Charcoal is a byproduct of incomplete combustion during fire events and can influence native soil carbon (C) mineralization. However, the influence of charcoal age and application rate on soil C mineralization remains unclear. In this study, we conducted a 78-day incubation experiment to assess CO2 emissions from subtropical forest soils amended with charcoal at three ages (fresh, 1 year, 6 years) and two application rates (1% and 3%). We measured physicochemical and surface properties of charcoal collected from the field and pH, total C and nitrogen (N), dissolved organic C, microbial biomass C and N, and enzyme activities of the soil/charcoal mixtures. We found that adding charcoal at the higher charcoal application rate (3%) significantly increased soil CO2 emissions, whereas the lower rate (1%) had no significant effect. Furthermore, the enhancement of CO2 emissions was reduced for older charcoal, likely due to physiochemical changes in charcoal with aging that reduced its capacity to stimulate microbial biomass and activity. Specifically, older charcoal exhibited lower pH, greater abundance of O-containing functional groups, and increased surface area and pore size. Partial least squares path modeling (PLS-PM) revealed that charcoal properties indirectly affected cumulative soil COQ emissions by altering soil properties, particularly pH and total C. Collectively, our findings demonstrate that the fire-derived charcoal can stimulate soil C mineralization, but this effect depends on the age of charcoal and the rate of its application. These results underscore the importance of incorporating charcoal aging into models that evaluate fire-related C cycling in forest ecosystems.

While wind-driven wildfires on the west slopes of the Cascades create extensive areas of stand-replacing (SR) effects, providing opportunities for Douglas-fir regeneration over multi-century time scales, recent studies have shown that forest development is strongly shaped by more frequent fires that cause predominantly non-stand replacing (NSR) effects. These NSR fires generate a complex array of stand structures and forest development pathways both within and outside of SR fire footprints. We build on these studies by describing mechanisms of tree mortality in old-growth Douglas-fir and western hemlock forest burned at low intensity on the 2023 Lookout Fire. Our data were collected in coordination with incident management staff and include pre-fire fuels and vegetation, fire behavior, and immediate post-fire and over-winter effects. We also consider implications for remote sensing and fire management. Average rate of spread (< 2 m h−1) and fireline intensity (22 kW m−1) were exceedingly low. High duff loadings (271 Mg ha−1), often derived from downed logs, were 92

Pile burning is an effective method for removing woody debris generated during forest management practices, yet the influence of fuel load on soil carbon (C) and nutrient dynamics remains insufficiently understood. In a clear-cut site of Pinus massoniana plantation in south China, we established twelve hand-built piles with two fuel loads (LF, 50 kg per pile; HF, 100 kg per pile). Surface soils (0–5 cm) were collected at 1, 60, 180, and 270 days after burning. We quantified total and labile C, nitrogen (N), and phosphorus (P) pools, measured enzyme activities related with C, N and P cycling, and calculated ecosystem multifunctionality indices for each nutrient cycle. The results showed that pile burning had no immediate effects on soil total C, total N, microbial biomass C, or NH4+-N. However, NH4+-N increased and MBC decreased significantly 60 days after burning. Fire-induced increases in dissolved organic C and N and decreases in NO3--N persisted for 60 days, whereas microbial biomass N remained lower throughout the 270-day experimental period. Fuel load had little influence on the overall responses of soil C and N pools to pile burning, whereas soil P was highly sensitive to fuel load. In the short term, HF piles significantly reduced total P, available P and P-cycle multifunctionality relative to LF piles and unburnt controls. These findings indicate that fuel load primarily mediates the ecological effects of pile burning through alterations in soil P availability and associated ecosystem functions in subtropical plantation forests.

