土地利用方式对湿润亚热带土壤硝化作用的影响

在土壤最大持水量60%和30℃条件下对采自江西的自然土壤(森林和灌丛)和农业利用土壤(稻田、旱地和茶园)进行了实验室培养,研究土地利用对硝化作用的影响。结果表明,由于土壤呈酸性(pH4.2～6.3,平均为4.9),供试土壤的硝化作用很弱甚至缺失。当无外加铵态氮时,土壤的硝化速率与有机氮矿化速率呈显著的线性关系(p<0.01),而与土壤pH无关;当外加铵态氮使基质饱和时,硝化速率与土壤pH显著相关(p<0.01)。农业利用显著提高土壤的硝化作用能力,绝大部分自然土壤(78%)的净硝化速率小于净矿化速率,无机氮以铵态氮为主,而绝大部分农业利用土壤(74%)的净硝化速率大于净矿化速率。农业利用通过提高土壤pH、氮肥施用刺激硝化作用及改善土壤磷素供应状况等途径促进土壤的硝化作用。农业利用土壤硝化作用能力的提高增加了氮肥以硝态氮形态淋失的风险。     

Properties and components of deposit which occurred inside a drainage tube

In poorly drained fields, tube drains are used to improve drainage. In some cases, however, there are fields where the effects of tube drainage have deteriorated within several years after installation. One cause of malfunction is low permeability of backfilled soils (Ishiwata et al. 1990, 1992, 1993). Another cause is clogging of tubes by deposits (Trafford et al. 1973; Dent 1986; Koutani et al. 1989; Kusaka et al. 1993; Kaneko et al. 1995).     

pH regulates key players of nitrification in paddy soils

Increasing lines of evidence have suggested the functional importance of ammonia-oxidizing archaea (AOA) rather than bacteria (AOB) for nitrification in upland soils with low pH. However, it remains unclear whether niche specialization of AOA and AOB occurs in rice paddy wetlands constrained by oxygen availability. Using DNA-based stable isotope probing, we conclude that AOA dominated nitrification activity in acidic paddy soils (pH 5.6) while AOB dominated in alkaline soils (pH 8.2). Nitrification activity was stimulated by urea fertilization and accompanied by a significant increase of AOA in acid soils and AOB in alkaline soils. DNA-based stable isotope probing indicated significant assimilation of ¹³CO₂ for AOA only in acidic paddy soil, while AOB was the solely responsible for ammonia oxidation in the alkaline paddy soil. Phylogenetic analysis further indicated that AOA members within the soil group 1.1b lineage dominated nitrification in acid soils. Ammonia oxidation in the alkaline soil was catalyzed by Nitrosospira cluster 3-like AOB, suggesting that the physiological diversity of AOA is more complicated than previously thought, and soil pH plays important roles in shaping the community structures of ammonia oxidizers in paddy field.     

N<Subscript>2</Subscript>O production pathways relate to land use type in acidic soils in subtropical China

Purpose

Agricultural practises impact soil properties and N transformation rate, and have a greater effect on N₂O production pathways in agricultural soils compared with natural woodland soils. However, whether agricultural land use affects N₂O production pathways in acidic soils in subtropical regions remains unknown.

Materials and methods

In this study, we collected natural woodland soil (WD) and three types of agricultural soils, namely upland agricultural (UA), tea plantation (TP) and bamboo plantation (BP) soils. We performed paired ¹⁵N-tracing experiment to investigate the effects of land use types on N₂O production pathways in acidic soils in subtropical regions in China.

Results and discussion

The results revealed that heterotrophic nitrification is the dominant pathway of N₂O production in WD, accounting for 44.6 % of N₂O emissions, whereas heterotrophic nitrification contributed less than 2.7 % in all three agricultural soils, due to a lower organic C content and soil C/N ratio. In contrast, denitrification dominated N₂O production in agricultural soils, accounting for 54.5, 72.8 and 77.1 % in UA, TP and BP, respectively. Nitrate (NO₃ ^?) predominantly affected the contribution from denitrification in soils under different land use types. Autotrophic nitrification increased after the conversion of woodland to agricultural lands, peaking at 42.8 % in UA compared with only 21.5 % in WD, and was positively correlated with soil pH. Our data suggest that pH plays a great role in controlling N₂O emissions through autotrophic nitrification following conversion of woodland to agricultural lands.

