Higher tree species richness generally increases the storage of soil organic carbon (SOC). However, less attention is paid to the influence of varied tree species composition on SOC storage. ...Recently, the perspectives for the stronger persistence of SOC caused by the higher molecular diversity of organic compounds were proposed. Therefore, the influences of tree species richness and composition on the molecular diversity of SOC need to be explored. In this study, an index of the evenness of diverse SOC chemical components was proposed to represent the potential resistance of SOC to decomposition under disturbances. Six natural forest types were selected encompassing a diversity gradient, ranging from cold temperate to tropical forests. We examined the correlations of tree species richness, composition, and functional diversity, with the evenness of SOC chemical components at a molecular level by 13C nuclear magnetic resonance. Across the range, tree species richness correlated to the evenness of SOC chemical components through tree species composition. The negative correlation of evenness of SOC chemical components with tree species composition, and the positive correlation of evenness of SOC chemical components with tree functional diversity were found. These indicate the larger difference in tree species composition and the lower community functional diversity resulted in the higher heterogeneity of SOC chemical components among the communities. The positive correlation of the evenness of SOC chemical components with the important value of indicator tree species, further revealed the specific tree species contributing to the higher evenness of SOC chemical components in each forest type. Soil fungal and bacterial α‐diversity had effect on the evenness of SOC chemical components. These findings suggest that the indicator tree species conservation might be preferrable to simply increasing tree species richness, for enhancing the potential resistance of SOC to decomposition.
Tree species richness correlated with the evenness of soil organic carbon (SOC) chemical compositions through the composition of tree species. The larger difference in tree species composition and the lower community functional diversity resulted in the higher heterogeneity of SOC chemical components among the communities. Indicator tree species conservation might be preferrable to simply increasing tree species richness, for enhancing the potential resistance of SOC to decomposition.
•Legume trees markedly improved soil Po accumulation and availability.•Po fractions were primarily driven by soil ALP, MBN and AM.•Legume trees introduction may be an efficient management of P ...cycling in karst areas.•Then, we hope the content of this study will meet the requirement of “Geoderma”.
Many studies have shown that introducing N2-fixing tree species into plantations can increase soil nitrogen (N) availability, via biological N2 fixation and faster N cycling. However, the effects and regulatory mechanisms of N2-fixing tree species in planting single species vs a combination of two species on phosphorus (P) accumulation and transformation in degraded karst soils remain poorly understood and appear site-dependent. This study aimed to determine the effects of introducing N2-fixing tree species (via single species vs a combination of two species) into a degraded karst region on organic phosphorus (Po) accumulation and transformation in topsoil aggregates. A comparative experiment was performed involving 8-year-old pure plantations of Dalbergia odorifera (PD) and Acrocarpus fraxinifolius (PA), a mixed plantation of Dalbergia odorifera and Acrocarpus fraxinifolius (MP), and an adjacent natural weed field (no trees, CK) in Mashan, Guangxi, subtropical China. The results showed that the contents of soil organic carbon (SOC), nitrate nitrogen (NO3−-N), available phosphorus (AP) and C:N ratios in bulk soil and aggregates, increased significantly (P < 0.05) in MP compared to CK. The levels of soil microbial biomass N (MBN) and microbial biomass P (MBP) in bulk and aggregate soils increased significantly (P < 0.05), except for micro-aggregates (<0.25 mm) in MP samples. In contrast, no significant differences of MBN or MBP were found among PD, PA and CK plots in bulk and most aggregate soils. The phospholipid fatty acid (PLFA) contents of all microbes, bacteria, fungi, arbuscular mycorrhizal (AM) fungi and actinomycetes were also significantly higher (P < 0.05) in MP than those in CK and PD in bulk and most aggregate soils. Labile Po and highly resistant Po, and the activities of all tested N and P hydrolytic enzymes, improved in bulk soil and most aggregate size classes in all forest types, especially in MP samples. Finally, redundancy analysis (RDA) indicated that Po fractions were primarily driven by alkaline phosphatase (ALP), MBN and AM. Our findings suggest that introducing N2-fixing tree species (especially MP) may be an effective method for increasing N availability and AM colonization of roots, and thereby promoting Po accumulation and transformation in degraded karst regions of southwest China.