Age-related alterations in nitrogen (N) acquisition by canopy trees has been extensively explored; however, little is known regarding N uptake strategy of coexisting plant species during forest plantation development. A field experiment was conducted to evaluate plant N uptake in subtropical Cunninghamia lanceolata plantations of varying ages (7, 15, 24, and 34 years). Using a hydroponic method, we assessed the root capacity to uptake NH4+, NO3−, and glycine by the coexisting tree (C. lanceolata), a shrub (Ficus hirta), and a herb (Pteris semipinnata). Both the canopy and understory vegetation preferred NH4+ as a N source in hydroponic culture, followed by glycine and then NO3−. Root N uptake rates with increasing plantation age varied by plant species and N source. For F. hirta, the NO₃⁻ uptake rate increased from 0.38 to 0.78 μg N·g⁻1 root·h⁻1, while it decreased from 1.64 to 0.30 μg N·g⁻1 root·h⁻1 for P. semipinnata as the C. lanceolata plantation developed. No clear pattern was observed for C. lanceolata. A positive relationship between root AM colonization rate and NO3−uptake rate was observed for F. hirta, but not for C. lanceolata and P. semipinnata. The contribution of glycine to P. semipinnata total N uptake increased progressively with plantation age. Our results indicate that N acquisition among coexisting tree and understory vegetation varied with plant species and N form in hydroponic culture. Notably, understory plants exhibited greater flexibility in N acquisition than overstory trees during the development of subtropical C. lanceolata plantations.

As one of the most durable legacies of fire, charcoal plays a key role in long-term soil carbon (C) storage due to its long residence time. However, few attempts have been made to investigate the impact of naturally deposited charcoal on soil organic C (SOC) stability in fire-affected forests in a long-term field trial. In this study, we used a field-based charcoal manipulation experiment to assess the input of charcoal on post-fire SOC stability in a subtropical plantation forest. The experimental design included four treatments: removal of all visible charcoal (C0), charcoal retained in-situ (C1), addition of charcoal removed from C0 plots to separate plots (C2), and an unburnt control (UB). Seven years after treatment implementation, soil samples were collected from 0 to 10 and 10-20 cm depth to measure soil organic C fractions, microbial biomass C (MBC), C pool management index (CPMI), aggregate stability and the distribution of organic C within aggregate size classes. Our results showed that charcoal had no significant effect on dissolved organic C (DOC) at either depth. However, charcoal significantly influenced MBC, CPMI, and the distribution of SOC in small aggregate fractions (<0.05 mm) in a depth-dependent manner. At the 0-10 cm depth, CPMI and the allocation of SOC to small aggregates were significantly higher in C2 and UB soils than in C0 (p < 0.05), whereas no differences were observed at the 10-20 cm depth. In contrast, MBC was significantly higher in C2 and UB than in C0 soils only at the 10-20 cm depth (p < 0.05). Despite the persistence of negative effects from the initial burning event, our findings suggest that fire-derived charcoal can enhance SOC stability by promoting microbial assimilation and facilitating SOC allocation to more stable aggregate fractions with longer turnover times. Taken together, these findings suggest that charcoal deposited during fire contributes to soil C stabilization in subtropical forest plantations subjected to broadcast burning.

Background Wind-driven wildfires on the west slopes of the Cascade Range create large areas of stand-replacing (SR) effects at multi-century timescales but less intense and more frequent non-stand-replacing (NSR) fires are now known to generate a complex array of stand structures and forest dynamics pathways in old growth, independent of, or in interaction with, SR fire. We report on the effects of low-intensity fire based on plot-based measurements of fuels and vegetation, fire behavior, and immediate and overwinter impacts in old-growth Douglas-fir and western hemlock forest ( Pseudotsuga menziesii var menziesii and Tsuga heterophylla (Raf.) Sarg.) on the 2023 Lookout Fire. Results In low intensity wildfire, high duff loadings, often in linear piles derived from downed logs, were largely consumed (89%, 247 Mg ha − 1 ). While towering, overstory Douglas-fir were minimally affected, 32% of poles, 7% of canopy trees (≥ 15.2 cm diameter), and 32% of snags of all sizes fell during or shortly after the fire. Most live trees fell from combustion impacts on primary roots which, for western hemlock, the most common tree species, was associated with how much duff was consumed. Further, 15% of live poles and 32% of live canopy trees, mostly western hemlock, experienced significant primary root heating. Western hemlock was particularly vulnerable to root impacts because its primary roots tended to grow exposed at the top of the mineral soil, especially where they were “perched” from having regenerated on nurse logs. Monitoring in the early growing season 7–8 months after the fire showed that, of trees alive before and standing immediately after the fire, 28% of poles and 6% of canopy trees fell and 31% of poles and 14% of canopy trees died standing with mortality strongly related to the extent of canopy injury from the fire. All told, 60% of poles and 13% of canopy trees had died by the early growing season after the fire. Primary root and root-collar heating was not significantly related to mortality of standing trees 7–8 months after the fire, but we expect that many trees will die from that cause in the coming years. Though high duff loadings were consumed by the fire and there was substantial thinning from below, the overstory of large Douglas-fir and other old-growth characteristics persisted, including most downed woody debris in large-diameter logs which will be augmented by fire-killed trees that have already fallen or will fall in the future. Conclusions NSR fire can cause substantial effects below the Douglas-fir overstory in old-growth on the west slopes of the Cascades, contributing to pyrodiversity in these ecosystems. Our coordinated pre-, active-, and post-wildfire measurements led to mechanistic insights about how these effects occur. Treefall during and immediately after fire and high loadings of duff and downed logs challenged fire suppression operations but treefall hazards for firefighters might be mitigated along shaded fuel breaks before fires ignite, guided by an understanding of why trees fall.

