[Effects of Biochar Application on Soil Organic Carbon Component in Eucalyptus Plantations After Five Years in Northern Guangxi]

To investigate the effects of biochar(BC) addition on soil organic carbon(SOC) contents and its fractions under different biochar applications, Eucalyptus waste twigs in Northern Guangxi were used to produce BC at 500℃. Additionally, we sought to clarify and define the carbon sequestration potential of soil and provide a basis for the preparation of biochar from Eucalyptus forest wastes and soil improvement. In a long-term positioning test of biochar application from 1997, six different treatments were selected:0(CK), 0.5%(T1), 1%(T2), 2%(T3), 4%(T4), and 6%(T5). The contents of SOC, light fraction organic carbon(LFOC), heavy fraction organic carbon(HFOC), easily oxidized organic carbon(EOC), dissolved organic carbon(DOC), particulate organic carbon(POC), microbial biomass carbon(MBC), and carbon stock(CS) following the different treatments were measured. The results showed that:① compared to that in the control, biochar application induced an increase in each soil organic carbon fraction with increasing application rate and reached a maximum under the T4 or T5 treatments; with the increase in biochar application, the contents of SOC, DOC, EOC, POC, MBC, and CS increased significantly by 101.62%, 67.46%, 143.03%, 164.78%, 110.88%, and 41.73%, respectively. ② The contents of LFOC and HFOC in the 0-10, 10-20, and 20-30 cm soil layers increased significantly by 41.41%-140.63%, 9.26%-87.04%, and -19.54%-106.90% and 15.32%-78.99%, 15.72%-75.25%, and 89.49%-148.64%, respectively, with the increase in biochar application. The average contents of LFOC and HFOC in the 0-30 cm soil layer also increased gradually. The soil carbon pool of the Eucalyptus forest was dominated by a relatively stable heavy fraction organic carbon. ③ The contents of carbon stock, soil organic carbon, and its fractions decreased with the increase in soil depth. In conclusion, the application of forestry waste biochar for five years could significantly increase the content of SOC and its components, thereby increasing soil organic carbon activity. Therefore, increasing the amount of biochar was an effective measure to enhance the carbon storage, soil stable carbon pool, and soil quality of the Eucalyptus plantation field. This study provides a reference for the resource utilization of forestry waste and improvements in soil fertility of Eucalyptus plantations.

[Effects of Biochar Application on Soil Organic Nitrogen Component and Active Nitrogen in Eucalyptus Plantations After Five Years in Northern Guangxi]

The objective of this study was to research the characteristics of fractions of organic nitrogen and active nitrogen and their relationship under different biochar applications and to provide a basis for the preparation and practical application of biochar from Eucalyptus forest wastes. In a long-term positioning test of biochar application from 2017, six different treatments were selected:0(CK), 0.5%(T1), 1%(T2), 2%(T3), 4%(T4), and 6%(T5). The contents of soil organic nitrogen components, total nitrogen(TN), dissolved organic nitrogen(DON), and microbial biomass nitrogen(MBN) following the different treatments were measured. The results showed that:① compared with that of the control, with the increase in biochar application, the contents of soil TN, acidolysis of total organic nitrogen(AHON), ammonia nitrogen(AN), amino acid nitrogen(AAN), MBN, DON, and nitrogen storage(NS) increased significantly by 45.48%-156.32%, 44.31%-171.31%, 38.06%-223.37%, 39.42%-163.32%, 36.72%-109%, 23.27%-113.51%, and 29.45%-62.37%, respectively. The contents of soil hydrolyzable unknown nitrogen(HUN) and non-hydrolyzable nitrogen(NHN) also increased significantly by 88.41%-158.71% and 50.24%-139.01%, respectively. The contents of soil amino sugar nitrogen(ASN) decreased by 7.72%-32.73%. The contents of different forms of organic nitrogen fractions in all treatments displayed an order of AN > AAN > NHN > HUN > ASN. Compared with the no biochar treatment, each biochar treatment increased the contents and proportion of AHON in the TN. ② With the exception of HUN, the contents of other soil organic nitrogen components and active nitrogen content decreased with the increase in soil depth. ③ There were significantly positive correlations between TN, MBN, and DON and AHON, NHN, and NS contents. The principal component analysis showed that bulk density and ASN and TN and HUN, AAN, DON, and AHON were closely related, respectively. In conclusion, the application of forestry waste biochar for five years could significantly increase the content of soil organic nitrogen component and active nitrogen, thereby improving the capacity of the soil to supply nitrogen. AHON, AN, and AAN were the main factors contributing to soil active nitrogen content.

