Mixed-species Plantations Research Articles

Soil carbon stocks in plantations and natural forests of the sub-tropics

PurposeSoil carbon (C) storage plays an important role in the mitigation of atmospheric CO2 emission. Soil C pools under different vegetation are distinct and need to be investigated. However, there are still large quantities of data shortages, which should be remedied by field and systematic studies. Materials and methodsSoil was collected at 0–10 cm depth from subtropical natural vegetation and plantations both in southeast China and southeast Queensland, Australia, respectively. Soil samples were assayed for soil organic C; organic N and inorganic N; and mineralization of SOC; total C, N, and P; and pH. Results and discussionOur results suggested soil C concentrations in natural vegetation ranged from 6.25% to 9.20%, whereas soil C concentrations in plantations ranged from 1.08% to 2.69%. No significant differences were found among vegetation along altitudinal gradients, whereas plantations with different tree species had different soil C concentrations, being higher in broadleaf-species plantations than in coniferous-species plantations. But there were no differences in soil C between single-species plantations and mixed-species plantations. Soil C concentrations in plantations were correlated with soil moisture, soil pH and dissolved organic C concentrations; Whereas soil C concentrations in natural vegetation were significantly correlated with soil moisture, soil pH and NO3− concentrations. ConclusionsThese results can contribute to the remedy of data shortages and provide the data necessary for model projections and informed decisions in the future.

Survival, growth, aboveground biomass, and carbon sequestration of mono and mixed native tree species plantations on the Coromandel Coast of India

ABSTRACT In India, reforestation programs with native indigenous tree species are a recent activity. Information on experiences comparing mono- and mixed-species plantations is limited. This study aims to estimate growth, aboveground biomass, and carbon sequestration between the mixed-species plantation and mono-species plantation. The growth, survival, height, aboveground biomass, and carbon sequestration of 82 native mixed species plantations were compared with Casuarina equisetifolia an exotic species planted in this region after over a decade (2006–2016). In the mixed species plantation, 7 species showed 100% survival rate and 19 species were not survived after over a decade intervals. While in the mono plantation, C. equisetifolia showed 92% of the survival rate. The growth rate of mixed species when compared to mono plantation, it showed highly significant differences (P < 0:05) values. Simple linear regression between annual girth increment and height produced very strong positive relations (R 2 0.759). The aboveground biomass estimated for the mixed native plantation was 8.007 tonnes and the mono plantation Casuarina had 5.585 tonnes. The total carbon stock estimated for the tree plantation in the two plots (both mixed native and mono) was 7.492 tonnes. A positive correlation was observed between the carbon stock and density of the top 10 species which contributed predominantly to the total carbon stock (rs = 0.773, p < 0.05). Plantation of C. equisetifolia seems to be well adapted and had more carbon stocking potential. On the other hand, mixed plantation with indigenous species would contribute more to sustainable management and they provide great shelters for many faunal communities and provide a greater range of ecological goods and ecosystem services than the mono plantations.

Assessment of tree diversity and above-ground biomass in coffee agroforest dominated tropical landscape of India’s Central Western Ghats

The purpose of this study was to quantify the changes in tree diversity and above-ground biomass associated with six land-use types in Kodagu district of India’s Western Ghats. We collected data on species richness, composition and above-ground biomass (AGB) of trees, shrubs and herbs from 96 sample plots of 0.1 ha. Totals of 83 species from 26 families were recorded across the land-uses. Tree species richness, diversity and composition were significantly higher in evergreen forest (EGF) than in other land-uses. Similarly, stem density and basal area were greater in EGF compared to other land-uses. Detrended correspondence analysis (DCA) yielded three distinct groups along the land-use intensities and rainfall gradient on the first and second axes, respectively. The first DCA axis accounted for 45% and second axis for 35% of the total variation in species composition. Together the first two axes accounted for over 2/3 of the variation in species composition across land-use types. Across the land-uses, AGB ranged from 58.6 Mg ha−1 in rubber plantation to 327.3 Mg ha−1 in evergreen forest. Our results showed that species diversity and AGB were negatively impacted by the land-use changes. We found that coffee agroforests resembled natural forest and mixed species plantation in terms of tree diversity and biomass production, suggesting that traditional coffee farms can help to protect tree species, sustain smallholder production and offer opportunities for conservation of biodiversity and climate change mitigation.