Charcoal, a byproduct of biomass burning, is widely and heterogeneously distributed in fire-affected ecosystems. However, few field studies have been conducted to evaluate the effects of fire-deposited charcoal on the post-fire soil quality. In this study, we aimed to investigate whether charcoal generated during post timber harvest broadcast burning influenced the recovery of individual soil properties and overall soil quality in subtropical forest plantations. Broadcast burning was conducted on experimental Pinus massoniana plantation timber harvest sites in southern China. Surface soils (0–10 cm) were collected in plots established on the burnt sites five years after the disturbance event. Plots were established immediately after burning with three different levels of charcoal input (C0, removal of all visible charcoal; C1, charcoal retained in-situ; C2, charcoal removed from C0 added to C2) and an unburnt control (UB). Thirty-two soil indicators representing soil physical, chemical, and biological properties were determined. The results showed that 11 indicators exhibited significant differences among the treatments, with significantly lower SOM, microbial biomass carbon (MBC), peroxidase (POD) and leucine aminopeptidase (LAP) activities for the C0 and C1 plots than the UB plots (P < 0.05), while no significant difference was observed between the UB and C2 plot (P > 0.05). The soil available N, P and exchangeable nutrient contents were not significantly different among the treatments (P > 0.05). Our results indicate that SOM and microbial attributes did not recover five years after the disturbance event and that charcoal appeared to play a positive role in the post-fire soil restoration. Whether the accelerated recovery of soil restoration induced by charcoal might contribute to higher forest productivity needs to be testified in combination with plant growth and performance analysis in the future.

Plants influence soil microbial communities through aboveground litter and root inputs. However, studies on the effects of various plant carbon inputs on soil microbial communities in grassland ecosystems are limited. We characterized bacteria, ammonia-oxidizing bacteria and ammonia-oxidizing archaea using 16S rRNA amplicon sequencing and quantified the amoA gene via real-time PCR. We assessed the impacts of different carbon inputs (litter addition, litter removal, plant removal, and their interactions) on soil bacterial community structure, composition, nitrogen cycle functions, co-occurrence networks and assembly in a temperate grassland ecosystem following over a decade of experimental manipulations. Plant removal significantly affected soil total carbon content and the ratio of total carbon to total nitrogen content. The impact of plant removal was stronger than that of litter changes, significantly influencing bacterial community structure. Compared to ammonia-oxidizing archaea, ammonia-oxidizing bacteria dominated semi-arid grassland communities, and plant removal inhibited potential denitrification and nitrogen fixation groups. Notably, plant removal increased the complexity but reduced the stability of bacterial co-occurrence networks. It also enhanced deterministic processes and decreased the relative contribution of stochastic processes in bacterial communities. This study elucidates the effects of various carbon input patterns on soil bacterial communities, highlighting their importance for comprehensively understanding the stability of these communities and their role in nitrogen cycling in temperate grasslands amid global change.

