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Although stand age affects biomass partitioning and allometric equations, the size of these effects and whether it is worth incorporating stand age into allometric equations, requires further attention. We sampled a total of 90 trees for 10 Chinese fir (Cunninghamia lanceolata) plantations at seven stand age classes to obtain the data of tree component biomass using destructive harvesting. A multilevel modeling approach was applied to examine how stand age effects differ among tree components and predictor variables (diameter at breast height, DBH and tree height, H). Age class-specific allometric equations and the best fitting generalized equation that included stand age as a complementary variable were developed for each tree component. Large differences in both the intercept and slope for different stand age classes indicated that stand age affected allometric models. Branch and leaves were more sensitive to the environment and were the tree components most affected by stand age. Age class-specific allometric equations fitted well (R2 > 0.65, p < 0.001) using DBH and the combined form DBH2H as predictor variables. Including stand age as a complementary variable improved the fit of generalized allometric equations. Stem, aboveground and total tree biomass predicted by the multilevel model and generalized equation were comparable to the observed data. However, the multilevel model and generalized equations had a relatively low predictive capacity for branch, leaf and root biomass. These results could improve our capacity to evaluate carbon sequestration and other ecosystem functions in plantations. [ABSTRACT FROM AUTHOR]

Predicting changes in carbon and nutrient cycles in plantations requires a mechanistic understanding of the effects of stand age on soil quality and microbial communities. Here, we evaluated soil quality by using an integrated soil quality index (SQI) and traced the parallel shifts in fungal community composition using high‐throughput sequencing in a chronosequence of Chinese fir (Cunninghamia lanceolata) plantations (stand age of 3, 16, 25, 32, >80 years). Soil properties showed pronounced changes with stand age in the topsoil. Soil organic carbon (SOC), total nitrogen (TN) and available phosphorus (AP) were 2.1, 1.9 and 2.2 times higher, respectively, in the oldest stands than in the youngest stands. SQI of the top 5 cm increased logarithmically with stand age. Mycorrhizal fungi initially increased in younger stands, but then they were gradually replaced by saprotrophs in older stands due to larger litterfall. Strong positive correlations between saprotrophic fungi and key soil quality indicators, such as TN, AP and NH4+, confirmed that abundance of decomposers is tightly linked with higher soil quality. Mycorrhizal orders Thelephorales, Sebacinales and Russulales increased in abundance and raised the activity of acid phosphatase to mobilise limiting phosphorus from organic matter. Consequently, mycorrhizal fungi are especially relevant in younger stands to acquire nutrients to sustain tree productivity. In developed stands, however, saprotrophic fungi are crucial in recycling nutrients from the litter. Collectively, the increase of topsoil quality during the life cycle of Chinese fir plantations is closely linked with the observed transition of fungal communities from mycorrhizae to saprotrophs. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a limiting nutrient for plant growth in most forest ecosystems. In response to P deficiency, plants alter root exudates (organic acids, phosphatases, and protons) to increase P bioavailability in soils. However, little is known about how bioavailable P pools (soluble-P, exchangeable-P, hydrolysable-P, and ligand-P extracted by CaCl2, citric acid, enzyme mixture, and HCl solution, respectively) change with stand age, especially for plantation forests. We selected a chronosequence of second-generation Chinese fir [Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae] plantations with increasing age including 3, 8–11, 16, 20, 25, 29, and 32 years. We measured total P and four bioavailable P pools in organic (O) and mineral horizons, and rhizosphere soil, as well as root exudates in the rhizosphere, litter biomass on the forest floor, and annual P uptake. Soluble-P, exchangeable-P, and ligand-P in the O horizon increased with stand age due to litter accumulation. Exchangeable-P and ligand-P in mineral soil decreased with stand age because of the increasing annual P uptake that depleted inorganic P. Exchangeable-P and ligand-P in the rhizosphere increased with stand age because the decrease in pH and citric acid concentration led to phosphate being more strongly bound to Fe and Al oxyhydroxides. Consequently, the trees' ability for P mobilization decreased with stand age, but the P recycling within the tree increased. Continuous mineralization of hydrolysable-P by acid phosphatase replenished inorganic P pools, especially in solution. The progressive incorporation of P in the biological cycle with increasing tree age indicates that extending rotation periods might be an appropriate measure to increase P supply. [ABSTRACT FROM AUTHOR]

