Plantations In Southern China Research Articles

Thinning increased fine root production, biomass, turnover rate and understory vegetation yield in a Chinese fir plantation

Quantifying the fine root (FR) dynamics of understory plants and canopy trees is essential to accurately assess the impact of forest operations on forest production and ecological stability. However, such information has been poorly quantified, and little is known about the underlying mechanism of FR dynamics in response to human disturbances such as thinning. We investigated the FR dynamics and the understory vegetation of a Chinese fir plantation in southern China under four levels of thinning intensity (30, 50 and 70% of trees removed and uncut controls). We found that the total FR biomass, production and mortality, and turnover linearly increased with thinning intensity, and the FRs were stimulated more in the deeper soil layer (10–20 cm) than in the surface soil layer (0–10 cm). Across all stands, understory plants contributed 35–42% and 34–49% to the total biomass and production, respectively. The biomass and species richness of the understory plants increased with increasing thinning intensity. The principal component analysis indicated that the increased FR production and turnover rate of Chinese fir mainly result from increased understory plant richness and diversity, whereas the increased FR production and turnover rate in understory vegetation result from warmer soil and lower soil phosphorus (P). Our findings provide evidence for the positive effects of thinning on FR dynamics. The results suggest that the FR dynamics of understory plants could play a more critical role than expected in determining forest carbon (C) and nutrient cycling. The mechanism affecting FR dynamics following thinning differed between the understory plants and the canopy trees.

Facilitation by Tree Species in Variable Retention Harvesting for the Restoration of Monoculture Plantations in Southern China

Facilitation can drive the successional dynamics and change the restoration trajectory of degraded forests. However, the relative importance of facilitation by tree species after variable retention harvesting is unclear. We used a field experiment to evaluate the effect of two facilitator species, Castanopsis fissa (C. fissa) and Manglietia glauca (M. glauca), managed with variable retention harvesting, on the development of two target species, Castanopsis hystrix (C. hystrix) and Erythrophloeum fordii (E. fordii), in a Masson pine ( Pinus massoniana) monoculture. The following variables were measured for all of the four interplanted tree species: structural growth, regeneration, aboveground biomass accumulation, leaf area index, and soil conditions. The results indicate that the abundance, growth, and aboveground biomass were relatively greater in plots planted with C. fissa compared with M. glauca and that the target species performed best with 50% retention harvesting of C. fissa, with an improved establishment of both target species indicating a positive interaction. In addition, the regeneration, leaf area index and soil conditions differed between the two facilitators in the variable retention harvesting treatments because of the different intrinsic characteristic of the facilitators. In summary, our results imply that managers have considerable flexibility to employ various types of facilitation schemes coupled with different harvesting systems for successful short-term restoration within a monoculture.

Phylogeny and Pathogenicity of Celoporthe Species from Plantation Eucalyptus in Southern China.

The family of Cryphonectriaceae (Diaporthales) includes many important tree pathogens, such as those that cause severe cankers on Eucalyptus trees. Recently, stem canker and cracked bark were observed on 8-year-old Eucalyptus grandis × E. urophylla trees in a plantation in southern China. Fruiting structures typical of Cryphonectriaceae fungi were observed on the surface of the diseased tissues. In this study, the isolated fungi were identified based on DNA sequence analyses and morphological characteristics, and their pathogenicity was tested on three Eucalyptus clones. DNA sequence comparisons of the internal transcribed spacer (ITS) regions (including the intervening 5.8S nrRNA gene), two regions of β-tubulin (BT2/BT1), and partial translation elongation factor1-α (TEF-1α), indicated that these isolates represent Celoporthe syzygii and one previously undescribed species. The undescribed species was also morphologically distinct from the other species of Celoporthe. The new species was described and named C. cerciana sp. nov. The results of this study based on the ITS, BT2/BT1, and TEF-1α sequences indicated that more than one haplotype was isolated from the same Eucalyptus tree. The findings of a previous study, whereby C. eucalypti was isolated from the same plantation as that of this study, revealed the high species diversity of Celoporthe within a single plantation, which is associated with a single Eucalyptus sp. in southern China. The results further suggested that hybridization may occur between C. syzygii and C. eucalypti. In addition to the Eucalyptus trees, C. syzygii was also isolated from native Melastoma candidum in the same Eucalyptus plantation. The inoculation results showed that these fungi isolated from E. grandis × E. urophylla and M. candidum are pathogenic to all three tested E. grandis hybrid clones. Significant differences in tolerance were observed between the tested Eucalyptus clones, suggesting that disease-tolerant Eucalyptus genotypes can be selected for disease management.