Conclusions

Our results demonstrate the variability in N₂O production pathways in soils of different land use types. Soil pH, the quantity and quality of organic C and NO₃ ^? content primarily determined N₂O emissions. These results will likely assist modelling and mitigation of N₂O emissions from different land use types in subtropical acidic soils in China and elsewhere.

     

Long-term fertilization effects on active ammonia oxidizers in an acidic upland soil in China

The effects of long-term fertilization of acidic soils on ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and its ecological implications remain poorly understood. We chose an acidic upland soil site under long-term (27-year) fertilization to investigate ammonia oxidizer communities under four different regimes: mineral N fertilizer (N), mineral NPK fertilizer (NPK), organic manure (OM) and an unfertilized control (CK). Soil net nitrification rates were significantly higher in OM soils than in CK, N or NPK soils. Quantitative analysis of the distribution of amoA genes by DNA-based stable isotope probing revealed that AOA dominate in CK, N and NPK soils, while AOB dominate in OM soils. Denaturing gradient gel electrophoresis and clone library analyses of amoA genes revealed that Group 1.1a-associated AOA (also referred to as Nitrosotalea) were the most dominant active AOA population (>92%), while Nitrosospira Cluster 3 and Cluster 9 were predominant among active AOB communities. The functional diversity of active ammonia oxidizers in acidic soils is affected by long-term fertilization practices, and the responses of active ammonia oxidizers to mineral fertilizer and organic manure are clearly different. Our results provide strong evidence that AOA are more highly adapted to growth at low pH and low substrate availability than AOB, and they suggest that the niche differentiation and metabolic diversity of ammonia oxidizers in acidic soils are more complex than previously thought.     

Heterotrophic nitrification by sodium chloride-tolerant fungi in soils added with sodium chloride

Abstract

Recently, fungi with the ability of heterotrophic nitrification have been isolated from acid forest soils (Lang and Jagnow 1986; Stroo et al. 1986). It is suggested that under unsuitable conditions for autotrophic nitrification, heterotrophic processes for NO₂ ^- and NO_{3 -} production could be advantageous.     

Urea Hydrolysis of Tea Soils as Influenced by Incubation Period,Soil pH,and Nitrification Inhibitor

Abstract

Laboratory incubation studies were conducted with south Indian tea soils to investigate the influence of soil pH, incubation period, and nitrification inhibitor on urea hydrolysis. The soils used in this experiment were sampled from six different regions of south India. The physicochemical properties, urea hydrolysis as influenced by soil pH, incubation period, and nitrification inhibitor were determined. There was a strong positive correlation between urease activity and organic‐matter content of tea soils, whereas physicochemical properties failed to show any relationship with urease activity. The urease activity was highest in Munnar soils. At 25°C, the activity reached maximum within 15 days after fertilizer application, and it was considerably high up to 36 days in the soils of Anamallais, 18 days in Munnar, and 27 days in other zones studied, which revealed the minimum interval between two successive urea fertilizer applications. Soils of different zones showed a different pattern of urease activity when the soil pH was changed artificially between 4 and 5.5. Addition of nitrification inhibitor [dicyandiamide, DCD] to urea prevented nitrate ion formation, resulting in the accumulation of desirable ammonium ions.     

Nitrification in acid tea soils and a neutral grassland soil: Effects of nitrification inhibitors and inorganic salts

Nitrification was much slower in five strongly acid (pH 4.0–4.3) soils from tea plantations in Sri Lanka than in a near-neutral grassland soil from the U.K., suggesting that the nitrifiers in these tea soils are close to the lower limit of their pH range. Nitrapyrin effectively inhibited nitrification in all the soils: dicyandiamide was less effective. Low concentrations of KC1 slowed nitrification in the acid tea soils but not in the near-neutral grassland soil. The concentrations of KC1 used (up to 20 mM) were sufficient to cause measurable decreases in soil pH in both acid and neutral soils. It is proposed that this salt-induced decrease in pH is detrimental to nitrifying organisms operating at the limit of their pH range but not to nitrifiers nearer their pH optimum.     

