Eucalyptus is a fast-growing, short-cycle, and high-efficiency tree species that is widely planted all over the world. Weeding is a special practice for Eucalyptus plantations that aims to cultivate seedlings and reduce vegetation competition for nutrients. In this study, a typical Eucalyptus plantation was selected as the research object, and the effects of two different weeding methods on soil evaporation and plant growth were studied. The results showed that mechanical weeding could effectively remove harmful weeds at an early stage, but after 30 days of weeding, all kinds of plants gradually recovered; herbicide weeding required long-term maintenance. The herbicide had the best control effect on Microstegium vagans (Nees ex Steud.) A. Camus, Dicranopteris dichotoma (Thunb.) Bernh, and Blechnum orientale, but the effect on shrubs was not obvious. The evaporation rate of soil increased rapidly within five days after mechanical weeding. After 139–200 days of weeding, the differences in evaporation between non-weeding, herbicide weeding, and mechanical weeding was decreased. The average daily evaporation was 0.52, 0.48, and 051 mm/d under these three practices. Meanwhile, weeding could promote Eucalyptus growth. Our results showed that weeding could significantly increase the height, diameter at breast height, and volume of Eucalyptus. One month after herbicide weeding or mechanical weeding (July), the height, DBH, and volume of Eucalyptus were significantly greater than those under non-weeding, but there was no significant difference between herbicide weeding and mechanical weeding. In addition, according to the different initial moisture contents, the evaporation rate increased with increasing initial moisture content and showed a very significant correlation.

Fish ponds polluted by the black water of eucalyptus forests (formed by the complexation of eucalyptus tannins with Fe³⁺) have experienced fish deaths. However, the toxicity of the components of black water is still unclear. To study the acute toxicities of eucalyptus leachate tannins to fish, their changes in the presence of Fe³⁺, and the underlying mechanisms, the static bioassay test method was adopted for acute exposure testing of zebrafish. Zebrafish were exposed to three kinds of tannins, namely, tannic acid (TA), epigallocatechin gallate (EGCG) and tannins from fresh eucalyptus leaf leacheate (TFL), and to solutions of these tannins with different molar ratios of Fe³⁺, under both no-aeration and aeration conditions. The results showed that the 48 h LC50 values of TA, EGCG and TFL were respectively 92, 47, and 186 mg·L^-1, under no aeration, and 171, 86, and 452 mg·L^-1 under aeration. When Fe³⁺ at 2, 1, and 6 times the molar amount of tannin was added to LC100 solutions of TA, EGCG and TFL, zebrafish mortality in 24 h was reduced to 0-33%. Acute fish death in eucalyptus plantation areas is related to high concentrations of eucalyptus tannins in the water. However, with increasing dissolved oxygen and Fe³⁺ levels, the acute toxicity of tannins to fish can be reduced. Thus, the black water in eucalyptus plantation areas reflects a water quality phenomenon that reduces the acute toxicity of eucalyptus tannins to fish. The mechanism of tannin toxicity to fish may be related to the impairment of oxygen delivery by fish blood, but the mechanism needs further study. These results provide a scientific basis for the prevention and control of fish suffering from acute eucalyptus tannin poisoning in eucalyptus plantation areas and for the protection of water resources.

The unclear mechanisms of interaction between plant-derived tannins and soil metal oxides (Al, Fe, Mn), especially in tannin-rich ecosystems like eucalyptus plantations, hinder accurate predictions of long-term soil health under continuous tannin exposure. Therefore, controlled soil column leaching experiments were conducted using different tannin types and concentrations. Metal oxide speciation (free, amorphous, and complexed) was quantified by a modified parallel extraction method, while aggregate stability was assessed through mean weight diameter (MWD) and geometric mean diameter (GMD) measurements. Results demonstrate that hydrolyzable tannins (e.g., gallic acid) exhibit superior metal mobilization capacity compared to condensed tannins (e.g., epigallocatechin gallate), establishing tannin chemistry as the primary determinant of oxides reactivity. A sequential dissolution-recomplexation pathway was identified, resulting in a 4 %-26 % decrease in amorphous oxides coupled with a 6 %-149 % increase in complexed oxides. The strong positive correlation between aggregate stability and complexed manganese content confirms its crucial cementing role. These findings resolve the apparent paradox of short-term stabilization versus long-term degradation in tannin-rich ecosystems by revealing that while initial complexation enhances aggregation, persistent tannin input ultimately depletes amorphous oxides, compromising soil structure. This mechanistic understanding provides a scientific basis for assessing metal-leaching risks and for developing sustainable management strategies in affected ecosystems.