Effects of sulfuric, nitric, and mixed acid rain on Chinese fir sapling growth in Southern China

The influence of acid rain on plant growth includes direct effects on foliage as well as indirect soil-mediated effects that cause a reduction in root growth. In addition, the concentration of NO3- in acid rain increases along with the rapid growth of nitrogen deposition. In this study, we investigated the impact of simulated acid rain with different SO42-/NO3- (S/N) ratios, which were 1:0, 5:1, 1:1, 1:5 and 0:1, on Chinese fir sapling growth from March 2015 to April 2016. Results showed that Chinese fir sapling height growth rate (HGR) and basal diameter growth rate (DGR) decreased as acid rain pH decreased, and also decreased as the percentage of NO3- increased in acid rain. Acid rain pH significantly decreased the Chlorophyll a (Chla) and Chlorophyll b (Chlb) content, and Chla and Chlb contents with acid rain S/N 1:5 were significantly lower than those with S/N 1:0 at pH 2.5. The chlorophyll fluorescence parameters, maximal efficiency of Photosystem II photochemistry (Fv/Fm) and non-photochemical quenching coefficient (NPQ), with most acid rain treatments were significantly lower than those with CK treatments. Root activities first increased and then decreased as acid rain pH decreased, when acid rain S/N ratios were 1:1, 1:5 and 0:1. Redundancy discriminant analysis (RDA) showed that the Chinese fir DGR and HGR had positive correlations with Chla, Chlb, Fv/Fm ratio, root activity, catalase and superoxide dismutase activities in roots under the stress of acid rain with different pH and S/N ratios. The structural equation modelling (SEM) results showed that acid rain NO3- concentration and pH had stronger direct effects on Chinese fir sapling HGR and DGR, and the direct effects of acid rain NO3- concentration and pH on HGR were lower than those on DGR. Our results suggest that the ratio of SO42− to NO3− in acid rain is an important factor which could affect the sustainable development of monoculture Chinese fir plantations in southern China.

Identification of indicators for evaluating and monitoring the effects of Chinese fir monoculture plantations on soil quality

Globally, forest conversion is known to affect soil quality. In the present study, we developed a soil quality index (SQI) to quantify the changes in soil quality due to conversion of native forests into Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations in southern China. We selected 11 Chinese fir stands of different ages (12-, 21-, 40-, and 97-year-old in the first rotation; 1-, 12-, 21-, and 31-year-old stands in the second rotation; 13- and 21-year-old stands in the third rotation; and a 10-year-old stand in the fourth rotation) from sub-tropical forest plantations in Nanping, Fujian Province, China. Soil samples were collected from different depths (0–20, 20–40, 40–60, 60–80, and 80–100 cm) and 20 soil properties were analysed. SQI was computed from the minimum data set derived from principal component analysis (PCA). Although the PCA included many soil properties, we identified total phosphorus (TP) and labile carbon pool II (LP-II-C) as key soil quality indicators, because they contributed 36.2 and 34.9% to SQI, respectively, followed by labile nitrogen pool I (LP-I-N) and soil pH. SQI values showed that continuous replanting of Chinese fir at the same site decreased soil quality significantly at 0–100 cm depth. Increasing rotation cycle (from first to fourth) strongly reduced LP-II-C (48.8%), LP-I-N (56.6%), labile nitrogen-II (70.2%), nitrate-nitrogen (67.7%), and available phosphorus (48.4%), indicating that successive rotation degrades soil quality. Thus, our results demonstrate that Chinese fir cultivation should be limited to only two rotations in the same site to preserve soil quality. We conclude that TP, LP-II-C, LP-I-N, and pH can be used as effective indicators in temporal soil quality monitoring programs under forest plantations.

