Dry Season Irrigation Promotes Leaf Growth in Eucalyptus urophylla × E. grandis under Fertilization

Fertilization- and Irrigation-Modified Bacterial Community Composition and Stimulated Enzyme Activity of Eucalyptus Plantations Soil

Irrigation and fertilization are essential management practices for increasing forest productivity. They also impact the soil ecosystem and the microbial population. In order to examine the soil bacterial community composition and structure in response to irrigation and fertilization in a Eucalyptus plantations, a total of 20 soil samples collected from Eucalyptus plantations were analyzed using high-throughput sequencing. Experimental treatments consisting of control (CK, no irrigation or fertilization), fertilization only (F), irrigation only (W), and irrigation and fertilization (WF). The results showed a positive correlation between soil enzyme activities (urease, cellulase, and chitinase) and fertilization treatments. These enzyme activities were also significantly correlated with the diversity of soil bacterial communities in Eucalyptus plantations.. Bacteria diversity was considerably increased under irrigation and fertilization (W, F, and WF) treatments when compared with the CK treatment. Additionally, the soil bacterial richness was increased in the Eucalyptus plantations soil under irrigation (W and WF) treatments. The Acidobacteria (38.92-47.9%), Proteobacteria (20.50-28.30%), and Chloroflexi (13.88-15.55%) were the predominant phyla found in the Eucalyptus plantations soil. Specifically, compared to the CK treatment, the relative abundance of Proteobacteria was considerably higher under the W, F, and WF treatments, while the relative abundance of Acidobacteria was considerably lower. The contents of total phosphorus, accessible potassium, and organic carbon in the soil were all positively associated with fertilization and irrigation treatments. Under the WF treatment, the abundance of bacteria associated with nitrogen and carbon metabolisms, enzyme activity, and soil nutrient contents showed an increase, indicating the positive impact of irrigation and fertilization on Eucalyptus plantations production. Collectively, these findings provide the scientific and managerial bases for improving the productivity of Eucalyptus plantations.

Responses of Fungal Community Structure and Functional Composition to Short-Term Fertilization and Dry Season Irrigation in Eucalyptus urophylla × Eucalyptus grandis Plantation Soils

Plantation forests productivity is severely limited by the seasonal drought and fertilization practices in South China. Soil nutrient and water availability influence soil fungal community, functional group diversity and the variation of plant productivity; however, the effects of irrigation and fertilization on fungal responses have rarely been studied. Here, we investigate the responses of fungal community structure and functional groups in Eucalyptus plantation soils to short-term fertilization (F), dry-season irrigation (W), short-term fertilization combined with dry-season irrigation (FW), and control (CK) treatments for ten months. A higher proportion of Basidiomycota was observed in the irrigation and/or fertilization treatments; conversely, lower proportions of Ascomycota and Mucoromycotina were observed in the only irrigation and fertilization treatments. Higher soil carbon contents and symbiotroph fungi (mainly Ectomycorrhizas) proportion were detected in the FW treatment, while low proportions of saprophytic and pathogenic fungi were observed in the FW treatment when compared with those in other treatments. These results may indicate that Eucalyptus tree growth under irrigation and fertilization condition was better than under fertilization only, irrigation only, or neither management. The results highlight that short-term fertilization and dry-season irrigation can shift fungal community structure and functional groups by regulating available soil moisture and nutrients. They also provide a theoretical basis for the development of more appropriate management approaches in the early stages of forest plantation.

Effects of Fertilization and Dry-Season Irrigation on Litterfall Dynamics and Decomposition Processes in Subtropical Eucalyptus Plantations

Nutrient management in Eucalyptus plantations is critical for wood production and sustainable development. The biogeochemical mechanisms in Eucalyptus plantations are not fully understood due to changes in the spatiotemporal pattern of precipitation and plantation management. The nutrients released from litterfall are important sources of soil nutrition. We measured the seasonal production of various litterfall types and the proportions of their released nutrients in Eucalyptus urophylla × E. grandis plantations under compound fertilization, dry-season irrigation, and a combined compound fertilization and dry-season irrigation treatment. Our results showed that fertilization increased aboveground biomass and annual litterfall production (except leaf), and that the peak of litterfall production occurred in the rainy season. We found that the decomposition rates of leaf were significantly higher than that of twig, which were mainly controlled by stoichiometric characteristics, followed by soil enzyme activity (β-glucosidase, urease, and polyphenol oxidase). Fertilization decreased the carbon: nitrogen ratio and carbon: phosphorus ratio in litter, and increased soil enzyme activities, which accelerates litter decomposition and nutrient release. Dry-season irrigation increased litter decomposition and only affected the proportion of released potassium by changing the carbon: potassium ratio. Fertilization and dry-season irrigation accelerated the nutrient cycle to enhance compensatory growth. These results help to comprehend the effects of forest management on litterfall dynamics and decomposition processes in Eucalyptus plantations with seasonal drought.