-Shashemene Forest Project Area, Ethiopia. The aim of the study was to test the hypothesis that tree plantations foster regeneration of native woody species. A total of 60 plots, having 10 × 10 m area each, were studied in monoculture plantations of 4 exotic species (Cupressus lusitanica, Eucalyptus globulus, E. saligna, Pinus patula) and an adjacent natural forest. Ages of the plantations ranged between 9 and 28 years. Soil seed bank analysis was also undertaken from soil samples collected in each of the 60 plots to examine the similarity between the soil seed flora and aboveground vegetation. A total of 56 naturally regenerated woody species were recorded beneath all plantation stands with densities ranging between 2300 and 18650 individuals / ha in different stands. There was a significant difference among plantation stands with regard to understorey density (standard deviation: 4836 ± 1341). Vegetation diversity was assessed through analyses of floristic composition, species richness and abundance. Generally, seedling populations were the most abundant components of the regeneration in most of the plantation stands, forming 68 % of the total regeneration count in all stands. A total of 77 plant species represented by 44 herbs, 13 woody species, 8 grasses and 12 unidentified species were recorded in the soil seed bank from all stands. Similarity between the soil seed bank and aboveground flora was very low implying that the role of soil seed banks is negligible rather dispersal plays an important role in the process of regeneration. These results support the concept that forest plantations can foster the regeneration of native woody species, thereby increasing biological diversity, provided that there are seed sources in the vicinity of the plantations.     

Microbial biomass in subtropical forest soils： effect of conversion of natural secondary broad-leaved forest to Cunninghamia lanceolata plantation

Conversion of natural secondary broad-leaved forest to Cunninghamia lanceolata plantation is a common management practice in subtropical China. In this study, we compared soil physico-chemical properties, microbial biomass in one natural secondary broad-leaved forest and two C. lanceolata plantation sites to estimate the effects of forest conversion on soil microbial biomass at the Huitong Experimental Station of Forestry Ecology, Chinese Academy of Sciences. Concentrations of soil organic carbon, total nitrogen, NH4^＋-N and microbial biomass carbon and nitrogen were much lower under C. lanceolata plantations as compared to natural secondary broad-leaved forest. Soil microbial biomass C in the first and second rotation of C. lanceolata plantations was only 53%, 46% of that in natural secondary broad-leaved forest, and microbial biomass N was 97% and 79%, respectively. The contribution of microbial biomass C to soil organic C was also lower in the plantation sites. However, the contribution of microbial N to total nitrogen and NH4^＋-N was greater in the C. lanceolata plantation sites. Therefore, conversion of natural secondary broad-leaved forest to C. lanceolata plantation and continuous planting of C. lanceolata led to the decline in soil microbial biomass and the degradation of forest soil in subtropical China.