Soil erosion and water retention varies with plantation type and age

Soil erosion control and water retention is a major ecological function of plantations and may be affected by both plantation type and age. In this study, we investigated both surface runoff and sediment load under different plantations in southern China for six years (2008–2013) in order to illustrate the influence of plantation type and age on water retention and soil erosion. Our results showed that mature plantations functioned better than young plantations in terms of soil erosion control and runoff reduction, which reduced runoff and soil erosion by 64.5 ± 6.2% and 72.2 ± 7.9% more than young plantations, respectively. Our study indicated that plantations play a beneficial role in controlling soil erosion and reducing water loss, and this effect is more pronounced with plantation age. Both runoff coefficient and sediment load were least under Eucalyptus spp. either in young or mature plantations, suggesting that Eucalyptus spp. is better adapted for water retention and soil conservation compared to other plant species. Correlation analysis showed that herb species and herb Margalef index were the top two factors affecting the surface runoff and sediment load in young plantations but litter storage and tree Shannon index were the top two affecting factors in mature plantations. This shift was consistent with the decreasing trend of herbs and increasing trend of litter storage with the time of vegetation restoration.

Stand Transpiration Estimates from Recalibrated Parameters for the Granier Equation in a Chinese Fir (Cunninghamia lanceolata) Plantation in Southern China

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species that is widely distributed in subtropical areas of southern China and cultivated for wood extraction. However, information on water use by Chinese fir plantations is still scarce. In this study, we performed species-specific parameter calibrations for the original Granier equation for sap flow density (SFD) estimates. Stand transpiration (Es) was related to environmental inputs, such as rainfall, air temperature (Ta), vapor pressure deficit (VPD), photosynthetically-active radiation (PAR), air relative humidity (RH), and potential evapotranspiration (PET) in order to examine how environmental factors affect the Es of Chinese fir plantations. According to our results, Granier’s original parameters set underestimated C. lanceolata SFD by up to 54% compared to our species-specific calibrated parameters set. A strong positive correlation was found between SFD, diameter at breast height (DBH), and tree height among trees populations. The total Es in 2015 was 522.1 mm, with obvious seasonal dynamics and an average of 1.4 mm·day−1. Daily and monthly Es were positively correlated with VPD, PAR, Ta, and PET. A negative relationship between Es and RH was detected only at a daily timescale. Our findings indicate that the original Granier equation requires a parameter calibration when it is applied to species-specific thermal dissipation probe (TDP) estimates, and our findings can also provide novel insights on the water use of Chinese fir in major wood production areas in Southern China.

Soil Nematode Trophic Groups in Four Different Plantations in Southern China: Implications for Restoration

Soil Nematode Trophic Groups in Four Different Plantations in Southern China: Implications for Restoration

Stand‐scale transpiration of a Eucalyptus urophylla × Eucalyptus grandis plantation and its potential hydrological implication