Nitrogen and carbon cycling associated with litterfall production in monoculture teak and mixed species teak and flueggea stands

High demand for teak (Tectona grandis L.f.), a species of economic importance, was the reason Solomon Islands experienced a surge in community-wide planting of monoculture teak stands in the last two decades. Mixed species planting of teak and flueggea (Flueggea flexuosa Muell. Arg.) was introduced to overcome the reluctance of growers to thin their stands. However, there is lack of information on the effect of changing from monoculture to mixed species plantings on the cycling of nutrients especially carbon (C) and nitrogen (N). This study assessed litter quantity and quality, total C (TC), total N (TN), C:N ratio and C and N isotope compositions (δ13C and δ15N) over 18 months at two sites (Ringgi and Poitete). The treatments included teak planted at 833 stems per hectare (sph) (T1), teak planted in rows with two rows of flueggea at 833 sph (T2), 625 sph (T3) and 416 sph (T4), and teak planted in alternating rows with flueggea at 833 sph (T5). Treatment 1 (T1) produced significantly higher total litter than T4 at Ringgi. However, based on individual tree litterfall production, teak in T4 (lowest stocking rate) at both trials produced higher litter per tree than the teak in T3, T2, T5 and T1 while there was no significant difference with litter production of flueggea. An enrichment of litter δ15N was observed over time in either species, which suggested an increased N loss and transformations in both experimental sites. When comparing each treatment and using individual tree productivity, T4 significantly produced and returned higher litter TC and TN than T3, T2, T5 and T1. Overall, individual tree productivity demonstrated that mixed species stands had a significant potential for cycling higher rates of C and N than monoculture teak stands. Therefore, establishment of mixed species stands, especially T4 and T3, was recommended as a practical measure to address the widely experienced problem of reluctance by growers to thin high value trees while preserving the balance of C and N inputs into the ground.

Afforesting savannas with Acacia mangium and eucalyptus improves P availability in Arenosols of the Congolese coastal plains

Phosphorus (P) is an essential constituent for all living organisms, scarce with finite reserves. P is deficient in Sub Saharan Africa threatening primary production. That in part is due to the occlusion of P in Fe and Al oxides in the weathered soils. This problem is aggravated by the high cost of P fertilizers, lack of both appropriate technologies for its application and government support to facilitate and strengthen its use in small-scale farming. Evaluation of soil P availability in the mixed-species plantations established on natural savannas in the Congolese coastal plains highlights that high C accretion involves low P availability in the mixed-species (50% acacia and 50% eucalyptus) stands relative to others. P availability in 0–0.05 m in the mixed-species stands (6.94 ± 0.45 mg kg−1) was lower than in acacia (8.07 ± 0.63 mg kg−1) and eucalyptus (8.46 ± 0.79 mg kg−1). C stock in the 0.25 m was higher in the mixed-species (17.8 ± 0.7 t.ha−1) relative to acacia (16.7 t.ha−1 ± 0.4) and eucalyptus (15.9 t.ha−1 ± 0.4). However, afforesting the inherently nutrient-poor and sandy soils beneath savannas evidenced an improvement in soil P availability to plant, along with soil N status and C sequestration in both soil and biomass, with a potential impact on mitigating climate change.