Carbon and water cycles in forest ecosystems are tightly coupled, but global warming-induced soil and atmospheric droughts alter the coupling, thereby greatly increasing uncertainty in predicting carbon and water cycles. Therefore, a carbon–water coupled model (TRIPLEX-CW-Flux) was developed, and an R package (rTRIPLEXCWFlux) was created to facilitate model application. TRIPLEX-CW-Flux integrates vapor pressure deficit and soil moisture into a stomatal conductance submodule to estimate forest carbon and water fluxes. Prediction accuracy of TRIPLEX-CW-Flux and rTRIPLEXCWFlux application were evaluated in a Chinese fir (Cunninghamia lanceolata) plantation. Simulated net ecosystem production (NEP) and evapotranspiration (ET) were in good agreement with flux observations (R 2 : 0.76 for NEP ; 0.71 for ET). Thus, the TRIPLEX-CW-Flux model can be used to predict and quantify effects of global warming-induced droughts on forest carbon and water cycles. The open-access rTRIPLEXCWFlux package facilitates estimations of carbon sequestration and water consumption in forest ecosystems using the observed flux data. • A physiological process model that couples carbon and water flux was developed. • Both atmospheric and soil drought stress were also integrated into the model. • An R package was encoded for the model to predict forest carbon and water flux. • The simulated values were comparable to the flux data observed in the forest. • This R package can be used to evaluate forest functions under climate change. [ABSTRACT FROM AUTHOR]

Red-heart Chinese fir is an excellent geographic provenance of Cunninghamia lanceolata, with high-value red heartwood. However, the formation of red heartwood is usually slow. To quickly cultivate red-heart Chinese fir, we studied perforation dyeing technology on living trees that were 7 years old and efficient in high-value red heartwood formation. Reactive dye (%), penetrant (%), KH2PO4 (%), and pH were selected as influencing factors, and an orthogonal test (L9(3)4) was used. The results showed that the total color difference between the experimental and CK groups ranged from 13.74 to 26.86 NBS, which was a significant visual perception (above 12 NBS). The total color difference before and after soaking in water for 6 h ranged from 2.30 to 5.12 NBS, which belonged to the detectable and identifiable value of the human eye (2~5 NBS). After the injection of the dye liquid, the wood basic density (WBD) was significantly affected after one year. After a comprehensive analysis of wood color difference, colorfastness, and WBD of the orthogonal test, the best dyeing process of juvenile red-heart Chinese fir was reactive dye: 0.8%, penetrant: 0.05%, KH2PO4: 0.3%, and pH: 3.5. The results of this study can provide a reference to improve the value of red-heart Chinese fir, a fast-cultivated, high-value decorative wood material. [ABSTRACT FROM AUTHOR]

• Change of soil N contents as stands age was pronounced in the topsoil. • Ratios of NO 3 −: NH 4 + increased while MBN: (NH 4 + + NO 3 −) decreased as stands aged. • Soil N availability increases and N cycling becomes more open in older stands. • Soil total N is co-regulated by trees' N demand and litter biomass return. • Gross N mineralization and nitrification control mineral N availability. Soil nitrogen (N) is frequently limiting forest productivity, especially in plantations. To investigate the soil N dynamics and the consequences of N accumulation as well as the losses in the ecosystem, we studied a chronosequence of Chinese-fir (Cunninghamia lanceolata [Lamb.] Hook) plantations with stands aged 3, 16, 25, 32, and >80 years. Total N (TN), dissolved organic N (DON), microbial biomass N (MBN) and mineral N (i.e., ammonium (NH 4 +) and nitrate (NO 3 −)) in the top 0–5 cm and 5–15 cm soils were compared with the annual N accumulation by trees, annual litter N return and microbial N transformation rates. Stronger changes with stand age were observed in all N forms in the top 5 cm compared to the 5–15 cm layer. Topsoil TN and DON increased steadily in stands from ages 3- to >80-years-old by 1.9-times and 2.1-times, respectively. MBN increased from 206 mg kg−1 to 327 mg kg−1 in the first 25 years and stabilized thereafter. NH 4 + content increased sharply from 3 to 16 years and then stabilized, while NO 3 − increased linearly with stand age. Both N demand of Chinese-fir and litter N input were clearly age dependent and defined the soil N status: rapid tree biomass accumulation in younger stands greatly depleted soil N, while the older stands with larger litter return and slower growth enabled N re-accumulation in the topsoil. The close positive correlation between total mineral N and gross mineralization rate, as well as between NO 3 − and gross nitrification rate indicated that the mineralization of soil organic matter and the nitrification of released NH 4 + were the two primary microbial processes controlling the available N supply. The topsoil NO 3 −: NH 4 + ratio in older stands (32- and >80 years) was greater than 1.0, and the MBN: (NH 4 + + NO 3 −) ratio was greatly reduced. This indicates that N availability increase and N cycling is accelerated with stands age. [ABSTRACT FROM AUTHOR]