Effect of phosphorus on zinc toxicity in tea pollen tube growth

Although zinc (Zn) is an essential element for the growth of higher plants, excess supply may lead to growth inhibition. Symptoms of Zn toxicity are characterized by a reduction in root growth and leaf expansion followed by chlorosis (Mengel and Kirkby 1987), especially root elongation is severely inhibited (Godbold et al. 1983). Due to the increase of input of Zn to farmland by the application of sewage sludge or large amounts of Zn-containing pig manure, Zn toxicity may become an important problem in certain regions (Ruano et al. 1987). In addition, Zn toxicity is also a problem in some acidic soils (Takahashi et al. 1980).

Increasing soil pH by liming is the most effective procedure for decreasing both Zn content and Zn toxicity in plants (White et al. 1979), because Zn solubility decreases 100 times for each unit increase in pH (Neue and Lantin 1994). As an alternative approach, application of large amounts of phosphorus (P) fertilizer was employed to detoxify Zn (Takahashi et al. 1980). However, the mechanisms responsible for the detoxification of the excess Zn by P is remained to be elucidated.

Interactions between Zn and P, which may occur in the rhizosphere and in the uptake and translocation processes, are complex. To separate these factors, in the present study, pollen tubes of tea (Camellia sinensis L.) were used as a model, and the efrect of P on pollen tube growth under Zn toxicity was studied.     

N2O and NO production in various Chinese agricultural soils by nitrification

Eleven types of agricultural soils were collected from Chinese uplands and paddy fields to compare their N₂O and NO production by nitrification under identical laboratory conditions. Before starting the assays, all air-dried soils were preincubated for 4 weeks at 25 °C and 40% WFPS (water-filled pore space). The nitrification activities of soils were determined by adding (NH₄)₂SO₄ (200 mg N kg⁻¹ soil) and incubating for 3 weeks at 25 °C and 60% WFPS. The net nitrification rates obtained fitted one of two types of models, depending on the soil pH: a zero-order reaction model for acidic soils and one neutral soil (Group 0); or a first-order reaction model for one neutral soil and alkaline soils (Group 1). The results suggest that pH is the most important factor in determining the kinetics of soil nitrification from ammonium. In the Group 1 soils, initial emissions (i.e. during the first week) of N₂O and NO were 82.6 and 83.6%, respectively, of the total emissions during 3 weeks of incubation; in the Group 0 soils, initial emissions of N₂O and NO were 54.7 and 59.9%, respectively, of the total emissions. The net nitrification rate in the first week and second-third weeks were highly correlated with the initial and subsequent emissions (i.e. during the second and third weeks), respectively, of N₂O and NO. The average percentages of emitted (N₂O+NO)-N relative to net nitrification N in initial and subsequent periods were 2.76 and 0.59 for Group 0, and 1.47 and 0.44 for the Group 1, respectively. The initial and subsequent emission ratios of NO/N₂O from Group 0 (acidic) soils were 3.77 and 2.52 times, respectively, higher than those from Group 1 soils (P<0.05).     

Effects of the herbicide glyphosate on nitrification in four soils from Atlantic Canada

The herbicide glyphosate, supplied as Roundup (Monsanto Canada Inc.), was tested for effects on nitrification in four soils from Atlantic Canada. These included a sandy loam (pH 6.8), two silt loam (pH 6.4 and 5.8) agricultural soils and a clay loam forest soil (pH 3.5). Glyphosate was tested at normal field exposure rates (FR) and levels up to 200 times higher. FR values ranged from 19.83 to 29.26 ppm (jig glyphosate g^?1 soil). Glyphosate had no deleterious effects on nitrification in any soil when tested at FR concentrations. In the sandy loam soil nitrification was significantly stimulated at a glyphosate level 50 times higher than FR. With this soil and one of the silt loam soils (pH 6.4) glyphosate levels of 100 times FR and higher were required for a significant inhibition of nitrification. With the other silt loam soil (pH 5.8) glyphosate significantly inhibited nitrification at concentrations 10 times FR and higher. Nitrification in the acidic forest soil was very low and accurate toxicity data could not be obtained. The EC₅₀ of glyphosate towards nitrification in soil ranged from 1435 to 2920 ppm, which corresponds to exposure levels from 67 to 150 times higher than recommended field application rates. The use of glyphosate in agriculture and forestry should have no toxic effects on nitrification in soil.     