AbstractQuantifying tree transpiration at a stand scale is important for understanding the hydrological impact of Eucalyptus plantations on the local water yield and water balance. In this study, we aimed to explore the seasonal and monthly changes in stand transpiration, its response to climatic factors, and hydrological impacts of a 5‐year‐old Eucalyptus urophylla × Eucalyptus grandis plantation in Guangxi Province, Southern China. Stand‐scale transpiration (Et) and potential evapotranspiration (ETo) were determined, and seasonal sensitivity of daily Et to vapour pressure deficit was analysed by using the monitored sap flux of the E. urophylla × E. grandis plantation and the associated environmental factors during a 2‐year experimental period from June 2012 to May 2014. The results showed that the monthly Et values in the wet seasons were higher than those in the dry seasons, and a temporal Et difference was observed between the 2 years of the experiment. Generally, within a whole experimental year, the highest water consumption mainly occurred from May to August, accounting for more than 40% of the annual total, and the lowest transpiration values (approximately 10 mm) mainly occurred from January to March. This monthly variation would be partly attributed to the difference of climatic factors. Clear seasonal variations were also observed for the ETo values, the Et/ETo and the Et/P (precipitation) ratios, and the dryness index (DI, ETo/P). Compared to the wet seasons, higher ETo and DI (>1) values occurred in the dry seasons. Moreover, the linear relationships between the daily stand‐scale transpiration and vapour pressure deficit for the selected months (representing spring, summer, autumn, and winter) suggest weak stomatal control of eucalypt trees. In consideration of the short rotation practices (5–7 years), the non‐conservative character of water use of eucalypt plantation, as well as the ratios of Et/ETo, Et/P, and DI, we suggested that Eucalyptus plantations in Guangxi Province might pose a potential threat to catchment water yield and management in this region. The findings of this study will assist in managing the increasing hydrological and water resource concerns related to the rapid expansion of Eucalyptus plantations in Southern China.

Excessive Accumulation of Chinese Fir Litter Inhibits Its Own Seedling Emergence and Early Growth—A Greenhouse Perspective

Litter accumulation can strongly influence plants’ natural regeneration via both physical and chemical mechanisms, but the relative influence of each mechanism on seedling establishment remains to be elucidated. Chinese fir (Cunninghamia lanceolata) is one of the most important commercial plantations in southern China, but its natural regeneration is poor, possibly due to its thick leaf litter accumulation. We used natural and plastic litter to study the effects of Chinese fir litter on its own seedling emergence and early growth, as well as to assess whether the effect is physical or chemical in nature. Results showed that high litter amount (800 g·m−2) significantly reduced seedling emergence and the survival rate for both natural and plastic litter. Low litter amount (200 g·m−2) exerted a slightly positive effect on root mass, leaf mass, and total mass, while high litter amount significantly inhibited root mass, leaf mass, and total mass for both natural and plastic litter. Root-mass ratio was significantly lower, and leaf-mass ratio was significantly greater under high litter cover than under control for both natural and plastic litter. Although the root/shoot ratio decreased with increasing litter amount, such effect was only significant for high litter treatment for both natural and plastic litter. Seedling robustness (aboveground biomass divided by seedling height) decreased with increasing litter amount, with high litter treatment generating the least robust seedlings. Because plastic and natural litter did not differ in their effects on seedling emergence and growth, the litter layer’s short-term influence is primarily physical. These data indicated that as litter cover increased, the initial slightly positive effects on seedling emergence and early growth could shift to inhibitory effects. Furthermore, to penetrate the thick litter layer, Chinese fir seedlings allocated more resources towards stems and aboveground growth at the expense of their roots. This study provided experimental evidence of litter amount as a key ecological factor affecting seedling development and subsequent natural regeneration of Chinese fir.

Legume Plants Enhance the Resistance of Soil to Ecosystem Disturbance.

Cultivation of legume plants is well known to improve soil N level and net primary productivity; besides, it may deliver other ecosystem benefits such as increasing soil carbon sequestration and soil food web complexity. However, little is known about whether legumes can improve the resistance of soils to ecosystem disturbances. In the present study, we compared the resistance of soils to an ecosystem disturbance (understory removal) in the presence or absence of a legume species (Cassia alata) in mixed tree species plantations in southern China. Soil physico-chemical and biotic properties were employed to quantify the resistance of soils to understory removal. Our results showed that the resistance indices of soil water content, omnivorous-predacious nematode abundance and nematode channel index to understory removal were greater in the presence of legumes than those without legumes in wet season. The resistance indices of fungal to bacterial ratio, fungivorous nematode abundance and total arthropod abundance were greater in the presence of legume than those without legume species in dry season. Our results indicate that legumes may enhance the resistances of soil physico-chemical and biological properties to the ecosystem disturbance. Our findings could provide a better understanding of the myriad ways in which legumes can positively affect ecosystem functioning.