• How nutrient limitation and nutrient-use strategy change with stand age are unknown. • Driver effects on resorption are differentiated by variation partitioning analyses. • Soil nutrient shift from N limitation to P limitation with plantation ageing. • Young plantations adopt more conservative nutrient-use strategy than older stands. • Tree growth (demand) and soil nutrient (supply) co-determine nutrient resorption. Nutrient resorption is a key nutrient-use strategy exhibited by perennial plants to overcome nutrient limitations and meet their nutritional demands. However, the factors that drive nutrient resorption with stand development remain largely unknown. In this study, we examined how a nutrient source (soil) and sink (trees) affected the resorption efficiency (RE) of nitrogen (N) and phosphorus (P). Fresh leaves, leaf litterfall, and soil samples were collected from a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae) plantations at the ages of 3, 8–11, 16, 20, 25, 29, and 32 years. The N and P concentrations in stems, branches, leaves, coarse roots, and fine roots, stocks of N and P in soils, and the relative growth rate (RGR) of trees were measured. Fresh leaf N and P concentrations and RE decreased with stand age, while the N:P ratio in fresh leaves as well as the N and P concentrations in leaf litterfall increased. The RGR of trees declined with stand age. Soil P stocks increased but soil N stocks slightly decreased with stand age. A variation partitioning analysis revealed that the combined effect of RGR and soil P stocks on the RE of P (PRE) was stronger than the individual effect of each factor, while the RE of N (NRE) was greatly affected by the individual effect of RGR. With increasing age, Chinese fir plantations shifted from N-limiting to P-limiting conditions, and the nutrient-use strategy changed from "conservative consumption" to "resource spending". These patterns were co-regulated by the tree growth rate and soil nutrient status. Thus, supply-demand relationships reflected the nutrient cycling status and could provide valuable information for sustainable nutrient management practices in tree plantations. [ABSTRACT FROM AUTHOR]

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is the most commonly grown afforestation species in subtropical China. It is essential that we understand the response of radial tree growth to climate factors, yet most experiments have been conducted based on total annual growth and not on monthly dynamics, which alone can detail the influence of climatic factors. In this study, we aimed to: (i) construct a monthly growth model and compare the growth rate of different social statuses of trees, and (ii) determine the response of radial increments of different social statuses to climate factors. The radial growth was monitored monthly during four years using manual band dendrometers (MBD). The data were fitted using the Gompertz function. Within-stand differences in the social status of Chinese firs resulted in growing period and growth rate length variations. The radial growth began in March, and suppressed trees—especially groups of AS1 and BS1 (suppressed trees of classes I in sites A and B)—stopped in September, whereas dominant and intermediate trees were delayed and stopped in November. The periodic monthly increment curve showed double peaks, and the maximum growth rate occurred in April and August. The peak values were affected by social status, which showed that dominant trees had the greatest radial growth rates. S-shaped Gompertz meant that monthly increment models were successfully fitted to our data, which explained more than 98% of the variation in increment data and passed the uncertainty test. Temperature and precipitation had a significant influence on radial growth, and the correlation between radial growth and air temperature was the highest. Our results also revealed that temperatures explain the double-peak features of Chinese fir. The limiting factors of radial growth changed with the seasons and were mainly affected by temperature and precipitation, which should be considered in predicting the response of tree growth to climate change. [ABSTRACT FROM AUTHOR]

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. lanceolataSFD 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. [ABSTRACT FROM AUTHOR]

• Only stem harvest can avoid P loss due to<23% P stock allocated in stem. • Higher P fluxes showed stronger P acquisition and recycling in mature plantations. • The combined use of acquisition and recycling strategies favors P biological cycle. • The maximum annual P uptake by trees occurred at stand age of 22 years. The cycling dynamics and supply–demand balance of nutrients can provide useful information for improving the management of tree plantations and maintaining their long-term productivity. Phosphorus (P) is an essential nutrient for plant growth; however, its cycling characteristics and availability in soils along different stand developmental stages remain unclear, especially in intensively managed plantations. In this study, we examined the stocks, distribution, flux, and supply–demand balance of P across a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.; Taxodiaceae) plantations aged 3, 8–11, 16, 21, 25, 29, and 32 years. <22.18% tree P stock allocated for stem across a chronosequence, suggesting that only stem harvest could return more than three-quarters of tree P stock to soil. The annual P resorption, P return, and P-use efficiency increased with stand age, indicating strong P recycling. Indicators of P acquisition and recycling strategies significantly increased with stand age and promoted P fluxes. The combination of acquisition and recycling strategies might favor the entrainment of P into the biological cycle. With the increase in stand age, the available soil P stocks initially decreased and then increased after 11 years, while the annual P uptake increased at first and then stabilized after 22 years. Based on the best fitted model, the lower soil P supply and higher tree P demand in 9- to 40-year-old plantations revealed that timely and appropriate fertilization could enhance soil P supply and improve stand productivity. This work provides crucial information about the time of fertilization and appropriate harvest methods for the sustainable management of forest P nutrition. [ABSTRACT FROM AUTHOR]