Soil pH controls nitrification and carbon substrate utilization more than urea or charcoal in some highly acidic soils

Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterized by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity, and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil, suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.     

Responses of bacterial and archaeal ammonia oxidisers of an acidic luvisols soil to different nitrogen fertilization rates after 9?years

It is still not clear which group of ammonia-oxidizing microorganisms plays the most important roles in nitrification in soils. Change in abundances and community compositions of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) under long-term different nitrogen (N) fertilization rates were investigated in an acidic luvisols soil using real-time polymerase chain reaction and denaturing gradient gel electrophoresis, respectively, based on the ammonia monooxygenase a-subunit gene. The experimental plan included the following treatments: control without N fertilization (N_CK), low N fertilization rate, middle N fertilization rate, and high N fertilization rate as 0, 100, 150, and 250?kg urea-N?ha^?1, respectively. Long-term different N fertilization rates did not significantly alter the total C and N contents of soil while it significantly decreased soil pH, which ranged from 5.60 to 5.20. The AOB abundance was more abundant in the N fertilization treatments than the N_CK treatment; the AOA abundance decreased by the increasing N fertilization rates, as did the ratios of AOA/AOB. The large differences in the potential nitrification rates among four treatments depended on the changes in AOA abundance but not to changes in AOB abundance. Phylogenetic analysis showed that the AOB communities were dominated by Nitrosospira clusters 1, 3, and 9 while all AOA sequences were grouped into soil/sediment cluster except for one sequence. Taken together, these results indicated that AOB and AOA preferred different soil N conditions and AOA were functionally more important in the nitrification than AOB in the acidic luvisols soil.     

土地利用方式对万木林土壤氨氧化微生物丰度的影响

以我国亚热带地区典型花岗岩发育酸性红壤为研究对象,选取福建建瓯万木林自然保护区封禁保护下5种自然植被和1种人工种植植被土壤,采用荧光实时定量PCR(Real-time PCR)技术测定了土壤氨氧化细菌(AOB)和氨氧化古菌(AOA)的群落丰度,采用15N稳定同位素成对标记和数值模型相结合的方法测定了土壤初级硝化速率。结果显示,长期封禁保护下的自然植被土壤pH低,土壤AOB数量偏低。人为种植和管理显著提高了土壤pH,促进了AOB的生长,其丰度比自然条件下提高了2个数量级,土壤初级硝化速率也显著提高,并与AOB数量存在显著的相关性,表明AOB是硝化作用的主要贡献者。5种自然植被条件下AOA的amoA基因拷贝数占泉古菌16S rRNA基因的比例都小于1%(0.01%～0.64%),在农业利用方式下上升到5.32%,表明并非所有泉古菌都具备氨氧化功能基因amoA,氮肥施用可能促进了氨氧化古菌的生长。     

Effect of aluminum on callose synthesis in root tips of tea (Camellia sinensis L.) plants

Aluminum (Al) toxicity is a major factor limiting yield production on acid soils (Foy 1983). The initial symptom of Al toxicity in many plants is manifested by the inhibition of root elongation (Ownby and Popham 1990; Llugany et al. 1994; Sasaki et al. 1994; Horst et al. 1997), which occurs during a very short period of time after exposure to Al (Llugany et al. 1994; Staß and Horst 1995). In a large number of recent reports, it was shown that the root apex plays a major role in the Al-sensitivity and response mechanisms (Zhang et al. 1994; Sasaki et al. 1997; Sivaguru and Horst 1998). However, it is interesting to note that stimulatory effects of Al on the growth of plants have also been reported in some studies (Chenery 1955; Konishi et al. 1985; Huang and Bachelard 1993; Osaki et al. 1997). In tea plant (Camellia sinensis L.) a stimulatory effect of Al on the growth was also demonstrated in some experiments, using intact plant (Chenery 1955; Konishi et al. 1985), cultured roots (Tsuji et al. 1994), and pollen tubes (Yokota et al. 1997). The growth of tea roots was typically more stimulated than that of shoots by Al (Konishi et al. 1985). It was assumed that Al effects might be due to the amelioration of phosphorus absorption (Konishi et al. 1985), secretion of malic acid from roots to dissolve aluminum phosphate in the rhizosphere (Jayman and Sivasubramaniam 1975), stimulation of growth of microorganisms on the root surface (Konishi 1990) or replacement of some functions of boron (Konishi 1992; Yokota et al. 1997). However, the stimulatory effects of Al on tea plant growth have not yet been el ucidated.