A management tool for reducing the potential risk of windthrow for coastal Casuarina equisetifolia L. stands on Hainan Island, China

Coastal forests are normally established to mitigate coastal natural disasters instead of artificial barriers because of their low cost, ecological friendliness and economic benefits. The stand stability of coastal forests is of great importance to protect against coastal natural disasters. In the present study, we produced a stand density management diagram (SDMD) that can quantitatively guide the management of stand density to reduce the potential risk of windthrow in the coastal Casuarina equisetifolia L. plantations in southern China. The SDMD was developed using a relative spacing index (RS), average slenderness coefficient (SC) and a system of two equations as the basic components. The RS was used to characterize the growing stock, and the average SC was included to assess stand stability. Finally, we illustrated the application of the SDMD in formulating thinning schedules to secure stand stability. For comparison purposes, management options both with and without considering stand stability were produced and discussed. The study indicated that the SDMD produced here can provide detailed quantitative guidance of regulating stand density to secure stand stability for C. equisetifolia plantations. Additionally, this SDMD can be used to develop thinning schedules for a wide range of site qualities and management objectives for C. equisetifolia plantations.

Acidobacteria Community Responses to Nitrogen Dose and Form in Chinese Fir Plantations in Southern China.

Acidobacteria is a new bacterial group, identified by molecular research, which is widely distributed and has specific ecological functions in forest soil. In this study, we investigated Acidobacteria response to N input, and the effects were related to N form and dose. The experimental design included two N forms (NH4+-N and NO3--N) and five levels of N deposition (0, 20, 40, 60, 80kgNha-1) for 2 years. Research into the Acidobacteria community was conducted using 16Sr RNA gene-based high-throughput pyrosequencing methods. Acidobacteria OTUs and N had a negative relationship in 0-60kgha-1year-1; however, at N doses beyond a certain size, nitrogen might promote an increase in Acidobacteria OTUs. The Acidobacteria relative abundance under NH4+-N treatment was higher than under NO3--N treatment. Acidobacteria relative abundance decreased with increasing of NH4+-N dose, but increased with increasing NO3--N dose. Overall, 13 different Acidobacteria subgroups were identified, with Gp1, Gp2, and Gp3 being dominant. Significant differences in Acidobacteria distribution were primarily caused by N input and pH value. The environmental factors of N were all negatively related to Acidobacteria distribution in low N dose treatments (0-20kgha-1year-1), but were positively related in response to N dose treatments (40-80kgha-1year-1).

Self-Thinning Trajectories of Chinese Fir Plantations in Southern China

Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) is the most important conifer species for timber production with a wide geographic distribution in southern China. Self-thinning is a dynamic equilibrium between forest growth and mortality in fully stocked stands. In this study, the segmented model was used to analyze the trajectory of stand density and quadratic mean diameter of Chinese fir plantations. Results showed that a linear-quadratic-linear model could simulate the self-thinning trajectories of Chinese fir plantations well. For a given province, the self-thinning slope was invariant with changes in planting densities. The self-thinning trajectories in Jiangxi and Fujian provinces were similar and were different from those in Guangxi and Sichuan provinces. The slope of the self-thinning line of Chinese fir plantations in Sichuan province was much steeper than that of the other three provinces (−4.2169 versus −2.4453). These slopes were steeper than the value of −1.605 as proposed by Reineke for many species.