Diversity–biomass relationships (DBRs) often vary with spatial scale in terrestrial ecosystems, but the mechanisms driving these scale‐dependent patterns remain unclear, especially for highly ...heterogeneous forest ecosystems. This study explores how mutualistic associations between trees and different mycorrhizal fungi, i.e., arbuscular mycorrhizal (AM) vs. ectomycorrhizal (EM) association, modulate scale‐dependent DBRs. We hypothesized that in soil‐heterogeneous forests with a mixture of AM and EM tree species, (i) AM and EM tree species would respond in contrasting ways (i.e., positively vs. negatively, respectively) to increasing soil fertility, (ii) AM tree dominance would contribute to higher tree diversity and EM tree dominance to greater standing biomass, and that as a result (iii) mycorrhizal associations would exert an overall negative effect on DBRs across spatial scales. To empirically test these hypotheses, we collected detailed tree distribution and soil information (e.g., nitrogen, phosphorus, organic matter, pH) from seven temperate and subtropical AM–EM mixed forest megaplots (16–50 ha). Using a spatial codispersion null model and structural equation modeling, we identified the relationships among AM or EM tree dominance, soil fertility, tree species diversity, and biomass and, thus, DBRs across 0.01‐ to 1‐ha scales. We found the first evidence overall supporting the three aforementioned hypotheses in these AM–EM mixed forests: (i) In most forests, with increasing soil fertility, tree communities changed from EM‐dominated to AM‐dominated; (ii) increasing AM tree dominance had an overall positive effect on tree diversity and a negative effect on biomass, even after controlling for soil fertility and number of trees. Together, (iii) the changes in mycorrhizal dominance along soil fertility gradients weakened the positive DBR observed at 0.01‐ to 0.04‐ha scales in nearly all forests and drove negative DBRs at 0.25‐ to 1‐ha scales in four out of seven forests. Hence, this study highlights a soil‐related mycorrhizal dominance mechanism that could partly explain why, in many natural forests, biodiversity–ecosystem functioning (BEF) relationships shift from positive to negative with increasing spatial scale.
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•The impact of overstorey species on AMF communities was studied.•AMF abundance increased with increasing soil alkalinity and macronutrient levels.•Soils under deciduous tree species ...were characterised by greater AMF abundance.•AMF species composition differed between soils of deciduous and coniferous species.•The differences resulted from several factors acting within groups of tree species.
Despite the presence of arbuscular mycorrhizal fungi (AMF) in temperate forests, knowledge concerning their diversity and interactions with plants is still insufficient. Therefore, we studied the impact of overstorey species identity on AMF abundance and species richness and composition in relation to herbaceous plant cover and soil chemical properties. The effects of 14 tree species grown for 48 years in monospecific plots in the Siemianice Experimental Forest (western Poland) were compared, including the following groupings: deciduous vs coniferous; native to Poland/Europe vs alien; forming vs not forming arbuscular mycorrhizas (AM). Coniferous tree plots were characterised by lower pH values, plots with deciduous trees by higher concentrations of total Ca and exchangeable forms of Ca, K and Mg. AMF abundance in soils and roots increased along with increasing soil alkalinity and macronutrient levels. Concentrations of the PLFA 16:1ω5 AMF hyphal biomass marker were higher in the soils of deciduous and AM-type tree species than those of coniferous and non-AM types. In addition, concentrations of the NLFA 16:1ω5 AMF spore biomass marker were higher in the soils of deciduous tree species. No significant differences were found between groups of native and alien tree species. AMF spore and species numbers were low in comparison to other unforested ecosystems, averaging 77.5 and 1.2 per 50 g of soils, respectively. The presence of 8 AMF species, both widespread (e.g. Funneliformis constrictus) and rare (Acaulospora cavernata) was revealed. Significant divergence in AMF species composition was noted between plots of deciduous and coniferous species. Our study showed that tree species identity, considered as a single factor, has only a slight impact on determining AMF community characteristics. The disparity between AMF community characteristics results from the effects of several factors, as pH and element concentrations in soils, acting within tree species groups.