Compatible Mycorrhizal Types Contribute to a Better Design for Mixed Eucalyptus Plantations

Mixed-species forest plantation is a sound option to facilitate ecological restoration, plant diversity and ecosystem functions. Compatible species combinations are conducive to reconstruct plant communities that can persist at a low cost without further management and even develop into natural forest communities. However, our understanding of how the compatibility of mycorrhizal types mediates species coexistence is still limited, especially in a novel agroforestry system. Here, we assessed the effects of mycorrhizal association type on the survival and growth of native woody species in mixed-species Eucalyptus plantations. To uncover how mycorrhizal type regulates plant-soil feedbacks, we first conducted a pot experiments by treating distinct mycorrhizal plants with soil microbes from their own or other mycorrhizal types. We then compared the growth response of arbuscular mycorrhizal plants and ectomycorrhizal plants to different soil microbial compositions associated with Eucalyptus plants. We found that the type of mycorrhizal association had a significant impact on the survival and growth of native tree species in the Eucalyptus plantations. The strength and direction of the plant-soil feedbacks of focal tree species depended on mycorrhizal type. Non-mycorrhizal plants had consistent negative feedbacks with the highest survival in the Eucalyptus plantations, whereas nitrogen-fixing plants had consistent positive feedbacks and the lowest survival. Arbuscular mycorrhizal and ectomycorrhizal plants performed varied feedback responses to soil microbes from distinct mycorrhizal plant species. Non-mycorrhizal plants grew better with Eucalyptus soil microbes while nitrogen-fixing plants grew worse with their own conspecific soil microbes. Different soil microbial compositions of Eucalyptus consistently increased the aboveground growth of arbuscular mycorrhizal plants, but the non-mycorrhizal microbial composition of the Eucalyptus soil resulted in greater belowground growth of ectomycorrhizal plants. Overall, Eucalyptus plants induced an unfavorable soil community, impeding coexistence with other mycorrhizal plants. Our study provides consistent observational and experimental evidence that mycorrhizal-mediated plant-microbial feedback on species coexistence among woody species. These findings are with important implications to optimize the species combinations for better design of mixed forest plantations.

[Effects of Eucalyptus Branches Biochar Application on Soil Physicochemical Properties of Acidified Soil in a Eucalyptus plantation in Northern Guangxi]

This study aims to explore the effects of different biochar applications on soil physical and chemical properties in a Eucalyptus plantation in Northern Guangxi, find the best biochar application amount, and provide scientific guidance for the efficient utilization of forest residue and soil improvement. The soil of a four-year Eucalyptus plantation at the Huangmian forest farm in Northern Guangxi was selected as the study area, and six treatments including 0 (CK), 0.5% (T1), 1.0% (T2), 2% (T3), 4% (T4), and 6% (T5) were set through a field-positioning experiment to analyze the changes in soil physical and chemical properties under different application rates. Compared with the 0-30 cm soil layer of the control treatment, biochar application decreased the mean soil bulk by 3.82%-33.55%, while it increased the soil natural water content, capillary porosity, and total capillary porosity by 7.67%-31.75%, 8.95%-33.19%, and 9.28%-35.86%, respectively. The contents of exchangeable acid, exchangeable aluminum, exchangeable hydrogen, and exchangeable sodium in the soil decreased by 8.28%-70.03%, 5.55%-70.34%, 5.10%-21.78%, and 12.81%-49.27%. Biochar application increased the cation exchange capacity, electrical conductivity, exchangeable magnesium, and exchangeable calcium by 27.08%-160.39%, 117.00%-546.64%, 17.10%-66.14%, and 17.38%-71.38%, respectively. Soil pH increased by 0.17-1.29 after biochar addition. Similarly, the contents of soil organic carbon, total phosphorus, total potassium, available nitrogen, available phosphorus, and available potassium increased by 10.94%-51.37%, 14.29%-59.45%, 6.48%-59.57%, 6.28%-29.41%, 4.79%-19.81%, and 7.72%-75.87%. There was a positive correlation among the main physical and chemical factors. The physical and chemical properties reached their maximum values in the T4 or T5 treatment (4% or 6%). Biochar application provided considerable relief from soil acidification in the Eucalyptus plantation and had a positive effect on soil physicochemical properties. The addition 4%-6% of ripe Eucalyptus biochar produced the optimum results. The results show that biochar can improve the physical and chemical properties of soil, increase soil fertility, and enhance the soil's ability to retain water and fertilizer after twelve months. The findings of this study can be used as a reference in practical applications for soil improvement and sustainable management of Eucalyptus plantations.