Crown and branch attributes of mid-aged Betula alnoides plantations in response to planting density

ABSTRACTBoth crown and branch characteristics greatly affect tree growth and timber quality, and their development is closely related to planting density (PD). Here crown and branch attributes of Betula alnoides were investigated in a 14-year-old experimental plantation in southern China with five planting densities ranging from 500 to 3333 stems per hectare (sph). The results showed that high PD significantly reduced crown and branch sizes. The ratios of crown diameter to stem diameter at breast height at the stand level and for dominant and co-dominant trees were almost constant regardless of PD. PD also had no significant influence on the number and angle of branches, and only planting with the highest density significantly increased branch density and mortality. Insertion angle (IA) of dead branches was greater than that of live branches and these differences were significant at the two low planting densities (833 and 500 sph). Linear mixed models revealed that branch diameter (BD) was negatively correlated with its relative height in the crown and IA. The binary-logistic regression model indicated that branch status (live or dead) was codetermined by BD and PD. These findings can help farmers cultivate high-quality wood of B. alnoides and obtain a higher economic return.

Soil Bacterial Community Response to Short-Term Manipulation of the Nitrogen Deposition Form and Dose in a Chinese Fir Plantation in Southern China

The changes of soil bacterial biomass and community composition were monitored in a simulated nitrogen (N) deposition experiment during 4 years of Cunninghamia lanceolata growth in a plantation site in southern China. The experimental design included two N forms (NH4Cl and KNO3) and five levels of N deposition (0, 20, 40, 60, 80 kg N ha−1) for 2 years. Research into the bacterial population was conducted using plate count, phospholipid fatty acid (PLFA) composition, and 16Sr DNA gene-based high-throughput pyrosequencing methods. The results of plate count and PLFA analysis indicated that ammonium (NH4 +) addition increased bacterial number and biomass, whereas nitrate (NO3 −) addition decreased these values. The high-throughput sequencing showed that N deposition of the two N forms inhibited the growth of bacteria compared with control plots, and the changing trend was related to the NH4 +-N/NO3 −-N ratio of soil. When the N deposition dose exceeded 20 kg N ha−1, there was a significant effect on cultured bacteria counts and bacterial biomass. When examining the bacterial community, we observed 22 bacterial phyla of which Proteobacteria, Acidobacteria, and Actinobacteria were dominant. Acidobacteria abundance was higher in NH4 + treatments than NO3 − treatments. When the rates of NH4 + deposition increased, Acidobacteria abundance decreased; however, it showed a positive correlation in NO3 − treatments. The bacterial cluster structures were significantly different between different N addition rates in the NO3 −-treated plots. This research will provide data support to addressing the negative influences of nitrogen deposition and provide reference for soil management.

Seasonal dynamics of soil respiration and nitrification in three subtropical plantations in southern China

Abstract: Numerous studies have documented that soil respiration and nitrogen cycling show a distinct seasonal dependence regulated by environmental factors (e.g., soil temperature and soil water content). The mechanisms controlling the seasonal dependence of these two key ecosystem processes have rarely been linked to both soil microbial community and soil environmental factors. Here, we present results on the seasonal patterns of soil respiration and gross nitrification rates in three subtropical plantations of Pinus massoniana, Castanopsis hystrix and Erythrophleum fordii over a period of 11 months. Turnover rates were measured with the Barometric Process Separation technique (BaPS). We elucidated how soil respiration and gross nitrification are controlled by the soil microbial community and by soil environmental factors. Soil respiration and gross nitrification showed strong seasonal dynamics, although no significant differences were observed among plantations. The turnover rates were the highest during the wet season and the lowest during the dry season. Microbial biomass, total phospholipid fatty acids (PLFAs), fungal PLFAs and bacterial PLFAs peaked during the dry season. Both soil respiration and gross nitrification rates were positively correlated with soil temperature and soil water content. Microbial biomass decreased with increasing turnover rates. Our findings highlight that carbon and nitrogen turnover rates were mostly controlled by soil temperature and soil water content.

