Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Characteristics of soil nitrogen and phosphorus fractions and microbial traits with increasing stand age in two-layered Cunninghumia lanceolata + Phoebe bournei plantations.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Isolation and screening of multifunctional phosphate solubilizing bacteria and its growth-promoting effect on Chinese fir seedlings.

Phosphorus-solubilizing microorganisms is a microbial fertilizer with broad application potential. In this study, 7 endophytic phosphate solubilizing bacteria were screened out from Chinese fir, and were characterized for plant growth-promoting traits. Based on morphological and 16S rRNA sequence analysis, the endophytes were distributed into 5 genera of which belong to Pseudomonas, Burkholderia, Paraburkholderia, Novosphingobium, and Ochrobactrum. HRP2, SSP2 and JRP22 were selected based on their plant growth-promoting traits for evaluation of Chinese fir growth enhancement. The growth parameters of Chinese fir seedlings after inoculation were significantly greater than those of the uninoculated control group. The results showed that PSBs HRP2, SSP2 and JRP22 increased plant height (up to 1.26 times), stem diameter (up to 40.69%) and the biomass of roots, stems and leaves (up to 21.28%, 29.09% and 20.78%) compared to the control. Total N (TN), total P (TP), total K (TK), Mg and Fe contents in leaf were positively affected by PSBs while showed a significant relationship with strain and dilution ratio. The content of TN, TP, TK, available phosphorus (AP) and available potassium (AK) in the soil increased by 0.23-1.12 mg g-1, 0.14-0.26 mg g-1, 0.33-1.92 mg g-1, 5.31-20.56 mg kg-1, 15.37-54.68 mg kg-1, respectively. Treatment with both HRP2, SSP2 and JRP22 increased leaf and root biomass as well as their N, P, K uptake by affecting soil urease and acid phosphatase activities, and the content of available nutrients in soil. In conclusion, PSB could be used as biological agents instead of chemical fertilizers for agroforestry production to reduce environmental pollution and increase the yield of Chinese fir.

Metabolomic Analysis of Pollen Grains with Different Germination Abilities from Two Clones of Chinese Fir (Cunninghamia lanceolata (Lamb) Hook).

Pollen grains produce certain metabolites, which can improve or inhibit germination and tube growth. Metabolomic analysis of germinating and growing Chinese fir pollen has not been reported. Therefore, this study aimed to analyse metabolites changes, content and expression in the germinating pollen of Chinese fir. To understand the metabolic differences, two clones from Chinese fir were selected. Metabolomics analyses were performed on three stages (1-, 24- and 48-h) during in vitro pollen germination. The metabolites profiles at different time points were analyzed by using liquid chromatography-mass spectrometry. The results showed that 171 peaks were screened; the corresponding differential metabolites of 121 peaks were classified into nine types of substances. The expression of metabolites showed significant differences across and between clones, and the variation was evident at all germination stages. The expression was obvious at the early stage of germination, which differed clearly from that of the late stage after pollen tube growth. Moreover, the metabolites were mainly enriched in 14 metabolic pathways. Pollen germination and tube growth and metabolites expressions changed per incubation time. Since this work is preliminary, we suggest further investigations to understand the relationship between the differential metabolites and pollen development, and factors affecting pollen germination process.

Physiological and proteomic analysis reveals the different responses of Cunninghamia lanceolata seedlings to nitrogen and phosphorus additions.