Forest floor temperature and greenness link significantly to canopy attributes in South Africa's fragmented coastal forests

Tropical landscapes are changing rapidly due to changes in land use and land management. Being able to predict and monitor land use change impacts on species for conservation or food security concerns requires the use of habitat quality metrics, that are consistent, can be mapped using above-ground sensor data and are relevant for species performance. Here, we focus on ground surface temperature (Thermal_ground) and ground vegetation greenness (NDVI_down) as potentially suitable metrics of habitat quality. Both have been linked to species demography and community structure in the literature. We test whether they can be measured consistently from the ground and whether they can be up-scaled indirectly using canopy structure maps (Leaf Area Index, LAI, and Fractional vegetation cover, FCover) developed from Landsat remote sensing data. We measured Thermal_ground and NDVI_down across habitats differing in tree cover (natural grassland to forest edges to forests and tree plantations) in the human-modified coastal forested landscapes of Kwa-Zulua Natal, South Africa. We show that both metrics decline significantly with increasing canopy closure and leaf area, implying a potential pathway for upscaling both metrics using canopy structure maps derived using earth observation. Specifically, our findings suggest that opening forest canopies by 20% or decreasing forest canopy LAI by one unit would result in increases of Thermal_ground by 1.2 °C across the range of observations studied. NDVI_down appears to decline by 0.1 in response to an increase in canopy LAI by 1 unit and declines nonlinearly with canopy closure. Accounting for micro-scale variation in temperature and resources is seen as essential to improve biodiversity impact predictions. Our study suggests that mapping ground surface temperature and ground vegetation greenness utilising remotely sensed canopy cover maps could provide a useful tool for mapping habitat quality metrics that matter to species. However, this approach will be constrained by the predictive capacity of models used to map field-derived forest canopy attributes. Furthermore, sampling efforts are needed to capture spatial and temporal variation in Thermal_ground within and across days and seasons to validate the transferability of our findings. Finally, whilst our approach shows that surface temperature and ground vegetation greenness might be suitable habitat quality metric used in biodiversity monitoring, the next step requires that we map demographic traits of species of different threat status onto maps of these metrics in landscapes differing in disturbance and management histories. The derived understanding could then be exploited for targeted landscape restoration that benefits biodiversity conservation at the landscape scale.

Ranking of industrial forest plantations in terms of sustainability: A multicriteria approach

As forest managers and owners must have precise assessments of sustainability, in this study we have proposed a methodology based on multi-criteria techniques for assessing sustainability in industrial forest plantations and establishing a ranking of these plantations in terms of sustainability. First, we identified and have briefly described a set of sustainability indicators (economic, environmental and social). Next, we developed a statistical procedure to determine if a linear relationship existed between the indicators. With this analysis, the final set of indicators was defined and normalized. Then, we formulated four goal programming models, by which to aggregate the different indicators. In these models, we introduced the preferences of the decision makers for each indicator, using a survey with questions formulated in a pairwise comparison format. The procedure was applied to 30 Eucalyptus globulus Labill. plantations in northwestern Spain and 11 indicators were selected in order to define the sustainability. The results showed several rankings under each goal programming model. Although the results may not be the same in the different models, some plantations are always the most sustainable, while others are always the worst in terms of sustainability. The combination of initial values of indicators, goal programming models and preferences of stakeholders (preferential weights and targets) influence the results, and it cannot be predicted a priori which plantation is the best/worst in terms of sustainability. In our case study, we show how changes in preferential weights and targets substantially modify the results obtained.

Novel species of Calonectria associated with Eucalyptus leaf blight in Southeast China

Leaf blight caused by Calonectria spp. is an important disease occurring on Eucalyptus trees grown in plantations of Southeast Asia. Symptoms of leaf blight caused by Calonectria spp. have recently been observed in commercial Eucalyptus plantations in FuJian Province in Southeast China. The aim of this study was to identify these Calonectria spp. employing morphological characteristics, DNA sequence comparisons for the β-tubulin, histone H3 and translation elongation factor-1α gene regions and sexual compatibility. Four Calonectria spp. were identified, including Ca. pauciramosa and three novel taxa described here as Ca. crousiana, Ca. fujianensis and Ca. pseudocolhounii. Inoculation tests showed that all four Calonectria spp. found in this study were pathogenic on two different E. urophylla × E. grandis hybrid clones, commercially utilised in eucalypt plantations in China.