Simulation study on the effects of climate change on aboveground biomass of plantation in southern China: Taking Moshao forest farm in Huitong Ecological Station as an example

Global climate warming has significant effect on territorial ecosystem, especially on forest ecosystem. The increase in temperature and radiative forcing will significantly alter the structure and function of forest ecosystem. The southern plantation is an important part of forests in China, its response to climate change is getting more and more intense. In order to explore the responses of southern plantation to climate change under future climate scenarios and to reduce the losses that might be caused by climate change, we used climatic estimated data under three new emission scenarios, representative concentration pathways (RCPs) scenarios (RCP2.6 scenario, RCP4.5 scenario, and RCP8.5 scenario). We used the spatially dynamic forest landscape model LANDIS-2, coupled with a forest ecosystem process model PnET-2, to simulate the impact of climate change on aboveground net primary production (ANPP), species' establishment probability (SEP) and aboveground biomass of Moshao forest farm in Huitong Ecological Station, which located in Hunan Province during the period of 2014-2094. The results showed that there were obvious differences in SEP and ANPP among different forest types under changing climate. The degrees of response of SEP to climate change for different forest types were shown as: under RCP2.6 and RCP4.5, artificial coniferous forest>natural broadleaved forest>artificial broadleaved forest. Under RCP8.5, natural broadleaved forest>artificial broadleaved forest>artificial coniferous forest. The degrees of response of ANPP to climate change for different forest types were shown as: under RCP2.6, artificial broadleaved forest> natural broadleaved forest>artificial coniferous forest. Under RCP4.5 and RCP8.5, natural broadleaved forest>artificial broadleaved forest>artificial coniferous forest. The aboveground biomass of the artificial coniferous forest would decline at about 2050, but the natural broadleaved forest and artificial broadleaved forest showed a rising trend in general. During the period of 2014-2094, the total aboveground biomass under RCP2.6, RCP4.5 and RCP8.5 scenarios increased by 68.2%, 79.3% and 72.6%, respectively. The total aboveground biomass under various climatic scenarios sort as: RCP4.5>RCP8.5>RCP2.6. We thought that an appropriate temperature might be beneficial to the biomass accumulation in this study area. However, overextended temperature might hinder the sustainable development of forest production and ecological function.

Biochemical quality and accumulation of soil organic matter in an age sequence of Cunninghamia lanceolata plantations in southern China

Biochemical protection is an important mechanism for maintaining the long-term stability of the soil carbon (C) pool. The labile and recalcitrant pools of soil organic matter (SOM) play different roles in regulating C and N dynamics; however, few studies have characterized the capacity of soil C sequestration while considering the biochemical quality of SOM. The aim of the present study was to assess the changes in the soil organic carbon (SOC) and nitrogen (N) pools during a traditional rotation period (25 years) of a Chinese fir (Cunninghamia lanceolata) plantation with an emphasis on SOM biochemical quality. Three different forest stand development stages—young (6 years old), middle-aged (16 years old) and mature (25 years old)—were selected for soil sampling to a depth of 100 cm. Total C and total N of the soil was analysed to determine the changes in the SOC and N stocks among the three development stages using an equivalent soil mass (ESM) approach. Bulk soils were fractionated into labile and recalcitrant fractions using the acid hydrolysis method to identify the quality of SOM. The mineral soil organic carbon pool at a 1-m depth slightly decreased from the young stand to the middle-aged stand and rapidly increased by 28 % to reach a maximum in the mature stand. SOC accumulation in the surface soil predominated the changes in total SOC stocks in all three stands. The increased N was reflected in the entire depth, and the highest soil N accumulation was in the mature stand. The recalcitrant C concentration and SOC were positively correlated. The non-hydrolysable C proportion was lower in the middle-aged stand versus the young stand (8.69 % loss), while the labile C percentage was higher (13.89 % gain). In the mature stand, the recalcitrant C index increased to 39.84 %. The recalcitrant index of C decreased with an increasing soil depth, whereas the recalcitrant index of N dramatically increased. These results highlighted the significant effect of the stand age and the soil depth on the storage and biochemical availability of SOM in Chinese fir plantations of southern China. The recalcitrant index of C changed with the change in SOC concentration, indicating that biochemical protection mechanism plays an important role in soil C sequestration. In addition, more attention should be paid to subsoil C protection in the management of Chinese fir plantations because of low biochemical stability.

Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.