Charcoal, a byproduct resulting from incomplete combustion of biomass in fire events, can modify the physical properties of soil due to its high porosity and large surface area. To evaluate the impact of fire-deposited charcoal on soil hydraulic characteristics, soil–charcoal mixtures were analyzed to investigate the effects of different application doses (wt%: 0, 1%, 3%, 5%, 10% and 20%) of charcoal on soil bulk density (BD), porosity (total, capillary, and non-capillary), residual moisture after free drainage (RM), saturated water content (SC), and saturated hydraulic conductivity (Ks) of loamy and sandy soils collected from subtropical forests in south China. The results showed that the impact of charcoal on soil’s physical and hydraulic properties depends on the soil type and the application dose. The incorporation of charcoal significantly decreased the BD of sandy soil (p < 0.001), while a significant decrease in BD in loamy soil was only observed as a result of the higher application doses (10% and 20%) (p < 0.001). Charcoal application doses of 5% or higher led to a significant increase in the total porosity (TP) of sandy soil (p < 0.001) and doses of 3% and 20% resulted in a significant increase in the TP of loamy soil (p < 0.001). The capillary porosity (CP) of both sand and loamy soils significantly increased when charcoal was applied at doses of 3% or higher (p < 0.001). The minimum charcoal application dose that significantly increased the RM in sandy soil was 5%, while for loamy soil, the minimum effective dose was 10%. Charcoal applied at a dose of 3% significantly increased the Ks of sandy soil (p < 0.001), while no significant effect on Ks was observed for loamy soil (p > 0.05). Collectively, our findings suggest that fire-derived charcoal enhances the soil water-retention capacity in subtropical forests, with the effects becoming more pronounced at higher application doses and being particularly notable in sandy soil compared to loamy soil.

Abstract Biochar is produced by burning biomass under oxygen‐limited conditions, and it has been widely used as a soil amendment to improve soil functions such as nutrient retention. However, whether the impact of biochar application on soil nitrogen (N) transformation and N2O emission varies with the pyrolysis temperature remains unclear, especially in different forest types in subtropical regions. In this study, a 60‐day laboratory incubation experiment was conducted to evaluate the impact of biochar with different pyrolysis temperatures (300°C [BC300], 500°C [BC500], and 800°C [BC800]) on net N transformation rates and N2O emission in soils collected from Castanopsis kawakamii dominated natural forest (NF) and Chinese fir (Cunninghamia lanceolate, CF) plantation in subtropical China. The results showed that the application of biochar significantly increased soil ammonium (NH4+) content (p < 0.001) but reduced nitrate (NO3−) content (p < 0.001) compared with the control. The soil NH4+ content of the BC800 treatment was significantly higher than that of other treatments (p < 0.001). Biochar application significantly reduced soil net N mineralization (NRmin) and nitrification (NRnit) rate (p < 0.001), but increased net ammonification (NRamm) rate (p < 0.001). The application of biochar led to a remarkable decrease in cumulative N2O emission compared to the control (p < 0.001). In particular, soils treated with high‐temperature biochar emitted significantly lower N2O compared to other treatments (p < 0.001). The partial least squares path model demonstrated that biochar influenced N2O emission through a direct effect in NF soil and an indirect effect in CF soil. This study highlights the distinct role of biochar, particularly that produced under high pyrolysis temperatures as a soil amendment to mitigate N2O emission and promote N retention in both subtropical natural and planted forests.

Tannin is the fourth most abundant biochemical compound in vascular plants. Due to its protein-binding capacity, tannin can interfere with soil nitrogen (N) biogeochemical cycling processes and potentially contribute to soil N conservation. Yet little is known about the effect and mechanism of tannin on regulating soil N transformation process. We devised microcosm study to evaluate the effects of different concentration and types of tannin on N-cycling processes. Soils were collected from subtropical Chinese fir plantation and incubated for 28 days. Two incubation experiments were carried out simultaneously; one was treated with different concentrations of condensed tannin (CT), including low (1 mg·g−1), middle (5 mg·g−1), and high (10 mg·g−1) concentrations of tannin, while the other was treated with different types of tannin including tannin acid (TA), catechin (CA), and tannin acid + catechin (TC). Soil enzyme activities, MBC, MBN, DOC, DON, soil N transformation rate and respiration were measured in both experiments. In both incubation experiments, tannin amendment significantly lowered soil nitrate content compared with control soil, as well as soil net nitrification and mineralization rates. In contrast, we observed consistent increase of soil enzyme activities involved in N cycling (amidase, N-acetyl-β-D-glocosaminidase, polyphenol oxidase, peroxidase, urease and laccase) under tannin treatments. This stimulating effect on soil enzyme activities is likely to due to the fact that tannin may serve as a carbon substrate for soil microorganisms rather than a toxic compound, as indicated by enhancing soil respiration with tannin addition. However, the stimulating effect on soil respiration eclipsed as the incubation proceeded. Furthermore, soil net mineralization rate, on average, decreased by 7.8