Nitrogen cycling in monospecific and mixed-species plantations of Acacia mangium and Eucalyptus at 4 sites in Brazil

Mixing N-fixing trees with eucalypts is an attractive option to improve the long-term soil N status in fast-growing plantations established in tropical soils. A randomized block design was replicated at four sites in Brazil to compare the biogeochemical cycles in mono-specific stands of Eucalyptus (100E) and Acacia mangium (100A) with mixed-species plantations in a proportion of 1:1 (50A50E). Our study aimed to assess the effects of introducing A. mangium trees in Eucalyptus plantations on atmospheric N2 fixation, N cycling and soil organic matter stocks. Litterfall and soil N mineralization were measured over the last two years of the rotation (4–6 years after planting). Aboveground N accumulation in the trees and C and N stocks in the forest floor and in the top soil were intensively sampled at harvesting age. N2 fixation rates were estimated using the natural abundance of 15N as well as by the difference between total N stocks in 100A and 50A50E relative to 100E (accretion method).While the 15N natural abundance method was unsuitable, the accretion method showed consistently across the four sites that atmospheric N fixation reached about 250 and 400 kg N ha−1 rotation−1 in 50A50E and 100A, respectively. Except at one site with high mortality, N contents within trees at harvesting were approximately 40% higher in 100A than in 100E. Mean N contents in litterfall and N mineralization rates were about 60% higher in 100A than in 100E, with intermediate values in 50A50E. The amounts of N in litterfall were much more dependent on soil N mineralization rates for acacia trees than for eucalypt trees. Soil C and N stocks were dependent on soil texture but not influenced by tree species. N budgets over a 6-year rotation were enhanced by about 65 kg N ha−1 yr−1 in 100A and 40 kg N ha−1 yr−1 in 50A50E relative to monospecific eucalypt plantations. Introducing N-fixing trees in eucalypt plantations might therefore contribute to reducing the need for mineral N fertilization in the long-term.

Changes in taxonomic and phylogenetic dissimilarity among four subtropical forest communities during 30 years of restoration

Enhancement and conservation of biodiversity in recovering communities is one of the primary goals of forest ecology and restoration. To achieve a better understanding of the mechanisms underlying community assembly during restoration, we examined changes in taxonomic and phylogenetic dissimilarity in four types of subtropical forests, consisting of a Eucalyptus plantation (EE), an Acacia mangium plantation (AM), a mixed native species plantation (NS), and a mixed coniferous plantation (MC), over 30 years of restoration (1985–2015). Temporal variation in taxonomic and phylogenetic dissimilarity patterns were found to differ among the four plantation types, although their taxonomic diversity (species richness) and phylogenetic diversity (PD) increased monotonically as succession proceeded. Community dissimilarity decreased nonlinearly over the 30 years, and species composition within each plantation tended to stabilize at around 20 years. Overall, the phylogenetic structure of each plantation was random during the succession period. Taxonomic and phylogenetic rates did not vary markedly along the 30 years of restoration, but the taxonomic turnover rate of MC increased significantly while the phylogenetic turnover rate of NC augmented remarkably. These results indicated that deterministic processes played a more important role in determining the temporal dynamics of community composition while stochastic processes were more important for phylogenetic structure. Our findings further inform the development and design of appropriate restoration strategies, and provide insights into understanding the mechanisms regulating community assembly during the process of forest restoration.

Growth and yield of 5 years old teak and flueggea in single and mixed species forestry systems in the Solomon Islands

Mixed species plantings of teak (Tectona grandis) and flueggea (Flueggea flexuosa) were introduced as a method for overcoming the reluctance of local growers to thin their teak. Flueggea is a well-used local species and removal of the flueggea for personal use would effectively thin the entire stand over time. Stocking rates and tree species composition are two important factors affecting tree growth and yield when a mixed species plantation is established. This study aimed to investigate the effects of stocking rates on early teak growth in a mixed species system in a humid tropical region of Western Province, Solomon Islands. The experimental design included: teak planted as a monoculture at standard stocking of 833 stems per hectare (sph) (Treatment 1); teak planted in rows alternating with 2 rows of flueggea at 833 sph; 625 sph; and 416 sph (Treatments 2,3 and 4 respectively); and teak planted in alternating rows with a single row of flueggea at 833 sph (Treatment 5). Teak basal area was optimum at the lowest stocking rates of 412 and 625 sph for both species. However, teak yield (volume per hectare) was greater in the higher stocking rate treatments. Teak basal area mean annual increment (BA MAI) decreased in higher stocking rates between the age of 4 and 5 years indicating the onset of suppression and the need for progressive thinning. Under correct silvicultural maintenance, the 833 sph planting density offers the benefits of higher stocking and lower maintenance. As the present investigation was confined to the establishment phase for teak, more studies are needed to understand the system development to maturity.

