A broadleaf species enhances an autotoxic conifers growth through belowground chemical interactions.[Pubmed: 27859072]

Plants may affect the performance of neighboring plants either positively or negatively through interspecific and intraspecific interactions. Productivity of mixed-species systems is ultimately the net result of positive and negative interactions among the component species. Despite increasing knowledge of positive interactions occurring in mixed-species tree systems, relatively little is known about the mechanisms underlying such interactions. Based on data from 25-year-old experimental stands in situ and a series of controlled experiments, we test the hypothesis that a broadleaf, non-N fixing species, Michelia macclurei, facilitates the performance of an autotoxic conifer Chinese fir (Cunninghamia lanceolata) through belowground chemical interactions. Chinese fir roots released the allelochemical cyclic dipeptide (6-hydroxy-1,3-dimethyl-8-nonadecyl-[1,4]-diazocane- 2,5-diketone) into the soil environment, resulting in self-growth inhibition, and deterioration of soil microorganisms that improve P availability. However, when grown with M. macclurei the growth of Chinese fir was consistently enhanced. In particular, Chinese fir enhanced root growth and distribution in deep soil layers. When compared with monocultures of Chinese fir, the presence of M. macclurei reduced release and increased degradation of cyclic dipeptide in the soil, resulting in a shift from self-inhibition to chemical facilitation. This association also improved the soil microbial community by increasing arbuscular mycorrhizal fungi, and induced the production of Chinese fir roots. We conclude that interspecific interactions are less negative than intraspecific ones between non-N fixing broadleaf and autotoxic conifer species. The impacts are generated by reducing allelochemical levels, enhancing belowground mutualisms, improving soil properties, and changing root distributions as well as the net effects of all the processes within the soil. In particular, allelochemical context alters the consequences of the belowground ecological interactions with a novel mechanism: reduction of self-inhibition through reduced release and increased degradation of an autotoxic compound in the mixed-species plantations. Such a mechanism would be useful in reforestation programs undertaken to rehabilitate forest plantations that suffer from problems associated with autotoxicity.

Schima superba outperforms other tree species by changing foliar chemical composition and shortening construction payback time when facilitated by shrubs.[Pubmed: 26814426]

A 3.5-year field experiment was conducted in a subtropical degraded shrubland to assess how a nurse plant, the native shrub Rhodomyrtus tomentosa, affects the growth of the target trees Pinus elliottii, Schima superba, Castanopsis fissa, and Michelia macclurei, and to probe the intrinsic mechanisms from leaf chemical composition, construction cost (CC), and payback time aspects. We compared tree seedlings grown nearby shrub canopy (canopy subplots, CS) and in open space (open subplots, OS). S. superba in CS showed greater growth, while P. elliottii and M. macclurei were lower when compared to the plants grown in the OS. The reduced levels of high-cost compounds (proteins) and increased levels of low-cost compounds (organic acids) caused reduced CC values for P. elliottii growing in CS. While, the levels of both low-cost minerals and high-cost proteins increased in CS such that CC values of S. superba were similar in OS and CS. Based on maximum photosynthetic rates, P. elliottii required a longer payback time to construct required carbon in canopy than in OS, but the opposite was true for S. superba. The information from this study can be used to evaluate the potential of different tree species in the reforestation of subtropical degraded shrublands.

Plant uptake, translocation, and return of polycyclic aromatic hydrocarbons via fine root branch orders in a subtropical forest ecosystem.[Pubmed: 25863163]

Fine roots of woody plants are a heterogeneous system differing markedly in structure and function. Nevertheless, knowledge about the plant uptake of organic pollutants via fine roots is scarce to date. In the present study, plant uptake, translocation, and return of polycyclic aromatic hydrocarbons (PAHs) via fine roots in a subtropical forest ecosystem were investigated. Levels of Σ15PAHs in different fine root branch orders of Michelia macclurei, Cryptocarya concinna, Cryptocarya chinensis, and Canthium dicoccums varied from 5072±1419 ng g(-1) to 6080±1656 ng g(-1), 4037±410 ng g(-1) to 6101±972 ng g(-1), 3308±1191 ng g(-1) to 4283±237 ng g(-1), and 3737±800 ng g(-1) to 4895±1216 ng g(-1), respectively. Overall, concentrations of low-molecular-weight PAHs with 2-3 aromatic rings were higher than high-molecular-weight PAHs with 4-6 aromatic rings in all fine root branch orders. There were obvious translocations of PAHs between adjacent branch orders and a net accumulation of PAHs may occur in the fourth- and fifth-order roots. The storage of PAHs in the fine root system showed an obvious increasing trend along the branch orders ascending for all tree species. The return flux of PAHs via fine roots mortality showed an obvious decreasing trend with the branch orders ascending across the four tree species. Lower order roots contributed greatly to the total PAHs return flux. Our results indicated that fine roots turnover is an effective pathway for perennial tree species to remove environmental toxicants absorbed into them.