Charcoal is a carbonaceous particulate matter with a highly aromatic structure produced by incomplete combustion, and it can cause persistent long-term effects on soil ecological functions. In this study, we determined soil organic carbon pools and associated enzyme activities following five years of different charcoal treatments[charcoal removal (B0), charcoal retained in situ (B1), and the addition of charcoal removed from B0(B2)] and the unburnt control (UB) in a recently harvested Pinus massoniana plantation subjected to broadcast burning. The results showed that dissolved organic carbon (DOC), microbial biomass carbon (MBC), coarse and fine particulate organic carbon (CPOC and FPOC), and recalcitrant carbon (RC) contents were significantly lower in B1 than those in UB soil (P<0.05). The MBC and FPOC contents of B2 soil were comparable to those of UB soil, which were significantly higher than those of B0 soil (P<0.001). There was no difference in MBC/TC between the B2 and UB soils, whereas MBC/TC was significantly lower in B0 than in UB soil (P<0.05). β-glucosidase and peroxidase activities of B0, B1, and B2 soils were significantly lower than that of UB soil (P<0.01), and polyphenol oxidase activity was significantly lower in B0 and B2 soils than in UB soil (P<0.01). No significant difference in soil TC, DOC, readily oxidized carbon (ROC), CPOC, and RC content as well as associated enzyme activities was observed among the charcoal treatments (P>0.05). Redundancy analysis showed that sucrose and polyphenol oxidase were the key drivers influencing soil organic carbon fractions, accounting for 16.3% and 12.7% of the total variance, respectively. Overall, our findings indicated that fire-deposited charcoal played a positive role in enhancing soil microbial biomass carbon recovery, soil organic carbon accumulation, and stability, highlighting the importance of charcoal in the management of subtropical plantations in the future.

IntroductionNutrient resorption is a key mechanism to conserve nutrients and overcome nutrient limitation in perennial plants. As an important afforested tree species in subtropical regions, Pinus massoniana grows well in nutrient-poor environments, however, the age-related pattern of nutrient acquisition strategy and the underlying mechanisms in P. massoniana plantations remain unclear.MethodsIn this study, concentrations of nitrogen (N) and phosphorus (P) were measured in green and senesced needles, roots and soil samples collected from P. massoniana plantations with different stand ages (9-, 17-, 26-, 34- and 43-year-old) in south China. From these samples, nutrient resorption efficiency (RE) and stoichiometry were calculated.ResultsNeedle PRE significantly decreased with stand age, while there was no clear pattern of NRE along the stand development. Green needle N:P in older stands was significantly lower than in younger ones. Senesced needle C:P and N:P significantly decreased with stand age. Root and soil available P concentrations were significantly higher in older stands than in younger ones, and PRE was negatively correlated with soil available P concentration.DiscussionThere was a shift from “conservative consumption” to “resource spending” P-use strategy, and P limitation decreased with stand development of P. massoniana plantations. The results provide information of changes in nutrients dynamics, which is relevant for the sustainable management of subtropical forest plantations.