Understanding and optimizing species mixtures using functional-structural plant modelling.

Plant species mixtures improve productivity over monocultures by exploiting species complementarities for resource capture in time and space. Complementarity results in part from competition avoidance responses that maximize resource capture and growth of individual plants. Individual organs accommodate to local resource levels, e.g. with regard to nitrogen content and photosynthetic capacity or by size (e.g. shade avoidance). As a result, the resource acquisition in time and space is improved and performance of the community as a whole is increased. Modelling is needed to unravel the primary drivers and subsequent dynamics of complementary growth responses in mixtures. Here, we advocate using functional-structural plant (FSP) modelling to analyse the functioning of plant mixtures. In FSP modelling, crop performance is a result of the behaviour of the individual plants interacting through competitive and complementary resource acquisition. FSP models can integrate the interactions between structural and physiological plant responses to the local resource availability and strength of competition, which drive resource capture and growth of individuals in species mixtures. FSP models have the potential to accelerate mixed-species plant research, and thus support the development of knowledge that is needed to promote the use of mixtures towards sustainably increasing crop yields at acceptable input levels.

Impacts of biomass production at civil airports on grassland bird conservation and aviation strike risk.

Growing concerns about climate change, foreign oil dependency, and environmental quality have fostered interest in perennial native grasses (e.g., switchgrass [Panicum virgatum]) for bioenergy production while also maintaining biodiversity and ecosystem function. However, biomass cultivation in marginal landscapes such as airport grasslands may have detrimental effects on aviation safety as well as conservation efforts for grassland birds. In 2011-2013, we investigated effects of vegetation composition and harvest frequency on seasonal species richness and habitat use of grassland birds and modeled relative abundance, aviation risk, and conservation value of birds associated with biomass crops. Avian relative abundance was greater in switchgrass monoculture plots during the winter months, whereas Native Warm-Season Grass (NWSG) mixed species plantings were favored by species during the breeding season. Conversely, treatment differences in aviation risk and conservation value were not biologically significant. Only 2.6% of observations included avian species of high hazard to aircraft, providing support for semi-natural grasslands as a feasible landcover option at civil airports. Additionally, varied harvest frequencies across a mosaic of switchgrass monocultures and NWSG plots allows for biomass production with multiple vegetation structure options for grassland birds to increase seasonal avian biodiversity and habitat use.

Mixed-species plantation with Pinus massoniana and Castanopsis hystrix accelerates C loss in recalcitrant coniferous litter but slows C loss in labile broadleaf litter in southern China

Litter decomposition varies with forest type in complex ways and is significantly dependent on tree species diversity. A field litterbag experiment was conducted in monospecific and mixed-species plantations of Pinus massoniana and Castanopsis hystrix in subtropical China, to examine the effects of litter mixing and changing stand environment on the litter decomposition rate and the composition-specific litter organic C loss rate of P. massoniana and C. hystrix. Admixing with the lower-quality P. massoniana litter slowed C. hystrix litter decomposition and recalcitrant C loss, whereas admixing with the higher-quality C. hystrix litter hastened P. massoniana litter decomposition in the mixed-species plantation. The P. massoniana litter exhibited a faster decomposition rate in the mixed-species plantation than in the P. massoniana monospecific plantation. The same trend was found in the loss rates of aromatic C and carbonyl C from P. massoniana litter. The greater soil organic matter content and nitrogen availability in the mixed-species plantation than in the P. massoniana monospecific plantation could have resulted in the increased rates of decomposition and organic C loss in P. massoniana litter. This study highlights that maintaining mixed conifer-broadleaf forests and/or adopting close-to-nature forest management could accelerate the decomposition of recalcitrant coniferous litter, facilitating C sequestration and mitigating the C emissions derived from the labile broadleaf litter.