Knowledge of tree species is required to inform management, planning, and monitoring of forests as well as to characterize habitat and ecosystem function. Remotely sensed data and spatial modeling ...enable mapping of tree species presence and distribution. Following an assessment of tree species identified in the sample-based National Forest Inventory (NFI), we mapped 37 tree species over the 650-Mha, forest-dominated ecosystems of Canada representing 2019 conditions. Landsat imagery and related spectral indices, geographic and climate data, elevation derivatives, and remote sensing-derived phenology are used as predictor variables trained with calibration samples from Canada's NFI using the Random Forests machine learning algorithm. Based upon prior knowledge of tree species distributions, classification models were implemented on a regional basis, meaning only the tree species that are expected in a given mapping region were modeled using local calibration samples. Modeling resulted in class membership probabilities values for each regionally eligible tree species for all treed pixels as well as an indicator of attribution confidence derived from the distance in feature space between the two leading classes. Accuracy assessment was conducted using independent validation data also drawn from the NFI following the same selection rules and indicated an overall accuracy of 93.1% ± 0.1% (95%-confidence interval). Predictor variables informing on geographic, climatic and topographic conditions had the largest importance on the classification models. Nationally, the most common leading tree species were black spruce (Picea mariana; 203 Mha or 57.3% of the treed area), trembling aspen (Populus tremuloides; 34.7 Mha, 9.8%), and lodgepole pine (Pinus contorta; 21.1 Mha, 5.9%). Regionally, there was ecozone-level dominance of other tree species, including subalpine fir (Abies lasiocarpa; Montane Cordillera), western hemlock (Tsuga heterophylla; Pacific Maritime), and balsam fir (Abies balsamea; Atlantic Maritime). Based upon the per-pixel class membership probabilities, species assemblages akin to those in forest inventories can also be produced. Further, given the calibrated reflectance of Landsat imagery, the methods presented herein can be implemented over a time series of images. The approach uses open data as predictor variables, making the method portable to other areas given availability of tree species training data.
•Methodological approach to map presence and distribution of tree species.•37 tree species mapped over the 650 Mha forest-dominated ecosystems of Canada.•Calibration data derived by refining Canada’s national forest inventory.•Predictor variables derived from Landsat imagery, climate, terrain, and phenology data.•Approach portable internationally due to common calibration data and use of open data.
Tree species diversity enhances productivity and soil carbon storage in subtropical forests. However, the effects of tree species diversity and N-fixing tree species on the chemical stability of soil ...organic carbon (SOC) have been poorly understood. In this study, a manipulative experiment involving varying tree species richness (i.e., one, two, four and six species) and the inclusion of N-fixing trees was conducted to investigate the effects of tree species richness and the presence of N-fixing tree species on the chemical stability of SOC. Biological traceability was used to separate SOC into plant- vs. microbial-derived components, and then assessed by four measures of the chemical stability, including the cyclic/acyclic lipid ratio, average carbon chain length (ACL), Pielou's evenness of acyclic lipids and Pielou's evenness of cyclic lipids. We found that tree species richness was positively correlated with the cyclic/acyclic lipid ratio, ACL and evenness of acyclic lipids. In the presence of N-fixing tree species, tree species richness significantly increased both plant- and microbial-derived lipids, resulting in a higher cyclic/acyclic lipid ratio through stimulated root-microorganism interactions. Plant-derived lipids were positively correlated with the cyclic/acyclic lipid ratio, ACL and evenness of acyclic lipids, suggesting the important role of plant-derived components in shaping the chemical stability of SOC. This study reveals that the chemical stability of SOC is not only a function of tree species richness, but also manifested by the presence of N-fixing tree species. These results demonstrate that mixed plantations with N-fixing trees as an appropriate silvicultural option will be beneficial to the enhancement of the chemical stability of SOC through increased soil recalcitrant C components.
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•Tree species richness has a positive effect on SOC chemical stability.•The chemical stability of SOC is mainly contributed by plant-derived C.•The presence of N-fixing tree increased SOC chemical stability.
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•Forest restoration aims to reverse damage, but evaluation of its success is scarce.•We assessed the influence of restoration on forest diversity and structure.•Active restoration ...enhanced adult tree diversity compared to natural regeneration.•The occurrence of rare adult tree species was promoted.•Restoration interventions are reflected in the forest structure decades after.