为揭示丛枝菌根真菌(AMF)群落组成和多样性随林木生长发育的变化特征,以中亚热带不同林龄(8、16、25 和35 a)杉木为研究对象,利用醋酸墨水法测定AMF侵染率,采用高通量Illumina MiSeq测序技术分析杉木根内AMF群落组成和多样性特征.结果表明:杉木AMF侵染率均>60％,随林龄增加呈现先升高后降低的趋势,25 a杉木AMF侵染率显著高于 8 a杉木(P<0.05).从 4 个不同林龄杉木根系AMF中得到 502516 条有效序列和 1070 个操作分类单元,隶属于 1 门、2 纲、3目、4 科、10 属.球囊霉属(Glomus)和根内球囊霉属(Rhizophagus)为杉木AMF群落的优势类群,其相对丰度在不同林龄间无显著差异(P>0.05).AMF多样性指数包括Chao1、Shannon、Simpson和PD-whole-tree指数,均随林龄增加而逐渐降低,35 a杉木Chao1 和PD-whole-tree指数极显著低于其他林龄(P<0.01).基于相似性和非度量多维尺度分析表明,35 a杉木根内AMF群落结构与其他林龄存在显著差异;冗余分析表明,土壤可溶性有机碳和铵态氮含量分别是影响杉木AMF群落多样性和组成的主要因子.杉木根内AMF侵染率和群落多样性在成熟林阶段发生显著改变,不同林龄杉木AMF类群组成也有差异,未来应深入研究AMF类群在杉木不同生长阶段的生态功能,为提高杉木人工林的养分利用效率和可持续经营提供依据.

Mangrove species are undergoing environmental changes from nutrient-poor to enrichment due to the large nutrient input. The potential difference in adaptive strategies between the slow- and fast-growing species may lead to great changes in species interaction and ecosystem stability. This study aims to test whether the slow-growing species Aegiceras corniculatum (L.) Blanco and Kandelia obovata Sheue, Liu & Yong sp. nov. are distinctly different from a fast-growing species Laguncularia racemosa (L.) Gaertn. f. in response to soil nutrient enrichment. With the increase of soil nutrients, L. racemosa shifted from a more conservative to a more acquisitive strategy. The potential causes included the increases in specific leaf area, nutrient resorption efficiency, and photosynthetic capacity as indicated by the increase of leaf δ13C and unchanged leaf succulence, as well as the relocation of photosynthetic products as indicated by the shift toward fast-growing at the cost of constructive and defense compounds. In contrast, A. corniculatum and K. obovata maintained conservative strategies at any soil nutrient levels with only a slight increase in growth. These findings implied that L. racemosa will be more competitive over the slow-growing species in nutrient-rich soils through altering adaptive strategies.

Soil enzyme activity is an important index to characterize the nutrient requirements and nutrient limitations of soil microorganisms. In this study, Pinus massoniana plantations of different stand ages (9, 17, 26, 34, and 43 a) in mid-subtropical China were taken as the research object; the activities of β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), leucine amino-peptidase (LAP), acid phosphatase (AP), polyphenol oxidase (POX), and peroxidase (POD) were determined; and soil enzyme stoichiometric ratios were also calculated to investigate the soil microbial nutrient limitations of P. massoniana plantation development. The results showed that the activities of BG, NAG, AP, POX, and POD were enhanced with the increase in stand age, and the activity of LAP was the lowest at 17 a, which showed a significant difference and fluctuated among the neighboring stand ages. The soil enzyme C:N:P stoichiometric ratio was 1:1:0.56, which deviated from the global ecosystem enzyme C:N:P stoichiometric ratio (1:1:1). The enzyme C:N increased, whereas the enzyme N:P decreased, with increasing stand age, and both ratios tended to be stable after 17 a. There was no significant difference in enzyme N:P among different stand ages. The vector length of enzyme stoichiometry was not significantly different among the five stand ages. The vector angles increased with the increase in stand ages and tended to be stable after 17 a of stand age, but the angles were less than 45°. Redundancy analysis (RDA) revealed that soil carbon quality index and pH were the main factors influencing soil enzyme activity and the associated stoichiometric ratio. Our findings indicated that P. massoniana plantation soil microorganisms at different growth stages were all subjected to N limitation, and the N limitation was alleviated with the increase in stand age; however, the P requirement was gradually enhanced. Therefore, the management of P. massoniana plantations should take care to increase nitrogen fertilizer at the early growth stage of P. massoniana, and more phosphorus fertilizers need to be applied with nitrogen at the late growth stage in order to maintain the productivity and sustainable development of P. massoniana plantations.