Nitrogen fixation rate of Acacia mangium Wild at mid rotation in Brazil is higher in mixed plantations with Eucalyptus grandis Hill ex Maiden than in monocultures

Inter-specific interactions with eucalypts in mixed plantations increased N 2 fixation rate of acacia trees compared to monocultures. N 2 fixation was higher during the wet summer than during the dry winter both in acacia monocultures and in mixed plantations. Introducing N-fixing trees in fast-growing tropical plantations may contribute to reducing the long-term requirements of N fertilizers. Management practices established in forest monocultures should be revisited in mixed-species plantations. This field experiment aimed to compare N2 fixation rates of Acacia mangium Wild in monospecific stands and in mixed-species stands with Eucalyptus grandis W. Hill ex Maiden. A secondary objective was to gain insight into the seasonal variations of N2 fixation. 15N was applied to acacia and eucalypt monocultures and mixed-species with a 1:1 ratio at mid rotation. Leaves were collected in autumn, winter, spring, and summer to determine the foliar N concentrations and 15N atom fraction. The N content in the above-ground biomass was estimated as well as the percentage of N derived from atmospheric N2 (%Ndfa) using eucalypts in monoculture as reference plants. %Ndfa values averaged over the year were 14% in monoculture and 44% in mixed-species stands. While the stocking density of acacia trees was twice as high in monoculture as in mixture, the amounts of N fixed in above-ground biomass of acacia trees were close (35–39 kg N ha−1) at 39 months after planting. %Ndfa values were higher during the wet summer than the dry winter both in acacia monocultures and in mixed plantations. The stocking density of acacia trees can be reduced in mixed plantations with eucalypts in comparison to acacia monocultures with a low influence on the input of N to soil through biological fixation.

Fate of Acacia mangium in eucalypt mixed-species plantations during drought conditions in the Congolese coastal plains

A mixed-species plantation of Acacia mangium (acacia) and Eucalyptus urophilla x grandis (eucalypt) hybrid was established on the Arenosols of the coastal Congolese plains to improve soil fertility and sustain forest plantation productivity. At one year into the second rotation, some of the acacia started to exhibit yellowing and drying of leaves, resulting in the death of the whole tree. One-third of the pure acacias (100A) and the mixed, 50 % acacia and 50 % eucalypt (50A50E) hybrid, exhibited these characteristics five months later. To limit the damage, the acacias were pruned up to 1.30 meters. The acacias were threatened by a dry season that extended two months longer than during the previous year, probably triggered by sandy textured soils and poor soil fertility (nitrogen < 0.07 % in the 0.05 meters). Soil moisture to a depth of 0.15 meters was higher under eucalypt compared to acacia. It appears that the acacia root structure may have been less tolerant to drought conditions compared with the eucalypts, leading to damage of acacias, which was exacerbated by the acacia’s young age, poor soil fertility and sandy soil texture. One year after pruning, acacias in both 100A and 50A50E presented a healthier tree structure. Furthermore, no negative impact on aboveground biomass -i.e., wood, bark, leaves and branch- has been recorded at 12 and 24 months.

Productivity and dynamics of pure and mixed-species plantations of Populous deltoids Bartr. ex Marsh and Alnus subcordata C. A. Mey

Abstract Mixed-forest plantation with native species have gradually become the focus of forest research. The need to better understand their performance and productivity is, nowadays, a matter of particular relevance to forestry practice. The objective of this study was a long-term analysis of the effects of species-mixing of Populus deltoides Bartr. ex Marsh and Alnus subcordata C. A. Mey on aboveground biomass and net primary production, growth dynamics, and their relative yields total in pure and mixed stands. The experiment consisted of a replacement series that was established in 1996, using a randomized block design with five treatments (100P:0A, 67P:33A, 50P:50A, 33P:67A, 0P:100A) in four replicate blocks and two species were systematically mixed within rows. In the early stages, both species had a similar growth trend, while the differences were more pronounced at higher ages. The results show that inter- and intraspecific competition and nutrient cycling had the most pronounced effect on stand growth over time. Populus deltoides benefited from growing in mixture; canopy stratification reduces interspecific competition for light, and this species functioned best in mixed stands. In contrast, A. subcordata was sensitive to competition and had the highest growth in pure stands. In general, positive interactions between the two species led to the highest relative yield total and productivity in mixtures compared with pure stands. Within the framework of this experiment, it seems that the relative proportions of 50% Populus deltoides and 50% Alnus subcordata could provide economic and environmental benefits and increase the stability and productivity of the stands.