The formation of callose (1,3-β-glucan) has been reported as a common plant response to a variety of stresses, as well as mechanical, biophysical, chemical, and biological injury (Jaffe and Leopold 1984; Zhang et al. 1994). Increased synthesis of callose has been observed upon exposure to excess amounts of some elements, such as boron (McNairn and Currier 1965), cobalt, nickel, zinc (Peterson and Rauser 1979), and manganese (Wissemeier and Horst} 1987, 1992). Callose synthesis was also induced by Al in the roots of Triticum aestivum (Zhang et al. 1994) and Zea mays (Horst et al. 1997; Sivaguru and Horst 1998), suspension-cultured cells of Glycine max (Staß and Horst 1995), and protoplasts of Avena sativa (Schaeffer and Walton 1990) and Zea mays (Wagatsuma et al. 1995). Induction of callose synthesis in roots seems to be a very rapid physiological indicator of Al-induced injury or genotypical differences in Al sensitivity (Wissemeier and Horst 1992; Zhang et al. 1994; Horst et al. 1997). Nevertheless, Al-induced callose synthesis in tea plant, whose growth is stimulated by suitable Al concentrations, has not been described yet. Therefore, to elucidate the physiological basic effects of Al on tea plant, callose synthesis affected by Al in the root tips of intact plants was analyzed in the present study.     

Effects of afforestation on ammonification and nitrification rates in former agricultural soils

Abstract. The effects of afforestation on potential nitrification, nitrification and ammonification rates were studied at an experimental site in NE Scotland 4½ years after afforestation of former arable land. The site had been planted with three tree species (Sitka spruce, sycamore and hybrid larch) at three different planting densities, with half the plots treated with inorganic NPK fertilizer. Laboratory measurements of potential nitrification, nitrification and ammonification rates, measured using a perfusion system, were compared between the unforested control and combinations of the various treatments. Differences in soil pH and soil moisture content were also investigated.
Potential nitrification rates measured in plantation soils were significantly lower than in the unplanted control soil. Nitrification and ammonification rates were also consistently lower, although these differences were only significant in a few of the treatments. Soils planted with a normal tree density had a tendency to show higher nitrification rates compared to soils planted with a high tree density.
The results suggest that afforestation of former agricultural soils may cause changes in important parts of the soil N cycle soon after planting. At this early stage in the life of the plantation this appears to be unrelated to changes in soil pH or moisture content, even though soils beneath the trees are drier. The apparent change may be the result of differences in the soil microbial community associated with the type of organic matter substrate present in the unplanted and planted soils.     

Effect of rewetting air-dried soils on pH and accumulation of mineral nitrogen

The effect of rewetting a number of air-dried soils on pH and on accumulation of mineral-N was examined in a laboratory incubation study. When rewetted-soils were incubated at 25°C three patterns of change in soil _pH and in accumulation of mineral-N were observed. Ammonification and nitrification proceeded together in soils with pH values greater than 6.0; soil pH decreased whilst concentrations of nitrate rose and those of ammonium remained low. By contrast, in soils with pH values less than 5.0, although ammonification proceeded there was no appreciable nitrification; soil pH increased whilst concentrations of ammonium rose and those of nitrate remained very low. In a third group of soils with pH values between 5.0 and 5.5, there was a delay in nitrification, but ammonification was not retarded; soil _pH initially rose as concentrations of ammonium increased, but when nitrification subsequently commenced the _pH decreased, concentrations of nitrate rose and those of ammonium declined. When microbial activity in rewetted soils was inhibited by incubation at 3°C, or in a chloroform atmosphere at 25°C, there was little change in concentrations of ammonium and nitrate, and soil pH remained relatively constant.
Such changes in soil _pH, induced by ammonification and nitrification, are likely to have important consequences to soil chemical studies where _pH-dependent reactions are being studied using rewetted soils. Changes in pH can be minimized by using field moist rather than air-dried soils.     