为探究中亚热带杉木土壤微生物群落随林龄变化特征,以中亚热带7,24,34 a生杉木人工林为研究对象,采用磷脂脂肪酸(PLFA)法分析其根际和非根际土壤微生物数量和群落结构及驱动土壤微生物变化的主要土壤环境因子.结果表明:随着杉木林龄的增长,非根际土壤各类微生物数量不断减少,根际土壤微生物数量不断增加,34 a生杉木人工林细菌含量、革兰氏阴性菌含量、Cy:MONO根际土壤显著高于非根际土壤,而其他各类微生物在根际和非根际土壤间均没有显著差异.相关分析和冗余分析结果表明:土壤环境因子对杉木土壤微生物群落有显著影响,其中有效磷和铵态氮含量对土壤微生物群落的影响较大,有效磷含量与土壤微生物群落呈正相关,土壤铵态氮含量与其呈负相关.因此,在杉木人工林管理过程中,可适当增加磷的输入,以增加土壤微生物数量,提高土壤质量,促进杉木的生长.

[目的]探讨土壤氮转化酶活性及根际效应随杉木生长发育的变化特征,为杉木人工林的施肥管理和可持续经营提供科学依据.[方法]以不同发育阶段杉木人工林(7、15、24、34?a)为研究对象,测定根际与非根际土壤氮转化酶活性(β-葡萄糖苷酶(BG)、乙酰-β-D-氨基葡萄糖苷酶(NAG)、蛋白水解酶(PRO)、脲酶(URE)、亮氨酸氨基肽酶(LAP)、硝酸还原酶(NR)),探讨不同发育阶段杉木人工林土壤氮转化酶活性、根际效应及其与土壤理化性质的关系.[结果]林龄和根际对6种土壤氮转化酶活性影响均存在显著差异(p<0.05);杉木林根际和非根际土壤氮转化酶活性均随林龄增加先下降后上升,不同林龄杉木根际土壤BG、NAG、PRO、URE和LAP活性均显著高于非根际土壤(p<0.05),根际与非根际土壤的NR活性差异因林龄而异,15?a和24?a杉木林根际土壤的NR活性极显著高于非根际土壤的(p<0.01),而7?a和34?a杉木林根际与非根际土壤的NR活性差异不显著(p>0.05).15?a杉木林土壤NR活性的根际效应显著高于7?a和34?a杉木林(p<0.05).杉木根际与非根际土壤酶活性的关键因素是碳氮比与铵态氮含量.[结论]中亚热带杉木人工林在中龄林阶段土壤氮转化酶活性最低,说明在受氮沉降影响严重的中亚热带地区,氮仍可能是杉木速生期的主要限制因素之一,在今后的营林施肥措施上,应把重点放在中龄林阶段,以满足杉木对氮的需求,达到可持续经营管理的目的.

以中亚热带不同林龄(7、15、24和34 a)杉木林为研究对象,测定了根际和非根际土壤可浸提态矿质养分含量,并分析了不同林龄杉木林对各矿质养分的根际效应.结果表明:随林龄增大,根际和非根际土壤pH均呈下降趋势,而土壤含水率呈现先增后减的趋势;根际和非根际土壤P含量随林龄增大呈下降趋势,K、Ca和Mg含量呈先增后减的趋势,在中龄林到近熟林阶段均显著降低,在近熟林到成熟林阶段均没有显著变化;微量元素Fe和Zn含量在不同林龄间没有显著变化,Mn和Cu含量呈先增后减的趋势;非根际土壤pH与K、Ca、Mn和Cu含量呈显著正相关,而根际土壤pH与P和Ca含量呈显著正相关;根际土壤含水率与Mg和Al含量呈显著正相关,非根际土壤含水率与Na含量呈显著负相关.幼龄林和中龄林对土壤矿质养分的根际效应均为正效应,而近熟林和成熟林对K、Na、Cu和Fe的根际效应显著降低.综上,在杉木近熟林阶段土壤有效养分含量显著降低,应注意该阶段的养分供给;同时,为实现杉木人工林可持续性经营,应注意杉木生长期土壤pH的调节.