Short Communication: Survival and growth of mono and mixed species plantations on the Coromandel coast of India

Anbarashan M, Padmavathy A, Alexandar R. 2017. Short Communication: Survival and growth of mono and mixed species plantations on the Coromandel coast of India. Asian J For 1: 70-76. There exists very little information on the growth of autochthonous tree species autochthonousin the tropics and on the experiences in conducting mono and mixed species plantations. The aim of this study was to compare the variation in growth parameter between the mixed species plantation and mono species plantation. The growth, survival, and height of 82 autochthonous mixed species plantations were compared with Casuarina equisetifolia, an exotic species broadly planted in this region after over a decade (2006 to 2016). In the mixed species plantation, seven species showed 100 % survival rate and 19 species were not survived after 10-year intervals. In the mono species plantation, Casuarina equisetifolia had 92 % of the survival rate. When it is compared to the mono plantation, the growth rate of mixed species plantation showed highly significant differences (P &lt; 0: 05) values. Simple linear regression between annual girth increment and height produced very strong positive relations (R2 0.759). Plantations of Casuarina equisetifolia seem to be well adapted to the coastal region. On the other hand, mixed plantation with autochthonous species would contribute more to sustainable management because they provide a greater range of ecological goods and ecosystem services than the single species plantations.

Understanding the enhanced litter decomposition of mixed-species plantations of Eucalyptus and Acacia mangium

Soil microbial-derived litter decomposition represents an important step in the global carbon and nutrient cycling and, at the local level, is primarily driven by litter chemistry. Here, we assessed how mixed-species plantations with Eucalyptus urograndis and Acacia mangium could be a key to enhancing litter production, decomposition, and soil microbial activity. The relationships between litter decomposition and litter quality and quantity were compared among 6-year-old monocultures of E. urograndis and A. mangium (E100+N and A100, respectively) and a mixed plantation of both species (E50A50). Additionally, we evaluated soil microbial biomass carbon (MBC) and nitrogen (MBN), soil basal respiration (SBR), soil enzymes and the N mineralization potential. The return to soil of N via litterfall in E50A50 was greater than E100+N, while the return of P in E100+N and E50A50 were higher than A100. The decomposition rate in A100 was slower than in the E50A50 and E100+N. The microbial activity, represented by soil enzyme activities (proteases and N-acetyl-β-glucosaminidases), was consistently higher in E50A50 than in A100. The E50A50 presented a more balanced supply of N and P associated to a better structural quality of the litter for microbial metabolism, with synergic reflections on decomposition rates and release of nitrogen.

A Synthesis of the Available Evidence to Guide the Design of Mixed-Species Forest Plantings for Smallholder and Community Forestry

There is growing interest in using multi-species plantation systems when undertaking reforestation for timber production. Such plantations can have ecological and socio-economic advantages over those of traditional monocultures. Despite increasing evidence about the functional advantages of increasing species richness in reforestation, there are few silvicultural guidelines to assist in the design and management of multi-species plantings. This paper presents the results of a systematic assessment of previous studies of mixed-species plantings with a particular focus on their advantages and disadvantages for meeting the needs of rural smallholders and communities in tropical regions. Research on mixed-species plantations has increased in recent years. Many earlier studies were concerned with the capacity of mixed-species plantings to improve productivity or the nutritional impacts of mixtures. Many of these studies emphasised young plantations and mixtures of a few relatively fast-growing Acacia, Eucalyptus and Pinus species. More recent studies have explored a wider range of outcomes arising from using mixtures including on the supply of ecosystem services. Issues deserving further study concern the economic advantages or disadvantages of mixed-species plantations, how these plantations might be designed to suit various environmental and socio-economic situations, and how to manage older mixed-species plantations where the interactions between species may be different to those in younger plantations. There is also a need to explore how increased species richness may affect the capacity of new plantations to withstand damage from insect pests or disturbances such as storms or wildfire.