UNLABELLED: Both nitrogen (N) and phosphorus (P) additions in soils can increase tree photosynthetic rate (Pn), biomass accumulation and further increase primary production of plantation. However, the improved photosynthetic ability is varied from the added nutrient types and the mechanisms are sophisticated. In this study, an iTRAQ-based quantitative proteome combined with physiological analysis of Chinese fir (Cunninghamia lanceolata) leaves was performed to determine the common and different responses on photosynthetic process to the N and P additions. The results showed that, either N or P added in soils significantly increased Pn, but N addition had more positive effects than P addition in improving photosynthetic ability. Physiologically, N addition caused more in improving photosynthetic rate than P addition, which attributes to higher leaf N and chlorophyll contents, enlarged chloroplast size and more number of thylakoids. Proteomic data revealed that the increased Pn to N and P additions may attribute to the increased abundance of proteins involved in carbon fixation and RuBP regeneration during the light-independent reactions. However, N addition increased the abundance of photosystem II related proteins and P addition increased the abundance of photosystem I related proteins. Additionally, proteomic data also gave some clues on the different metabolic processes caused by N and P additions on glycolysis and TCA cycle, which were potentially related to higher growth and developmental rates of C. lanceolata. Therefore, this study provides new insights into the different photosynthesis and metabolic processes of Chinese fir in response to N and P additions. BIOLOGICAL SIGNIFICANCE: Fertilization is an important management measure to improve timber yield and primary production of Cunninghamia lanceolata, which is the largest planted coniferous species in southeast China. Nitrogen (N) and phosphorus (P) additions into soils can improve tree photosynthesis, and further increase plantation production. However, the mechanism of N and P additions in improving photosynthesis is still unclearly. In this study, a physiological measurement combined with proteomic analysis was performed on a controlled experiment in the greenhouse. These results improve understanding of the essentially photosynthetic activity and metabolic process of C. lanceolata responding to N and P fertilization.

Seasonal development of cambial activity in relation to xylem formation in Chinese fir.

The vascular cambium is a lateral meristem which can differentiate into secondary phloem and xylem. The secondary growth of woody plants resulting from vascular cambium activity has been a focus of considerable attention, but the quantitative relationships between cambial activity and secondary xylem formation have been little studied. Our analysis of cytological changes in the cambium of Chinese fir (Cunninghamia lanceolata), revealed a significant positive correlation between vascular cambium cell numbers and cambium zone width through the seasonal cycle. Cambium cell numbers and the cambium cell radial diameter were closely related to xylem formation. Immuno-labeling showed that de-esterified homogalacturonan and (1-4)-ß-d-galactan epitopes were highly abundant in cell walls of dormant-stage cambium, whereas high methylesterified homogalacturonan was strongly labeled in the active stage. Raman spectroscopy detected significant changes in the chemical composition of cell walls during the active-dormant stage transition. More pectin and less monolignols occurred in radial cell walls than in tangential walls during the dormant stage, but no significant changes were found in other stages, indicating that pectin accumulation facilitates cell wall expansion, with cambium activity transition. Our quantitative analysis of the relationship between cambial activity and xylem formation, as well as the cell wall modification during the active stage provides useful information about cambial characteristics and xylogenesis.

Effects of increased nitrogen deposition and rotation length on long-term productivity of Cunninghamia lanceolata plantation in southern China.

Cunninghamia lanceolata (Lamb.) Hook. has been widely planted in subtropical China to meet increasing timber demands, leading to short-rotation practices that deplete soil nutrients. However, increased nitrogen (N) deposition offsets soil N depletion. While long-term experimental data investigating the coupled effects related to short rotation practices and increasing N deposition are scarce, applying model simulations may yield insights. In this study, the CenW3.1 model was validated and parameterized using data from pure C. lanceolata plantations. The model was then used to simulate various changes in long-term productivity. Results indicated that responses of productivity of C. lanceolata plantation to increased N deposition were more related to stand age than N addition, depending on the proportion and age of growing forests. Our results have also shown a rapid peak in growth and N dynamics. The peak is reached sooner and is higher under higher level of N deposition. Short rotation lengths had a greater effect on productivity and N dynamics than high N deposition levels. Productivity and N dynamics decreased as the rotation length decreased. Total productivity levels suggest that a 30-year rotation length maximizes productivity at the 4.9 kg N ha(-1) year(-1) deposition level. For a specific rotation length, higher N deposition levels resulted in greater overall ecosystem C and N storage, but this positive correlation tendency gradually slowed down with increasing N deposition levels. More pronounced differences in N deposition levels occurred as rotation length decreased. To sustain C. lanceolata plantation productivity without offsite detrimental N effects, the appropriate rotation length is about 20-30 years for N deposition levels below 50 kg N ha(-1) year(-1) and about 15-20 years for N deposition levels above 50 kg N ha(-1) year(-1). These results highlight the importance of assessing N effects on carbon management and the long-term productivity of forest ecosystems.