Forest restoration figures prominently on climate action plans, both in the public and private sector. Restoration has the potential to enhance forest recovery and carbon storage, yet could cause unanticipated alterations of forest biodiversity and functioning. In particular little is known about the long-lasting effects of active forest restoration. We therefore evaluated the effects of such management on adult trees and seedlings of actively restored forest to comparable areas where forest regenerated naturally. We investigated a forest site in Sabah, Malaysian Borneo that is recovering from selective logging between 1981 and 1991. Some of the area has been left to naturally regenerate, and some areas have been actively restored for production purposes between 1994 and 2004 through climber cutting and enrichment-planting of exclusively indigenous tree species. We hypothesized that active forest restoration affects forest diversity and composition negatively (i.e., reduction in diversity and presence of pioneer species), and that the silvicultural interventions had long-lasting effects (i.e., higher density of species that were planted, fewer climbers).
Surprisingly, our findings suggest that active forest restoration promoted the recovery of adult tree species diversity, expressed as Shannon Diversity Index, and in particular promoted rare species. In actively restored plots, the number of adult individuals of tree species that were planted was enhanced, and the density of liana seedlings was reduced, demonstrating that these silvicultural interventions were effective and had long-lasting effects on the forest structure. Nevertheless, we could not detect differences in the number of seedlings of species that were planted nor in the density of adult lianas between actively restored and naturally regenerating forest sites. We also did not find differences in the species diversity of seedlings, but we observed a compositional shift in the species community for seedlings that were younger than one year. Furthermore, we did not detect a difference between actively restored and naturally regenerating forest plots in the abundance of the present tree guilds (i.e., pioneer or late-succession species) for neither adult trees nor seedlings, as all of our forest plots were dominated by late-succession species.
Our results show that active forest restoration can promote species diversity and highlight that active forest restoration focusing on biomass production does not need to adversely affect biodiversity. This work emphasizes the potential of active forest restoration on biodiversity and potentially other key ecosystem functions which are needed to be restored in order to mitigate climate change and the current ecological crisis.
Pie chart represents the distribution of carbon fractions within aggregates. The arrows indicate the positive and negative effects of tree species richness on aggregate-associated organic carbon ...fractions, respectively. LMAC, large macroaggregate carbon; SMAC, small macroaggregate carbon; MIC, microaggregate carbon; SCC, silt and clay fraction carbon; c-iPOC, coarse intra-aggregate particulate organic carbon; f-iPOC, fine intra-aggregate particulate organic carbon; MAOC, mineral associated organic carbon.
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•N-fixing tree species promoted species richness effect on aggregate-associated C.•Positive tree species richness effect on aggregate C as N-fixing trees were present.•Richness effect occurred directly or indirectly by increasing root length density.
Soil aggregation is an important mechanism shaping soil organic carbon (SOC) fractions, but the effects of tree species richness on soil aggregate-associated organic carbon fractions are poorly understood. In this study, a manipulative experiment was conducted to examine whether and how tree species richness (1, 2, 4 and 6) together with or without the presence of nitrogen (N)-fixing tree species affect soil aggregate-associated organic carbon. Soil aggregates were classified into four fractions: large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and silt and clay (<0.053 mm). And then large and small macroaggregates were further separated into coarse (c-iPOC), fine intra-aggregate particulate organic carbon (f-iPOC) and mineral associated organic carbon (MAOC), and microaggregates were divided into f-iPOC and MAOC. We observed that the effects of tree species richness on soil aggregate-associated organic carbon fractions were depended on the presence or absence of N-fixing tree species. In the presence of N-fixing tree species, organic carbon contents of small macroaggregate, microaggregate and silt and clay fractions were increased across the gradient of tree species richness (+10.4%, +31.3% and + 26.7% from monocultures to 6-species mixture), and the similar responses occurred for c-iPOC within small macroaggregates (+42.9%) and f-iPOC within microaggregates (+50.0%). In the absence of N-fixing tree species, however, only f-iPOC within large macroaggregates (+60.0%) had a positive linear relationship with tree species richness. Structural equation modeling was then used to dissect the mechanism underlying the positive effects of tree species richness on the aggregate-associated organic carbon fractions, indicating either direct or indirect effects by increasing root length density. Our study highlights the important roles of N-fixing tree species in shaping tree species richness effects on soil aggregate-associated organic carbon fractions, and therefore, N-fixing tree species should be preferentially considered in mixed-species plantations to enhance long-term SOC stabilization.
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