Carbon and nutrient stocks of three Fabaceae trees used for forest restoration and subjected to fertilization in Amazonia.

Amazonia is crucial to global carbon cycle. Deforestation continues to be one of the main causes of the release of C into the atmosphere, but forest restoration plantations can reverse this scenario. However, there is still diffuse information about the C and nutrient stocks in the vegetation biomass. We investigated the carbon and nutrient stocks of Fabaceae trees (Inga edulis, Schizolobium amazonicum and Dipteryx odorata) subjected to fertilization treatments (T1 - no fertilization; T2 - chemical; T3 - organic; and T4 - organic and chemical fertilization) in a degraded area of the Balbina Hydroelectric Dam, AM - Brazil. As an early successional species, I. edulis stocked more C and nutrients than the other two species independent of the fertilization treatment, and S. amazonicum stocked more C than D. odorata under T1 and T4. The mixed species plantation had the potential to stock 4.1 Mg C ha-1 year-1, while I. edulis alone could stock 9.4 Mg C ha-1 year-1. Mixing species that rapidly assimilate C and are of significant ecological and commercial value (e.g., Fabaceae trees) represents a good way to restore degraded areas. Our results suggest that the tested species be used for forest restoration in Amazonia.

Arbuscular Mycorrhizal Fungi Enhanced Growth of Magnolia macclurei (Dandy) Figlar Seedlings Grown under Glasshouse Conditions

A glasshouse experiment was conducted to investigate the effects of arbuscular mycorrhizal fungi (AMF) (Glomus manihotis, Glomus versiforme, and Glomus caledonium) on growth of Magnolia macclurei seedlings from two seed sources in southern China. Two-month-old seedlings were inoculated and grown in pots for 5 months. All three AMF were effective in root mycorrhization (68–82%). Phosphorus uptake in inoculated seedlings increased by 10–35%, accompanied by significantly enhanced seedling growth (16–27% increase in height and diameter and 35–45% increase in dry matter production), whereas only small increases in nitrogen and potassium uptake were observed. Seed sources varied significantly in several growth traits, implying possible genetic variation and the potential for selection of superior genotypes in this species. The results are discussed in the context of nursery management and production of inoculated seedlings for pure and mixed-species plantations of M. macclurei.

Biomass production, nitrogen accumulation and symbiotic nitrogen fixation in a mixed-species plantation of eucalypt and acacia on a nutrient-poor tropical soil

The success of mixed-species tree plantations depends on the balance between positive and negative interactions. Mixtures of Acacia mangium and Eucalyptus urophylla×grandis out-yield their respective monocultures in term of wood production on the Congolese coastal plain, suggesting that facilitation and/or competitive reduction surpass interspecific competition. We investigated how these interactions affected biomass production and N accumulation during the early growth stage of a second rotation of a mixed-species stand of these two species. We used the 15N dilution method to estimate symbiotic nitrogen fixation and its contribution to N accumulation in acacia monoculture and mixture, and we assessed how much N derived from the atmosphere is transferred to the eucalypt trees in the mixed-species stand. Eucalypts grew taller and acacias grew larger in the mixture compared to the monocultures. N mineralomass was greater in the mixture relative to the average values in the two monocultures, with both species contributing to this enhanced N mineralomass. The amount of N derived from the atmosphere in the mixture was 60% higher than that expected given the amount found in acacia monoculture, and 16% of the nitrogen accumulated in eucalypt trees and aboveground eucalypt litterfall was derived from the atmosphere. Reduced competition for light and soil water also contributed to the increased growth of acacias in the mixture, showing that both species benefit from growing in a mixed stand.