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In this study, the interacting effects of shade and planting methods on the growth and competitive ability of two understory plants Heracleum moellendorffii Hance and Adenophora divaricata Franch. & Sav. were investigated under different soil moisture and nutrient conditions. One-year-old seedlings were subjected to different light levels (0%, 35%, and 55% shade) and planting methods (monoculture and mixed) under contrasting soil moisture (1.2 L/m2 and 2.3 L/m2 of water) and soil nutrient conditions (unfertilized and fertilized). Here, shading significantly improved the height growth of H. moellendorffii (10–20 cm increase) in unfertilized and fertilized plots and at high soil moisture conditions. Contrarily, A. divaricata seedlings planted singly at full sunlight yielded a higher aboveground biomass growth (8–17 g plant−1), compared with those shaded and intercropped seedlings (0.9–3.9 g plant−1). The increased competitiveness of H. moellendorffii suppressed the growth of A. divaricata across different light conditions when planted together. The amount of light, soil moisture, and nutrients and their interactions significantly affected the growth of the seedlings, resulting in asymmetric interspecific competition between the two species. Results provide us with a better understanding of the environmental factors affecting plant growth for forest farming in the understory.

BackgroundThe impacts of climate change, such as increased soil dryness and nutrient deficiency, highlight the need for environmentally sustainable restoration of forests and groundwater resources. However, it is important to consider that extensive afforestation efforts may lead to a depletion of groundwater supply due to higher evapotranspiration rates, exacerbating water scarcity issues. Consequently, we conducted a study to examine how the fast-growing tree species Populus sibirica (Horth ex Tausch) and Ulmus pumila (L.) respond morpho-physiologically to varying watering regimes and types of fertilizers, aiming to better understand their specific water and nutrient requirements. MethodsWe used two-year-old nursery-growth seedlings (N = 512) of P. sibirica and U. pumila with initial root collar diameter (RCD) and the height of 0.51 ± 0.02 mm and 68 ± 2.94 cm and 0.33 ± 0.01 mm and 51 ± 1.14 cm, respectively. The leaf area (LA), specific leaf area (SLA), chlorophyll concentration, stomatal conductance (gs), chlorophyll fluorescence, and predawn and midday leaf water potential were measured across treatments. Four different irrigation regimes and two different fertilizer types were applied: no irrigation (control, 0 L h−1), 2 L h−1 = 0.25 mm m−2, 4 L h−1 = 0.5 mm m−2, 8 L h−1 = 1.0 mm m−2 and 120 g and 500 g tree−1 of NPK and compost (COMP). Twelve plots (600 m2) were established in the study site for each species and treatments. ResultsDuring the first growing season (2021), the LA of P. sibirica was larger in the 4–8 L h−1 without fertilizer, but it was smaller in the 4 L h−1+ COMP during the second growing season (2022). The 2 L h−1 without fertilizer and 2 L h−1 + NPK had larger LA compared with the control (CONT) for the first and second growing seasons, respectively, for U. pumila. P. sibirica seedlings at 4 L h−1 without fertilizer had the highest SLA for 2021 and at 2 L h−1 + NPK for 2022, whereas CONT and 4 L h−1 had the highest SLA than the other treatments for 2021 and 2022 growing seasons, respectively, for U. pumila. The chlorophyll concentration of P. sibirica seedlings in the first year was generally higher in CONT, while the 2 L h−1 without any fertilizer yielded a significantly higher chlorophyll concentration of U. pumila. Chlorophyll fluorescence parameters (PIABS and Fm) were generally lower in CONT with/without NPK or COMP for both species. The CONT with NPK/COMP generally had a higher gs compared with the other treatments in both experimental periods for U. pumila, whereas CONT and 2 L h−1+ NPK-treated P. sibirica seedlings had a significantly greater gs during the first year and second year, respectively. The predawn and midday leaf water potentials of both species were generally the lowest in CONT, followed by 2 L h−1+ NPK/COMP during the first growing season, but a different pattern was observed during the second growing season. Overall, the morpho-physiological traits of the two species were affected by watering and fertilizer treatments, and the magnitude of the effects varied depending on growing season, amount of irrigation, and fertilizer type, and their interactions.

A harsh environment, slow tree growth, nutrient deficiencies, and competition between trees and weeds can impede forest establishment on reclaimed lands. We investigated the effects of torrefied wood chips (TWC) and vermicompost (VC) soil amendments on the growth of Populus euramericana Guinier, weed biomass, and soil chemical properties on reclaimed land in Saemangeum. The 2.5 Mg ha−1 and 5.0 Mg ha−1 TWC had a similar effect on tree diameter and height growth (i.e., 2.5 = 5.0 > 0 TWC) and tended to have similar, higher effect on the total biomass of P. euramericana than the 0 Mg ha−1. The 2.5 Mg ha−1 TWC resulted in a significantly larger root biomass than the 5.0 Mg ha−1 TWC. The weed biomass was significantly larger at the 2.7 Mg ha−1 VC (i.e., 730.5–810.5 g m−2) than the control (605.1–610.6 g m−2), but VC alone was not effective for tree growth and soil amelioration. The TWC had no effect on weed biomass. Thus, the TWC and VC had contrasting effects on tree growth and weed biomass when they were used as soil amendments on salt-affected reclaimed land. VC application may promote weed proliferation, whereas TWC application may potentially increase the growth of P. euramericana and control weed growth on reclaimed lands. Our results enhance the existing knowledge on tree and weed responses to torrefied wood chips and vermicompost amendments for the sustainable management of salt-affected reclaimed lands.