[Phosphorus characteristics in rhizosphere soil of Cunninghamia lanceolata, Pinus massoniana and their mixed plantations].

In 2007-2010, a comparative study was conducted on the phosphorus characteristics in the rhizosphere soil of Cunninghamia lanceolata, Pinus massoniana and C. lanceolata-P. massoniana mixed plantations in a forest farm in Nanping City of Fujian Province, East China. In the rhizosphere soil of pure C. lanceolata and P. massoniana plantations, the content of available P was higher than that in non-rhizosphere soil. As compared with non-rhizosphere soil, the rhizophere soil in the three plantations had lower pH and O-P content but higher Al-P and Fe-P contents, and its P adsorption capacity was lower while the P desorption rate and desorbed P were in adverse. In the rhizophere soil of pure P. massoniana plantation, the contents of available P, Fe-P, and Al-P, their desorption rates, and desorption capacity were higher, but the O-P content and the adsorbed P were lower, as compared with those in the rhizophere soil of pure C. lanceolata plantation. In the mixed plantation, the P activation in rhizophere soil was further improved, being more obvious under C. lanceolata, which suggested that mixed plantation of C. lanceolata and P. massoniana could promote the phosphorus nutrition of C. lanceolata.

[Dynamics of biomass- and nutrient accumulation in a Chinese-fir plantation].

Based on the over 30 years observation data in Huitong National Research Station of Forest Ecosystem under Chinese Academy of Sciences and related literatures, this paper analyzed the dynamics of the biomass- and nutrient accumulation and allocation in a Chinese-fir (Cunninghamia lanceolata) plantation, and the effects of rotation length and harvest intensity on the nutrient input/output. The results showed that stand age was the main factor affecting the biomass- and nutrient accumulation and allocation, and different organs had significant differences in their biomass- and nutrient storage. Stand age and different organs explained 37.1% and 40.3% of the variations of biomass- and nutrient storage, respectively. With the increase of stand age, the proportions of biomass and nutrients allocated to stem increased, while those allocated to foliage decreased. The accumulation rates of biomass and nutrients peaked at the age of 17 and 13, respectively, indicating that the nutrients reached their maximum accumulation rate ahead of the biomass. The nutrient requirement per unit dry biomass production decreased rapidly from the stand age 3 to 20 and reached a steady state after then, suggesting that the nutrient use efficiency increased with stand age. The analysis of different harvest scenarios showed that to prolong rotation length and to lower utilization intensity could reduce nutrient output. For example, if the rotation length was prolonged from 28 years to 56 years and only stem was harvested, the harvested biomass would be decreased by 31.57%, and the output of N, P, K, Ca, and Mg would be decreased by 42.02%, 58.93%, 27.70%, 31.07%, and 45.26%, respectively.

[Soil active organic matter in broadleaved forest and Chinese fir plantation in subtropical region of China].