Comparisons of carbon storages in Cunninghamia lanceolata and Michelia macclurei plantations during a 22-year period in southern China.[Pubmed: 19803086]

Tree species composition was important for carbon storage within the same climate range. To quantify the dynamics of ecosystem carbon allocation as affected by different tree species, we measured the above- and below-ground biomass accumulation in 22 years, as well as the tissue carbon concentrations of trees in Cunninghamia lanceolata plantation and Michelia macclurei plantation. Results indicated that M. macclurei plantation significantly stored more carbon (174.8 tons/hm2) than C. lanceolata plantation (154.3 tons/hm2). Most of the carbon was found in the soil pool (57.1% in M. macclurei plantation, 55.2% in C. lanceolata plantation). Tree and soil component of M. macclurei plantation possessed significantly higher carbon storage than that of C. lanceolata plantation (p <0.05). No significant difference was found in the carbon storage of understory and forest floor. These results suggest that the broadleaved species (M. macclurei) possesses greater carbon sequestration potential than the coniferous species (C. lanceolata) in southern China.

[Effects of Cunninghamia lanceolata-broadleaved tree species mixed leaf litters on active soil organic matter].[Pubmed: 17763716]

With incubation test, this paper studied the effects of Cunninghamia lanceolata leaf litter and its mixture with the litters of main broadleaved tree species in subtropical China, such as Alnus cremastogyne, Kalopanax septemlobus and Michelia macclurei on active soil organic matter. The results showed that adding leaf litters into soil could significantly increase soil microbial biomass C and N, respiration rate and dissolved organic C, and mixed leaf litters were more effective than C. lanceolata leaf litter in increasing soil dissolved organic C. By the end of the incubation, the increment of soil microbial biomass C and N, respiration rate, and dissolved organic C in treatments C. lanceolata leaf litter and C. lanceolata-broadleaved tree species mixed leaf litters was 49% and 63%, 35% and 75%, 65% and 100%, and 66% and 108%, respectively, compared with control. The addition of leaf litters had no significant effects on soil microbial quotient and microbial biomass C/N ratio.

[Effects of tree species fine root decomposition on soil active organic carbon].[Pubmed: 17552179]

With incubation test, this paper studied the effects of fine root decomposition of Alnus cremastogyne, Cunninghamia lanceolata and Michelia macclurei on the content of soil active organic carbon at 9 degrees C , 14 degrees C , 24 degrees C and 28 degrees C. The results showed that the decomposition rate of fine root differed significantly with test tree species, which was decreased in the order of M. macclurei > A. cremastogyne > C. lanceolata. The decomposition rate was increased with increasing temperature, but declined with prolonged incubation time. Fine root source, incubation temperature, and incubation time all affected the contents of soil microbial biomass carbon and water-soluble organic carbon. The decomposition of fine root increased soil microbial biomass carbon and water-soluble organic carbon significantly, and the effect decreased in the order of M. macclurei > A. cremastogyne > C. lanceolata. Higher contents of soil microbial biomass carbon and water-soluble organic carbon were observed at medium temperature and middle incubation stage. Fine root decomposition had less effect on the content of soil readily oxidized organic carbon.

[Soil properties and water holding capacites of Michelia macclurei, Schima superba and Castanopis fissa stands].[Pubmed: 16355772]

The study showed that the soil density, total porosity, natural water capacity and capillary moisture capacity were 1.19 g x cm(-3), 56.73%, 15.7% and 43.2% in Michelia nacclurei stand, 1.26 g x cm(-3), 54.18%, 13.0% and 37.8% in Schima superb stand, and 1.06 g x cm(-3), 60.74%, 19.4%, and 45.8% in Castanopsis fissa stand, respectively. Soil water holding capacity and aeration were good in Castanopsis fissa stand but bad in Schima superba stand, whereas Michelia macclurei stand had a medium water holding capacity and a bad aeration. The water holding capacity of litter per tree was in order of Michelia nuacclurei (20 kg) > Castanopsis fissa (15 kg) > Schima superba (8 kg), whereas that of litter in stand was Castanopsis fissa (17 t x hm(-2)) > Michelia macclurei (16 t x hm(-2)) > Schima superba (13 t x hm(-2)). The nutrient storage of litter per tree was 112.71, 31.20 and 87.30 g in Michelia macclurei, Schima superba and Castanopsis fissa stands, respectively, and that of litter in stand was 84.35,51.86 and 98.11 kg x hm(-2), respectively. The soil in the three stands was strong acidic, and the content of soil organic matter, total N, total P, total K, alkalized N, available P and available K was 18.43 g x kg(-1), 0.69 g x kg(-1), 0.17 g x kg(-1), 5.83 g x kg(-1), 45.67 mg x kg(-1), 0.83 mg x kg(-1) and 23.13 mg x kg(-1) in Michelia macclurei stand, 13.40 g x kg(-1), 0.68 g x kg(-1), 0.20 g x kg(-1), 12.32 g x kg(-1), 40.78 mg x kg(-1), 0.85 mg x kg(-1) and 90.63 mg x kg(-1) in Schima superba stand, and 28.50 g x kg(-1), 0.97 g x kg(-1), 0.23 g x kg(-1), 18.77 g x kg(-1), 73.40 mg x kg(-1), 1.45 mg x kg(-1) and 66.50 mg x kg(-1) in Castanopsis fissa stand, respectively. Soil bacteria accounted for > 94% of soil microbes, and their individuals were 41 x 105, 34 x 104 and 5.3 x 104 g(-1) in Michelia macclurei, Schima superba and Castanopsis fissa stands, respectively. The activities of soil urease, catalase and phosphatase in Castanopsis fissa stand were the greatest among the three stands, while soil cellulase activity in Michelia macclurei stand was greater than that in other two stands. In a word, soil fertility of Castanopsis fissa stand was the highest among three test stands.