尿素施用对砷污染土壤pH值及砷活性的影响

砷污染土壤在我国较为常见,是影响农作物生产的主要环境胁迫因子之一。本试验对两种砷污染土壤施用不同的尿素浓度后的研究表明:两种污染土壤的pH值在短期内都随着施入尿素浓度的增大而急剧上升,交换性As随着施用尿素浓度的增大同步增加。动态试验证实,pH值上升的现象是短期的,pH值在达到最大值后,缓慢下降,pH值下降幅度最大的阶段在3~4周时段;交换性As的含量与土壤pH值的变化密切相关,其变化趋势与土壤pH值呈正相关。生物毒理结果显示:短期内,施用尿素能显著增加玉米(Z.MaysL.)苗吸收污染的土壤中As。     

Autotrophic nitrification in a fertilized acid heath soil

The nature of nitrification in fertilized, acid heath soils was studied. Autotrophic ammoniumand nitrite-oxidizing bacteria were enumerated in non-fertilized and fertilized heath soils. Ammoniumoxidizing bacteria were not detected in the non-fertilized soils, whereas nitrite-oxidizing bacteria were only found in the organic layer. Enrichment of acid heath soils with NPK fertilizer increased the number of autotrophic ammonium- and nitrite-oxidizing bacteria in the organic (F + H) layer as well as in the upper part of the mineral (Ah) layer, although the pH of the soil hardly changed with fertilization. In soil suspensions of the upper mineral layer of fertilized heath soils, nitrification was shown to be autotrophic as nitrification was completely inhibited by the addition of nitrapyrin under both neutral and acid conditions. Stimulation of nitrification by addition of peptone appeared to be due to the increase in pH caused by ammonification of peptone. Under acid conditions, nitrification seemed to be coupled with net nitrogen mineralization. The possible influence of vegetation on nitrification is discussed.     

Soil microbial biomass and activity in Chinese tea gardens of varying stand age and productivity

Tea (Camellia sinensis) is a globally important crop and is unusual because it both requires an acid soil and acidifies soil. Tea stands tend to be extremely heavily fertilized in order to improve yield and quality, resulting in a great potential for diffuse pollution. The microbial ecology of tea soils remains poorly understood; an improved understanding is necessary as processes affecting nutrient availability and loss pathways are microbially mediated. We therefore examined the relationships between soil characteristics (pH, organic C, total N, total P, available P, exchangeable Al), the soil microbial biomass (biomass C, biomass ninhydrin-N, ATP, phospholipid fatty acids—PLFAs) and its activities (respiration, net mineralization and nitrification). At the Tea Research Institute, Hangzhou (TRI), we compared fields of different productivity levels (low, medium and high) and at Hongjiashan village (HJS) we compared fields of different stand age (9, 50 and 90 years). At both sites tea soils were compared with adjacent forest soils. At both sites, soil pH was highest in the forest soil and decreased with increasing productivity and age of the tea stand. Soil microbial biomass C and biomass ninhydrin-N were significantly affected by tea production. At TRI, microbial biomass C declined in the order forest>low>high>middle production and at HJS in the order stand age 50>age 9>forest>age 90. Soil pH had a strong influence on the microbial biomass, demonstrated by positive linear correlations with: microbial biomass C, microbial biomass ninhydrin-N, the microbial biomass C:organic C ratio, the microbial biomass ninhydrin-N:total N ratio, the respiration rate and specific respiration rate. Above pH_(KCl) 3.5 there was net N mineralization and nitrification, and below this threshold some samples showed net immobilization of N. A principal component (PC) analysis of PLFA data showed a consistent shift in the community composition with productivity level and stand age. The ratio of fungal:bacterial PLFA biomarkers was negatively and linearly correlated with specific respiration in the soils from HJS (r²=0.93, p=0.03). Our results demonstrate that tea cultivation intensity and duration have a strong impact on the microbial community structure, biomass and its functioning, likely through soil acidification and fertilizer addition.