A comparative study was made on the soil active organic matter in a broadleaved forest and two Chinese fir (Cunninghamia lanceolata) plantations in subtropical region of China, aimed to understand the effects of forest conversion and continuous plantation on soil organic C and nutrient status. After the conversion from broadleaved forest to Chinese fir plantation, the contents of soil total organic C, humus C, humic acid, and fulvic acid decreased by 27.8%-52.1%, 32.2%-52.8%, 36.4%-59.0%, and 29.7%-50.0%, respectively. Continuous plantation also resulted in the decrease of soil organic C and humus contents. The contents of soil total organic C, humus C, humic acid, and fulvic acid in second generation of Chinese fir plantation were 9.0%-25.0%, 25.0%-38.0%, 28.6%-39.2% and 23.1%-36.4% lower than those in the first generation of Chinese fir plantation, respectively. More obvious effects were observed on the soil active organic matter. After the conversion from broadleaved forest to Chinese fir plantation, the maximum decrement of soil microbial biomass C and N and dissolved organic C and N was 61.8%, 38.2%, 43.3%, and 69.0%; while comparing with the first generation of Chinese fir plantation, the second generation of Chinese fir plantation had the maximum decrement of soil microbial biomass C and N and dissolved organic C and N being 34.7%, 29.3%, 30.4%, and 18.4%, respectively. Soil nutrient contents also decreased due to forest conversion and continuous plantation. In comparing with broadleaved forests, Chinese fir plantations had a decrease of soil N, P, and K contents being 15.7%-31.2%, 11.5%-49.3%, and 15.1%-33.8%, respectively. There were close relationships between soil nutrients and soil active organic matter fractions except cold water extractable organic N.

[Effects of replacing natural secondary broad-leaved forest with Cunninghamia lanceolata plantation on soil biological activities].

This paper studied the effects of replacing natural secondary broad-leaved forest with Cunninghamia lanceolata plantation in the south, central and upstate areas of subtropical China on the changes of soil chemical and biological properties. The results showed that after replacing with Cunninghamia lanceolata plantation, the total organic carbon (TOC) content in surface soil decreased by 31.51% - 58.24%, and the contents of soil total N and P, pH value, C/N and C/P also decreased to different degree. Soil microbial amount was less than that under natural secondary broad-leaved forest, soil urease, invertase, catalase and dehydrogenase activities decreased, while soil polyphenol oxidase activity increased by 8% - 40%. The respiration rate of Cunninghamia lanceolata soil was 51.15% - 54.48% lower than that of natural secondary broad-leaved forest soil. The correlation between soil TOC and polyphenol oxidase activity was negative (R = - 0.723, n = 18), while those between soil TOC, N, P and other enzyme activities were positive. It could be concluded that replacing natural secondary broad-leaved forest with Cunninghamia lanceolata plantation worsened soil quality, and the loss of soil organic matter in Cunninghamia lanceolata plantation ecosystem might be one of the important factors resulted in the decrease of soil nutrients and enzyme activities.

[Effects of different ground clearance on soil fertility of Chinese fir stands].

The study on the soil physical properties, nutrient contents, microbial amounts and enzyme activities of clear cutting and controlled burning Chinese fir stands showed that in comparing with the control, soil non-capillary porosity of clear cutting stand increased by 23%, whereas soil natural water capacity and capillary moisture capacity decreased by 25%. In controlled burning stand, soil bulk density increased by 10%, while soil non-capillary porosity, natural water capacity and capillary moisture capacity decreased by 61%, 48% and 26%, respectively. The contents of soil organic matter, total N, total P and total K in clear cutting stand decreased by 14%, 14%, 35% and 22%, and in controlled burning stand, they decreased by 37%, 37%, 47% and 7%, respectively. Soil alkalized N and available K in clear cutting stand increased by 24% and 31%, respectively, but soil available P decreased by 15%. The contents of soil alkalized N, available P and available K in controlled burning stand decreased by 25%, 43% and 40%, respectively. In clear cutting stand, the amounts of soil bacteria, fungi and actinomyces increased by 1.4, 11.3 and 0.8 times, respectively, but in controlled burning stand, the amounts of soil bacteria decreased by 24%, while those of soil fungi and actinomyces increased by 5.0 and 0.5 times, respectively. The activities of soil urease, catalase and cellulase in clear cutting stand increased by 1.9, 1.6 and 2.1 times, and in controlled burning land, they were 35%, 90% and 106% of the control, respectively. Damp soil had higher contents of organic matter, total N and total P, whereas porous soil was favorable for the accumulation of alkalized N, available P and available K and for the increase of soil urease activity. The amount of soil fungi decreased with increasing soil capillary porosity. Aerated soil was favorable for the increase of soil catalase activity.