Stand development affects soil properties, nitrogen (N) dynamics, and soil microbial community composition, but the question remains whether differences in N mineralization rates are mirrored by the abundance of relevant functional genes. In this study, we used the 15N pool-dilution method to estimate N mineralization (i.e. , ammonification and nitrification) rates across a Chinese fir (Cunninghamia lanceolata) chronosequence, with stands aged 7, 16, 29, 36, and >80 years. Gene copy numbers of bacteria (16S rRNA), fungi (ITS), ammonia-oxidizing archaea (AOA) and bacteria (AOB) (amoA), denitrifiers (nirS , nirK), N 2 fixers (nifH) and organic N decomposers (chiA) were quantified by qPCR. Gross ammonification and nitrification rates increased linearly with stand age in the topsoil (0–5 cm depth) and were strongly positively correlated with the abundance of the bacterial 16S rRNA gene and AOA amo A, respectively. Higher net nitrification but lower NO 3 − immobilization rates in older stands (32 and > 80 years) drove higher N availability for vegetation than in young stands (7 years). Older stands also had higher rates of NH 4 + consumption than younger stands due to the increased fungal ITS abundance and higher microbial biomass N (MBN), and AOA amoA was more abundant and active than AOB amoA due to the more acid conditions characteristic of mature forests. Redundancy analysis showed that functional gene abundance was strongly affected by soil properties such as pH, NH 4 +-N content, and MBN. We also found that microbial N storage potential was lower, and the NO 3 −-N leaching and gaseous N loss potential were higher in older stands than in younger stands. Collectively, stand developmental stage gave rise to the observed spatial gradient of gross ammonification and nitrification rates by altering the abundance of microbial functional genes, which affected plantation productivity via its modulation of the supply of bioavailable N. [Display omitted] [ABSTRACT FROM AUTHOR]

Afforestation is an effective method to increase carbon (C) sinks and address climate change. It is crucial to understand how the stand growth affects C sequestration capacity, especially when the trade-offs with timber production from plantations have not been fully examined. We used a chronosequence approach to estimate C storage in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations (including the trees, understory, litter, and soils) at seven stand ages (3, 8–11, 16, 21, 25, 29, and 32 years). Ecosystem C storage increased nonlinearly from 76.4 to 282.2 t ha−1 with stand age and was fitted with a logistic model that had a maximum C storage and age of 271.9 t ha−1 and 33 years, respectively, to reach 95% of the maximum stored C. The C increment was mainly contributed by an increase in tree biomass, which ranged from 2.8 to 177.7 t ha−1 and comprised 4–64% of the total ecosystem C. Live root C (sum of the stump, coarse, and fine root C) showed a logistic increase from 2.0 to 26.3 t ha−1 with stand age and constituted 2.5–9.3% of ecosystem C. Understory plants and litter represented a small pool (<2% of ecosystem C). The C storage in shrubs and litter slightly increased, while that in herbs decreased as the stands aged. Soil C storage was an important and relatively stable pool, ranging from 69.6 to 130.1 t ha−1. Stand volume was also best fitted with a logistic model with a maximum value of 552.6 m3 ha−1. Additionally, the time needed to reach 95% of the maximum volume was 25 years. Hence, extending the rotation age to over 30 years for Chinese fir plantations could potentially maximize the synergistic benefits of C storage to mitigate climate change and obtain timber products for economic profit. [Display omitted] • Chinese fir plantations have high carbon (C) sequestration capacity. • Accumulation of ecosystem C was mainly contributed by increase in tree biomass C. • Soil C storage remained relatively stable except for stand at age of 21 years. • Rotation extension enhances ecosystem C storage and large-trees' timber production. [ABSTRACT FROM AUTHOR]