[Plantation stocks and their affecting factors in western Liaoning Province].

Employing real-site investigation and data analysis methods, this paper analyzed the distribution of plantation stocks and its affecting factors in western Liaoning Province. The results showed that the average plantation stock of western Liaoning was 49.08 m3.hm(-2), which has been improved obviously since 1949. At the time of the third forest resource investigation, the plantation stock increased 20.19 m3.hm(-2), 5.16 times higher than that of the first forest resource investigation. But, the general plantation stock of western Liaoning was still at a rather lower level, with only a 63.5% increase of the whole province and 51.1% of the national average plantation stock at the same period. The difference of plantation stock among cities in western Liaoning was observable, that even reached 68.47 m3.hm(-2). In general, the proportion of young forest was too high, reached to 49 % of the total plantation, while the stock of mature forest was much lower, only 38% of the national average level. The plantation stock of national property was only 55.1% and 32.3% of the personal and collective property, respectively. Moreover, the plantation stock of timber forest was 36.4% lower than that of windbreak. Besides climatic factors, simple plantation structure, few forest tree species, and poor plantation management were the main causes of the low plantation stock.

[Alleviation effect of exogenous Ca, P and N on the growth of Chinese fir seedlings under Al stress].

In this study, three month-old seedlings of Chinese fir (Cunninghamia laceolata) were grown in solution culture with 1 mmol x L(-1) Al at pH 4.0 for 80 days to evaluate the effects of varying concentrations of Ca, P, and NH4+-N or NO3(-)-N in solution on their growth. The morphological indexes (fresh weight, dry weight, shoot length, root length and relative elongation ratio) and physiological indexes (MDA content and POD activity) were submitted to statistical analysis and compared. The results indicated that the seedlings weight or shoot length had a significantly positive correlation with the molar ratio of solution Ca/Al. The MDA content and POD activity decreased with the increasing molar ratio of Ca/Al, and Ca/Al > or = 2.8 was the critical ratio. Similar to Ca/Al, high P/Al molar ratio also had an obvious effect on the growth of Chinese fir seedlings under Al stress, and P/Al > or = 4.5 was the critical ratio. The growth of Chinese fir seedlings was improved by increased NH4+-N supply, but the effect was less obvious than Ca and P. Solution NH4+-N/Al > or = 4.7 was the critical molar ratio. Solution NO3(-)-N could mitigate some adverse effects of Al on Chinese fir seedlings growth, but no regular effects were found with the change of solution NO3(-)-N/Al molar ratio.

[Degradation mechanism of Chinese fir plantation].

Chinese fir (Cunninghanzia lanceolata) is a fast-growing species native to China, and has a very important status in production of commercial timber. In response to the growing need for timber, pure Chinese fir plantations have been extensively replanted on the same site in successive rotations, which has resulted in serious problems of soil fertility degradation and productivity decline, and these problems have caused considerable attention from foresters, microbiologists, soil scientists and ecologists. They have also done a lot of work on these problems and studied the mechanism of productivity decline of replanted Chinese fir plantation. In this article, the author described the characteristics of productivity decline and soil degradation, and summed up the factors caused lower productivity, and analyzed the degradation mechanism of replanted Chinese fir plantation. In sum, productivity decline and soil physical and chemical characteristics deterioration were the main properties of replanted Chinese fir plantation. The factors summarized primarily as two kinds of reasons. One was the unreasonable management that was the edogenic factor, and another was the biotic self-characteristics of Chinese fir that was the intrinsic factor of poor establishment of replanted Chinese fir plantation. The combination of the edogenic and intrinsic factors reduced the productivity decline and soil degradation of the replanted Chinese fir plantation.